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

TL;DR

This study uses NV scanning probe magnetometry to image and analyze how boron doping affects antiferromagnetic domain structures and voltage control mechanisms in Cr2O3 thin films, revealing new insights into their magnetic behavior.

Contribution

It provides the first direct imaging of B doping effects on AFM domains and elucidates the mechanism of voltage-controlled spin manipulation in Cr2O3 thin films.

Findings

B doping reduces domain size and increases Néel temperature.

B-doped films exhibit 90-degree AFM domains, unlike pure films with 180-degree domains.

Voltage control induces a 90-degree rotation of AFM domains in B-doped Cr2O3.

Abstract

Chromia (Cr2O3) is a magnetoelectric oxide which permits voltage-control of the antiferromagnetic (AFM) order, but it suffers technological constraints due to its low Neel Temperature (TN ~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 N\'eel vector rotation. Here, we directly image the impact of B doping on the formation of AFM domains in Cr2O3 thin films and elucidate the mechanism of voltage-controlled manipulation of the spin structure using nitrogen vacancy (NV) scanning probe magnetometry. We find a stark reduction and thickness dependence of domain size in B-doped Cr2O3 (B:Cr2O3) films, explained by the increased germ density, likely associated with the B doping. By reconstructing the surface magnetization from the NV stray-field maps, we find a qualitative distinction between the undoped and B-doped Cr2O3 films, manifested by the histogram distribution of the AFM ordering, i.e., 180 degree domains for pure films, and 90 degree domains for B:Cr2O3 films. Additionally, NV imaging of voltage-controlled B-doped Cr2O3 devices corroborate the 90 degeree rotation of the AFM domains observed in magnetotransport measurement.