Imaging Local Effects of Voltage and Boron Doping on Spin Reversal in Antiferromagnetic Magnetoelectric Cr2O3 Thin Films and Devices

Chromia (Cr2O3) is a magnetoelectric oxide that permits voltage-control of the antiferromagnetic (AFM) order, but it suffers technological constraints due to its low Neel Temperature (TN approximate to 307 K) and the need of a symmetry-breaking applied magnetic field to achieve reversal of the Neel vector. Recently, boron (B) doping of Cr2O3 films led to an increase TN >400 K and allowed the realization of voltage magnetic-field free controlled Neel vector rotation. Here, the impact of B doping is directly imaged on the formation of AFM domains in Cr2O3 thin films and elucidates the mechanism of voltage-controlled manipulation of the spin structure using nitrogen-vacancy (NV) scanning probe magnetometry. A stark reduction and thickness dependence of domain size in B-doped Cr2O3 (B:Cr2O3) films is found, explained by the increased germ density, likely associated with the B doping. By reconstructing the surface magnetization from the NV stray-field maps, a qualitative distinction between the undoped and B-doped Cr2O3 films is found, manifested by the histogram distribution of the AFM ordering, that is, 180 degrees domains for pure films, and 90 degrees domains for B:Cr(2)O(3 )films. Additionally, NV imaging of voltage-controlled B-doped Cr(2)O(3 )devices corroborates the 90 degrees rotation of the AFM domains observed in magnetotransport measurement.