Polarization analysis of the magnetic excitations in Invar and non‐Invar amorphous alloys

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Abstract
Conventional spin wave theory works remarkably well in describing the spin dynamics of both Invar and non‐Invar isotropic ferromagnets, with the important exception that for Invar systems the magnetization decreases much more rapidly with temperature than can be explained based on the measured spin wave dispersion relations. We have been carrying out triple‐axis polarized inelastic neutron scattering experiments on the amorphous ferromagnets Fe86B14 (Invar system) and Fe40Ni40P14B6 (METGLAS■ 2826) in order to separate the longitudinal magnetic fluctuations from the transverse (spin wave) excitations, and thereby determine if the presence of longitudinal excitations might resolve this discrepancy. The present measurements exhibit longitudinal excitations below Tc, but in both materials. Possible interpretations of the results are discussed.