Studying the effect of boron doping and thickness on antiferromagnetic domains in epitaxial B-Cr₂O₃ films using diamond scanning probe microscopy

The magnetoelectric antiferromagnetic (AFM) chromia (Cr₂O₃) offers voltage-controlled manipulation of the Néel vector in the presence of a magnetic field [1]. However, its practical utility is constrained by its low Néel Temperature (T_N) ~ 307 K. Boron (B) doping can elevate T_N to 400 K with the advantage of a voltage-controlled Néel vector in the absence of an applied magnetic field [2]. This development holds promise for the field of AFM spintronics [3]. However, there has been no direct assessment of AFM spin textures in B-Cr₂O₃, and the impact of B doping on its AFM properties remains unclear. In this study, we employ nitrogen vacancy (NV)-diamond scanning probe microscopy [4] to directly image AFM domains in B-Cr₂O₃ films (thickness = 50 – 200 nm) grown by pulsed laser deposition on AL₂O₃ substrates. We measure the magnetization profile, which shows well-defined magnetized nano-domains, affected strongly by B doping, i.e., domain size varies from 50 to 200 nm [5], way below the size of AFM domains imaged in pure Cr₂O₃ films [4]. We investigate the effect of the thickness on the characteristics of AFM domains in B-Cr₂O₃ films and find a correlation between AFM domain size and film thickness, which we attempt to ascribe to Fatuzzo-Labrune growth model [5]. [1] N. Wu et al., Phys. Rev. Lett. 106, 087202 (2011). [2] A. Mahmood et al., Nat. Comm. 12, 1674 (2021). [3] V. Baltz, et al., Rev. Mod. Phys. 90, 015005 (2018). [4] A. Erickson et al., RSC advances 13 (1), 178-185 (2023). [5] A. Erickson et al., under preparation.