Suppression of the γ–α structural phase transition in Ce_0.8La_0.1Th_0.1by large magnetic fields

Abstract

The γ-α transition in Ce 0.8 La 0.1 Th 0.1 is measured as a function of applied magnetic field using both resistivity and magnetization. The γ-α transition temperature decreases with increasing magnetic field, reaching zero temperature at around 56 T. The magnetic-field dependence of the transition temperature is quantitatively reproduced by a model that invokes the field and temperature dependence of the entropy of the 4f-electron moments of the γ phase.

Fermi-surface topologies and low-temperature phases of the filled skutterudite compoundsCeOs4Sb12andNdOs4Sb12

“…In common with our observations of CeOs 4 Sb 12 , the valence transitions from L to H phases in YbInCu 4 , Ce and Ce alloys are marked by (very frequently broadened) changes in resistivity and magnetic susceptibility, both accompanied by hysteresis in field and temperature sweeps 23,[32][33][34][35][36][37] . This type of transition is most spectacular in elemental Cerium and Ce alloys 23,[35][36][37] , where the L phase is known as the α phase, and H as the γ phase 23,[35][36][37] .…”

“…21 and 24 are in fact associated with the broadened L to H transition that we observe in the PDO data. Both of these collections of points lie within the extended field range of the fall in −∆f , and the scatter between the two data sets probably reflects the difficulty of assigning a precise field to such a broadened feature 23 . The switching of the order of the up-and downsweep L to H PDO inflection points at low temperatures ( Fig.…”

“…Hence, Figure 2 has been plotted as −∆f versus H, so that upward shifts in the data indicate increasing resistivity. As the field increases, the resistivity rises steeply to a broad peak before falling to a minimum at about 25 T; note that within the region where the resistance falls there is hysteresis between the up-and downsweeps of the magnetic field, suggestive of a phase boundary 23 . From now on, we shall refer to the field regions on either side of this boundary as the L (low-field, low-temperature) and H (high-field, high-temperature) phases.…”

“…Based on experimental evidence, we propose that the L to H phase transition in CeOs 4 Sb 12 is a valence transi- tion 23,31 analogous to those observed in YbInCu 4 [31][32][33][34], elemental Ce [31,[35][36][37] and Ce alloys such as Ce 0.8 La 0.1 Th 0.1 [23]. In these materials, the valence transition occurs between a higher-temperature, higher-field phase in which quasi-localized 4f moments (on the Yb or Ce ions) are stabilized by entropy terms in the free energy, and a band-like state of the f electron at low temperatures and low fields 31 .…”

“…Therefore, increasing the temperature will drive the L to H transition. Similarly, a magnetic field affects the free energy of the quasi-localized 4f electrons in the H phase more strongly than the energies of the band quasiparticles in either the L or H phases 23,31 . Thus, the H phase becomes more energetically favorable with increasing field, so that a field-driven L to H transition occurs, as observed in CeOs 4 Sb 12 and the other systems 23,[32][33][34] .…”