Effect of magnetism on the lattice dynamics in the σ-phase FeCr alloys

¹ AGH University of Science and Technology, Faculty of Physics and Applied Computer Science al. Mickiewicza 30, 30-059 Krakow, Poland, EU
² Institute of Solid State Physics, Vienna University of Technology - Wiednerhauptstr. 8-10, A-1040 Wien, Austria, EU

^(a) stanislaw.dubiel@fis.agh.edu.pl (corresponding author)

Received: 11 July 2012
Accepted: 18 December 2012

Abstract

Anomalies in the temperature dependences of the recoil-free factor, f, and the average center shift, 〈CS〉, measured by ⁵⁷Fe Mössbauer spectroscopy, were observed for the first time in the archetype of the σ-phase alloys system, FeCr. In both cases the anomaly started at the temperature close to the magnetic ordering temperature, and in both cases it was indicative of lattice vibrations hardening. As no magnetostrictive effects were found, the anomalies seem to be entirely due to a spin-phonon coupling. The observed changes in f and in 〈CS〉 were expressed in terms of the underlying changes in the potential, ΔE_p, and the kinetic energy, ΔE_k, respectively. The former, with the maximum value larger by a factor of six than the latter, decreases, while the latter increases with T. The total mechanical-energy change, ΔE, was, in general, not constant, but it resembled that of ΔE_p. Only in the range of 4–15 K, ΔE was hardly dependent on T. The decrease of ΔE on lowering T can be interpreted as an increase of the spin-phonon coupling.