Anomalous binding of Fe atoms in chromium

TL;DR

This study investigates the anomalous binding behavior of 57Fe atoms in chromium using Mossbauer spectroscopy, revealing temperature-dependent changes in binding force possibly linked to spin-density wave polarization.

Contribution

It provides the first detailed analysis of Fe atom binding forces in chromium across different temperature phases using Mossbauer spectroscopy.

Findings

Binding force increases by a factor of ~1.9-2 at higher temperatures.

Two distinct temperature-dependent binding regimes identified.

Potential link between binding anomaly and spin-density wave polarization.

Abstract

Binding of 57Fe atoms in a metallic chromium was investigated in a Cr-Fe alloy, containing less than 0.1 at% Fe enriched to ~95 % in 57Fe isotope, using 57Fe-site Mossbauer spectroscopy. The binding force was derived from the Debye temperature, T_D, that, in turn, was calculated from the temperature dependence of the central shift of the Mossbauer spectra recorded in the range of 80 to 330 K. Following a temperature dependence of the line width that shows a minimum at ~155 K, two temperature intervals were considered: a low temperature one (LT) ranging from 80 to 155 K, and the T_D - value of 292 (12) K or 279 (34) K, and a high temperature one (HT) ranging from 155 to 330 K with the T_D - value of 399 (15) or 399 (25) K, depending on the fitting procedure. The corresponding values of the harmonic force (spring) constant are: 35.4 N/m and 66.1 N/m or 33.8 N/m and 66.1 N/m for the LT and HT, respectively. This means that in the HT range the binding force of 57Fe atoms by the Cr matrix is by a factor of ~1.9 - 2 stronger than that in the LT range. This anomaly is possibly related with a different polarization of the spin-density waves in the LT and HT "phases".