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The antiferromagnetic insulating ground state of the π–d molecular conductor λ-(BETS)2FeCl4 has been under intense debate for the last decades. One of the difficulties in studying this system comes...

ESR measurements of β-(BDA-TTP)2FeCl4 have been performed to investigate its magnetic properties. At room temperature, the angular dependence of the ESR linewidth shows the typical behavior of a one-dimensional magnetic system. The ESR line shape profiles also support this result. These results suggest that significant π-d interactions exist in the system. The angular dependence of ESR at several temperature ranges will be presented.

The detailed topology of the Fermi surface of the quasi-one-dimensional conductor (DMET)2I3 was investigated by the magnetooptical measurements. A pair of planar Fermi surface which has higher corrugations of Fourier components was observed. This result seems to suggest that the metallic state of this salt is stabilized by the higher corrugations of the Fermi surface.

Recently, advanced research into fine filament technology for tape-shaped superconducting-coated conductors composed of REBa2Cu3O7–δ (RE123, RE: rare earth such as Gd or Y, 0 < δ < 1) has been carried out to improve performance in high magnetic fields by reducing the large diamagnetism of the RE123 superconducting layer. The major challenge for high-field NMR/MRI applications is to obtain high tensile stress tolerance above 500 MPa with a high critical current. In this study, a RE123 multi-core superconductor was fabricated via an 'inner split' method using a commercially available RE123 single-core coated conductor, where only the ceramics (RE123 and buffer layers) in wire are electrically separated to multi-filaments without superconducting current flow between the filaments. Experimental results show that wires having 2, 3, 4, or 5 cores have a high critical current (above 95% of the original) and maintain tensile stress tolerance above 650 MPa. The diamagnetism of the five-core wire is reduced ~85% of the original at 7 T. Thus, the wire was optimized via inner split method for high-field use.

The quasi-two-dimensional molecular conductor $\ensuremath{\lambda}$-(BETS)${}_{2}$FeCl${}_{4}$, where BETS is bis(ethylenedithio)tetraselenafulvalene, shows a superconductivity in the high magnetic field environment. This is due to the compensation effect between the external field and the internal field created by the Fe${}^{3+}$ magnetic moment. Here, we report the simultaneous transport and electron spin resonance (ESR) measurements in the field-induced superconducting state down to 1.65 K. We find that the field-induced superconductivity is partially destroyed by ESR transitions, namely, by dynamical spin reversals of Fe${}^{3+}$. Moreover, it is found from our ESR results that the field-induced superconducting state is inhomogeneous, coexisting with the residual paramagnetic metal state.

Electron spin resonance reveals the spin behavior of conduction ($\ensuremath{\pi}$) and localized ($d$) electrons in $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}(\mathrm{BDA}\mathrm{\text{\ensuremath{-}}}\mathrm{TTP}{)}_{2}M{\mathrm{Cl}}_{4}$ ($M=\mathrm{Fe}$, Ga). Both the ${\mathrm{Ga}}^{3+}(S=0)$ and ${\mathrm{Fe}}^{3+}(S=5/2)$ compounds exhibit a metal-insulator transition at 113 K with the simultaneous formation of a spin-singlet ground state in the $\ensuremath{\pi}$ electron system of the donor molecules. The behavior is consistent with charge ordering in $\ensuremath{\beta}\mathrm{\text{\ensuremath{-}}}(\mathrm{BDA}\mathrm{\text{\ensuremath{-}}}\mathrm{TTP}{)}_{2}M{\mathrm{Cl}}_{4}$ at the metal-insulator transition. At 5 K, the ${\mathrm{Fe}}^{3+}$ compound orders antiferromagnetically, even though the $\ensuremath{\pi}$ electrons, which normally would facilitate magnetic exchange, are localized nonmagnetic singlets.

Magnetooptical measurements of a quasi-two-dimensional (q2D) organic conductor (BEDT-TTF)2Br(DIA) (DIA=diiodoacetylene) were performed using a cavity perturbation technique with a millimeter vector network analyzer (MVNA). Harmonic resonances were observed periodically as a function of the inverse field up to the 7th order. This is the first observation of higher-order harmonics up to the 7th order in an organic conductor. The observed resonance is assigned as a periodic orbit resonance (POR) which arises from a q2D elliptic Fermi surface (FS). The obtained effective mass (4.7me) is consistent with Shubnikov-de Haas measurements. Temperature dependence of the spectra observed in two different sample configurations will be presented., 7 pages, 5 figures, to be published in J. Phys. Soc. Jpn Vol. 71 No.4

A rotational resonant cavity equipped with a millimeter vector network analyzer (MVNA) and a 14 T solenoid type superconducting magnet has been developed. The available frequency range is about 50–100 GHz. The temperature can decrease to 1.5 K. The cavity can rotate within the precision of one degree. As an example of the application of the new resonant cavity, we have performed detailed magnetooptical measurements of an organic conductor to estimate the Fermi surface topology. The Fermi surface of the quasi-one-dimensional conductor (DMET)2I3 is discussed.