Journal of Magnetism and Magnetic Materials 76 & 77 (1988) 125-127 125 North-Holland, Amsterdam HEAVY FERMION BEHAVIOUR DRIVEN BY A SUBSTITUTION OF Cu BY A! OR Ga IN CeCu s E. BAUER, E. GIL~TZ, N. PILLMAYR Institute of Experimental Physics, T, U. Vienna, A-1040 Vienna, Austria D. GIGNOUX, D. SCHMITT Lab. Louis NOel, CNRS Grenoble F-38042 Grenoble, France K. WINZER and J. KOHLMANN 1. Phys. lnstitut Universitiit Grttingen, D-3400 GiSttingen, Fed, Rep. German)' The temperature dependence of the electrical resistivity, thermopower, specific heat, susceptibility and the field dependence of the magnetization of the pseudobinary Ce(CuxM 1 x)5 (M = AI, Ga; 0.8 ~ x < 1.0) show that due to the exchange of Cu a nonmagnetic heavy, fermion behaviour can be obtained. In CeCu4Ga, for example, the "~, value of the electronic specific heat attains about 3200 m J/tool K 2 at T- 0.9 K. 1. Introduction Recently we proved that many of the physical properties of CeCu 5 can be drastically changed due to the substitution of one or two Cu-atoms by AI or Ga [1-3]. CeCu 5 itself was found to behave very similar to magnetically ordered Kondo com- pounds. A Kondo type interaction is present at somewhat elevated temperature and a transition to a magnetically ordered regime appears below 4 K. The aim of this paper is to study in more detail the vanishing of long range magnetic order due to the exchange of Cu by A1 or Ga in Ce(CuxA1 t -:,)5 and in Ce(CuxGa 1-:~)5 [0.8 < x < 1.0]. 2. Results and discussion In fig. 1 we have plotted the specific heat (%) vs. T of Ce(CuxA1 t_~)5 which demonstrates that the antiferromagnetic phase transition becomes depressed due to the substitution of Cu by A1. The inset in this figure shows the magnetic phase di- agram of Ce(CuxA1 l_x)s and Ce(CuxGa 1_~)5 for 0.8_<x<1.0. In the range from 1.0 to 0.92 a linear decrease of Ty can clearly be resolved from susceptibility (X) and specific heat measurements. For x = 0.88 X vs. T shows a shoulder around 1.5 K; this value seems to be the borderline for the long range ordered magnetic regime. For x = 0.84 a smooth maximum around 1 K and a nearly temperature independent behaviour of x(T) be- low this temperature serves as an indication of nonmagnetic behaviour at low temperatures. For x = 0.80 neither a magnetic transition was ob- served from our x(T) data nor from specific heat measurements down to 150 mK [4]. Fig. 2 displays the reduced electrical resistivity (P/P3o K) for the A1 series below 30 K. From this figure it can be concluded that there are two distinct concentration ranges: (i) for concentra- tions x > 0.88 only shallow minima can be ob- served which indicates weak Kondo interaction, I rNtKl rmax [K] ~ Ce,%% i,,f ~ .,,: 7 ",i ooo ~ \o o ...... °i ..... 2 Ce(Cux Air.x)5 o T[K] 0 2 Z, 5 8 Fig. 1. The specific heat cp as a function of temperature for Ce(Cu~All_~) s. The inset displays the magnetic phase di- agram for Ce(CuxMl_0 5 M = AI(o), Ga(zx); full and open symbols refer to long range order as well as to the transition into the nonmagnetic ground state, respectively. 0304-8853/88/$03.50 © Elsevier Science Publishers B.V.