Yusei Maruyama

Possible competition of superconductivity and ferromagnetism in CexC60 compounds

Abstract Solid-phase reaction of cerium and C 60 powders under 600xa0°C may yield unusual magnetic materials which involve fairly strong dia- and ferro-magnetism at almost similar low temperature range, below 13.5xa0K. The temperature dependence of the electrical resistivity of this material may indicate that the diamagnetism is due to the superconductivity and there are possible interplays between the superconductivity and the ferromagnetism in this material.

Moussbauer Spectroscopic Study of the Reentrant Phase Transitions in TBA[Fe(tdas)2]

Abstract Temperature dependence of 57Fe Mossbauer spectra for TBA[Fe(tdas)2] is measured to obtain the information on the spin state and the phase transitions. The large quadrupole splitting due to the S = 3/2 spin state increases reenteringly in the intermediate temperature region (190–230 K on cooling and 200–240 K on heating). The small increase in the quadrupole splitting and the continuous decrease in the isomer shift suggests the 3/2 spin state does not change, supporting the interpretation of the magnetic susceptibility.

Structures and magnetic properties of high-temperature reaction products of cerium metal and C60 solid

Abstract Structures and magnetic properties of high temperature reaction products of Ce metal and C60 solid have been investigated by means of X-ray diffraction and SQUID magnetometory. The X-ray diffraction patterns of relatively low temperature products show that they seem to undergo metal–ion-intercalation to C60 crystals. Unusual behaviors in the temperature dependence of the magnetization of the products have revealed the coexistence or competition of the ferromagnetic and diamagnetic (superconducting) natures occurrence of which depends on the reaction temperatures and times.

Characterization by Stm and Electrical Conductivity of Single-Walled Carbon Nanotubes

Abstract Single-walled carbon nanotubes (SWCNT) prepared by a DC-Arc-Discharge and purified by a hydrothermal treatment followed by several steps of procedures including heating, burning, extracting and acid-washing are investigated by a conventional STM technique morphologically and spectroscopically. The electical resistivities of compacted pellets (mats) of SWCNT are measured as a function of temperature in the range from the room-temperature to 1.5K. The behaviors seems to be essentially originated in the metallic nature of individual SWCNT.

Competition of superconductivity and ferromagnetism in CexC60 compounds

High temperature-treated compounds of mixed powders of cerium metal and C 60 solid show fairly strong diamagnetic signal in the zero-field-cooling process and distinct ferromagnetic behavior in the field-cooling path below 13.5K and 15K, respectively. In the resistivity measurement of a compacted and long-term heated pellet of the powder a distinct drop of the resistivity with decreasing temperature is recognized around 20K, which is followed by a steep rise of the resistivity below 14K. These findings indicate an existing competition of superconductivity and ferromagnetism in this compound.

Structure and Electronic Property of C60 and RbxC60 Thin Films Analyzed by STM/STS Technique

Scanning tunneling microscopy (STM) studies for C60 crystalline thin films at low temperatures have revealed the orientation ordering of C60 molecules in the C60 crystal at low temperatures. In the rubidium-doped C60 films, the results of a spatially resolved scanning tunneling spectroscopy (STS) study have clearly indicated the possible hybridization of the wave functions of rubidium ions with those of C60 molecules, which causes the metallic nature of the compound.

Scanning tunneling spectroscopic characterization of single walled carbon nanotubes in bundles

Single walled carbon nanotubes (SWCNTs) prepared by a contact-arc-discharge followed by a hydrothermal purification are analyzed in the mat-form samples with the use of UHV scanning tunneling microscopy and spectroscopy (STM/STS). The characteristic electronic states of individual tubes in a bundle are found to be specified to the bundle.

Annealing effect for LaxC60 thin films

Numerous studies on metal-doped C 60 compounds had been done since the discovery of superconducting C 60 compounds. It is interesting to study physical properties of trivalent-meta-doped C 60 . We examined La-doped C 60 thin films fabricated by layer-by-layer ( LBL) deposition with a multi-source evaporation system. The physical properties of La x C 60 depend on the diffusion of La atoms in the film, so we studied the effect of annealing. The crystal structure and morphology of La x C 60 thin films were examined by X-ray diffraction and AFM and electronic structure was also examined by UPS. We found that annealing promotes orientation of the crystal. UPS spectra showed the change depends on the concentration of La atoms. Moreover, the spectrum of annealed thin film was quite different from that of as-deposited thin film.

Preparation and characterization of LaxC60 thin films fabricated by layer-by-layer deposition

Abstract A modification of physical properties of solid-state C60 when La was doped to C60 thin film as a trivalent metal was examined. the thin film was fabricated by using Layer-by-Layer deposition technique with the multi-sources evaporation system. We found that the C60 film changes its electrical character from the insulator to the semiconductor rapidly upon La doping. the temperature dependence of the electrical conductivity is semiconductive with the activation energy of about 0.3eV.

Recent studies on electrical and magnetic properties of molecular solids

Recent progress in studies on electrical and magnetic properties of some typical molecular solids is described, focussing on research in Japan. Especially we focus on two recent topics, organic semiconductor BTQBT and organic superconductors. Two types of compound are discussed, (BEDT-TTF)2Cu(NCS)2 and M3C60 (M = K or Rb). Finally, two kinds of molecular ferromagnet, nitronyl nitroxide radicals and C60(TDAE), are briefly introduced.