Polarization analysis of the magnetic excitations in Fe72Pt28 alloys

Abstract The discrepancy in Invar alloys between the magnetic excitation spectrum determined directly by neutron scattering and that inferred from magnetization measurements may be due to the significant contribution of longitudinal spin fluctuations to the excitation spectrum for 0≤ T ≤ T C . We have performed inelastic polarized neutron measurements about 000 of both ordered and disordered Fe 72 Pt 28 single crystals below the critical temperature. As in crystalline Fe 65 Ni 35 Invar, longitudinal excitations are observed only near T C and are diffusive in nature. In contrast, similar measurements on the amorphous Invar alloy Fe 86 B 14 found longitudinal propagating excitations below T C .