Pressure-induced valence change in the rare earth metals; The Case of praseodymium

Tateiwa, Naoyuki   ; Nakagawa, Akitoshi*; Fujio, Kazuhiko*; Kawae, Tatsuya*; Takeda, Kazuyoshi*

The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal structure (Pr-III) to -U one (Pr-IV) at 20 GPa with a large volume collapse ( = 0.16), which is associated with the valence change of the Pr ion. The two 4f electrons in the Pr ion is supposed to be itinerant in the Pr-IV phase. In order to investigate the electronic state of the phase IV, we performed the high-pressure electrical resistance measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the temperature dependence of the resistance shows an upward negative curvature, suggestting the narrow quasiparticle band of the 4f electrons near the Fermi energy. A new phase boundary is found at in the Pr-IV phase. From the temperature and magnetic field dependences of the resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be magnetic. Several possibilities for the origin of are discussed.