Applied magnetic field synthesis and processing of iron nitride magnetic material

Abstract

To facilitate formation of iron nitride magnetic material.SOLUTION: A technique regarding applied magnetic field synthesis and processing of iron nitride magnetic material is disclosed. Some methods relate to casting iron-containing materials in presence of an applied magnetic field to form a workpiece containing at least one iron basal phase domain containing uniaxial magnetic anisotropy. Here, the applied magnetic field has intensity of at least about 0.01 Tesla (T). A workpiece produced by such a method, a device for producing such a workpiece, and a bulk material produced by such a method are also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Related Applications This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 107,700, entitled "APPLIED MAGNETIC FIELD SYNTHESIS AND PROCESSING OF IRON NITRIDE MAGNETIC MATERIALS," filed January 26, 2015, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to techniques for forming iron nitride magnetic materials. [Background technology]

[0003] Permanent magnets play a role in many electromechanical systems, including alternative energy systems. For example, permanent magnets are used in sensors, actuators, electric motors, or generators, which can be used in transportation, wind turbines, and other alternative energy mechanisms. Many permanent magnets currently in use contain rare earth elements, such as neodymium, which provide high energy products. These rare earth elements are in relatively short supply and may face rising prices and / or supply shortages in the future. Furthermore, certain permanent magnets containing rare earth elements are expensive to manufacture. For example, the production of NdFeB and ferrite magnets typically involves crushing materials, compressing the materials, and sintering them at temperatures exceeding 1000°C, all of which contribute to the high manufacturing costs of magnets. Furthermore, the mining of rare earth elements can cause significant environmental degradation. Summary of the Invention [Problem to be solved by the invention]

[0004] This disclosure describes techniques for forming magnetic materials that include at least one iron-based phase domain that includes uniaxial magnetic anisotropy. For example, the iron-based phase domain that includes uniaxial magnetic anisotropy may be iron having a body-centered tetragonal structure, α″-Fe. 16 N2, α”-Fe 16 The iron-nitrogen phase may include C2, Fe, or other Fe-based magnetic materials. Techniques described herein may include at least one of casting a mixture of iron and nitrogen in an applied magnetic field or consolidating a plurality of workpieces, at least some of which include at least one iron-based phase domain with uniaxial magnetic anisotropy, while exposing the plurality of workpieces to an applied magnetic field. [Means for solving the problem]

[0005] During the casting technique, iron nitride crystals may nucleate and grow from a molten mixture containing iron and nitrogen. Applying a magnetic field during the casting process can influence the nucleation and growth of iron nitride crystals such that the growth of crystals with a predetermined orientation may be energetically favored. For example, iron nitride crystals with (002) or (004) crystal faces substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field may be more energetically favorable than iron nitride crystals with a different orientation (e.g., (110), (112), (202), or (200) crystal faces substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field). Therefore, an applied magnetic field can increase the likelihood that some or all of the iron nitride crystals have a similar crystal orientation. A material containing multiple iron nitride crystals with a substantially similar crystal orientation can increase the magnetic anisotropy of the material.

[0006] During integration, e.g., α”-Fe 16A magnetic field may be applied to the material being consolidated to substantially align (e.g., align or nearly align (e.g., within about 5 degrees of perfect alignment)) the magnetic easy axes of multiple workpieces including at least one iron-based phase domain that includes uniaxial magnetic anisotropy, such as N2. The magnetic easy axis is the direction of the iron-based phase domain crystalline cell in which alignment of magnetic moments is energetically favorable and metastable. In some examples, the magnetic easy axis of the iron-based phase domain that includes the uniaxial magnetic anisotropy unit cell is <001> or c-axis. In some examples, the plurality of workpieces may comprise powders, particles, ribbons, sheets, wires, or other geometric shapes. By applying a magnetic field during the compaction process, the magnetic easy axes of the plurality of workpieces comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy may be aligned substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field. This helps define the magnetization direction of the consolidated magnetic material and can also increase the magnetic anisotropy of the consolidated magnetic material.

[0007] In some examples, the present disclosure describes a method that includes casting a material that includes iron in the presence of an applied magnetic field to form a workpiece that includes at least one iron-based phase domain that includes uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T).

[0008] In some examples, the present disclosure describes a method that includes compressing a plurality of workpieces, each workpiece including at least one iron-based phase domain including uniaxial magnetic anisotropy, in the presence of an applied magnetic field to form a bulk material including a plurality of iron-based phase domains including uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T), and the applied magnetic field defines a magnetization direction of the bulk material.

[0009] In some examples, this disclosure describes apparatus configured to implement any of the techniques described herein.

[0010] In some examples, the present disclosure describes a workpiece formed by any of the techniques described herein.

[0011] In some examples, the present disclosure describes bulk materials formed by any of the methods described herein.

[0012] In some examples, the present disclosure describes a method that includes casting a material that includes at least one of nickel, iron, and cobalt in the presence of an applied magnetic field to form a workpiece that includes at least one nickel-, iron-, or cobalt-based phase domain that includes uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T).

[0013] In some examples, the present disclosure describes a workpiece including at least one anisotropically shaped iron-based grain, wherein the at least one anisotropically shaped iron-based grain has an aspect ratio of about 1.1 to about 50, where the aspect ratio is defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic grain, and the longest dimension and the shortest dimension may be substantially orthogonal.

[0014] In some examples, the present disclosure describes a bulk permanent magnet comprising at least one anisotropically shaped iron-based grain, wherein the at least one anisotropically shaped iron-based grain has an aspect ratio of about 1.1 to about 50, where the aspect ratio is defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic grain. The longest and shortest dimensions may be substantially orthogonal.

[0015] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. [Brief explanation of the drawings]

[0016] [Figure 1]FIG. 1 is a flow diagram illustrating an exemplary technique for casting iron and nitrogen containing materials in the presence of an applied magnetic field. [Figure 2] FIG. 2 is a conceptual diagram illustrating an exemplary system for performing the casting technique on a mixture containing iron and nitrogen using an RF furnace, a crucible, and an optional quenching medium. [Figure 3] FIG. 3 is a conceptual diagram illustrating an exemplary system including a crucible heating stage that can be used to cast iron and nitrogen containing materials in the presence of an external magnetic field. [Figure 4] FIG. 4 is a schematic diagram showing further details of one example of the crucible heating step shown in FIG. [Figure 5] FIG. 5 is a conceptual diagram illustrating another example system for belt casting an exemplary iron nitride workpiece in the presence of an external magnetic field. [Figure 6] FIG. 6 is a conceptual diagram showing the α″-Fe16N2 unit cell. [Figure 7] FIG. 7 is a conceptual diagram illustrating exemplary α″-Fe16N2 crystals or grains having anisotropic shapes. [Figure 8] FIG. 8 is a conceptual diagram illustrating an exemplary workpiece including a plurality of α″-Fe16N2 crystals or grains in a matrix of another material. [Figure 9] FIG. 9 illustrates an exemplary hysteresis curve for the exemplary workpiece shown in FIG. [Figure 10] FIG. 10 is a flow diagram illustrating an exemplary technique for consolidating multiple workpieces containing at least one α″-FeN phase domain to form a bulk magnetic material. [Figure 11] FIG. 11 is a flow diagram illustrating an exemplary technique for forming a bulk magnetic material containing α″-FeN phase domains from raw materials containing iron and nitrogen. [Figure 12] FIG. 12 shows exemplary X-ray diffraction spectra from iron nitride materials cast with and without the application of an external magnetic field. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present disclosure may be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings and examples, which form a part of this disclosure. The present disclosure is not limited to the specific devices, methods, applications, conditions, or parameters described and / or illustrated herein, and the terminology used herein is for the purpose of describing particular examples and does not limit the scope of the claims. When a range of values ​​is expressed, another example includes the one particular value and / or the other particular value. Similarly, when values ​​are expressed as approximations, by use of the prefix "about," it will be understood that the particular value constitutes another example. All ranges are inclusive and combinable. Furthermore, reference to values ​​stated within a range includes each value within that range.

[0018] It will be understood that certain features of the disclosure that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any subcombination.

[0019] The present disclosure relates to magnetic materials including at least one iron-based phase domain with uniaxial magnetic anisotropy, bulk permanent magnets including at least one iron-based phase domain with uniaxial magnetic anisotropy, techniques for forming magnetic materials including at least one iron-based phase domain with uniaxial magnetic anisotropy, and techniques for forming bulk permanent magnets including at least one iron-based phase domain with uniaxial magnetic anisotropy. Bulk permanent magnets including at least one iron-based phase domain with uniaxial magnetic anisotropy can provide an alternative to permanent magnets including rare earth elements because iron-based phase domains with uniaxial magnetic anisotropy can have high saturation magnetization, high magnetic anisotropy constant, and therefore high energy product. An example of an iron-based compound with uniaxial magnetic anisotropy is α″-Fe 16Other examples of iron-based compounds include those with a body-centered tetragonal crystal structure, such as distorted iron, and some compounds containing iron and at least one of N, C, B, O, P, Y, Mn, Co, Cr, Si, Al, Zn, etc.

[0020] α”-Fe 16 N2 has a high saturation magnetization, a high magnetic anisotropy constant, and therefore a high energy product. The high saturation magnetization and magnetic anisotropy constant result in a magnetic energy product that can, in some instances, be higher than that of rare earth magnets. Bulk α″-Fe produced according to the techniques described herein 16 N2 permanent magnet is the α”-Fe 16 When N2 permanent magnets are anisotropic, they can have desirable magnetic properties, such as a high energy product of approximately 130 MGOe. 16 In embodiments where the N2 magnet is isotropic, the energy product can be as high as about 33.5 MGOe. The energy product of a permanent magnet is proportional to the product of the remanence and the residual magnetization. For comparison, Nd2Fe 14 The energy product of Fe permanent magnets can be as high as about 60 MGOe. A higher energy product can improve the efficiency of permanent magnets when used in sensors, actuators, motors, generators, etc. Furthermore, Fe 16 Permanent magnets containing the N2 phase may be free of rare earth elements, which can reduce the material cost of the magnet and reduce the environmental impact of manufacturing the magnet.

[0021] Without being limited to any theory of action, α”-Fe 16 N2 is believed to be a metastable phase that competes with other stable phases of iron nitride. 16 It can be difficult to form bulk magnetic materials and bulk permanent magnets containing N phase domains. 16 This technique can facilitate the formation of magnetic materials containing N2 iron nitride phase domains. In some instances, this technique can also be used to16 Compared to other techniques for forming magnetic materials containing N2 iron nitride phase domains, α”-Fe 16 Reduce the cost of forming magnetic materials containing N2 iron nitride phase domains and 16 N2 increases the volume fraction of the iron nitride phase domain, and Fe 16 Facilitate mass production of magnetic materials containing N2 iron nitride phase domains and / or Fe 16 The magnetic properties of magnetic materials containing N2 iron nitride phase domains can be improved.

[0022] For example, α”-Fe 16 Bulk permanent magnets described herein that include at least one iron-based phase domain with uniaxial magnetic anisotropy, such as N2, can have anisotropic magnetic properties, characterized as having different energy products, coercive forces, and magnetization moments at different relative orientations with respect to an applied electric or magnetic field. Accordingly, the disclosed bulk iron nitride magnets can be used in any of a variety of applications (e.g., electric motors) to provide low energy losses and high energy efficiency for such applications.

[0023] The present disclosure provides, for example, at least one α″-Fe 16 Techniques are described for forming magnetic materials comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, such as an N2 phase domain. The techniques described herein involve casting a mixture of iron and nitrogen in an applied magnetic field, or forming at least one iron-based phase domain, at least some of which comprise uniaxial magnetic anisotropy, such as at least one α″-Fe 16 The method can include at least one of consolidating a plurality of workpieces including an N2 phase domain while exposing the plurality of workpieces to an applied magnetic field.

[0024] During the casting technique, iron nitride crystals may nucleate and grow from a molten mixture containing iron and nitrogen. Applying a magnetic field during the casting process can influence the nucleation and growth of iron nitride crystals such that the growth of crystals with a predetermined orientation may be energetically favored. For example, iron nitride crystals with (002) or (004) crystal faces substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field may be more energetically favorable than iron nitride crystals with a different orientation (e.g., (110), (112), (202), or (200) crystal faces substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field). Therefore, an applied magnetic field can increase the likelihood that some or all of the iron nitride crystals have a similar crystal orientation. A material containing multiple iron nitride crystals with a substantially similar crystal orientation can increase the magnetic anisotropy of the material.

