The Study of the REPdSn (RE = La, Pr and Nd) Single Crystals M. Mihalik and V. Sechovský Charles University, Faculty of Mathematics and Physics, Department of Condensed Matter Physics, 121 16 Prague, Czech Republic. H. Kitazawa National Institute for Materials Science, Tsukuba, Japan. Abstract. We present the results of specific heat, magnetization and resistivity measurements done on the single crystals of intermetallic compounds REPdSn (RE = La, Pr, Nd). All these compounds crystallize in the orthorhombic TiNiSi-type crystal structure. In case of PrPdSn we have found a paramagnetic-antiferromagnetic phase transition at 4.2(1) K. For NdPdSn an analogous transition has been observed at 3.4(1) K followed by an order-to-order phase transition at 1.91(3) K. The two compounds exhibit strong magnetocrystalline anisiotropy. We discuss our results with respect to the previous literature information. Introduction The intermetallic compounds of the type RTX (R – rare earth + La, T – d-metal, X – p-metal) crystallize in a variety of crystal structures, depending mainly upon the nature of T and X elements [Szytuła, 1991]. In these compounds it is usual that the magnetic moment is located only on the R atom. In the most cases the crystal structure depends only on T and X element, which is very convenient for studying the magnetism of the whole series of compounds by varying only the rare earth atom. The REPdSn (RE = La, Pr, Nd) compounds crystallize in the orthorhombic TiNiSi-type crystal structure (space group Pnma). In this structure the RE atoms occupy 4(c) crystallographic position, forming a zigzag chains running along the a-axis. These chains are interconnected to adjacent chains along the c-axis, forming a three-dimensional network. The local symmetry of RE atoms is monoclinic, which result to large set of parameters for theoretical calculation of the physical properties of the compound. LaPdSn was found to be a normal metal down to 2 K [Canepa et. al., 1996]. In case of PrPdSn compound the published results are somewhat contradictory: Adroja et al. [1992] refers that the compound does not order down to 4.2 K, but the neutron powder diffraction experiment done by Kolenda et. al. [1998] resulted to antiferromagnetic ordering with k = (0 ½ ½) at temperatures lower than 4.6 K. Similar for NdPdSn: Zygmunt et al. [1995] refers the paramagnetic-antiferromagnetic phase transition at T N = 2.4 K, but Kolenda et al. [1998] refers antiferromagnetic ordering already below 3.6 K with complicated incommensurate magnetic structure with the k-vector of the magnetic structure k = (0.273 ½ ½). As all previously published results were measured on polycrystalline samples, these facts motivated us to grow single crystals of these REPdSn compounds and measure the physical properties with respect to magnetocrystalline anisotropy in these compounds. Sample preparation and characterization The studied single crystals were grown by Czochralski technique in the tetra-arc furnace in NIMS, Tsukuba under the protective Ar atmosphere. The crystal growth was performed using about eight grams of the melt consisting of the stoichiometric composition of the elemental constituents. The purity of starting materials was 3N for RE, 3N5 for Pd and 5N for Sn. As a seed we have used a tungsten wire. We have used the random necking procedure and pulling speed 6 mm/h to ensure high quality of the grown crystals. The products were analyzed by X-ray Laue method and confirmed to be good single crystals. We have also pulverized part of the grown ingots and characterized by X-ray powder diffraction. The samples have been found single phased and the subsequent Rietveld analysis of diffractograms confirmed good agreement of our refined lattice parameters with those published in the literature [Canepa et. al., 1996; Adroja et al., 1992]. 107 WDS'08 Proceedings of Contributed Papers, Part III, 107–112, 2008. ISBN 978-80-7378-067-8 © MATFYZPRESS