Studying Spin Transport and Spin-charge Conversion using Dynamical Spin Injection

Dynamical spin injection, also known as spin pumping,^1,2 is a method used to generate pure spin current in the material via coupling of the interface spins to the magnetization precession of the adjacent ferromagnet. It quickly gained popularity as a spin injection method that can easily be used in any bilayer nonmagnetic/ferromagnetic system, whereas the electrical spin injection needs elaborate surface treatment, formation of tunnel barriers and nanofabrication. In this talk, the author will present how the spin pumping can be used to study two main pillars of spintronics: spin transport and spin-charge conversion.

In the first part of the talk, the author will focus on the spin transport in germanium (Ge) using the spin pumping. To use advantages of spintronics one needs a material that can carry spins over long distance at room temperature. In this light, Ge is very attractive for spintronics application: it is compatible with modern electronics and has mobility order of magnitude higher than in Si, making Ge devices superior to its Si counterparts. However, in contrast to Si, non-local spin transport in Ge was only achieved at low temperatures until recently. The author used spin pumping to achieve room-temperature spin transport in Ge for the first time.³ As a result, the spin transport has now been shown in both pivotal semiconductor materials, Ge and Si, providing new opportunities for the future of semiconductor spintronics.

While spin transport allows to use spin as an information carrier, the spin to charge conversion allows integration of spintronics with electronics—importance of such alliance for the future of both fields cannot be stressed enough. The inverse spin Hall effect in heavy metals is the most commonly used mechanism for interconversion between charge and spin currents. However, so far, gate control over it in metals was unthinkable. In the second part of the talk, the author will show how spin pumping in combination with ionic liquid gate technique allows to study inverse spin Hall in platinum and tune it by two orders of magnitude—a breakthrough in the spin-charge conversion field that can be used in the gate-controlled spin-charge converters, spin torque and other types of spintronics devices.⁴

1. Tserkovnyak, Y., Brataas, A. & Bauer, G. E. W. Enhanced Gilbert Damping in Thin Ferromagnetic Films. Phys. Rev. Lett. 88, 117601 (2002).
2. Mizukami, S., Ando, Y. & Miyazaki, T. Effect of spin diffusion on Gilbert damping for a very thin permalloy layer in Cu/permalloy/Cu/Pt films. Phys. Rev. B 66, 104413 (2002).
3. Dushenko, S. et al. Experimental demonstration of room-temperature spin transport in n-type Germanium epilayers. Phys. Rev. Lett. 114, 196602 (2015).
4. Dushenko, S. et al. Gate-tuned inverse spin Hall effect in Pt, submitted to Nat. Mater.