The electrical control of spin magnetization aims to be used in next-generation magnetic devices, allowing information to be written electronically. Recently, developments of spintronics functionalities of topological materials have been drawn interests for achieving novel electrical manipulation of the magnetization, and generation of spin currents [1,2].

In this presentation, we theoretically study the spin-transfer torque effect and dynamics of magnetic textures in magnetic Weyl semimetals [3-6]. Due to the strong spin-orbit coupling in Weyl semimetal, the spin-transfer torque can be significantly enhanced. We evaluate the electrically-induced non-equilibrium spin density in the Weyl semimetal and obtain the analytical expression of the spin torque corresponding to a non-adiabatic spin-transfer torque. Importantly, the obtained spin torque is independent of impurity scattering when magnetization varies steeply, indicating that the phenomenon is an intrinsic effect and its strength outstrips that of conventional materials. Furthermore, due to a suppression of the longitudinal conductivity in this regime, the dissipation from the Joule heating for the spin-transfer torque is smaller than that in conventional ferromagnetic metals. We analyze the dynamics of domain walls driven by the obtained spin-transfer torque and find that a domain wall velocity can be one order of magnitude faster than that of a conventional ferromagnetic nanowire. Consequently, fast control of domain walls can be achieved with less dissipation from the Joule heating in the Weyl semimetal. Therefore, the Weyl semimetal may be a new candidate material for low-energy-consumption spintronics devices, such as a racetrack memory.

In the latter part of the presentation, we study spin pumping and spin-orbit torques in magnetic heterostructures consisting of a magnetic insulator and a topological Dirac semimetal. It is shown that, due to the spin pumping and the large spin Hall angle, the induced charge current in the topological Dirac semimetal is semi-quantized. We also demonstrate that this system generates large spin-orbit torques which switch the direction of the local magnetization in the ferromagnetic insulator [7].

Professor Kentaro Nomura received his Ph.D. in theoretical physics at the University of Tokyo in 2003. He is an Associate Professor of the Institute for Materials Research (IMR) at Tohoku University.

Ken Nomura Associate Professor of the Institute for Materials Research (IMR), Tohoku University

1. K. Nomura and D. Kurebayashi, Phys. Rev. Lett. 115, 127201(2015).
2. D. Kurebayashi and K. Nomura, Phys. Rev. Applied. 6, 044013 (2016).
3. D. Kurebayashi and K. Nomura, Sci. Rep. 9, 5365 (2019).
4. Y. Araki, A. Yoshida, and K. Nomura, Phys. Rev. B 94, 115312 (2016).
5. Y. Araki and K. Nomura, Phys. Rev. Applied. 10, 014007 –1-7 (2018).
6. Y. Araki, A. Yoshida, and K. Nomura, Phys. Rev. B 98, 045302 – 1-10 (2018).
7. T. Misawa and K. Nomura, arXiv:1907.10459.

Researchers should cite this work as follows:

• (2020), "Spintronics Functionalities of Topological Semimetals," https://nanohub.org/resources/34442.

  BibTex | EndNote

1. devices
2. semimetals
3. spin orbit coupling
4. spin transfer torque
5. spintronics
6. Weyl semimetal