Polycrystalline Spin Wave Theory of Ferromagnetic Resonance Compared with the Tilting Experiment

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Abstract
Schlömann's spin wave theory of polycrystalline ferromagnetic resonance has been tested in detail using the tilting method reported earlier. Among the quantities measured were the linewidth ΔH, and the maximum value of the imaginary part of the effective susceptibility (χm″)eff. The measurement method is equivalent to measuring asymmetric (Nx≠Ny) ellipsoids and thus, introduces another shape dependence in addition to that due to spin waves. Direct comparison with the symmetric (Nx=Ny) form of the theory is inaccurate. A proper comparison can be made in two ways: (1) generalizing the theory to include the Nx≠Ny case and then using the data directly, (2) transforming the data and then comparing with the Nx=Ny theory. Both comparisons are reported and their equivalence is demonstrated. It is concluded that Schlömann's theory does not fit the data within the spin wave (SW) manifold. It is suggested that the theory of Sparks may provide a better fit. The difference between coupling models seems to be the basic difference between the two theories. Experimentally and theoretically, ΔH and (χm″)eff are different quantities. The dispersive effects of spin wave coupling are shown to be the cause of the difference between the theoretical ΔH and (χm″)eff.