Spin‐Wave Dispersion Relation in Fe‐Ni Alloys

Spin‐wave dispersion in Permalloys of composition Fe0.2Ni0.8 and Fe0.5Ni0.5 was investigated by neutron‐scattering methods. Values of D in the expression for the spin‐wave energy, ħω = Dq2(1−βq2), were found to agree with spin‐wave resonance measurements, but the quartic coefficients β were an order of magnitude smaller.