Patent Application
20200318222
The present invention relates permanent magnets, and more particularly, this invention relates to SmCo5-based magnets.
Among the great challenges of materials science is discovering a material that satisfies conflicting requirements and also possesses specific properties for a particular application. There is a need for strong permanent magnets to withstand higher temperatures, for example Curie temperatures ranging from 800 K to 1200 K, which the widely used neodymium-based magnets (Nd2Fe14B, Neomax®) cannot tolerate. Pure Samarium-Cobalt (SmCo) magnets (both SmCo5 and Sm2Co17) satisfy this requirement and are less subject to corrosion than the neodymium-based magnets and thus do not require a coating. Moreover, pure SmCo magnets have strong resistance to demagnetization.
Three basic material parameters determine the intrinsic properties of hard magnetic materials: (i) spontaneous (saturation) magnetization, (Ms), (ii) Curie temperature (Tc), and (iii) magnetocrystalline anisotropy energy (MAE). An optimal technological permanent magnet has a large spontaneous magnetization (Ms≥˜1 MA), high Curie temperature (Tc≥˜550 K), and large MAE constant (K1≥˜4 MJ/m3).
Pure SmCo5 permanent magnets exhibit enormously high uniaxial MAE constant of K1˜17.2 MJ/m3, nearly four times higher than Sm2Co17 magnets (MAE with a K1 of 4.2 MJ/m3) and have high Curie temperature, Tc˜1020 K. However, the Nd2Fe14B magnet currently dominates the world market for permanent magnets (˜62% of world market), since the Nd2Fe14B magnet has large spontaneous magnetization and possesses the highest energy performance measured by a record high energy product. The Maximum Energy Product (BH)max of the Nd2Fe14B magnet at 512 kJ/m3 is more than twice as high as the (BH)max of SmCo5 magnets, at 231 kJ/m3. Although SmCo5 magnets are more suitable for high temperature applications than Nd2Fe14B magnets, the relatively low energy performance of SmCo5 magnets results in a low distribution of 3% of the world market.
It would be desirable to formulate a permanent magnet with a greater spontaneous magnetization, high MAE and thermostability comparable to SmCo5 magnets while having a high Curie temperature.
In accordance with one aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: SmFe3(Ni1−xCox)2, where x is greater than 0 and x is less than 1.
In accordance with another aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: SmFe3(Ni1−xCox)2, where x is greater than 0 and x is less than 1, and where the material has a CuCa5-type crystal structure
Other aspects and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.
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.
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.
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.
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, e.g., during ceramic processing.
In accordance with one general aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: SmFe3(Ni1−xCox)2, where x is greater than 0 and x is less than 1.
In accordance with another general aspect of the presently disclosed inventive concepts, a magnet includes a material having a chemical formula: SmFe3(Ni1−xCox)2, where x is greater than 0 and x is less than 1, and where the material has a CuCa5-type crystal structure
A list of acronyms used in the description is provided below.
According to various inventive concepts described herein, a permanent magnet may be formed that has a high spontaneous magnetization, thermostability at high Curie temperatures and high magnetocrystalline anisotropy energy (MAE). Ideally, transition-metal dopants may boost the energy product of SmCo5 magnets without compromising the high MAE and thermostability at 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.
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 stand point, it would be beneficial to substitute Co atoms in SmCo5 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).
As shown in
In the SmFe5 compound that only include 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.
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., SmCo5→SmFe5) may result in a thermodynamically unstable crystal structure of an ordinary hexagonal phase. Moreover, SmFe5 does not appear in the equilibrium Sm—Fe phase diagram, although the alloy compound Sm(Co1−xFex)5 with CaCu5-type structure has been synthesized by the melt-spinning method for x=0.0-0.3.
In contemplated approaches, Sm(Co1−xFex)5 materials have been synthesized. Furthermore, the Curie temperatures (Tc) for Sm(Co1−xFex)5 alloys were found to increase from about 1020 K to about 1080 K when increasing x from 0.0 to 0.2. In contrast, Sm2(Co1−xFex)17 alloys exhibit a monotonic decrease in Curie temperature (Tc) with increasing Fe content.
Accordingly, the inventive concepts presented herein, in several embodiments, involve ab initio calculations to add nickel (Ni) and iron (Fe) to a SmCo5 magnet in order to stabilize Sm(Co—Fe—Ni)5 alloys containing a sufficient amount of Fe to boost the energy product of the Sm(Co—Fe—Ni)5 magnet.
In accordance with inventive concepts described herein, a magnet includes a material having a chemical formula: SmFe3(Ni1−xCox)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: SmFe3(Ni1−xCox)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: SmFe3(Ni1−xCox)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: SmFe3(Ni1−xCox)2, where x is about equal to 1-x.
Preferably, the magnet as described in the inventive concepts herein includes a reduced amount of cobalt (up to 80% less Co) than the amount of Co in SmCo5. Moreover, the magnet as described may be a permanent magnet.
