Current-driven Spin-Orbit Fields in Dilute Magnetic Semiconductors

Manipulating the magnetization of a ferromagnet using spin-polarized current has been made possible via the theoretical and experimental demonstration of spin transfer torque. This mechanism requires the presence of a pinned magnetic layer playing the role of the spin- polarizer, as well as a free magnetic layer playing the role of the spin-analyzer. Alternatively, it has been recently demonstrated that appropriately designed spin-orbit coupling (SOC) can be used to generate spin torque (coined as SOC-torque) in a single ferromagnet, without the need of an external polarizer. This effect has been observed experimentally in both metallic and semiconducting systems. The case of dilute magnetic semiconductors (DMSs) is of particular interest due to their tunable bulk inversion asymmetry allowing for the generation of both cubic and linear Dresselhaus SOC. A theoretical understanding of the microscopic nature of the SOC- torque in DMSs is still needed to accurately interpret the recently obtained experimental results.
In this seminar, I will present the general principle of SOC-torque and its most illustrative paradigm, the Rashba torque, will be described. Then, I will address the nature of SOC-torque in DMS in the framework of Luttinger Hamiltonian (GaMnAs, InMnAs etc…). Both cubic and linear Dresselhaus SOC are examined and the angular dependence and magnitude of the SOC-torque are studied for a wide range of parameters. Interestingly, the cubic Dresseulhaus SOC does generate a spin torque as long as the Fermi surface is not spherical. The role of the carrier concentration and shape of the Fermi surface are emphasized and experimental implications.
Aurelien C. Manchon received the Engineering Diploma and M.S. in Engineering from Ecole Polytechnique, the M.S. in Physics from Orsay University, and Ph.D. from Joseph Fourier University (France). He served in Research Positions with the National Office for Aerospatial Studies and Research and CEA/SPINTEC (both in France) and the University of Missouri and University of Arizona (both in U.S.A.) before joining KAUST as an Assistant Professor of Materials Science and Engineering in 2009. His research interests include the interaction between spin- dependent electronic transport and magnetization in heterogeneous magnetic systems. He is a member of the American Physical Society.