Magnon auto-oscillations with low current density in lithium aluminum ferrite thin films

Spin wave-based spintronics are an alternative to conventional electronics due to their potential for efficient energy consumption, improved processing speed and smaller device dimensions. The success of spin wave spintronics relies on the existence of low damping magnetic insulators that allow for efficient spin wave generation, manipulation, and detection. A promising candidate is the recently developed thin film Li_0.5Al_1.0Fe_1.5O₄ (LAFO) with low Gilbert damping parameter on the order of 10^-4 in 15 nm thick LAFO. In this talk, we present our results on non-local magnon transport in LAFO, a magnetic insulator, grown on (100) oriented MgAl₂O₄(MAO). By studying the non-local voltage amplitude generated via the inverse spin Hall effect as a function of the separation of two overlaying Pt electrodes, we deduce a spin diffusion length of 1.9 um in 15 nm thick LAFO which is consistent with our previous results. By adding a third DC bias Pt electrode (modulator) between the two Pt electrodes, we can modulate the non-local voltage amplitude by a factor of 3.5 with current densities on the order of 10¹¹ A/cm², significantly lower than the current densities needed to achieve the same modulation in Y₃Fe₅O₁₂ (YIG). Additionally, from the relationship between the voltage amplitude and DC bias current, we can extract a critical current I_c, where the damping-like torque on the magnons underneath the Pt electrode is fully compensated by the spin-orbit torque from Pt. Brillouin light scattering experiments together with micromagnetic simulationsindicate that I_c marks the onset of auto-oscillations which are suppressed for currents greater than I_c  because of non-linear damping effects. Together, these results show the promise of spin-wave based technology using LAFO as a new platform for information processing using high frequency modulated magnons and coherent auto-oscillations.