The magnet compound of SmFe3(Ni1−xCox)2 material as described herein may have a CaCu5-type crystal structure. Referring again to
In the inventive concepts described herein, a thermodynamically stable permanent magnet, for example having the chemical formula SmFe3(Ni0.5Co0.5)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
According to inventive concepts described, the addition of Ni to Sm(Co1−xFex)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.
According to inventive concepts described herein, the resulting SmFe3(Ni1−xCox)2 magnet may have a large energy product. State of the art electronic structure calculations confirmed that addition of Ni to SmCo5 magnets stabilized Sm(Co1−xFex)5 and maintained a reasonably high MAE comparable with the MAE of SmCo5 magnets (see below in Experiments).
According to inventive concepts described herein, a magnet with SmFe3(Ni1−xCox)2 material includes Ni atoms and the Co atoms may be distributed in transition metal 2c nonequivalent atomic sites. Moreover, high axial MAE may be obtained with energetically stable SmFe3(Ni1−xCox)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 SmCo5 prototype compound. Some approaches may include a SmFe3(Ni1−xCox)2 compound with partial ordering on the 2c-type sites.
A magnet of SmFe3(Ni1−xCox)2 includes a spin orientation of the Sm 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 (μB). Theoretical measurements of the SmFe3(Ni1−xCox)2 magnet show magnetic moments of Sm to be opposite atoms of each of the transition metals (e.g. Co, as shown below in Table 1).
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 K1>0, where the MAE constant K1 is expressed in MJ/m3 units. The opposite case, K1<0, corresponds to the planar anisotropy. The magnitude of the MAE constant, K1, reflects the magnitude of MAE such that a larger positive value of K1 constant corresponds to a larger uniaxial MAE.
A magnet of SmFe3(Ni1−xCox)2 may have a MAE that is about twice a MAE of Nd2Fe14B. In some approaches, a magnet of SmFe3(Ni1−xCox)2 has a magnetocrystalline anisotropy energy constant (K1) that may be greater than about 9 MJ/m3.
In some approaches, the SmFe3(Ni1−xCox)2 material may have a high MAE that may be comparable to the MAE of praseodymium (PrCo5) and yttrium (YCo5) magnets of 8.1 MJ/m3 and 6.5 MJ/m3, respectively. The theoretical values of the SmFe3(Ni1−xCox)2 compounds described herein were derived using novel computational material science approaches (see below in Experiments).
It is desirable for a magnet material to have a high Curie temperature (Tc) 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 SmFe3(N1−xCox)2 has a Curie temperature (Tc) that may be about equal to a Curie Temperature of SmCo5. In some approaches, the material of the magnet SmFe3(Ni1−xCox)2 may have a Tc greater than about 1100 K.
Moreover, the SmFe3(Ni1−xCox)2 compound may have a high magnetic energy product, comparable to neodymium-based magnets. The material of the magnet SmFe3(Ni1−xCox)2 may have a maximum energy product of the material greater than about 361 kJ/m3.
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.
An illustrative method to form a permanent magnet, which is presented by way of example only, may include starting with a SmNi5 compound that is in a CaCu5-type structure. A maximum amount of Fe metal (e.g., ˜50 at %) may be dissolved with the SmNi5 compound to form a stable SmFe3Ni2 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.
The formation method may subsequently include gradual alloying of the SmFe3Ni2 compound with Co, while keeping the amount of Sm and Fe constant. In a preferred embodiment, half of the Ni atoms may be replaced with Co atoms.
Experiments
The heat of formation (y-axis,
Moreover, a related alloy SmNi2Fe3, as shown in
A combination of Co and Ni were substituted at sites at the position 2c for the Sm(CoxNi1−x)2Fe3 alloy (
One approach to predict magnetic properties of theoretical SmCo5 compounds included statistical analysis of compositional disorder of TM-types sites. Another approach includes state-of-the-art analysis of electronic structure to treat RE (Sm) metal with almost localized 4f-electrons. The maximum energy product and the magnetic moment are measures of magnetic strength. A material of SmCoNiFe3 compound demonstrated a magnetic moment of ˜10μB. Without wishing to be bound by any theory, it was believed that the Fe atoms of the SmCoNiFe3 contributed a magnetic moment of about ˜2.7μB per Fe atom. Looking to Table 1 (above) that lists calculated and measured magnetic moments for SmCo5, a magnetic moment of a SmCoNiFe3 compound may be substantially greater than for the magnetic moment of a magnet of conventional SmCo5 having a total moment of about 8μB
Calculations described herein for MAE of the SmCo5 compounds used an accurate parameter-free first-principles theory based on the standard rare-earth model. This model is shown to be consistent with dynamical mean-field theory (DMFT) that captured electronic spectra and magnetic moments of the materials. In brief, correlated and localized samarium (Sm) 4f electrons were treated within the Hubbard I approximation (HIA) and the cobalt 3d electrons were treated with the spin-polarized T—matrix fluctuation exchange (SPTF) solver. DMFT analysis of SmCo5 included a description of the electronic structure of SmCo5. However, the standard rare-earth model (SRM) was a simpler method than the DMFT method, and captured the main physics of the DMFT analysis. Briefly, the SRM includes the assumption, without wishing to be held to any theory, that the 4f shell is part of the samarium (Sm) atomic core and does not specifically hybridize with any valence states. Experiments appeared to confirm this theory, in that the Sm—Co alloy system showed no significant overlap between samarium 4f and cobalt 3d states. Moreover, the respective peak intensity of Sm 4f and Co 3d states were far apart (6 eV).
