Domain-Wall Motion in Yttrium-Iron Garnets

Domain-wall motion in pure and doped yttrium-iron-garnet single crystals with composition Y3Fe5−δSiδO12, 0<δ<0.12, has been investigated over the temperature range 4.2°−300°K. Samples were prepared in a picture-frame geometry to carry a single movable wall. Wall mobility for our pure sample showed a temperature dependence similar to that reported by Hagedorn and Gyorgy; however, our values for wall mobility are 4–7 factors lower than theirs, probably reflecting the simpler domain structure of our samples. As expected, the wall inverse mobility increases linearly with the increase in silicon concentration (or equivalently, with Fe2+ ion concentration). However, as a function of temperature the inverse mobility of silicon-doped samples, unexpectedly, shows a peak at about 20°K. The over-all temperature dependence does not agree with the diffusion after-effect model which is based on the assumption that wall damping is the result of 3d-electron transitions between Fe2+ and Fe3+ cations in the octahedral sublattice. The behavior, however, is very similar to that found for the temperature dependence of the microwave-resonance linewidth of silicon-doped samples. In both cases, because of the short time of spin reorientation relative to the electron-diffusion relaxation time, it is more likely that the loss mechanism is dominated by a localized relaxation process occurring between the energy levels of Fe2+ ions.