L Journal of Alloys and Compounds 317–318 (2001) 419–422 www.elsevier.com / locate / jallcom The effect of Th substitution for U in the heavy fermion U Pt In 2 2 a, a a,b a,b c a * L.C.J. Pereira , J.C. Waerenborgh , I. Catarino , G. Bonfait , M. Godinho , M. Almeida a ´ ´ ´ Instituto Tecnologico e Nuclear, Departamento de Quımica, Estrada Nacional 10, P-2686-953 Sacavem, Portugal b ´ ˆ Departamento de Fısica, Faculdade de Ciencias e Tecnologia da Universidade Nova de Lisboa, P-2825-114 Monte de Caparica, Portugal c ´ ˆ Departamento de Fısica; Faculdade de Ciencias da Universidade de Lisboa, P-1700-016 Lisboa, Portugal Abstract Polycrystalline (U Th ) Pt In solid solutions with x50.03, 0.05, 0.08 and 0.10 were synthesized by arc melting the constituents 12x x 2 2 under a purified Ar atmosphere. All the compounds crystallize in a tetragonal U Si -type structure, with the space-group P4 / mbm,( Z52). 3 2 The effects of Th substitution for U on the magnetic properties suggest pronounced electron correlations as in the heavy fermion U Pt In. 2 2 However, no clear indication of magnetic ordering in all the compounds was found. The magnetic phase transitions around 3 and 19 K, found by means of ac-susceptibility and magnetization measurements are most likely due to the presence of minority phases.  2001 Elsevier Science B.V. All rights reserved. Keywords: U Pt In; Intermetallics; Non-Fermi liquid behaviour; Structure determination; Magnetic characterization 2 2 1. Introduction evidence for NFL behaviour and pronounced spin-fluctua- tion (SF) phenomena. During the past few years, intensive studies devoted to Previous results observed for (U Th ) Pt In (0 #x # 12x x 2 2 the magnetic and electrical properties of the isostructural 1) compositions where U atoms are randomly replaced by family of ternary intermetallics, An T X (An5actinide Th [5,6] have shown for the x 50.10 compound a knee at 2 2 element, T5transition element, X5p-element) [1–3] have T 519 K on the electrical resistivity vs. T curve suggesting been performed in order to clarify hybridization phenom- magnetic order below this temperature. This transition is ena in the 5f electron compounds. Within the series of followed upon cooling by a quadratic decrease of r ( T ) U T X intermetallics, the Pauli-paramagnet U Pt In at- suggesting that the NFL behaviour on U Pt In is replaced 2 2 2 2 2 2 tracts special attention because of its strongly enhanced by a Kondo lattice behaviour on (U Th ) Pt In. The 0.9 0.10 2 2 electronic specific heat at low-temperatures with C / T ( T 5 presence of the UPt impurity phase was however reported 2 1.5 K) ¯850 mJ/mol K [4]. Experiments carried out on a [5]. UPt shows two magnetic phase transitions at 27 and 19 polycrystalline sample in the temperature range 1.3–300 K K [13,15]. In order to check the influence of impurity [4] also revealed the presence of an enhanced low tempera- phases on the measured properties and to further investi- ture magnetic susceptibility and a broad maximum in the gate the effects of the Fermi level changes on the physical resistivity around 80 K, characteristic of heavy-fermion properties of U Pt In we have also undertaken the substi- 2 2 compounds and Kondo systems. Electrical and magnetic tution of small amounts of U by Th. Besides careful resistivity measurements down to 1.4 K on polycrystalline structural characterization, magnetization measurements U Pt In [5,6] indicated a linear temperature dependence of and specific heat data on the (U Th ) Pt In samples 2 2 12x x 2 2 the electrical resistivity below 15 K suggesting a non- (0 #x #1) are presented here for the first time. Fermi liquid (NFL) behaviour in this compound. More recently, specific heat data on U Pt In single crystals [7] 2 2 below 6 K, together with electrical resistivity and magnetic 2. Experimental susceptibility data on these single crystals [8,9] provided Polycrystalline (U Th ) Pt In solid solutions with x 5 12x x 2 2 0.03, 0.05, 0.08 and 0.10, in a total weight of 4 g each, were prepared by arc melting the stoichiometric amounts *Corresponding author: Tel.: 1351-1-994-6000; fax: 1351-1-994- of the constituent elements under a purified Ar atmosphere. 1455. E-mail address: lpereira@itn1.itn.pt (L.C.J. Pereira). The starting materials were used with purity higher than 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(00)01419-5