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Layered double perovskite, SmBa 1−x Sr x Co 2 O 5+δ (x = 0, δ = 0.5 and x = 1, δ = 1) samples were prepared by solid state reaction method. X-ray diffraction studies show that the SmBaCo 2 O 5.5 sample crystallizes in the orthorhombic crystal structure with Pmmm space group, whereas SmSrCo 2 O 6 sample crystallizes in the orthorhombic crystal structure with Pnma space group. The temperature dependent magnetization of the SmBaCo 2 O 5.5 sample shows a paramagnetic (PM)–ferromagnetic (FM) and a FM-antiferromagnetic (AFM) transitions at T C = 267 K and T N = 221 K, respectively. In contrast, the SmSrCo 2 O 6 sample shows a PM-FM transition at T C = 175 K. According to Goodenough-Kanamori-Anderson rules, the ferromagnetic behavior in SmSrCo 2 O 6 can be understood from the super exchange interaction between the intermediate spin Co 3+ and low spin Co 4+ via O 2- (IS Co 3+ -O 2- - LS Co 4+ ). The change in magnetic entropy ( ∆ S M max ) is found to be maximum for the SmSrCo 2 O 6 sample. [ABSTRACT FROM AUTHOR]

This work presents the role of excess oxygen in CuFeO 2.06 compounds on thermoelectric and optical properties. The CuFeO 2.06 specimens were synthesized by solid state reaction method. X-ray diffraction technique has confirmed the CuFeO 2 structure for the specimens. In particularly, CuFeO 2.06 specimen revealed the structural extension of lattice parameter: a and c . Also, the specimen found increasing excess oxygen of approximately 3% as a resulted enhancement of mixed valence state of Cu + and Cu 2+ ions. XPS showed mixed valence state of the Cu + /Cu 2+ ions, and Fe 3+ and Fe 2+ ions was also found in the CuFeO 2.06 specimen. Mixed valence states contributed the co-existence of hole and electron carriers for conduction. Consequently, electrical conductivity of the CuFeO 2.06 specimen increased up to 23 S/cm at 873 K. Also, increasing Seebeck coefficient was shown to be approximately 302 μV/K at 873 K. The CuFeO 2.06 specimen was found power factor to be approximately 2.1 × 10 −4 W/m∙K 2 at 873 K. The indirect optical gap of CuFeO 2.06 (2.40 eV) was lower than that of the CuFeO 2 (2.60 eV). Thus, thermoelectric and optical properties were governed by an existence of excess oxygen. [ABSTRACT FROM AUTHOR]

Abstract: The 2D channel mixed-valent iron (II/III) monophosphate SrFe3(PO4)3 was synthesized via one step mild hydrothermal method at 210°C and characterized by X-ray diffraction techniques and magnetization measurements. Coexistence of antiferromagnetic superexchange and ferromagnetic superexchange interactions was supposed to be in the lattice according to the Goodenough–Kanamori–Anderson rules. Temperature dependent DC magnetization measurement shows that SrFe3(PO4)3 is ferrimagnet with three magnetic transitions between 2 and 350K. Through AC magnetization measurement, re-entrant spin glass was observed due to the competition between ferromagnetic and antiferromagnetic interactions. Furthermore, an interesting field induced stepped magnetization was observed in SrFe3(PO4)3 at 2K with the saturation magnetization Ms=2.4μB/f.u. at 5T. [Copyright &y& Elsevier]

Abstract: Two batches of poly-crystalline lithium manganate were prepared by a fuel assisted solution combustion method. LiMn2O4(S) was prepared using starch as the fuel and LiMn2O4(P) was prepared using poly vinyl alcohol (PVA) as the fuel. XRD studies indicated a significant and consistent shift in the 2θ values of all the hkl peaks to higher values in LiMn2O4(P) compared to LiMn2O4(S) indicating a lattice contraction in the former. TG/DTA studies indicated a higher formation temperature (∼25°C higher) for LiMn2O4(P). The higher formation temperature most likely promotes the oxidation of some Mn3+ to Mn4+ with a lower ionic radius causing a lattice contraction. This hypothesis is confirmed through XPS studies which indicated the presence of a higher fraction of Mn4+ in LiMn2O4(P) than that present in LiMn2O4(S). A crystal shape algorithm was used to generate the crystal habits of lithium manganate from their XRD data leading to an understanding on the exposed hkl planes in these materials. From the atomic arrangement on the exposed hkl planes it is predicted that LiMn2O4(P) would be less prone to manganese dissolution and hence would possess a higher cycle life when compared to LiMn2O4(S). [Copyright &y& Elsevier]

