Abstract
Hydrogenation effects on the crystal structures and magnetic properties of Tb2Co2Ga, Tb2Co2Ga, and Tb3Co3Ga were studied. Tb2Co2Ga, Tb2Ni2Ga (both structure type W2CoB2), and Tb3Co3Ga (structure type W 3 CoB 3 ) are structurally related belonging to inhomogeneous linear structure series based on the TR- (also referred to as CrB type) and YAlGe- (ordered derivative of the binary type UPt2) type structure motives.
The hydrides Tb2Co2GaH6.2, Tb3Co3GaH9.7, and Tb2Ni2GaH5.1 were synthesized at room temperature with hydrogen pressures of 52-53 kPa. Hydrogenation results in strongly anisotropic lattice volume expansion Delta V/V = 19.2-20.0%.
It also leads to a decrease of the Curie temperature in ferromagnetic Tb2Co2Ga and Tb3Co3Ga and practically suppresses the antiferromagnetic ordering in Tb2Co2Ga. A model of the crystal structure of the hydride Tb3Co3GaH10 with four hydrogen positions was suggested based on stronger effect of hydrogenation on the TlI-type slabs.
The more complex character of the magnetic phase transitions for Tb2Co2Ga and Tb3Co3Ga presumes involvement of Co in the magnetism of these compounds, while Tb2Ni2Ga acts as a typical 4f-electron system with dominating RKKY exchange interactions.