Applied Magnetic Field Synthesis and Treatment of Iron Nitride Magnetic Materials

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 of U.S. Provisional Patent Application No. 62 / 107,700, filed on January 26, 2015, entitled "APPLIED MAGNETIC FIELD SYNTHESIS AND PROCESSING OF IRON NITRIDE MAGNETIC MATERIALS", the entire content of which is incorporated herein by reference.

[0002] The present disclosure relates to a technique for forming an iron nitride magnetic material.

Background Art

[0003] Permanent magnets play a role in many electromechanical systems, including, for example, alternative energy systems. For example, permanent magnets are used in sensors, actuators, electric motors or generators, which can be used in transportation vehicles, wind turbines and other alternative energy mechanisms. Many of the permanent magnets currently in use contain rare earth elements that provide a high energy product, such as neodymium. These rare earth elements are relatively in short supply and may face price increases and / or supply shortages in the future. Furthermore, certain permanent magnets containing rare earth elements are expensive to manufacture. For example, the manufacture of NdFeB and ferrite magnets generally involves crushing the materials, compressing the materials, and sintering at temperatures above 1000°C, all of which contribute to the high manufacturing cost of the magnets. Furthermore, rare earth mining can cause serious environmental degradation.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present disclosure describes techniques for forming a magnetic material that includes 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 include iron having a body-centered tetragonal crystal structure, α”-Fe 16 N2, α”-Fe 16 C2, Fe, or other Fe-based magnetic materials. The techniques described herein may include 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 that includes uniaxial magnetic anisotropy, while exposing the plurality of workpieces to the applied magnetic field.

Means for Solving the Problem

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

[0006] During consolidation, for example, α”-Fe 16A magnetic field may be applied to the integrated materials to substantially align (e.g., align or nearly align, e.g., within about 5 degrees of perfect alignment) the easy axes of magnetization of a plurality of workpieces including at least one iron-based phase domain including uniaxial magnetic anisotropy such as N2. The easy axis of magnetization is the direction of the iron-based phase domain crystal cell in which the alignment of the magnetic moment is energetically favorable and metastable. In some examples, the easy axis of magnetization of the iron-based phase domain including the uniaxial magnetic anisotropy unit cell is <001> or the c-axis. In some examples, the plurality of workpieces may include powders, particles, ribbons, sheets, wires, or other geometric shapes. By applying a magnetic field during the compression process, the easy axes of magnetization of a plurality of workpieces including at least one iron-based phase domain including uniaxial magnetic anisotropy can 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 to define the magnetization direction of the integrated magnetic material and can increase the magnetic anisotropy of the integrated magnetic material.

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

[0008] In some examples, the present disclosure 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, describes a method in which the applied magnetic field has an intensity of at least about 0.01 tesla (T), and the applied magnetic field defines the magnetization direction of the bulk material.

[0009] In some examples, the present disclosure describes an apparatus configured to perform 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 a bulk material formed by any of the methods described herein.

[0012] In some examples, the present disclosure includes 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, the applied magnetic field having an intensity of at least about 0.01 tesla (T).

[0013] In some examples, the present disclosure describes a workpiece comprising at least one anisotropically shaped iron-based grain, the at least one anisotropically shaped iron-based grain having an aspect ratio of from 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 grain. 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, the at least one anisotropically shaped iron-based grain having an aspect ratio of from 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 grain. The longest dimension and the shortest dimension may be substantially orthogonal.

[0015] 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 DESCRIPTION OF THE DRAWINGS

[0016]

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DETAILED DESCRIPTION OF THE INVENTION

[0017] This disclosure will 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. This disclosure is not limited to the specific devices, methods, applications, conditions, or parameters described and / or shown herein, and the terms used herein are for the purpose of describing particular examples and are not intended to limit the scope of the claims. Where a range of values is expressed, another example includes a particular value and / or other particular values. Similarly, when values are expressed as approximations by use of the prefix “about,” it will be understood that the particular value forms another example. All ranges are inclusive and combinable. Further, references to values within a range include each value within that range.

[0018] For clarity, it should be understood that certain features of this disclosure, which are described in the context of separate examples herein, may be provided in combination in one example. Conversely, various features of this disclosure that are described in the context of a single example may be provided separately or in any sub-combination.

[0019] This disclosure relates to magnetic materials including at least one iron-based phase domain having uniaxial magnetic anisotropy, bulk permanent magnets including at least one iron-based phase domain having uniaxial magnetic anisotropy, techniques for forming magnetic materials including at least one iron-based phase domain having uniaxial magnetic anisotropy, and techniques for forming bulk permanent magnets including at least one iron-based phase domain having uniaxial magnetic anisotropy. A bulk permanent magnet including at least one iron-based phase domain having uniaxial magnetic anisotropy can provide an alternative to permanent magnets containing rare earth elements because the iron-based phase domain having uniaxial magnetic anisotropy can have a high saturation magnetization, a high magnetic anisotropy constant, and thus, a high energy product. Examples of iron-based compounds having uniaxial magnetic anisotropy include α”-Fe 16It is N2. As other examples of iron-based compounds, those having a body-centered tetragonal crystal structure, such as strained iron, and several compounds containing iron and at least one of N, C, B, O, P, Y, Mn, Co, Cr, Si, Al, Zn, etc. can be mentioned.

[0020] α”-Fe 16 N2 has a high saturation magnetization and a high magnetic anisotropy constant, and thus has a high energy product. The high saturation magnetization and magnetic anisotropy constant result in a magnetic energy product that can be higher than that of rare-earth magnets in some examples. The bulk α”-Fe produced according to the techniques described herein 16 N2 permanent magnets are the said α”-Fe 16 When the N2 permanent magnet is anisotropic, it can have desirable magnetic properties such as a high energy product of about 130 MGOe. α”-Fe 16 In examples 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 remanent coercive force and the remanent magnetization. The energy product of this permanent magnet is proportional to the product of the remanent magnetization and the remanent magnetization. For comparison, Nd2Fe 14 B permanent magnets can have an energy product as high as about 60 MGOe. The higher the energy product, the more it 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 not contain rare-earth elements, thereby reducing the material cost of the magnets and the environmental impact caused by manufacturing the magnets.

[0021] Without being limited to any theory of operation, α”-Fe 16 N2 is considered to be a metastable phase that competes with other stable phases of iron nitride. Therefore, it may be difficult to form bulk magnetic materials and bulk permanent magnets containing α”-Fe 16 N2 phase domains. The various techniques described herein can facilitate the formation of magnetic materials containing Fe 16 N2 iron nitride phase domains. In some examples, this technique is Fe16 Compared with other techniques for forming a magnetic material including an N2 iron nitride phase domain, α”-Fe 16 can reduce the cost of forming a magnetic material including an N2 iron nitride phase domain, and α”-Fe in the magnetic material 16 can increase the volume fraction of the N2 iron nitride phase domain, and Fe 16 can facilitate the mass production of a magnetic material including an N2 iron nitride phase domain, and / or improve the magnetic properties of a magnetic material including an N2 iron nitride phase domain. 16

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

[0023] The present disclosure describes techniques for forming a magnetic material including at least one iron-based phase domain including uniaxial magnetic anisotropy such as, for example, at least one α”-Fe 16 N2 phase domain. The techniques described herein can include casting a mixture of iron and nitrogen in an applied magnetic field, or integrating a plurality of workpieces including at least one iron-based phase domain including uniaxial magnetic anisotropy, such as, for example, at least one α”-Fe 16 N2 phase domain, while exposing the plurality of workpieces to the applied magnetic field.

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

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

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

[0027] In some examples, the casting and integration techniques are uniaxial magnetic anisotropy α”-Fe 16It can be used in combination as part of a large-scale technique for forming a bulk magnetic material including at least one iron-based phase domain including an N2 phase domain. In some examples, this large-scale technique can include additional processes such as, for example, rapid cooling of a cast magnetic material, annealing of the rapidly cooled magnetic material, etc. In some examples, an external magnetic field is applied during at least a part of these other steps to produce uniaxial magnetic anisotropy α”-Fe 16 It can promote the formation of at least one iron-based phase domain including an N2 phase domain. For example, a magnetic field is applied during the annealing process to produce uniaxial magnetic anisotropy α”-Fe in the material 16 It can facilitate the formation of at least one iron-based phase domain including an N2 phase domain. In the following description, mainly α”-Fe 16 Iron nitride materials such as N2 will be described. However, those skilled in the art will understand that the following description also applies to other iron-based materials including uniaxial magnetic anisotropy, such as strained iron, or iron-based materials having a body-centered tetragonal crystal structure and including at least one of N, C, B, O, P, Y, Mn, Co, Cr, Si, Al, Zn, etc.

