Spin Pumping at Ytrium Iron Garnet Interfaces

Abstract

A brief review is presented of spin pumping theory at ferromagnetic metal (FM)/normal metal (NM) interfaces or at magnetic insulator (MI)/normal metal (NM) interfaces. Spin transport in a NM is discussed using either spin diffusion theory or spin current decoherence via a spin fluctuation mechanism. These concepts were applied to our experimental results on spin pumping at YIG/Au and YIG/Pd interfaces. Thin YIG films (between 9 and 20 nm thick) were prepared by means of pulsed laser deposition (PLD) on a gallium gadolinium garnet substrate, GGG(111). Quantitative studies of spin pumping at the YIG/Au interface was carried out using magnetic double layers, YIG/Au/Fe, where the Fe layer acted as a spin sink. Spin pumping was first investigated at untreated YIG surfaces where the spin mixing conductance g ↑↓ at the YIG/Au interface was found to be ∼1×1014 cm−2. Removing the YIG surface contamination using Ar gun sputtering increased the spin mixing conductance to 5×1014 cm−2 which is 70 % of that predicted by theory and 50 % of that found for the Fe/Au interface. In the YIG/Pd system, the spin transport in Pd is affected by spin fluctuations caused by a large Stoner enhancement factor in this material. The spin mixing conductance was found to be 2.9×1014 cm−2, and the spin current decoherence length was found to be about 5 nm.