Composites, inductor cores, inductors and methods thereof

Abstract

The present disclosure provides a composite comprising: (a) a core of soft-magnetic alloy particles; and (b) an electrically insulating magnetically active shell, wherein the shell forms a conformal coating on the core particles; the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, cobalt, manganese, chromium, rare earth metals, or combinations thereof; and the shell comprises oxides of metals selected from Mg, Ni, Zn, Cu, Co, Mn, Cr, Ti, Fe, Sr, Ba, or rare earth metals. The present disclosure provides an inductor core comprising at least one strip of the composite as disclosed herein. The present disclosure further provides an inductor comprising at least one inductor core as disclosed herein.

Description

COMPOSITES, INDUCTOR CORES, INDUCTORS AND METHODS THEREOFFIELD OF INVENTION

[0001] The subject matter of the present disclosure broadly relates to magnetic materials, in particular the present disclosure relates to composites for inductors and process of making thereof.BACKGROUND OF THE INVENTION

[0002] Power conversion devices are integral components in a wide range of technologies, such as electric vehicles and consumer electronics, and call for power conversion devices. These devices often incorporate inductors which are ubiquitous in power circuits such as in power converters, filters, isolators etc. Inductors and other magnetic components in power converters, such as transformers, are typically the bulkiest and the components with the greatest loss. This results in suboptimal power conversion efficiency and low power density. It is, therefore, necessary to reduce their size to meet future demand for miniaturization, and to stem core loss to save energy.

[0003] In general, inductors in today’s converters have magnetic cores typically made of soft ferromagnetic metals, such as iron, or ferromagnetic alloys based on iron, such as Finemet (the trade name of an iron-rich alloy made by the Hitachi Company, Japan). Finemet has a very high permeability (p, as high as 100,000 at 10 Hz) at frequencies up to several hundred kHz, but p diminishes rapidly to less than 100 at frequencies higher than 100 kHz (Ref.l) Finemet is available commercially in the form of a poorly crystalline ribbon 18 pm in thickness, as well as in powder form comprising spherical particles of average diameter of 10 - 15 pm. Inductors using Finemet in either form as the magnetic core are commercially available. It must be noted that high-permeability soft ferromagnetic metal alloys similar to Finemet, made by other companies, are commercially available. However, to reduce the size of inductors with soft magnetic metal alloys and still achieve stable inductance at higher frequencies, is a tedious task.

[0004] It is well known that miniaturization of power converters can be achieved at high frequencies, i.e., frequencies in the MHz range; in contrast most converters today operate in the kHz range. Therefore, the development of new materials and techniques for the construction of inductors that can operate at higher frequencies, thereby enabling the miniaturization of power converters, is of great interest in the field of power electronics.SUMMARY OF THE INVENTION

[0005] In an aspect of the present disclosure, there is provided a composite comprising: a) a core of soft- ferromagnetic metallic alloy; and b) an electrically insulating magnetically active shell, wherein the shell forms a conformal coating on the core; the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, cobalt, manganese, chromium, rare earth metals, or combinations thereof; and the shell comprises oxides of metals selected from Mg, Ni, Zn, Cu, Co, Mn, Cr, Ti, Sr, Ba, Fe or rare earth metals.

[0006] In another aspect of the present disclosure, there is provided an inductor core comprising at least one strip of the composite as disclosed herein, optionally with a binder. Such strip(s) may be in the shape of a toroid or one of the other geometric shapes known in the art.

[0007] In one another aspect of the present disclosure, there is provided an inductor comprising the inductor core as disclosed herein; and an inductive coil.

[0008] In yet another aspect of the present disclosure, there is provided a low- temperature (^300°C) process of preparing the composite as disclosed herein, the process comprising: a) dissolving at least one metallic precursor in a solvent to obtain a precursor solution; b) dispersing alloy in the precursor solution; and c) treating the solution by microwave irradiation or hydrothermal method to obtain the composite. The said low temperature ensures that the magnetic characteristics of the soft magnetic alloy are not degraded, while also ensuring that the “shell” is formed and adheres to the core of the soft magnetic alloy. The said low temperature also ensures that the electrically insulating shell is nanocrystalline, thereby enabling a pore-free, conformal coverage of the soft magnetic alloy core.

[0009] In more aspect of the present disclosure, there is provided a method of making the inductor core as disclosed herein, the method comprising compacting the composite optionally with the binder to obtain the inductor core of a toroidal, pot core, or other geometric shapes known in the art.

[0010] In further aspect of the present disclosure, there is provided a device comprising the inductor as disclosed herein, wherein the device is selected from power converters, transformers, filters, isolators, or other power circuits.

[0011] These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1A depicts scanning electron microscope (SEM) image of spherical Finemet-like particles having particle size ranging from 5 to 40 microns, in accordance with an implementation of the present disclosure.

[0013] Figure IB depicts Finemet ribbons of thickness ranging from 5 to 40 microns, in accordance with an implementation of the present disclosure.

[0014] Figure 1C depicts SEM image of Finemet flakes obtained from ball-milling of annealed Finemet ribbon pieces, in accordance with an implementation of the present disclosure.

[0015] Figure 2A depicts SEM image of Finemet-like alloy particle conformally coated with zinc ferrite, in accordance with an implementation of the present disclosure.

[0016] Figure 2B depicts SEM image of the composite (C2) showing a Finemet flake coated conformally with a thin layer of zinc ferrite, in accordance with an implementation of the present disclosure.

[0017] Figure 2C depicts SEM image of the composite (C3) showing egg-shaped alloy particle coated with a ferrite layer uniformly, in accordance with an implementation of the present disclosure.

[0018] Figure 2D depicts (i) Focused ion beam microscope images of the composite (Cl) and corresponding (ii) trench formation (enlarged trench-ii(a)), in accordance with an implementation of the present disclosure.

[0019] Figure 2E depicts the SEM image of the cross section of the ferrite layer (shell) upon the composite C4, in accordance with an implementation of the present disclosure.

[0020] Figure 3 depicts the X-ray diffraction (XRD) plots of nickel ferrite-coated Finemet spherical particle, in accordance with an implementation of the present disclosure.

[0021] Figure 4 depicts the SEM image of the nickel ferrite-coated Finemet spherical particle, in accordance with an implementation of the present disclosure.

