YCO5-BASED COMPOUNDS DOPED WITH FE AND NI FOR HIGH-PERFORMANCE PERMANENT MAGNETS

Abstract

In accordance with one aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x is greater than 0 and x is less than 1.

Claims

1. A magnet, comprising: a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, wherein x is greater than 0 and x is less than 1.

2. A magnet as recited in claim 1, wherein x is greater than 1−x.

3. A magnet as recited in claim 1, wherein x is less than 1−x.

4. A magnet as recited in claim 1, wherein x is about equal to 1−x.

5. A magnet as recited in claim 1, the material has a CuCa.sub.5-type crystal structure.

6. A magnet as recited in claim 5, wherein the Fe atoms are distributed in a plurality of transition metal 3g nonequivalent atomic sites.

7. A magnet as recited in claim 5, wherein the Ni atoms and the Co atoms are distributed in a plurality of transition metal 2c nonequivalent atomic sites.

8. A magnet as recited in claim 1, wherein the magnet is a permanent magnet.

9. A magnet as recited in claim 1, wherein a spin orientation of the Y atom is antiparallel to a spin orientation of the Fe, Ni, and Co atoms.

10. A magnet as recited in claim 1, wherein a magnetocrystalline anisotropy energy of the material is about twice a magnetocrystalline anisotropy energy of Nd.sub.2Fe.sub.14B magnet.

11. A magnet as recited in claim 1, wherein a magnetocrystalline anisotropy energy of the material is greater than about 10 MJ/m.sup.3.

12. A magnet as recited in claim 1, wherein a Curie Temperature of the material is about equal to a Curie Temperature of YCo.sub.5.

13. A magnet as recited in claim 1, wherein a Curie Temperature of the material is greater than about 1000 K.

14. A magnet as recited in claim 1, wherein a maximum energy product of the material is greater than about 351 kJ/m.sup.3.

15. A magnet as recited in claim 1, wherein the magnet comprises a reduced amount of Co than an amount of Co in YCo.sub.5.

16. A magnet as recited in claim 15, wherein the reduced amount of Co is up to 75% less Co than the amount of Co in YCo.sub.5.

17. A magnet, comprising: a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, wherein x is greater than 0 and x is less than 1, wherein the material has a CuCa.sub.5-type crystal structure.

18. A magnet as recited in claim 17, wherein x is greater than 1−x.

19. A magnet as recited in claim 17, wherein x is about equal to 1−x.

20. A magnet as recited in claim 17, wherein the Fe atoms are distributed in a plurality of transition metal 3g nonequivalent atomic sites.

21. A magnet as recited in claim 17, wherein the Ni atoms and the Co atoms are distributed in a plurality of transition metal 2c nonequivalent atomic sites.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic drawing of a crystal structure (CaCu.sub.5-type) of a YCo.sub.5 compound, according to inventive concepts described.

[0012] FIG. 2A depicts the heat of formation of the pseudo-binary YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys predicted via ab initio (0K) and CALculation of PHAse Diagrams (CALPHAD) (298 K) calculations, according to inventive concepts described.

[0013] FIG. 2B depicts the heat of formation of the pseudo-binary SmFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys predicted via ab initio calculations, according to inventive concepts described.

[0014] FIG. 3 depicts a Y—Co phase diagram calculated using the CALPHAD assessment where RE=Y and TM=Co, according to inventive concepts described.

[0015] FIG. 4 depicts the Curie temperature of the pseudo-binary YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys, according to inventive concepts described.

DETAILED DESCRIPTION

[0016] The following description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. Further, particular features described herein can be used in combination with other described features in each of the various possible combinations and permutations.

[0017] Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc.

[0018] It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified.

[0019] The term “dopant” as used in the instant descriptions shall be understood to encompass any element or compound that is included in a host medium material, so as to convey a particular functional characteristic or property on the resulting structure. In most cases, the dopant will be incorporated into a crystal structure of the host medium material.

[0020] In accordance with one general aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x is greater than 0 and x is less than 1.

[0021] In accordance with another general aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x is greater than 0 and x is less than 1, and where the material has a CuCa.sub.5-type crystal structure.

[0022] A list of acronyms used in the description is provided below.

