Formation of heavy-fermion state in Ce 5-x La x CuSn 3 * ) V. H. Tran † ) Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroc law, P. O. 1410, Poland Received 18 May 2004; final version 9 July 2004 We report on measurements of magnetization, electrical resistivity, specific heat and thermoelectric power of heavy-fermion alloys Ce5-xLaxCuSn3 for x = 0 and 4. The exper- imental results show that the Kondo lattice ground state with antiferromagnetic ordering for x = 0 evolves into a single-ion Kondo state for x = 4. For the latter alloy the electronic coefficient of the specific heat increases with decreasing temperatures attaining a value of 839 mJ/K 2 mol Ce at 2 K. PACS : 71.27.+a Key words : Kondo effect, heavy-fermion 1 Introduction Recently, we have investigated magnetic properties of the 4f - and 5f -electron intermetallic compounds crystallizing in structures, which are characterized by two nonequivalent crystallographic sites for magnetic atoms [1, 2]. Of these compounds, remarkably Ce 5 CuSn 3 adopting the hexagonal Ga 4 Ti 5 -type structure (space group P 6 3 /mcm) [3], orders antiferromagnetically below T N ≈ 3.5 K and exhibits a mod- erate heavy-fermion behaviour with the electronic specific heat coefficient of 570 mJ/K 2 mol Ce at 2 K and 270 mJ/K 2 mol Ce above T N [2]. This fact gains spe- cial interest within the study of the competitive Ruderman-Kittel-Kasuya-Yosida (RRKY) and Kondo interactions. To study the formation of the heavy-fermion state in the presence of different exchange parameters, we have undertaken an in- vestigation of solid solutions Ce 5-x La x CuSn 3 by measurements of magnetization, electrical resistivity, thermoelectric power and heat-capacity. In this paper, we focus on the data of CeLa 4 CuSn 3 , where one suspects a dominating role of a single-ion Kondo effect. 2 Experimental Polycrystalline samples of CeLa 4 CuSn 3 were prepared by arc melting stoichio- metric constituent elements with purities 99.98 % for Ce and La, and 99.999 % for Cu and Sn, respectively, under a high-purity argon atmosphere. The buttons were remelted several times to ensure homogeneity. The quality of samples was checked * ) Presented at 12-th Czech and Slovak Conference on Magnetism, Koˇ sice, 12-15 July 2004 † ) Corresponding author. e-mail address:VHTran@int.pan.wroc.pl Czechoslovak Journal of Physics, Vol. 54 (2004), Suppl. D D411