Journal of ALLOYS AHD COMFOUND5 ELSEVIER Journal of Alloys and Compounds 224 (1995) 39--41 ,, Effect of pressure on magnetic susceptibility of UCus_xAux alloys A.S. Panfilov a, I.V. Svechkarev a, R. Tro6 b,., V.H. Tran b " S. Verka'n Institute for Low Temperature Physics and Engineering, Academy of Sciences of Ukraine, 47 Lenin Ave., 310164 Kharkov, Ukraine b W.. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroclaw, Poland Received 30 September 1994 Abstract The magnetic susceptibility of UCuaAu2 and UCu3Au 2 has been measured at 78 and 290 K under hydrostatic pressures up to 2 kbar. The pressure dependence of the susceptibility is correlated with the change in the paramagnetic Curie temperature. For both compounds the dO/dP value was determined to be about -0.2+0.05 K kbar -1. Keywords: Magnetic susceptibility; Hydrostatic pressure; RKKY-type interaction 1. Introduction The study of magnetic and transport properties of the UCus_#~ux system, crystallizing in the cubic AuBes- type structure [1], shows that doping of the initial antiferromagnetic UCu5 (TN = 15 K) causes an appre- ciable change in the magnetic ordering temperature. The substitution of one Au atom for one Cu atom nearly doubles the N6el temperature. With further growth of the Au content, TN decreases and finally the antiferromagnetic state disappears at x>~0.3. These observed properties have been explained within the framework of a competition between the Kondo effect and RKKY exchange interactions [2]. At high enough temperatures the magnetic susceptibility X of UCus_~Aux alloys shows the modified Curie-Weiss be- haviour C x(r)=Xo+ T- 0 (1) It appears that the effective magnetic moment per U atom stays roughly constant (/zcfr=3 IzB) and the paramagnetic Curie temperature O (about - 100 K for UCu5) increases monotonically (decreases in modulus) with increasing Au content. In this system the strength of hybridization between f and ligand sp electrons, which influences the magnetic behaviour, is believed to be correlated with the preferential occupation of Au atoms at the 4c sites of the AuBe:type structure * Corresponding author. 0925-8388/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0925-8388(94)01519-1 [2]. The substitution of Au for Cu increases appreciably the crystal lattice parameter a and hence also the spacing between the U-U and U-Au(Cu) atoms. The increase in the interatomic distances also modifies the effective exchange interactions between the 5f electrons [1]. In this paper the effect of hydrostatic pressure on the magnetic susceptibility of some alloys of the UCus_xAux system will be presented. 2. Experimental Polycrystalline samples of UCu3Au 2 and UCuaAu 3 (about 0.5 g) were spark cut from the ingot used earlier [1]. Their magnetic susceptibility was measured under helium gas pressures up to 2 kbar at 290 and 78 K using a pendulum magnetometer placed directly in the pressure cell [3]. The relative measurement error was no larger than _+ 0.05%. The experimental dependence x(P) appears to be linear for these two compounds. As an example, in Fig. 1 we display such a dependence for UCu2Au 3. The resulting derivatives dlnx/dP of the compounds are given in Table 1. 3. Discussion of results According to Eq. (1), the pressure effect can be described as