Thermal Diffuse X-Ray Scattering Measurements of the Fermi Surface of Chromium

Thermal diffuse x-ray scattering measurements have been made on the [100] L-dispersion curve of chromium in the vicinity of the zone boundary at 329^∘{}K in the paramagnetic state and at 277^∘{}K in the anti-ferromagnetic state. Anomalies in the differential scattering intensity [I(329^∘K)-I(277^∘K)] were observed in reciprocal space at (0.87,0,0), (1.11,0,0), and (2.90,0,0) (in units of 2πa). These anomalies are interpreted as arising from the intersection of the x-ray resolution function with a Kohn surface about H. This surface is due to transitions between the Γ and H octahedra of the paramagnetic Fermi surface. In the antiferromagnetic state, this surface vanishes. Correcting for a shift due to the resolution function, an average value for the Γ-H transitions along [100] is obtained which is given by qqₘₐₓ=0.90±0.01. By comparing the angular dependence of the scattered intensity with that calculated from known dispersion curves, an estimate of the one-phonon contributions is obtained. This yields an estimate of Δωω=3% at the anomaly.