Microwave Absorption Spectrum of Magnetically Ordered Dysprosium Metal

摘要

The heavy rare earth metals all crystallize in a hexagonal close-packed structure and exhibit a tendency toward spatially periodic ordering of magnetic moments at low temperatures. An experimental study was made of the excited states in such magnetic systems for the various phases of ground state ordering. Dysprosium was chosen because of the relative simplicity of its ground state ordering and because of the abundance of experimental evidence concerning its static magnetic properties. Ferromagnetic resonance was observed at 37 Gc/sec by using the anisotropy in the hexagonal plane. The temperature dependence of the field for resonance gives a measure of the temperature dependence of the hexagonal anisotropy which is in good agreement with the behavior estimated from static measurements of magnetization. The most striking feature of this resonance absorption is its extremely large width. Absorption measured at temperatures in the spiral range with the field applied along an easy axis in the hexagonal plane shows an abrupt increase corresponding to a sharp rise in permeability at the field required to induce ferromagnetic ordering. This abrupt change is followed at higher fields by a gradual fall-off of absorption consistent with the increasing separation of the resonant frequency above the experimental frequency at higher fields.