Polarization analysis of the magnetic excitations in Fe65Ni35 Invar

Abstract
Triple‐axis inelastic polarized neutron measurements have been performed as a function of temperature on a single crystal of the Invar alloy Fe65Ni35 to distinguish longitudinal from transverse magnetic excitations in the magnetically ordered phase. Well below the Curie temperature of 501 K the magnetic excitation spectrum is dominated by conventional transverse spin‐wave excitations, which in fact follow the predictions of spin‐wave theory very well. In particular, we find no evidence for propagating longitudinal excitations in this system, in sharp contrast to the behavior observed in the amorphous Invar Fe86B14 material as well as the non‐Invar amorphous system Fe40Ni40P14B6.