[0025] In some instances, in addition to having uniaxial magnetic anisotropy, the casting technique can form at least one iron nitride crystal or grain exhibiting an anisotropic shape. The at least one anisotropically shaped iron nitride crystal or grain can exhibit an aspect ratio of about 1.1 to about 50, e.g., about 1.4 to about 50, or 2.2 to about 50, or about 5 to about 50, etc. As used herein, aspect ratio is defined as the ratio of the length of the longest dimension of the anisotropic grain to the length of the shortest dimension, where the shortest dimension is measured in a direction substantially perpendicular to the longest dimension (e.g., perpendicular or nearly perpendicular (e.g., within about 5 degrees of perpendicular)). In some instances, the longest dimension of the at least one anisotropically shaped iron nitride crystal or grain is substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field, and thus to the direction of the uniaxial magnetic anisotropy. Similarly, the longest dimension of at least one anisotropically shaped iron nitride crystal or grain can be parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the easy axis of magnetocrystalline anisotropy of the anisotropically shaped iron nitride crystal or grain. For example, body-centered tetragonal (bct) Fe16 In the case of N2 and Fe, the (002) texture is substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the longest dimension of the crystals or grains. Thus, the shape anisotropy of anisotropically shaped iron nitride crystals or grains can contribute to the magnetic anisotropy of the material. In another example, (bc)Fe 16 In the case of N2, the (002) texture can be substantially parallel (eg, parallel or nearly parallel (eg, within about 5 degrees of parallel)) to the shortest dimension of the crystals or grains.

[0026] During integration, e.g., α”-Fe 16 A magnetic field may be applied to the material being consolidated to substantially align (e.g., align or nearly align (e.g., within about 5 degrees of perfect alignment)) the magnetic easy axes of multiple workpieces including at least one iron-based phase domain including uniaxial magnetic anisotropy, such as N2. The magnetic easy axis is the direction of the crystalline cell in which alignment of magnetic moments is energetically favorable and metastable. In some examples, the magnetic easy axis of the unit cell of the iron-based phase domain including uniaxial magnetic anisotropy is <001> or c-axis. In some examples, the plurality of workpieces may comprise powders, particles, ribbons, sheets, wires, or other geometric shapes. By applying a magnetic field during the compaction process, the magnetic easy axes of the plurality of workpieces comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy may be aligned substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field. This helps define the magnetization direction of the consolidated magnetic material and can also increase the magnetic anisotropy of the consolidated magnetic material.

[0027] In some instances, the casting and consolidation techniques may be used to produce uniaxial magnetic anisotropy α″-Fe 16The present invention can be used in conjunction with a large-scale technique for forming a bulk magnetic material comprising at least one iron-based phase domain, including an N2 phase domain. In some examples, the large-scale technique can include additional steps, including, for example, quenching the cast magnetic material, annealing the quenched magnetic material, etc. In some examples, an external magnetic field can be applied during at least some of these other steps to form a uniaxial magnetic anisotropy α″-Fe 16 For example, a magnetic field may be applied during the annealing step to promote the formation of at least one iron-based phase domain, including an N2 phase domain. 16 The present invention can facilitate the formation of at least one iron-based phase domain, including an N2 phase domain. In the following description, the term "α"-Fe 16 Although iron nitride materials such as N are described, one skilled in the art will understand that the following description also applies to other iron-based materials that contain uniaxial magnetic anisotropy, such as strained iron or iron-based materials that contain at least one of N, C, B, O, P, Y, Mn, Co, Cr, Si, Al, Zn, etc., and have a body-centered tetragonal structure.

[0028] FIG. 1 is a flow diagram illustrating an exemplary technique for casting a material comprising iron and nitrogen in the presence of an applied magnetic field. The technique of FIG. 1 includes forming a molten mixture comprising iron and nitrogen (12). The molten mixture can be formed using any one of a number of techniques. For example, a solid material comprising iron and nitrogen can be first formed, and then the solid material comprising iron and nitrogen can be melted to form the molten mixture comprising iron and nitrogen. As another example, molten iron can be mixed with a nitrogen source to form the molten mixture comprising iron and nitrogen.

[0029] An exemplary technique for forming a solid material containing iron and nitrogen includes nitriding an iron-containing workpiece. The iron-containing workpiece may be, for example, a powder, particle, ribbon, sheet, wire, or other geometric shape. In some examples, nitriding the iron-containing workpiece may include heating the iron-containing workpiece for a time sufficient to diffuse nitrogen to a predetermined concentration substantially throughout the iron-containing workpiece. Thus, heating time and temperature are related and may be affected by the composition and / or geometry of the iron-containing workpiece. For example, iron wire or sheet 28 may be heated to a temperature of about 125°C to about 600°C for about 2 hours to about 9 hours.

[0030] In addition to heating the iron-containing workpiece, nitriding the iron-containing workpiece includes exposing the iron-containing workpiece to an atomic nitrogen substance that diffuses into the iron-containing workpiece. In some examples, the atomic nitrogen substance is provided as diatomic nitrogen (N), which is then dissociated (decomposed) into individual nitrogen atoms. In other examples, the atomic nitrogen may be provided from other atomic nitrogen precursors, such as ammonia (NH). In other examples, the atomic nitrogen may be provided from urea (CO(NH)). The nitrogen may be provided solely in the gas phase (e.g., substantially pure ammonia or diatomic nitrogen gas) or as a mixture with a carrier gas. In some examples, the carrier gas is argon (Ar).

[0031] In some examples, nitriding the iron-containing workpiece may include a urea diffusion process in which urea is utilized as the nitrogen source (e.g., rather than diatomic nitrogen or ammonia). Urea (also known as carbamide) is an organic compound having the chemical formula CO(NH). To nitride the iron-containing workpiece, urea can be heated, for example, in a furnace surrounding the iron-containing workpiece to generate decomposed nitrogen atoms that can diffuse into the iron-containing workpiece. As described further below, the composition of the resulting iron nitride material can be controlled to some extent by the temperature of the diffusion process and the ratio (e.g., mass ratio) of iron-containing workpiece to urea used in the process. Further details regarding these nitriding processes (including urea diffusion) can be found in International Patent Application No. PCT / US12 / 51382, filed August 17, 2012, the entire contents of which are incorporated herein by reference.

[0032] As another example of forming a solid material comprising iron and nitrogen, nitrogen may be generated using a plasma, such as an RF plasma or a DC plasma, from a nitrogen source, such as a gaseous nitrogen source. The iron-containing workpiece is placed in a plasma environment, such as a plasma chamber, and nitrogen atoms generated by the plasma process can be implanted into and diffuse into the iron-containing workpiece.

[0033] As another example of forming a solid material containing iron and nitrogen, ion implantation can be used to implant nitrogen atoms into an iron-containing workpiece. For example, the iron-containing workpiece can be a foil. The foil can exhibit a thickness on the order of hundreds of nanometers to several millimeters. In some examples, the foil can exhibit a thickness of about 500 nanometers (nm) to about 1 millimeter (mm). The thickness of the foil can affect the parameters used for ion implantation and annealing of the foil, as described below. The thickness of the foil can be measured in a direction substantially perpendicular (e.g., perpendicular or nearly perpendicular (e.g., within about 5 degrees of perpendicular)) to the surface of the substrate to which the foil is attached.

[0034] The average depth to which N+ ions are implanted into the iron-containing workpiece may depend on the energy to which the N+ ions are accelerated. Generally, the average implantation depth of N+ ions may increase with increasing implant energy.

[0035] The implantation energy used to implant the N+ ions can be selected based at least in part on the thickness of the iron-containing workpiece. The implantation energy can also be selected to implant the N+ ions without causing excessive damage to the iron-containing workpiece, including the crystal lattice of the iron crystals in the iron-containing workpiece. For example, a higher implantation energy can enable implantation of the N+ ions at a greater average depth, but the higher implantation energy can increase damage to the iron workpiece, including damaging the crystal lattice of the iron crystals and ablating some of the iron atoms due to bombardment of the N+ ions. Therefore, in some examples, the implantation energy may be limited to less than about 180 keV. In some examples, the incidence angle of the implantation can be about 0 degrees (e.g., substantially normal (e.g., parallel or near normal, e.g., within about 5 degrees of normal)) to the surface of the iron workpiece. In other examples, the incidence angle of the implantation can be adjusted to reduce lattice damage. For example, the incidence angle of the implantation can be about 3° to about 7° from normal.

[0036] As an example, if the iron-containing workpiece exhibits a thickness of about 500 nm, an implant energy of about 100 keV can be used to implant N+ ions into the iron-containing workpiece. An implant energy of about 100 keV can also be used to implant N+ ions into iron-containing workpieces of other thicknesses. In other examples, different implant energies can be used for iron-containing workpieces exhibiting a thickness of about 500 nm, and the same or different implant energies can be used for iron-containing workpieces exhibiting thicknesses different from 500 nm.

[0037] Additionally, the flow rate of N+ ions can be selected to implant a desired amount of N+ ions into the iron-containing workpiece. In some instances, the flow rate of N+ ions can be selected to implant a near-stoichiometric number of N+ ions into the iron-containing workpiece. 16 The stoichiometric ratio of iron to nitrogen in N2 is 8:1. Therefore, the approximate number of iron atoms in the iron-containing workpiece can be determined, and a number equal to about 1 / 8 (12.5%) of the iron atoms, e.g., about 8 atomic % to about 15 atomic % of N+ ions can be implanted into the iron-containing workpiece. For example, an iron-containing workpiece having dimensions of about 1 cm x 1 cm x 500 nm can be implanted with about 4.23 x 10 18 Therefore, to achieve a stoichiometric ratio of iron atoms to N+ ions in the iron-containing workpiece, approximately 5.28×10 17 N+ ions can be implanted into the sample.

[0038] The temperature of the iron-containing workpiece during ion implantation can also be controlled. In some examples, the temperature of the iron-containing workpiece can be from about room temperature to about 500° C. Further details regarding the ion implantation of N+ ions into iron-containing workpieces can be found in International Application No. PCT / US14 / 15104, filed February 6, 2014, the entire contents of which are incorporated herein by reference.

[0039] Another example technique for forming a solid material containing iron and nitrogen includes grinding an iron-containing material, such as a powder, in the presence of a nitrogen source. The grinding device used to grind the iron-containing material includes a rolling mode, stirring mode, or vibration mode grinding device. The grinding device includes a bin that encloses the iron-containing material, the nitrogen source, and grinding media.

[0040] Grinding media can include, for example, grinding balls. The grinding media can comprise a material hard enough to abrade the iron-bearing material when contacted with sufficient force, reducing the iron-bearing material particles to a smaller average size. In some instances, the grinding media can be formed from steel, stainless steel, or the like. In some instances, the material from which the grinding media is formed does not chemically react with the iron-bearing material and / or the nitrogen source.

[0041] The iron-containing material may include any material containing, for example, atomic iron, iron oxide, iron chloride, etc. In some examples, the iron-containing material may include substantially pure iron (e.g., iron containing less than about 10 atomic percent (at.%) dopants or impurities). In some examples, the dopants or impurities may include oxygen or iron oxide.

[0042] The nitrogen source can include ammonium nitrate (NH4NO3) or an amide-containing material, such as a liquid amide or a solution containing an amide, or hydrazine or a solution containing hydrazine. Amides contain a CNH bond, and hydrazine contains an N-N bond. Ammonium nitrate, amides, and hydrazine serve as nitrogen donors to form powders containing iron nitride. Example amides include carbamide ((NH2)2CO; also known as urea), methanamide, benzamide, and acetamide, although any amide can be used. In some instances, amides can be derived from carboxylic acids by replacing the hydroxyl group of the carboxylic acid with an amine group. This type of amide can be referred to as an acid amide.

[0043] In some instances, the crusher bin can also contain a catalyst. The catalyst can include, for example, cobalt (Co) particles and / or nickel (I) particles. The catalyst catalyzes the nitridation of iron-containing materials. One possible conceptualized reaction pathway for nitriding iron using a Co catalyst is shown in Reactions 1-3 below. A similar reaction pathway can be followed when using Ni as the catalyst.

[0044] [ka]

[0045] [ka]

[0046] Thus, iron-containing feedstock 18 can be converted to an iron nitride-containing material by mixing sufficient amide and catalyst 22. Further details regarding grinding iron-containing materials in the presence of a nitrogen source to form solid materials containing iron and nitrogen can be found in International Application No. PCT / US14 / 43902, filed June 24, 2014, which is incorporated herein by reference.

[0047] Regardless of the technique by which the iron- and nitrogen-containing solid material is formed, the iron- and nitrogen-containing solid material can include an iron-to-nitrogen atomic ratio of about 8:1. For example, the mixture can include about 8 atomic percent (at.%) to about 15 at.% nitrogen, with the remainder being iron, other elements, and dopants. As another example, the mixture can include about 10 at.% to about 13 at.% nitrogen, or about 11.1 at.% nitrogen.