To investigate the mixed-valence (MV) state in CeRu3Si2, we measured the magnetic susceptibility χ(T) in the temperature range 8–300 K. The magnetic susceptibility is constant below 100 K, and slightly increases with increasing temperature. We estimated the spin fluctuation temperature Tsf by plotting χ(T)T/C against T, where C is the Curie constant of a Ce3+ ion. CeRu3Si2 is found to be a typical MV system, indicating that χ(T)T/C is a function of T/Tsf. This scaling relation is applied to the other MV compounds such as CeSn3. [Copyright &y& Elsevier]

Abstract: We study the evolution of conductance regimes in carbon nanotubes with doubly degenerate orbitals (“shells”) by controlling the contact transparency within the same sample. For sufficiently open contacts, Kondo behavior is observed for 1, 2, and 3 electrons in the topmost shell. As the contacts are opened more, the sample enters the “mixed valence” regime, where different charge states are strongly hybridized by electron tunneling. Here, the conductance as a function of gate voltage shows pronounced modulations with a period of four electrons, and all single-electron features are washed away at low temperature. We successfully describe this behavior by a simple formula with no fitting parameters. Finally, we find a surprisingly small energy scale that controls the temperature evolution of conductance and the tunneling density of states in the mixed valence regime. [Copyright &y& Elsevier]

Abstract: A single crystal of uranium ternary intermetallic of U2RuGa8 was grown by the Ga self-flux method. This compound crystallizes in the tetragonal unit cell of space group P4/mmm. Despite the fairly large U–U shortest distance of 4.22Å, this compound shows no signs of any magnetic ordering down to 1.9K. Instead, the susceptibility measured along the a and c axes, goes through a broad maximum at showing a distinct anisotropy. For j||a there is a weak temperature dependence of the electrical resistivity with a large value of , while for j||c the curve goes through a maximum at about 130K. The magnetoresistivity measured along two crystallographic directions is small and positive. The thermopower S for the two directions studied is positive and larger along the a-axis. It goes through a broad maximum at 175K reaching a value of 45μV/K. The electronic structure has been calculated by the tight-binding linear muffin-tin orbital method (TB-LMTO) and the results were used in calculation of the valence band near the Fermi level compared next to that found in photoemission experiment. The core 4f spectra are also presented. All the above properties are discussed in view of mixed valence behaviour of uranium atom in this compound. [Copyright &y& Elsevier]

Abstract: We report the infrared charge dynamics of in a series of - and -dependent reflectivity measurements. Within the low-temperature coherent phase, characteristics of a low energy (0.25eV) excitation appear to be controlled by the same Kondo scale, , which is relevant to the magnetic response (Phys. Rev. B 56 (1997) 7993). We show that the observed dependence of the frequency and strength of this excitation is consistent with an interpretation in terms of a coherent-to-incoherent quasiparticle transition between the correlation-induced bands of the periodic Anderson model (Phys. Rev. Lett. 92 (2004) 186405). Additionally, we consider an interpretation of -dependence in the higher frequency optical response in terms of a rigid band structure picture where the filling is depleted by Ag doping, augmented by a Kondo resonance which tracks the -dependent Fermi level. In addition to the properties of the low-temperature phase, our results also encompass the anomalous temperature dependent behavior in the vicinity of the electronic phase transition at low doping . [Copyright &y& Elsevier]

Abstract: We report on results of resistivity and Hall effect measurements performed on a single crystal. The resistivity, studied in the temperature range from 2–300K and in the magnetic fields up to 12T, was found to be field independent, showing no anomaly and no pronounced anisotropy between - and -axis in the temperature dependence. The Hall coefficient increases monotonously with increasing temperature. The normal Hall constant at 2K is . The susceptibility of the compound is of the order and decreases with the increasing temperature. [Copyright &y& Elsevier]

Abstract: A dispersive two-branch structure in the magnetic excitation spectra is reported for mixed-valence . This behavior is ascribed to Sm–Sm exchange interactions and discussed in connection with the possible formation of a local excitonic singlet ground state in this class of mixed-valence semiconductors. [Copyright &y& Elsevier]

Abstract: The high-pressure (type-II) antiferromagnetic phase of the mixed-valence semiconductor TmSe has been studied by neutron diffraction at in high magnetic fields. Surprisingly, the phase diagram reveals the existence, above 1.6T, of an AF I phase reminiscent of the ambient-pressure, zero-field structure. This result provides a new opportunity to investigate the relationship between magnetic and electronic structures in Tm monochalcogenides. [Copyright &y& Elsevier]

