We report precision c-axis magnetic measurements on a high-quality single crystal of the heavy fermion metamagnet UCoAl. The metamagnetic transition at H M changes from 1st order at low temperature to a crossover at high temperature. H M is nearly linearly increasing with increasing temperature up to a critical temperature T 0 . The critical temperature T 0 is determined from both the field and the temperature dependences of magnetization to be ∼ 11 K. The field dependence of the Sommerfeld coefficient γ is estimated from M(T) by using a Maxwell relation. γ(H) shows a step-like decrease at H M . This behavior is consistent with the previous reports of specific heat and resistivity measurements at low temperatures. © 2013 The Korean Physical Society.

We have performed NMR measurements under pressure in UCoAl with a quantum critical endpoint of the metamagnetic transition from the paramagnetic phase to the ferromagnetic (FM) phase. 59 Co-NMR sensitively detects the evolution of the internal field caused by applying the external field. The metamagnetic field H m increases with increasing pressure consistently with other experimental methods, accompanied by the suppression of the magnetization in the field-induced FM phase and the magnetization jump at H m . The loss of the NMR signal on approaching the QCEP indicates the development of the spin fluctuations. © 2013 The Korean Physical Society.

We report 59Co-NMR measurements in UCoAl where metamagnetism occurs owing to the enhancement of ferromagnetism by a magnetic field. The metamagnetic transition from a paramagnetic (PM) state to a ferromagnetic state is a first-order transition at low temperatures, but it changes to a crossover at high temperatures on crossing the critical end point (CEP) at Tcep ∼ 12 K. The contrasting behavior between the relaxation rates 1/T 1 and 1/T2 suggests that the longitudinal magnetic fluctuation of the U moments is strongly enhanced, especially near the CEP. A wide diffusion of the fluctuation from the CEP can be confirmed even in the PM state where the magnetic transition does not occur. © 2011 The Physical Society of Japan.

Resistivity and specific heat measurements were performed in the low carrier unconventional superconductor URu2Si2 on various samples with very different qualities. The superconducting transition temperature (TSC) and the hidden order transition temperature (T HO) of these crystals were evaluated as a function of the residual resistivity ratio (RRR). In high quality single crystals the resistivity does not seem to follow a T2 dependence above TSC, indicating that the Fermi liquid regime is restricted to low temperatures. However, an analysis of the isothermal longitudinal magnetoresistivity points out that the T2 dependence may be "spoiled" by residual inhomogeneous superconducting contribution. We discuss a possible scenario concerning the distribution of TSC related with the fact that the hidden order phase is very sensitive to the pressure inhomogeneity. © 2011 The Physical Society of Japan.