Unusual dynamics of Fe atoms in chromium matrix

TL;DR

This study investigates the unusual temperature-dependent dynamics of 57Fe atoms in a chromium matrix using Mossbauer spectroscopy, revealing harmonic and anharmonic modes linked to underlying electronic waves.

Contribution

It provides new insights into the vibrational behavior of impurity atoms in chromium, highlighting a transition from harmonic to anharmonic dynamics at 145 K.

Findings

Harmonic mode below 145 K with Qeff = 185 K

Anharmonic mode above 145 K with two temperature intervals

Record-low binding force constants for Fe atoms

Abstract

57Fe site Mossbauer Spectroscopy (MS) was used to investigate a dynamics of 57Fe atoms embedded into chromium lattice as impurities. From the Mossbauer spectra recorded in the temperature range of 80 to 350 K, a temperature dependence of the Lamb-Mossbauer factor, f, was determined. The latter revealed an unusual dynamics of 57Fe atoms viz. harmonic mode below T = 145 K with a characteristic effective Debye temperature, Qeff = 185 K and anharmonic one above T o 145 K. The latter mode exists in two clearly separated temperature intervals with slightly different Qeff - values viz. (i) 156 K for 145 K < T < 240 K and the record-high anharmonic coefficient e = 18 * 10-4 K-1 and (ii) 152 K for T > 240 K and e = 13.6 * 10-4 K-1. Based on the Visscher's theory, the record-low values of relative binding force constants for Fe atoms were determined as 0.0945, 0.0673 and 0.0634, respectively. It is suggested that the unusual dynamics observed in this study might be related to the underlying spin- and charge- and strain-density waves of chromium.