Characterization of low-energy magnetic excitations in chromium

TL;DR

This study investigates the low-energy magnetic excitations in chromium using inelastic neutron scattering, revealing complex spectral features and temperature-dependent behaviors of the Fincher-Burke modes in its spin-density-wave phase.

Contribution

It provides new insights into the energy spectra and temperature evolution of magnetic excitations in chromium, highlighting unexpected asymmetries and spectral-weight transfer.

Findings

Dispersive FB modes show peaks at specific Q points.

Energy spectra exhibit asymmetry that decreases with temperature.

Spectral-weight transfer occurs between upper and lower FB modes.

Abstract

The low-energy excitations of Cr, i.e. the Fincher-Burke (FB) modes, have been investigated in the transversely polarized spin-density-wave phase by inelastic neutron scattering using a single-(Q+-) crystal with a propagation vector (Q+-) parallel to [0,0,1]. The constant-momentum-transfer scans show that the energy spectra consist of two components, namely dispersive FB modes and an almost energy-independent cross section. Most remarkably, we find that the spectrum of the FB modes exhibits one peak at 140 K near Q = (0,0,0.98) and two peaks near Q = (0,0,1.02), respectively. This is surprising because Cr crystallizes in a centro-symmetric bcc structure. The asymmetry of those energy spectra decreases with increasing temperature. In addition, the observed magnetic peak intensity is independent of Q suggesting a transfer of spectral-weight between the upper and lower FB modes. The energy-independent cross section is localized only between the incommensurate peaks and develops rapidly with increasing temperature.