[0023] Å angstrom

[0024] at % atomic percent

[0025] (BH).sub.max Maximum Energy Product

[0026] Co Cobalt

[0027] DFT Density functional theory

[0028] LDA Local density approximation

[0029] GGA General gradient approximation

[0030] EF Fermi level

[0031] Fe Iron

[0032] GPa gigapascal

[0033] K Kelvin, T.sub.c temperature

[0034] K.sub.1 Magnetocrystalline anisotropy energy constant

[0035] kJ kilojoules

[0036] m meters

[0037] MA mega amperes

[0038] meV milli-electronvolts

[0039] MJ megajoules

[0040] MAE Magnetocrystalline anisotropy energy

[0041] DLM Disordered local moment

[0042] AF Antiparallel fashion

[0043] FREMTO Fully relativistic exact muffin-tin orbital

[0044] CPA Coherent potential approximation

[0045] FPLMTO Full-potential linear muffin-tin orbital method

[0046] m.sup.(tot) total moment

[0047] m.sup.(s) spin magnetic moment

[0048] m.sup.(o) orbital magnetic moment

[0049] M.sub.s spontaneous magnetization

[0050] Nd Neodymium

[0051] Ni Nickel

[0052] Ca Calcium

[0053] Cu Copper

[0054] RE Rare earth metal

[0055] Sm Samarium

[0056] Y Yttrium

[0057] T.sub.c Curie temperature

[0058] TM Transition-Metal

[0059] μ.sub.B Bohr magneton

[0060] According to various inventive concepts described herein, a permanent magnet may be formed that has a high spontaneous magnetization, thermostability, high Curie temperatures and high magnetocrystalline anisotropy energy (MAE). Ideally, transition-metal dopants may boost the energy product of YCo.sub.5 magnets without compromising the high MAE and high Curie temperatures of these magnets. For example, combining transition-metal (TM) with rare-earth-metal (RE) atoms in various intermetallic compounds may result in material in which RE and TM atoms induce a large magnetic anisotropy and provide a large magnetization and high Curie temperature.

[0061] Iron (Fe) is more readily available than cobalt (Co) such that Fe is ˜2000 times more abundant in the Earth's crust than Co. Thus, at least from a cost standpoint, it would be beneficial to substitute Co atoms in YCo.sub.5 with Fe atoms since the relative abundance of available Fe could result in a less expensive component. In addition, Fe may be desirable as an added component to a magnet material since its ferromagnetic metal properties have a large magnetization at room temperature (1.76 MA/m).

[0062] FIG. 1 depicts a structure 100 of a material of a magnet, in accordance with inventive concepts described herein. As an option, the present structure 100 may be implemented in conjunction with features from any other inventive concepts listed herein, such as those described with reference to the other FIGS. Of course, however, such structure 100 and others presented herein may be used in various applications and/or in permutations which may or may not be specifically described in the illustrative concepts listed herein. Further, the structure 100 presented herein may be used in any desired environment.

[0063] As shown in FIG. 1, the crystal structure of a CaCu.sub.5(D.sub.2d)-type Structure 100 with three distinct atoms displayed, may represent a YCo.sub.5 compound crystal structure in accordance with some approaches. An yttrium atom (Y.sub.1) may be in the Wyckoff position 1a 102 centered in a plane with two Co.sub.1 atoms in the position 2c 104 surrounding the Y.sub.1 in the position 1a 102 and a second layer with three more Co.sub.2 atoms in the position 3g 106 for a total of six atoms in the unit cell. Bonding and energy between the atoms of a crystal structure may be defined by the interactions between 3d-orbital electrons of the transition metals in the position 2c 104 or position 3g 106 and the 5d-orbital electrons from yttrium (Y.sub.1) in the center position 1a 102 as shown in FIG. 1.

[0064] In the YFe.sub.5 compound that only includes Fe atoms without any Co atoms, the instability of the crystal structure may be related to a decrease in the number of 3d electrons in the electronic structure. Indeed, crystal stabilities of the magnetic 3d transition metals may be governed by the number of 3d electrons.

[0065] Thus, substituting all cobalt atoms with a transition metal with higher magnetic moment, such as iron, in order to optimize the maximum energy product (i.e., YCo.sub.5.fwdarw.YFe.sub.5) may result in a thermodynamically unstable crystal structure of an ordinary hexagonal phase. Moreover, YFe.sub.5 does not appear in the equilibrium Y—Fe phase diagram, although the alloy compound Y(Co.sub.1-xFe.sub.x).sub.5 with CaCu.sub.5-type structure has been synthesized for x=0.2 to 0.4.

[0066] For synthesized Y(Co.sub.1-xFe.sub.x).sub.5 materials, the Curie temperatures (T.sub.c) for Y(Co.sub.1-xFe.sub.x).sub.5 alloys were found to increase from about 930 K to about 1020 K when increasing x from 0.0 to 0.2. In contrast, Y.sub.2(Co.sub.1-xFe.sub.x).sub.17 alloys exhibit a monotonic decrease in Curie temperature (T.sub.c) with increasing Fe content. The orbital moment of cobalt is larger compared to iron, and a decrease of the MAE occurs for x>0. The lattice constant and magnetization are enhanced for x=0 to 0.4 in Y(Co.sub.1-xFe.sub.x).sub.5 alloys.