[0022] Figure 5 depicts the pictorial images of A) comparative inductor core (IC2) comprising uncoated alloy particles in a binder; B) inductor core (IC1) comprising ferrite coated alloy particles (Cl); C) inductor (II) comprising the inductor core (IC1), (D) disc-shaped Finemet alloys; (E) strips of the composite C4 comprising zinc ferrite coated Finemet alloys; and (F) inductor 14 comprising the composite of the present disclosure, in accordance with an implementation of the present disclosure.

[0023] Figure 6 depicts flow chart of the preparation of the inductor, in accordance with an implementation of the present disclosure.

[0024] Figure 7 depicts (A-B) M-H curves for inductor (12) and (C-D) for inductor (II), in accordance with an implementation of the present disclosure.

[0025] Figure 8 depicts (A) (i, ii)the magnetic characteristics of the Finemet alloy; (B) a plot of the inductance (E) vs. frequency (f) of an inductor; (C) variation of inductance of the inductor II with frequency, in the range of 100 kHz to 10 MHz; (D) variation of the Q-factor of the inductor II in the frequency range of 100 kHz to 10 MHz, in accordance with an implementation of the present disclosure.

[0026] Figure 9 depicts impedance of inductor (II) at a voltage range of 0 to 1.4 V at varying applied frequency, in accordance with an implementation of the present disclosure.

[0027] Figure 10 depicts the impedance measurements (A) real part q’ and (B) imaginary part q” of the inductor II, in accordance with an implementation of the present disclosure.

[0028] Figure 11 depicts (A) the variation of the inductance of the inductors 14 and I4a as a function of frequency; (B) depicts the variation of Q-factors of the inductors 14 and I4a as a function of frequency, in accordance with an implementation of the present disclosure.DETAILED DESCRIPTION OF THE INVENTION

[0029] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features. Definitions

[0030] For convenience, before further description of the present disclosure, certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below.

[0031] The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0032] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.

[0033] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.

[0034] The term “including” is used to mean “including but not limited to”. “Including” and “including but not limited to” are used interchangeably.

[0035] The term “soft-magnetic alloy particles” refers to alloy comprising more than two elements which has lower coercivity and higher permeability ( / / > 100 ). These soft-magnetic alloys are capable of rapidly switching their magnetization in response to magnetic field. These soft-magnetic alloys are useful in making inductors. The soft-magnetic alloy particles of the present disclosure comprise two or more metals selected from iron, niobium, copper, silicon, boron, and cobalt. Preferably the soft-magnetic alloy particles is Fe73.5Nb3Cu1Si13.5B9 sold under the trade name Finemet by Hitachi or the one sold under trade name Vitroperm. For the purpose of the present disclosure, the terms “alloy particles”, “Finemet”, “Finemet particles”, “Finemet-like alloy particles” are used interchangeably. It should be noted that the particles / flakes of the present invention could be those of any soft magnetic metal or soft magnetic metallic alloy, of any composition. Such a particle forms the ‘core” of the “core / shell” structure as described below. It must be noted that the word “core” is also used to describe the magnetic core of inductors. The meaning of the “core”, as used in the following description, will be evident from the context.

[0036] The term “rare earth metals” refers to metallic elements on the Periodic Table with atomic number in the range 58 - 71. Examples of rare earth metallic elements include lanthanum, holmium, gadolinium, and dysprosium.

[0037] The term “electrically insulating magnetically active shell” refers to an oxide covering the core of soft-magnetic alloy particles, which is non-conducting yet having magnetic properties (including ferrimagnetic ferromagnetic, etc.),capable of magnetically coupling with the core of alloy particles. The electrically insulating shell prevents direct contact of alloy particles with one another thereby leading reduced eddy current loss at higher frequencies. The electrically insulating shell forms a thin, uniform, conformal, adherent coating on the core.

[0038] The term “conformal coating” refers to a uniform and adherent coating of a material upon the surface of a substance without pores. A material to form thin yet uniform coating upon the particulate substance, the material has to be nanocrystalline or amorphous, made of particles with dimensions of a few tens of nanometres or less. In an aspect of the present disclosure, the shell forms a conformal coating on the core particles or strips

[0039] The term “inductor core” refers to a magnetic material that increases the inductance of a coil of wire, which is placed inside a coil of an electrically conducting wire. The core can be made of iron, ferrite, or other ferro-, ferri-, or antiferro-magnetic substances. In an aspect of the present disclosure, the inductor core comprises the composite as disclosed herein.

[0040] The term “stacked one over the other” refers to the arrangement of the strips in a vertical fashion wherein the portion of the strip having higher surface area are in contact with each other to form a cylindrical toroid with a (total) cross-sectional thickness in a range of 0.01 to 100 mm Alternatively, the stack of strips may have a different geometric shape known in the art of inductor cores, with a cross-sectional thickness in a range of 0.01 to 100 mm.

[0041] The term “eddy current” refers to loops of electrical current induced within conductors by a varying magnetic field. They flow in closed loops within conductors, in planes perpendicular to the magnetic field. In an aspect of the present disclosure, the inductor core comprising a plurality of strips stacked one over the other exhibits minimal eddy current losses at elevated frequencies in the range of 1 - 10 MHz. Reducing eddy current loss improves the efficiency of electrical devices like transformers, motors, and generators by minimizing energy wastage. Lowering eddy current loss helps in managing the temperature rise in electrical components, preventing overheating and potential damage. Minimizing these losses helpsmaintain the structural integrity of the magnetic materials used in electrical devices, extending their lifespan.

[0042] The term “inductance” refers to the ability of a conductor to oppose changing current. In an aspect of the present disclosure, the inductor comprising the composition as disclosed herein exhibits an inductance in a range of 2-30 pH at a frequency in a range of 1 - 10 MHz. However, the inductance range can be extended by enlarging the dimension of the inductor core and increasing the number of turns in the inductor coil, as is well known in the art.

[0043] The term “Q-factor” refers to a parameter that represents the ratio of a material’s inductive reactance to its resistance at a specific frequency. A high Cofactor value indicates low energy loss and high performance of the material in applications like filters and oscillators. In an aspect of the present disclosure, the inductor of the present disclosure exhibits a Q-factor in a range of 2 to 5, at a frequency in a range of 1 to 5 MHz. The Q-factor can be increased by various means in the design of the inductor, such as by using thick copper wire to wind the inductor coil that lowers the resistance, as is well known in the art.

