Increased low-temperature damping in yttrium iron garnet thin films
  We report measurements of the frequency and temperature dependence of ferromagnetic resonance (FMR) for a 15-nm-thick yttrium iron garnet (YIG) film grown by off-axis sputtering. Although the FMR linewidth is narrow at room temperature (corresponding to a damping coefficient $\alpha$ = (9.0 $\pm$ 0.2) $\times 10^{-4}$), comparable to previous results for high-quality YIG films of similar thickness, the linewidth increases strongly at low temperatures, by a factor of almost 30. This increase cannot be explained as due to two-magnon scattering from defects at the sample interfaces. We argue that the increased low-temperature linewidth is due to impurity relaxation mechanisms that have been investigated previously in bulk YIG samples. We suggest that the low-temperature linewidth is a useful figure of merit to guide the optimization of thin-film growth protocols because it is a particularly sensitive indicator of impurities. 
C. L. Jermain, S. V. Aradhya, J. T. Brangham, M. R. Page, N. D.   Reynolds, P. C. Hammel, R. A. Buhrman, F. Y. Yang, D. C. Ralph
cond-mat.mes-hall