[0067] Accordingly, the inventive concepts presented herein, in several embodiments, involve ab initio calculations to add nickel (Ni) and iron (Fe) to a YCo.sub.5 magnet in order to stabilize Y(Co—Fe—Ni).sub.5 alloys containing a sufficient amount of Fe to boost the energy product of the Y(Co—Fe—Ni).sub.5 magnet.

[0068] In accordance with inventive concepts described herein, a magnet includes a material having a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, wherein x may be greater than 0 and x may be less than 1. In some approaches, the material may have a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x may be greater than 1−x such that the compound has a greater amount of Co compared to Ni. Accordingly, x may be a value between 0.5 and 1, such as 0.51, 0.52 . . . 0.98, 0.99. In other approaches, the material may have a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x may be less than 1−x, such that the compound has a greater amount of Ni compared to Co. Accordingly, x may be a value between 0 and 0.5, such as 0.01, 0.02 . . . 0.48, 0.49. Preferably, whether x is greater than or less than 1−x, the values are within a 10% difference of one another, e.g., x is a value in a range of 0.45-0.55. In preferred approaches, the material may have a chemical formula: YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2, where x is about equal to 1−x.

[0069] In at least one contemplated approach, in addition to iron and nickel, copper may be used to dope the YCo.sub.5 magnets as described herein. In contrast to the Y(Co.sub.1-xFe.sub.x).sub.5 system, Y(Co.sub.1-xNi.sub.x).sub.5 and Y(Co.sub.1-xCu.sub.x).sub.5 compounds are stable across the composition domain comprising x=0 to 1. Substituting cobalt atoms with nickel and/or copper atoms gradually decreases magnetization and magnetic anisotropy.

[0070] Preferably, the magnet as described in the inventive concepts herein includes a lower (e.g., reduced) amount of cobalt (up to 75% less Co) than the amount of Co in YCo.sub.5. Moreover, the magnet as described may be a permanent magnet.

[0071] The magnet compound of YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 material as described herein may have a CaCu.sub.5-type crystal structure. Referring again to FIG. 1, the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 may form a hexagonal CaCu.sub.5-type structure 100: Y.sub.1 in position 1a 102, Co atoms, Fe atoms, and Ni atoms sharing transition metal position 2c 104 sites and position 3g 106 non-equivalent atomic sites with 6 atoms per formula unit. In at least one exemplary aspect, Fe atoms occupy all 3g 106 positions of the CaCu.sub.5-type structure and the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloy remains thermodynamically stable until approximately all Ni atoms (which occupy all the 2c 104 positions) are substituted by Co atoms.

[0072] In the inventive concepts described herein, a thermodynamically stable permanent magnet, for example having the chemical formula YFe.sub.3(Ni.sub.0.5Co.sub.0.5).sub.2, may include no more than three Fe atoms per unit of the compound. Ideally, the Fe atoms would be distributed in the transition metal position 3g 106 nonequivalent atomic sites (as shown in FIG. 1) of the crystal structure 100.

[0073] According to inventive concepts described herein, the addition of Ni to Y(Co.sub.1-xFe.sub.x).sub.5 magnets may stabilize the magnet. Transition metals have increasing 3d electron count in the following order: Fe<Co<Ni. Thus, replacing Co atoms with Fe atoms decreases the amount of 3d electrons in the compound, whereas replacing Co atoms with Ni atoms increases the amount of 3d electrons in the compound.

[0074] According to inventive concepts described herein, the resulting YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 magnet may have a large energy product. State of the art electronic structure calculations confirmed that addition of Ni to YCo.sub.5 magnets stabilized Y(Co.sub.1-xFe.sub.x).sub.5 and maintained a reasonably high MAE comparable with the MAE of YCo.sub.5 magnets (see below in Experiments and Modeling Results).

[0075] According to inventive concepts described herein, a magnet with YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 material includes Fe atoms, Ni atoms and the Co atoms which may be distributed in transition metal 2c 104 nonequivalent atomic sites. Moreover, high axial MAE may be obtained with energetically stable YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys using abundant and cost-effective Fe and Ni in place of expensive Co, and thereby achieving higher magnetic energy product compared to the YCo.sub.5 prototype compound. Some approaches may include a YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 compound with partial ordering on the 2c-type 104 sites.

[0076] A magnet of YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 includes a spin orientation of the Y atom that may be antiparallel to a spin orientation of the Fe, Ni, and Co atoms. The spin properties of the electrons in an atom generate a magnetic moment of the atom, as measured in terms of Bohr magneton (μ.sub.B). Theoretical measurements of the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 magnet show magnetic moments of Y to be opposite atoms of each of the transition metals (e.g., Co, as shown below in Table 1).