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

[0029] Exemplary techniques for forming a solid material containing iron and nitrogen include nitriding an iron-containing workpiece. Examples of the iron-containing workpiece include powders, particles, ribbons, sheets, wires, or other geometric shapes. In some examples, nitriding the iron-containing workpiece can include heating the iron-containing workpiece for a time sufficient to diffuse nitrogen to a predetermined concentration substantially throughout the iron-containing workpiece. Thus, the heating time and temperature are related and can also be affected by the composition and / or geometric shape of the iron-containing workpiece. For example, an 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, the step of 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 supplied as diatomic nitrogen (N2), which is then separated (dissociated) into individual nitrogen atoms. In other examples, atomic nitrogen may be supplied from other atomic nitrogen precursors such as, for example, ammonia (NH3). In other examples, atomic nitrogen may be supplied from urea (CO(NH2)2). Nitrogen may be supplied in the gas phase only (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 an iron-containing workpiece may involve a urea diffusion process in which urea is utilized as the nitrogen source (e.g., rather than diatomic nitrogen or ammonia). Urea (also called carbamide) is an organic compound having the chemical formula CO(NH2)2. To nitride an iron-containing workpiece, urea can be heated, for example, in a furnace surrounding the iron-containing workpiece to generate dissociative nitrogen atoms that can diffuse into the iron-containing workpiece. As will be further described 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 of the iron-containing workpiece to the urea used for the process (e.g., mass ratio). Further details regarding these nitriding processes (including urea diffusion) can be found in International Patent Application No. PCT / US12 / 51382 filed on August 17, 2012, the entire content of which is incorporated herein by reference.

[0032] As another example of forming a solid material containing iron and nitrogen, nitrogen can be generated using a plasma from a nitrogen source, such as a gaseous nitrogen source, e.g., an RF plasma or a DC plasma. The iron-containing workpiece is placed in a plasma environment, such as a plasma chamber, and the nitrogen atoms generated by the plasma process can be injected 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 will be further 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 from perpendicular) to the surface of the substrate to which the foil is attached.

[0034] The average depth at which N+ ions are implanted into the iron-containing workpiece can depend on the energy at which the N+ ions are accelerated. Generally, the average implantation depth of N+ ions can increase with an increase in the implantation energy.

[0035] The implantation energy used to implant 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 N+ ions into the iron-containing workpiece without unduly damaging the crystal lattice of the iron crystals in the iron-containing workpiece. For example, a higher implantation energy can enable implantation of N+ ions at a greater average depth, but a higher implantation energy can increase the damage to the iron workpiece, including damaging the crystal lattice of the iron crystals and ablating some of the iron atoms due to the impact of the N+ ions. Thus, in some examples, the implantation energy may be limited to less than about 180 keV. In some examples, the angle of incidence of implantation can be about 0 degrees (e.g., substantially perpendicular to the surface of the iron workpiece (e.g., parallel or nearly perpendicular (e.g., within about 5 degrees from perpendicular, etc.))). In other examples, the angle of incidence of implantation can be adjusted to reduce lattice damage. For example, the angle of incidence of implantation can be from about 3° to about 7° from perpendicular.

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

[0037] Furthermore, the mobility of the N+ ions can be selected to inject a desired amount of N+ ions into the iron-containing workpiece. In some examples, the mobility of the N+ ions can be selected to inject a stoichiometric number of N+ ions into the iron-containing workpiece. Fe 16 The stoichiometric ratio of iron to nitrogen in N2 is 8:1. Thus, 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, for example, about 8 atomic % to about 15 atomic % of N+ ions can be injected into the iron-containing workpiece. For example, an iron-containing workpiece having dimensions of about 1 cm × 1 cm × 500 nm can contain about 4.23×10 18 iron atoms. Thus, to achieve the stoichiometric ratio of iron atoms to N+ ions in the iron-containing workpiece, about 5.28×10 17 N+ ions can be injected 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 approximately room temperature to about 500 °C. Further details regarding the ion implantation of N+ ions into the iron-containing workpiece can be found in International Application No. PCT / US14 / 15104, filed on February 6, 2014, the entire contents of which are incorporated herein by reference.

[0039] Another example of a technique for forming a solid material containing iron and nitrogen involves grinding an iron-containing material, such as a powder, in the presence of a nitrogen source. Examples of grinding devices used to grind the iron-containing material include grinding devices in a rolling mode, a stirring mode, or a vibration mode. Examples of grinding devices include a bin that encloses the iron-containing substance, the nitrogen source, and the grinding medium.

[0040] Examples of the grinding medium include grinding balls. The grinding medium can include a hard material that is capable of wearing the iron-containing material when contacting the iron-containing material with sufficient force and making the particles of the iron-containing material smaller on average. In some examples, the grinding medium can be formed of steel, stainless steel, etc. In some examples, the material forming the grinding medium does not chemically react with the iron-containing material and / or the nitrogen source.

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

[0042] The nitrogen source can include ammonium nitrate (NH4NO3), or amide-containing substances such as liquid amide or a solution containing amide, or hydrazine or a solution containing hydrazine. Amides contain C-N-H bonds and hydrazine contains N-N bonds. Ammonium nitrate, amides, and hydrazine serve as nitrogen donors for forming powders containing iron nitride. Examples of amides include carbamide ((NH2)2CO; also called urea), methanamide, benzamide, and acetamide, but any amide can be used. In some examples, amides can be derived from carboxylic acids by substituting the hydroxyl group of the carboxylic acid with an amine group. This type of amide can be called an acid amide.

[0043] In some examples, the bins of the grinding device can also enclose a catalyst. Examples of the catalyst include, for example, cobalt (Co) particles and / or nickel (Ni) particles. The catalyst catalyzes the nitridation of the iron-containing material. One possible conceptualized reaction pathway for nitriding iron using a Co catalyst is shown in Reactions 1-3 below. When Ni is used as the catalyst, a similar reaction pathway can be followed.

[0044] [Chemistry]

[0045] [Chemistry]

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

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

[0048] In some examples, the mixture containing iron and nitrogen can include at least one iron nitride in addition to iron and / or nitrogen, such as FeN, Fe2N (e.g., ξ-Fe2N), Fe3N (e.g., ε-Fe3N), Fe4N (e.g., γ'-Fe4N and / or γ-Fe4N), Fe2N6, Fe8N, Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5) may be included. In some examples, the mixture containing iron and nitrogen can have a purity of at least 92 atomic percent (at.%) (e.g., the combined iron and nitrogen content).

[0049] In some examples, a mixture containing iron and nitrogen can include at least one dopant such as a ferromagnetic or non-magnetic dopant and / or a phase stabilizer. In some examples, at least one ferromagnetic or non-magnetic dopant can be referred to as a ferromagnetic or non-magnetic impurity, and / or a phase stabilizer can be referred to as a phase stabilizing impurity. A ferromagnetic or non-magnetic dopant can be used to increase at least one of the magnetic moment, coercivity, or thermal stability of a magnetic material formed from a mixture containing iron and nitrogen. Examples of ferromagnetic or non-magnetic dopants are 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 In an iron nitride material containing 16 Fe 16 N2 phase domains, by including Mn dopant atoms at a level of about 5 at.% to about 15 at.%, the thermal stability of the 16 Fe

[0050]

Table 1

[0051] Alternatively or additionally, a mixture containing iron and nitrogen may include at least one phase stabilizer. The at least one phase stabilizer is Fe 16It may be an element selected to improve at least one of the N2 volume ratio, thermal stability, coercivity, and erosion resistance. When present in the mixture, at least one phase stabilizer may be present in the mixture of 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 from about 0.1 at.% to about 15 at.%. Examples of at least one phase stabilizer 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 an iron nitride material containing at least one Fe 16 N2 phase domain, the thermal stability of the Fe

[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 the nitrogen source and molten iron are illustrated and described below with respect to FIG. 5.

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

[0054] The technique of FIG. 1 also includes casting a material containing iron and nitrogen in the presence of an applied magnetic field (14) as shown in FIG. 1. FIGS. 2 - 4 show exemplary apparatuses that can be used to cast a material containing iron and nitrogen in the presence of an applied magnetic field.

[0055] Figure 2 is a conceptual diagram showing an exemplary system 20 that performs a casting technique on a mixture containing iron and nitrogen using an RF furnace 22, a crucible 26, and an optional quench medium 28. The system 20 includes an RF furnace 22 surrounding the crucible 26. The crucible may be formed of a material that is thermally stable at the temperature within the RF furnace 22 during heating of the mixture containing iron and nitrogen. For example, the crucible 26 can include one or more refractory materials, such as graphite, refractory ceramics, and the like.

[0056] The RF furnace 22 also includes an RF source 24 shown in Figure 2 as a plurality of coils used to generate an RF magnetic field and heat at least the mixture containing iron and nitrogen within 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 mixture containing iron and nitrogen directly, or by heating a structure (e.g., the crucible 26) within the RF furnace 22 and then heating the mixture containing iron and nitrogen, the mixture containing iron and nitrogen can be inductively heated. To form a molten mixture containing iron and nitrogen, the mixture containing iron and nitrogen can be heated within the RF furnace 22 above the melting temperature of the mixture containing iron and nitrogen.