[0048] In some examples, the iron and nitrogen containing mixture may contain, in addition to iron and / or nitrogen, at least one iron nitride, such as FeN, FeN (e.g., ξ-FeN), FeN (e.g., ε-FeN), FeN (e.g., γ'-FeN and / or γ-FeN), FeN, FeN, Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). In some examples, the iron and nitrogen containing mixture may have a purity (e.g., collective iron and nitrogen content) of at least 92 atomic percent (at.%).

[0049] In some examples, the iron and nitrogen-containing mixture can include at least one dopant, such as a ferromagnetic or non-magnetic dopant and / or a phase stabilizer. In some examples, the at least one ferromagnetic or non-magnetic dopant can be referred to as a ferromagnetic or non-magnetic impurity, and / or the phase stabilizer can be referred to as a phase-stabilizing impurity. The ferromagnetic or non-magnetic dopant can be used to increase at least one of the magnetic moment, coercivity, or thermal stability of the magnetic material formed from the iron and nitrogen-containing mixture. Examples of ferromagnetic or non-magnetic dopants include those selected from the group consisting of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Ca, Pt, Au, Sm, C, Pb, W, Ga, Y, Mg, Hf, and Ta. For example, at least one Fe 16 By including Mn dopant atoms at a level of about 5 at.% to about 15 at.% in an iron nitride material containing N2 phase domains, the Fe 16 The thermal stability of the N2 phase domain and the coercivity of the material can be improved. In some examples, two or more (e.g., at least two) ferromagnetic or nonmagnetic dopants containing iron and nitrogen can be included in the mixture. In some examples, the ferromagnetic or nonmagnetic dopants can function as domain wall pinning sites and improve the coercivity of a magnetic material formed from a mixture containing iron and nitrogen. Table 1 includes examples of ferromagnetic or nonmagnetic dopant concentrations in a mixture containing iron and nitrogen.

[0050] [Table 1]

[0051] Alternatively or additionally, the mixture containing iron and nitrogen may include at least one phase stabilizer. The at least one phase stabilizer may be Fe 16The at least one phase stabilizer may be an element selected to improve at least one of the iron and nitrogen volume ratio, thermal stability, coercivity, and erosion resistance. When present in a mixture, the at least one phase stabilizer may be present in a mixture containing iron and nitrogen at a concentration of about 0.1 at.% to about 15 at.%. In some examples where at least two phase stabilizers are present in the mixture, the total concentration of the at least two phase stabilizers can be about 0.1 at.% to about 15 at.%. The at least one phase stabilizer may include, for example, B, Al, C, Si, P, O, Co, Cr, Mn, and / or S. For example, at least one Fe 16 By including Mn dopant atoms at a level of about 5 at.% to about 15 at.% in iron nitride materials containing N2 phase domains, the Fe 16 The thermal stability of the N2 phase domain and the magnetic coercivity of the material can be improved.

[0052] Alternatively, instead of forming a solid material containing iron and nitrogen, a nitrogen source may be mixed with molten iron to form a molten mixture containing iron and nitrogen. Further details regarding mixing a nitrogen source with molten iron are illustrated and described below with respect to FIG. 5.

[0053] In some examples, instead of forming a molten material (12) including iron and nitrogen, the technique of FIG. 1 may include forming a molten material including only iron, or forming a molten material including iron and at least one of N, C, B, O, P, Y, Mn, Co, Cr, Si, Al, Zn, etc., in relative proportions such that at least some of the material forms a body-centered tetragonal crystal structure upon casting.

[0054] The technique of Figure 1 also includes casting iron and nitrogen containing materials in the presence of an applied magnetic field (14), and Figures 2-4 show exemplary apparatus that can be used to cast iron and nitrogen containing materials in the presence of an applied magnetic field.

[0055] 2 is a conceptual diagram illustrating an exemplary system 20 for performing a casting technique on an iron and nitrogen containing mixture utilizing an RF furnace 22, a crucible 26, and an optional quenching medium 28. System 20 includes an RF furnace 22 surrounding a crucible 26. The crucible may be formed of a material that is thermally stable at the temperatures within RF furnace 22 during heating of the iron and nitrogen containing mixture. For example, crucible 26 may include one or more refractory materials, such as graphite, refractory ceramic, etc.

[0056] The RF furnace 22 also includes an RF source 24, shown in FIG. 2 as a plurality of coils used to generate an RF magnetic field and heat at least the iron- and nitrogen-containing mixture in the crucible 26. In some examples, the RF source 24 can generate RF energy having a frequency of about 13.56 GHz or about 900 MHz, in some examples. The RF source 24 can inductively heat the iron- and nitrogen-containing mixture directly, or by heating a structure (e.g., the crucible 26) in the RF furnace 22 and then heating the iron- and nitrogen-containing mixture. The iron- and nitrogen-containing mixture can be heated in the RF furnace 22 above the melting temperature of the iron- and nitrogen-containing mixture to form a molten iron- and nitrogen-containing mixture.

[0057] In some examples, the shape of the crucible 26 can define the shape of the iron and nitrogen-containing mixture, such as at least one wire, ribbon, or other article having a length greater than its width or diameter. In some examples, the temperature of the crucible 26 can be maintained at a temperature of about 650°C to about 1200°C during the casting process. In some examples, the temperature of the crucible 26 can be maintained at a temperature of about 800°C to about 1200°C during the casting process. The casting process can be carried out in air, a nitrogen environment, an inert environment, a partial vacuum, a full vacuum, or any combination thereof. The casting process can be carried out at any pressure, such as from about 0.1 GPa to about 20 GPa.

[0058] The system 20 also includes a magnetic field generator 30 that generates an external magnetic field 32 to which the RF furnace 22 and the material (e.g., a molten mixture comprising iron and nitrogen) within the RF furnace are exposed. The external magnetic field 32 can be applied to the molten mixture comprising iron and nitrogen while the molten mixture cools into a solid material. In some examples, the external magnetic field 32 can be applied throughout the entire time the mixture comprising iron and nitrogen is melting. In some examples, the external magnetic field 32 can be applied while the solid material comprising iron and nitrogen is melted to form the molten mixture comprising iron and nitrogen.

[0059] The external magnetic field 32 may affect the nucleation and growth of crystal grains during cooling and solidification of the molten mixture of iron and nitrogen into a solid mixture of iron and nitrogen. For example, without wishing to be bound by any theory of action, the Gibbs free energy of a crystal grain may depend on its orientation with respect to the external magnetic field 32. For example, a crystal grain whose (002) or (004) plane is substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the external magnetic field 32 may have a lower Gibbs free energy than a crystal grain whose (110), (112), (202), or (200) plane is substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the external magnetic field 32. Thus, crystal grains are more likely to nucleate and grow with their (002) or (004) planes substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the external magnetic field 32. This can promote substantial orientation (e.g., oriented or near-oriented) of the crystallographic axes of the iron or iron nitride crystals formed during the casting process, thereby increasing the α″-Fe 16 When N2 is formed, α”-Fe 16 The crystallographic axes of N2 can be encouraged to be substantially aligned (eg, aligned or nearly aligned (eg, within about 5 degrees of alignment)).

[0060] Additionally or alternatively, the external magnetic field 32 may promote the diffusion of nitrogen into the interstitial spaces within the iron lattice, thereby reducing or substantially preventing nitrogen from diffusing out of the iron and nitrogen-containing material. While not wishing to be bound by any theory of operation, it is currently believed that the external magnetic field 32 may interact with the iron crystal lattice, distorting the crystal lattice as the iron crystals nucleate and grow. The distortion of the iron crystal lattice may allow nitrogen to more easily diffuse into the interstitial spaces in the iron lattice. Once nitrogen diffuses into the interstitial spaces within the iron lattice, it may become more difficult for the nitrogen to diffuse out of the iron lattice. Additionally or alternatively, while not wishing to be bound by any theory of operation, it is currently believed that the external magnetic field 32 may weaken convection in the molten iron nitride mixture, thereby reducing the movement of nitrogen atoms forward of the solid-liquid interface during the growth of the iron nitride crystals.

[0061] Because the external magnetic field 32 can affect the nucleation density and defect density during the nucleation and growth process, the external magnetic field 32 can also affect the iron grain size, grain size uniformity, grain boundaries, and grain shape. For example, due to the application of the external magnetic field 32, in addition to having uniaxial magnetic anisotropy, a workpiece formed by casting a material comprising iron and nitrogen in the presence of an applied magnetic field (14) can include at least one iron nitride crystal or grain that exhibits an anisotropic shape. The at least one anisotropically shaped iron nitride crystal or grain can exhibit an aspect ratio of about 1.1 to about 50, e.g., about 1.4 to about 50, or 2.2 to about 50, or about 5 to about 50. As used herein, aspect ratio is defined as the ratio of the length of the longest dimension to the length of the shortest dimension of an anisotropic grain, where the shortest dimension is measured in a direction substantially perpendicular (e.g., perpendicular or nearly perpendicular (e.g., within about 5 degrees of perpendicular)) to the longest dimension. In some examples, α″-Fe 16 The shortest dimension of the N2 crystals or crystal grains 84 is about 5 nm to about 300 nm.

[0062] In some examples, the longest dimension of at least one anisotropically shaped iron nitride crystal or grain can be substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the direction of the applied magnetic field 32, and thus the direction of the uniaxial magnetic anisotropy. Similarly, the longest dimension of at least one anisotropically shaped iron nitride crystal or grain can be substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the easy axis of the magnetocrystalline anisotropy of the anisotropically shaped iron nitride crystal or grain. For example, body-centered tetragonal (bct) Fe 16 In the case of N2 and Fe, the (002) texture can be substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)) to the longest dimension of the crystals or grains. Thus, the shape anisotropy possessed by anisotropically shaped iron nitride crystals or grains can contribute to the magnetic anisotropy of the material.

[0063] In some instances, the applied magnetic field can affect the properties of grain boundaries, such as by hardening the grain boundaries. The applied magnetic field can promote the creation of pinning sites, such as dopant atoms or defects, located at or near the grain boundaries during the casting process (14), thereby increasing the hardness of the grain boundaries (e.g., regions within about 1 nm to about 100 nm of the grain boundaries). For example, the applied magnetic field can promote the migration of dopant atoms or defects within the grains to the grain boundaries.

[0064] In some examples, the external magnetic field 32 may be a static magnetic field generated by a DC mode electromagnet. The static magnetic field may not change as a function of time during the casting technique. The DC mode external magnetic field 32 may have a magnetic flux density of about 0.01 Tesla (T) to about 50 T. In some examples, the external magnetic field 32 may be at least 0.2 T. In some examples, the external magnetic field 32 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 32 is about 5 T to about 10 T. In other examples, the external magnetic field 32 is about 8 T to about 10 T. In other examples, the external magnetic field 32 is a varying magnetic field generated by an AC mode electromagnet. The varying magnetic field may change as a function of time during the casting technique. The AC mode external magnetic field 32 may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field 32 can be at least about 0.2 T. In some examples, the external magnetic field 32 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 32 is between about 5 T and about 10 T. In other examples, the external magnetic field 32 is between about 8 T and about 10 T.

[0065] In some examples, the external magnetic field 32 may be substantially uniform (e.g., uniform or nearly uniform (e.g., within about 5%)) throughout the RF furnace 22, or at least throughout the volume occupied by the crucible 26. In other examples, the external magnetic field 32 may vary as a function of position. For example, the external magnetic field 32 may vary along the direction of the external field (indicated by the direction of the arrow in FIG. 2). For example, the gradient can be from about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter), e.g., from about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) to about 50 Tesla / meter (about 0.05 Tesla / millimeter), or from about 1 Tesla / meter (about 0.001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter). In some examples, the gradient can be a monotonically increasing or decreasing flux density of the external magnetic field 32 .

[0066] During casting of the iron- and nitrogen-containing material in the presence of the external magnetic field 32 (14), the molten iron- and nitrogen-containing material can be cooled and solidified. In some instances, this cooling process can be relatively slow; for example, cooling can be triggered by turning off the heat of the RF furnace 22. In other instances, the molten iron- and nitrogen-containing material can be quenched in a quench medium to more quickly cool and solidify the iron- and nitrogen-containing material. The system of FIG. 2 optionally includes a quench medium 28. In some instances, the quench medium 28 can include water (room temperature, cryogenic, or ice water), oil, brine, aqueous ammonia, or an amide. The molten iron- and nitrogen-containing material can be poured into the quench medium, or the quench medium can be circulated around the crucible 26 or the solidified (but still hot) iron- and nitrogen-containing material. If used, the temperature of the quench medium 28 can be from about -269°C to about 210°C.

[0067] The cast material containing iron and nitrogen may include at least one iron nitride. In addition to iron and / or nitrogen, the at least one iron nitride may be, for example, FeN, FeN (e.g., ξ-FeN), FeN (e.g., ε-FeN), FeN (e.g., γ'-FeN and / or γ-FeN), FeN, α-FeN, α″-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). The cast material is then mixed with at least some of the iron nitride of the type described above to form an α″-Fe 16 It may be subjected to further processing to convert it to N2. Some examples of further processing are described below with respect to FIG.