[0077] Permanent magnets preferably include material with a high magnetocrystalline anisotropy energy (MAE). The MAE is the very small energy difference between phases with spin moments oriented in the easy and hard directions. The MAE may be defined by appropriate representation of the electronic and magnetic structures. In terms of uniaxial anisotropy, the MAE constant K.sub.1>0, where the MAE constant K.sub.1 is expressed in MJ/m.sup.3 units. The opposite case, K.sub.1<0, corresponds to the planar anisotropy. The magnitude of the MAE constant, K.sub.1, reflects the magnitude of MAE such that a larger positive value of K.sub.1 constant corresponds to a larger uniaxial MAE.

[0078] A magnet of YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 may have a MAE that is about twice a MAE of Nd.sub.2Fe.sub.14B. In some approaches, a magnet of YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 has a magnetocrystalline anisotropy energy constant (K.sub.1) that may be greater than about 10.6 MJ/m.sup.3.

[0079] In some approaches, the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 material may have a high MAE that may be comparable to the MAE of praseodymium (PrCo.sub.5), samarium (SmCo.sub.5), yttrium (YCo.sub.5) magnets of 8.1 MJ/m.sup.3, 17.2 MJ/m.sup.3 and 6.5 MJ/m.sup.3, respectively. The theoretical values of the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 compounds described herein were derived using novel computational material science approaches (see below in Experiments and Modeling Results).

[0080] It is desirable for a magnet material to have a high Curie temperature (T.sub.c) in order to continue to function as a magnet under conditions with elevated temperatures. According to inventive concepts described herein, the material of the magnet YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 has a Curie temperature (T.sub.c) that may be about equal to a Curie Temperature of YCo.sub.5. In some approaches, the material of the magnet YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 may have a T.sub.c greater than or equal to about 1000 K.

[0081] Moreover, the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 compound may have a high magnetic energy product, comparable to neodymium-based magnets. The material of the magnet YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 may have a maximum energy product of the material greater than or equal to about 351 kJ/m.sup.3. In one exemplary aspect, a YFe.sub.3CoNi magnet may have a maximum energy product of the material greater than about 309 kJ/m.sup.3. In various aspects, a YFe.sub.3CoNi magnet may have a maximum energy product of the material greater than or equal to about 300 kJ/m.sup.3.

[0082] In at least one exemplary aspect, a thermodynamically stable YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet may be created by substituting up to an additional 30 at. % Ni for Co having a T.sub.c of 900 K which is close to the calculated T.sub.c of YCo.sub.5 magnet's T.sub.c of 892 K. The YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet may have a maximum energy product of the material greater than about 351 kJ/m.sup.3.

[0083] In another exemplary aspect, a YFe.sub.3Co.sub.2 magnet may be created having a Curie temperature T.sub.c of 1098 K and a maximum energy product of 365 kJ/m.sup.3, according to various aspects described herein. The foregoing maximum energy product is about 71% of the maximum energy product for Nd.sub.2Fe.sub.14B magnets (e.g., 512 kJ/m.sup.3).

[0084] There are potentially many ways to produce the magnets described here, as would be readily apparent to one skilled in the art after reading the present disclosure. Any such method may be used to present the novel materials described herein.

[0085] An illustrative method to form a permanent magnet, which is presented by way of example only, may include starting with a YNi.sub.5 compound that is in a CaCu.sub.5-type structure. A maximum amount of Fe metal (e.g., ˜60 at %) may be dissolved with the YNi.sub.5 compound to form a stable YFe.sub.3Ni.sub.2 compound in the same structure modification where iron atoms predominantly occupy 3g sites of the crystal structure. In an ideal crystal structure, Fe atoms occupy all 3g positions.

[0086] The formation method may subsequently include gradual alloying of the YFe.sub.3Ni.sub.2 compound with Co, while keeping the amount of Y and Fe constant. In a preferred embodiment, up to 92% of the Ni atoms may be replaced with Co atoms.

[0087] Experiments and Modeling Results

[0088] YCo.sub.5 compounds crystallize in the hexagonal CaCu.sub.5-type structure with three non-equivalent atomic sites: Y.sub.1-(1a) 102, Co.sub.1-(2c) 104, and Co.sub.2(3g) 106 (see FIG. 1) with six atoms per formula unit and per computational cell.

[0089] Earlier neutron-diffraction studies of the Th(Co.sub.1-xFe.sub.x).sub.5 alloys (also based on the CaCu.sub.5-type structure) show that the larger Fe atoms preoccupies the 3g-type 106 sites, whereas the smaller Co atoms choose to occupy the 2c-type 104 sites. This occupational inclination has been affirmed by DFT calculations for YCo.sub.5 and SmCo.sub.5 compounds. In line with these calculations, the total energy for Fe at the 3g 106 site (E.sub.3g) is lower that than for Fe at the 2c 104 site (E.sub.2c) by 0.21 eV/f.u. and 0.10 eV/f.u. for YCo.sub.5 and SmCo.sub.5 magnets, correspondingly. If the YCo.sub.5 magnet is doped with Fe and Ni, Fe atoms occupy preferentially 3g 106 sites, while Ni atoms favor 2c 104 sites.

