Anisotropic spin-orbit torques in thin film bilayers of Li_0.5(Al,Fe)_2.5O₄and Pt studied with spin-torque ferromagnetic resonance

Low loss magnetic insulators with perpendicular magnetic anisotropy (PMA) are of great interest for exploring spin wave-based phenomena as well as integrating into higher density, more energy-efficient memory storage. However, there are very few materials that exhibit low loss, PMA and insulating behavior. Recently, we have stabilized epitaxial thin films of Li_0.5(Al,Fe)_2.5O₄ (LAFO) on single crystal (001) MgGa₂O₄ substrates which have strong PMA and are low loss, with a typical Gilbert damping parameter of ~7x10^-4. We have demonstrated spin pumping from LAFO into an adjacent Pt layer. Conversely, in this talk we demonstrate the excitation of LAFO magnetization by a microwave charge current in the Pt via spin-torque ferromagnetic resonance (ST-FMR). ST-FMR enables us to characterize charge to spin interconversion in bilayers with Pt. We find a highly anisotropic ST-FMR voltage signal depending on the relative orientation of the microwave charge current and the external in-plane magnetic field along the (110) direction, suggesting the presence of an out-of-plane anti-damping torque exerted by the Pt. The presence of this torque indicates a possibility of field-free SOT switching in this system.