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Organic salts represent an ideal experimental playground for studying the interplay between magnetic and charge degrees of freedom, which has culminated in the discovery of several spin-liquid candidates such as $\ensuremath{\kappa}\text{\ensuremath{-}}(\mathrm{ET}{)}_{2}{\mathrm{Cu}}_{2}(\mathrm{CN}{)}_{3}$ ($\ensuremath{\kappa}\text{\ensuremath{-}}\mathrm{Cu}$). Recent theoretical studies indicate the possibility of chiral spin liquids stabilized by ring exchange, but the parent states with chiral magnetic order have not been observed in this material family. In this Letter, we discuss the properties of the recently synthesized $\ensuremath{\kappa}\text{\ensuremath{-}}(\mathrm{BETS}{)}_{2}\mathrm{Mn}[\mathrm{N}(\mathrm{CN}{)}_{2}{]}_{3}$ ($\ensuremath{\kappa}\text{\ensuremath{-}}\mathrm{Mn}$). Based on analysis of specific heat, magnetic torque, and NMR measurements combined with ab initio calculations, we identify a spin-vortex crystal order. These observations definitively confirm the importance of ring exchange in these materials and support the proposed chiral spin-liquid scenario for triangular lattice organics.

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2− and diamagnetic [ReO4]− anions have been synthesized: κ-(BDH-TTP)4ReF6 (1), κ-(BDH-TTP)4ReF6·4.8H2O (2) and pseudo-κ″-(BDH-TTP)3(ReO4)2 (3). The crystal and band structures, as well as the conducting properties of the salts, have been studied. The structures of the three salts are layered and characterized by alternating κ-(1, 2) and κ″-(3) type organic radical cation layers with inorganic anion sheets. Similar to other κ-salts, the conducting layers in the crystals of 1 and 2 are formed by BDH-TTP dimers. The partial population of positions of Re atoms and disorder in the anionic layers of 1–3 are their distinctive features. Compounds 1 and 2 show the metallic character of conductivity down to low temperatures, while 3 is a semiconductor. The ac susceptibility of crystals 1 was investigated in order to test the possible slow relaxation of magnetization associated with the [ReF6]2− anion., This research was funded by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2020-779). Work in Spain was supported by MICIU (through the Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Centre distinction and Grant PGC 2018-096955-B-C44), and by Generalitat de Catalunya (2017SGR1506).

We report the first highly conducting single-molecule magnet, (BEDO)4[ReF6]·6H2O [1; BEDO = bis(ethylenedioxo)tetrathiafulvalene], whose conductivity and single-molecule magnetism coexist in the same temperature range. The compound was synthesized by BEDO electrocrystallization in the presence of (Ph4P)2[ReF6]·2H2O and characterized by crystallography and measurements of the conductivity and alternating-current magnetic susceptibility.

A new metallic radical cation salt κ-(BETS)2Co0.13Mn0.87[N(CN)2]3, where BETS is bis(ethylenedithio)tetraselenafulvalene, C10S4Se4H8, has been synthesized. In this salt, a part of Mn2+ ions are replaced by Co2+ which acts as a magnetic dopant with a different effective magnetic moment. Crystal structure, band structure, conducting and magnetic properties of the salt have been studied. Below 30 K the material undergoes a metal-insulator transition, which is suppressed by applying a pressure of ~ 0.5 kbar, leading to a superconducting ground state. While the structural and conducting properties are very similar to those of the parent salt κ-(BETS)2Mn[N(CN)2]3, magnetic properties associated with localized moments in the anion layer are found to be surprisingly different., We thank Prof. A. Kobayashi for providing BETS used in the work. N.D.K. and E.B.Y. were supported by the RFBR grant No. 14-0300119 and by Program No. 2 of the Presidium of the Russian Academy of Sciences. N.D.K., O.M.V, W.B., and M.V.K. acknowledge support by the German Research Foundation (DFG) via the grant KA 1652/4-1. E.C. acknowledges support by MINECO (Spain) through Grant FIS2015-64886-C5-4-P, Generalitat de Catalunya (2014SGR301), and by the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2015-0496.