[0090] FIG. 2A depicts the heat of formation calculated within the EMTO-CPA technique of the pseudo-binary YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys where Fe atoms occupy all 3g-type 106 sites, and the occupation of the 2c-type 104 sites continuously changes from pure Ni (the YFe.sub.3Ni.sub.2 compound) to pure Co (the YFe.sub.3Co.sub.2 compound). The current calculations show that the YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys remain stable until almost all Ni atoms are replaced by Co atoms.

[0091] FIG. 2B depicts the heat of formation calculated within the EMTO-CPA formalism of the pseudo-binary SmFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys where Fe atoms occupy all 3g-type 106 sites, and the occupation of the 2c-type 104 sites continuously changes from pure Ni (the SmFe.sub.3Ni.sub.2 compound) to pure Co (the SmFe.sub.3Co.sub.2 compound). These calculations show that the pseudo-binary SmFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys could remain stable until almost half of Ni atoms are replaced by Co atoms.

[0092] Nickel metal forms the stable CaCu.sub.5-type compounds with both yttrium and samarium metals. Calculated within EMTO formalism, the heat of formation of SmNi.sub.5 and YNi.sub.5 compounds (in the CaCu.sub.5-type structure) is −18.95 mRy/atom and −22.91 mRy/atom, correspondingly, which is in accord with the experimental measurements of −23.08 mRy/atom (−30.3 kJ/mole, SmNi.sub.5) and −25.98 mRy/atom (−34.1 kJ/mole, YNi.sub.5). The YFe.sub.5 compound as well as the SmFe.sub.5 compound do not exist in the equilibrium Y—Fe and Sm—Fe phase diagrams, correspondingly, thus no experimental information about the heat of formation of these hypothetical compounds is available. However, the EMTO calculations show that the heat of formation of the YFe.sub.5 compound is positive, +6.46 mRy/atom, and is half of the calculated heat of formation of the SmFe.sub.5 compound, +12.68 mRy/atom. As a result, the calculated heat of formation of the YFe.sub.3Co.sub.2 compound, +0.09 mRy/atom, appears to be smaller than the calculated heat of formation of the SmFe.sub.3Co.sub.2 compound, +2.15 mRy/atom. The computed heats of formation of the YFe.sub.3Ni.sub.2 and the SmFe.sub.3Ni.sub.2 compounds are both negative (stable compounds), however, the absolute value of the calculated heat of formation of the YFe.sub.3Ni.sub.2 compound, |−6.20| mRy/atom, is more than twice as high as the absolute value of the heat of formation of the SmFe.sub.3Ni.sub.2 compound, |−2.72| mRy/atom. As a result, the region of stability of the pseudo-binary YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys appears to be almost twice as wide as the region of stability of the pseudo-binary SmFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys.

[0093] FIG. 3 depicts a Y—Co phase diagram exhibiting agreement with experiments: (i) congruent melting of Y.sub.2Co.sub.17 and YCo.sub.5 at 1630 K (exp.: 1630 K) and 1615 K (exp.: 1623 K), correspondingly; (ii) decomposition temperature of YCo.sub.5 at 914 K (exp.: ˜998 K); (iii) heat of formation of YCo.sub.5 equal to ‘−12.46 kJ/mole and ‘−13.61 kJ/mole at 298 and 1000 K, correspondingly, compared with ‘−12.20±0.87 kJ/mole measured between 850 and 1200 K; (iv) heat of formation of Y.sub.2Co.sub.17 equal to ‘−8.74 kJ/mole and ‘−9.47 kJ/mole at 298 and 1000 K, correspondingly, compared with ‘−7.6±0.80 kJ/mole measured between 850 and 1200 K.

TABLE-US-00001 TABLE 1 Site-projected spin, m.sup.(s), and orbital m.sup.(o), magnetic moments for the YCo.sub.5 compound FREMTO calculations. m.sup.(tot) = 7.82 μ.sub.B/f.u. Component Y.sub.1(1a) Co.sub.1(2c) Co.sub.2(3g) m.sup.(s) (μ.sub.B) +0.31 −1.55 −1.47 m.sup.(o) (μ.sub.B) −0.01 −0.14 −0.11

