Spin injection with large DC currents in YIG/Pt nanostructures

Highlights: • Fully electrical method of spin injection and detection in nanostructures by simple DC measurement. • Large spin orbit torque at the interface drives the magnetization out of a quasi-equilibrium state. • Nonlinear magnon transport in ferromagnetic insulator. -- Abstract: Through the simple electrical measurement, the spin injection to magnetic insulators via large DC currents applied in heavy metals is reported. The measured nonlocal voltages are divided into two types: the electrical-generated magnons (V_odd) and the thermal-generated magnons (V_even) according to the different symmetry with respect to the applied current. With the current increasing, a nonlinear behavior of V_odd is observed. The dependences of V_odd on the current and temperature are compared, excluding the effect of current-induced heating on the nonlinear transport. The field dependence of the nonlocal voltages is also systematically studied which indicates the frequency-dependent mechanism needs to be introduced to explain the nonlinearity. It is possible that the frequency change of the dominate magnons when the current is large enough to drive the magnetization out of thermal equilibrium induces the deviation from the linear relationship in the low current region.