Magnetic anisotropy in UTX compounds

We compare results of measurements of magnetization, specific heat, electrical resistivity and neutron diffraction on single crystals and oriented polycrystalline powders of various UTX compounds. Very strong anisotropy, persisting also in the paramagnetic state, is a general feature of these materials. Compounds with the hexagonal ZrNiAl-type structure exhibit, as a rule, a uniaxial anisotropy with an easy-magnetization direction along the c axis. Energies of the magnetic anisotropy (of the order of hundreds of kelvins) correlate with the expected development of hybridization strength within planes of the highest coordination of uranium atoms. As a result of this evidence the hybridization-mediated anisotropic exchange is tentatively assumed to be a source of the huge anisotropy. Particular symmetry of anisotropy reflects the type of arrangement of uranium atoms. 1. I n t r o d u c t i o n Nearly 50 ternary intermetallic compounds of the formula UTX (Tt rans i t ion metal; X-=p electron metal) constitute one of the largest isostoichiometric groups of uranium intermetallics. The UTX compounds crystallize in six different crystal structure types [1 ]. The hexagonal ZrNiA1type structure (Fig. 1) is observed in 21 cases, whereas 15 UTX compounds adopt the orthorhombic TiNiSi (CeCu2) structure type [1-4]. ~ u OT ~ x Fig. 1. Schematic drawing of the ZrNiAl-t:~e structure adopted by a large group of UTX compounds. 0925-8388/92/$5.00 © 1992 Elsevier Sequoia. All rights reserved