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

## TL;DR

This study reports a complete cancellation of phonon intensity in a magnetocaloric compound due to nuclear-magnetic interference, observed via polarized neutron scattering, revealing complex interactions between nuclear and magnetic excitations.

## Contribution

It demonstrates the first observation of total interference between nuclear and magnetovibrational phonon scattering cross sections in a ferromagnetic material.

## Key findings

- Phonon intensity cancels out in certain polarization channels at low temperatures.
- The effect diminishes near the Curie temperature, with phonons appearing in both channels.
- The cancellation is accidental and confirmed across different Brillouin zones.

## 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 $\textbf{G}$=(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.