Anomalous lattice dynamics in a σ-Fe60V40 alloy: Mössbauer spectroscopic study

Abstract

Lattice dynamics in a σ-Fe60V40 compound, which shows a re-entrant magnetism and orders ferromagnetic at TC≈170K, was investigated with the Mössbauer spectroscopy in the temperature interval of 5–300K. Two relevant spectral parameters viz. the average center shift, 〈CS〉, and the relative recoil-free fraction, f/fo, were explored. The former yielded the Debye temperature, TD1, and the mean-square velocity of vibration, 〈v2〉, while the latter TD2 and the mean-square amplitude of vibrations, 〈x2〉. Significant differences in the lattice-dynamical behaviors in the magnetic and paramagnetic phases were revealed. In particular, the values of TD were notably lower and those of f/fo greatly higher in the former. This anomalous result has likely its origin in a remarkably high anharmonic contribution to the vibrations found for the ground magnetic state (spin-glass). Especially anomalous behavior vs. temperature exhibits 〈x2〉 where four well defined ranges could have been identified and ascribed to the paramagnetic, ferromagnetic and two spin-glass phases. Linear correlations between 〈v2〉-〈x2〉 were found within each of the four ranges. They enabled determination of force constants, hence a change of the potential energy, Ep, in each of the ranges. The total change of Ep≈30meV while the corresponding one of the kinetic energy, determined from the knowledge of 〈v2〉, was Ek≈21meV. The lack of balance between Ep and Ek follows from the anharmonic lattice-dynamical behavior observed in the spin-glass state. The results give a strong evidence that magnetism can significantly affect the lattice dynamics.