FMR LINEWIDTH IN BAIN1.5FE10.5O19 SINGLE-CRYSTAL

Ferromagnetic resonance, FMR, has been observed in a BaIn1.5Fe10.5O19 ferrite single crystal. The FMR resonance field Hres, effective linewidth ΔHeff, and effective Landau-Lifshitz-Gilbert damping parameter λeff were obtained at 22.67 GHz for temperatures from 80 to 425 K and for two sample orientations in the applied field, namely perpendicular and parallel to the easy magnetization axis. The FMR parameters reveal anomalous values near the characteristic temperature Tcr = 204 K in qualitative agreement with previous measurements of magnetization and magnetocrystalline anisotropy constants. The absorption line for all temperatures is Lorentzian and for Tcr extreme exchange narrowing is observed with the correlation time of the dipolar field τc ≈ 1.5×10-13 s and the exchange constant J/kB ≈ 5 K. The effective linewidth for T < Tcr fits the empirical formula ΔHeff = ΔHcr(T/Tcr)-γcr. Since the present material at low temperatures can be classified as a random spin system, ΔH(T) has also been analysed in terms of another empirical form suggested previously: ΔΓ = Γ(T) - Γ0 = Γ1 exp(-T/T0). Agreement was obtained with this model for temperatures up to T0 = 91 K. The effective parameter λeff for Tcr < T < Tc is temperature independent and for T < Tcr, dependent. © 1990.