Spin Transfer Oscillators (STOs)
Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications.
We study new device geometries that are potentially interesting for optimising the output signal quality of the spin-torque oscillators, but also allow for quantifying key magneto-transport parameters.
We focus on a one-of-a-kind fundamental study of the underlying physical mechanisms that govern the interplay between spin-polarized currents and magnetization, leading to both magnetoresistance effects and spin-transfer torques. The transfer of angular momentum from conduction electrons to the magnetization (known as “spin-transfer”) allows for a controlled manipulation of the magnetization via the injected currents. Furthermore, it exhibits advantageous scaling behaviour compared to conventional field-induced magnetization switching, thus paving the way for novel devices and applications.
This project aims at a quantitative analysis of spin-dependent transport and spin-transfer torques in specially designed superlattice nanostructures with tailored perpendicular magnetic anisotropy. We believe that a combination of low and high frequency magnetotransport measurements to characterize magnetoresistance, current-induced switching and spin-transfer driven precession, correlated with numerical modelling based on the extended Valet - Fert giant magnetoresistance theory and spin-transfer induced magnetization dynamics analytical calculations, will enable us to quantitatively and simultaneously determine parameters such as the damping constant, the spin-torque/ magnetoresistance angle asymmetry coefficient, the current spin polarization and possibly the interfacial spin scattering asymmetry for the considered multilayers. This will provide the necessary input to motivate further work on the basic aspects of spin-transfer – such as ab-initio calculations for the asymmetry parameter, which governs the dynamic states excited by the current and thus the output power of spin-transfer oscillators, for given geometries.
The results will then be used to optimize the materials and geometries for applications, such as memory and in particular microwave oscillators, in order to develop industrially competitive spin-transfer devices.