[0068] In some instances, other types of apparatus can be used to cast a mixture containing iron and nitrogen in the presence of an external magnetic field rather than using the system shown in Figure 2. Figure 3 shows a schematic diagram of a system 40 including a crucible heating stage 42 that can be used to cast a material containing iron and nitrogen 46 in the presence of an external magnetic field. Figure 4 is a schematic diagram illustrating in more detail one example of the crucible heating stage 42 shown in Figure 3.

[0069] As best shown in FIG. 3 , the iron- and nitrogen-containing material 46 is encased in a cladding material 48. The cladding material 48 can be glass or another amorphous material with a melting point similar to glass. The cladding material 48 can substantially encapsulate (e.g., encase or nearly encapsulate) the iron- and nitrogen-containing material 46. Because the cladding material 48 is amorphous, it can tightly encase and apply stress to the material. In this manner, the cladding material 48 can facilitate the introduction of strain into the iron- and nitrogen-containing material 46, which can result in the formation of a material with a high saturation magnetization. The iron- and nitrogen-containing material 46 can be in the form of a wire, ribbon, film, or the like before entering the crucible heating stage 42.

[0070] 3 and 4, the iron and nitrogen containing material 46 passes vertically from the top to the bottom of the figure through the crucible heating stage 42. In other examples, the iron and nitrogen containing material 46 may pass vertically from the bottom to the top of the figure through the crucible heating stage 42.

[0071] The crucible heating stage 42 defines an opening 56 through which the iron- and nitrogen-containing material 46 passes (e.g., through which a portion of the iron- and nitrogen-containing material 46 is disposed). In some examples, no portion of the crucible heating stage 42 contacts the iron- and nitrogen-containing material 46 during heating of the iron- and nitrogen-containing material 46. In some embodiments, this is advantageous because it reduces the risk of undesirable elements or species contacting and diffusing into the iron- and nitrogen-containing material 46. Undesirable elements or species may affect the properties of the iron- and nitrogen-containing material 46. Therefore, it may be desirable to reduce or limit contact between the iron- and nitrogen-containing material 46 and other materials.

[0072] The crucible heating stage 42 also includes an inductor 44 that surrounds at least a portion of the opening 56 defined by the crucible heating stage 42. The inductor 44 includes a conductive material, such as aluminum, silver, or copper, through which an electric current can flow. The electric current passing through the inductor 44, due to alternating current (AC), can induce eddy currents in the iron- and nitrogen-containing material 46, causing the iron- and nitrogen-containing material 46 to heat.

[0073] The iron and nitrogen containing material 46 is heated by eddy currents to form a molten iron and nitrogen containing material 46. In some examples, not shown in Figures 3 and 4, during the melting process, the iron and nitrogen containing material 46 is axially stretched such that the thickness or diameter of the iron and nitrogen containing material 46 is reduced relative to the solid iron and nitrogen containing material 46. The iron and nitrogen containing material 46 remains substantially encapsulated by the cladding material 48 during the melting process.

[0074] In some examples, the molten material comprising iron and nitrogen may be drawn through openings in the coil 50, which may define the cross-sectional size and shape of the cast material 52 comprising iron and nitrogen.

[0075] Optionally, to facilitate cooling of the iron- and nitrogen-containing cast material 52, the iron- and nitrogen-containing cast material 52 may be exposed to a cooling medium, such as water (room temperature, cold, or ice water), oil, brine, aqueous ammonia, or an amide. In another example, the iron- and nitrogen-containing cast material 52 may be air-cooled.

[0076] During the melting and cooling portions of the casting process, the iron- and nitrogen-containing material 48 (solid, molten, and cast 52) ​​is exposed to an external magnetic field 56 generated by magnets 54. The external magnetic field 56 can affect grain nucleation and growth during cooling and solidification of the iron- and nitrogen-containing molten material 48 into the iron- and nitrogen-containing cast material 52, as described with respect to FIG. 2. Additionally or alternatively, the external magnetic field 56 can promote the diffusion of nitrogen into interstitial spaces in the iron lattice, thereby reducing or substantially preventing (e.g., preventing or nearly preventing) nitrogen from diffusing out of the iron- and nitrogen-containing material. Because the external magnetic field 56 can affect nucleation density and defect density during the nucleation and growth process, the external magnetic field 56 can also affect the iron grain size and grain boundaries.

[0077] In some examples, the external magnetic field 56 may be similar or substantially the same (e.g., the same or nearly the same) as the external magnetic field 32 described with respect to FIG. 2 . For example, the external magnetic field 56 may be a static magnetic field generated by a DC-mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In other examples, the external magnetic field 56 may be a varying magnetic field generated by an AC-mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field 56 can be at least 0.2 T. In some examples, the external magnetic field 56 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 56 is about 5 T to about 10 T. In other examples, the external magnetic field 56 is about 8 T to about 10 T. In some examples, the external magnetic field 56 can be substantially uniform (e.g., uniform or nearly uniform (e.g., within about 5%)) throughout the crucible heating stage 42, or at least throughout the volume of the iron- and nitrogen-containing material 48. In other examples, the external magnetic field 56 may vary as a function of position. For example, the external magnetic field 56 may vary along the direction of the external field (as indicated by the direction of the arrow in FIG. 3). For example, the gradient can be between about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) and about 1000 Tesla / meter (about 1 Tesla / millimeter), e.g., between about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) and about 50 Tesla / meter (about 0.05 Tesla / millimeter), or between about 1 Tesla / meter (about 0.001 Tesla / millimeter) and about 1000 Tesla / meter (about 1 Tesla / millimeter). In some examples, the gradient can be a monotonically increasing or decreasing magnetic flux density of the external magnetic field 56 .

[0078] The iron and nitrogen containing cast material 52 may include at least one iron nitride. In addition to iron and / or nitrogen, the at least one iron nitride may be, for example, FeN, FeN (e.g., ξ-FeN), FeN (e.g., ε-FeN), FeN (e.g., γ'-FeN and / or γ-FeN), FeN, α-FeN, α″-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). The cast material is then mixed with at least some of the iron nitride of the type described above to form an α″-Fe 16 It may be subjected to further processing to convert it to N2. Some examples of further processing are described below with respect to FIG.

[0079] 5 is a conceptual diagram illustrating another exemplary system 60 for belt casting an exemplary iron nitride workpiece in the presence of an external magnetic field. The belt casting system 60 may include an ingot chamber 62 containing a molten iron ingot 64 and is heated by a heat source, for example, in the form of a heating coil 66. In some examples, the temperature of the molten iron ingot 64 in the ingot chamber 62 may be greater than about 1800 Kelvin (K; about 1526.85°C). The pressure of the iron ingot 64 in the ingot chamber 62 may be between about 0.06 MPa and about 0.12 MPa.

[0080] Ingot chamber 62 includes a nitrogen inlet 68 through which a nitrogen source is introduced into molten iron ingot 64 to form molten iron nitride mixture 70. Nitrogen may be supplied through nitrogen inlet 68 in a variety of forms or from a variety of sources. For example, nitrogen may be supplied in the form of ammonia, ammonium azide, or urea, which is introduced through nitrogen inlet 68 and then decomposes to release nitrogen atoms upon mixing with the molten iron in molten iron nitride mixture 70.

[0081] In some instances, the nitrogen source may be provided to provide an approximately stoichiometric number of nitrogen atoms in the iron nitride mixture 70. 16The stoichiometric ratio of iron to nitrogen in N2 is 8:1. Therefore, the approximate number of iron atoms in iron nitride mixture 70 can be determined, and nitrogen atoms equal to about 1 / 8 (12.5%) of the iron atoms, for example, about 8 at.% to about 15 at.%, can be supplied to iron nitride mixture 70 from nitrogen inlet 68.

[0082] The molten iron nitride mixture 70 flows out of the ingot chamber 62 through a nozzle head 72 and forms an iron nitride strip 74. The iron nitride strip 74 is fed into a gap region between the surfaces of counter-rotating first and second pinch rollers 76a and 76b (collectively "pinch rollers 76"). In some examples, the distance from the nozzle head 72 to the surfaces of the pinch rollers 76 may be between about 1 mm and about 50 mm, for example, about 4 mm.

[0083] In some examples, the rotational speed of the first pinch roller 76a and the second pinch roller 76b can range from about 10 revolutions per minute (rpm) to 5000 rpm, and the rotational speed of the rollers 76 can be approximately the same. In some examples, the pinch roller 76 is actively cooled, for example, using water cooling, to maintain the surface of the roller 76 at a temperature lower than that of the iron nitride strip 74 and aid in cooling and casting the iron nitride strip 74. For example, the temperature of the pinch roller 76 may be maintained at about 300 K (about 26.85°C) to about 400 K (about 126.85°C). The pressure exerted by the pinch roller 76 on the iron nitride strip 74 can be about 0.04 MPa to about 0.1 MPa.

[0084] After the iron nitride strip 74 is pressed between the pinch rollers 76 and cooled, the iron nitride strip 74 forms textured iron nitride sheets 78a and 78b. In some examples, the textured iron nitride sheets 78a and 78b (collectively "textured iron nitride sheets 78") may form textured iron nitride ribbons (either individually or after compression of multiple textured iron nitride sheets 78) having at least one dimension (e.g., thickness) of about 1 μm to about 10 mm, e.g., about 5 μm to about 1 cm. Each of the textured iron nitride sheets 78 may include, for example, a (002) or (004) crystal texture. In other words, the major surfaces of each of the textured iron nitride sheets 78 may be parallel to the (002) or (004) surfaces of all or substantially all of the iron crystals within each of the textured iron nitride sheets 78. By using textured iron nitride sheets 78a and 78b in which all or substantially all (e.g., all or nearly all (e.g., greater than 95%)) of the iron crystals have crystallographic axes that are substantially aligned (e.g., aligned or nearly aligned (e.g., within about 5 degrees of being aligned)), FeN and Fe 16 The anisotropy formed when forming the N2 phase domains can be substantially aligned between the crystals.

[0085] During the belt casting technique, the magnet 80 can generate an external magnetic field 82 to which at least the molten iron nitride mixture 70 and the iron nitride strip 74 are exposed. The external magnetic field 82 can affect grain nucleation and growth during cooling and solidification of the molten iron nitride mixture 70 into the iron nitride strip 74, as described above with respect to FIG. 2 . Additionally or alternatively, the external magnetic field 82 can promote the diffusion of nitrogen into the interstitial spaces of the iron lattice, thereby reducing or substantially preventing (e.g., preventing or nearly preventing) nitrogen from diffusing out of the iron and nitrogen-containing material. Because the external magnetic field 82 can affect nucleation density and defect density during the nucleation and growth process, the external magnetic field 82 can also affect the iron grain size and grain boundaries.

[0086] In some examples, the external magnetic field 82 may be similar or substantially the same as the external magnetic field 32 described with respect to FIG. 2 . For example, the external magnetic field 82 may be a static magnetic field generated by a DC-mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field 82 may be at least about 0.2 T. In some examples, the external magnetic field 82 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 82 may be about 5 T to about 10 T. In other examples, the external magnetic field 82 is about 8 T to about 10 T. In other examples, the external magnetic field 82 may be a varying magnetic field generated by an AC-mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field 82 may be at least about 0.2 T. In some examples, the external magnetic field 82 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 82 is between about 5 T and about 10 T. In other examples, the external magnetic field 82 is between about 8 T and about 10 T. In some examples, the external magnetic field 82 can be substantially uniform (e.g., uniform or nearly uniform (within about 5%)) throughout the belt casting system 60, or at least throughout the volume of the molten iron nitride mixture 70 and the iron nitride strip 74. In other examples, the external magnetic field 82 may vary as a function of position. For example, the external magnetic field 82 may vary along the direction of the external magnetic field (indicated by the direction of the arrow in FIG. 5 ).For example, the gradient can be from about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter), e.g., from about 0.01 Tesla / meter to about 50 Tesla / meter (about 0.05 Tesla / millimeter), or from about 1 Tesla / meter (about 0.001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter). In some examples, the gradient can be a monotonic increase or decrease in the magnetic flux density of the external magnetic field 82.

[0087] The iron nitride strip 74 may include at least one iron nitride, in addition to iron and / or nitrogen, such as, for example, FeN, FeN (e.g., ξ-FeN), FeN (e.g., ε-FeN), FeN (e.g., γ'-FeN and / or γ-FeN), FeN, α-FeN, α″-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). The iron nitride strip 74 is then formed by dissolving at least some of the iron nitride of the type described above in α″-Fe 16 It may be subjected to further processing to convert it to N2. Some examples of further processing are described below with respect to FIG.

[0088] In the above examples, casting techniques were described in which a material containing a mixture of iron and nitrogen was exposed to a magnetic field during the casting technique. The present disclosure also describes the casting of α″-Fe in the presence of an external magnetic field. 16 A compression technique for joining multiple workpieces containing N2 phase domains is also described. Figure 6 shows the α″-Fe 16 Schematic diagram showing the N2 unit cell. As shown in Figure 6, the α″-Fe 16 In the N2 phase, the N atoms are aligned along the (002) (iron) crystallographic plane. The iron nitride unit cell is distorted, <001> The length of the unit cell along the axis is about 6.28 angstroms (Å), <010> Axle and <100> The length of the unit cell along the axis is approximately 5.72 Å. α”-Fe 16 The N2 unit cell, when in a distorted state, can be called a body-centered tetragonal (bct) unit cell. α”-Fe16 When the N2 unit cell is in a distorted state, <001> The axis can be called the c-axis of the unit cell. This c-axis is 16 N2 unit cell. In other words, α″-Fe 16 N2 crystals exhibit magnetic anisotropy.

[0089] α”-Fe 16 N2 has high saturation magnetization and magnetic anisotropy constant. The high saturation magnetization and magnetic anisotropy constant result in a magnetic energy product that can be higher than that of rare earth magnets. For example, thin film α″-Fe 16 Experimental evidence from N2 permanent magnets indicates that bulk Fe 16 N2 permanent magnets have been shown to have desirable magnetic properties, including a high energy product of approximately 134 Megagauss-Oersted (MGOe), which is about twice the energy product of NdFeB (which has an energy product of approximately 60 MGOe). Calculations and experiments suggest that α"-Fe 16 The magnetocrystalline anisotropy of N2 is approximately 1.0 to 2.0 × 10 7 erg / cm 3 It is shown that α”-Fe 16 N2 is approximately 2.9 Bohr magnetons per iron atom μ B It also has a relatively high theoretical magnetic saturation moment of 0.1 / Fe. ​​Furthermore, iron and nitrogen are abundant elements and are therefore relatively cheap and easy to procure.

[0090] Without wishing to be bound by theory, it is believed that three types of anisotropy exist in α”-Fe 16 These three types of anisotropy can contribute to the magnetic anisotropy energy or magnetic anisotropy field of N2 or other iron-based magnetic materials. These three types of anisotropy include magnetocrystalline anisotropy, shape anisotropy, and strain anisotropy. As mentioned above, magnetocrystalline anisotropy may be related to the distortion of the bcc iron crystal lattice to the bct iron nitride crystal lattice shown in Figure 6. Shape anisotropy may be related to the shape of the iron nitride crystals or grains, or the shape of the iron nitride workpiece. For example, as shown in Figure 7, the α"-Fe 16The N2 crystals or grains 84 may exhibit a longest dimension (substantially parallel to the z-axis in FIG. 7; orthogonal x, y, and z axes are shown for ease of illustration only). 16 The N crystals or grains 84 may exhibit a shortest dimension (e.g., substantially parallel to the x-axis or y-axis of FIG. 7). 16 Measurements can be taken perpendicular to the longest axis of the N2 crystal or grain 84.

[0091] In some instances, α″-Fe 16 The N2 crystals or grains 84 can exhibit an aspect ratio of about 1.1 to about 50, e.g., about 1.4 to about 50, or 2.2 to about 50, or about 5 to about 50. In some examples, the α″-Fe 16 The shortest dimension of the N2 crystals or crystal grains 84 is about 5 nm to about 300 nm.

[0092] The strain anisotropy is α”-Fe 16 This may be related to the strain on N2 or other iron-based magnetic materials. In some instances, α"-Fe 16 The N2 grains are located or embedded in a matrix containing grains of iron or other types of iron nitride (e.g., Fe4N). 16 The N2 grains may have a different thermal expansion coefficient than the grains of iron or other types of iron nitride. This difference can be attributed to the α”-Fe 16 Due to differential dimensional changes in the N2 grains and the grains of iron or other types of iron nitrides, the α″-Fe 16 This may introduce strain into the N2 grains. Alternatively or additionally, α″-Fe 16 During processing to form N2 grains, a material or workpiece may be subjected to strain, either mechanically or by exposure to an applied magnetic field, and at least some of this strain may remain in the processed material or workpiece. Annealing may result in a redistribution of the internal stress and local microstructure of the sample to reduce the magnetoelastic energy under stress. The magnetic domain structure under strain anisotropy depends on the magnetoelastic energy, magnetostatic energy, and exchange energy.

[0093] FIG. 8 shows multiple α″-Fe nanoparticles in a matrix 88 of another material. 16 8 is a conceptual diagram illustrating an exemplary workpiece 86 including N2 crystals or grains 84. As shown in FIG. 16 Each of the N2 crystals or grains 84 exhibits an anisotropic shape. 16 N2 crystals or grains 84, respectively, α”-Fe 16 The easy axis of magnetization of the N2 crystals or grains is the same as that of the respective α”-Fe 16 N2 crystals or grains. In some examples, each α″-Fe 16 The magnetic easy axes of the N2 crystals or grains are substantially parallel (e.g., parallel or nearly parallel, e.g., within about 5 degrees of parallel) to each of the other easy axes (and thus substantially parallel (e.g., parallel or nearly parallel, e.g., within about 5 degrees of parallel) to each of the other longest dimensions). In some examples, this can be achieved by casting the material used to form workpiece 86 in the presence of an applied magnetic field, as described with respect to FIGS. 1-5. In this manner, workpiece 86 can have structural properties that result in magnetocrystalline anisotropy, shape anisotropy, and strain anisotropy, all of which contribute to the anisotropy field of workpiece 86.

[0094] Fig. 9 is a diagram showing an exemplary hysteresis curve for the workpiece 86. The hysteresis curve shown in Fig. 9 indicates that the workpiece 86 has magnetic anisotropy because the coercive force (x-axis intercept) of the workpiece 86 when a magnetic field is applied parallel to the c-axis direction in Fig. 8 is different from the coercive force (x-axis intercept) of the workpiece 86 when a magnetic field is applied parallel to the a-axis and b-axis directions in Fig. 8.

[0095] α”-Fe 16 It can be difficult to directly produce bulk materials containing N2 phase domains. An alternative technique described herein is to use α″-Fe 16forming smaller pieces containing N2 phase domains, and then joining (or consolidating) the smaller pieces to form α″-Fe 16 10 shows a method for forming a bulk magnetic material comprising: adding at least one α″-Fe to form a bulk magnetic material comprising N2 phase domains; 16 FIG. 1 is a flow diagram illustrating an exemplary technique for consolidating multiple workpieces containing an N2 phase domain.

[0096] In some instances, at least one α″-Fe is added to form the bulk magnetic material. 16 Instead of consolidating multiple workpieces containing N phase domains, the technique of FIG. 10 consolidates at least one iron-based phase domain containing uniaxial magnetic anisotropy, e.g., strained iron, Fe 16 The method may include consolidating a plurality of workpieces comprising C2 or iron and at least one of B, O, P, Y, Mn, Co, Cr, Si, Al, and the like.

[0097] The technique of FIG. 10 includes mixing (92) a plurality of workpieces including iron nitride with a binder material. At least some of the plurality of workpieces including iron nitride include at least one α″-Fe 16 In some examples, each of the plurality of workpieces comprising iron nitride may comprise at least one α″-Fe 16 Additionally, the workpieces may contain other iron nitride phase domains (e.g., FeN, FeN (e.g., ξ-FeN), FeN (e.g., ε-FeN), FeN (e.g., γ'-FeN and / or γ-FeN), FeN, α-FeN, or FeN x (where x is about 0.05 to about 0.5)), iron phase domains, and the like.

[0098] The multiple workpieces can include any shape and size. In some examples, the workpieces include one dimension that is longer than the other dimensions of each workpiece. Examples of workpieces having a longer dimension than the other dimensions include fibers, wires, filaments, cables, films, thick films, foils, ribbons, sheets, etc. In other examples, the workpieces may not have a longer dimension than the other dimensions of the workpiece. For example, the workpieces can be particles or powders, such as spheres, cylinders, platelets, flakes, regular polyhedra, irregular polyhedra, and any combination thereof. Examples of suitable regular polyhedra include tetrahedrons, hexahedrons, octahedrons, decahedrons, dodecahedrons, etc., and non-limiting examples of which include cubes, prisms, pyramids, etc.

[0099] Binder materials include any material that can be pressed together with multiple workpieces to form a cohesive bulk material. In some examples, binders include resins, waxes, or low-melting-point metals. Low-melting-point metals include, for example, zinc (Zn), tin (Sn), bismuth (Bi), gallium (Ga), sodium (Na), or lithium (Li). Exemplary resins include natural or synthetic resins, including ion-exchange resins such as those available under the trade name Amberlite™ from The Dow Chemical Company, Midland, Michigan; epoxy resins, such as bismaleimide-triazine (BT)-epoxy; polyacrylonitrile; polyesters; silicones; prepolymers; polyvinyl butyral; urea-formaldehyde; and the like.

[0100] The mixture including the plurality of workpieces and the binder may then be exposed to an external magnetic field (94). The external magnetic field may have a predetermined orientation relative to the mixture including the plurality of workpieces and the binder. This predetermined orientation may be used to define the magnetization direction of the bulk material. For example, when the mixture including the plurality of workpieces and the binder is first mixed, the easy axes (e.g., α″-Fe16 The easy axes of the N2) may be substantially randomly oriented (randomly oriented or nearly randomly oriented). When a bulk material is formed in which the easy axes of each of the multiple workpieces are substantially randomly oriented, the magnetic anisotropy of the bulk material may be relatively small, which may reduce the magnetic properties (e.g., energy product) of the bulk magnetic material.

[0101] By using an external magnetic field to substantially align at least some of the easy axes of each of the workpieces, the magnetic anisotropy of the bulk magnetic material can be increased, thereby improving the magnetic properties (e.g., energy product) of the bulk magnetic material. The external magnetic field can also enable the magnetization direction of the bulk material to be determined, for example, by substantially aligning at least some of the easy axes of each of the plurality of workpieces. For example, a mixture of the binder and the plurality of workpieces can be placed in a mold that defines the near-net shape of the final magnetic material, and an external magnetic field can be oriented in a selected direction relative to the mold to determine the magnetization direction of the bulk material.

[0102] In some examples, the external magnetic field may be a static magnetic field generated by a DC mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field can be at least 0.2 T. In some examples, the external magnetic field may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field is about 5 T to about 10 T. In other examples, the external magnetic field is about 8 T to about 10 T.

[0103] In other examples, the external magnetic field 82 may be a varying magnetic field generated by an AC mode electromagnet and may have a magnetic flux density of about 0.01 Tesla to about 50 Tesla. In some examples, the external magnetic field 82 can be at least about 0.2 T. The external magnetic field 82 may be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the external magnetic field 82 is about 5 T to about 10 T. In other examples, the external magnetic field 82 is about 8 T to about 10 T. In some examples, the external magnetic field 82 is substantially uniform throughout the belt casting system 60, or at least throughout the volume of the molten iron nitride mixture 70 and the iron nitride strip 74. In other examples, the external magnetic field 82 may vary as a function of position. For example, the external magnetic field 82 may vary along the direction of the external magnetic field (indicated by the direction of the arrow in FIG. 5 ). For example, the gradient can be from about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter), e.g., from about 0.01 Tesla / meter (about 0.00001 Tesla / millimeter) to about 50 Tesla / meter (about 0.05 Tesla / millimeter), or from about 1 Tesla / meter (about 0.001 Tesla / millimeter) to about 1000 Tesla / meter (about 1 Tesla / millimeter). In some examples, the gradient can be a monotonic increase or decrease in the magnetic flux density of the external magnetic field 82.

[0104] While the mixture including the binder and the plurality of workpieces is exposed to an external magnetic field (94), the mixture may be compressed (96) to bond the binder and the plurality of workpieces and form a bulk magnetic material. Compressing the mixture including the binder and the plurality of workpieces (96) may include applying a pressure to the mixture. For example, the pressure may be from about 1 megapascal (MPa) to about 100 gigapascals (GPa) at room temperature. Compressing the mixture including the binder and the plurality of workpieces may be performed at a relatively low temperature (e.g., from about -268.93°C (the boiling point of liquid helium at atmospheric pressure) to about room temperature (about 23°C)). Alternatively, compressing the mixture including the binder and the plurality of workpieces may be performed at a relatively high temperature (e.g., from about room temperature (about 23°C) to about 210°C). The product of the compressing step may be α″-Fe 16 It can be a bulk magnetic material containing N2 phase domains.

[0105] In some instances, the casting and compaction processes described herein may be used to produce α″-Fe 16 This can be accomplished together with the same overall technique for forming bulk magnetic materials containing N2 phase domains. Figure 11 shows the formation of α"-Fe from raw materials containing iron and nitrogen. 16 1 is a flow diagram illustrating an exemplary method for forming a bulk magnetic material containing an N2 phase domain. The technique of FIG. 11 includes forming a molten mixture containing iron and nitrogen (102). This step is substantially the same as step (12) described with respect to FIG. 1. The technique of FIG. 11 also includes casting the molten mixture containing iron and nitrogen in the presence of an external magnetic field (104). This step may be similar or substantially the same as step (14) described with respect to FIG. 1.

[0106] The technique of FIG. 11 also optionally includes pressing (106) the iron and nitrogen-containing material. The iron and nitrogen-containing material may be pressed to obtain a predetermined size of the iron and nitrogen-containing material. During the pressing process, the temperature of the iron and nitrogen-containing material is maintained below about 250°C, and the iron and nitrogen-containing material may be subjected to a pressure of about 5 tons to 50 tons, depending on the desired final dimensions (e.g., thickness or diameter) of the iron and nitrogen-containing material. In some examples, upon completion of the pressing process, the iron and nitrogen-containing material may be in the form of a workpiece having dimensions of about 0.001 mm to about 50 mm in one or more axes (e.g., about 0.1 mm to about 50 mm diameter for wire, about 0.001 mm to about 5 mm thickness for ribbon). The iron and nitrogen-containing material may include at least one FeN iron nitride phase domain after pressing is completed.

[0107] In some examples, the technique also includes, if desired, quenching (108) the iron- and nitrogen-containing material. Quenching can fix the crystal structure and phase composition of the iron- and nitrogen-containing material. For example, quenching can promote the formation of FeN phase domains in the iron- and nitrogen-containing material. In some examples, during the quenching process, the iron- and nitrogen-containing material can be heated to a temperature above 650°C for about 0.5 hours to about 20 hours. In some examples, the temperature of the iron- and nitrogen-containing material can be rapidly reduced below the martensite temperature (Ms) of the workpiece alloy. For example, Fe 16 For N2, the martensite temperature (Ms) is about 250°C. The medium used for quenching can be a liquid, such as water, brine (having a salt concentration of about 1% to about 30%), a non-aqueous liquid or solution, such as oil, or liquid nitrogen. In other examples, the quenching medium can be a gas, such as nitrogen gas, at a flow rate of about 1 sccm to about 1000 sccm. In other examples, the quenching medium can include a solid, such as salt, sand, or the like. In some examples, a workpiece containing iron and nitrogen can be cooled at a rate exceeding 50°C per second during the quenching process. In some examples, the quenching process can be assisted by a magnetic field and / or an electric field.

[0108] The technique of FIG. 11 may further include stretching (or drawing) and annealing (110), (112) the iron and nitrogen containing material. This stretching and annealing process converts at least some of the FeN iron nitride phase domains in the iron and nitrogen containing material into Fe 16 The iron- and nitrogen-containing material can be transformed into a N2 phase domain. Various strain-inducing devices can be used to apply strain to the iron- and nitrogen-containing material. For example, the iron- and nitrogen-containing material can be received (e.g., wrapped) by a first set of rollers and a second set of rollers, and these sets of rollers can be rotated in opposite directions to apply a tensile force to the iron- and nitrogen-containing material. In another example, both ends of the iron- and nitrogen-containing material can be held by mechanical grippers, e.g., clamps, and the mechanical grippers can be moved away from each other to apply a tensile force to the iron- and nitrogen-containing material.

[0109] In some examples, the iron and nitrogen containing material comprises at least one iron crystal in the iron and nitrogen containing material. <001> The material may be stretched along a direction substantially parallel to the axis (e.g., parallel or nearly parallel (e.g., within about 5 degrees of parallel)). The strain-inducing device can stretch the iron and nitrogen-containing material to a specific elongation. For example, the strain for the iron and nitrogen-containing material can be about 0.3% to about 12%. In other examples, the strain for the iron and nitrogen-containing material can be less than about 0.3% or greater than about 12%. In some examples, applying a certain strain to the iron and nitrogen-containing material induces a substantially similar strain in the individual unit cells of the iron (or iron nitride), resulting in a unit cell strain of about 0.3% to about 12%.

[0110] The iron and nitrogen containing material can be annealed by heating the iron and nitrogen containing material while it is strained (112). The iron and nitrogen containing material may be annealed by heating the iron and nitrogen containing material to a temperature between about 100°C and about 250°C, for example, between about 120°C and about 200°C. Annealing the iron and nitrogen containing material while straining the iron and nitrogen containing material converts at least some of the iron nitride phase domains into α″-Fe 16It can promote the transformation into the N2 phase domain.

[0111] The annealing process may continue for a predetermined time sufficient to diffuse the nitrogen atoms into the appropriate interstitial spaces. In some examples, the annealing process may continue for about 20 hours to about 100 hours, for example, about 40 hours to about 60 hours. In some examples, the annealing process may be carried out under an inert atmosphere, such as Ar, to reduce or substantially prevent oxidation of the iron. In some embodiments, the temperature is kept substantially constant while annealing the iron and nitrogen containing material. The stretching (110) and annealing (112) of the iron and nitrogen containing material results in the formation of at least one α″-Fe 16 A magnetic material containing N2 phase domains can be obtained.

[0112] In some examples, the iron and nitrogen containing material may be exposed to an external magnetic field during stretching (110) and annealing (112) of the iron and nitrogen containing material. Annealing the iron nitride material in the presence of an applied magnetic field can increase the Fe content in the iron nitride material. 16 It can promote the formation of N2 phase. 16 Increasing the volume fraction of the N2 phase can improve the magnetic properties of magnetic materials containing iron nitride. Improved magnetic properties include, for example, coercivity, magnetization, and magnetic orientation. In some examples, the applied magnetic field can be at least 0.2 Tesla (T). The temperature at which the magnetic field annealing is performed can depend, at least in part, on the additional element additions to the iron nitride-based composition and the approach used to initially synthesize the iron nitride-based composition. In some examples, the magnetic field can be at least about 0.2 T, at least about 2 T, at least about 2.5 T, at least about 6 T, at least about 7 T, at least about 8 T, at least about 9 T, at least about 10 T, or higher. In some examples, the magnetic field is between about 5 T and about 10 T. In other examples, the magnetic field is between about 8 T and about 10 T. Further details regarding annealing materials containing iron and nitrogen are described in U.S. Provisional Application No. 62 / 019,046, filed June 30, 2014.

[0113] The technique of FIG. 11 involves the use of at least one α″-Fe 16 The process may include compressing 114 a plurality of workpieces of the magnetic material including the N2 phase domains to form a bulk magnetic material, which may be similar or substantially the same as the technique described with reference to FIG.

[0114] The technique of FIG. 11 may further include shaping (116) the bulk magnetic material (if desired). This shaping process may include, for example, slicing or grinding the surface of the bulk magnetic material to form the bulk magnetic material into a predetermined final shape. Finally, the technique of FIG. 11 may further include magnetizing (118) the bulk magnetic material (if desired). Thus, the technique of FIG. 11 may further include magnetizing (118) the bulk magnetic material. 16 Exemplary techniques are described for forming bulk magnetic materials containing N2 phase domains.

[0115] Item 1: A method comprising casting a material comprising iron in the presence of an applied magnetic field to form a workpiece comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T).

[0116] Clause 2: The method of clause 1, wherein casting the iron-containing material includes casting the iron- and nitrogen-containing material in the presence of an applied magnetic field to form a workpiece including at least one iron nitride phase domain.

[0117] Clause 3: The method of clause 1, wherein casting the material comprising iron comprises casting a material comprising iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al in the presence of an applied magnetic field to form a workpiece comprising at least one phase domain having uniaxial magnetic anisotropy.

[0118] Clause 4: The method of any one of clauses 1-3, wherein casting the iron-containing material in the presence of an applied magnetic field comprises casting the iron-containing material in the presence of an applied magnetic field to form a workpiece comprising at least one anisotropically shaped iron-based crystal grain, wherein the at least one anisotropically shaped iron-based crystal grain has an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic crystal grain, wherein the longest dimension and the shortest dimension are substantially perpendicular.

[0119] Item 5: The method of item 4, wherein at least one anisotropically shaped iron-based grain exhibits a shortest dimension of about 5 nm to about 300 nm.

[0120] Item 6: The method of items 4 or 5, wherein the at least one anisotropically shaped iron-based crystal grain comprises a plurality of anisotropically shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropically shaped iron-based crystal grains are oriented substantially parallel to one another.

[0121] Item 7: The method according to any one of items 4 to 6, wherein the major axis of each of the plurality of anisotropically shaped iron-based crystal grains is oriented substantially parallel to the direction of the applied magnetic field.

[0122] Item 8: The method of any one of items 4 to 7, wherein for each anisotropically shaped iron-based crystal grain, the respective easy axis of the magnetocrystalline anisotropy is substantially parallel to the respective longest axis.

[0123] Item 9: The method according to any one of items 1 to 8, wherein the strength of the applied magnetic field exceeds about 0.02T.

[0124] Item 10: The method according to any one of items 1 to 8, wherein the strength of the applied magnetic field exceeds about 2.5T.

[0125] Item 11: The method according to any one of items 1 to 8, wherein the strength of the applied magnetic field exceeds about 9T.

[0126] Item 12: The method according to any one of items 1 to 11, wherein the strength of the applied magnetic field is less than about 50T.

[0127] Item 13: The method according to any one of items 1 to 12, wherein the material further comprises at least one dopant.

[0128] Item 14. The method of item 13, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

[0129] Item 15: The method of item 13, wherein the at least one dopant comprises at least one of B, C, P, Si, or O.

[0130] Item 16: The method of item 2, wherein prior to casting, the concentration of nitrogen in the material is between about 8 atomic percent (at.%) and about 9 at.%.

[0131] Article 17: Casting heating the iron-containing mixture to form a molten iron-containing mixture; and cooling the iron-containing molten mixture to form a workpiece; 17. The method according to any one of items 1 to 16, comprising:

[0132] Item 18: The method of item 17, wherein cooling the molten mixture comprises quenching the molten mixture in a quenching medium.

[0133] Item 19: The method of item 18, wherein the quenching medium comprises at least one of water, ice water, brine, oil, aqueous ammonia, or an amide.

[0134] Item 20: The method of any one of items 17 to 19, wherein heating the iron-containing mixture comprises heating the iron-containing mixture in the presence of an applied magnetic field, and cooling the iron-containing molten mixture comprises cooling the iron-containing molten mixture in the presence of an applied magnetic field.

[0135] Item 21: The method according to any one of items 17 to 20, wherein heating the iron-containing mixture includes heating the iron-containing mixture in a crucible using a high-frequency furnace.

[0136] Item 22: The method of any one of items 17 to 20, wherein heating the iron-containing mixture includes heating the iron-containing mixture in a cold crucible, and the mixture is substantially encapsulated in a coating material.

[0137] Item 23: The method of any one of items 17 to 20, wherein cooling the iron-containing molten mixture includes cooling the iron-containing molten mixture between cooling rollers to form a workpiece.

[0138] Item 24: A method comprising: compressing a plurality of workpieces, each workpiece comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, in the presence of an applied magnetic field to form a bulk material comprising a plurality of iron-based phase domains comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least 0.01 Tesla (T), and the applied magnetic field defines a magnetization direction of the bulk material.

[0139] Item 25: At least one iron-based phase domain containing uniaxial magnetic anisotropy is composed of at least one α″-Fe 16 25. The method of paragraph 24, comprising an N2 phase domain.

[0140] Item 26: The method of item 24 or 25, wherein the at least one iron-based phase domain comprising uniaxial magnetic anisotropy comprises at least one of a body-centered tetragonal iron phase domain or a phase domain having a body-centered tetragonal crystal structure and comprising iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Al, or Zn.

[0141] Item 27: The method of items 24-26, wherein each workpiece comprises at least one iron-based phase domain having uniaxial magnetic anisotropy and at least one anisotropically shaped iron-based grain, the at least one anisotropically shaped iron-based grain having an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of the longest dimension to the length of the shortest dimension, the longest dimension and the shortest dimension being substantially perpendicular.

[0142] Item 28: The method of item 27, wherein at least one anisotropically shaped iron-based grain exhibits a shortest dimension of about 5 nm to about 300 nm.

[0143] Item 29: The method of item 27 or 28, wherein the at least one anisotropically shaped iron-based crystal grain comprises a plurality of anisotropically shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropically shaped iron-based crystal grains are oriented substantially parallel to one another.

[0144] Item 30: The method of any one of items 27 to 29, wherein the major axis of each of the plurality of anisotropically shaped iron-based crystal grains is oriented substantially parallel to the direction of the applied magnetic field.

