Heavy-fermion characteristics in ${\mathrm{UCu}}_5\mathrm{Al}$ single crystals

Electronic properties of the antiferromagnetic Kondo compound ${\mathrm{UCu}}_5\mathrm{Al}$ have been investigated through magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance, and Hall coefficient measurements on single-crystal and polycrystalline samples. ${\mathrm{UCu}}_5\mathrm{Al}$ 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, ${\mathrm{UCu}}_5\mathrm{Al}$ 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 ${\mathrm{UCu}}_5\mathrm{Al}.$