[0057] In some examples, the shape of the crucible 26 can define the shape of the mixture containing iron and nitrogen, such as at least one wire, ribbon, or other article having a length greater than its width or diameter. In some examples, during the casting process, the temperature of the crucible 26 may be maintained at a temperature of about 650 °C to about 1200 °C. In some examples, during the casting process, the temperature of the crucible 26 may be maintained at a temperature of about 800 °C to about 1200 °C. 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 at any pressure, such as about 0.1 GPa to about 20 GPa.

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

[0059] The external magnetic field 32 can affect the nucleation and growth of crystal grains during the 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 operation, the Gibbs free energy of the crystal grains can depend on their orientation with respect to the external magnetic field 32. For example, crystal grains with their (002) plane or (004) plane substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) to the external magnetic field 32 may have a lower Gibbs free energy than crystal grains with their (110) plane, (112) plane, (202) plane, or (200) plane substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) to the external magnetic field 32. For this reason, crystal grains are more likely to nucleate and grow with their (002) plane or (004) plane substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) to the external magnetic field 32. This can facilitate a substantial orientation (e.g., orientation or nearly orientation) of the crystal axes of the iron or iron nitride crystals formed during the casting process, thereby 16 when α”-Fe 16 N2 is formed, facilitating the substantial alignment (e.g., alignment or nearly alignment (e.g., within about 5 degrees from alignment)) of the crystal axes of α”-Fe

[0060] Additionally or alternatively, the external magnetic field 32 can promote the diffusion of nitrogen into the interstitial spaces within the iron lattice, thereby reducing or substantially preventing the diffusion of nitrogen out of the material containing iron and nitrogen. Without 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 and distort the crystal lattice when iron crystals nucleate and grow. The distortion of the iron crystal lattice would likely enable nitrogen to more easily diffuse into the interstitial spaces within the iron lattice. Once nitrogen has diffused into the interstitial spaces within the iron lattice, it would be more difficult for the nitrogen to diffuse out of the iron lattice. Additionally or alternatively, without wishing to be bound by any theory of operation, it is currently believed that the external magnetic field 32 may reduce convection in the molten iron nitride mixture, thereby reducing the movement of nitrogen atoms towards the front of the solid-liquid interface during the growth of iron nitride crystals.

[0061] Since 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 crystal grain size, crystal grain size uniformity, crystal grain boundaries, and crystal grain shape of iron. 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 containing iron and nitrogen in the presence of an applied magnetic field (14) may include at least one iron nitride crystal or crystal grain exhibiting an anisotropic shape. The at least one anisotropic-shaped iron nitride crystal or crystal grain can exhibit an aspect ratio of from about 1.1 to about 50, such as from about 1.4 to about 50, or from 2.2 to about 50, or from about 5 to about 50. As used herein, 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 crystal grain, where the shortest dimension is measured in a direction that is substantially orthogonal (e.g., orthogonal or nearly orthogonal (e.g., within about 5 degrees from orthogonal)) to the longest dimension. In some examples, α”-Fe 16 The shortest dimension of the N2 crystal or crystal grain 84 is from about 5 nm to about 300 nm.

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

[0063] In some examples, the applied magnetic field can affect the properties of the grain boundaries, such as by hardening the grain boundaries. The applied magnetic field can promote the formation 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 crystallites 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 can have a magnetic flux density of from about 0.01 tesla (T) to about 50 T. In some examples, the external magnetic field 32 can be at least 0.2 T. In some examples, the external magnetic field 32 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 external magnetic field 32 is from about 5 T to about 10 T. In other examples, the external magnetic field 32 is from 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 can change as a function of time during the casting technique. The AC mode external magnetic field 32 can have a magnetic flux density of from 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 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 external magnetic field 32 is from about 5 T to about 10 T. In other examples, the external magnetic field 32 is from about 8 T to 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 magnetic 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), such as 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 32.

[0066] During the casting of a material containing iron and nitrogen in the presence of the external magnetic field 32(14), the molten material containing iron and nitrogen can be cooled and solidified. In some examples, this cooling process can be relatively slow. For example, the cooling can be caused by stopping the heating of the RF furnace 22. In other examples, the molten material containing iron and nitrogen can be quenched in a quenching medium to more rapidly cool and solidify the material containing iron and nitrogen. The system of FIG. 2 includes a quenching medium 28 if desired. In some examples, the quenching medium 28 can include water (room temperature, low temperature or ice water), oil, brine, aqueous ammonia or amide. The molten material containing iron and nitrogen can be poured into the quenching medium or the quenching medium can be circulated around the crucible 26 or the solidified (but still hot) material containing iron and nitrogen. When used, the temperature of the quenching medium 28 can be from about -269 °C to about 210 °C.

[0067] The cast material containing iron and nitrogen may contain at least one kind of iron nitride. In addition to iron and / or nitrogen, the at least one kind of iron nitride may be, for example, FeN, Fe2N (e.g., ξ-Fe2N), Fe3N (e.g., ε-Fe3N), Fe4N (e.g., γ’-Fe4N and / or γ-Fe4N), Fe2N6, α-Fe8N, α”-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). Next, the cast material may be subjected to further processing to convert at least some of the above types of iron nitride into α”-Fe 16 N2. Some examples of the further processing will be described below with respect to FIG. 11.

[0068] In some examples, rather than using the system shown in FIG. 2, a different type of apparatus can be used to cast a mixture containing iron and nitrogen in the presence of an external magnetic field. FIG. 3 shows a conceptual 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. FIG. 4 is a conceptual diagram showing an example of the crucible heating stage 42 shown in FIG. 3 in more detail.

[0069] As best shown in FIG. 3, the material 46 containing iron and nitrogen is encapsulated by a coating material 48. The coating material 48 can be glass or another amorphous material having a melting point similar to that of glass. The coating material 48 can substantially enclose (e.g., enclose or nearly enclose) the material containing iron and nitrogen 46. Since the coating material 48 is amorphous, it can firmly wrap the material and apply stress to the material. In this way, the coating material 48 can facilitate the introduction of strain into the material containing iron and nitrogen 46, which can result in the formation of a material having a high saturation magnetization. The material 46 containing iron and nitrogen may be in the form of a wire, ribbon, film, etc. before entering the crucible heating stage 42.

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

[0071] The crucible heating stage 42 defines an opening 56 through which the material 46 containing iron and nitrogen passes (e.g., a portion of the material 46 containing iron and nitrogen is disposed). In some examples, no part of the crucible heating stage 42 contacts the material 46 containing iron and nitrogen during heating of the material 46 containing iron and nitrogen. In some embodiments, this is advantageous because it reduces the risk of unwanted elements or species contacting and diffusing into the material 46 containing iron and nitrogen. Unwanted elements or species can affect the properties of the material 46 containing iron and nitrogen. Thus, it would be desirable to reduce or limit the contact between the material 46 containing iron and nitrogen 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 through which an electric current can flow, such as aluminum, silver, or copper. The electric current passing through the inductor 44 can induce eddy currents in the material 46 containing iron and nitrogen by alternating current (AC) to heat the material 46 containing iron and nitrogen.

[0073] The material containing iron and nitrogen 46 is heated by eddy currents to form a molten material 46 containing iron and nitrogen. In some examples, although not shown in FIGS. 3 and 4, during the melting process, the molten material 46 containing iron and nitrogen is axially stretched such that the thickness or diameter of the molten material 46 containing iron and nitrogen decreases compared to the solid material 46 containing iron and nitrogen. During the melting process, the molten material 46 containing iron and nitrogen continues to be substantially encapsulated by the coating 48.

[0074] In some instances, the molten material containing iron and nitrogen may be drawn through an opening of the coil 50 that can define the cross-sectional size and shape of the cast material 52 containing iron and nitrogen.

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

[0076] Between the melting and cooling portions of the casting method, the material 48 containing iron and nitrogen (solid, molten, and cast 52) is exposed to an external magnetic field 56 generated by a magnet 54. As described with respect to FIG. 2, the external magnetic field 56 can affect the nucleation and growth of crystal grains during the cooling and solidification of the molten material 48 containing iron and nitrogen into the cast material 52 containing iron and nitrogen. Additionally or alternatively, the external magnetic field 56 can facilitate the diffusion of nitrogen into the interstitial spaces in the iron lattice, thereby reducing or substantially preventing (e.g., preventing or nearly preventing) the diffusion of nitrogen out of the material containing iron and nitrogen. Since the external magnetic field 56 can affect the nucleation density and defect density during the nucleation and growth processes, the external magnetic field 56 can also affect the crystal grain size and grain boundaries of iron.

