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

TL;DR

This study demonstrates that the FeRh(100) surface exhibits a stable ferromagnetic phase at room temperature due to surface symmetry breaking, supported by spectroscopic experiments and first-principles calculations.

Contribution

It reveals the stabilization of a ferromagnetic surface layer on FeRh(100) at room temperature, a novel finding supported by combined experimental and theoretical approaches.

Findings

Surface ferromagnetic layer involves five atomic planes.

Symmetry breaking at Rh-terminated surface stabilizes ferromagnetism.

First-principles calculations support experimental observations.

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 $\sim$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 thus reveal 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 fully support the experimental findings.