New Characteristic in the Temperature Dependence of Ferrimagnetic Resonance Linewidth in Some Rare-Earth Doped Yttrium Iron Garnets

Abstract

Measurements have been made of the ferrimagnetic resonance linewidth of YIG doped with each of the rare earths. These results will be presented in full elsewhere. For the most part there is a peak in the ΔH(T) curve at some temperature between 20° and 150°K. The position of this peak varies with the impurity, the frequency, and the crystal direction of the steady field. However,several cases have been observed in which the linewidth increases very rapidly with decreasing temperature down to the lowest temperature reached, about 1.5°K. This behavior occurs over a very narrow angular range. For ytterbium-doped YIG, it is associated with a very mild peak in the field for resonance. For the case of europium there appears to be no anomaly in Hres, though a plot of linewidth against angle shows an increase of about fifteen fold with a half-width of perhaps 1.5°. It is suggested that this anomalous linewidth vs angle and temperature curve, as well as the more generally encountered peak in ΔH(T), represent the excitation of transitions between sublevels of the rare-earth multiplet which approach within an energy comparable to that of a photon of the exciting radiation.