Analysis of the Theoretical Expressions Used for the Computation of the Ferromagnetic Resonance Linewidths in Ferrites

A comparative study of the linewidths (ΔH) calculated from different theoretical expressions for typical ferrites is presented. Bloch-Bloembergen, Landau-Lifshitz and Landau-Lifshitz-Gilbert equations for the precession of the magnetization are used as starting points and several approximations are applied for simplifying the final mathematical result. From the three theoretical expressions, the most frequently used approximated Lorentzian formula for the description of the ferromagnetic resonance can be obtained. It is observed that the Lorentzian curve provides the same result as the exact theoretical curves for ΔH < 600 Oe while for larger linewidths the exact formulations are needed. Comparison with experimental results on YIG, Li, Ni, Mn, MnCd and LiZnTiMn-ferrites studied by our group in the last few years is also presented.