Effects of Annealing on the Structure and Properties of Mn$_{\mathrm{5-x}}$Fe$_{\mathrm{x}}$Si$_{3}$

Materials forming with the Mn$_{5}$Si$_{3}$ crystal structure have been found to exhibit interesting magnetic, magnetocaloric, and spin polarization properties. In particular, alloys of Mn$_{\mathrm{5-x}}$T$_{\mathrm{x}}$Si$_{3}$ (T $=$ transition metal) have been investigated as possible magnetocaloric materials. Previous research has shown that Mn$_{\mathrm{5-x}}$Fe$_{\mathrm{x}}$Si$_{3}$, with x $=$ 4, exhibits the largest magnetic entropy of the system (4 J/kgK) and orders ferromagnetically just below 300 K, making it a possible candidate for room temperature magnetic refrigeration applications.\footnote{Songlin, et al., J. of Alloys and Compounds. \textbf{334} (2002) 249} Our work aims to study changes in the magnetic and magnetocaloric properties of MnFe$_{4}$Si$_{3}$ as a result of substitution at the silicon site. The effect of annealing, without quenching, on crystal structure homogeneity was investigated for the parent compounds Fe$_{5}$Si$_{3}$ and Mn$_{5}$Si$_{3}$ and for Mn$_{4}$FeSi$_{3}$ by x-ray diffraction. A reduction in x-ray diffraction peaks due to impurities was observed after annealing the Mn$_{5}$Si$_{3}$ and Mn$_{4}$FeSi$_{3}$ samples. The x-ray profile of Fe$_{5}$Si$_{3}$ was greatly improved by annealing and it adopted the proper Mn$_{5}$Si$_{3}$ D8$_{8}$ hexagonal crystal structure without quenching.