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We have studied transport properties of composite oxides composed of ferrimagnetic conductor Fe 3 O 4 (magnetite) and insulating α -Fe 2 O 3 (hematite) at room temperature. High-density composite oxides with different Fe 3 O 4 /Fe 2 O 3 ratios were successfully synthesized by melting Fe 2 O 3 rods at high temperatures in ambient atmosphere. Transport properties of Fe 3 O 4 -Fe 2 O 3 composites were measured and compared with that of Fe 3 O 4 single crystals. As the ratio of the insulating Fe 2 O 3 concentration to the conductive Fe 3 O 4 one increases, the longitudinal resistivity increases exponentially, while the Seebeck coefficient decreases linearly. The contrasting dependences of electric and thermoelectric transports on the insulating Fe 2 O 3 concentration indicate that the thermoelectric transport is less susceptible to disorder effects than electric ones. The measurement of the Hall effect shows that the anomalous Hall effect due to the ferrimagnetic Fe 3 O 4 phase is clearly observed in the composite oxides. In line with the resistivity increase with the Fe 2 O 3 concentration, the anomalous Hall resistivity increases, following the universal scaling relation established in the dirty limit. The anomalous Nernst effect due to the Fe 3 O 4 phase is also observed in the composite oxides. The anomalous Nernst coefficient decreases with increasing Fe 2 O 3 concentration, and the decrease is found to be related to the anomalous Hall effect through the Mott relation. [ABSTRACT FROM AUTHOR]

Phase transitions of quantum dimer magnets can be explained in terms of Bose-Einstein condensation of magnons. Here we consider a natural extension of the dimer magnets to SU(4)-symmetric tetramer systems, which could be created with four nuclear-spin components (named "u," "d," "c," and "s") of 173Yb atoms in optical superlattices. We apply the cluster mean-field approximation to the SU(4) Heisenberg model on a tetramerized square lattice, and study the phase transition phenomena in the presence of the field that creates a population imbalance between the two components u , d and the other two c , s . When the population of the four components is balanced, the ground state is approximately given by the direct product of local SU(4)-singlet states. When the field is applied, the population ratio of the components u and d is increased and the system eventually reaches a "saturated" state, which is a SU(2) system with only u and d. We show that in the saturation process, the system exhibits two successive step-like transitions, in contrast to the standard dimer magnets with continuous transition process associated with Bose-Einstein condensation of magnons. The intermediate phase in between the two step-like transitions is a nontrivial solid phase with alternating arrangement of the SU(4)-singlet and four-site resonating-valence-bond states. [ABSTRACT FROM AUTHOR]

We investigate the relation between the morphology and thermoelectric properties of iodine-doped pentacene thin films grown on the glass substrate. The electrical conductivity and thermoelectric power factor are enhanced with decreasing the film thickness and growth temperature due to the volumetric increase in the thin film phase relative to the bulk phase in the film. The 115 and 190 nm thin films grown at room temperature, whose majority phase is the thin film phase, exhibit high power factor of 1.3×10-5 W m-1 K-2. Also, we demonstrate an improved stability of thermoelectric properties by covering the iodine-doped film with a polyimide tape. [ABSTRACT FROM AUTHOR]

Atomic force microscopy has enabled imaging at the sub-molecular level, and 3D mapping of the tip-surface potential field. However, fast identification of the surface still remains a challenging topic for the microscope to enjoy widespread use as a tool with chemical contrast. In this paper, as a step towards implementation of such function, we introduce a control scheme and mathematical treatment of the acquired data that enable retrieval of essential information characterizing this potential field, leading to fast acquisition of images with chemical contrast. The control scheme is based on the tip sample distance modulation at an angular frequency ω, and null-control of the ω component of the measured self-excitation frequency of the oscillator. It is demonstrated that this control is robust, and that effective Morse Parameters that give satisfactory curve fit to the measured frequency shift can be calculated at rates comparable to the scan. Atomic features with similar topography were distinguished by differences in these parameters. The decay length parameter was resolved with a resolution of 10 pm. The method was demonstrated on quenched silicon at a scan rate comparable to conventional imaging. [ABSTRACT FROM AUTHOR]

In studying large molecular systems, insights can better be extracted by selecting a limited number of physical quantities for analysis rather than treating every atomic coordinate in detail. Some information may, however, be lost by projecting the total system onto a small number of coordinates. For such problems, the generalized Langevin equation (GLE) is shown to provide a useful framework to examine the interaction between the observed variables and their environment. Starting with the GLE obtained from the time series of the observed quantity, we perform a transformation to introduce a set of variables that describe dynamical modes existing in the environment. The introduced variables are shown to effectively recover the essential information of the total system that appeared to be lost by the projection.

