Study of local effects of boron doping and voltage on antiferromagnetic domains switching in chromia thin films and devices

Chromia (Cr₂O₃) is a magnetoelectric antiferromagnetic (AFM) oxide that allows voltage-control of the Néel vector under the presence of a magnetic field [1]. Boron doping of Cr₂O₃ increases the Néel temperature from 307 to 400 K [2] and it is believed to break the local symmetry giving rise to transient polarization under an applied electric field, and thus to voltage magnetic field free control of the Néel vector [2]. Here, we use magnetic microscopy based on nitrogen-vacancy (NV) centers in diamond [3] to image the stray fields resulting from single layers of uncompensated spins on the surface and interface of pure and B-doped Cr₂O₃ films with Al₂O₃ substrates [4]. The acquired image confirms the presence of homogeneously AFM domains with size ∼ 50 – 300 nm that depends strongly on the film thickness (50 – 300 nm), explained by the increased germ density, likely associated with the B doping [5]. Reconstruction of the surface magnetization from the NV stray-field maps unveils a clear difference between the pure and B-doped Cr₂O₃ films, displayed by the histogram distribution of the AFM ordering, i.e., 90° domains for the B doped films, and 180°domains for pure films [5]. We discuss preliminary results on voltage induced Néel vector 90° switching in B:Cr₂O₃/V₂O₃ devices [5], a promising result for AFM spintronics. [1] X. He, et al., Nat. Mat. 9, 579 (2010). [2] A. Mahmood, et al., Nat. Comm. 12, 1674 (2021). [3] A. Laraoui, K. Ambal, Appl. Phys. Lett. 121, 060502 (2022). [4] A. Erickson, A. Laraoui, et al., RSC Adv. 13, 178 (2023). [5] A. Erickson, A. Laraoui. et al., Advanced Functional Materials 2408542 (2024).