Quantum critical point and unusual phase diagram in the itinerant-electron metamagnet UCoAl

Abstract

We present the temperature--pressure--magnetic-field phase diagram of the itinerant-electron metamagnet UCoAl determined from the ac susceptibility measurement. The quantum critical point (QCP) was found to be located at $2.9\ifmmode\pm\else\textpm\fi{}0.2$ GPa ($\ensuremath{\equiv}{P}_{\mathrm{QCP}}$) and $130\ifmmode\pm\else\textpm\fi{}5$ kOe. In addition to the determination of the phase diagram, we report magnetic and transport properties in the paramagnetic state and around the phase boundary. The critical divergence of the magnetic susceptibility is suppressed toward the QCP. From the longitudinal magnetoresistance and the resistivity under magnetic fields, enhancement of the resistivity is observed in the so-called supercritical region. In the paramagnetic region, the magnetoresistance and temperature dependence of the resistivity exhibit complex behaviors, especially in the vicinity of 1.5 GPa and ${P}_{\mathrm{QCP}}$.