The effect of ellipticity on the direction of spinwave rays

Parallel pumping high signal power microwave radiation is a powerful tool to detect spinwave instabilities, since it allows to infer intrinsic damping properties of ferrimagnets. Several experiments of the last years have shown that the spinwave linewidth
\DeltaH_{k}
does not always follow the
(H_{c}-H_{i})^{1/2}
law for π/2 magnon scattering. This feature is attributed to the existence of a non zero
\underline{z}
-component of the spinwave propagation vector
\underline{k}
. Simple formulas, derived from the dispersion relation are presented in this paper, which evidence the dependence on the spinwave ellipticity
\varepsilon(\vartheta_{k})
of the propagation characteristics of the excited magnons. Also, in the case of three boson processes, the influence of ε on
\DeltaH_{k}(H_{i})
is briefly discussed in the light of the spinwave transit-time theory.