Ferromagnetic Resonance Relaxation, Wide Spin-Wave Coverage by Ellipsoids

Abstract

The role of degenerate spin‐wave coupling in ferromagnetic resonance (FMR) losses has been studied as a function of sample shape. Measurements of linewidth ΔH and peak absorption intensity s″ both show that FMR loss above the 90°, k→0 limit of the spin‐wave spectrum is much less than within the spectrum. An investigation of unsymmetrically magnetized spheroids, i.e., with the external field H₀ not along the symmetry axis revealed that there are regions of the spin‐wave spectrum which can be reached by more than one sample shape and that in these regions of overlap the different shapes yield different values of ΔH and s″. A similar result can be calculated from the usual equation of motion using either Landau‐Lifshitz or Bloch‐Bloembergen damping. (The asymmetric case has not yet been treated by the spin‐wave model.) Despite the strong variations of ΔH and s″, the gyromagnetic ratio changed less than 1% under all variations of shape and orientation. The variable shape technique gives greater coverage of the spectrum than previous variable frequency work. Another advantage is that the unknown effects of changing frequency on other possible loss mechanisms are avoided.