We present results of temperature and magnetic field dependent resistivity ρ(H,T) and bulk magnetization M(H,T) measurements on post-annealed La0.7Ca0.3MnO3 thin films that were grown via pulsed-laser deposition. Both the resistivity and the anomalously large negative magnetoresistance peak near the ferromagnetic ordering temperature (Tc=250 K), with Δρ/ρ0=−85% at 50 kOe. A clear correlation is found between ρ and M that is described by the phenomenological expression ρ(H,T)∝exp[−M(H,T)/M0]. This correlation reflects the important interplay between transport and magnetism in this system, and suggests that the transport below Tc involves polaron hopping.

Using neutron pair distribution function analysis over the temperature range from 1000 to 15 K, we demonstrate the existence of local polarization and the formation of medium-range, polar nanoregions (PNRs) with local rhombohedral order in a prototypical relaxor ferroelectric Pb(Mg(1/3)Nb(2/3))O3. We estimate the volume fraction of the PNRs as a function of temperature and show that this fraction steadily increases from 0% to a maximum of approximately 30% as the temperature decreases from 650 to 15 K. Below T approximately 200 K the volume fraction of the PNRs becomes significant, and PNRs freeze into the spin-glass-like state.

Zero-field muon-spin-resonance and lower-critical-field data are presented for a wide range of Th concentrations in Uix Th v Bei3, spanning the region where both a superconducting and a second, lowertemperature phase transition are observed. Overall T-x phase boundaries are assigned and discussed according to the nature of the lower phase transition. Arguments for associating the lower phase with a possible magnetic (time-reversal-violating) superconducting state are given.

The temperature and pressure dependence of the thermal displacements and lattice parameters were obtained across the γ → α phase transition of Ce using high-pressure, high-resolution neutron and synchrotron x-ray powder diffraction. The estimated vibrational entropy change per atom in the γ → α phase transition, ∆S γ−α vib ≈ (0.75±0.15)kB, is about half of the total entropy change. The bulk modulus follows a power-law pressure dependence which is well described using the framework of electron-phonon coupling. These results clearly demonstrate the importance of lattice vibrations, in addition to the spin and charge degrees of freedom, for a complete description of the γ → α phase transition in elemental Ce.PACS numbers: 64.70. Kb, 71.27.+a, 61.12.Ld Materials with electrons near the boundary between itinerant and localized behavior continue to present a major theoretical challenge to a complete description of their properties, including multiple phases and anomalous thermodynamics. This is particularly true in the 4f and 5f systems, where this boundary appears to occur in or near the elements Ce and Pu, respectively [1]. In Pu, which possesses five allotropic phases at ambient pressure, a partial localization of some of the five 5f electrons appears necessary to understand the higher temperature phases [2]. Partial localization may also be present in U compounds [3]. Ce metal is in principle simpler, possessing only a single 4f electron, but still displays four different phases at ambient pressure. One of the most interesting and still not completely understood phenomena in Ce is the isostructural (fcc) γ → α phase transition, which involves about 17% volume collapse at room temperature and pressure of roughly 0.8 GPa [4].In the majority of theoretical models [4,5,6,7,8,9, 10] the γ → α transition has been attributed to an instability of the single 4f 1 electron. The earliest models focused on charge instability, while later models dealt with spin instability. The promotional model postulates a transition from 4f 1 5d 1 6s 2 (γ-phase) to 4f 0 5d 2 6s 2 (α-phase), but is inconsistent with the 4f binding energy and the cohesive energies of other 5d 2 6s 2 materials [5]. In the Mott transition (MT) model [5,6] the 4f electron in the γ phase is localized and non-binding, but is itinerant and binding in the lower volume α phase. The energy for the phase transition is provided by the kinetic energy of the itinerant f electron. In the Kondo-volumecollapse (KVC) model [9, 10] the 4f electron is assumed to be localized in both the γ and α phases, and the phase transition is driven by the Kondo spin fluctuation energy and entropy within the context of the single-impurity Anderson model. These early models ignored altogether an explicit treatment of the lattice degrees of freedom; even the lattice entropy is not considered. More recent treatments [8,11,12] include both the lattice and spin entropies, but still do not deal explicitly with the consequences of electron-lattice coupling despite the large volume collapse at t...

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