M. Tamura

Reexamination of angle dependent magnetoresistance oscillationin θ-(BEDT-TTF)2I3

Abstract It is found that the angle-dependent magnetoresistance oscillation in θ-(BEDT-TTF) 2 I 3 consists of the short-period oscillation and the long-period one. They are attributed to the magnetic breakdown orbit and the closed orbit at the Brillouin zone boundary, respectively.

Fermi surface and absence of additional mass enhancement near the insulating phase in (DMe-DCNQI)2Cu

Abstract The de Haas - van Alphen measurements of the deuterated molecular conductor (DMe-DCNQI) 2 Cu have been carried out to investigate the Fermi surface and the possibility of the mass enhancement of the conduction electrons near the insulating phase. The Fermi surfaces and the cyclotron masses of the deuterated samples which show the drastic metal - insulator - metal transition are found to be the same as those of the undeuterated sample. The fact shows that the additional mass enhancement due to many body effects is absent near the insulating phase.

Ferromagnetic resonance and nonlinear absorption in p-NPNN

Summary form only given. The FMR(Ferromagnetic Resonance) measurements have been performed on /spl beta/-phase p-NPNN(nitrophenyl nitronyl nitroxide) ferromagnetic below 0.6 K. We used an X-band resonance apparatus which can be used down to 0.5 K. We observed clear magnetostatic modes and non-linear line shapes for the as grown samples at the lowest temperature. We have also observed the effect known as the foldover effect. We should be careful about the demagnetization effect when the magnetization is large, therefore we performed the FMR measurement using nearly spherically shaped samples. We studied the temperature dependences of g-factor below 1.3 K, and found the intrinsically anisotropic behavior. This may be due to the anisotropy field along the crystal b-axis, which is consistent with the result reported by L.P. Le et at. using the /spl mu/SR measurement.

Magnetic properties of DCNQI salts studied using μSR

Abstract Examples from the (R 1 ,R 2 -DCNQI) 2 X family of molecular conductors have been studied using μSR in order to provide information about the microscopic magnetic properties of the various phases. For the fully deuterated dimethyl Cu salt (d 8 -DMe-Cu) there is a metalinsulator (MI) transition around 80 K and a magnetic transition around 7 K. The muon spin relaxation rate becomes enhanced in the region of the MI transition and below, reflecting the quenching of valence fluctuations and the appearance of localised spins on the Cu sites. A zero field precession signal develops below 7 K as a result of the 3D magnetic ordering of the Cu spins; the field distribution derived from the precession frequency is consistent with the proposed magnetic structure. In addition to the zero field studies, nuclear quadrupolar level crossing resonance between the muon and the imine nitrogen of the DCNQI has been used to study the temperature dependence of the electronic state of the molecular conductor.

The Shubnikov-de Haas oscillations and a small closed orbit in θ-(BEDT-TTF)2I3

Abstract The Shubnikov-de Haas (SdH) experiments on an organic conductor θ-(BEDT-TTF) 2 I 3 have been carried out. In addition to the two SdH frequency branches due to the quasi two-dimensional Fermi surfaces, new branches due to small three-dimensional Fermi surfaces are found.

Magnetic properties of DCNQI-Cu systems

Abstract Recent advances in the study of magnetic properties of a series of molecular conductors, Cu salts of DCNQIs, are presented. First, the antiferromagnetic order of Cu spins in the insulating phases below about 10 K is found to be accompanied by weak ferromagnetism with the spontaneous moment perpendicular to the tetragonal c -axis. Second, our susceptibility study of the metal-insulator-metal (M-I-M) reentrant system, (DMe-DCNQI-α,α′- d 2 ) 2 Cu, has lead to the absence of many-body enhancement of the susceptibility in the low temperature metallic phase. Finally, (DI-DCNQI) 2 Cu is found to exhibit considerably enhanced and temperature dependent susceptibility, suggesting the effect of spin fluctuation in the metallic state.

Charge transfer and reentrant phenomenon in deuterated (DMe-DCNQI)/sub 2/Cu

Abstract Li-doping in Cu salt of deuterated DMe-DCNQI- d 7 system has shown drastic effects on physical properties. Undoped (DMe-DCNQI- d 7 ) 2 Cu exhibits a first-order metal-insulator (M-I) transition at 80K, and the Li salt, which is isostructural with the Cu salt, is a one-dimensional (1D) conductor. A small amount of Li-doping suppresses the M-I transition. The M-I-M (reentrant) transition which is similar to that in selectively deuterated (DMe-DCNQI) 2 Cu appears in a narrow region of Li contents x . The x — T phase diagram under ambient pressure well reproduces P - T phase diagram of (DMe-DCNQI) 2 Cu system. Based on these results, an importance of the degree of charge transfer is described.

Deuterium freedom and M-I transition in (DMe-DCNQI)2Cu system

Abstract We have discovered that orientation freedom in a deuterated methyl group introduces two kinds of anomalous specific heat on the deuterated (DMe-DCNQI) 2 Cu system. In systems containing methyl groups with one deuterium atom (CH 2 D), we find the Schottky type of specific heat. In systems with CHD 2 , we observe peaks not of the Schottky type. To find out the origin and mechanism of these anomalies, we carried out the thermal study on the mixed crystals. We clarified the possibility of the order–disorder transition of CHD 2 orientation along the c -axis.

Anomalous specific heat of (DMe-DCNQI d2[1,1;0]1−xd4[2,2;0]x)2Cu-system

A (DMe-DCNQI) 2 Cu crystal composed of molecules having deuterated methyl groups (CH 2 D) shows a typical Schottky type specific heat It is caused by orientation degree of freedom of CH 2 D. The system that has methyl groups with two deuterium atoms (CHD 2 ), on the other hand, shows a specific heat that apparently differs from the Schottky type. Based on the thermal measurement on the mixed crystals, we propose a possible mechanism of the anomalous specific heat in the CHD 2 system.