Spin polarization asymmetry at the surface of chromia

Shi Cao,W Echtenkamp,Ning Wu,Xin Zhang,G Chen,A T N’Diaye,Ch Binek,Xumin Chen,P A Dowben,A Enders,A K Schmid

doi:10.1088/1367-2630/16/7/073021

Abstract

We demonstrate boundary spin polarization at the surface of a Cr2O3 single crystal using spin-polarized low-energy electron microscopy (SPLEEM), complementing prior spin polarized photoemission, spin polarized inverse photoemission, and x-ray magnetic circular dichroism photoemission electron microscopy measurements. This work shows that placing a Cr2O3 single crystal into a single domain state will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the SPLEEM contrast for the two polarization states may be different, consistent with scanning tunneling microscopy spectroscopy results obtained from ultrathin films of Cr2O3.

Highlights

The predicted boundary spin polarization [1,2,3] at the surface of magnetoelectric chromia, Cr2O3(0001), was confirmed experimentally by the combination of spin polarized photoemission [3], spin polarized inverse photoemission [4], x-ray magnetic circular dichroism photoemission electron microscopy [4] and magnetic force microscopy [4]
The exchange bias field, HEB, in a bilayer of chromia and an adjacent exchange coupled ferromagnetic thin film, observed after isothermal switching through an applied electric field, E, in the simultaneous presence of a constant magnetic field, was found to differ in magnitude between the Cr2O3(0001) single domain states of opposite surface/interface magnetization [3, 6]
Extensive investigations and comparison between complete and partial isothermal switching in chromia based voltage-controlled exchange bias heterostructures show that the magnitude of the exchange bias field near its maximum values is not a rigorous measure to determine whether the antiferromagnet is in a true single domain state or if unreversed seed domains are present [6]

Summary

Introduction

The predicted boundary spin polarization [1,2,3] at the surface of magnetoelectric chromia, Cr2O3(0001), was confirmed experimentally by the combination of spin polarized photoemission [3], spin polarized inverse photoemission [4], x-ray magnetic circular dichroism photoemission electron microscopy [4] and magnetic force microscopy [4]. The exchange bias field, HEB, in a bilayer of chromia and an adjacent exchange coupled ferromagnetic thin film (as seen in figure 1), observed after isothermal switching through an applied electric field, E, in the simultaneous presence of a constant magnetic field, was found to differ in magnitude between the Cr2O3(0001) single domain states of opposite surface/interface magnetization [3, 6]. The electric field associated with this dipole does not switch on reversal of the antiferromagnetic domain state It breaks the symmetry by favoring one domain state over the other when it superimposes with the applied positive or negative electric field to form the local field which determines via magnetoelectric response the magnitude of the boundary magnetization. We find indications of these contrast variations in spin-polarized low-energy electron microscopy (SPLEEM) and this finding is consistent with our results from scanning tunneling microscopy and spectroscopy (STM, STS)

Methods and experimental details

Conclusion