The heavy-fermion compound Ce(Cu 1Ϫx Ni x ) 2 Ge 2 is investigated by Gd 3ϩ electron spin resonance ͑ESR͒ within the whole concentration range (0рxр1). The Kondo-lattice system exhibits an alloying-induced transition from an antiferromagnetically ordered heavy-fermion ground state (xϭ0) to pure Kondo-like behavior with strongly enhanced effective masses (xϭ1). The temperature dependence of the ESR linewidth ⌬H allows one to distinguish between the different ground states. The nature of the magnetic order changes significantly from concentrations xՇ0.5 to xϾ0.5. The ESR data provide some further experimental evidence for a transition from a local-moment type (xϽ0.5) to some kind of itinerant heavy-fermion band magnetism (0.5ϽxϽ0.8). Non-Fermi-liquid behavior is discussed for xϭ0.8 where the magnetism is suppressed. Our results agree very well with the 63 Cu NMR spin-lattice relaxation rate 1/T 1 and the dynamic structure factor S(Q,) obtained from inelastic neutron-scattering experiments.

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The Kondo-lattice system CeCu2(Si 1 xGex)2 exhibits an alloying induced transition from a coherent Fermi-liquid (x = 0) with strongly enhanced effective masses to an antiferromagnetically ordered heavy-fermion system (x = 1). This transition is studied by Gd 3+ ESR in oriented powder samples. The temperature dependence of the ESR line width follows a characteristic pattern which allows one to distinguish between the different ground states. The results obtained in polycrystalline CeCu2Si 2 are in good agreement with the measurements performed in single crystals. Finally we compare our results with 63Cu-NMR data obtained from CeCu2Si 2 and CeCu2Ge 2.

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