Journal of Magnetism and Magnetic Materials 102 (1991) 74-86 North-Holland Magnetic and transport properties of the UTSn series (T = Co, Ni, Ru, Rh, Pd, Ir and Pt) V.H. Tran and R. TroC W Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy zyxwvutsrqponmlkjihgfedcbaZYX of Sciences, 50-950 Wrociaw, Poland Received 9 January 1991; in revised form 1 May 1991 Magnetic susceptibility and electrical resistivity were measured for a series of intermetallic, ternary compounds UTSn, where T stands for Co, Ni, Ru, Rh, Pd, Ir and Pt. For the first time it was shown that UNiSn, except for the well-known cubic MgAgAs-type (low temperature) form, crystallizes also in the orthorhombic CeCuz-type (high temperature) form, which probably exhibits the antiferromagnetic properties below 21 K and has a metallic character of conductivity. Also the off-stoichiometric UPta,,Sn,,, alloy was found to have two polymorphic forms, where the low temperature form is the MgAgAs-type and shows the complex magnetic properties at low temperatures, while the high temperature one is the FezP-type, which is ferromagnetic below 28 K. For the remaining UTSn compounds we discuss the differences occurring between our and other authors’ findings. Especially we emphasize the presence of two magnetic transitions in URhSn; the ferromagnetic one at 17 K and the probably antiferromagnetic one at 52 K. Moreover, two phase transitions of antiferromagnetic character with close lying transition temperatures were found for UPdSn. The obtained experimental results which we analyzed in terms of different crystal structures and the degree of Sf-ligand hybridization which are the main factors influencing the magnetic and transport properties of considered UTSn compounds. 1. Introduction In recent years the uranium-transition metal stannides, UTSn, have attracted much interest owing to their large variety in physical properties [1,2]. Among them, UNiSn, which crystallizes in the cubic MgAgAs-type structure, has focused the largest attention. The first obtained magnetic data on this compound were controversial [3,4] due to the unusual behaviour of the susceptibility at low temperatures, which still remains puzzling in view of recent neutron diffraction measure- ments. Despite the lack of the characteristic sus- ceptibility maximum, this compound is antiferro- magnetic below about 46 K with the uranium moment aligned parallel to the [OOl] axis [5,6]. Furthermore, UNiSn has been regarded as a half-metallic magnet (HMM) [3,4,6], because of the appearance of a semiconductor-metal transi- tion near its NCel temperature. This interesting feature has been interpreted by assuming an en- ergy gap, A, in one of the spin bands, which in turn disappears when the system approaches TN [3]. This HMM picture of UNiSn has been sup- ported by the band structure calculations by Al- bers et al. [7] and Daalderop et al. [8], who utilized a spin-polarized LMTO method without and with the spin-orbit coupling involved, re- spectively. In these calculations it was assumed that UNiSn is a ferromagnet. In the very recent band structure calculations also based on the LMTO method but with the correction terms included, Eriksson et al. 191 have taken into account, in addition, the orbital polar- ization (OP) and spin-orbit coupling (SOC) as well as the antiferromagnetic type I alignment of uranium moments in UNiSn. All calculation vari- ants obtained, which comprised both OP and SOC, have lead the above authors to the conclu- sion that the uranium moment consists of a spin 0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. All rights reserved