[0044] For the purpose of the present disclosure, the terms “coated alloy particles”, “ferrite-coated alloy particles”, “coated Finemet”, “coated Finemet particles”, “coated Finemet alloy particles”, “ferrite-coated Finemet”, “ferrite-coated Finemet particles”, “ferrite-coated Finemet alloy particles” “ferrite-coated Finemet strip” or “ferrite-coated Finemet washers” refers to the composite of the present disclosure having a core of soft-magnetic alloy particles / strip and an electrically insulating magnetically active shell. The terms “uncoated alloy particles”, “uncoated alloy particles”, “uncoated Finemet”, “uncoated Finemet particles”, “uncoated Finemet alloy particles”, “uncoated Finemet strip” refers to the comparative soft magnetic alloy / strip without an electrically insulating shell.

[0045] The term “disc-shaped” refers to a circular planar shaped thin sheet of the alloy material which has a hole in the middle. The terms “disc-shaped” and “washer” are used interchangeably.

[0046] The term “strip” refers to the thin sheet-like form of a material. In an aspect of the present disclosure, the disc-shaped alloy core is coated with a ferrite shell to form a strip having a thickness in a range of ~10 to 200 microns.

[0047] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a temperature range of 130 °C to 300 °C should be interpreted to include not only the explicitly recited limits of 130 °C to 300 °C, but also to include subranges, such as 131 °C to 160 °C, 130 °C to 150 °C, 135 °C to 255°C and so forth, as well as individual amounts, including fractional amounts, within the specified ranges, such as 137 °C, 140 °C, 145.5 °C and 150 °C, for example.

[0048] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described.

[0049] As discussed in the background, there is a need for inductors to function at higher frequencies with reduced core loss (meaning loss in the inductor core) for the development of miniaturization of the devices. Presently, high flux-density soft magnetic alloys are used as inductor cores, which suffer high core losses and are limited to operation at frequencies of the order of a few hundred kHz. These high flux amorphous ferromagnetic metal-alloys are embedded in resin medium to stem the core loss. However, it leads to reduced effective permeability of the magnetic inductor core. There is also the risk that, in power applications, the resin gets heated enough to cause “shorting”. Hence there is a need for inductors which can exhibit undergo reduced core loss at higher frequencies. Accordingly, the present disclosure provides a composite comprising: a) a core of soft-magnetic alloy particles; and b) an electrically insulating magnetically active shell, wherein theshell forms a conformal coating on the core particles. The alloy particles are coated with a thin, electrically insulating layer of an oxide preferably a ferrite, thus forming core-shell structures. The shell, i.e., ferrite coating serves to electrically insulate the core alloy particles from one another, thereby reducing core loss. The said core / shell structure also describes the strip of magnetic alloy (the “core”) coated with an electrically insulating, magnetically active layer, such as that of a ferrite oxide (the “shell”). Thus, when the strips are stacked one over another and they are electrically insulated from one another. Despite this insulation, the alloy particles / strips remain magnetically coupled, allowing for operation at high frequencies. This is a distinctive feature of the present subject matter, which enables the construction of high-frequency power inductors with reduced core loss. The inductor core with the composite and a minimum of a binder allows dense packing of such core-shell entities, which provides greatly reduced “core loss”, as well as a relatively high inductance, to inductor prepared thereof.

[0050] The present disclosure is not to be limited in scope by the specific embodiments described herein, which are intended for the purposes of exemplification only. Functionally-equivalent products, compositions, and methods are clearly within the scope of the disclosure, as described herein.

[0051] In an embodiment of the present disclosure, there is provided a composite comprising: a) a core of (metallic) soft- magnetic alloy particles; and b) an electrically insulating magnetically active shell, wherein the shell forms a conformal coating on the core particles; the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, cobalt, manganese, chromium, rare-earth metals, or combinations thereof; and the shell comprises oxides of metals selected from Mg, Ni, Zn, Cu, Co, Mn, Cr, Ti, Sr, Ba, Fe, or the rare earth metals

[0052] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the core is in form of particles or flakes of the said soft magnetic alloy.

[0053] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the core has particle size or thickness in a range of 1to 1000 microns. In another embodiment of the present disclosure, the core is in form of particles having particle size in a range of 1 to 1000 microns, preferably 1 to 500 microns, and more preferably 5 to 40 microns. This range of particle size allows for the creation of a composite with a high degree of uniformity, density, and consistency, which in turn can lead to improved performance in high-frequency power inductors.

[0054] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the core is in the form of flakes having thickness in a range of 1 to 1000 microns, preferably 1 to 500 microns and more preferably 1 to 50 microns. The range of thickness and extension dimensions for the flakes allows for flexibility in the design and construction of the inductor core, enabling the creation of cores that are tailored to specific applications or performance requirements. The specific dimensions of these flakes contribute to the overall performance of the composite, particularly in terms of its ability to operate at high frequencies while minimizing core loss.

[0055] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the shell has a thickness in a range of 50 to 1000 nm, more preferably in the range of 100 to 200 nm.

[0056] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the shell is crystalline or amorphous, preferably nanocrystalline.

[0057] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, cobalt, manganese, chromium, rare earth metals, or combinations thereof. In another embodiment of the present disclosure, wherein the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, rare earth, or combinations thereof. In one another embodiment of the present disclosure, the alloy particles comprise iron, niobium, copper, silicon, and boron. In another embodiment, the particles / flakes of the present invention could be those of any soft magnetic metal or soft magnetic metallic alloy, of any composition.

[0058] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the shell comprises oxides of metals selected from Mg, Ni, Zn, Cu, Co, Mn, Cr, Ti, Sr, Ba, Fe, or rare earth metals. In another embodiment of the present disclosure, the shell comprises oxides of metals selected from Ni, Zn, Mn, or Fe. In one another embodiment of the present disclosure, the shell comprises nanocrystalline ferrites of the spinel or the hexaferrite structure. Preferably, the shell comprises nanocrystalline ferrimagnetic spinel ferrite.

[0059] In an embodiment of the present disclosure, there is provided a composite as disclosed herein, wherein the shell comprises an inorganic, electrically insulating oxide such as (but not limited to) MgO, AI2O3, SiCh, NiFe2O4, ZnFe2O4, (Ni, Zn)Fe2O4 or (Mn,Zn)Fe2O4. In another embodiment of the present disclosure, the shell is NiFe2O4 or ZnFe2O4. In one another embodiment of the present disclosure, the shell is nanocrystalline (Ni, Zn)Fe2O4 or nanocrystalline (Mn,Zn)Fe2O4. In (Ni, Zn)Fe2O4 or (Mn,Zn)Fe2O4, the relative molar proportions of Ni / Zn and Mn / Zn are adjusted for superior magnetic characteristics in a manner well known in the art.

