Nonlinear Optical Imaging of Current Induced Spin Switching in Antiferromagnetic Materials

Electrical switching of the Neel order in Antiferromagnetic (AF) materials via spin transfer (STT) has attracted considerable attention [1,2]. Experiments have shown that AF switching is non-uniform, influenced by magneto-elastic coupling, and the efficacy of STT in inducing AF switching has also been questioned [3]. In this paper, we show that scanning optical second harmonic generation (SHG) can be used to image and identify magnetic domains in inversion symmetric AF materials. Using this technique, we image magnetic domains in nanometer thick epitaxial AF layers. We show that the SHG technique can image even when AF materials are covered with metallic spin Hall layers such as Pt. We use scanning SHG to study electrical switching in NiO/Pt devices. Our results show that AF switching is non-uniform across our 100 sq-micron devices. We observe regions that show AF switching in agreement with the STT predictions and regions where magnetoelastic effects seem to dominate, and we also see regions which exhibit no evidence of switching. The contributions of various effects will be discussed. [1] Phys. Rev. Lett. 120, 207204 (2018). [2] Scientific Reports 8, 14167 (2018). [3] arXiv:1907.00314 (2019).