The effect of ellipticity on the direction of spinwave rays

Abstract

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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\DeltaH_{k}</tex> does not always follow the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(H_{c}-H_{i})^{1/2}</tex> law for π/2 magnon scattering. This feature is attributed to the existence of a non zero <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\underline{z}</tex> -component of the spinwave propagation vector <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\underline{k}</tex> . Simple formulas, derived from the dispersion relation are presented in this paper, which evidence the dependence on the spinwave ellipticity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\varepsilon(\vartheta_{k})</tex> of the propagation characteristics of the excited magnons. Also, in the case of three boson processes, the influence of ε on <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\DeltaH_{k}(H_{i})</tex> is briefly discussed in the light of the spinwave transit-time theory.