Magnetoresistance and magnetization anomalies in CeB6

High precision magnetoresistance (MR) Δρ/ρ(H,T) and magnetization M(H,T) measurements have been carried out for well known and typical strongly correlated electron system—cerium hexaboride. The detailed measurements have been fulfilled on single crystalline samples of CeB₆ over a wide temperature range in magnetic fields up to 70 kOe. It was shown that the MR anomalies in the magnetic heavy fermion compound under investigation can be consistently interpreted in the frameworks of a simple relation between resistivity and magnetization—Δρ/ρ∼M² obtained by Yosida [Phys. Rev. 107(1957)396]. A local magnetic susceptibility χ_loc(T,H)=(1/H^*(d(Δρ/ρ)/dH))^1/2 was deduced directly from the MR Δρ(H,T) measurements and compared with the experimental data of magnetization M(H,T). The magnetic susceptibility dependences χ_loc(T,H) and χ(T,H) obtained in this study for CeB₆ allow us to analyze the complicated H-T magnetic phase diagram of this so-called dense Kondo-system.     

Low-Temperature Electronic Properties of the Lan+1NinO3n+1 (n = 2, 3, and ∞) System: Evidence for a Crossover from Fluctuating-Valence to Fermi-Liquid-like Behavior

Measurements of the temperature dependence of the electrical resistivity ρ(T), magnetic susceptibility χ(T), and Seebeck coefficient S(T) have been carried out on the n = 2, 3, and ∞ members of the homologous lanthanum nickel oxide systems La_n+1Ni_nO_3n+1 that were annealed in air. With increasing n, a progressive decrease in the electrical resistivity and a gradual change from insulating to metallic behavior are observed. La₃Ni₂O₇ is nonmetallic, showing a gradual increase in ρ when T decreases (dp/dT < 0) from 300 to 4.2 K, whereas La₄Ni₃O₁₀ and LaNiO₃ exhibit metallic resistivity (dp/dT > 0). A minimum in ρ(T) near 140 K is observed for La₄Ni₃O₁₀, while LaNiO₃ exhibits a T² dependence for ρ(T) below 50 K. The magnetic susceptibility of LaNiO₃ is Pauli-like, but the χ(T) data for La₃Ni₂O₇ and La₄Ni₃O₁₀ below 350 K show a decrease with decreasing temperature. The Seebeck coefficient of all these compounds is negative at high temperatures; La₃Ni₂O₇ and La₄Ni₃O₁₀ exhibit a sign change in S at low temperatures. These results suggest a crossover from a fluctuating-valence to a Fermi-liquid-like behavior with increasing n.     

Observation of possible quantum interference effects in SrRuO3 epitaxial thin films grown by high-oxygen pressure dc sputtering

A careful study of the electronic transport and magnetotransport properties of metallic ferromagnetic SrRuO₃ (SRO) thin films is reported. Epitaxial (～150 nm) SRO films were grown on (001)-oriented SrTiO₃ (STO) substrates by dc sputtering technique at high oxygen pressure. Resistivity measurements were performed up to temperatures as low as 2 K in magnetic fields strengths of up to 9 T, applied perpendicular to the film plane. The films featured excellent metallic behavior at room temperature, with a resistivity, ρ(300 K) < 600 μΩ cm. The presence of minima in the ρ–T plots at ～4 K was clearly detected from these measurements. The 9 T magnetic field did not remove the minima signaling its nonmagnetic origin In addition, the ρ(μ₀H = 9 T,T) minima was slightly shifted to higher temperature and the ρ(μ₀H = 9 T,T ≤ 4 K) was larger when it was compared with ρ(μ₀H = 0 T,T ≤ 4 K). Increasing relevance of quantum corrections to the conductivity as the temperature is lowered has been invocated as possible cause of this anomalous electrical behavior. In this case, effects arising from quantum interference of the electronic wavelength are expected. Weak localization and renormalized electron–electron interaction have been considered as possible sources giving rise to quantum correction to the conductivity.     

