Surface-Independent Spin-Wave Relaxation in Ferromagnetic Resonance of Yttrium Iron Garnet

In contrast to the ferromagnetic resonance tine width $\mathrm{\Delta H}$ , which depends strongly upon surface polish, the “line width” ${\mathrm{\Delta H}}_k$ of a z‐directed spin wave is shown to be surface independent. This permits observation of a relaxation process which appears to be determined primarily by collisions between thermally excited spin waves rather than by a volume or surface distribution of magnetic inhomogeneities. In yttrium iron garnet ${\mathrm{\Delta H}}_k$ is observed to be 0.10 oe at room temperature and to increase monotonically with increasing temperature. The 0.10 oe corresponds to a relaxation time of 1.14 μsec. It is believed this is the narrowest line width yet indicated for a ferromagnetic material.