[0077] In some examples, the external magnetic field 56 may be the same as or substantially the same (e.g., the same or approximately 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 from 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 from about 0.01 tesla to about 50 tesla. In some examples, the external magnetic field 56 can be at least 0.2T. In some examples, the external magnetic field 56 can be at least about 0.2T, at least about 2T, at least about 2.5T, at least about 6T, at least about 7T, at least about 8T, at least about 9T, at least about 10T, or higher. In some examples, the external magnetic field 56 is from about 5T to about 10T. In other examples, the external magnetic field 56 is from about 8T to about 10T. In some examples, the external magnetic field 56 can be substantially uniform (e.g., uniform or approximately uniform (e.g., within about 5%)) throughout the crucible heating stage 42 or at least throughout the volume of the material 48 containing iron and nitrogen. 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 magnetic field (indicated by the direction of the arrow in FIG. 3). 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), such as 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 56.

[0078] The cast material 52 containing iron and nitrogen may contain at least one iron nitride. In addition to iron and / or nitrogen, the at least one iron nitride may be, for example, FeN, Fe2N (e.g., ξ-Fe2N), Fe3N (e.g., ε-Fe3N), Fe4N (e.g., γ’-Fe4N and / or γ-Fe4N), Fe2N6, α-Fe8N, α”-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). Then, the cast material may be subjected to further processing to convert at least some of the above types of iron nitrides to α”-Fe 16 N2. Some examples of further processing will be described below with respect to FIG. 11.

[0079] FIG. 5 is a conceptual diagram showing 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 that houses a molten iron ingot 64 and is heated by a heat source in the form of, for example, a heating coil 66. In some examples, the temperature of the molten iron ingot 64 in the ingot chamber 62 may be higher than about 1800 Kelvin (K; about 1526.85 °C). The pressure of the iron ingot 64 in the ingot chamber 62 can be from about 0.06 MPa to about 0.12 MPa.

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

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

[0082] The molten iron nitride mixture 70 flows out of the ingot chamber 62 through the nozzle head 72 to form an iron nitride strip 74. The iron nitride strip 74 is supplied to a gap region between the surfaces of a first pinch roller 76a and a second pinch roller 76b (collectively "pinch roller 76") that rotate in opposite directions. In some examples, the distance from the nozzle head 72 to the surface of the pinch roller 76 may be from about 1 mm to about 50 mm, for example, about 4 mm.

[0083] In some examples, the rotational speeds of the first pinch roller 76a and the second pinch roller 76b can take values from about 10 revolutions per minute (rpm) to 5000 rpm, and the rotational speeds of the rollers 76 may be approximately the same. In some examples, the pinch roller 76 is actively cooled, for example, using water cooling, thereby maintaining the surface of the roller 76 at a temperature lower than the temperature of the iron nitride strip 74 and assisting 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 on the iron nitride strip 74 by the pinch roller 76 can be from about 0.04 MPa to about 0.1 MPa.

[0084] After the iron nitride strip 74 is pressed and cooled between pinch rollers 76, 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 sheet 78") may form a textured iron nitride ribbon having at least one dimension (e.g., thickness) of from about 1 μm to about 10 mm, such as from about 5 μm to about 1 cm (either individually or after compression of a plurality of textured iron nitride sheets 78). Each of the textured iron nitride sheets 78 may include, for example, a (002) or (004) crystal texture. In other words, each major surface of each of the textured iron nitride sheets 78 may be parallel to all or substantially all of the (002) or (004) surfaces 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 crystal axes that are substantially aligned (e.g., aligned or nearly aligned (e.g., within about 5 degrees of being aligned)) in a subsequent process, Fe8N and Fe 16 the anisotropy formed when forming the 16 FeN2 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 the nucleation and growth of crystal grains during the cooling and solidification of the molten iron nitride mixture 70 onto the iron nitride strip 74, as described above with respect to FIG. 2. Additionally or alternatively, the external magnetic field 82 can facilitate the diffusion of nitrogen into the interstitial spaces of the iron lattice, thereby reducing or substantially preventing (e.g., preventing or nearly preventing) the diffusion of nitrogen out of the material containing iron and nitrogen. Since the external magnetic field 82 can affect the nucleation density and defect density during the nucleation and growth processes, the external magnetic field 56 can also affect the crystal grain size and grain boundaries of the iron.

[0086] In some examples, the external magnetic field 82 may be the same as 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 can be at least about 0.2 T. In some examples, the external magnetic field 82 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 external magnetic field 82 can 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 can be at least about 0.2 T. In some examples, the external magnetic field 82 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 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 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 entirety of 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 (as 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), such as 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 contain at least one type of iron nitride. In addition to iron and / or nitrogen, the at least one type of iron nitride can be, for example, FeN, Fe2N (e.g., ξ-Fe2N), Fe3N (e.g., ε-Fe3N), Fe4N (e.g., γ’-Fe4N and / or γ-Fe4N), Fe2N6, α-Fe8N, α”-Fe 16 N2, or FeN x (where x is from about 0.05 to about 0.5). Then, the iron nitride strip 74 may be further processed to convert at least some of the above types of iron nitride to α”-Fe 16 N2. Some examples of the further processing will be described below with respect to FIG. 11.

[0088] In the above example, a casting technique was described in which a material containing a mixture of iron and nitrogen is exposed to a magnetic field during the casting technique. The present disclosure also describes a compression technique for joining a plurality of workpieces containing α”-Fe 16 N2 phase domains in the presence of an external magnetic field. FIG. 6 is a conceptual diagram showing the α”-Fe 16 N2 unit cell. As shown in FIG. 6, in the α”-Fe 16 N2 phase, the N atoms are aligned along the (002)(iron) crystal plane. The iron nitride unit cell is distorted, and the length of the unit cell along the <001> axis is about 6.28 angstroms (Å), while the lengths of the unit cell along the <010> axis and <100> axis are about 5.72 Å. α”-Fe 16 N2 unit cell can be called a body-centered tetragonal (bct) unit cell when in a distorted state. α”-Fe16 When the N2 unit cell is in a strained state, the <001> axis can be called the c-axis of the unit cell. This c-axis is α”-Fe 16 can be the easy magnetization axis of the N2 unit cell. In other words, α”-Fe 16 The N2 crystal exhibits magnetic anisotropy.

[0089] α”-Fe 16 N2 has a 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 From experimental evidence obtained from N2 permanent magnets, bulk Fe 16 N2 permanent magnets have desirable magnetic properties including a high energy product of about 134 megagauss*oersteds (MGOe), which is about twice the energy product of NdFeB (having an energy product of about 60 MGOe). From calculations and experiments, α”-Fe 16 The magnetic crystal anisotropy of N2 can be about 1.0 - 2.0×10 7 erg / cm 3 as shown. α”-Fe 16 N2 also has a relatively high theoretical magnetic saturation moment of about 2.9 Bohr magnetons per iron atom μ B / Fe. Furthermore, iron and nitrogen are abundant elements and are thus relatively inexpensive and easy to obtain.

[0090] Although not wishing to be bound by theory, three types of anisotropy can contribute to the magnetic anisotropy energy or magnetic anisotropy field of α”-Fe 16 N2 or other iron-based magnetic materials. These three types of anisotropy are magnetic crystal anisotropy, shape anisotropy, and strain anisotropy. As described above, the magnetic crystal anisotropy will likely be related to the distortion of the bcc iron crystal lattice to the bct iron nitride crystal lattice shown in FIG. 6. The shape anisotropy will likely be related to the shape of the iron nitride crystal or crystal grains, or the shape of the iron nitride workpiece. For example, as shown in FIG. 7, α”-Fe 16The N2 crystal or crystallite 84 may exhibit a longest dimension (substantially parallel to the z-axis in FIG. 7, and x-y-z axes are shown for simplicity of explanation only and are orthogonal). α”-Fe 16 The crystal or crystallite 84 of N2 may exhibit a shortest dimension (substantially parallel to the x-axis or y-axis in FIG. 7, for example). The shortest dimension is α”-Fe 16 It can be measured in a direction orthogonal to the longest axis of the N2 crystal or crystallite 84.

[0091] In some examples, α”-Fe 16 The N2 crystal or crystallite 84 can exhibit an aspect ratio of about 1.1 to about 50, such as about 1.4 to about 50, or 2.2 to about 50, or about 5 to about 50. In some examples, α”-Fe 16 The shortest dimension of the N2 crystal or crystallite 84 is from about 5 nm to about 300 nm.

