Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

Xianzhong Zhou,Frank Matthes,Claus M Schneider,Daniel E Bürgler

doi:10.1063/1.4940758

Abstract

The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

Highlights

The CsCl-ordered, equiatomic alloy of Fe and Rh is a magnetic material with a unique temperature-induced metamagnetic transition from antiferromagnetic (AFM) below the transition temperature Ttrans ≈ 350 K1 to ferromagnetic (FM) above Ttrans
Epitaxial equiatomic FeRh thin films were deposited on MgO(001) and investigated by scanning electron microscopy with polarization analysis (SEMPA) and magneto-optical Kerr effect (MOKE) without intermediate exposure to ambient pressure
MOKE confirmed the presence of the AFM-to-FM metamagnetic phase transition in the body of the film between 143 K and room temperature (RT)

Summary

INTRODUCTION

The CsCl-ordered, equiatomic alloy of Fe and Rh is a magnetic material with a unique temperature-induced metamagnetic transition from antiferromagnetic (AFM) below the transition temperature Ttrans ≈ 350 K1 to ferromagnetic (FM) above Ttrans. The coexistence of laterally separated FM and AFM phases as well as temperature-induced nucleation and growth of FM domains across the transition were directly imaged on oxidized FeRh films. Films capped with 2.5 nm Al showed stable FM domains at the FeRh/Al interface below the metamagnetic transition temperature of the film Interfacial ferromagnetism of this form was observed in XMCD measurements by Ding et al.[14] for FeRh thin films capped with MgO or Au. The occurrence of stable interfacial FM domains below the bulk transition temperature is assumed to be related to interdiffusion, deviations in composition (e.g. Fe deficiency), or strain effects induced by the capping layers.[13,14]. We use in-situ scanning electron microscopy with polarization analysis (SEMPA) to directly image the intrinsic magnetic domain structure at the surface of uncapped 10 nm thick single-crystalline FeRh(001) films at various temperatures from far below to well above the metamagnetic phase transition

EXPERIMENTAL SETUP AND PROCEDURES

SAMPLE PREPARATION

SURFACE DOMAIN IMAGING

CONCLUSION