Strong correlation between uniaxial magnetic anisotropic constant and in-plane tensile strain in Mn4N epitaxial films

摘要

Ferrimagnetic Mn 4 N is a promising candidate for current-induced domain wall motion assisted by spin-transfer and spin–orbit torques. Mn 4 N can be doped to have perpendicular magnetic anisotropy (PMA) and a small spontaneous magnetization. However, the origin of the PMA of Mn 4 N has yet to be fully understood. Here, we investigated the relationship between the ratios of the perpendicular lattice constant c to the in-plane lattice constant a of Mn 4 N epitaxial thin films ( c/a ) and the uniaxial magnetic anisotropic constant ( K u ) in Mn 4 N thin films grown on MgO(001), SrTiO 3 (001), and LaAlO 3 (001) substrates. The lattice mismatches between Mn 4 N and these substrates are approximately ?6%, ?0.1%, and +2%, respectively. All the Mn 4 N thin films had PMA and in-plane tensile distortion ( c/a 1) regardless of the Mn 4 N thickness and substrate. Although the magnitude of c/a depended on several factors, such as the Mn 4 N layer thickness and substrate, we found a strong correlation between c/a and K u ; K u increased markedly when c/a deviated from 1. This result indicates that the origin of PMA is tensile distortion in Mn 4 N films; hence, it might be possible to control the magnitude of K u by tuning c/a through the Mn 4 N layer thickness and the substrate.