[0092] The strain anisotropy will be related to the strain applied to the α”-Fe 16 N2 or other iron-based magnetic materials. In some examples, α”-Fe 16 The N2 crystallites are disposed or embedded in a matrix containing crystallites of iron or other types of iron nitride (such as Fe4N). α”-Fe 16 The N2 crystallites may have a different coefficient of thermal expansion from the crystallites of iron or other types of iron nitride. This difference can cause α”-Fe 16 Differential dimensional changes in the N2 crystallites, and the crystallites of iron or other types of iron nitride, resulting in α”-Fe 16 There is a risk of introducing strain into the N2 crystallites. Alternatively or additionally, α”-Fe 16 During the process of forming the N2 crystallites, strain can be applied to the material or workpiece by exposing it to mechanical strain or an applied magnetic field, and at least some of such strain can remain in the processed material or workpiece. Annealing can result in a redistribution of the internal stress and local microstructure of the sample in order to reduce the magnetoelastic energy in the stress state. The magnetic domain structure under strain anisotropy depends on the magnetoelastic energy, the magnetostatic energy, and the exchange energy.

[0093] FIG. 8 is a conceptual diagram showing an exemplary workpiece 86 including a plurality of α”-Fe 16 N2 crystals or grains 84 in a matrix 88 of another material. As shown in FIG. 8, each of the α”-Fe 16 N2 crystals or grains 84 exhibits an anisotropic shape. Further, each of the α”-Fe 16 N2 crystals or grains 84 of the 16 easy magnetization axis of the N2 crystal or grain is substantially parallel to (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) the respective longest dimension of the α”-Fe 16 N2 crystal or grain. In some examples, the easy magnetization axis of each of the α”-Fe 16 N2 crystals or grains is substantially parallel to (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) each of the other easy magnetization axes (and thus substantially parallel to (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) each of the other longest dimensions). In some examples, this can be achieved by casting the material used to form the workpiece 86 in the presence of an applied magnetic field, as described with respect to FIGS. 1-5. Thus, the workpiece 86 can have structural properties that result in magnetic crystalline anisotropy, shape anisotropy, and strain anisotropy, all of which contribute to the anisotropic magnetic field of the 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 coercivity (x-axis intercept) of the workpiece 86 when a magnetic field is applied parallel to the c-axis direction of FIG. 8 is different from the coercivity (x-axis intercept) of the workpiece 86 when a magnetic field is applied parallel to the a-axis and b-axis directions of FIG. 8.

[0095] α”-Fe 16 It can be difficult to directly manufacture a bulk material containing α”-Fe 16Form a smaller material containing the N2 phase domain, and then bond (or integrate) the smaller material to form α”-Fe 16 Including forming a bulk magnetic material containing the N2 phase domain. FIG. 10 shows at least one α”-Fe for forming the bulk magnetic material 16 FIG. 10 is a flowchart showing an exemplary technique for integrating a plurality of workpieces including the N2 phase domain.

[0096] In some examples, at least one α”-Fe for forming the bulk magnetic material 16 Instead of integrating a plurality of workpieces including the N2 phase domain, the technique of FIG. 10 includes integrating at least one iron-based phase domain including uniaxial magnetic anisotropy, such as strained iron, Fe 16 It may include integrating a plurality of workpieces including C2 or iron and at least one of B, O, P, Y, Mn, Co, Cr, Si, Al, etc.

[0097] The technique of FIG. 10 includes mixing a plurality of workpieces including iron nitride with a binder material (92). At least some of the plurality of workpieces including iron nitride may include at least one α”-Fe 16 It may include the N2 phase domain. In some examples, each of the plurality of workpieces including iron nitride may include at least one α”-Fe 16 It may include the N2 phase domain. Further, the plurality of workpieces may include other iron nitride phase domains (e.g., FeN, Fe2N (e.g., ξ-Fe2N), Fe3N (e.g., ε-Fe3N), Fe4N (e.g., γ’-Fe4N and / or γ-Fe4N), Fe2N6, α-Fe8N or FeN x (where x is from about 0.05 to about 0.5) domains), iron phase domains, etc.

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

[0099] Binder materials include any material that can be pressed together with the plurality of workpieces to form a consolidated bulk material. In some examples, binders include resins, waxes, or low melting point metals. Examples of 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, for example, ion exchange resins such as those available under the trade name Amberlite (trademark) from The Dow Chemical Company of Midland, Michigan; epoxy resins such as bismaleimide-triazine (BT)-epoxy; polyacrylonitrile; polyester; silicone; 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 with respect 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 initially mixing the mixture including the plurality of workpieces and the binder, each easy axis of the plurality of workpieces (e.g., α”-Fe16 The c-axis of 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 a plurality of 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, for example, make it possible to define the magnetization direction of the bulk material by substantially aligning at least some of the magnetization easy axes of each of the plurality of workpieces. For example, a mixture of a binder and a plurality of workpieces may be disposed within a mold that defines the near-net shape of the final magnetic material, and the magnetization direction of the bulk material can be defined by orienting the external magnetic field in a selected direction with respect to the mold.

[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 from about 0.01 tesla to about 50 tesla. In some examples, the external magnetic field can be at least 0.2T. In some examples, the external magnetic field can be at least about 0.2T, at least about 2T, at least about 2.5T, at least about 6T, at least about 7T, at least about 8T, at least about 9T, at least about 10T, or higher. In some examples, the external magnetic field is from about 5T to about 10T. In other examples, the external magnetic field is from about 8T to about 10T.

[0103] In other examples, the external magnetic field may be a varying magnetic field generated by an AC mode electromagnet and may have a magnetic flux density of from 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 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 external magnetic field 82 is from about 5 T to about 10 T. In other examples, the external magnetic field 82 is from 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 entirety of 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), such as 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 a mixture comprising a binder and a plurality of workpieces is exposed to an external magnetic field (94), the mixture may be compressed (96) to join the binder and the plurality of workpieces to form a bulk magnetic material. Compressing the mixture comprising a binder and a plurality of workpieces (96) may include applying pressure to the mixture. For example, the pressure can be from about 1 megapascal (MPa) to about 100 gigapascals (GPa) at room temperature. Compression of the mixture comprising a binder and a plurality of workpieces can be carried out at a relatively low temperature (e.g., about -268.93 °C (boiling point of liquid helium at atmospheric pressure) to approximately room temperature (about 23 °C)). Alternatively, compression of the mixture comprising a binder and a plurality of workpieces can be carried out at a relatively high temperature (e.g., approximately room temperature (about 23 °C) to about 210 °C). The product of the compression step is α”-Fe 16 It can be a bulk magnetic material containing α”-Fe

[0105] In some examples, the casting and compression processes described herein can be carried out together with the same overall technique for forming a bulk magnetic material containing α”-Fe 16 N2 phase domains. FIG. 11 is a flow diagram showing an exemplary method for forming a bulk magnetic material containing α”-Fe 16 N2 phase domains from a raw material containing iron and nitrogen. 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 the same as or substantially the same as step (14) described with respect to FIG. 1.

[0106] The technique of FIG. 11 also includes, if necessary, pressing a material containing iron and nitrogen (106). The material containing iron and nitrogen may be pressed to obtain a material of a predetermined size containing iron and nitrogen. During the pressing process, the temperature of the material containing iron and nitrogen is maintained below about 250° C., and the material containing iron and nitrogen 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 material containing iron and nitrogen. In some examples, when the pressing process is completed, the material containing iron and nitrogen may be in the shape of a workpiece having dimensions of about 0.001 mm to about 50 mm (e.g., a diameter of about 0.1 mm to about 50 mm in the case of a wire, and a thickness of about 0.001 mm to about 5 mm in the case of a ribbon) on one or more axes. The material containing iron and nitrogen may contain at least one Fe8N iron nitride phase domain after the pressing is completed.

[0107] In some examples, this technique also includes, if necessary, quenching a material containing iron and nitrogen (108). By quenching, the crystal structure and phase composition of the material containing iron and nitrogen can be fixed. For example, quenching can promote the formation of Fe8N phase domains in the material containing iron and nitrogen. In some examples, during the quenching process, the material containing iron and nitrogen 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 material containing iron and nitrogen may be rapidly decreased below the martensite temperature (Ms) of the workpiece alloy. For example, in the case of Fe 16 N2, the martensite temperature (Ms) is about 250° C. Media used for quenching include liquids such as water, brine (salt concentration of about 1% to about 30%), non-aqueous liquids or solutions such as oil, etc., or liquid nitrogen. In other examples, the quenching medium may 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 solids such as salts, sand, etc. In some examples, the workpiece containing iron and nitrogen may 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 can further include stretching (or pulling) and annealing (110), (112) of a material containing iron and nitrogen. This pulling and annealing process can convert at least some of the Fe8N iron nitride phase domains in the material containing iron and nitrogen into Fe 16 N2 phase domains. Various strain-inducing devices can be used to apply strain to the material containing iron and nitrogen. For example, the material containing iron and nitrogen can be received (e.g., wound) 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 pulling force to the material containing iron and nitrogen. In other examples, both ends of the material containing iron and nitrogen can be gripped by mechanical grippers, such as clamps, and the mechanical grippers can be moved in a direction away from each other to apply a pulling force to the material containing iron and nitrogen.