Synthesis and characterization of a new layered organic-inorganic hybrid nickel(II) 1,4:5,8-naphthalenediimide bis-phosphonate, exhibiting canted antiferromagnetism, with Tc∼21 K

A new Ni(II) layered hybrid organic-inorganic compound of formula Ni₂[(NDI-BP)(H₂O)₂]·2H₂O has been prepared in very mild conditions from N,N′-bis(2-phosphonoethyl)napthalene-1,4:5,8-tetracarboximide (NDI-BP ligand) and NiCl₂. The X-ray powder structure characterization of the title compound suggests a pillared layered organic-inorganic hybrid structure. The distance between the organic and inorganic layers has been found to be 17.8 Å. The inorganic layers consist of corner sharing [NiO₅(H₂O)] octahedra and they are pillared by the diphosphonate groups. DC and AC magnetic measurements as a function of temperature and field indicate the presence of 2D antiferromagnetic exchange interactions between the nearest-neighbor Ni(II) ions below 100 K. A long-range magnetic ordering at T_c∼21 K has been established and is attributed to the presence of spin canting. AC magnetic measurements as a function of temperature at different frequencies confirm the occurrence of the magnetic ordering temperature at T=21 K and the presence of a slight structural disorder in the title compound.     

Thermodynamic properties of 1-butyl-3-methylpyridinium tetrafluoroborate

Pressure, density, temperature (p, ρ, T) data of 1-butyl-3-methylpyridinium tetrafluoroborate [C4mpyr][BF₄] at T = (283.15 to 393.15) K and pressures up to p = 100 MPa are reported with an estimated experimental relative combined standard uncertainty of Δρ/ρ = ±(0.01 to 0.08)% in density. The measurements were carried out with a newly constructed Anton-Paar DMA HPM vibration-tube densimeter. The system was calibrated using double-distilled water, methanol, toluene and aqueous NaCl solutions. An empirical equation of state for fitting of the (p, ρ, T) data of [C4mpyr][BF₄] has been developed as a function of pressure and temperature to calculate the thermal properties of the ionic liquid (IL), such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient and internal pressure. Internal pressure and the temperature coefficient of internal pressure data were used to make conclusions on the molecular characteristics of the IL.     

Ternary rare-earth nickel arsenides R3Ni7As5 (R=La, Ce, Pr, Nd, Sm) with a new variant of the BaAl4-type: crystal structure and physical properties

The ternary rare-earth nickel arsenides R₃Ni₇As₅ (R=La, Ce, Pr, Nd, Sm) were prepared by arc melting the elemental components and subsequent annealing at T=1070 K. The crystal structure of Ce₃Ni₇As₅ was determined from single-crystal X-ray data: space group Pmmn, Z=2; a=1.24210(6), b=0.40797(2), c=0.96436(5) nm, R_F=0.037 (R_w=0.044); 596 independent reflections; 53 variable parameters. It is a new structure type, which belongs to the family of BaAl₄-related structures. The magnetic properties are as follows: La₃Ni₇As₅ is a Pauli-type paramagnet above 4.2 K, Pr₃Ni₇As₅ remains paramagnetic in the temperature range investigated and Nd₃Ni₇As₅ undergoes a ferromagnetic ordering at T_C=24 K. Sm₃Ni₇As₅ orders antiferromagnetically at a Néel temperature of T_N=18 K followed by a spin flip towards parallel spin-alignment below T_C=6 K. Ce₃Ni₇As₅ reveals a strong deflection of the linear temperature dependence of the inverse susceptibility due to an intermediate valence behavior. The temperature dependence of the electrical resistivities for the La, Pr, Nd, Sm containing samples corroborates with the metallic state of the non-magnetic (La) and the magnetically ordered compounds, whereas in case of Ce₃Ni₇As₅ the resistivity seems to be determined by an interplay of Kondo scattering and crystalline field effects. L_III X-ray absorption spectra confirm the demagnetization effects owing from valence fluctuations, the actual valence thereby changes from ν=3.10-3.14 at room temperature and 10 K, respectively.     

Temperature and concentration dependent electrical resistivity of Ho1−xTixCo2–hydrogen system

The structure and electrical resistivity of Ho_1−xTi_xCo₂–hydrides (x = 0.1–0.6) have been determined through the powder X-ray diffraction (XRD) and temperature dependence of electrical resistivity (ρ(T)) at different hydrogen concentrations. The variations in the lattice parameters in different phase regions and the lattice expansion with respect to the hydrogen concentration have been studied. The temperature dependent electrical resistivity of hydrides has been discussed based on the conduction electron scattering and spin fluctuation scattering mechanisms. The changes in ρ(T) upon Ti substitution and increasing concentration of hydrogen have been discussed and the results have been correlated with their structural properties.     

