Tuning the Structural Transitions and Magnetocaloric Response in Gd5Si1.7Ge2.3 Alloys Through Cobalt Addition

Abstract

Materials with a large magnetocaloric effect are of great significance for applications in thermomagnetic power generation and magnetic refrigeration. We report the effect of cobalt addition on the structural, magnetic, and magnetocaloric properties of Gd5 Si1.7 Ge2.3− x Co x with $x = 0$ , 0.1, 0.2, 0.3, and 0.4. Rietveld refinement of the X-ray diffraction patterns reveals that the Gd5 Si1.7 Ge2.3− x Co x compounds with $x\le 0.3$ crystallize in a mixed state of monoclinic and orthorhombic structures. With the increase in Co concentration, the compounds stabilize in orthorhombic structure with the Pbnm space group. Magnetization measurements indicate first-order and second-order transitions for lower Co concentrations ( $x\le 0.3$ ), while for the composition with $x=0.4$ , only a second-order transition is evident, which is due to the stabilization of the orthorhombic structure for higher compositions. At lower fields, short-range ferromagnetic correlations are apparent, which is attributed to the presence of competing intra-layer and inter-layer magnetic interactions. An enhancement in Curie temperature has been observed from 243 to 283 K with an entropy change ( $-\Delta S_{M}$ ) of 12.8 at 243 K, 14.5 at 262 K, 10.4 at 270 K, and 5.8 J/kg $\cdot \text{K}$ at 283 K for $x = 0.1$ , 0.2, 0.3, and 0.4, respectively, for a field change of 5 T. Universal curve analysis corroborates the transition of first order to second order as evidenced by magnetization measurements. The ability to tune the transition temperature to near room temperature through the proper addition of transition elements could provide an interesting pathway toward the development of materials for room temperature refrigeration applications.