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

Taku Hirose,Akihito Anzai,Toshiki Gushi,Kaoru Toko,Taro Komori,Takashi Suemasu

doi:10.1063/1.5141818

Abstract

Ferrimagnetic Mn4N is a promising candidate for current-induced domain wall motion assisted by spin-transfer and spin–orbit torques. Mn4N can be doped to have perpendicular magnetic anisotropy (PMA) and a small spontaneous magnetization. However, the origin of the PMA of Mn4N 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 Mn4N epitaxial thin films (c/a) and the uniaxial magnetic anisotropic constant (Ku) in Mn4N thin films grown on MgO(001), SrTiO3(001), and LaAlO3(001) substrates. The lattice mismatches between Mn4N and these substrates are approximately −6%, −0.1%, and +2%, respectively. All the Mn4N thin films had PMA and in-plane tensile distortion (c/a &lt; 1) regardless of the Mn4N thickness and substrate. Although the magnitude of c/a depended on several factors, such as the Mn4N layer thickness and substrate, we found a strong correlation between c/a and Ku; Ku increased markedly when c/a deviated from 1. This result indicates that the origin of PMA is tensile distortion in Mn4N films; hence, it might be possible to control the magnitude of Ku by tuning c/a through the Mn4N layer thickness and the substrate.

Highlights

Nonvolatile memory devices with fast operation, low power consumption, and high-density information storage would be highly desirable
We found a strong correlation between c/a and Ku values in Mn4N films, meaning that the Ku can be controlled by c/a
The reflection high-energy electron diffraction (RHEED) image of sample 8 was not obtained because of mechanical issues, the RHEED image of sample 7 indicated a spotty pattern and rings, which suggested the formation of polycrystalline Mn4N films

Summary

INTRODUCTION

Nonvolatile memory devices with fast operation, low power consumption, and high-density information storage would be highly desirable. Mn4N films have been grown on MgO(001),[19] SrTiO3[STO](001),[19] (LaAlO3)0.3(Sr.2TaAlO6)0.7(001),20 6H–SiC(0001),[21] and GaN(0001)[21] substrates by molecular beam epitaxy (MBE). Recent experiments have shown that when Mn4N films exhibit PMA, the ratio of the perpendicular lattice constant c to the in-plane lattice constant a, c/a, is approximately 0.99, regardless of the lattice mismatch to various substrates.[19,22,23]. There have been no systematic studies of the relationship between c/a and Ku in Mn4N epitaxial films, the origin of PMA is likely to be in-plane tensile distortion in Mn4N films. We have grown Mn4N thin films only on substrates that induce in-plane tensile distortion (c/a < 1), such as MgO and STO, from the viewpoint of lattice mismatch between Mn4N and the substrates. We found a strong correlation between c/a and Ku values in Mn4N films, meaning that the Ku can be controlled by c/a

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION