Pure spin currents generated by surface acoustic waves
The ability of spin-polarized currents to interact with magnetic states has strongly impacted computation technologies, being exploited by read-heads and by writing–heads on spin-transfer-torque MRAM memories. Today, the most active field in spintronics aims at the generation of pure spin currents, which differ from spin-polarized currents in that they do not involve net flow of charge. Thus, Joule heat losses and Oersted fields are drastically cut down increasing the stability and reducing the energy consumption of electronic nano-devices. The two main strategies to generate spin currents are focused on (i) the spin-pumping effect arising from magnetization excitations in a ferromagnet, and (ii) the spin Seebeck effect. The latter is particularly interesting, since it involves temperature gradients to create the spin currents. Thus, any generation of heat dissipation –usually unwelcome in electronic devices– would be harnessed to produce useful spin currents by creating temperature gradients. The downside is that heat dissipation is a non-directional phenomenon, spreading slowly in all directions, which makes it unattractive for applications. Interestingly, surface acoustic waves (SAW) are fast and strongly directional strain waves that produce local and directional heat, which could eventually be used to generate spin currents through spin Seebeck effect. Moreover, SAWs can dynamically couple by strain to nano-magnets leading to spin excitations that could also be exploited to generate spin currents through spin pumping. Finally, SAWs constitutes an energy efficient technology well established in commercial applications. Therefore, by using SAWs the two strategies to generate spin currents can be contrived to cooperate in an energy-efficient way extremely appealing for the implementation of pure spin currents in commercial devices. In this project we propose to develop the proof of concept of a spintronic nano-device based on pure spin currents created by SAWs.