Anomalous thermal expansion in ErFe11.4Nb0.6

Abstract

The thermal expansion properties of the rare earth transition metal compound ErFe11.4Nb0.6 (Curie temperature Tc = 520(10) K) have been investigated in detail by variable temperature high resolution synchrotron x-ray diffraction measurements over the temperature range 300 K–640 K. The findings from the Rietveld analyses reveal significant anomalies in the thermal expansion of ErFe11.4Nb0.6 below the Curie temperature with negative thermal expansion also evident around Tc = 520(10) K. The structural changes that occur around the Curie temperature lead to a spontaneous volume magnetostriction of ∼6.3 × 10−3 at 300 K. The minimum values of the linear thermal expansion coefficients αa and αc for ErFe11.4Nb0.6 around TC are determined to be −3.56 × 10−6 K−1 and -1.30 × 10−6 K−1 respectively. Details of the structural features of ErFe11.4Nb0.6 (including Wigner-Seitz cell volumes and average bond lengths for Er atoms (2a site) and Fe atoms (8i, 8j, 8f sites) to neighbouring Fe atoms) that contribute to the thermal expansion behaviour have been investigated in detail. The persistence of finite magnetostriction values λa and λc (along the a-axis and the c-axis respectively) and volume magnetostriction ωs, above the magnetic transition temperature, indicates the likely occurrence of short-range magnetic correlations in this region.