Ab initiostudy of magnetocrystalline anisotropy, magnetostriction, and Fermi surface of L1₀FeNi (tetrataenite)

Abstract

The ordered L1 0 FeNi phase (tetrataenite) is recently considered as a promising candidate for the rare-earth free permanent magnets applications. In this work we calculate several characteristics of the L1 0 FeNi, where most of the results come form the fully relativistic full potential FPLO method with the generalized gradient approximation (GGA). A special attention deserves the summary of the magnetocrystalline anisotropy energies (MAE's), the full potential calculations of the anisotropy constant K 3 , and the combined analysis of the Fermi surface and three-dimensional k-resolved MAE. Other calculated parameters presented in this article are the magnetic moments ms and m l , magnetostrictive coefficient λ 001 , bulk modulus B 0 , and lattice parameters. The MAE's summary shows rather big discrepancies between the experimental MAE's from literature and also between the calculated MAE's. The MAE's calculated in this work with the full potential and GGA are equal to 0.47 MJ m −3 from WIEN2k, 0.34 MJ m −3 from FPLO, and 0.23 MJ m −3 from FP-SPR-KKR code. These last results strongly suggest that the value of MAE in GGA is below 0.5 MJ m −3 . It is also expected that this value is significantly underestimated due to the limitations of the GGA. Unfortunately, as other authors suggest, even the MAE equal 1.3 MJ m −3 would be insufficient to raise the L1 0 FeNi from the category of semi-hard magnets. However the L1 0 FeNi has still a potential to improve its MAE by modifications, like e.g. tetragonal strain or alloying. The presented three-dimensional k-resolved map of the MAE combined with the Fermi surface gives a complete picture of the MAE contributions in the Brillouin zone. The calculated Fermi surface consists of closed hole pockets and open sheets. It reflects a four-fold symmetry of the crystal and is closely related to the MAE(k). The analysis of the effects of external factors, like strain, on the k-resolved MAE and Fermi surface should be beneficial in engineering of the hard magnetic properties. The obtained from full potential FP-SPR-KKR method magnetocrystalline anisotropy constants K 2 and K 3 are several orders of magnitude smaller than the MAE/K 1 and equal to -2.0 kJ m −3 and 110 J m −3 , respectively. The calculated partial spin and orbital magnetic moments of the L1 0 FeNi are equal to 2.72 and 0.054 µ B for Fe and 0.53 and 0.039 µ B for Ni atoms, respectively. The calculations of geometry optimization lead to a c/a ratio equal to 1.0036, B 0 equal to 194 GPa, and λ 001 equal to 9.4 × 10 −6 .

First-principles study of electronic structure and magnetic properties of L10-ordered FeNi, FePd, and FePt alloys

“…For FeNi as an example, our calculations yield B 0 ¼ 182.5 GPa at 0K. This is very close to the range of the experimental values for Fe 0.5 Ni 0.5 alloy at room temperature, which is expanding from 165 GPa to 177 GPa [42,43].…”

“…The estimated value is less than 0.5 MJ m À3 which is below the reported values in the literature. This expected limitation in the GGA result can be improved by including additional factors such as tetragonal strain and alloying [27]. Burzo et al [28] studied band structure and magnetic properties of FePd ordered compounds using first-principles calculations.…”

“…Werwiński et al. [ 27 ] calculated MCA for L1 0 FeNi using generalized gradient approximation (GGA) with WIEN2K, FLPO, and FP-SPR-KKR code. The estimated value is less than 0.5 MJ m −3 which is below the reported values in the literature.…”

“…Method a (Å) c (Å) B (GPa) dB PZ PBE PBEsol PW91 PZ PBE PBEsol PW91 PBE PBE FeNi Model 1 3.41 3.55 3.49 3.55 3.41 3.55 3.49 3.55 164.7 5.96 Model 2 3.43 3.57 3.48 3.54 3.43 3.57 3.47 3.59 172.4 5.57 Model 3 3.47 3.57 3.49 3.55 3.47 3.57 3.56 3.62 182.5 5.43 Theor. 3.56 [ 27 ] 3.58 [ 27 ] 194 Exp. 3.57 [ 44 ] 3.57 [ 44 ] 165–177 - FePd Model 1 3.78 3.94 3.86 3.92 3.63 3.63 3.55 3.60 145.4 4.81 Model 2 3.78 3.86 3.83 3.87 3.65 3.78 3.75 3.78 151.4 5.29 Model 3 3...…”

Исследования из первых принципов структурных свойств сплавов Гейслера Co-Ni-Sn

“…Поиски материалов с такими характеристиками активно ведутся среди бинарных соединений Fe−Ni [8][9][10], Fe−N [11], Fe−B [12], Co−Ni, Mn−Al, Mn−Ga [8], а также трех-и четырехкомпонентных соединений на их основе: Fe−Co−С [13], Fe−P−B с добавкой Со [14], Fe−Si−B с добавками P, S, и Co [15], Fe−Co−B [12,16]. В течение последних десятилетий на роль постоянных магнитов серьезно рассматриваются сплавы Гейслера X 2 Y Z. В ряде работ [17][18][19], посвященных первопринцип-ным исследованиям новых магнитотвердых материалов, рассматривались сплавы Гейслера на основе Ni [17,18], Fe [18,19], Co [18,19] Rh, Au, Mn, а также бинарные составы Fe 3 Ga и Fe 3 Ge [18].…”