[0109] In some examples, the material containing iron and nitrogen can be pulled along a direction that is substantially parallel (e.g., parallel or nearly parallel (e.g., within about 5 degrees from parallel)) to the <001> axis of at least one iron crystal in the material containing iron and nitrogen. The strain-inducing device can pull the material containing iron and nitrogen to a specific elongation rate. For example, the strain for the material containing iron and nitrogen can be from about 0.3% to about 12%. In other examples, the strain for the material containing iron and nitrogen can be less than about 0.3% or more than about 12%. In some examples, when a certain amount of strain is applied to the material containing iron and nitrogen, substantially the same strain occurs in the individual unit cells of iron (or iron nitride), and as a result, the unit cells are from about 0.3% to about 12%.

[0110] While the material containing iron and nitrogen is strained, the material containing iron and nitrogen can be heated to anneal the material containing iron and nitrogen (112). The material containing iron and nitrogen can be annealed by heating the material containing iron and nitrogen to a temperature of about 100°C to about 250°C, such as about 120°C to about 200°C. By annealing the material containing iron and nitrogen while straining the material containing iron and nitrogen, at least some of the iron nitride phase domains are converted to α”-Fe 16It can promote the conversion to the N2 phase domain.

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

[0112] In some examples, during stretching (110) and annealing (112) of the material containing iron and nitrogen, the material containing iron and nitrogen may be exposed to an external magnetic field. By annealing the iron nitride material in the presence of an applied magnetic field, Fe in the iron nitride material 16 The formation of the N2 phase can be promoted. Fe 16 The increase in the volume fraction of the N2 phase can improve the magnetic properties of the magnetic material containing iron nitride. Examples of the 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 magnetic field annealing is performed may depend, at least in part, on further 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 is 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 from about 5 T to about 10 T. In other examples, the magnetic field is from about 8 T to about 10 T. Further details regarding annealing the material 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 may include compressing a plurality of workpieces of a magnetic material including at least one α”-Fe 16 N2 phase domain together with a binder material to form a bulk magnetic material (114). This step may be the same as or substantially the same as the technique described with reference to FIG. 10.

[0114] The technique of FIG. 11 may further include (optionally) shaping the bulk magnetic material (116). This shaping process may include, for example, slicing or grinding the surface of the bulk magnetic material to form a predetermined final shape of the bulk magnetic material. Finally, the technique of FIG. 11 may further include (optionally) magnetizing the bulk magnetic material (118). Thus, the technique of FIG. 11 describes an exemplary technique for forming a bulk magnetic material including α”-Fe 16 N2 phase domain.

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

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

[0117] Claim 3: The method according to claim 1, wherein casting the material containing iron comprises casting a material containing at least one of 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 including at least one phase domain having uniaxial magnetic anisotropy.

[0118] Claim 4: Casting a material containing iron in the presence of an applied magnetic field includes casting a material containing iron in the presence of an applied magnetic field to form a workpiece including at least one anisotropically shaped iron-based crystal grain, where the at least one anisotropically shaped iron-based crystal grain has an aspect ratio of from 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, and the longest dimension and the shortest dimension being substantially orthogonal, the method according to any one of claims 1 to 3.

[0119] Claim 5: The method according to claim 4, wherein the at least one anisotropically shaped iron-based crystal grain exhibits a shortest dimension of from about 5 nm to about 300 nm.

[0120] Claim 6: The method according to claim 4 or 5, wherein the at least one anisotropically shaped iron-based crystal grain includes 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 each other.

[0121] Claim 7: The method according to any one of claims 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] Claim 8: The method according to any one of claims 4 to 7, wherein for each anisotropically shaped iron-based crystal grain, each easy axis of magnetocrystalline anisotropy is substantially parallel to its respective longest axis.

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

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

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

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

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

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

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

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

[0131] Item 17: The casting includes heating a mixture containing iron to form a molten mixture containing iron, and cooling the molten mixture containing iron to form a workpiece, The method according to any one of Items 1 to 16, including.

[0132] Item 18: The method according to Item 17, wherein cooling the molten mixture includes quenching the molten mixture in a quenching medium.

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

[0134] Item 20: The method according to any one of Items 17 to 19, wherein heating the mixture containing iron includes heating the mixture containing iron in the presence of an applied magnetic field, and cooling the molten mixture containing iron includes cooling the molten mixture containing iron 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 comprises heating the iron-containing mixture in a crucible using a high-frequency furnace.

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

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

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

[0139] Item 25: The method according to Item 24, wherein at least one iron-based phase domain having uniaxial magnetic anisotropy includes at least one α”-Fe 16 N2 phase domain.

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

[0141] Claim 27: The method according to any one of claims 24 to 26, wherein each workpiece includes at least one iron-based phase domain including uniaxial magnetic anisotropy and at least one iron-based crystal grain having an anisotropic shape, at least one iron-based crystal grain having an anisotropic shape having an aspect ratio of from 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, and the longest dimension and the shortest dimension being substantially orthogonal to each other.

[0142] Claim 28: The method according to claim 27, wherein at least one iron-based crystal grain having an anisotropic shape has a shortest dimension of from about 5 nm to about 300 nm.

[0143] Claim 29: The method according to claim 27 or 28, wherein at least one iron-based crystal grain having an anisotropic shape includes a plurality of iron-based crystal grains having an anisotropic shape, and the major axes of each of the plurality of iron-based crystal grains having an anisotropic shape are substantially parallel to each other.

[0144] Claim 30: The method according to any one of claims 27 to 29, wherein the major axes of each of the plurality of iron-based crystal grains having an anisotropic shape are substantially parallel to the direction of the applied magnetic field.

[0145] Claim 31: The method according to any one of claims 27 to 30, wherein for each iron-based crystal grain having an anisotropic shape, each easy axis of the magnetocrystalline anisotropy is substantially parallel to each longest axis.

[0146] Claim 32: The method according to any one of claims 24 to 31, wherein the intensity of the applied magnetic field exceeds about 0.02 T.

[0147] Claim 33: The method according to any one of claims 24 to 31, wherein the intensity of the applied magnetic field exceeds about 2.5 T.

[0148] Claim 34: The method according to any one of claims 24 to 31, wherein the intensity of the applied magnetic field exceeds about 9 T.

[0149] Claim 35: The method according to any one of claims 24 to 34, wherein the intensity of the applied magnetic field is less than about 50 T.

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

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

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

[0153] Item 39: The method according to any one of Items 24 to 38, wherein the applied magnetic field promotes substantially aligning the easy magnetization axes of at least some of the plurality of workpieces.

[0154] Item 40: The method according to any one of Items 24 to 39, wherein compressing the plurality of workpieces includes mixing the plurality of workpieces with at least one of resin, 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 according to 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 according to Item 40 or 41, wherein pressing the mixture includes cold pressing the mixture at a temperature of about 4.2 Kelvin to about 295 Kelvin.

[0157] Item 43: The method according to 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] Claim 44: The method according to any one of claims 40 to 43, wherein mixing a plurality of workpieces with at least one of resin, 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] Claim 45: The method according to any one of claims 24 to 44, wherein one of the plurality of workpieces consists of at least one of powder, ribbon, or wire.

[0160] Claim 46: The method according to any one of claims 24 to 43, further including the method according to any one of claims 1 to 22, and the workpiece is one of the plurality of workpieces.

[0161] Claim 47: An apparatus configured to perform the method according to any one of claims 1 to 46.

[0162] Claim 48: A workpiece formed by the method according to any one of claims 1 to 23.

[0163] Claim 49: A bulk material formed by the method according to any one of claims 24 to 46.

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

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

[0166] Claim 52: The method according to claim 51, wherein the metal includes iron.

[0167] Claim 53: The method according to claim 52, wherein casting a material containing iron comprises casting a material containing iron and nitrogen in the presence of an applied magnetic field to form a workpiece comprising at least one iron nitride phase domain.

[0168] Claim 54: The method according to any one of claims 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] Claim 55: The method according to any one of claims 51 to 54, wherein the material further contains at least one dopant, and the at least one dopant contains at least one of B, C, P, Si or O.

[0170] Claim 56: The method according to any one of claims 51 to 55, further comprising compressing a plurality of workpieces.

[0171] Claim 57: A workpiece comprising at least one anisotropic-shaped iron-based crystal grain, wherein the at least one anisotropic-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, and the longest dimension and the shortest dimension are substantially orthogonal.

[0172] Claim 58: The workpiece according to claim 57, wherein the at least one anisotropic-shaped iron-based crystal grain has a shortest dimension of about 5 nm to about 300 nm.

[0173] Claim 59: The workpiece according to claim 57 or 58, wherein the at least one anisotropic-shaped iron-based crystal grain contains a plurality of anisotropic-shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropic-shaped iron-based crystal grains are oriented substantially parallel to each other.

[0174] Item 60: The workpiece according to any one of Items 57 to 59, further comprising at least one iron-based phase domain including 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 according to any one of Items 57 to 60, wherein at least one anisotropically shaped iron-based crystal grain contains iron nitride.

