Control of the Effective Damping in Heusler/Pt Microstructures via Spin-Transfer Torque

In this contribution, we present the control of the effective damping by the spin-transfer torque of a pure spin current injected into Heusler compound microstructures. Here, the pure spin current is generated by a DC current in a Pt layer on top of the magnetic layer via the spin-Hall effect. By changing the current density and the direction of the DC current in the Pt layer, the generated pure spin current can be manipulated. Via the spintransfer torque this pure spin current can act on the magnetization in the magnetic layer and, for example, decrease or even compensate the Gilbert damping.
The damping, i.e. the Gilbert damping, is a very crucial parameter for any magnetization dynamics and the possibility to control this parameter, i.e. to further reduce the damping, could give rise to novel nonlinear phenomena. Especially, cobalt-based Heusler compounds as used in this work provide a large spin-wave propagation length and an already very low Gilbert damping. Thus, the threshold for all spin-torque driven phenomena is decreased and only small current densities in the Pt layer are needed. By determining the threshold power for parallel parametric amplification of spin waves, for example, the change of the damping in dependence of the DC current can be determined.
The presented results were obtained using Brillouin light scattering microscopy. Brillouin light scattering is the inelastic scattering of photons on magnons, the quanta of spin waves. By investigating the frequency and the intensity of the inelastically scattered light, the frequency and the intensity of the spin waves can be obtained. Using a microfocussed laser allows for a spatial resolution of about 400 nm.
The results show a strong influence of the pure spin current on the effective damping in the magnetic layer. They show the feasibility of using a DC current in a Platinum layer to control the effective damping an adjacent Heusler layer. Thus, this is very interesting for possible applications using spin waves or for the investigation of nonlinear effects especially in Heusler compounds.