Increased Gilbert damping in yttrium iron garnet by low temperature vacuum annealing

The effect of thermal surface cleaning on the Gilbert damping ( α ) of yttrium iron garnet (YIG), before capping with a metallic layer, has been investigated. Our results show that α is strongly affected by relatively mild annealing conditions (T = 300 °C) when performed in a vacuum. This increase needs to be taken into account when obtaining the spin-mixing conductance from spin pumping measurements. We measure an increase in α by a factor of × 8 when the YIG is vacuum annealed at 300 °C. No such changes in α are observed when annealed at the same temperature in 1 × 10−1 mbar of oxygen. We suggest that the main driver for the increase in α is the reduction of Fe3+ to Fe2+, as demonstrated by soft x-ray magnetic spectroscopy.