Origin of crystaline magnetic anisotropy of Sm2Fe17N3 permanent magnet material
ICM2018(San Francisco, USA)
Abstract
Electronic structure and magnetic properties of Sm2Fe17Nx are studies on the basis of thefirst- principles electronic structure calculation in the framework of the den- sity functionaltheory within the local density and coherent potential approximations. The magnetic anisotropyof the system as a function of nitrogen concentration x is discussed by taking account notonly of the crystal field effects but also of the effects of the hybridization of f-states of Smwith the neighboring N p-states[1]. Without N atoms, the hybridization of Sm-f states withsurrounding atoms is rather small and the f states keep a feature of narrow atomic-like stateirrespective of the relative angle between the magnetization and crystal axes. In this situation,the rotation of crystal axes has little effect on the Sm-f states and causes no significantmagnetic anisotropy. When N atoms are introduced, the hybridization between Sm-4f and N-2p states occurs. When the magnetization lies along the c-axis, the strongest hybridizationoccurs between N-2p and Sm- 4f with magnetic quantum number m = ±3 states. On theother hand, for the in-plane magnetization, the strongest hybridization is between the Sm m =0 state and N-2p states. Comparing these two cases, we may say that an energy gain isexpected only when the hybridization occurs between m = −3 and the N-2p states. This isbecause the spin- orbit douping pushes up only the m = −3 state above the Fermi level andthus causes the energy gain due to the lowering of the occupied state energy levels[2]. Theimportance of hybridization is also proven by the fact that, if the open-core scheme for Sm-fstates be adopted, where no hybridization occurs between Sm-f and N-2p states, the uniaxialmagnetic anisotropy does not occur.