On the structural and magnetic properties of the ternary silicides Ce6M1.67Si3 (M=Co, Ni) and Ce5Ni1.85Si3

Contrary to that reported previously, the ternary silicide “Ce₆Ni₂Si₃” does not exist. The melting of this alloy, followed or not by annealing, leads to the existence of the two new ternary compounds, Ce₆Ni_1.67Si₃ and Ce₅Ni_1.85Si₃. The investigation of these ternary silicides based on nickel and Ce₆Co_1.67Si₃ by X-ray diffraction on single crystal reveals an ordered distribution between Ni (or Co) and Si atoms. The nickel or cobalt positions in the chains of face-shared octahedra of cerium are not fully occupied with a strong delocalisation of their electron density. The structural investigations of these compounds confirm that the “Ce₆Ni₂Si₃” and “Ce₅Ni₂Si₃” structural type have to be rewritten as Ce₆Ni_2−xSi₃ and Ce₅Ni_2−xSi₃. Magnetisation and specific heat measurements evidence a magnetic ordering at 3.8(2) K for Ce₆Ni_1.67Si₃ and a heavy fermion behaviour for Ce₆Co_1.67Si₃.     

On the structural and magnetoelectrical characterization of epitaxial SrRuO3 thin films grown on (001) SrTiO3 substrates

High-quality epitaxial thin films of the ferromagnetic metallic oxide SrRuO₃ (SRO) were fabricated by dc-sputtering at high oxygen pressure and their structural and magnetoelectrical properties were carefully studied. The films featured a Curie temperature T_C ～ 160 K and a magnetic moment of ～0.7 μ_B per Ru ion. The temperature dependent magnetization could be well described by the scaling relation M(T) ∝ (T_C ? T)^β with a critical exponent β = 0.53 over the entire ferromagnetic temperature range. A negative magnetoresistance, MR, on the order of a few percent was found up to room temperature. MR showed a maximum of ～4% right at T_C where a kink structure of the resistivity, ρ, at zero field was flattened out on magnetic field application. This ρ contribution could be related to scattering due to orientational disorder of the Ru magnetic moments which become aligned by an external magnetic field. In addition, an equally strong MR effect, related to localization phenomena, could be observed at lower temperature. Particularly, the second MR peak at ～35 K might be related to a Fermi-liquid to non-Fermi-liquid crossover. A scaling behavior dρ/dT ∝ |T ? T_C|^α was observed only above T_C. Here, values for the exponent α ≈ ?0.4 and α ≈ ?1.4 were obtained in zero field and in a field of 9 T, respectively. The commonly observed ρ minimum, appearing at low temperatures (～3 K in the present case), is correlated with the structural disorder of the SRO films and is believed to have its origin in quantum corrections to the conductivity (QCC).     

Physical properties of binary cerium gallides and ternary cerium-germanium gallides

Binary and ternary cerium-gallium germanides have been synthesized by arc melting and the existence of five binary cerium-gallium compounds and four ternary phases Ce₂Ge_5.4Ga_1.6, Ce₄Ge₇Ga₄, CeGeGa and Ce₅GeGa₂ has been confirmed from X-ray powder diffraction analysis. Low temperature magnetization and electrical resistivity data in the temperature range from 2 to 300 K reveal the absence of magnetic ordering except for CeGa, which was found to be antiferromagnetic below T_N = 7 K. Effective paramagnetic moments in all cases are close to a tripositive behaviour of cerium with a small tendency for the effective moments in the binary cerium gallides to move towards smaller values when the gallium content decreases in close correspondence with the interatomic cerium distances.     

(p, ρ, T) properties and apparent molar volumes Vϕ of CaCl2 in methanol at T = (298.15 to 398.15) K and pressure up to 40 MPa

The (p, ρ, T) properties and apparent molar volumes V_ϕ of CaCl₂ in methanol at T = (298.15 to 398.15) K, at pressures up to 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T) values were described by an equation of state. The experiments were carried out at m = (0.10819, 0.28529, 0.65879 and 2.39344) mol · kg⁻¹ of calcium chloride.     

