Surface contribution to the ferrimagnetic resonance linewidth of single‐crystal YIG versus frequency and temperature

摘要

The knowledge of microwave intrinsic losses of ferrimagnetic single crystals is often obscured by the scattering process induced by surface defects. The existing data and the corresponding model dealing with this effect are far from sufficient to understand the phenomenon; in the millimetric range, the importance of the surface imperfection linewidth ΔHs is a major difficulty for obtaining the single‐crystal intrinsic linewidth ΔHi from ΔH measurements. We have investigated on a pure YIG single crystal the full dependence of the surface effect as a function of the surface pit size, the frequency, and the temperature. An automatic linewidth spectrometer is used, which allows measurements in the frequency range 1–18 GHz and the temperature range -100 to 270 °C. The dc magnetic field is aligned with the 111] easy axis of the crystal. Three main conclusions are obtained: (1) For a constant sample diameter, the variation of the surface contribution ΔHs is found to be a nonlinear function of the pit size. (2) Whatever the surface roughness, ΔHs is a minimum when passing the top of the spin‐wave manifold. This is similar to the behavior of the volume porosity line‐broadening contribution observed in polycrystalline materials. (3) For a constant reduced internal field Ω (Ω=Hi/4πMs), the temperature dependence of ΔHs follows the temperature dependence of the saturation magnetization.