[0060] In an embodiment of the present disclosure, there is provided a composite comprising a core-shell structure, said structure including a core and a shell, characterized in that the core is a high flux-density soft magnetic alloy in the form of powder or flakes or a strip and the shell is preferably a thin, electrically insulating layer of a nanocrystalline, ferrimagnetic spinel ferrite, wherein the ferrite coating of the alloy particles is done by a microwave-assisted solution process or by a hydrothermal process.

[0061] In an embodiment of the present disclosure, there is provided an inductor core comprising at least one strip comprising the composite as disclosed herein, optionally with a binder. The core / shell particles or flakes may also be compacted into an inductor core optionally with a binder.

[0062] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, wherein the binder is in a weight range of 0.1 to 5% with respect to total weight of the inductor core. In another embodiment of the present disclosure, the binder is in a weight range of 0.5 to 1.5% with respect to total weight of the inductor core. In one another embodiment of the present disclosure, thebinder is present in a weight of about 1% with respect to total weight of the inductor core.

[0063] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, wherein the binder is selected from an epoxy, a resin, or a varnish such as GE7031. In another embodiment of the present disclosure, the binder is epoxy resin.

[0064] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, wherein at least one strip has a thickness in a range of 50 - 200 micrometers.

[0065] In an embodiment of the present disclosure, the inductor core of the present disclosure has a core-shell structure, wherein the core of the inductor would be made of a cylindrical stack of thin strips of the disclosed composite, in the form of strips assembled one on top of each other. The inductor core of the present disclosure would comprise a stack of thin Finemet alloy washers, each of which is coated on both sides and on the inner and outer circumference with a thin layer of an electrically insulating, magnetically active, spinel- structured nanocrystalline ferrite shell, such as zinc ferrite or nickel ferrite to obtain a strip. As each strip in the stack is only about 18 pm-thick, a stack of about 50 ferrite-coated washer will have a thickness of about 1 mm only, providing a very compact form factor for the inductor made using the stack. Depending on the size of the strips (outer diameter (OD) and inner diameter (ID)) and the number of strips in a stack, inductors of high inductance is prepared with such a core. The Finemet washers in a “stack” would be electrically insulated from one another because each of them is coated with a layer electrically insulating ferrite (shell).

[0066] In an embodiment of the present disclosure, the inductor core of the present disclosure is made by pressing or compacting the strips together to form a compact, Imm-tall toroid comprising about 50 thin “strips”. For the reasons outlined above in describing the advantage of an inductor core made of core / shell particles (flakes or spheres), the “washer-stack-inductor-core” would lead to minimal eddy current losses at elevated frequencies in the range of 1 - 10 MHz. Such inductors, therefore, would be suitable for fabricating “power inductors” of a compact size

[0067] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, wherein the inductor core comprises plurality of strips stacked one over the other. In another embodiment of the present disclosure, the inductor core comprises 5 to 500 strips stacked one over the other. In yet another embodiment of the present disclosure, the inductor core comprises 10 to 100 strips stacked one over the other. In still another embodiment of the present disclosure, the inductor core comprises 40 to 80 strips stacked one over the other.

[0068] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, wherein the inductor core has a cross-sectional thickness in a range of 0.01 to 100 mm; and diameter in a range of 5 to 100 mm. In another embodiment of the present disclosure, the inductor core has a cross-sectional thickness in a range of 1.2 to 1.8 mm; and diameter in a range of 5 to 75 mm. In another embodiment of the present disclosure, the inductor core has a cross- sectional thickness in a range of 1.4 to 1.6 mm; and diameter in a range of 5 to 50 mm. It is nevertheless to be noted that the dimensions of such an inductor core can be scaled to meet the value of the inductance required.

[0069] In an embodiment of the present disclosure, there is provided an inductor core as disclosed herein, the inductor core in the form of toroid, pot-core, or EE. In another embodiment of the present disclosure, the inductor is in the form of toroid. The shape of the inductor core can be tailored to meet specific requirements or preferences. For instance, the inductor core may be shaped as a toroid. A toroidal shape is advantageous in some cases as it can provide a closed magnetic path, which can help to minimize magnetic leakage and improve the efficiency of the inductor. In other cases, the inductor core may be shaped as a pot-core. A pot-core shape can provide a high inductance per turn and can be beneficial in applications where a high inductance value, as well as low flux leakage, are desired.

[0070] In an embodiment of the present disclosure, there is provided an inductor comprising inductor core as disclosed herein, and an inductive coil.

[0071] In an embodiment of the present disclosure, there is provided an inductor as disclosed herein, wherein the inductive coil is wound on the inductor core and the coil is made of a low-resistivity metal, preferably copper.

[0072] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, the process comprising: a) dissolving at least one metallic precursor in a solvent to obtain a precursor solution; b) dispersing the alloy in the precursor solution; and c) treating the solution by microwave irradiation or hydrothermal method to obtain the composite.

[0073] In an embodiment of the present disclosure, , there is provided a process of making the composite as disclosed herein, the process comprising: a) dissolving at least one metallic precursor in a solvent to obtain a precursor solution; b) dispersing the alloy in the form of particles, flakes or disc-shaped, in the precursor solution; and c) treating the solution by microwave irradiation or hydrothermal method to obtain the composite. In yet another embodiment of the present disclosure, the alloy is in the form of particles or disc-shaped.

[0074] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein the metallic precursor is selected from metalorganic P-diketonate complexes, for example acetylacetonates, namely, iron acetyl acetonate, nickel acetyl acetonate, copper acetyl acetonate, zinc acetyl acetonate, magnesium acetyl acetonate, manganese acetyl acetonate, cobalt acetyl acetonate, or combinations thereof. In another embodiment of the present disclosure, wherein the metallic precursor is selected from iron acetyl acetonate, nickel acetyl acetonate, copper acetyl acetonate, zinc acetyl acetonate, or combinations thereof. In one embodiment of the present disclosure, the metallic precursor is a combination of iron acetyl acetonate and zinc acetyl acetonate taken in a mole ratio of 2:1. In one embodiment of the present disclosure, the metallic precursor is a combination of iron acetyl acetonate and nickel acetyl acetonate taken in a mole ratio of 2:1. For the hydrothermal process for the formation of the shell in the core / shell structure, the precursors can be the nitrates or chlorides of the relevant metals. In another embodiment of the present disclosure, to prepare a shell od (Ni, Zn)Fe2O4, the acetylacetonates of Ni and Zn together form one mole and iron acetylacetonate forms 2 moles.

