Mössbauer-effect study of dynamic, magnetic, and electronic properties of C14 Laves phase Nb0.975Fe2.025

Abstract

C14 Laves phase Nb0.975Fe2.025 compound was investigated by means of the Mössbauer spectroscopy. Spectra were recorded in the temperature range of 5–300 K. Their analysis in terms of three sub-spectra yielded information on magnetic and lattice dynamical properties of Fe atoms regularly occupying 2a and 6h lattice sites and, excessively, 4f sites. No indication of magnetism was observed down to the temperature of T ≈ 60 K, and spectral parameters, viz., center shift, CS, and the main component of the electric field gradient, Vzz, behave regularly. In particular, analysis of CS(T) in terms of the Debye model yielded the following values of the Debye temperature, TD: 453(5) K for the site 6h, 544(10) K for the site 2a, 479(4) K for the weighted average over 6h and 2a sites, and 363(35) K for the site 4f. Below ∼60 K, anomalous behavior was observed: a broadening of the spectrum appeared indicating thereby a transition into a magnetic phase. Analysis of a temperature dependence of the hyperfine field, B, associated with the 6h and 2a sub-spectra yielded different values of the magnetic ordering temperature. The maximum values of the hyperfine field at 5 K, Bo, were 8.2 kGs and 3.3 kGs, for 6h and 2a, respectively. The Bo-values were used to estimate values of the underlying magnetic moments, μFe(6h) = 0.055–0.065 μB and μFe(2a) = 0.02–0.025 μB. Noteworthy, they are over one order of magnitude lower than those theoretically calculated. The CS and Vzz parameters showed anomalies in the magnetic phase, in particular the former exhibited a strong departure from the Debye model prediction testifying to a significant effect of magnetism on the lattice vibrations.