Comparison of rare earth relaxation effects in YIG from perpendicular and parallel-pump measurements

Samples of polycrystalline YIG have been doped at various concentrations with terbium and dysprosium. The effects on spin wave linewidth, ΔHk, effective linewidth, W, and resonance field shift, S, have been measured and compared. An empirical relation between the spin wave linewidth, the spin wave vector, and doping concentration is given with rare earth dependent constants. It has been observed that in the low field region the behaviour of W is consistent with coupling to high k spin waves (wavelength m). Almost exactly the same behaviour has been observed in the high field region. Within the degenerate region the relative effects of the two rare earths were reduced. No changes in either the shape or magnitude of the S behaviour were observed. The conclusions are that the rare earth doping does not affect the degenerate coupling and that within the degenerate region both rare earth relaxation and polycrystalline inhomogeneity relaxation are effective. It is suggested that the high and low field behaviour of W can be explained if there exist localised, near atomic scale inhomogeneities producing coupling to very high k vector spin waves. More detailed quantitative analysis is required to verify this.