[0075] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein the solvent is selected from water, alcohol or combinations thereof.

[0076] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein the alcohol is selected from Ci- 12 alcohol, preferably the solvent is a combination of alcohols selected from methanol, ethanol, benzylalcohol, and decanol.

[0077] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein the solvent is combination of decanol and ethanol in a volume ratio range of 9: 1 to 3:5. In another embodiment of the present disclosure, the solvent is combination of decanol and ethanol in a volume ratio of 5:3.

[0078] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein 0.1 mg to 10 g by weight of the alloy particles are dispersed in the precursor solution. In another embodiment of the present disclosure, 1g by weight of the alloy particles are dispersed in the precursor solution. In one another embodiment of the present disclosure, 150 mg by weight of the alloy particles are dispersed in the precursor solution.

[0079] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein treating the solution by microwave irradiation is carried out at a permitted frequency in a range of 915 MHz to 3 GHz., preferably at 2.450 GHz, for a time period of 10 to 60 minutes. In another embodiment of the present disclosure, wherein treating the solution by microwave irradiation is carried out at a frequency of in a range of 950MHz to 2.5 GHz, preferably at 2.450 GHz, for a time period of 20 to 40 minutes. In one another embodiment of the present disclosure, treating the solution by microwave irradiation is carried out for 30 mins at 300 W of power.

[0080] In an embodiment of the present disclosure, there is provided a process of making the composite as disclosed herein, wherein treating the solution by hydrothermal method is carried out at a temperature in a range of 130 to 300°C for a time period in a range of 20 to 30 hours. In another embodiment of the presentdisclosure, wherein treating the solution by hydrothermal method is carried out at a temperature in a range of 140 to 250°C for a time period in a range of 22 to 26 hours. In one another embodiment of the present disclosure, treating the solution by hydrothermal method is carried out at a temperature of 150°C for a time period of 24 hours.

[0081] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, the method comprising: compacting the powder, flakes, or disc-shaped composite as disclosed herein, optionally with a binder, into a desired shape such as that of a toroid, to from the inductor core. In another embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, the method comprising compacting the composite as disclosed herein, optionally with a binder to obtain the inductor core having at least one strip of the composite.

[0082] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, wherein the method comprises compacting the composite as disclosed herein, optionally with a binder to obtain a stack of a plurality of the strips to obtain the inductor core.

[0083] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, wherein said compacting (of either the powder / flake composite or the stack of strips) is carried out at a temperature in range of 25 to 40°C under a pressure in a range of 5 to 15 kN, preferably 10 kN. The compaction process involves applying pressure to the composite, causing the individual particles or flakes or strips to come into close contact with one another. This results in a dense, compact structure that forms the inductor core.

[0084] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, wherein the shape of the inductor core can be tailored to meet specific requirements or preferences. For instance, the inductor core may be shaped as a toroid or pot-core. The ability to form the inductor core into a desired shape provides flexibility in the design and construction of the inductor. This flexibility allows the inductor to be tailored to specific applications or performance requirements, contributing to the versatility and adaptability of thenanocomposite material. It is to be understood that the specific shape of the inductor core is not limited to a toroid or a pot-core, and other shapes may be used as well, depending on the specific requirements of the application in which the inductor is to be used.

[0085] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, wherein the (optional) binder is selected from an epoxy, a resin, or a varnish such as GE7031, each of which may be diluted as needed, using solvents well known in the art

[0086] In an embodiment of the present disclosure, there is provided a method of making the inductor core as disclosed herein, wherein the (optional) binder is in a weight range of 0.1 to 2% with respect to total weight of the inductor core.

[0087] In an embodiment of the present disclosure, there is provided an inductor as disclosed herein, wherein the inductor exhibits a relatively constant inductance in a range of 2-30 pH at a frequency in a range of 1 - 10 MHz.

[0088] In an embodiment of the present disclosure, there is provided an inductor as disclosed herein, wherein the inductor exhibits a Q-factor in a range of 2 to 5, at a frequency in a range of 1 to 5 MHz. It is to be understood that a higher Q-factor is generally desired and can be achieved through means well known in the art, such as reducing the resistance of the inductor coil.

[0089] In another embodiment of the present disclosure, there is provided an inductor as disclosed herein, wherein the inductor is capable of operating at a frequency in a range of 1 - 50 MHz.

[0090] In an embodiment of the present disclosure, there is provided a device comprising the inductor as disclosed herein, wherein the device is selected from power converters, transformers, filters, isolators, or other power circuits.

[0091] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.EXAMPLES

[0092] The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to take restrictivelyto imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply.Materials and Methods:

[0093] For the purpose of the present disclosure the following materials were used. Finemet ribbon (Fe73.5Nb3Cu1Si13.5B9) from Hitachi Metals, Finemet-like particles from Atomix, zinc acetyl acetonate (Zn(acac)2), and iron acetyl acetonate (Fe(acac)3) were purchased from Merck (AR grade), decanol, and ethanol from Merck (AR grade). The binder GE- varnish 7031 made by the General Electric Company was optionally used.Example 1Preparation of Composites

[0094] Microwave-assisted synthesis was carried out in preparing the composite of the present disclosure. About 1 mmol(millimol) of Zn(acac)2 and 2 mmol of Fe(acac)3 were dissolved in 20 ml of solvent comprising decanol and ethanol in volume ratio of 5:3 to obtain a precursor solution. To this precursor solution, 150 mg of Finemet particles of size 5 to 40 microns (Figure 1A) was added. The solution was then taken in a sealed glass or quartz vessel and was irradiated in a microwave system (Discover, made by CEM, USA) for 30 mins at 300 W of power (2.45 GHz of frequency) to obtain the composite (Cl). The composite comprised Finemet alloy particles as a core and nanocrystalline ZnFe2O4 forming a shell over the core particles.

