Ultrabroad Ferromagnetic Resonance in Dysprosium Metal

Abstract

An extremely broad ferromagnetic resonance has been observed in single-crystal Dy metal at 37 Gc/sec. Although the large planar anisotropy results in a much higher resonance frequency, the resonance was brought down by applying a high field along a hard direction of the in-plane anisotropy. The temperature dependence of the field for resonance, in the temperature range from 78° to 103°K, was found to follow the behavior of the in-plane anisotropy. Above 87°K the zero field ordering is spiral but ferromagnetic ordering is induced by the applied field. The resonance peak cannot be seen above 103°K because the field for resonance is no longer sufficient to induce ferromagnetic ordering. The absorption was found to be extremely broad in field so that appreciable absorption occurs even where the resonant frequency is far above the experimental frequency. This feature may be interpreted on the basis of either or both of two distinct models. The first relies upon the fact that the spin-wave spectrum decreases to a minimum at a nonzero wave vector k0 and might thereby provide a number of k≠0 modes degenerate with the experimental frequency which may be coupled to through various sample inhomogeneities. The second model considers a very large dynamic broadening of the ferromagnetic resonance such as might arise from large magnon-phonon coupling due to the extremely large magnetoelastic interaction in dysprosium. On this model, the shape and width of the absorption curve indicate a relaxation frequency on the order of the resonance frequency.