Large Enhancement of Spin-Flip Scattering Efficiency at Y3Fe5O12/Pt Interfaces Due to Vertical Confinement.

Magnons, the quanta of spin angular momentum, can be excited in magnetic insulators by spin-flip scattering processes induced by currents applied to a heavy-metal overlayer. The efficiency of generating nonequilibrium magnons is characterized by the interface spin current jsint, whose magnitude is considered to depend on the thermal magnon population. Here, we investigate nonlinear magnetoresistance phenomena in Pt arising from current-driven nonequilibrium magnons in Y3Fe5O12 (YIG). Remarkably, we find that spin-flip scattering processes are dominated by subthermal magnons at room temperature, resulting in a large modulation of jsint with the magnetic field and YIG thickness. Concretely, reducing the YIG thickness from 100 to 10 nm increases jsint by a factor ∼20, while increasing the magnetic field exponentially suppresses the magnon generation efficiency. These findings challenge the current understanding on jsint and indicate that electrically driven magnonic effects such as damping compensation and magnon condensation can be largely boosted through device miniaturization.