Quadrupolar Phase Diagram and Fermi Surface Properties in the Localized 5f²-Electron System UPd₃

We measured the electrical resistivity, specific heat, magnetostriction, magnetization and de Haas-van Alphen (dHvA) oscillation in UPd3 with the hexagonal structure in order to clarify the quadrupolar and magnetic properties as well as the nature of conduction electrons. The high-field magnetization measurement at 4.2 K in magnetic fields up to about 50 T reveals two-successive metamagnetic transitions at 10.2 and 17.9 T for the field along the [0001] direction, and one transition at 27.6 T along [112̄0]. From the results of magnetization as well as the magnetostriction measurements at various temperatures, we determined the magnetic phase diagram. Phase boundaries are discussed on the basis of the crystalline electric field scheme of the 5f² configuration and the quadrupolar interaction of O_zx. Reflecting the localized 5f-electrons, the conduction electrons have small cyclotron effective masses ranging from 0.24 to 3.62 m₀, which were determined by the dHvA experiment. The dHvA data are compared to the result of band calculations based on the 5f²-localized band model.