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Rare-earth iron oxides of the form RFe2O4 (R = Y, Ho–Lu) show a new mechanism of ferroelectricity owing to the charge ordering of Fe ions below ∼330 K. To determine the physical properties of this system, the magnetic and dielectric properties of HoFe2O4 and R1-xR'xFe2O4 were investigated (R, R': rare earths). All the materials showed dielectric constants of ∼1000–10000, as reported for some other RFe2O4 oxides. For HoFe2O4, magnetic ordering occurred at a temperature lower than those of RFe2O4 reported thus far. On the other hand, the dielectric measurements of this material suggested the development of a correlation between polar regions at higher temperatures, which was also observed for the Sc-substituted system Lu1-xScxFe2O4. These results encourage detailed investigations of these materials from the viewpoints of both fundamental and applied sciences, and suggest the existence of other new properties of RFe2O4. [ABSTRACT FROM AUTHOR]

Abstract: It was found that the manganese perovskite oxides Ln 0.5Ca0.5MnO3 (Ln=Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn–O–Mn angles were calculated to be ∼148–150°, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism of Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln 3+ and Ca2+, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu0.5Ca0.5MnO3 containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu3+ and Ca2+. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system. [Copyright &y& Elsevier]

The magnetocapacitance effect was investigated using impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below TFerri ~ 240 K under the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of the dielectric property related to the motion of the nanosized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe2O4. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic and dielectric properties of perovskite manganites R 0.5Sr0.5MnO3 (R =Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T g ∼40K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R 3+ and Sr3+ settled randomly at the same crystallographic site. Dielectric constants for each material were ∼1000–10,000 between ∼50 and ∼300K and showed broad maximums above T g. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan δ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons. [ABSTRACT FROM AUTHOR]

Abstract: O2 gas sensing behaviors are studied in picene thin film field-effect transistors (FETs) with hydrophobic polymer (Cytop™ or polystyrene) coated SiO2 gate dielectrics. Picene thin film FETs show a rapid reduction of hysteresis in transfer curves recorded in forward and reverse measurement modes, compared to a picene FET with hexamethydisilazane-coated SiO2. The picene FETs show very sensitive O2 gas sensing effects down to ∼10ppm. A quantitative analysis is presented of the gate voltage (V G) dependent mobility induced by O2 exposure, i.e., the suppression of drain current at high V G. [Copyright &y& Elsevier]

Abstract: C60 and picene thin film field-effect transistors (FETs) in bottom contact structure have been fabricated with poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes for a realization of mechanical flexible organic FETs. The C60 thin film FETs showed n-channel enhancement-type characteristics with the field-effect mobility μ value of 0.41cm2 V−1 s−1, while the picene thin film FET showed p-channel enhancement-type characteristics with the μ of 0.61cm2 V−1 s−1. The μ values recorded for C60 and picene thin film FETs are comparable to those for C60 and picene thin film FETs with Au electrodes. [Copyright &y& Elsevier]

A graphite-like material boron carbide (BC x ) was synthesized under various heat treatment conditions and extensively characterized. First, we synthesized the BC x precursor phase by a single-step reaction using a mixed solution of BBr 3 and C 6 H 6 . We confirmed that the precursor phase had a graphite-like structure with B-C chemical bonds, but its crystallinity was poor. To improve their crystallinity, we annealed the precursor sample at high temperature using a high-frequency furnace and determined the annealing condition. We also investigated the magnetic properties of BC x . The high-temperature annealing for the precursor phase yields the highest Pauli paramagnetic susceptibility χ Pauli , indicating the highest density of states at the Fermi level. Accordingly, the high-temperature treatment for the precursor phase is significant to improve its crystallinity and physical properties. In addition, we synthesized a Ti-intercalated material TiBC by using the same procedure as that for making the BC x precursor phase. The crystal structure can be indexed by the AlB 2 structure, indicating that Ti atoms are intercalated between the BC layers. The χ Pauli value of TiBC is obtained to be 1 order of magnitude smaller than that of BC x , suggesting the compensation of hole carriers by electron doping through Ti intercalation into the BC x system.