Control of spin orientation in antiferromagnetic NiO by epitaxial strain and spin–flop coupling

A Kozioł-Rachwał,H Nayyef,M Szpytma,T Ślęzak,P Dróżdż,W Janus,M Ślęzak,M Zając

doi:10.1063/5.0011736

Abstract

A ferromagnet/antiferromagnet (FM/AFM) Fe/NiO bilayer was grown using molecular beam epitaxy on MgO(001) and Cr buffered MgO(001) substrates. X-ray linear dichroism measurements showed a dominating out-of-plane component for the NiO spins in Fe/NiO/MgO and an in-plane spin direction for NiO layers grown on the Cr buffer. Furthermore, systematic studies on the magnetic properties of Fe/NiO grown on the wedge-shaped Cr buffer revealed a continuous strain-induced spin reorientation transition from out-of-plane to in-plane NiO spin directions when the Cr thickness increased from 0 nm to 3.5 nm. The analysis of the in-plane magnetic structure of NiO in Fe/NiO/Cr showed a pronounced uniaxial anisotropy in thin AFM layers. The AFM spins are perpendicular to the Fe spins due to spin–flop interaction. These results demonstrate the feasibility of using strain and coupling with FMs to manipulate spin structures in NiO.

Highlights

Antiferromagnets (AFMs) have recently attracted attention due to their potential application as the active element for spintronic devices.1,2 A unique set of properties such as robustness to external magnetic fields, high packing density due to the lack of stray fields, and the potential terahertz operation speed3 makes AFMs serious candidates to replace ferromagnetic materials in future spintronic devices
In the case of ferromagnets (FMs), a moderate external magnetic field can be used to align the magnetic moments of ferromagnetic layers, but the magnetic field necessary to manipulate spin structures in AFMs is usually relatively large
Analogous results with comparable amplitudes of RL2 were obtained at 300 K, which suggests that the Néel temperature of the NiO layer with dNiO = 21 Å is well above room temperature (RT)

Summary

INTRODUCTION

Antiferromagnets (AFMs) have recently attracted attention due to their potential application as the active element for spintronic devices. A unique set of properties such as robustness to external magnetic fields, high packing density due to the lack of stray fields, and the potential terahertz operation speed makes AFMs serious candidates to replace ferromagnetic materials in future spintronic devices. Besides interactions at the FM/AFM interface, manipulation of spin structures in AFMs can be realized using strain. Lattice distortion induced by strain can modify the magneto-crystalline anisotropy and reorient the direction of magnetic moments in the AFM layer.. An out-of-plane spin orientation was observed in NiO films grown on MgO(001) with a larger lattice constant (aNiO = 4.176 Å < aMgO = 4.212 Å). We used strain and interface coupling to manipulate the spin structure in NiO. The analysis of in-plane magnetic structures for NiO in the Fe/NiO/Cr stack revealed a pronounced uniaxial anisotropy in the thin AFM layers with a spin direction perpendicular to that of Fe due to spin–flop interaction

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS