Unusually strong electronic correlation and field-induced ordered phase in YbCo.

We report the first study of electrical resistivity, magnetization, and specific heat on YbCo. The measurements on a single-phased sample of YbCobring no evidence of magnetic ordering down to 0.3 K in a zero magnetic field. The manifestations of low Kondo temperature are observed. The specific heat value divided by temperature,, keeps increasing logarithmically beyond 7 J/mol Kwith decreasing temperature down to 0.3 K without no sign of magnetic ordering, suggesting a very large electronic specific heat. Analysis of the magnetic specific heat indicates that the large portion of the low-temperature specific heat is not explained simply by the low Kondo temperature but is due to the strong intersite magnetic correlation in both the 3and 4electrons. Temperature-dependent measurements under static magnetic fields up to 7 T are carried out, which show the evolution of field-induced transition above 2 T. The transition temperature increases with increasing field, pointing to a ferromagnetic character. The extrapolation of the transition temperature to zero field suggests that YbCois in the very proximity of the quantum critical point. These results indicate that in the unique case of YbCo, the itinerant electron magnetism of Co 3-electrons and the Kondo effect within the vicinity of quantum criticality of Yb 4-local moments can both play a role.