A model of spin wave resonance in grain-surface-layers for effective linewidth and channels of energy transfer on polycrystals

The spin wave dispersion relation for the grain-surface-layer region is calculated by assuming that the anisotropy constant K^s and the anisotropy field H^s in the gain-surface-layer region are different from the other region. In comparison with the manifold of the grain-interior, the resonance region, for the grain-surface-layer region is much broader than that for the grain-interior. The high field and the low field effective linewidths are given respectively: ΔH_eff=2χ+^s"V_sf(H)(H_i-ω/γ-S)²/M_s and ΔH_eff=2[χ+^s"V_sf(H)+χ+^b"(1-V_s)](H_i-ω/γ-S)²/M_s, by setting χ+ⁱ= χ+^b(1-V_s)+χ+^sV_s, where χ+ⁱ is the intrinsic susceptibility, χ+^b, V_b=1-V_s, χ+^s and V_s denote the susceptibility and the volume fraction respectively for the grain-interior and the grain-surface-layer region. The dependence of ΔH_eff on the grain size, porosity, temperature, M_s and H, as well as the field shift S vs. H are explained with this model. The value of K^s≈-2×10⁵ erg/cm³ is estimated by fitting data for YIG and NiZn ferrite. An additional basic channel of energy transfer from the rf field via spin wave system of the grain-surface-layer region to the lattice is suggested for polycrystals.