Magnetocaloric prospects of mutual substitutions of rare-earth elements in pseudobinary Tb1−xHoxNi2 compositions (x = 0.25–0.75)

Abstract As the magnetocaloric characterization of polycrystalline Tb1−xHoxNi2 intermetallic compounds (with x = 0.25, 0.5, and 0.75), their relative cooling power (RCP) and refrigerant capacity (RC) are estimated based on comprehensive investigations of the magnetic and thermodynamic properties of the compositions, the structure of which was studied in detail by x-ray diffraction analysis and scanning electron microscopy. The taken x-ray diffraction patterns demonstrate the similarity between the Ho-depleted compound (x = 0.25) and the parent TbNi2 and HoNi2 compounds, i.e., the regular C15 cubic structure forms in them, whereas, in the case of x = 0.5 and 0.75, the C15-based superstructure is found. Both magnetic and heat capacity measurements showed that all of the studied compounds exhibit the transition from the ferromagnetic to paramagnetic state, which is confirmed to be the second order magnetic phase transition with the Curie temperature that decreases from 31.1 to 18.6 K in passing from the Tb-enriched Tb0.75Ho0.25Ni2 to the Ho-enriched Tb0.25Ho0.75Ni2 composition. The high values of RCP and RC are shown can be reached for the compositions and experimentally are demonstrated based on the performed measurements of magnetic and thermodynamic parameters. Under an external magnetic field change of 0–5 T, the maximum magnetic entropy change -ΔSmag for the Tb1−xHoxNi2 compounds increases from 13.9 to 19.5 J/kgK as x increases from 0.25 to 0.75. These experimental results are compared with and confirmed by available theoretical data. The maximum adiabatic temperature change ΔTad for Tb0.75Ho0.25Ni2 and Tb0.5Ho0.5Ni2 at the 2 T magnetic field change reaches 3.0 K, and substantially increases, namely, to 4.5 K in the case of the Tb0.25Ho0.75Ni2 composition near its Curie temperature TC. The effect of increasing Ho content in the Laves-phase compounds on their magnetic and magnetocaloric properties is discussed.