We present magnetoresistance studies of the quasi-two-dimensional organic conductor $\kappa$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, where BETS stands for bis\-(ethylene\-dithio)\-tetra\-selena\-fulvalene. Under a moderate pressure of 1.4\,kbar, required for stabilizing the metallic ground state, Shubnikov - de Haas oscillations, associated with a classical and a magnetic-breakdown cyclotron orbits on the cylindrical Fermi surface, have been found at fields above 10\,T. The effective cyclotron masses evaluated from the temperature dependence of the oscillation amplitudes reveal strong renormalization due to many-body interactions. The analysis of the relative strength of the oscillations corresponding to the different orbits and its dependence on magnetic field suggests an enhanced role of electron-electron interactions on flat parts of the Fermi surface., Comment: 6 pages, 4 figures

The electrochemical oxidation of bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of simple dicyanamide salts of rare-earth metals with the general formula M[N(CN)2]3 (M = Gd3+, Dy3+, and Ho3+) as electrolytes was studied for the first time. A novel radicalcаtion salt α-ЕТ2[С(NCN)2NH2] with the unexpected (2,1-dicyano)guanidine anion was synthesized. The crystal structure of the salt and its conducting properties were studied. The structure of the salt is layered with alternating conducting radical-cation and insulating anionic layers. The cationic layers of the α-type are formed by two crystallographically independent radical-cations of ET of various charges. The anionic layers are formed of [С(NCN)2NH2]– anions linked by hydrogen contacts into chains. The crystals of ЕТ2[С(NCN)2NH2] demonstrate a semiconducting character of conductivity in a temperature range of 300—100 K.

Electrocrystallization of bis(ethylenedithio)tetraselenafulvalene (BETS) and bis(ethylenedithio)tetrathiafulvalene (ET) in the presence of an electrolyte (Ph4P)[Cu(dca)]3⋅H2O [(dca) = N(CN)2] has been studied using different solvents. A new organic metal (BETS)2Cu(dca)3 (1), and the first radical cation salt with 3D dicyanamidocuprate anion, incorporating both diamagnetic Cu1+ and paramagnetic Cu2+atoms, (ET)2Cu1.8(dca)4 (2) have been obtained. Crystal structure, conducting properties of both salts, as well as the electronic structure of 2 and its structural analog (ET)2CuMn(dca)4 (3) were analysed. The salts 1 and 2 have layered structures. In contrast to the BETS radical cation salt 1, complex 2 is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. At ambient pressure, the resistance of the crystals 1 shows semimetal behaviour down to 30 K. Below 30 K, the resistance sharply increases and the sample becomes insulating. The application of a pressure of about 3 kbar suppresses the metal-insulator transition. The salt 2 undergoes a semiconductor I - semiconductor II phase transition, which is manifested by a jump in the resistance and a hysteresis in the R(T) curves in a very large temperature range (185 – 250 K). The phase transition is accompanied by changes in the charge state of the ET molecules, and notable structure changes in the anion layer, especially in the environment of Cu2+. For the salt 3 the calculated selfconsistent charges show upon cooling a sharp increase of charge order between 291 K and 285 K.

In the organic charge transfer salt $\ensuremath{\kappa}$-(BETS)${}_{2}\mathrm{Mn}{[\mathrm{N}{(\mathrm{CN})}_{2}]}_{3}$ the metallic conductivity is provided by itinerant $\ensuremath{\pi}$ electrons in the layers of BETS molecules, whereas magnetization is largely dominated by the localized $d$ electrons of the ${\mathrm{Mn}}^{2+}$ ions in the insulating anionic layers. We study magnetic properties of the compound in its low-temperature, Mott-insulating state by means of magnetic torque technique. The complex behavior of the torque can be consistently explained by the coexistence of two weakly interacting magnetic subsystems associated with paramagnetic $d$-electron spins and antiferromagnetically ordered $\ensuremath{\pi}$-electron spins, respectively. Based on the experimental data, we determine the principal axes of magnetization of the ${\mathrm{Mn}}^{2+}$ sublattice and propose a qualitative model for the $\ensuremath{\pi}$-electron spin arrangement, implying an important role of the Dzyaloshinskii-Moriya interaction.

