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 MnFe4Si3, a ferromagnet with TCurie ≈ 305 K. The TA[100] phonon polarized along the c-axis measured from the Brillouin zone center G=(0, 0, 2) is observed only in one (σ ++ z ) of the two non-spinflip polarization channels and is absent in the other one (σ −− z ) at low temperatures. This effect disappears at higher temperatures, in the vicinity of TCurie, 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. arXiv:1812.02564v1 [cond-mat.mtrl-sci] 6 Dec 2018 located after the velocity selector and the Heusler analyzer was set at fixed k f =2Å −1 . The sample is the same single crystal as the one used in Ref. [3]. It was placed in a vertical field magnet, the field being along the b-axis of the hexagonal structure and the horizontal scattering plane being thus defined by a * and c * . A magnetic field of 1 T was applied in the paramagnetic state and the sample was field-cooled in order to get a single domain ferromagnetic sample. Hence, the polarization at the sample position is kept along the magnetic field which defines the z-axis. Two Mezei spin flippers were used before and after the sample in order to measure the four possible polarized neutron cross-sections σ αβ z ={σ ++