[0176] Item 62: The workpiece according to Item 61, wherein the iron nitride contains α”-Fe 16 N2.

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

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

[0179] Item 65: The workpiece according to Item 64, wherein at least one anisotropically shaped iron-based crystal grain contains the dopant.

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

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

[0182] Item 68: The workpiece according to any one of Items 57 to 67, wherein for each anisotropically shaped iron-based crystal grain, each easy axis of the magnetocrystalline anisotropy is substantially parallel to each longest axis.

[0183] Claim 69: A bulk permanent magnet comprising at least one anisotropic-shaped iron-based crystal grain, wherein the at least one anisotropic-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, and the longest dimension and the shortest dimension are substantially orthogonal to each other.

[0184] Claim 70: The bulk permanent magnet according to Claim 69, wherein the at least one anisotropic-shaped iron-based crystal grain has a shortest dimension of about 5 nm to about 300 nm.

[0185] Claim 71: The bulk permanent magnet according to Claim 69 or 70, wherein the at least one anisotropic-shaped iron-based crystal grain comprises a plurality of anisotropic-shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropic-shaped iron-based crystal grains are oriented substantially parallel to each other.

[0186] Claim 72: The bulk permanent magnet according to any one of Claims 69 to 71, further comprising at least one iron-based phase domain having uniaxial magnetic anisotropy, and the longest dimension of the at least one anisotropic-shaped iron-based crystal grain is substantially parallel to the direction of the uniaxial magnetic anisotropy.

[0187] Claim 73: The bulk permanent magnet according to any one of Claims 69 to 72, wherein the at least one anisotropic-shaped iron-based crystal grain contains iron nitride.

[0188] Claim 74: The bulk permanent magnet according to Claim 73, wherein the iron nitride contains α”-Fe 16 N2.

[0189] Claim 75: The bulk permanent magnet according to any one of Claims 69 to 72, wherein the at least one anisotropic-shaped iron-based crystal grain contains iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn or Al.

[0190] Claim 76: The bulk permanent magnet according to any one of Claims 69 to 75, further comprising at least one dopant.

[0191] Claim 77: The bulk permanent magnet according to claim 76, wherein at least one anisotropic-shaped iron-based crystal grain contains the dopant.

[0192] Claim 78: The bulk permanent magnet according to claim 76 or 77, wherein the at least one dopant contains at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal.

[0193] Claim 79: The bulk permanent magnet according to claim 76 or 77, wherein the at least one dopant contains at least one of B, C, P, Si, or O.

[0194] Claim 80: The bulk permanent magnet according to any one of claims 69 to 79, wherein for each anisotropic-shaped iron-based crystal grain, each easy axis of magnetic crystal anisotropy is substantially parallel to its respective longest axis.

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 casting was performed in the presence of a magnetic field. The lighter traces show the phase composition when casting was performed without applying a magnetic field. The nitrogen concentration in the samples averaged about 5 at.% and about 8 at.%. The samples were heated at about 650 °C for about 4 hours with and without an applied magnetic field of 9 T. The samples were cast into ice water. The cooling rate was estimated to be about 200 °C / second. Table 2 shows the changes in the peaks shown in FIG. 12 after magnetic casting.

[0196]

