Inelastic neutron scattering in amorphous ${\mathrm{Fe}}_{0.78}$${\mathrm{P}}_{0.22}$ and crystalline ${\mathrm{Fe}}_3$P systems

Pulsed inelastic neutron scattering measurements have been performed on amorphous a-${\mathrm{Fe}}_{0.78}$ ${\mathrm{P}}_{0.22}$ and its crystalline counterpart, c-${\mathrm{Fe}}_3$P. Measurements of the generalized distribution function G(Q,E) for Q=5–9 A${̊}^{\mathrm{-}1}$ were employed to determine G(E), the neutron-weighted density of states. The a-${\mathrm{Fe}}_{0.78}$ ${\mathrm{P}}_{0.22}$ results indicate a low-energy Fe-Fe derived band and a distinct high-energy Fe-P, opticlike band. This contrasts with amorphous metal-metal alloys which exhibit a single low-frequency peak in the phonon spectrum. A comparison with theoretical calculations of the neutron-weighted partial densities of states indicates very good qualitative agreement in band shape and relative intensities. Differences in the peak positions are attributed to weaker Fe-Fe and Fe-P interactions. The results are consistent with similar short-range order in a-${\mathrm{Fe}}_{0.78}$ ${\mathrm{P}}_{0.22}$ and c-${\mathrm{Fe}}_3$P. Similarities between the low-energy experimental a-${\mathrm{Fe}}_{0.78}$ ${\mathrm{P}}_{0.22}$ and theoretical a-Fe spectra are also noted.