Total interference between nuclear and magnetovibrational one-phonon scattering cross sections

Abstract

A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron scattering experiment performed on the magnetocaloric compound MnFe${}_4$Si${}_3$, a ferromagnet with $T_{Curie}$ $\approx$ 305 K. The TA[100] phonon polarized along the $c$-axis measured from the Brillouin zone center $\text{G}$=(0, 0, 2) is observed only in one (${\sigma }_z^{++}$) of the two non-spin-flip polarization channels and is absent in the other one (${\sigma }_z^{--}$) at low temperatures. This effect disappears at higher temperatures, in the vicinity of $T_{Curie}$, where the phonon is measured in both channels with nonetheless marked different intensities. The effect is understood as originating from nuclear-magnetic interference between the nuclear one-phonon and the magnetovibrational one-phonon scattering cross-sections. The total cancellation reported is accidental, i.e. does not correspond to a systematic effect, as established by measurements in different Brillouin zones.

8 pages, 5 figures