Damping of magnetic domain-wall motion in pure and ytterbium-doped yttrium iron garnet

The domain-wall switching properties of pure yttrium iron garnet, YIG, and Yb-doped YIG are investigated from 1·5 to 300 °K. The measured domain-wall velocity ν depends on the applied field H according to the relation ν = R ( H - H 0 ) for walls parallel to the (110) and (211) crystallographic planes in YIG and to the (211) plane in Yb 0·15 Y 2·85 Fe 5 O 12 . For YIG negative values are deduced for H 0 , the threshold field; this is puzzling. The domain-wall mobility R is in order-of-magnitude agreement with the measurements of previous workers, though the detailed agreement is not good. We confirm the report that domain-wall motion in pure YIG is much more heavily damped than would be predicted, using a phenomenological model, from ferromagnetic resonance damping. The mechanism is not elucidated but extensive experimental measurements are recorded. For Yb-doped YIG a large additional damping of the wall motion is found at low temperatures, with a minimum in R at about 10 °K, and its magnitude is predicted by the longitudinal relaxation model applied to the anisotropic single-ion energy levels of the Yb 3+ ion. Best agreement is found here, as in earlier work on ferromagnetic resonance, when the thermal relaxation time of the populations of Yb 3+ levels is assumed to have contributions from the single-magnon process of spin-magnon relaxation and from Raman processes.