Enhancement of spin pumping efficiency in Fe₄N/Pt bilayer films

A DC electric voltage was generated on a Pt-capped Fe₄N bilayer film (Fe₄N/Pt) by inverse spin-Hall effect (ISHE) under ferromagnetic resonance (FMR) conditions at room temperature. Sign reversal of the electric voltage was observed with the application of an external DC field with opposite direction, and the magnitude of the voltage was proportional to the applied microwave power. The spin current was pumped out of the Fe₄N film into the Pt capping film. The real part of the spin mixing conductance (g _r^{double arrow, left up, right down sign}) was quantified for Fe₄N/Pt and Ni₇₈Fe₂₂/Pt bilayer films to investigate the spin pumping efficiency at the interface. The g_r ^{double arrow, left up, right down sign} value was larger for the Fe₄N/Pt film than for the Ni₇₈Fe₂₂/Pt film. Such a large g_r^{double arrow, left up, right down sign} could reflect the large population of conduction electrons with minority spins in the Fe₄N film compared with that with majority spins.