H. Uozaki

Magnetic torque of λ-(BETS)2FeCl4

Magnetic torque of λ-(BETS) 2 FeCl 4 is measured up to 15 T and down to 0.4 K. Clear first-order spin flop transition between the antiferromagnetic (AF) and the canted antiferromagnetic (CAF) phases is observed in the magnetic field of about 1.2 T and below 9.5 K. The AF easy axis is found to be in the direction tilted by about 30° from the c-axis to the b-axis, which is different from the previous reports on the easy axis (the c-axis). At the step-like transition with hysteresis around H = 10 T between CAF and the field induced ferromagnetic (F) (paramagnetic) phases, the direction of the magnetic easy axis changes. The two transitions on the H - T phase diagram are considered on the basis of the coupled two spin system; Fe 3+ (S = 5/2) and (BETS) 2 (S = 1/2).

Magnetization of (ET)2- and κ-(BETS)2-FeCl4

Both (ET)2FeCl4 and κ-(BETS)2FeCl4 have Fe3+ ions in the anion layer. The former is a semiconductor with an energy gap of 0.12 eV and the latter remains normal metallic down to below 0.5 K. Their magnetizations, which are very similar to each other, are scaled by the Brillouin function (S=5/2) modified by the effective temperature T* = T − Θ. The Weiss temperature Θ is estimated^to be −3 K and −1K for ET and BETS salts, respectively. Both systems are concluded to have the high spin states (S = 5/2) of Fe3+ ions which are antiferromagnetically interacting each other very weakly.

Electrical resistivity of κ-(BETS)2X (X=FeCl4, GaCl4)

We have measured the electrical resistivity ρ (0,5 K<T<300 K) of κ-type (BETS)2X (X=FeCl4, GaCl4) salts. Both salts which remain normal metallic show a similar behavior to each other: dρ/dT takes a minimum around 160–180 K, a maximum around 110 K and a kink around 20 K, and ρ = ρ0+AT+BT2 holds below 20 K. In contrast to λ-(BETS)2FeCl4, π-electrons in the κ-type counterpart seem to interact little with the localized 3d-electrons of Fe3+ (S=5/2).

Magnetic torque measurements on superconducting λ-(BETS)2GaCl4

Abstract The magnetic torque of a quasi two-dimensional superconductor λ-(BETS) 2 GaCl 4 ( T c =5.5 K) is measured at T >1.5 K and H

NMR evidence for antiferromagnetic spin fluctuations in superconducting λ-(BETS)2GaCl4

The microscopic magnetic properties of superconducting λ-(BETS) 2 GaCl 4 (T C ≅6 K) have been investigated by both 77 Se and 1 H NMR in the normal state. Both the Knight shifts and the linewidths of 77 Se NMR decrease significantly below 30 K, whereas 1/( 77 T 1 T) does not show any corresponding decrease down to 7.1 K. 1/( 1 T 1 T) of 1 H NMR, on the other hand, increases remarkably below 25 K. These results are explained consistently in terms of the development of antiferromagnetic spin fluctuations in π-electrons at low T.

A dielectric metal λ-(BEDT-TSF)2FeCl4

Abstract We report here on novel dielectric states and related properties revealed in low-frequency and microwave dynamical conductivity, specific heat, and proton nuclear magnetic resonance measurements on the highly metallic states and low-temperature antiferromagnetic insulating states in a π–d coupled λ-(BEDT-TSF) 2 FeCl 4 .

Deuteration effect in α-(h8-ET)2NH4Hg(SCN)4

Abstract We have synthesized differently isotope-labelled deuterated salts for the hydrogens of the terminal ethylene and /or the NH4+ ion. The magnetic susceptibility is measured by SQUID, using a piece of the single crystal each. We report on the Pauli paramagnetic spin susceptibility and Fermi surface parameters obtained by the Shubnikov-de Hass oscillations and the cyclotron resonance.

2D- and 1H-NMR in α-(h8-ET)2ND4Hg(SCN)4 and α-(d8-ET)2NH4Hg(SCN)4*

Abstract We have measured the temperature dependence of the spectrum and the spin-lattice relaxation time T1 by 2D nuclear-magneticresonance (NMR) for α-(h8-ET)2ND4Hg(SCN)4 and 1H-NMR for α-(d8-ET)2NH4Hg(SCN)4 in order to clarify the molecular dynamics of the non-centrosymmetric ND4+ and NH4+ ions. Both the systems show the peak in T1−1 around 40 K explained by Bloembergen-Purcell-Pound model, while the temperature dependence of the spectra were quite different.

Lattice parameters of α-(h8-ET)2NH4Hg(SCN)4 and α-(h8-ET)2ND4Hg(SCN)4

Abstract We have measured the temperature dependence of lattice parameters of the title salts from 300 down to 11 K by a four circle X-ray diffractometer. It is confirmed that the ND 2 Hg(SCN) 4 salt shows essentially the same anisotropic contraction of the c/a with the NH 4 Hg(SCN) 4 salt. The deuteration enhances the c/a ratio by 0.3 % at low temperatures.

Observations of acoustic de Haas-van Alphen effect in α-(ET)2NH4Hg(SCN)4

Abstract The acoustic de Haas-van Alphen (dHvA) effect is observed as a function of magnetic field for the longitudinal ultrasound frequency 53.4 MHz traveling along the b * direction in the quasi-two-dimensional superconductor α-(ET) 2 NH 4 Hg(SCN) 4 with T c ~ 1 K. From calculating the oscillatory amplitude with the use of the Kataoka and Goto formulations, the area coefficient relating to the electron-lattice coupling is estimated to be about 3.5. The dominant contribution comes from the multiband term corresponding to the inter-band charge transfer. The anomaly in the longitudinal velocity around 20 and 60 K is also described.