Physics Colloquium: Tailoring Magnetic Spin Textures in Complex Oxide Nanostructures

Prof. Yayoi Takamura, University of California, Davis

Abstract: Traditional electronic devices involve the flow (or lack therefore) of electrical current to denote the 1’s and 0’s signals that make up binary logic. To achieve next generation devices with further improvements in device speed and energy efficiency, may involve spintronics, where device functionality is derived from the spin of the electron, in addition to its charge. The development of these types of spin-based devices required the ability to design the “spin textures” or the spatial variation in the local magnetization of a material. Within the vast range of magnetic materials, complex oxides such as ferromagnetic (FM) La_0.7Sr_0.3MnO₃ (LSMO) and antiferromagnetic (AF) La_1-xSr_xFeO₃ (LSFO) provide an ideal platform for tailoring magnetic spin textures when lithographically patterned as nano/micromagnets. This unique tunability arises due to the strong interactions between charge, spin, lattice, and orbital degrees of freedom. In this talk I will demonstrate how an intricate interplay exists between shape and magnetocrystalline anisotropy energies as well as exchange coupling interactions at LSMO/LSFO interfaces, and therefore, the resulting AF and FM spin textures can be controlled using parameters such as the LSMO and LSFO layer thicknesses, micromagnet shape, and temperature. LSMO nanomagnets were also patterned into artificial spin ice (ASI) structures, where large arrays of nanomagnets are arranged into geometries where all the magnetic interactions cannot be satisfied simultaneously. While one might expect shape anisotropy to dictate Ising states in the nanomagnets, the unique combination of magnetic parameters associated with LSMO enables the formation of both Ising and complex spin textures (CSTs) based on the nanoisland width and spacing. These CSTs consist of single and double vortices and alter the nature of dipolar coupling between nanomagnets, giving rise to exotic physics in the ASI lattices. These studies demonstrate that complex oxide provide a unique platform for engineering FM and AF spin textures for next generation spintronics applications.

Yayoi Takamura received her B.S. from Cornell University in 1998 and her M.S. and Ph.D. degrees from Stanford University in 2000 and 2004, respectively, all in the field of Materials Science and Engineering. She was a postdoctoral researcher at UC Berkeley with Prof. Yuri Suzuki in the Dept. of Materials Science and Engineering before joining the Dept. of Materials Science and Engineering at UC Davis in July 2006. Since July 2020, she has been serving as Department Chair. Her research focuses on the growth of complex oxide thin films, heterostructures, and nanostructures and the characterization of the novel functional properties associated with their interfaces. Prof. Takamura is a recipient of the NSF CAREER Award, the DARPA Young Faculty Award, and the 2020 College of Engineering Mid-Career Research Award.