Looking to
Looking to Table 1 (see above) theoretical magnetic moments of SmCo5 have been compared with polarized-neutron diffraction experiments. Comparing the different methods of measurement, the magnetic moments were comparable. Moreover, the theoretical results of magnetic moments using the different methods of measurement combined with the results of the electronic spectra of
With continued reference to Table 1, in the ground-state configuration, the Sm1 (negative sign) and Co1 and Co2 (positive sign) spin moments align anti-parallel in agreement as would be expected by one skilled in the art. In contrast, when the spins couple parallel, the energy of the system may be considerably higher (about 0.1 eV, not shown) at an excited energy state that is metastable and not relevant for SmCo5.
Moreover, the orbital magnetic moment on the Co1 atom (0.24 and 0.22) was greater than on the Co2 atom (0.20 and 0.18) for both methods. Without wishing to be bound by any theory, these measurements may confirm experimental results where polarized nuclear magnetic-resonance measurements have shown that the two Co atoms (Co1 and Co2) have opposing effects on the magnetic anisotropy. Thus, the cobalt orbital moments may be described as Co1>Co2 when predicting the axial MAE of the SmCo5 compounds.
Using the above theoretical values of total energies of SmCo5, a crystal structure was optimized, and a unit-cell volume was obtained at 86.0 Å3 with a bulk modulus of 141.9 GPa, which compared similarly to an experimental crystal structure of SmCo5 compound formed at room temperature with a unit-cell volume of 85.74 Å3 and bulk modulus of 138.7 GPa. The theoretical hexagonal axial c/a ratio was found to be somewhat small (0.77) relative to the hexagonal axial c/a ratio of 0.798 in the experimental crystal structure.
In Table 2 the theoretical magnetocrystalline anisotropy energies (MAE) for α-Co, SmCo5, and SmNi5 were compared with conventional experimental reports, for example, the MAE for SmCo5 was 17.20 MJ/m3. The theoretical values of α-Co, SmCo5, and SmNi5 corresponded similarly to the experimental values, and thus, the theoretical value of SmNiCoFe3 compound, 9.216 MJ/m3, derived by similar methods may be credible.
Furthermore, the increased presence of Ni appeared to affect the MAE sensitivity of the compound. As shown in the Table 2, replacing 5% Co in the SmCoNiFe3 compound with 5% Ni, resulting in SmCo0.45Ni0.55Fe3 compound, lowered the theoretical MAE by 12% from 9.216 MJ/m3 to 8.094 MJ/m3.
Table 3 summarizes the theoretical magnetic values of the SmCoNiFe3 compound with the experimental magnetic values of conventional Nd2Fe14B and SmCo5 compounds. Notably the MAE constant of the SmCoNiFe3 compound (9.2 MJ/m3) is smaller than SmCo5 (17.2 MJ/m3).
Theoretical values of Curie temperature, Tc, are calculated with exchange-coupling parameters mapped onto a Heisenberg model and mean field method (as shown in Table 3). When comparing theoretical value of the Tc for SmCoNiFe3 relative to the Tc for SmCo5, there was a modest decrease (5%) in Tc for SmCoNiFe3(1103 K for SmCoNiFe3 and 1158 K for SmCo5). Calculated Curie temperature for SmCo5 (Tc=1158 K) is comparable to the experimental value (Tc=1020 K), which was nearly twice as high as the Tc of the conventional Nd2Fe14B magnet (Tc=588 K).
The maximum energy product, [BH]max, for the SmCoNiFe3 compound (361 kJ/m3) is predicted to be significantly higher than the maximum energy product of SmCo5 compound (231 kJ/m3). Thus, the maximum energy product increases from 45.3% (SmCo5) to 70.5% (SmCoNiFe3) of the magnitude (taken as 100%) of the highest industrially achievable maximum energy product of the Nd2Fe14B magnet (512 kJ/m3).
+Experiment
In Use
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. The SmCoNiFe3 alloy formulations described may be used for cost-effective clean energy products.
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.
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.
The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC for the operation of Lawrence Livermore National Laboratory.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2018/014040 | 1/17/2018 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62447373 | Jan 2017 | US |
