Magnetic phase diagram and Fermi surface properties of the heavy-fermion antiferromagnet UPd2Cd20.

The electronic state of UPd2Cd20, which exhibits a magnetic transition atTN∼5 K, is investigated by means of transport, high-field magnetization up to 55 T, specific heat in magnetic fields, and de Haas-van Alphen (dHvA) measurements, and compared with the non-5fcompound ThPd2Cd20. A metamagnetic transition is observed atμ0Hc∼15-20T, which continuously connects toTNin theH-Tphase diagram. Although the magnetization reaches large values at high fields reminiscent of 5flocalized character, the ordered magnetic moment is estimated to be small, as inferred from the weak anomalies in specific heat atTNand in the magnetization atHc, suggesting an itinerant character of the 5felectrons. The observed dHvA frequencies reveal enhanced cyclotron effective masses of 30m0, which are much heavier than those in ThPd2Cd20. These experimental results indicate that5f-derived bands contribute to the large electronic specific heat coefficient of 670 mJ (K2⋅mol)-1, demonstrating the dual localized-itinerant character of 5felectrons in UPd2Cd20.