Bulk properties of the UCoGe Kondo-like system

Abstract

We report on extensive experimental investigations of a single crystal of the orthorhombic uranium compound UCoGe. Bulk measurements on as-grown and annealed single crystals, recording magnetization, magnetic susceptibility, electrical resistivity, magnetoresistivity, thermopower, thermal conductivity and heat capacity data do not reproduce the previously reported coexistence of ferromagnetism with superconductivity. The latter phenomenon was only observed for the annealed sample at T _SC = 0.65 K. New observations show a crossover at around 13 K, visible in thermal and transport measurements as well as the coherent state around 50 K, signaled by a wide knee in ρ(T). Above this temperature, UCoGe exhibits a single-ion Kondo-like effect. The magnetoresistivity of the annealed single crystal increases negatively down to 4.2 K, reaching as a large value about −27% at a field of 8 T. The latter may be interpreted in terms of fairly strong magnetic fluctuations existing in UCoGe at low temperatures.

Keywords:

• actinides
• superconductors
• Kondo effect
• thermal properties
• transport properties
• magnetoresistance
• magnetization
• electrical transport

Acknowledgements

We are grateful to B. Coqblin for his interest in this paper and E. Talik for synthesizing the single crystal. The technical assistance of G. Badurski and R. Gorzelniak with experiments and fitting the thermal conductivity by J. Mucha are acknowledged.