Specific-Heat Anomaly around Metamagnetic Transition in UCoAl

We have measured the specific heat and magnetocaloric effect of an UCoAl single crystal down to ∼0.1 K in fields applied along the c -axis to investigate the thermodynamic aspects of the metamagnetic behavior. Hysteresis behavior observed in both physical quantities below ∼3 K confirms the first order character of the metamagnetic transition. We have found that an apparent decrease of the electronic part of specific heat C e / T by 20% at 0.25 K with increasing field across the metamagnetic transition field of ∼1 T, evidencing the change in the density-of-states at the Fermi energy. C e / T gradually decreases with increasing temperature in zero field. This anomalous temperature dependence can be explained by taking into account a spin fluctuation contribution in the low-field state.