Structure and magnetic properties of RNi (R = Gd, Tb, Dy, Sm) and R6M1.67Si3 (R = Ce, Gd, Tb; M = Ni, Co) hydrides

The paper reports the influence of hydrogen absorption on the structure and magnetic properties of intermetallic compounds RNi (R = Gd, Tb, Dy, Sm) and R6M1.67Si3 (R = Ce, Gd, Tb; M = Ni, Co). It is demonstrated that the ternary hydrides GdNiH3.2, TbNiH3.4, DyNiH3.4, and SmNiH3.7 have similar CrB-type orthorhombic structures. In the structures of TbNiD3.4 and DyNiD3.4, deuterium atoms occupy tetrahedral 8f-interstices [R3Ni], trigonal bipyramidal 4c-interstices [R3Ni2], and octahedral 4b-interstices [R4Ni2]. The hydrides of R6M1.67Si3 retain the hexagonal structure of their parent compound. In the structures of Tb6Co1.67Si3D11.2 and Ce6Ni1.67Si3D12.3, deuterium atoms occupy tetrahedral 4f-interstices [R3M] and two types of tetrahedral interstices [R3Si]: 12i1 and 12i2. The formation of the hydrides causes a substantial expansion of the metallic sublattice, a weakening of ferromagnetic interactions, and a decrease in the magnetic transition temperature.

Research highlights▶ GdNiH3.2, TbNiH3.4, DyNiH3.4, SmNiH3.7, Tb6Co1.67Si3D11.2, Gd6Co1.67Si3D12.6, Gd6Ni1.67Si3D12.3, and Ce6Ni1.67Si3D12.3 hydrides were synthesized. ▶ The influence of hydrogenation on the structure and magnetic properties of intermetallic compounds RNi and R6M1.67Si3 was studied. ▶ The hydrides of the RNi compounds have a CrB-type orthorhombic structure. The R6M1.67Si3 compounds retain their Ce6Ni2Si3-type structure upon hydrogenation. ▶ Hydrogen absorption makes the exchange interactions between magnetic moments of the rare earth atoms much weaker.