[0145] Item 31: The method of any one of items 27 to 30, wherein for each anisotropically shaped iron-based crystal grain, the respective easy axes of the magnetocrystalline anisotropy are substantially parallel to the respective longest axes.

[0146] Item 32: A method according to any one of items 24 to 31, wherein the strength of the applied magnetic field is greater than about 0.02T.

[0147] Item 33: A method according to any one of items 24 to 31, wherein the strength of the applied magnetic field is greater than about 2.5T.

[0148] Item 34: A method according to any one of items 24 to 31, wherein the strength of the applied magnetic field is greater than about 9T.

[0149] Item 35: The method of any one of items 24 to 34, wherein the strength of the applied magnetic field is less than about 50T.

[0150] Item 36: The method of any one of items 24 to 35, wherein at least one of the plurality of workpieces further comprises at least one dopant.

[0151] Item 37: The method of item 36, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

[0152] Item 38: The method of item 36, wherein the at least one dopant comprises at least one of B, C, P, Si, or O.

[0153] Clause 39: The method of any one of clauses 24 to 38, wherein the applied magnetic field promotes substantial alignment of the easy magnetic axes of at least some of the plurality of workpieces.

[0154] Item 40: The method of any one of items 24 to 39, wherein compressing the plurality of workpieces includes mixing the plurality of workpieces with at least one of a resin, a wax, or a low-melting-point metal to form a mixture, and pressing the mixture to form a bulk material.

[0155] Item 41: The method of item 40, wherein pressing the mixture includes pressing the mixture at a pressure of about 1 MPa to about 100 GPa.

[0156] Item 42: The method of item 40 or 41, wherein pressing the mixture comprises cold-pressing the mixture at a temperature of about 4.2 Kelvin to about 295 Kelvin.

[0157] Item 43: The method of item 40 or 41, wherein pressing the mixture includes hot pressing the mixture at a temperature of about 295 Kelvin to about 533 Kelvin.

[0158] Item 44: The method of any one of items 40 to 43, wherein mixing the plurality of workpieces with at least one of a resin, a wax, or a low-melting-point metal includes mixing the plurality of workpieces with a low-melting-point metal material, and the low-melting-point metal includes at least one of Zn, Sn, Bi, Ga, Na, or Li.

[0159] Item 45: The method of any one of items 24 to 44, wherein one workpiece of the plurality of workpieces comprises at least one of a powder, a ribbon, or a wire.

[0160] Clause 46: The method of any one of clauses 24 to 43, further comprising the method of any one of clauses 1 to 22, wherein the workpiece is one of a plurality of workpieces.

[0161] Clause 47: An apparatus configured to carry out the method of any one of clauses 1 to 46.

[0162] Item 48: A workpiece formed by the method of any one of items 1 to 23.

[0163] Item 49: A bulk material formed by the method of any one of items 24 to 46.

[0164] Item 50: The bulk material according to item 49, wherein the bulk material is a bulk permanent magnet.

[0165] Item 51: A method comprising casting a material comprising at least one of nickel, iron, and cobalt in the presence of an applied magnetic field to form a workpiece comprising at least one nickel-, iron-, or cobalt-based phase domain comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T).

[0166] Item 52: The method of item 51, wherein the metal comprises iron.

[0167] Item 53: The method of item 52, wherein casting the iron-containing material includes casting the iron- and nitrogen-containing material in the presence of an applied magnetic field to form a workpiece including at least one iron nitride phase domain.

[0168] Item 54: A method according to any one of items 51 to 53, wherein the material containing at least one of nickel, iron or cobalt further contains at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn or Al.

[0169] Item 55: The method of any one of items 51 to 54, wherein the material further comprises at least one dopant, and the at least one dopant comprises at least one of B, C, P, Si, or O.

[0170] Item 56: The method of any one of items 51 to 55, further comprising compressing the plurality of workpieces.

[0171] Item 57: A workpiece comprising at least one anisotropically shaped iron-based grain, said at least one anisotropically shaped iron-based grain having an aspect ratio of about 1.1 to about 50, said aspect ratio being defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic grain, said longest dimension and shortest dimension being substantially perpendicular.

[0172] Item 58: The workpiece of item 57, wherein at least one anisotropically shaped iron-based grain exhibits a shortest dimension of about 5 nm to about 300 nm.

[0173] Item 59: The workpiece of item 57 or 58, wherein the at least one anisotropically shaped iron-based crystal grain comprises a plurality of anisotropically shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropically shaped iron-based crystal grains are oriented substantially parallel to one another.

[0174] Item 60: The workpiece of any one of items 57 to 59, further comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, wherein the longest dimension of at least one anisotropically shaped iron-based crystal grain is substantially parallel to the direction of the uniaxial magnetic anisotropy.

[0175] Item 61: The workpiece of any one of items 57 to 60, wherein at least one anisotropically shaped iron-based grain comprises iron nitride.

[0176] Item 62: Iron nitride is α”-Fe 16 62. The workpiece of claim 61, including N2.

[0177] Item 63: The workpiece of any one of items 57 to 60, wherein at least one anisotropically shaped iron-based grain comprises iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al.

[0178] Item 64: The workpiece of any one of items 57 to 63, further comprising at least one dopant.

[0179] Item 65: The workpiece of item 64, wherein at least one anisotropically shaped iron-based grain comprises the dopant.

[0180] Item 66: The workpiece of item 64 or 65, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

[0181] Item 67: The workpiece of item 64 or 65, wherein the at least one dopant comprises at least one of B, C, P, Si, or O.

[0182] Item 68: A workpiece according to any one of items 57 to 67, wherein for each anisotropically shaped iron-based crystal grain, the respective easy axes of magnetocrystalline anisotropy are substantially parallel to the respective longest axes.

[0183] Item 69: A bulk permanent magnet comprising at least one anisotropically shaped iron-based crystal grain, the at least one anisotropically shaped iron-based crystal grain having an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic crystal grain, the longest dimension and the shortest dimension being substantially perpendicular.

[0184] Item 70: The bulk permanent magnet of item 69, wherein at least one anisotropically shaped iron-based grain exhibits a shortest dimension of about 5 nm to about 300 nm.

[0185] Item 71: The bulk permanent magnet of item 69 or 70, wherein the at least one anisotropically shaped iron-based crystal grain comprises a plurality of anisotropically shaped iron-based crystal grains, the major axes of each of the plurality of anisotropically shaped iron-based crystal grains being oriented substantially parallel to one another.

[0186] Item 72: A bulk permanent magnet described in any one of items 69 to 71, further comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, wherein the longest dimension of at least one anisotropically shaped iron-based crystal grain is substantially parallel to the direction of the uniaxial magnetic anisotropy.

[0187] Item 73: The bulk permanent magnet described in any one of items 69 to 72, wherein the at least one anisotropically shaped iron-based crystal grain comprises iron nitride.

[0188] Item 74: The iron nitride is α″-Fe 16 74. The bulk permanent magnet of paragraph 73, comprising N2.

[0189] Item 75: A bulk permanent magnet described in any one of items 69 to 72, wherein the at least one anisotropically shaped iron-based crystal grain comprises iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al.

[0190] Item 76: A bulk permanent magnet according to any one of items 69 to 75, further comprising at least one dopant.

[0191] Item 77: The bulk permanent magnet of item 76, wherein at least one anisotropically shaped iron-based grain comprises said dopant.

[0192] Item 78: A bulk permanent magnet described in item 76 or 77, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

[0193] Item 79: A bulk permanent magnet according to item 76 or 77, wherein the at least one dopant comprises at least one of B, C, P, Si, or O.

[0194] Item 80: A bulk permanent magnet described in any one of items 69 to 79, wherein for each anisotropically shaped iron-based crystal grain, the respective easy axes of magnetocrystalline anisotropy are substantially parallel to the respective longest axes. [Example]

[0195] FIG. 12 shows exemplary X-ray diffraction spectra from iron nitride materials cast with and without an applied external magnetic field. The darker traces show the phase composition when cast in the presence of a magnetic field. The lighter traces show the phase composition when cast without an applied magnetic field. The nitrogen concentrations in the samples averaged about 5 at.% and about 8 at.%. The samples were heated to about 650°C with and without a 9 T magnetic field for about 4 hours. The samples were cast in ice water. The cooling rate was estimated to be about 200°C / sec. Table 2 shows the changes in the peaks shown in FIG. 12 after magnetic casting.

[0196] [Table 2]

[0197] Various examples are described. These and other examples are within the scope of the following claims. Some of the embodiments of the invention related to the present invention are shown below. [Aspect 1] 1. A workpiece comprising at least one anisotropically shaped iron-based crystalline grain, the at least one anisotropically shaped iron-based crystalline grain having an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of the longest dimension of the anisotropic crystalline grain to the length of the shortest dimension, the longest and shortest dimensions being substantially perpendicular. [Aspect 2] 2. The workpiece of embodiment 1, wherein the at least one anisotropically shaped iron-based grain exhibits a shortest dimension of from about 5 nm to about 300 nm. [Aspect 3] 3. The workpiece of claim 1 or 2, wherein the at least one anisotropically shaped iron-based grain comprises a plurality of anisotropically shaped iron-based grains, wherein the major axes of each of the plurality of anisotropically shaped iron-based grains are oriented substantially parallel to one another. [Aspect 4] 4. The workpiece of any one of aspects 1-3, further comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, wherein the longest dimension of the at least one anisotropically shaped iron-based grain is substantially parallel to the direction of the uniaxial magnetic anisotropy. [Aspect 5] 5. The workpiece of any one of aspects 1-4, wherein the at least one anisotropically shaped iron-based grain comprises iron nitride. [Aspect 6] The iron nitride is α″-Fe 16 6. The workpiece of embodiment 5, comprising N2. [Aspect 7] 5. The workpiece of any one of aspects 1-4, wherein the at least one anisotropically shaped iron-based grain comprises iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al. [Aspect 8] Embodiment 8. The workpiece of any one of embodiments 1 to 7, further comprising at least one dopant. [Aspect 9] 9. The workpiece of claim 8, wherein the at least one anisotropically shaped iron-based grain comprises the dopant. [Aspect 10] 10. The workpiece of claim 8 or 9, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal. [Aspect 11] 10. The workpiece of embodiment 8 or 9, wherein the at least one dopant comprises at least one of B, C, P, Si, or O. [Aspect 12] 12. The workpiece of any one of embodiments 1-11, wherein for each anisotropically shaped iron-based grain, the respective easy axis of magnetocrystalline anisotropy is substantially parallel to the respective longest axis. [Aspect 13] A bulk permanent magnet comprising a plurality of workpieces, at least one of the plurality of workpieces comprising the workpiece of any one of embodiments 1-12. [Aspect 14] 14. The bulk permanent magnet of embodiment 13, wherein each of the plurality of workpieces comprises iron nitride. [Aspect 15] 15. An article comprising the bulk permanent magnet of embodiment 13 or 14. [Aspect 16] 16. The article of embodiment 15, wherein the article comprises an electric motor, a generator, a sensor, an actuator, a component of an automobile, or a component of a wind turbine. [Aspect 17] 1. A method comprising: casting a material comprising iron in the presence of an applied magnetic field to form a workpiece comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T). [Aspect 18] 18. The method of embodiment 17, wherein casting the material comprising iron comprises casting a material comprising iron and nitrogen in the presence of an applied magnetic field to form a workpiece comprising at least one iron nitride phase domain. [Aspect 19] 18. The method of embodiment 17, wherein casting the material comprising iron comprises casting a material comprising iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al in the presence of an applied magnetic field to form a workpiece comprising at least one phase domain having uniaxial magnetic anisotropy. [Aspect 20] 20. The method of any one of aspects 17-19, wherein casting the material comprising iron in the presence of the applied magnetic field comprises casting the material comprising iron in the presence of the applied magnetic field to form a workpiece comprising at least one anisotropically shaped iron-based crystalline grain, wherein the at least one anisotropically shaped iron-based crystalline grain has an aspect ratio of about 1.1 to about 50, wherein the aspect ratio is defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the anisotropic crystalline grain, and wherein the longest and shortest dimensions are substantially orthogonal. [Aspect 21] 21. The method of embodiment 20, wherein the at least one anisotropically shaped iron-based grain exhibits a shortest dimension of from about 5 nm to about 300 nm. [Aspect 22] 22. The method of claim 20 or 21, wherein the at least one anisotropically shaped iron-based crystalline grain comprises a plurality of anisotropically shaped iron-based crystalline grains, wherein the major axes of each of the plurality of anisotropically shaped iron-based crystalline grains are oriented substantially parallel to one another. [Aspect 23] 23. The method of any one of aspects 20-22, wherein a major axis of each of the plurality of anisotropically shaped iron-based crystalline grains is oriented substantially parallel to the direction of the applied magnetic field, and wherein, for each anisotropically shaped iron-based crystalline grain, a respective easy axis of magnetocrystalline anisotropy is substantially parallel to its respective longest axis. [Aspect 24] 24. The method of any one of embodiments 17-23, wherein the strength of the applied magnetic field is greater than about 0.02 T. [Aspect 25] 24. The method of any one of embodiments 17-23, wherein the strength of the applied magnetic field is greater than about 2.5 T. [Aspect 26] 24. The method of any one of embodiments 17-23, wherein the strength of the applied magnetic field is greater than about 9 T. [Aspect 27] 27. The method of any one of aspects 17-26, wherein the applied magnetic field has a gradient of from about 0.01 Tesla / meter to about 1000 Tesla / meter. [Aspect 28] 28. The method of any one of embodiments 17 to 27, wherein the material further comprises at least one dopant. [Aspect 29] 29. The method of embodiment 28, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal. [Aspect 30] 29. The method of embodiment 28, wherein the at least one dopant comprises at least one of B, C, P, Si, or O. [Aspect 31] 20. The method of embodiment 18, wherein prior to casting, the concentration of nitrogen in the material is about 8 atomic percent (at.%) to about 9 at.%. [Aspect 32] The casting, heating the iron-containing mixture to form a molten iron-containing mixture; and cooling the molten mixture containing iron to form a workpiece; 32. The method of any one of embodiments 17 to 31, comprising: [Aspect 33] 33. The method of embodiment 32, wherein cooling the molten mixture comprises quenching the molten mixture in at least one of water, ice water, brine, oil, aqueous ammonia, or an amide. [Aspect 34] 33. The method of claim 32, wherein cooling the molten mixture comprising iron comprises cooling the molten mixture comprising iron between cooling rollers to form a workpiece. [Aspect 35] 35. The method of any one of aspects 32-34, wherein heating the mixture comprising iron comprises heating the mixture comprising iron in the presence of an applied magnetic field, and cooling the molten mixture comprising iron comprises cooling the molten mixture comprising iron in the presence of an applied magnetic field. [Aspect 36]

