Inelastic neutron scattering measurements on incommensurate antiferromagnetic chromium

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Abstract
Inelastic coherent neutron scattering experiments on a single crystal of unalloyed chromium at 295K have been performed in the neighbourhood of the (100) reciprocal lattice point using the IN1 triple-axis spectrometer of ILL, Grenoble. The results obtained from constant energy scans at energy transfers up to 18 THz suggest that a band gap of approximately 6.5 THz ( approximately 26.9 meV) exists for the incommensurate spin density wave state. This is in agreement with static susceptibility measurements but at variance with light scattering results. In addition the excitations are characterised by the appearance of a broad peak centred on the (100) position rather than by linear dispersion from the adjacent satellite positions. This is not predicted by any of the current theories.