[0094] Y and Co spins align in an antiparallel fashion (AF) that is predicted in the present self-consistent calculations. The calculated total moment, m.sup.(tot)=7.82μ.sub.B/f.u., is slightly smaller than the experimentally reported value of 8.30μ.sub.B/f.u. The calculated spin moments are 1.55μ.sub.B and 1.47μ.sub.B for 2c 104 and 3g 106 sites, correspondingly, which are larger than the recorded experimental values of 1.44μ.sub.B and 1.31μ.sub.B. The calculated orbital moments are 0.14μ.sub.B and 0.11μ.sub.B for 2c 104 and 3g 106 sites, correspondingly, which are smaller than recorded experimental data of 0.26μ.sub.B and 0.24μ.sub.B. The present FREMTO calculations reflect the experimental (spin flip-neuron scattering) observation; for the YCo.sub.5 compound, the orbital moment of Co.sub.1(2c) 104 atoms is bigger than the orbital moment of Co.sub.2(3g) 106 atoms. The large MAE of the YCo.sub.5 compound comes from a big orbital allowance from Co.sub.1(2c) 104 sites, which are located in the same plane as Y.sub.1(1a) 102 sites. Appropriately, Co.sub.1(2c) 104 atoms have a big positive MAE allowance, while Co.sub.2(3g) 106 atoms have a small negative MAE allowance. The axial (positive) MAE of the YCo.sub.5 magnet can be achieved only if orbital moments on the Co.sub.1(2c) 104 atoms are bigger than the orbital moments of the Co.sub.2(3g) 106 atoms.

[0095] A mean-field treatment for the Curie temperature, T.sub.c, can be formulated as:

[00001]$T_c=\frac{2}{3}\times \frac{E_{\mathrm{tot}}^{\mathrm{DLM}}-E_{\mathrm{tot}}^{\mathrm{AF}}}{k_B}$

[0096] where

[00002]$\left(\frac{E_{\mathrm{tot}}^{\mathrm{DLM}}-E_{\mathrm{tot}}^{\mathrm{AF}}}{k_B}\right)$

is the difference among the ground state total energies of the DLM and the AF state, and k.sub.B is the Boltzmann constant. Principally, an assessment of the Curie temperature can be achieved from the total energy difference between the ferromagnetic (or antiferromagnetic) and the paramagnetic states. The difference between the total energies can be substituted by the difference between the effective single-particle (one atomic specie) energies, which are directly associated with AF and DLM states (the so-called mean-field treatment). In the present work, E.sub.tot.sup.DLM and E.sub.tot.sup.AF are calculated at the equilibrium volumes for DLM and AF states, correspondingly. According to the present EMTO-DLM and EMTO-AF calculations, T.sub.c=891.8 K for the YCo.sub.5 magnet, which is in good accord with the experimental data T.sub.c=920 K, which is relatively larger than that of the commonly used Nd.sub.2Fe.sub.14B magnet (T.sub.c=588 K). Similar EMTO calculations reveal T.sub.c=1149.3 K for the YFe.sub.5 compound, although this compound does not exist in the Y—Fe phase diagram. There is an experimentally observed tendency of the Curie temperature to increase with Fe doping of the YCo.sub.5 magnet, i.e., from T.sub.c=930 K (the YCo.sub.5 compound) to T.sub.c=1020 K (the Y(Co.sub.0.8Fe.sub.0.2).sub.5 compound).

[0097] FIG. 4 depicts the Curie temperature calculated within the EMTO-CPA technique of the pseudo-binary YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys where Fe atoms occupy all 3g-type 106 sites, and the occupation of the 2c-type 104 sites continuously changes from pure Ni (the YFe.sub.3Ni.sub.2 compound) to pure Co (the YFe.sub.3Co.sub.2 compound). The dotted line corresponds to the calculated Curie temperature of the YCo.sub.5 magnet, T.sub.c=891.8 K. The calculated Curie temperature is equal to 572.6 K and 1097.7 K for the YFe.sub.3Ni.sub.2 and YFe.sub.3Co.sub.2 magnets, correspondingly. Although the calculated Curie temperature of the YFe.sub.3Ni.sub.2 compound lies about 320 K below of the Curie temperature of the YCo.sub.5 magnet, this deficiency can be removed by substituting 70 at. % of Ni by Co. The Curie temperature of the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet is equal to 899.9 K.

[0098] According to the present calculations, the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet shows an enormous total moment of m.sup.(tot)˜9.79μ.sub.B, essentially due to the iron atoms that each contribute with 2.45μ.sub.B. The total moment of the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet is thus essentially bigger than that of the traditional YCo.sub.5 magnet that has a calculated total moment of m.sup.(tot)˜7.82μ.sub.B. The experimental values of saturation magnetization (M.sub.s) and the maximum energy product ((BH).sub.max) for the YCo.sub.5 magnet are 0.85 MA/m and 224 kJ/m.sup.3, correspondingly. Because saturation magnetization and magnetic moment are approximately proportional, M.sub.s˜ m.sup.(tot), and the maximum energy product is approximately proportional to the square of the saturation magnetization, (BH).sub.max˜(M.sub.s).sup.2, one can evaluate that saturation magnetization for the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet is proportional to 1.064 MA/m and the maximum energy product for the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet should be approximately 351 kJ/m.sup.3, which is ˜69% of the record maximum energy product of the Nd.sub.2Fe.sub.14B magnet, (BH).sub.max=512 kJ/m.sup.3. Particularly, the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet, which has a Curie temperature similar to the YCo.sub.5 magnet, is a substantially steadier magnet than the YCo.sub.5 magnet (its maximum energy product should be ˜57% larger).

