Permanent magnetic properties of NdFe_(12)N_x sputtered films epitaxially grown on V buffer layer

摘要

To clarify the magnetic properties of the NdFe_(12)N_x compound, which shows promise as a high-performance permanent magnet material, NdFe_(12)N_x epitaxial films fabricated by using a V under-layer on MgO (100) single-crystalline substrates were investigated. Nd-Fe films deposited on a V underlayer consist of NdFe_(12) grains, which have a c-axis orientation perpendicular to the film plane, as well as α-Fe and Nd_2Fe_(17) phases. In the Nd-Fe-N film obtained by subsequent nitridation of the Nd-Fe film, NdFe_(12)N_x grains grew as the dominant phase, and the volume fractions of a-Fe phases dropped below 5%. A Nd-Fe-N film with a thickness of 50 nm exhibits a saturation magnetization (M_s) of 1.7 T, an anisotropy field (H_A) of ~60 kOe, a magnetocrystalline anisotropy energy (K_1) of ~4.1 MJ/m~3, and a coercivity (H_c) of 1.7 kOe. The H_c of a Nd-Fe-N film with a thickness of 25 nm is 4.3 kOe. These results indicate that NdFe_(12)N_x compounds have a superior M_s compared to Nd-Fe-B magnets, while the enhancement in H_c is indispensable.