Nanometer-Thick Yttrium Iron Garnet Films With Extremely Low Damping

Yttrium iron garnet (YIG) films that are in the nanometer thickness range and show extremely low damping are reported. The films were deposited via sputtering at room temperature and were then annealed in O$_{2}$at high temperature. A 22-nm-thick YIG film showed a Gilbert damping constant$\alpha = (8.58\pm 0.21)\times 10^{-5}$, which represents the lowest damping ever reported for nanometer-thick magnetic films. The film had a gyromagnetic ratio of$\vert\gamma \vert = 2.83$MHz/Oe and a saturation induction of$4\pi M_{\rm s} = 1766$G, which are both very close to those of single-crystal YIG bulk materials. The film had a very smooth surface, with an rms surface roughness of about 0.13 nm.