[0099] The magnetic anisotropy energy (MAE) is one of the more important properties of an efficient magnet. In the quest to increase the saturation magnetic moment or energy product, by substituting cobalt for iron, the impact of the doping on the MAE is reviewed.

TABLE-US-00002 TABLE 2 Calculated MAEs for the YCo.sub.5-type magnets alloyed with iron, nickel, or both. Unit Cell Vol. K.sub.1 (Å.sup.3) c/a Ratio (meV/cell) K.sub.1 (MJ/m.sup.3) Material GGA LDA GGA LDA GGA LDA GGA LDA YFe.sub.5 84.84 77.46 0.79 0.79 0.51 1.17 0.96 2.42 YCo.sub.5 82.65 76.38 0.80 0.80 9.89 6.44 19.17 13.51 YNi.sub.5 81.96 74.94 0.81 0.81 1.40 0.48 2.74 1.03 YeFe.sub.3Co.sub.2 86.40 77.28 0.79 0.79 2.01 6.71 3.73 13.91 YeFe.sub.3CoNi 86.22 76.38 0.81 0.82 4.51 5.04 8.38 10.57 YeFe.sub.3Ni.sub.2 86.34 76.64 0.84 0.83 1.93 3.69 3.58 7.69

[0100] For the YFe.sub.3Co.sub.2 and the YFe.sub.3CoNi magnets, the iron atoms are kept on the energetically favorably 3g 106 sites. In the case of YFe.sub.3CoNi, Co and Ni are modeled as on the 2c 104 sites as two average atoms consistent with modeling of SmFe.sub.3CoNi. In all calculations, the atomic volume is relaxed and the c/a axial ratio of the hexagonal phase. Some sensitivity is found (not shown) of the MAE to the axial ratios, suggesting that the structural relaxation is important.

[0101] According to the values calculated in Table 2, both YFe.sub.5 and YNi.sub.5 have relatively small magnetic anisotropy and, for that reason alone, they are not particularly strong magnets. YFe.sub.5 is included in the table to provide context to the other magnets, as it does not exist in the hexagonal phase. YCo.sub.5 contrarily exists and is predicted to have significant magnetic anisotropy. DFT-GGA calculations are relied on for these magnetic compounds because GGA performs better for the magnetic 3d transition metals relative to the LDA or even more modern approximations. GGA reproduces the proper magnetic ground state of iron, as opposed to the LDA. The GGA calculations reproduce the experimental atomic volume very well but overestimate the MAE for YCo.sub.5 relative to experimental data. DFT-GGA (T=0 K) gives the unit cell volume V.sub.cell=82.65 Å.sup.3 and anisotropy K.sub.1=9.89 meV/cell (19.2 MJ/m.sup.3). These numbers are compared to experimental data at T=4.1 K, V.sub.cell=82.50 Å.sup.3, K.sub.1=3.80 meV/cell (7.38 MJ/m.sup.3) and at T=293 K, V.sub.cell=83.99 Å.sup.3, K.sub.1=3.04 meV/cell (5.80 MJ/m.sup.3). Here, the unit cell volume at T=4.1 K, V.sub.cell=82.50 Å.sup.3 is identified using the experimental value of the MAE coefficient, K.sub.1, presented in the units of (MJ/m.sup.3), and (meV/cell).

[0102] Replacing most of Co with Fe in the YCo.sub.5 magnet and using Ni as a thermodynamic mediator results in an YFe.sub.3CoNi magnet with desired magnetic properties such as a very high Curie temperature, robust magnetic anisotropy, and a relatively large maximum energy product. YFe.sub.3CoNi magnets use nickel metal as the stabilizing material in the YCo.sub.5 magnet in order to accommodate the maximum amount of iron metal to favor a very high magnetization.