We present bulk magnetization and 140Ce local susceptibility (χloc) results for the alloy series Ce1−xUxPd3. The compounds upto x=0.3 form in single phase with AuCu3 type FCC crystal structure. With increasing U content, the alloys show higher effective magnetic moment (μeff) and smaller (θP) values. The χloc data reveal large reduction of Ce Kondo temperature with U concentration. We believe, interaction between Ce-4f and U-5f band electrons play an important role on the magnetic behaviour of these alloys. [Copyright &y& Elsevier]

A new interpretation of a specific heat and thermal expansion anomalies is proposed for mixed valence compounds and applied to Sm1−xLaxB6 and Ce1−xLaxNi. These thermodynamic quantities are considered as a superposition of contributions resulting from lattice and electron (f- and conduction electron) excitation spectra. [Copyright &y& Elsevier]

The electronic structures of Yb2Co3X9 (X=Ga, Al), which show properties of heavy-fermion antiferromagnet for X=Al and mixed-valent behavior for X=Ga, are studied by means of high-resolution photoemission spectroscopy. A sharp Yb 4f related peak, which shows characteristics consistent with the prediction by the single impurity Anderson model, was observed just below EF only for X=Ga. The origin of the difference between the Ga-based and Al-based compounds is attributed to the difference in the 4f energy level and the 4f-ligand hybridization strength. [Copyright &y& Elsevier]

The magnetic response function and the valence of 154Sm1−xYxS (0⩽x⩽0.33) have been determined by powder and single-crystal inelastic neutron scattering and by LIII-edge spectroscopy, in the temperature range 10–300 K. Considerable influence of the Sm–Sm interactions has been observed on the excitation spectrum of the mixed-valence f-electrons. [Copyright &y& Elsevier]

Abstract: In this paper we report on the magnetization and specific heat results on single crystals of the series (Eu,Yb)Ga4 aiming to study a possible valence change on both RE ions. The results show a decrease on and unit cell volume due to the chemical pressure. The enhancement of the effective moment suggests the presence of while the constancy of the saturation magnetization points to a fixed for Eu. [Copyright &y& Elsevier]

Abstract: We present an X-ray absorption near-edge structure (XANES) study at Ce L3-, and Co K-edges of CeCo2 thin films with the thickness varying from 30 to 140nm. Ce L3-edge spectra exhibit the mixed valence nature and the tetravalent contribution increases with the thickness of CeCo2. The variation in the spectral intensity observed at Co K-edge threshold indicates that there is a change in 3d occupancy and also in 3d–4f–5d hybridization. This study shows the effect of surface to bulk ratio and how it influences the charge transfer between Ce and Co ions and hence the electronic structure of CeCo2 thin films. [Copyright &y& Elsevier]

Abstract: The present study was motivated by the scaling characterization of the first example of mixed valence (MV) RE-like behaviour found recently among intermetallic ternary uranium compounds. The χ(T) function for both title compounds has been fitted to the interconfigurational fluctuation (ICF) model of Sales and Wohlleben in order to determine the characteristic fluctuation temperatures T sf and interconfigurational excitation energies E ex. A good scaling, with similar values of T sf like from those derived from the ICF model, has been achieved for both these ternaries by plotting Tχ(T)/C against the reduced T/T sf . Moreover, this scaling follows almost exactly those found earlier in a number of MV- RE compounds. [Copyright &y& Elsevier]

The study of DC- and low-frequency AC-conductivity in combination with the Hall and Seebeck coefficients measurements has been carried out in the temperature interval 1.6–300 K along different crystallographic directions in classic mixed-valence compound–narrow-gap semiconductor SmB6. The experiments on high-quality single crystals of samarium hexaboride have revealed a strong anisotropy of the low-temperature transport parameters. [Copyright &y& Elsevier]

Metallic YbInCu4 undergoes a first-order valence transition at 42 K, where the specific volume increases by 0.5% upon cooling. It is believed that the valence transition is driven by band structure effects that help quench Yb localized moments via a Kondo mechanism. The known phase diagram indicates that the transition can be suppressed with external magnetic fields. We used an adiabatic calorimeter to measure the specific heat in the high-field phase of the material. Data obtained in magnetic fields up to 50 T show an enhanced Sommerfeld coefficient and anomalies in the specific heat that are compatible with a much depressed Kondo temperature. Our data indicate quite different energy scales in the low-field and high-field phases of YbInCu4. [Copyright &y& Elsevier]