Stable room-temperature ferromagnetic phase at the FeRh(100) surface.

Federico Pressacco,Fausto Sirotti,Matteo Gatti,Vojtěch Uhlίř,Azzedine Bendounan,Eric E Fullerton

doi:10.1038/srep22383

Abstract

Interfaces and low dimensionality are sources of strong modifications of electronic, structural, and magnetic properties of materials. FeRh alloys are an excellent example because of the first-order phase transition taking place at ~400 K from an antiferromagnetic phase at room temperature to a high temperature ferromagnetic one. It is accompanied by a resistance change and volume expansion of about 1%. We have investigated the electronic and magnetic properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies characterized by different probing depths, namely X-ray magnetic circular dichroism and photoelectron spectroscopy. We find that the symmetry breaking induced at the Rh-terminated surface stabilizes a surface ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally antiferromagnetic phase at room temperature. First-principles calculations provide a microscopic description of the structural relaxation and the electron spin-density distribution that support the experimental findings.

Highlights

Electronic and magnetic properties are strongly modified by symmetry breaking and reduced dimensionality at surfaces and interfaces
Using synchrotron-radiation spectroscopy techniques with different probing depths we demonstrate the presence of a stable ferromagnetic surface for FeRh at room temperature while the bulk is antiferromagnetic
The procedure was reproduced on several samples, indicating a stable electronic and magnetic properties and low reactivity since no oxidation occurred over several days

Summary

Introduction

Electronic and magnetic properties are strongly modified by symmetry breaking and reduced dimensionality at surfaces and interfaces. Spatial confinement and interface engineering can lead to fundamental discoveries of new phases and functionalities (e.g. topological insulators[1] or interface phenomena in complex oxides2,3) revealing emerging behavior that is not present or is very different in the bulk[4,5] In this regard the FeRh compound is a promising material showing a metamagnetic first-order phase transition above room temperature that is of great interest for future technologies such as heat assisted magnetic random access memories (HA-MRAM)[6,7], magnetic cooling[8,9] and spintronics devices[10,11,12]. Using synchrotron-radiation spectroscopy techniques with different probing depths we demonstrate the presence of a stable ferromagnetic surface for FeRh at room temperature while the bulk is antiferromagnetic This experimental finding agrees with first-principles calculations which give a detailed description of the atomic, electronic and spin distribution at the material/vacuum interface

Methods

Results

Discussion

Conclusion