Coalescence of the Fermi-surface-related diffuse intensity peaks in disordered alloys

The possibility of disappearance of the diffuse-intensity peak splitting induced by the Fermi surface (i.e., of coalescence of the intensity maxima) with decreasing temperature is predicted. The underlying mechanism is the compensation of the reciprocal-space curvatures of the self-energy and the interaction. The theory also describes similar results obtained earlier for two low-dimensional models with competing interactions. The coalescence is compared with the recently observed "thermal" splitting in Pt-V which can be explained in the same way.Comment: 6 pages, 3 EPS figures, RevTeX, submitted to Philosophical Magazine Letter

Quadratic short-range order corrections to the mean-field free energy

A method for calculating the short-range order part of the free energy of order-disorder systems is proposed. The method is based on the apllication of the cumulant expansion to the exact configurational entropy. Second-order correlation corrections to the mean-field approximation for the free energy are calculated for arbitrary thermodynamic phase and type of interactions. The resulting quadratic approximation for the correlation entropy leads to substantially better values of transition temperatures for the nearest-neighbour cubic Ising ferromagnets.Comment: 7 pages, no figures, IOP-style LaTeX, submitted to J. Phys. Condens. Matter (Letter to the Editor

Origin of the anomaly in diffuse scattering from disordered Pt-V alloys

An explanation of the anomalous concentration dependence of diffuse scattering from the Pt-V alloy system (splitting of the (100) short-range order intensity peak with increasing Pt content) is proposed. The effect is attributed to the competition between the interaction and self-energy curvatures. A similar temperature behaviour is predicted.Comment: 5 pages, 5 EPS figures, RevTeX; minor editorial corrections, text as publishe

Theory of temperature dependence of the Fermi surface-induced splitting of the alloy diffuse-scattering intensity peak

The explanation is presented for the temperature dependence of the fourfold intensity peak splitting found recently in diffuse scattering from the disordered Cu3Au alloy. The wavevector and temperature dependence of the self-energy is identified as the origin of the observed behaviour. Two approaches for the calculation of the self-energy, the high-temperature expansion and the alpha-expansion, are proposed. Applied to the Cu3Au alloy, both methods predict the increase of the splitting with temperature, in agreement with the experimental results.Comment: 4 pages, 3 EPS figures, RevTeX, submitted to J. Phys. Condens. Matter (Letter to the Editor