[0103] For YFe.sub.3(Ni.sub.1-xCo.sub.x).sub.2 alloys, it is possible to have stable solutions until approximately all Ni atoms are substituted by Co atoms. The ab initio heat of formation predictions are confirmed by CALPHAD modeling at 298 K. The combination of negative heat of formation and extended solubility limits experimentally observed in the YTM.sub.5 (TM=Co, Fe, Ni) magnets (e.g., complete solubility from YCo.sub.5 to YNi.sub.5 at 1073 K and 1273 K; solubility of ˜20 at. % Fe in Y(Co,Fe).sub.5 at 1323 K; solubility of ˜30 at. % Fe in Y(Fe,Ni).sub.5 at 873 K) is promising for synthesis of the foregoing magnets. A specific example includes a YFe.sub.3Co.sub.2 magnet for which the calculated the Curie temperature, T.sub.c, which is equal to 1097.7 K and the maximum energy product, (BH).sub.max(YFe.sub.3Co.sub.2), as ˜365 kJ/m.sup.3, which is ˜71% of the record maximum energy product of the Nd.sub.2Fe.sub.14B magnet, (BH).sub.max=512 kJ/m.sup.3. Here, the maximum energy products of YFe.sub.3Co.sub.2 and YFe.sub.3CoNi magnets are estimated using the calculated total magnetic moments of YFe.sub.3Co.sub.2, YFe.sub.3CoNi, and YCo.sub.5 magnets as well as the experimental values of the saturated magnetization and the maximum energy product of the YCo.sub.5 magnet. Calculations are performed in the same fashion as for the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet.

[0104] According to the presently disclosed calculations, the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet has a Curie temperature T.sub.c˜900 K that is relatively close to the calculated Curie temperature of the YCo.sub.5 magnet, T.sub.c˜ 892 K. In addition, the maximum energy product of the YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 magnet is significantly improved compared to the YCo.sub.5 magnet (˜57% larger). The calculated intrinsic properties of the magnets are reported in Table 3 in conjunction with the experimental data of Nd.sub.2Fe.sub.14B, SmCo.sub.5, and YCo.sub.5 magnets for comparison. All four suggested permanent magnets have a Curie temperature significantly higher than that of Nd.sub.2Fe.sub.14B, T.sub.c˜ 588 K, spanning from 785 K to 1103 K. In addition, their maximum energy products are significantly higher than that of the commercially used SmCo.sub.5 and YCo.sub.5 magnets (231 kJ/m.sup.3 and 224 kJ/m.sup.3, respectively), reaching a maximum value of 365 kJ/m.sup.3 for YFe.sub.3Co.sub.2. Our calculated (Table 3, LDA) MAEs for YFe.sub.3CoNi magnet is not much smaller than that of YCo.sub.5 magnet (10.6 MJ/m.sup.3 and 13.5 MJ/m.sup.3, respectively).

TABLE-US-00003 TABLE 3 Intrinsic magnetic properties of Nd.sub.2Fe.sub.14B, SmCo.sub.5, and YCo.sub.5 permanent magnets (experiment) and SmFe.sub.3CoNi, YFe.sub.3CoNi, (K.sub.1, LDA), YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2, and YFe.sub.3Co.sub.2 permanent magnets (theory). M.sub.s, T.sub.c K.sub.1 (BH).sub.max Material (MA/m) (K) (MJ/m.sup.3) (kJ/m.sup.3) Nd.sub.2Fe.sub.14B 1.28 588 4.9 512 SmCo.sub.5 0.86 1020 17.2 231 YCo.sub.5 0.85 987 6.5 224 SmFe.sub.3CoNi 1.08 1103 9.2 361 YFe.sub.3CoNi 1.00 785 10.6 309 YFe.sub.3(Ni.sub.0.3Co.sub.0.7).sub.2 1.06 900 351 YFe.sub.3Co.sub.2 1.14 1098 365

[0105] In Use

[0106] Considering SmFe.sub.3CoNi and YFe.sub.3CoNi magnets comprise up to 80% less Co than their SmCo.sub.5 and YCo.sub.5 precursors, maturing of these magnets becomes even more captivating from the current economic viewpoint. Replacing part of cobalt with iron in SmCo.sub.5 and YCo.sub.5 magnets stabilized with a small portion of nickel results in permanent magnets having many desirable characteristics. These permanent magnets are anticipated to have outstanding magnetic properties, a large maximum energy product, a strong magnetic anisotropy, and an exceptionally high Curie temperature.

[0107] In use, the alloy formulations described herein may be useful as permanent magnets with high MAE and energy product, and useful for high-temperature applications (e.g., Curie temperatures in a range of about 900 K to about 1100 K). The YCoNiFe.sub.3 and SmCoNiFe.sub.3 alloy formulations described herein may be used for cost-effective clean energy products, turbines, electric car battery applications, etc.

[0108] The inventive concepts disclosed herein have been presented by way of example to illustrate the myriad features thereof in a plurality of illustrative scenarios, embodiments, and/or implementations. It should be appreciated that the concepts generally disclosed are to be considered as modular, and may be implemented in any combination, permutation, or synthesis thereof. In addition, any modification, alteration, or equivalent of the presently disclosed features, functions, and concepts that would be appreciated by a person having ordinary skill in the art upon reading the instant descriptions should also be considered within the scope of this disclosure.

[0109] While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of an embodiment of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.