[0095] In another preparation, Finemet ribbons (Figure IB) of thickness of 18 micron was taken to prepare the composite. The ribbons were cut to small pieces(several mm in extension) and were rendered brittle by annealing them in inert ambient (flowing N2) at ~450°C for several hours. The annealed pieces were then reduced to flakes by ball-milling them using zirconia balls in ethanol medium for several hours at 400 rpm. This resulted in flakes of irregular shape, with a wide range of sizes, i.e., 25 to 60 microns (Figure 1C), which were then sieved to obtain flakes of specific thickness. These flakes (about 150 mg) were added to the precursor solution containing about Immol (millimol) of Zn(acac)2 and 2 mmol of Fe(acac)3 were dissolved in 20 ml of solvent comprising decanol and ethanol in volume ratio of 5:3. The solution was then taken in a sealed glass or quartz vessel and was irradiated in a microwave system for 30 mins at 300 W of power (2.45 GHz of frequency, Discover, made by CEM, USA) to obtain the composite (C2). The composite comprised alloy particles in the core and nanocrystalline ZnFe2O4 forming a shell over the core particles.

[0096] Alternatively, the composite of the present disclosure was prepared by hydrothermal treatment. About 1 mmol of Zn(acac)2 and 2 mmol of Fe(acac)3 were dissolved in 20 ml of solvent comprising decanol and ethanol in volume ratio of 5:3 to obtain a precursor solution. To this precursor solution, 1 g of Finemet particles of size 5 to 30 microns was added. The solution was then taken in a Teflon-lined steel autoclave of 100 ml capacity and was subjected to heat treatment at a temperature of 150°C for 24 hours to obtain the composite (C3). The composite comprised alloy particles in the core and nanocrystalline ZnFe2O4 forming a shell over the core particles.

[0097] In another example, disc-shaped Finemet alloy having a thickness of about 18 pm with the outer diameter 20 mm and inner diameter 8 mm was taken. The disc-shaped Finemet alloy was then coated by depositing nanocrystalline zinc ferrite (about 100 nm in coating thickness) using the microwave-assisted coating technique. The disc-shaped Finemet washers were added to the precursor solution containing about Immol (millimol) of Zn(acac)2 and 2 mmol of Fe(acac)3 were dissolved in 20 ml of solvent comprising decanol and ethanol in volume ratio of 5:3. The solution was then taken in a sealed glass or quartz vessel and was irradiatedin a microwave system for 30 mins at 300 W of power (2.45 GHz of frequency, Discover, made by CEM, USA), to obtain the composite C4 strips.

[0098] Similarly, a composite C5 comprising of Finemet particles coated with nanocrystalline nickel ferrite were prepared via hydrothermal coating using 1 mmol of Ni(acac)2 and 2 mmol of Fe(acac)3 as metallic precursors in alcohol solution.Example 2Characterization of composites

[0099] Scanning electron microscope (SEM) characterization of the composite (Cl) obtained by microwave-assisted synthesis (MAS) illustrates a Finemet particle conformally coated with nanocrystalline zinc ferrite as can be seen from Figure 2A. SEM image of the composite (C2) as depicted in Figure 2B shows a Finemet flake coated conformally with a thin layer of zinc ferrite. Similarly, the composite C3 prepared hydrothermally as explained above was subjected to SEM analysis and the corresponding SEM image (Figure 2C) depicted egg-shaped alloy particle coated with a nanocrystalline ferrite layer uniformly.

[0100] The conformality and the thickness of the nanocrystalline ferrite coating on the Finemet particles was examined by Focused Ion Beam (FIB) microscopy. Using FIB, a tiny groove was cut into the core / shell structure to reveal the thickness of the layer and the conformality of the coverage of the core (Finemet particle) by the shell (the ferrite layer). In the Figure 2D (ii), the conformality of coverage was evident and the thickness of the ferrite layer was ~60 nm. Focused Ion Beam microscope analysis of the composite Cl was carried out and the formation of the ferrite coating over the core alloy particles and its thickness were further confirmed by “trench formation” and subsequent SEM images as illustrated in Figure 2D (i, ii and ii(a)). The trench dimensions were found to be 8-micron thickness, 2-micron breadth and 0.4-micron depth.

[0101] X-ray diffraction analysis of the composites confirmed the formation of crystalline ferrite coating on the alloy particles.

[0102] For the analysis of the thickness of the ferrite coating on the composite C4, SEM was performed on the samples. The thickness of the nanocrystalline ferritelayer deposited by the hydrothermal method on the thin disc-shaped Finemet alloy (18 pm in thickness) was examined by scanning electron microscopy. Figure 2E shows the ferrite layer (the dark portion) that was separated deliberately from the disc-shaped Finemet alloy underneath. The thickness of the ferrite layer was found to be -410 nm.

[0103] Figure 3 depicts the XRD plot of nickel ferrite coated Finemet particles. The broad peaks confirmed that the nickel ferrite deposit was nanocrystalline in nature.

[0104] Figure 4 depicts the SEM images of nickel ferrite coated Finemet particles of composite C5. The ferrite layer deposited by the hydrothermal method coated the sphere conformally and completely and had a thickness of about 60 nm. As the ferrite layer was electrically insulating, the coated spheres, when compacted into a toroid, remained electrically isolated, yielding an inductor core with minimal eddy current losses.Example 3Fabrication of inductor

[0105] Inductor core was obtained by compacting the composite (Cl) as prepared above with an epoxy binder. About 1.5 g of the composite (Cl) was mixed with diluted GE-7031 varnish and were made into toroidal pellets. These pellets were then fed into a mold of desired shape such as toroid and a load of 10 kN (Universal Testing Machine) was applied to obtain the toroidal inductor core (IC1). Subsequently, the binder was burned off by heating the toroid in air at 70°C for 30 minutes. Similarly, a comparative inductor core (IC2) was prepared using uncoated Finemet particles with a binder. It could be observed that the cross-sectional thickness (1.53 mm) of inductor core (IC1, Figure 5(B)) of the present disclosure was slightly higher in comparison to cross-sectional thickness (1.52 mm) of the comparative inductor core (IC2, Figure 5(A)).

[0106] A copper wire was then wound the inductor core (IC1) to obtain the inductor (II, Figure 5C). A schematic representation of the preparation of the inductor as explained above is summarized in Figure 6. The obtained inductor (II)had an inner diameter of 8.1 mm, an outer diameter of 20 mm and a cross-sectional thickness of 1.84 mm. Similarly, a comparative inductor (12) with the comparative inductor core (IC2 with uncoated Finemet) was prepared.

