Spin Dynamics and Topological States in Complex Oxide Thin Films with Low Magnetic Loss

Magnetic insulators are promising materials for efficient propagation and transduction of spin waves and for the stabilization of topological phenomena. Of recent interest is the class of spinel structure ferrite thin films where we have realized ultrathin ferromagnetic insulating thin films with low magnetic damping. More specifically, we have developed nanometer thick low loss spinel ferrite thin films with Gilbert damping parameter as low as a ~1 x 10 -4 and spin diffusion lengths on the order of a few microns. By combining with an epitaxial layer with strong spin-orbit coupling, we can electrically detect spin waves generated in the spinel ferrite and find efficient spin pumping from these spinel ferrites into the adjacent layer. Conversely we demonstrate electrical current-induced spin-orbit torque switching of a magnet at record low current densities and large spin-orbit torque efficiencies. We have also demonstrated modulation of spin waves in these spinel ferrites by the application of a dc bias, suggesting their utility in spin wave devices.

These spinel ferrite-based bilayers are also an excellent model system for the demonstration of fluctuation driven topology. Surprisingly we find definitive magnetotransport signatures of topology in the paramagnetic state of the spinel ferrite. We performed a detailed transport study as a function of field, temperature, field angle and ferrite thickness and found novel scaling behaviors consistent with fluctuation driven topology as predicted by Monte Carlo simulations.

Speaker: Yuri Suzuki, Stanford University