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Abstract

Electronic properties of the antiferromagnetic Kondo compound UCu5Al have been investigated through magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance, and Hall coefficient measurements on single- crystal and polycrystalline samples. UCu5Al orders antiferromagnetically below 16 K and shows a large magnetocrystalline anisotropy. In the paramagnetic state, pronounced incoherent Kondo interactions and crystal field effects are observed. At low temperatures, in spite of the lack of coherence, UCu5Al exhibits some characteristic properties of heavy-fermion systems, namely, an enhanced susceptibility, and enhanced electronic specific heat coefficient, revealing an enhanced effective electron mass. The specific heat and transport properties evidence a competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interactions. This feature, together with the frustration of the magnetic interactions originating from atomic disorder appear to be important for the development of the heavy-fermion state in UCu5Al.