[0107] In another example, the composite C4 washer (50 washers; Figure 5 (E)) were stacked one on top of each other and pressed (compacted) to form a compact, 1mm- tall toroid inductor core IC4. A copper wire was wound upon the inductor core IC4 to obtain the inductor (14, (Figure 5 (F) (i)).

[0108] Similarly, in another example, the uncoated disc-shaped Finemet alloy washers (50 washers) were stacked and compacted to form an inductor core IC4a. A copper wire was wound upon the inductor core IC4a to obtain the inductor I4a.

[0109] Further, in another example, the composite C5 washers (50 washers) were stacked one on top of each other and pressed to obtain an inductor core IC5.Example 4Characterization and Analysis of inductorsMagnetic measurement

[0110] The soft magnetic alloy (core material), the ferrite-coated composite powder material, and the inductors as prepared above, were subjected to magnetic measurements. Vibrating Sample Magnetometry (VSM) was used for magnetic characterization of inductor core of the present disclosure(Il) and the comparative inductor (12). The magnetic measurements of the inductor core material were carried out at room temperature by varying the applied magnetic field and by measuring the corresponding magnetic moments.

[0111] VSM analysis of M-H curves obtained for the core material of inductor (II) is shown in Figure 7A-B and for the core material of inductor (12) is shown in Figure 7C-D. The results as depicted in Figures 7A-D, confirmed that the magnetization of the core material of inductor II comprising ferrite coated alloy particles, was not much affected due to the ferrite coating.Inductance measurement

[0112] Inductance of the inductors (Il and 12) and inductors (14 and 16) as prepared in Example 3 were measured using a standard impedance meter by varying the frequency up to 10 MHz. The variation of the inductance of 14 with frequency is shown in Figure 8(C). From Figure 8 (C)), it could be inferred that the inductance (E) of the inductor (14) of the present disclosure is largely independent of frequency up to 10 MHz. This contrasts with the sharp reduction in L above ~ 10 kHz of an inductor made with a magnetic alloy core, as shown in Figure 8(B). Such a loss was consistent with the sharp drop in permeability (q) of a soft magnetic metallic alloy (such as Finemet), as shown in Figure 8(A).

[0113] The rapid drop in L of an inductor with soft-magnetic metallic core at frequences as low as tens of kHz is due to eddy current losses. In contrast, the inductor 14 with the Inductor core IC4 made of a stack of zinc ferrite-coated washer strips retained a high inductanceeven beyond 10 MHz (Figure 11 (A)). This characteristic is attributable to the prevention of eddy current loss due to the presence of insulating ferrite layer. In fact, the eddy current loss could be reduced further and the inductance could be increased further by minimising the “electrical shorting” that occurs due to contact between successive washers along the inner and outer circumference. If the washers were made mechanically, the electrical shorting along the circumferences could be minimised or eliminated, leading to a significantly larger inductance at high frequencies.

[0114] The inductor of the present disclosure II and 14, comprising ferrite-coated Finemet could be operated at frequencies (at least) up to 10 MHz. This is in contrast with inductors with core made of Finemet alone, which generally were limited to operating frequencies of tens of kHz, as shown in Figure 8(B). An inductor’s physical size (foot print) scales inversely with the operating frequency. Thus, if an inductor could operate at a high frequency, say 4 MHz, it could be significantly smaller than one that operated at 500 kHz, all other parameters being the same. Hence, if inductors were prepared from ferrite-coated Finemet, they could achieve significantly smaller size, leading to miniaturization of electronic circuitry.

[0115] Figure 11 (A) shows the experimental data on inductors I4a and 14 with cores made of uncoated and ferrite-coated Finemet washers, respectively. Theinductor I4a has a high inductance (L) at low frequency but the inductance decreases rapidly beyond - 100 kH. The L of the inductor 14 stayed effectively independent of frequency of the core which was made of zinc ferrite-coated Finemet. Hence, the inductance of inductor 14 was found to be constant and better performing than the inductor I4a at high frequencies.Impedance measurement

[0116] Impedance analysis of inductor comprising ferrite coated Finemet flakes(C2) of the present disclosure was analyzed by varying frequencies up to 1 MHz. The results obtained are depicted in Figure 9. It was observed that there was an increase in impedance over uncoated Finemet by a factor > 104, which confirmed that the inductor of the present disclosure II met the needs for a low-loss inductor core.Permeability measurement

[0117] Permeability (real and complex) of uncoated Finemet particles and ferrite- coated Finemet particles was obtained through measurements on toroidal inductors Il and 12, respectively. It was found that for the inductor II, the real part of the permeability (q’) remained high up to nearly 100 MHz. Also, the complex part of the permeability (q”) for II remained low in the range of 5 - 20 MHz, limiting the current losses in the inductor core. Figure 10 shows the (A) real part and (B) imaginary part of the permeability measurements for the inductor II. In case of the inductor I4a, q’ falls rapidly with frequency, consistent with the data shown in Figure 8 (A) for the Finemet alloy.Q-factor measurement

[0118] Another crucial parameter of an inductor is its quality factor, which should be high. The following data as depicted in Figure 11(B), confirmed that the quality factor of the inductor (II) of the present disclosure remained high even at high frequencies. Figure 11 shows a plot of Q-factor for (A) Finemet powder, zinc ferrite -coated Finemet powder.

[0119] Figure 11 (B) depicts the Q-factor plot for inductor 14, inductor I4a. The Q-factor for I4a was found to be 0.513 and the Q-factor for 14 was found to be 3.01, at 4 MHz frequency. Thus, the Q-factor for the inductor 14 with zinc ferrite shell showed high inductance at higher frequencies. The Q-factor was found to be rather low at ~ 2 MHz for the inductor 14 having inductor core made of a stack of zinc ferrite-coated finemet washer strips. However, Q-factor could be improved by minimising or eliminating the electrical shorting between successive washers.

