Structure and magnetism of R₂T₂X compounds and their hydrides; comparison of lanthanides and actinides

Chem. Met. Alloys 6 (2013) 170-176

https://doi.org/10.30970/cma6.0255

Ladislav HAVELA, Silvie MAŠKOVÁ, Pavel SVOBODA, Khrystyna MILIYANCHUK, Alexandre KOLOMIETS, Alexander V. ANDREEV

The group of “221” compounds crystallizing in the Mo₂FeB₂ structure type comprises more than 400 members known so far. The onset of magnetic moments and their ordering can be studied in the actinide representatives by tuning the 5f-ligand hybridization strength, including detailed investigations of the non-Fermi liquid regime. The mechanism of specific two-ion anisotropy, depending exclusively on the positions of the nearest-neighbor U atoms, can be tested due to the variety of coordinations observed within a single structure type. Possible dimerization of the magnetic structures, representing a practical realization of a Shastry-Sutherland lattice, has been the motivation for several studies of rare-earth based materials, and can be a reason for the tendency to magnetic frustration. Hydrogen absorption, being an additional degree of freedom for tuning the physical properties, was found to be limited to 2 H atoms per f.u. in U-based materials. The strengthening of U magnetism may be attributed to predominant volume expansion and consequent 5f-band narrowing. In several rare-earth based compounds much higher H absorption has been observed (the limit seems to be 8 H/f.u.). The structure reacts either by distortion or amorphization in such cases. H absorption leads to weakening of the magnetic interactions, probably related to the reduced concentration of conduction electrons.

Reaction of the R₃T tetrahedra in Mo₂FeB₂-type R₂T₂X compounds to H insertion for light (left) and heavy (right) rare earths.

Keywords

Hydrides / Intermetallic compounds / Lanthanides / Actinides / Magnetic properties