Deposition and investigation of lanthanum-cerium hexaboride thin films

Thin films of lanthanum-cerium hexaboride, the promising thermoelectric material for low-temperature applications, are deposited on various substrates by the electron-beam evaporation, pulsed laser deposition and magnetron sputtering. The influence of the deposition conditions on the films X-ray characteristics, composition, microstructure and physical properties, such as the resistivity and Seebeck coefficient, is studied. The preferred (100) orientation of all films is obtained from XRD traces. In the range of 780-800 °C deposition temperature the highest intensity of diffractions peaks and the highest degree of the preferred orientation are observed. The temperature dependence of the resistivity and the Seebeck coefficient of films are investigated in the temperature range of 4-300 K. The features appropriate to Kondo effect in the dependences ρ(T) and S(T) are detected at temperatures below 20 K. Interplay between the value of the Seebeck coefficient, metallic parameters and Kondo scattering of investigated films is discussed.     

A new method to calculate the thermodynamical properties of liquids from accurate speed-of-sound measurements

In this work, a new method for the determination of the thermodynamical properties of fluids, based on experimental speed-of-sound measurements, is described. This method consists in the solution of recursive equations (REM, Recursive Equations Method) for the determination of the density ρ(p,T) and specific heat capacity at constant pressure c_p(p,T), using the initial values of density ρ(p₀,T) and isobaric specific heat capacity c_p(p₀,T) known at a reference pressure p₀, as a function of the temperature, if the speed-of-sound function, u(p,T), is known, at least over a certain temperature and pressure range. A complete uncertainty analysis has also been developed. As an example of the good performances of this analysis method, firstly density and isobaric specific heat capacity have been calculated for water and the results have been compared with those predicted by the International Association for the Properties of Water and Steam 95 Formulation (IAPWS-95), as delivered by Wagner and Pruss. One more application has been made starting from experimental speed-of-sound values in pure acetone. These results have been compared with those calculated by the most advanced numerical integration methods and with the prevision of the dedicated NIST equation of state (EoS) by Lemmon and Span.     

Thermophysical properties of 1-butyl-4-methylpyridinium tetrafluoroborate

Thermophysical properties, {(p, ρ, T) at T = (283.15 to 393.15) K, pressures up to p = 100 MPa, and viscosity at T = (283.15 to 373.15) K and p = 0.101 MPa}, of 1-butyl-4-methylpyridinium tetrafluoroborate [b4mpy][BF₄] are reported. The measurements were carried out with a recently constructed Anton-Paar DMA HPM vibration-tube densimeter and a fully automated SVM 3000 Anton-Paar rotational Stabinger viscometer. The vibration-tube densimeter was calibrated using double-distilled water, methanol, toluene, and aqueous NaCl solutions.An empirical equation of state for fitting of the (p, ρ, T) data of [b4mpy][BF₄] has been developed as a function of pressure and temperature to calculate the thermal properties of the ionic liquid (IL), such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, and internal pressure. Internal pressure and the temperature coefficient of internal pressure data were used to make conclusions on the molecular characteristics of the IL.     

(p, ρ, T) properties, and apparent molar volumes V? of ZnBr2 in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa

The (p, ρ, T) properties of pure methanol, the (p, ρ, T) properties and apparent molar volumes V_? of ZnBr₂ in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T, m) values were described by an equation of state. For the solutions the experiments were carried out at molalities m = (0.05772, 0.37852, 0.71585 and 1.95061) mol · kg⁻¹ of zinc bromide.     

Superconductivity and magnetism in LuRh1.2Sn4.0

The electrical resistivity, magnetoresistance and upper critical field of single-crystal LuRh_1.2Sn_4.0 have been studied. A superconducting transition temperature T_c = 4.1K was observed and the critical-field slope near T_c was found to be 17kOeK⁻¹. The most remarkable observation was a logarithmic decrease in the resistivity with increasing temperature and a minimum at 210 K as in the case of dense Kondo materials. Our low temperature resistivity and magnetoresistance data suggested a weak itinerant antiferromagnetic ordering below 5.2 K.     

New (p, ρ, T) data for carbon dioxide – Nitrogen mixtures from (250 to 400) K at pressures up to 20 MPa

Comprehensive (p, ρ, T) measurements on two binary mixtures (0.10 CO₂ + 0.90 N₂ and 0.15 CO₂ + 0.85 N₂) were carried out in the gas phase at seven isotherms between (250 and 400) K and pressures up to 20 MPa using a single sinker densimeter with magnetic suspension coupling. A total of 69 (p, ρ, T) data for the first mixture and 69 (p, ρ, T) data for the second are presented in this article. The uncertainty in density was estimated to be (0.02 to 0.15)%, while the uncertainty in temperature was 3.9 mK and the uncertainty in pressure was less than 0.015% (coverage factor k = 2). Experimental results were compared with densities calculated from the GERG equation of state and with data reported by other authors for similar mixtures. Results yielded that, while deviations between experimental data and values calculated from the GERG equation were lower than 0.05% in density for low pressures, the relative error at high pressures and low temperatures increased to about (0.2 to 0.3)%. The main aim of this work was to contribute to an accurate density data base for CO₂/N₂ mixtures and to check or improve equations of state existing for these binary mixtures.     

