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Strong damping enhancement in nm-thick yttrium iron garnet (YIG) films due to Pt capping layers was observed. This damping is substantially larger than the expected damping due to conventional spin pumping, is accompanied by a shift in the ferromagnetic resonance field, and can be suppressed by the use of a Cu spacer in between the YIG and Pt films. The data indicate that such damping may originate from the ferromagnetic ordering in Pt atomic layers near the YIG/Pt interface and the dynamic exchange coupling between the ordered Pt spins and the spins in the YIG film.

Spin injection across the ferrimagnetic insulator yttrium iron garnet (YIG)/normal metal Au interface was studied using ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping parameter α in YIG/Au and YIG/Au/Fe heterostructures. The main purpose of this study was to correlate the spin pumping efficiency with chemical modifications of the YIG film surface using in situ etching and deposition techniques. By means of Ar+ ion beam etching, one is able to increase the spin mixing conductance at the YIG/Au interface by a factor of 5 compared to the untreated YIG/Au interface.

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