[0039] Aspect 35. The method of any one of aspects 32 to 34, wherein heating the iron-containing mixture comprises heating the iron-containing mixture in a crucible using a radio frequency furnace. [Aspect 37]

[0039] Aspect 35. The method of any one of aspects 32-34, wherein heating the iron-containing mixture comprises heating the iron-containing mixture in a cold crucible, wherein the mixture is substantially encapsulated in a coating. [Aspect 38] 38. The method of any one of embodiments 17-37, further comprising compressing a plurality of workpieces to form a bulk material. [Aspect 39] 39. The method of claim 38, wherein compressing the plurality of workpieces to form the bulk material comprises compressing the plurality of workpieces in the presence of an applied magnetic field to form a bulk material comprising a plurality of iron-based phase domains comprising uniaxial magnetic anisotropy, the applied magnetic field having a strength of at least about 0.01 Tesla (T). [Aspect 40] 1. A method comprising: compressing a plurality of workpieces, each workpiece comprising at least one iron-based phase domain comprising uniaxial magnetic anisotropy, in the presence of an applied magnetic field to form a bulk material comprising a plurality of iron-based phase domains comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least 0.01 Tesla (T), and the applied magnetic field defines a magnetization direction of the bulk material. [Aspect 41] The at least one iron-based phase domain containing uniaxial magnetic anisotropy is at least one α″-Fe 16 41. The method of embodiment 40, comprising an N2 phase domain. [Aspect 42] 42. The method of claim 40 or 41, wherein the at least one iron-based phase domain comprising uniaxial magnetic anisotropy comprises at least one of a body-centered tetragonal iron phase domain, or a phase domain having a body-centered tetragonal crystal structure and comprising iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al. [Aspect 43] 43. The method of any one of Aspects 40-42, wherein the at least one iron-based phase domain comprising uniaxial magnetic anisotropy comprises at least one anisotropically shaped iron-based crystal grain, the at least one anisotropically shaped iron-based crystal grain having an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of its longest dimension to the length of its shortest dimension, the longest dimension and the shortest dimension being substantially perpendicular. [Aspect 44] 44. The method of embodiment 43, wherein the at least one anisotropically shaped iron-based grain exhibits a shortest dimension of from about 5 nm to about 300 nm. [Aspect 45] 45. The method of claim 43 or 44, wherein the at least one anisotropically shaped iron-based crystalline grain comprises a plurality of anisotropically shaped iron-based crystalline grains, wherein the major axes of each of the plurality of anisotropically shaped iron-based crystalline grains are oriented substantially parallel to one another. [Aspect 46] 46. ​​The method of any one of aspects 43 to 45, wherein a major axis of each of the plurality of anisotropically shaped iron-based crystalline grains is oriented substantially parallel to the direction of an applied magnetic field, and wherein, for each anisotropically shaped iron-based crystalline grain, a respective easy axis of magnetocrystalline anisotropy is substantially parallel to its respective longest axis. [Aspect 47] 47. The method of any one of embodiments 40-46, wherein the strength of the applied magnetic field is greater than about 0.02 T. [Aspect 48] 47. The method of any one of embodiments 40-46, wherein the strength of the applied magnetic field is greater than about 2.5 T. [Aspect 49] 47. The method of any one of embodiments 40-46, wherein the strength of the applied magnetic field is greater than about 9 T. [Aspect 50] 50. The method of any one of aspects 40-49, wherein the applied magnetic field has a gradient of about 0.01 Tesla / meter to about 1000 Tesla / meter. [Aspect 51] 52. The method of any one of embodiments 40-51, wherein at least one of the plurality of workpieces further comprises at least one dopant. [Aspect 52] 52. The method of embodiment 51, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal. [Aspect 53] 52. The method of embodiment 51, wherein the at least one dopant comprises at least one of B, C, P, Si, or O. [Aspect 54]

[0082] Aspect 54. The method of any one of aspects 40-53, wherein the applied magnetic field promotes substantially aligning easy axes of at least some of the plurality of workpieces. [Aspect 55] Aspect 55. The method of any one of aspects 40 to 54, wherein compressing the plurality of workpieces includes mixing the plurality of workpieces with at least one of a resin, a wax, or a low-melting point metal to form a mixture, and pressing the mixture to form a bulk material. [Aspect 56] 56. The method of embodiment 55, wherein pressing the mixture comprises pressing the mixture at a pressure of from about 1 MPa to about 100 GPa. [Aspect 57] 57. The method of claim 55 or 56, wherein pressing the mixture comprises cold-pressing the mixture at a temperature of about 4.2 Kelvin to about 295 Kelvin. [Aspect 58] 57. The method of claim 55 or 56, wherein pressing the mixture comprises hot-pressing the mixture at a temperature of about 295 Kelvin to about 533 Kelvin. [Aspect 59] Aspects 55-58, wherein mixing the plurality of workpieces with at least one of a resin, a wax, or a low-melting point metal comprises mixing the plurality of workpieces with a low-melting point material, wherein the low-melting point metal comprises at least one of Zn, Sn, Bi, Ga, Na, or Li. [Aspect 60] Aspect 60. The method of any one of aspects 40 to 59, wherein one workpiece of the plurality of workpieces comprises at least one of a powder, a ribbon, or a wire. [Aspect 61] The method of any one of aspects 40 to 60, further comprising the method of any one of aspects 17 to 39, wherein the workpiece formed by the method of any one of aspects 17 to 39 is one of the plurality of workpieces. [Aspect 62] An apparatus configured to perform the method according to any one of aspects 17 to 61. [Aspect 63] A workpiece formed by the method of any one of embodiments 17 to 39. [Aspect 64] A bulk material formed by the method of any one of embodiments 40 to 61. [Aspect 65] 65. The bulk material of embodiment 64, wherein the bulk material is a bulk permanent magnet. [Aspect 66] 66. The bulk permanent magnet of embodiment 65, wherein each of the plurality of workpieces comprises iron nitride. [Aspect 67] 67. An article comprising the bulk permanent magnet of embodiment 65 or 66. [Aspect 68] 68. The article of embodiment 67, wherein the article constitutes an electric motor, a generator, a sensor, an actuator, an automotive component, or a wind turbine component. [Aspect 69] 1. A method comprising: casting a material comprising at least one of nickel, iron, and cobalt in the presence of an applied magnetic field to form a workpiece comprising at least one nickel-, iron-, or cobalt-based phase domain comprising uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T). [Aspect 70] 70. The method of embodiment 69, wherein the metal comprises iron. [Aspect 71] 71. The method of embodiment 70, wherein casting the iron-containing material comprises casting the iron- and nitrogen-containing material in the presence of an applied magnetic field to form a workpiece comprising at least one iron nitride phase domain. [Aspect 72] 72. The method of any one of embodiments 69-71, wherein casting a material comprising at least one of nickel, iron, or cobalt in the presence of an applied magnetic field forms a workpiece comprising at least one phase domain comprising at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al, and having uniaxial magnetic anisotropy. [Aspect 73] 73. The method of any one of embodiments 69-72, wherein the material further comprises at least one dopant, and the at least one dopant comprises at least one of B, C, P, Si, or O. [Aspect 74] 74. The method of any one of embodiments 69-73, further comprising compressing the plurality of workpieces. [Aspect 75] 75. The method of any one of embodiments 69-74, wherein the applied magnetic field has a gradient of about 0.01 Tesla / meter to about 1000 Tesla / meter. [Aspect 76] A workpiece formed by the method of any one of embodiments 69 to 75. [Aspect 77] 77. A bulk material comprising a plurality of workpieces according to embodiment 76. [Aspect 78] 78. The bulk material of embodiment 77, wherein the bulk material is a bulk permanent magnet. [Aspect 79] 79. An article comprising the bulk permanent magnet of embodiment 78. [Aspect 80] 80. The article of embodiment 79, wherein the article constitutes an electric motor, a generator, a sensor, an actuator, an automotive component, or a wind turbine component.

Claims

1. A bulk magnetic material comprising a plurality of workpieces and a binder, the workpiece comprises a plurality of anisotropically shaped iron-based grains each comprising iron nitride and at least one iron-based phase domain comprising uniaxial magnetic anisotropy, at least one of the anisotropically shaped iron-based grains having an aspect ratio of about 1.1 to about 50, the aspect ratio being defined as the ratio of the length of the longest dimension to the length of the shortest dimension of the at least one anisotropically shaped iron-based grain, the longest and shortest dimensions being substantially perpendicular; the longest dimension of the at least one anisotropically shaped iron-based grain is parallel to the direction of uniaxial magnetic anisotropy; the workpiece further comprises at least one dopant; The workpiece is a bulk magnetic material cast from a mixture comprising iron and nitrogen in the presence of an applied magnetic field.

2. 10. The bulk magnetic material of claim 1, wherein the at least one dopant comprises at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

3. 2. The bulk magnetic material of claim 1, wherein the at least one dopant comprises at least one of Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Ca, Pt, Au, Sm, C, Pb, W, Ga, Y, Mg, Hf, or Ta.

4. The iron nitride is α″-Fe １６ N ２ The bulk magnetic material of claim 1 , comprising:

5. 2. The bulk magnetic material of claim 1, wherein the at least one anisotropically shaped iron-based grain comprises the dopant and further comprises at least one dopant of B, C, P, Si, or O.

6. 10. The bulk magnetic material of claim 1, wherein for each anisotropically shaped iron-based grain, the respective easy axis of magnetocrystalline anisotropy is substantially parallel to the respective longest axis.

7. The bulk magnetic material of claim 1 , wherein the binder comprises a resin, a wax, or a low-melting metal.

8. 8. The bulk magnetic material of claim 7, wherein the low melting point metal is selected from zinc (Zn), tin (Sn), bismuth (Bi), gallium (Ga), sodium (Na), or lithium (Li).

9. 8. The bulk magnetic material of claim 7, wherein the resin is selected from an ion exchange resin, an epoxy resin, polyacrylonitrile, a polyester, a silicone, a prepolymer, polyvinyl butyral, or urea-formaldehyde.

10. 10. A method of forming the bulk magnetic material of claim 1, comprising: mixing a plurality of workpieces with a binder to form a mixture; applying an external magnetic field to the mixture; and compressing the mixture to form the bulk magnetic material.

11. The method of claim 10 , wherein applying the external magnetic field to the mixture substantially aligns the easy axes of magnetization of the plurality of workpieces.

12. The method of claim 10, wherein the external magnetic field is a static magnetic field having a magnetic flux density of about 0.01 Tesla to about 50 Tesla.

13. The method of claim 10, wherein the external magnetic field is a varying magnetic field having a magnetic flux density of about 0.01 Tesla to about 50 Tesla.

14. 11. The method of claim 10, wherein the pressure in the step of compressing the mixture is from about 1 megapascal (MPa) to about 100 gigapascals (GPa).

15. 15. The method of claim 14, wherein the temperature in the step of compressing the mixture is from about 23°C to about 210°C.

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