Nano- and Flexomagnetism of Magnetoelectric Cr₂O₃ Antiferromagnets

Antiferromagnetic insulators are a prospective material science platform for magnonics, spin superfluidity, THz spintronics and non-volatile data storage. Due to linear magnetoelectric effect at room temperature, Cr2O3 is a convenient playground to test fundamental predictions and new device ideas. In this presentation, we will cover our activities on physics and applications of Cr2O3. In particular, we provide insight into the nanoscale mechanics of antiferromagnetic domain walls in single crystals of Cr2O3 [1]. Furthermore, we will discuss the family of flexomagnetic effects in Cr2O3 thin films [2]. It is demonstrated that in addition to the conventional magnetic moment induced by the strain gradient, there is another flexomagnetic effect which impacts the magnetic phase transition resulting in the distribution of the Néel temperature along the film thickness. The details on the study of the defect nanostructure in Cr2O3 thin films [3,4] and bulks [5] and their impact on magnetism and magnetoelectricity of Cr2O3 will be discussed as well. We identified spin Hall magnetoresistance as a possible mechanism to explain all-electric readout of the magnetic state of Cr2O3 interfaced with a heavy metal like Pt [6,7]. The possibility to read-out the antiferromagnetic order parameter of magnetoelectric Cr2O3 all-electrically enabled realisation of antiferromagnetic magnetoelectric random access memory (AF-MERAM) [8].

[1] N. Hedrich et al., “Nanoscale mechanics of antiferromagnetic domain walls”. Nature Physics 17, 574 (2021).
[2] P. Makushko et al., “Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films”. Nature Comm. 13, 6745 (2022).
[3] I. Veremchuk et al., “Defect Nanostructure and its Impact on Magnetism of α-Cr2O3 Thin Films”. Small 18, 2201228 (2022).
[4] P. Appel et al., “Nanomagnetism of Magnetoelectric Granular Thin-Film Antiferromagnets”. Nano Lett. 19, 1682 (2019).
[5] I. Veremchuk et al., “Magnetism and Magnetoelectricity of Textured Polycrystalline Bulk Cr2O3 Sintered in Conditions Far out of Equilibrium”. ACS Appl. Electron. Mater. 4, 2943 (2022).
[6] R. Schlitz et al., “Evolution of the spin hall magnetoresistance in Cr2O3/Pt bilayers close to the Neel temperature”. Appl. Phys. Lett. 112, 132401 (2018).
[7] T. Kosub et al., “All-Electric Access to the Magnetic-Field-Invariant Magnetization of Antiferromagnets”. Phys. Rev. Lett. 115, 097201 (2015).
[8] T. Kosub et al., “Purely antiferromagnetic magnetoelectric random access memory”. Nature Comm. 8, 13985 (2017).