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

Abstract

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 - H0) for walls parallel to the (110) and (211) crystallographic planes in YIG and to the (211) plane in Yb0·15 Y2·85Fe5O12. For YIG negative values are deduced for H0, 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 Yb3+ ion. Best agreement is found here, as in earlier work on ferromagnetic resonance, when the thermal relaxation time of the populations of Yb3+ levels is assumed to have contributions from the single-magnon process of spin-magnon relaxation and from Raman processes.