Spin-orbit torque phenomena in complex oxide heterostructure

Energy-efficient magnetic spin orbit torque nano-oscillators and coupled oscillator arrays are being explored for low-power neuromorphic computing systems. Commonly studied oscillator systems are mostly based on metallic bilayers of ferromagnet (FM)/ heavy metal (HM) (FM=CoFeB, Py and NM=Pt, Ta, W). I will discuss recent efforts to replace the metallic layers with complex oxides with coupled spin, electron and lattice degrees of freedom providing opportunity for new device functionality. Large spin-charge conversion, low damping, and small resonance linewidth are essential constituents for the development of energy efficient oscillators. In this regard half-metallic perovskite ferromagnet, La₀.₆₇Sr₀.₃₃MnO₃ (LSMO) films are studied as the magnetic free layers combined with transition metal oxides such as iridates (e.g. IrO₂ and CaIrO₃) and NdNiO₃ as the spin-orbit torque layer. NdNiO₃ (NNO) exhibits a first-order metal-insulator transition centered near 200K in bulk. We observe thickness and temperature dependent modulation of spin-charge conversion through the phase transition of NNO and harness the disorder in NNO to generate a pronounced enhancement of the inverse spin Hall effect signal at the transition temperature. IrO₂ and CaIrO₃ have topological band structures providing significant enhancement of the spin to charge conversion with spin Hall angles exceeding 1 for CaIrO₃. Finally, progress towards an all-oxide nano-oscillator will be discussed. This work is supported by the U.S. Department of Energy under Grant No. DE-SC0019273.