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

 

Chem. Met. Alloys 6 (2013) 170-176

 

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