Farzad Mahfouzi
Affiliations
- Department of Physics, California State University, Northridge, CA 91330-8268, USA
Title
Spin-orbit torque and spin pumping in topological-insulator/ferromagnet heterostructures
Abstract
Topological insulators (TIs) are newly discovered class of Dirac materials which possess an energy gap in the bulk, akin to conventional band insulators, while hosting metallic surfaces where electrons behave as massless Dirac fermions analogous to the ones found in graphene. However, unlike graphene where spin-orbit coupling (SOC) is negligible due to the lightness of carbon atoms, in TIs it plays a crucial role by locking the direction of spin and momentum of surface electrons. This feature is considered to be a great resource for spintronic applications where combinations of TIs with ferromagnets (FM) could lead to ultralow-power memory and logic devices. On the other hand, graphene is envisaged as interconnect in lateral devices due to long spin diffusion lengths or perfect spin filtering barrier in vertical heterostructures where it is sandwiched by Co or Ni layers. In this talk, I will discuss possible routes of integration of grapheme and TIs with FMs into vertical and lateral heterostructures exhibiting: (i) perfect spin filtering at finite bias voltage and spin-transfer torque driven by low injected current in Ni/few-layer-graphene/Ni and Co/few-layer-graphene/Co vertical heterostructures; (ii) current-driven SO torques by which TI surface induces magnetization dynamics of the FM layer; and (iii) spin-to-charge conversion after the magnetization of the FM overlayer on the surface of TI is brought into steady state precession by the microwave absorption.
References
[1] F. Mahfouzi, B. K. Nikolić, and N. Kioussis, Large antidamping-like spin-orbit torque driven by spin-flip reflection mechanism on the surface of a topological insulator, arXiv:1506.01303. [3] F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, “Spin-to-charge conversion in lateral and vertical topological-insulator/ferromagnet heterostructures with microwave-driven precessing magnetization,” Phys. Rev. B 90, 115432 (2014). [4] K. K. Saha, A. Blom, K. S. Thygesen, and B. K. Nikolić, “Magnetoresistance and negative differential resistance in Ni/Graphene/Ni vertical heterostructures driven by finite bias voltage: A first-principles study,” Phys. Rev. B 85, 184426 (2012). [5] F. Mahfouzi, N. Nagaosa, and B. K. Nikolić, “Spin-orbit coupling induced spin-transfer torque and current polarization in topological-insulator/ferromagnet vertical heterostructures,” Phys. Rev. Lett. 109, 166602 (2012). [6] F. Mahfouzi, B. K. Nikolić, S.-H. Chen, and C.-R. Chang, “Microwave-driven ferromagnet–topological-insulator heterostructures: The prospect for giant spin battery effect and quantized charge pump devices,” Phys. Rev. B 82, 195440 (2010).
