Unraveling Magnetic Spin Texture Behavior Using Cryo Electron Microscopy

Several emergent magnetic phenomena occur at cryogenic temperature, so that the development of advanced cryogenic capability to probe magnetic structures in quantum materials is important. Here, we leveraged cryo Lorentz transmission electron microscopy (LTEM) to map and understand local spin textures and microstructure of ferromagnetic van der Waals (vdW) and ferrimagnetic crystals with high-resolution, and correlate with their behavior. 2D magnetic vdW materials possess unique crystal structures characterized by atomic layers separated by vdW gaps, and hence display strong intra-plane interaction but weak inter-plane interaction [1]. This layered structure and strong intrinsic spin interactions give rise to fascinating phenomena such as rich magnetic spin textures. We have explored magnetic spin textures of Fe_5-xGeTe₂ crystal as a function of temperature and magnetic field using cryo LTEM. The (anti)merons appear at a high temperature and coexistence of merons and skyrmions is observed in a lower temperature regime [2]. We will present that this behaviour is strongly dependent on Fe content and microstructures. Ferrimagnets, which have both ferromagnetic and antiferromagnetic couplings, are attracting increased attention in the realm of spintronic devices due to advantages such as ultrafast dynamics and a suppressed skyrmion Hall effect. We explored the topological spin textures as a function of temperature and magnetic field in ferrimagnetic Mn_2-xZn_xSb (x=0.85) by using cryo LTEM and magneto-optic Kerr effect (MOKE) microscopy. Mn_1.15Zn_0.85Sb displays two phase transitions at around 286 K and 170 K and hence possess rich magnetic phases [3]. We discovered unique and diverse magnetic structures as a function of magnetic field and temperature in each phase regime. Importantly, the displacement and randomization of various Mn atoms break the local structure symmetry, which introduces effective Dzyaloshinkii-Moriya interaction and eventually forms Néel spin textures.<br/><br/>[1] K.S. Burch, D. Mandrus, J.G. Park, Nature, 563 47 (2018).<br/>[2] B. W. Casas, Y. Li, A. Moon et al., Adv. Mater., Adv. Mater. 35, 2212087 (2023,)<br/>[3] M.R.U Nabi, R. Basnet, K. Pandey et al., Acta Mater., 259 119251 (2024).<br/>[4] This work is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Science and Engineering Division. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.