Effect of hydrogenation on the structure, magnetic and magnetocaloric properties of the Tb–Dy–Co alloys with Laves phase structure

A comprehensive study of the structure, phase composition, surface topology, magnetic and magnetocaloric properties of the compounds TbCo$_{2}$, Tb$_{0.3}$Dy$_{0.7}$Co$_{2}$ and the hydride with a low hydrogen content Tb$_{0.3}$Dy$_{0.7}$Co$_{2}$H$_{0.5}$ was carried out. The features of the structure at the micro- and nano- levels, as well as changes in the fundamental and functional properties during hydrogenation, were established. It was shown that the introduction of a small amount of hydrogen into the crystal lattice of the Tb$_{0.3}$Dy$_{0.7}$Co$_{2}$ compound leads to an increase in both the Curie temperature and the magnetic moment on the cobalt atoms. The type of magnetic phase transition from a paramagnetic to a magnetically ordered state changes from the first (in the compound Tb$_{0.3}$Dy$_{0.7}$Co$_{2}$) to the second (in TbCo$_{2}$, Tb$_{0.3}$Dy$_{0.7}$Co$_{2}$H$_{0.5}$), which leads to a significant decrease in the magnitude of the magnetocaloric effect.