Observation of a new field-induced phase transition and its concomitant quantum critical fluctuations in CeCo(In1-xZnx)5

We demonstrate a close connection between observed field-induced antiferromagnetic (AFM) order and quantum critical fluctuation (QCF) in the Zn7%-doped heavy-fermion superconductor CeCoIn5. Magnetization, specific heat, and electrical resistivity at low temperatures all show the presence of new field-induced AFM order under the magnetic field B of 5-10 T, whose order parameter is clearly distinguished from the low-field AFM phase observed for B<5T and the superconducting phase for B<3T. The 4f electronic specific heat divided by the temperature, Ce/T, exhibits -lnT dependence at B∼10T (≡B0), and furthermore, the Ce/T data for B≥B0 are well scaled by the logarithmic function of B and T: ln[(B-B0)/T2.7]. These features are quite similar to the scaling behavior found in pure CeCoIn5, strongly suggesting that the field-induced QCF in pure CeCoIn5 originates from the hidden AFM order parameter equivalent to high-field AFM order in Zn7%-doped CeCoIn5.