Table 2

[0197] Various examples are described. These examples and other examples are within the scope of the following claims. Some embodiments of the invention related to the present invention are shown below. [Aspect 1] A workpiece including at least one anisotropic-shaped iron-based crystal grain, wherein the at least one anisotropic-shaped iron-based crystal grain has an aspect ratio of about 1.1 to about 50, and 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 crystal grain, and the longest dimension and the shortest dimension are substantially orthogonal to each other. [Aspect 2] The workpiece according to Aspect 1, wherein the at least one anisotropic-shaped iron-based crystal grain exhibits a shortest dimension of about 5 nm to about 300 nm. [Aspect 3] The workpiece according to Aspect 1 or 2, wherein the at least one anisotropic-shaped iron-based crystal grain includes a plurality of anisotropic-shaped iron-based crystal grains, and the major axes of each of the plurality of anisotropic-shaped iron-based crystal grains are oriented substantially parallel to each other. [Aspect 4] Furthermore, including at least one iron-based phase domain including uniaxial magnetic anisotropy, and the longest dimension of the at least one anisotropic-shaped iron-based crystal grain is substantially parallel to the direction of the uniaxial magnetic anisotropy. The workpiece according to any one of Aspects 1 to 3. [Aspect 5] The workpiece according to any one of Aspects 1 to 4, wherein the at least one anisotropic-shaped iron-based crystal grain includes iron nitride. [Aspect 6] The iron nitride is α”-Fe 16 N2. The workpiece according to Aspect 5. [Aspect 7] The workpiece according to any one of Aspects 1 to 4, wherein the at least one anisotropic-shaped iron-based crystal grain includes iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al. [Aspect 8] Furthermore, including at least one dopant. The workpiece according to any one of Aspects 1 to 7. [Aspect 9] The workpiece according to Aspect 8, wherein the at least one anisotropic-shaped iron-based crystal grain includes the dopant. [Aspect 10] The workpiece according to aspect 8 or 9, wherein the at least one dopant contains at least one of Al, Mn, La, Cr, Co, Ti, Ni, Zn, Zr, Ca, or a rare earth metal. [Aspect 11] The workpiece according to aspect 8 or 9, wherein the at least one dopant contains at least one of B, C, P, Si, or O. [Aspect 12] The workpiece according to any one of aspects 1 to 11, wherein for each anisotropic-shaped iron-based crystal grain, each easy axis of magnetic crystal anisotropy is substantially parallel to each longest axis. [Aspect 13] A bulk permanent magnet including a plurality of workpieces, wherein at least one of the plurality of workpieces includes the workpiece according to any one of aspects 1 to 12. [Aspect 14] The bulk permanent magnet according to aspect 13, wherein each of the plurality of workpieces contains iron nitride. [Aspect 15] An article including the bulk permanent magnet according to aspect 13 or 14. [Aspect 16] The article according to aspect 15, wherein the article constitutes an electric motor, a generator, a sensor, an actuator, a component of an automobile, or a component of a wind turbine. [Aspect 17] A method including casting a material containing iron in the presence of an applied magnetic field to form a workpiece including at least one iron-based phase domain including uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 tesla (T). [Aspect 18] The method according to aspect 17, wherein casting the material containing iron includes casting a material containing iron and nitrogen in the presence of an applied magnetic field to form a workpiece including at least one iron nitride phase domain. [Aspect 19] Casting the material containing iron includes casting a material containing 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 including at least one phase domain having uniaxial magnetic anisotropy, according to the method described in aspect 17. [Aspect 20] Casting the material containing iron in the presence of the applied magnetic field includes casting the material containing iron in the presence of the applied magnetic field to form a workpiece including at least one iron-based crystal grain having an anisotropic shape, where the at least one iron-based crystal grain having an anisotropic shape has an aspect ratio of about 1.1 to about 50, 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 crystal grain, and the longest dimension and the shortest dimension are substantially orthogonal, according to the method described in any one of aspects 17 to 19. [Aspect 21] The at least one iron-based crystal grain having an anisotropic shape exhibits a shortest dimension of about 5 nm to about 300 nm, according to the method described in aspect 20. [Aspect 22] The at least one iron-based crystal grain having an anisotropic shape includes a plurality of iron-based crystal grains having anisotropic shapes, and the major axes of each of the plurality of iron-based crystal grains having anisotropic shapes are oriented substantially parallel to each other, according to the method described in aspect 20 or 21. [Aspect 23] The major axes of each of the plurality of iron-based crystal grains having anisotropic shapes are oriented substantially parallel to the direction of the applied magnetic field, and for each iron-based crystal grain having an anisotropic shape, each easy axis of magnetic crystal anisotropy is substantially parallel to its respective longest axis, according to the method described in any one of aspects 20 to 22. [Aspect 24] The intensity of the applied magnetic field exceeds about 0.02 T, according to the method described in any one of aspects 17 to 23. [Aspect 25] The intensity of the applied magnetic field exceeds about 2.5 T, according to the method described in any one of aspects 17 to 23. [Aspect 26] The intensity of the applied magnetic field exceeds about 9 T, according to the method described in any one of aspects 17 to 23. [Aspect 27] The method according to any one of Aspects 17 to 26, wherein the applied magnetic field has a gradient of from about 0.01 tesla / meter to about 1000 tesla / meter. [Aspect 28] The method according to any one of Aspects 17 to 27, wherein the material further comprises at least one dopant. [Aspect 29] The method according to Aspect 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] The method according to Aspect 28, wherein the at least one dopant comprises at least one of B, C, P, Si, or O. [Aspect 31] The method according to Aspect 18, wherein the concentration of nitrogen in the material is from about 8 atomic percent (at.%) to about 9 at.% before casting. [Aspect 32] The casting comprises heating a mixture containing iron to form a molten mixture containing iron, and cooling the molten mixture containing iron to form a workpiece, The method according to any one of Aspects 17 to 31. [Aspect 33] The method according to Aspect 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] The method according to Aspect 32, wherein cooling the molten mixture containing iron comprises cooling the molten mixture containing iron between cooling rollers to form a workpiece. [Aspect 35] Heating the mixture containing iron includes heating the mixture containing iron in the presence of an applied magnetic field, and cooling the molten mixture containing iron includes cooling the molten mixture containing iron in the presence of an applied magnetic field, according to any one of aspects 32 to 34. [Aspect 36] Heating the mixture containing iron includes heating the mixture containing iron in a crucible using a high-frequency furnace, according to any one of aspects 32 to 34. [Aspect 37] Heating the mixture containing iron includes heating the mixture containing iron in a cold crucible, and the mixture is substantially enclosed within a coating material, according to any one of aspects 32 to 34. [Aspect 38] Furthermore, according to any one of aspects 17 to 37, the method includes compressing a plurality of workpieces to form a bulk material. [Aspect 39] Compressing the plurality of workpieces to form the bulk material includes compressing the plurality of workpieces 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, and the applied magnetic field has an intensity of at least about 0.01 tesla (T), according to the method described in aspect 38. [Aspect 40] The method includes compressing a plurality of workpieces each 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, the applied magnetic field has an intensity of at least 0.01 tesla (T), and the applied magnetic field defines the magnetization direction of the bulk material. [Aspect 41] The at least one iron-based phase domain including uniaxial magnetic anisotropy includes at least one α”-Fe 16 and includes N2 phase domains, according to the method described in aspect 40. [Aspect 42] The method according to aspect 40 or 41, wherein the at least one iron-based phase domain including uniaxial magnetic anisotropy includes at least one of a body-centered tetragonal iron phase domain or a phase domain having a body-centered tetragonal crystal structure and including iron and at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al. [Aspect 43] The method according to any one of aspects 40 to 42, wherein the at least one iron-based phase domain including uniaxial magnetic anisotropy includes at least one iron-based crystal grain having an anisotropic shape, and the at least one iron-based crystal grain having an anisotropic shape has an aspect ratio of about 1.1 to about 50, and the aspect ratio is defined as the ratio of the length of the longest dimension to the length of the shortest dimension, and the longest dimension and the shortest dimension are substantially orthogonal. [Aspect 44] The method according to aspect 43, wherein the at least one iron-based crystal grain having an anisotropic shape has a shortest dimension of about 5 nm to about 300 nm. [Aspect 45] The method according to aspect 43 or 44, wherein the at least one iron-based crystal grain having an anisotropic shape includes a plurality of iron-based crystal grains having an anisotropic shape, and the major axes of the plurality of iron-based crystal grains having an anisotropic shape are oriented substantially parallel to each other. [Aspect 46] The method according to any one of aspects 43 to 45, wherein the major axes of the plurality of iron-based crystal grains having an anisotropic shape are oriented substantially parallel to the direction of the applied magnetic field, and for each of the iron-based crystal grains having an anisotropic shape, each easy axis of magnetic crystal anisotropy is substantially parallel to each longest axis. [Aspect 47] The method according to any one of aspects 40 to 46, wherein the intensity of the applied magnetic field exceeds about 0.02 T. [Aspect 48] The method according to any one of aspects 40 to 46, wherein the intensity of the applied magnetic field exceeds about 2.5 T. [Aspect 49] The method according to any one of aspects 40 to 46, wherein the intensity of the applied magnetic field exceeds about 9 T. [Aspect 50] The method according to any one of aspects 40 to 49, wherein the applied magnetic field has a gradient of from about 0.01 tesla / meter to about 1000 tesla / meter. [Aspect 51] The method according to any one of aspects 40 to 51, wherein at least one of the plurality of workpieces further comprises at least one dopant. [Aspect 52] The method according to aspect 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] The method according to aspect 51, wherein the at least one dopant comprises at least one of B, C, P, Si or O. [Aspect 54] The method according to any one of aspects 40 to 53, wherein the applied magnetic field promotes substantially aligning at least some of the magnetization easy axes of the plurality of workpieces. [Aspect 55] 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, according to any one of aspects 40 to 54. [Aspect 56] Pressing the mixture includes pressing the mixture at a pressure of from about 1 MPa to about 100 GPa, according to aspect 55. [Aspect 57] Pressing the mixture includes cold pressing the mixture at a temperature of from about 4.2 kelvin to about 295 kelvin, according to aspect 55 or 56. [Aspect 58] Pressing the mixture includes hot pressing the mixture at a temperature of from about 295 kelvin to about 533 kelvin, according to aspect 55 or 56. [Aspect 59] Mixing the plurality of workpieces with at least one of resin, wax, or low melting point metal includes mixing the plurality of workpieces with a low melting point material, the method according to any one of aspects 55 to 58, wherein the low melting point metal contains at least one of Zn, Sn, Bi, Ga, Na, or Li. [Aspect 60] The method according to any one of aspects 40 to 59, wherein one of the plurality of workpieces constitutes at least one of powder, ribbon, or wire. [Aspect 61] Furthermore, including the method according to any one of aspects 17 to 39, and the workpiece formed by the method according to any one of aspects 17 to 39 is one of the plurality of workpieces, the method according to any one of aspects 40 to 60. [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 according to any one of aspects 17 to 39. [Aspect 64] A bulk material formed by the method according to any one of aspects 40 to 61. [Aspect 65] The bulk material according to aspect 64, wherein the bulk material is a bulk permanent magnet. [Aspect 66] The bulk permanent magnet according to aspect 65, wherein each of the plurality of workpieces contains iron nitride. [Aspect 67] An article including the bulk permanent magnet according to aspect 65 or 66. [Aspect 68] The article according to aspect 67, wherein the article constitutes an electric motor, a generator, a sensor, an actuator, a component of an automobile, or a component of a wind turbine. [Aspect 69] A method including casting a material containing at least one of nickel, iron, and cobalt in the presence of an applied magnetic field to form a workpiece including at least one phase domain based on nickel, iron, or cobalt and including uniaxial magnetic anisotropy, wherein the applied magnetic field has a strength of at least about 0.01 Tesla (T). [Aspect 70] The method according to aspect 69, wherein the metal contains iron. [Aspect 71] The method according to aspect 70, wherein casting a material containing iron includes casting a material containing iron and nitrogen in the presence of an applied magnetic field to form a workpiece including at least one iron nitride phase domain. [Aspect 72] The method according to any one of aspects 69 to 71, wherein casting a material containing at least one of nickel, iron, or cobalt includes forming a workpiece including at least one phase domain containing at least one of C, B, O, P, Y, Mn, Co, Cr, Si, Zn, or Al and having uniaxial magnetic anisotropy in the presence of an applied magnetic field. [Aspect 73] The method according to any one of aspects 69 to 72, wherein the material further includes at least one dopant, and the at least one dopant includes at least one of B, C, P, Si, or O. [Aspect 74] The method according to any one of aspects 69 to 73, further including compressing a plurality of workpieces. [Aspect 75] The method according to any one of aspects 69 to 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 according to any one of aspects 69 to 75. [Aspect 77] A bulk material including a plurality of the workpieces according to aspect 76. [Aspect 78] The bulk material according to aspect 77, wherein the bulk material is a bulk permanent magnet. [Aspect 79] An article including the bulk permanent magnet described in Aspect 78. [Aspect 80] The article according to Aspect 79, wherein the article constitutes an electric motor, a generator, a sensor, an actuator, a component of an automobile, or a component of a wind turbine.

Claims

1. A bulk magnetic material comprising a plurality of workpieces and a binder, wherein each of the workpieces includes a plurality of anisotropically shaped iron-based crystal grains each containing iron nitride, and at least one iron-based phase domain containing uniaxial magnetic anisotropy, at least one of the anisotropically shaped iron-based crystal grains having an aspect ratio of from 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 crystal grain, the longest dimension and the shortest dimension being substantially orthogonal, the longest dimension of the at least one anisotropically shaped iron-based crystal grain being parallel to the direction of the uniaxial magnetic anisotropy, the workpiece further includes at least one dopant, the workpiece is cast from a mixture containing iron and nitrogen in the presence of an applied magnetic field, the bulk magnetic material.

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

3. The bulk magnetic material according to claim 1, wherein the at least one dopant includes 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 according to claim 1, which contains

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

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

7. The bulk magnetic material according to claim 1, wherein the binder includes a resin, a wax, or a low melting point metal.

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

10. A method for forming the bulk magnetic material according to claim 1, comprising: mixing a plurality of workpieces and 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 according to claim 10, wherein the magnetization easy axes of the plurality of workpieces are substantially aligned by applying the external magnetic field to the mixture.

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

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

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

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