Effect of hydrogen on the structural, magnetic and magnetocaloric properties of the Gd5Ge2.1Si1.9 compound

The effect of hydrogen absorption (≤2.50 hydrogen atoms per formula unit) in the Gd5Ge2.1Si1.9 magnetocaloric compound is investigated by magnetic and X-ray diffraction measurements. Room temperature Rietveld refinement shows that even at low hydrogen content in the base sample (1600 °C/48 h annealed Gd5Ge2.1Si1.9) an orthorhombic Gd5Si4-type structure is stabilized. The hydrogen absorption: (i) increases a-axis and b-axis and decreases the c-axis parameter; (ii) destroys the first-order magneto-structural transition (magnetization versus temperature data); (iii) decreases the Curie temperature and, (iv) drastically reduces the isothermal variation of entropy (ΔST), as expected for this compound when stabilized in the orthorhombic structure.