We show specific heat data for Na4C60 and Li4C60 in the range 0.4-350 K for samples characterized by Raman spectroscopy and X-ray diffraction. At high temperatures, the two different polymer structures have very similar specific heats both in absolute values and in general trend. The specific heat data are compared with data for undoped polymeric and pristine C60. At high temperatures, a difference in specific heat between the intercalated and undoped C60 polymers of 100 J K(-1) mol(-1) is observed, in agreement with the Dulong-Petit law. At low temperatures, the specific heat data for Li4C60 and Na4C60 are modified by the stiffening of vibrational and librational molecular motion induced by the polymer bonds. The covalent twin bonds in Li4C60 affect these motions to a somewhat higher degree than the single intermolecular bonds in Na4C60. Below 1 K, the specific heats of both materials become linear in temperature, as expected from the effective dimensionality of the structure. The contribution to the total specific heat from the inserted metal ions can be well described by Einstein functions with TE = 386 K for Li4C60 and TE = 120 K for Na4C60, but for both materials we also observe a Schottky-type contribution corresponding to a first approximation to a two-level system with ΔE = 9.3 meV for Li4C60 and 3.1 meV for Na4C60, probably associated with jumps between closely spaced energy levels inside "octahedral-type" ionic sites. Static magnetic fields up to 9 T had very small effects on the specific heat below 10 K.

The S1 state dynamics of methoxy methylcinnamate (MMC) has been investigated under supersonic jet-cooled conditions. The vibrationally resolved S1-S0 absorption spectrum was recorded by laser induced fluorescence and mass-resolved resonant two-photon ionization spectroscopy and separated into conformers by UV-UV hole-burning (UV-UV HB) spectroscopy. The S1 lifetime measurements revealed different dynamics of para-methoxy methylcinnamate from ortho-methoxy methylcinnamate and meta-methoxy methylcinnamate (hereafter, abbreviated as p-, o-, and m-MMCs, respectively). The lifetimes of o-MMC and m-MMC are on the nanosecond time scale and exhibit little tendency of excess energy dependence. On the other hand, p-MMC decays much faster and its lifetime is conformer and excess energy dependent. In addition, the p-MMC-H2O complex was studied to explore the effect of hydration on the S1 state dynamics of p-MMC, and it was found that the hydration significantly accelerates the nonradiative decay. Quantum chemical calculation was employed to search the major decay route from S1(ππ(∗)) for three MMCs and p-MMC-H2O in terms of (i) trans → cis isomerization and (ii) internal conversion to the (1)nπ(∗) state. In o-MMC and m-MMC, the large energy barrier is created for the nonradiative decay along (i) the double-bond twisting coordinate (∼1000 cm(-1)) in S1 as well as (ii) the linear interpolating internal coordinate (∼1000 cm(-1)) from S1 to (1)nπ(∗) states. The calculation on p-MMC decay dynamics suggests that both (i) and (ii) are available due to small energy barrier, i.e., 160 cm(-1) by the double-bond twisting and 390 cm(-1) by the potential energy crossing. The hydration of p-MMC raises the energy barrier of the IC route to the S1/(1)nπ(∗) conical intersection, convincing that the direct isomerization is more likely to occur.

Heat capacity of Cs2(18-crown-6)3[Ni(dmit)2]2 was measured by adiabatic calorimetry. A broad thermal anomaly was observed around 225 K. The entropy gain (about 52 J K(-1) mol(-1)) is much larger than that expected for twofold disordering of 18-crown-6 assumed in the previous structure analysis. The shape of thermal anomaly was qualitatively explained by a linear Ising model developed for cooperative disordering in polymers. The 18-crown-6 molecules forming a one-dimensional chain in the crystal are orientationally disordered with moderate cooperativity.