Recent progress in magnetic skyrmions and unusual anisotropic magnetoresistance in bilayer heterostructure
X. R. Wang (1The Hong Kong University of Science and Technology, China 2Chinese University of Hong Kong (Shenzhen), China)

In this talk, I will first discuss several progresses made in our group about fundamental properties of skyrmions in chiral magnetic films. These include 1) skyrmion sizes in isolated, in crystal, or in stripy forms; 2) skyrmion nucleation, formation, and potential barrier energies; 3) the roles of magnetic field in skyrmion crystal formation; 4) the stability and existing conditions of composite skyrmions such as target skyrmions and skyrmion bags/cluster; 5) topological equivalence of stripy phases and skyrmion crystals. Then I will discuss a new theory about widely observed unusual anisotropic magnetoresistance (UAMR) in bilayers which leads to the notion of the spin-Hall MR (SMR) in the famous SMR theory. The theory is based on the universal features in all bilayer heterostructure: resistivity tensor depends on magnetization and interfacial field. I will show that the angular dependencies of UAMR do not depend on the microscopic details, thus are universal. Experiments that can test this theory against the SMR theory are also proposed.

** This work is supported by the National Key Research and Development Program (No. 2020YFA0309600), the NSFC Grant (No. 11974296), and HK RGC Grants (No. 16300523, 16300522, and 16302321).