Critical parameters for propane determined by the image analysis

The (p, ρ, T) measurements and visual observations of the meniscus for propane were carried out carefully in the critical region over the range of temperatures: ?60 mK ? (T ? T_c) ?  40 mK and of densities: ?4 kg · m^?3 ? (ρ ? ρ_c) ? 6 kg · m^?3 by a metal-bellows volumometer with an optical cell. Vapour pressures were also measured at T = (320.000, 343.132, 369.000, and 369.625) K. The critical point of T_c, ρ_c, and p_c was determined by the image analysis of the critical opalescence. Comparisons of the critical parameters with values given in the literature are presented.     

Metamagnetism in DyBaCo2O5+x, x≈0.5

The temperature dependence of the paramagnetic susceptibility χ_m(T) taken in 2500 Oe, the resistivity ρ(T), and the thermoelectric power α(T) of DyBaCo₂O_5+x, which has Ba and Dy ordered into alternate (001) planes of an oxygen-deficient perovskite, have revealed a phase segregation in the compositional range 0.3?x<0.5. Orthorhombic DyBaCo₂O_5.51 has, in addition, oxygen vacancies ordered into alternate rows of the DyO_0.51 (001) planes; a cold-pressed polycrystalline sample exhibits a first-order insulator-metal transition at T_IM=320 K, a Curie temperature T_C=300 K, and a broadened metamagnetic transition temperature T_M≈265 K in 2500 Oe. A ferromagnetic M-H hysteresis curve fails to saturate at 5 T, and a minority ferromagnetic phase below T_M has a volume fraction that decreases with decreasing temperature, vanishing below 50 K. Oxygen vacancies in the DyBaCo₂O_5.5 phase suppress the metallic state; interstitial oxygen does not. A thermoelectric power α(T)>0 of DyBaCo₂O_5.51 changing continuously across T_IM is interpreted to manifest a metallic minority phase crossing a percolation threshold; α(T) also provides evidence for a progressive excitation of higher-spin Co(III) with increasing temperature from below 50 K to above T_IM. A previous model of the RBaCo₂O_5.5 phase is extended to account for the Ising spin configuration below T_C, the magnetic order in the presence of higher-spin octahedral-site Co(III), and the α(T) data.     

On the magnetic structure of DyNiO3

The crystallographic structure of DyNiO₃ has been investigated at T=200, 100, and 2 K from high-resolution neutron powder diffraction (NPD) data. We show that the structure is monoclinic, space group P2₁/n, from the metal-insulator transition temperature at T_MI=564 K down to 2 K. The Ni atoms occupy two different sites 2d (Ni1) and 2c (Ni2), whose valences, estimated from bond-valence consideration, are +2.43(1) and +3.44(1) at 2 K, respectively. This is interpreted as the result of a partial charge disproportionation of the type 2Ni³⁺→Ni1^(3−δ)++Ni2^(3+δ)+, with δ≈0.55 at T=2 K. The magnetic structure has been studied from a NPD pattern at T=2 K, well below the establishment of the antiferromagnetic (AFM) ordering at T_N=154 K, as well as from sequential data collected from 16 K down to 2 K. The magnetic order is defined by the propagation vector k=(1/2,0,1/2). Two possible magnetic structures are compatible with the magnetic intensities. In the second solution both Ni sublattices participate in the magnetic order, as well as Dy since it corresponds to a total disproportionation of Ni³⁺ to Ni²⁺ and Ni⁴⁺. In the second solution both Ni sublattices participate in the magnetic order, as well as Dy. The magnetic moments for Ni1 and Ni2 atoms at T=2 K are 1.8 (2) and 0.8 (2) μ_B, respectively. These values are also compatible with a partial charge disproportionation. Dy³⁺ ions exhibit long-range magnetic ordering below 8 K. An abrupt contraction of the unit-cell volume is observed at this temperature, due to a magnetoelastic coupling. The magnetic moment for Dy³⁺ at T=2 K is 7.87 (6) μ_B.