Spin-Wave Dispersion Relation in Fe-Ni Alloys

Abstract

Spin‐wave dispersion in Permalloys of composition ${\mathrm{Fe}}_{\text{0.2}}{\mathrm{Ni}}_{\text{0.8}}$ and ${\mathrm{Fe}}_{\text{0.5}}{\mathrm{Ni}}_{\text{0.5}}$ was investigated by neutron‐scattering methods. Values of $D$ in the expression for the spin‐wave energy, ${\mathrm{ħ\omega \hspace{0.17em}=\hspace{0.17em}Dq}}^2{\text{(1−βq}}^2)$ , were found to agree with spin‐wave resonance measurements, but the quartic coefficients $\beta$ were an order of magnitude smaller.