First-Principles Study of Structural and Magnetic Properties of R(Fe,Ti)₁₂ and R(Fe,Ti)₁₂N (R = Nd, Sm, Y)

Abstract

We study the effects of interstitial nitrogenation to magnetic properties of ThMn 12 -type compounds RFe 11 Ti and RFe 12 with R=Nd, Sm, Y by using first-principles technique. The magnetocrystalline anisotropy is estimated from the crystalline-electric-field parameter A 0 2 at the rare-earth site. The change in r 2 A 0 2 by nitrogenation is nearly independent of Ti substitution and has a little dependence on the rare-earth element. NdFe 12 N has considerably larger magnetization and slightly less (but strong enough) uniaxial magnetocrystalline anisotropy compared with NdFe 11 TiN, thereby NdFe 12 N is expected to be a quite high performance permanent magnet material.

First-principles study on stability and magnetism of NdFe11M and NdFe11MN for M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn

“…In fact, the magnetization is even smaller than naive expectation from the iron concentration. 2,10 This substantial reduction is explained qualitatively by Friedel's concept of virtual bound state. 2,22,23 Therefore, a substitutional element that stabilizes the crystal structure without substantial magnetization reduction is required for applications to permanent magnets.…”

“…It is favorable for achieving large magnetization, hence iron-based ThMn 12 -type compounds have been studied as potential candidates for permanent magnet materials. [3][4][5][6][7][8][9][10] It was reported in the late 80's that SmFe 11 Ti has reasonably large magnetization and magnetocrystalline anisotropy. Although NdFe 11 Ti does not show uniaxial anisotropy, interstitial nitrogenation induces strong uniaxial anisotropy, and also increases the magnetization.…”

Relevance of 4f-3d exchange to finite-temperature magnetism of rare-earth permanent magnets: An ab-initio-based spin model approach for NdFe12N

“…Comparing the calculated temperature dependence of magnetization between NdFe 12 and NdFe 12 N as shown in Fig. 3 (b), we see that the experimentally observed We note that Nd in NdFe 12 has the easy-plane magnetic anisotropy 5,15 which would compete against the easy-axis anisotropy from at least a part of the Fe sublattices. Here we just track the origin of the difference in the Curie temperature between NdFe 12 and NdFe 12 N to the nitrogenation-enhanced exchange couplings as demonstrated in Fig.…”

“…Also the experimental anisotropy field near the liquid-nitrogen temperature seems to come close to 14 [T] 21 which suggests possible systematic underestimate in our calculated magnetic anisotropy which falls below 10 [T] in the limit T → 0. The ab initio estimation for the crystal-field coefficients for the estimation of the uni-axial magnetic anisotropy energy indeed involves a certain uncertainty 15 . An improved data collapse between theory and experiment in the lowest temperature range of H a (T ) can be observed by manually setting K Nd = 2K…”

“…Taking the ThMn 12 crystal structure as the starting point, the crystal structure is optimized from first principles. Then the crystal field parameters on Nd 3+ are calculated on the basis of open-core description for the 4f -shell 15 . Up to here the calculations are done with the ab initio electronic-structure computational code package, QMAS 16 .…”