[0120] Further, Figure 11(B) shows the Q-factor variation of inductors towards higher frequencies (up to values beyond 10 MHz). It was observed that at 4 MHz (for example), the inductor 14 had a much higher quality factor (Q) factor than the inductor 16. There was significant increase in Q-factor for the inductor 14 and showed about 6 times higher Q-factor than the inductor 16 at a frequency of 4 MHz. This demonstrates further that an inductor core made with the composite of ferrite shell on the soft-magnetic metallic alloy enables the performance of inductors to be extended to ~10 MHz.ADVANTAGES OF THE PRESENT DISCLOSURE

[0121] The present disclosure provides a composite comprising a core of soft- magnetic alloy particles with a shell of an electrically insulating magnetically active material. The shell forms a thin, adherent, pore-free, conformal, and uniform coating over the core alloy particles. The shell is formed using a low-temperature process so that the magnetic characteristics of the core soft-magnetic alloy are not degraded, and so that the shell is a nanocrystalline layer that provides the said pore- free, conformal coating. The present disclosure also provides an inductor core comprising the composite and an inductor thereof. The core-shell structure of the composite material provides a ferrite layer which electrically insulates the alloy particles from one another, thereby reducing core loss. Despite this insulation, the alloy particles remain magnetically coupled, allowing for operation at high frequencies. This high-frequency operation, up to 10 MHz, enables the miniaturization of power converters, which is particularly beneficial in applications such as electric vehicles and consumer electronics. The high-frequency operationalso contributes to improved power conversion efficiency and increased power density, providing substantial improvements over traditional inductors that are limited to operation at frequencies up to several hundred kHz.

[0122] The composite of the present disclosure can be compacted to form an inductor core of a desired shape, such as a toroid or a pot-core, providing flexibility in the design and construction of the inductor. This flexibility allows the inductor to be tailored to specific applications or performance requirements, illustrating the versatility and adaptability of the composite. 1

Claims

I / We Claim:

1. A composite comprising: a) a core of soft-magnetic alloy; and b) an electrically insulating magnetically active shell, wherein the shell forms a conformal coating on the core; the alloy particles comprise at least two elements selected from iron, niobium, copper, silicon, boron, cobalt, manganese, chromium, rare earth metals, or combinations thereof; and the shell comprises oxides of metals selected from Mg, Ni, Zn, Cu, Co, Mn, Cr, Ti, Sr, Ba, Fe, or rare earth metals.

2. The composite as claimed in claim 1, wherein the core is in form of particles, flakes, or disc shaped.

3. The composite as claimed in claim 1, wherein the core has a particle size or a thickness in a range of 1 to 1000 microns.

4. The composite as claimed in claim 1, wherein the core is in the form of flakes having thickness in a range of 1 to 1000 microns.

5. The composite as claimed in claim 1, wherein the core in the form of disc-shape is coated with the electrically insulating magnetically active shell.

6. The composite as claimed in claim 1, wherein the shell has a thickness in a range of 50 to 1000 nm.

7. The composite as claimed in claim 1, wherein the shell is nanocrystalline or amorphous.

8. The composite as claimed in claim 1, wherein the shell comprises an inorganic, electrically insulating oxide selected from MgO, AI2O3, SiCh, NiFe2O4, ZnFe2O4, (Ni,Zn)Fe2O4, or (Mn,Zn)Fe2O4.

9. An inductor core comprising at least one strip of the composite as claimed in claim 1, optionally with a binder.

10. The inductor core as claimed in claim 9, wherein the binder is in a weight range of 0.1 to 5% with respect to total weight of the inductor core; and the binder is selected from an epoxy, a resin, or a varnish.

11. The inductor core as claimed in claim 9, wherein at least one strip has a thickness in a range of 50 to 200 micrometers.

12. The inductor core as claimed in claim 9, wherein the inductor core comprises plurality of strips stacked one over the other.

13. The inductor core as claimed in claim 9, wherein the inductor core has a cross- sectional thickness in a range of 0.01 to 100 mm.; and diameter in a range of 5 to 100 mm.

14. The inductor core as claimed in claim 9, wherein the inductor core is in the form of toroid, pot-core, or EE.

15. An inductor comprising the inductor core as claimed in claim 9, and an inductive coil.

16. The inductor as claimed in claim 15, wherein the inductive coil is wound on the inductor core and the coil is made of a low-resistivity metal selected from copper, gold, or silver.

17. The inductor as claimed in claim 15, wherein the inductor exhibits a relatively constant inductance in a range of 1-50 pH at a frequency in a range of 1 - 10 MHz.

18. The inductor as claimed in claim 15, wherein the inductor exhibits a Q-factor in a range of 2 to 100, at a frequency in a range of 1 to 5 MHz.

19. A process of preparing the composite as claimed in claim 1, the process comprising: a) dissolving at least one metallic precursor in a solvent to obtain a precursor solution; b) dispersing the alloy in the precursor solution; and c) treating the solution by microwave irradiation or hydrothermal method to obtain the composite.

20. The process as claimed in claim 19, wherein the metallic precursor is selected from metalorganic P-diketonate complexes, such as acetylacetonates, and selected from iron acetyl acetonate, nickel acetyl acetonate, copper acetyl acetonate, zinc acetyl acetonate, magnesium acetyl acetonate, manganeseacetyl acetonate, cobalt acetyl acetonate,, chromium acetyl acetonate, or combinations thereof.

21. The process as claimed in claim 19, wherein the solvent is selected from water, alcohol or combinations thereof.

22. The process as claimed in claim 21, wherein the alcohol is selected from Ci-12 alcohol, preferably the solvent is combination of alcohols selected from methanol, ethanol, benzylalcohol, or decanol.

23. The process as claimed in claim 19, wherein the solvent is combination of decanol and ethanol in a volume ratio range of 9:1 to 3:5.

24. The process as claimed in claim 19, wherein treating the solution by microwave irradiation is carried out at a frequency in a range of 915 MHz to 3 GHz, for a time period of 10 to 60 minutes.

25. The process as claimed in claim 19, wherein treating the solution by hydrothermal method is carried out at a temperature in a range of 130 to 300°C for a time period in a range of 20 to 30 hours.

26. A method of making the inductor core as claimed in claim 9, the method comprising: compacting the composite optionally with a binder to obtain the inductor core having at least one strip of the composite.

27. The method as claimed in claim 26, wherein the method comprises compacting the composite optionally with a binder to obtain a strip of the composite and stacking plurality of the strips to obtain the inductor core.

28. The method as claimed in claims 26 and 27, wherein compacting is carried out at a temperature in range of 25 to 40°C, under a pressure in a range of 5 to 15 kN.

29. A device comprising the inductor as claimed in claim 15, wherein the device is selected from power converters, transformers, filters, isolators, or other power circuits.

Images