Electrochemical oxidation of donor bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) in 1,1,2-trichloroethane-ethanol in the presence of electrolytes including two type of ligands, namely, (Ph4P)2[M(dca)2(SCN)2], M = Mn, Ni; dca = [N(CN)2]−, has been performed and analyzed for the first time. It has been found that in the reaction of electrochemical oxidation of BEDT-TTF, [M(dca)2(SCN)2]2− anion decomposes to form new metal-complex anions, [Mn(dca)3(SCN)2·H2O]3− and [Mn(SCN)6]4− or [Ni(SCN)6]4−, respectively, as well as (dca) and SCN anions. New radical cation salts, (BEDT-TTF)4Mn[(dca)3(SCN)2·H2O](SCN)x, x

de Haas-van Alphen oscillations of the organic metal κ-(ET)

De Haas-van Alphen oscillations of the organic metal \k{appa}-(ET) 2 Cu(SCN) 2 have been measured up to 55 T at liquid helium temperatures. The Fermi surface of this charge transfer salt is a textbook example of linear chain of orbits coupled by magnetic breakdown. Accordingly, the oscillation spectrum is composed of linear combinations of the frequencies linked to the $\alpha$ and magnetic breakdown-induced $\beta$ orbits. The field and temperature dependence of all the observed Fourier components, in particular the "forbidden frequency" $\beta$ -- $\alpha$ which cannot correspond to a classical orbit, are quantitatively accounted for by analytical calculations based on a second order development of the free energy, i.e. beyond the first order Lifshitz-Kosevich formula., Comment: Accepted in Journal of Physics: Condensed Matter (2016)

Coupling of a magnetic field to the orbital and spin degrees of freedom of charge carriers is well known to cause suppression of superconductivity. While the orbital pair-breaking generally dominates in conventional superconductors, the Pauli paramagnetic effect may become important in some heavy fermion compounds or strongly anisotropic materials such as high-Tc or organic superconductors. The same two mechanisms are predicted to be operative also in the case of charge-density-wave (CDW) ordering. However, now they lead to opposite effects: the paramagnetic coupling weakens the CDW interaction whereas the orbital coupling enhances it in a system with an imperfectly nested Fermi surface. Here we report on the experimental evidence of both kinds of magnetic field effects on the CDW and superconducting instabilities in the layered organic metal α - ( BEDT - TTF ) 2 KHg ( SCN ) 4 under quasihydrostatic pressure.

Properties of the spin systems of the localized 3d Mn2+ ions and the conduction π electrons in quasi-two-dimensional organic conductor κ-(BETS)2Mn[N(CN)2]3 were accessed using 1H and 13C NMR in order to find their relation to the metal-insulator transition which occurs at ∼23 K. The transition of the system into the insulating state is shown to be followed by localization of the π spins into a long-range ordered staggered structure of AF type. In contrast, the 3d Mn2+ electron spin moments form a disordered tilted structure, which may signify their trend to AF order, frustrated geometrically by the triangular arrangement of Mn in the anion layer. This result suggests that the MI transition in κ-(BETS)2Mn[N(CN)2]3 is not the consequence of the interactions within the Mn2+ spins but due to the interactions within the π-electron system itself. Vice versa, it is more likelythat the disordered tilted structure of the Mn2+ spins is induced by the ordered π-spins via the π-d interaction.

Electrochemical oxidation of bis(ethylenedithio)tetraselenafulvalene (BETS) has been investigated. Simple and complex dicyanamides of transition metals (Mn 2 þ ,N i 2 þ and Fe 2 þ ) were used as electrolytes. The correlation between composition of prepared radical cation salts and metal nature in electrolytes was established. Manganese dicyanamides provide the formation of BETS salts with the {Mn[N(CN)2]3}- and [N(CN)2]-XH2O anions. When Ni- or Fe-containing electrolytes were used only metalless BETS salts, a 00 -BETS2[N(CN)2] � 2H2 O( I) and y-BETS2[N(CN)2] � 3.6H2 O( II), formed. Structures and conducting properties of these salts were analyzed. Both salts exhibit layered structure. Conducting radical cation layers have a 00

Magnetic properties of the organic conductor κ-(BETS)2Mn[N(CN)2]3 above and below the temperature of the metal-insulator transition that occurs at T MI ≈ 25 K are studied by 1H NMR. The proton spectrum is shown to be determined by the static dipolar fields from Mn2+ localized moments, while the 1H spin-lattice relaxation is dominated by fluctuating fields from Mn2+ electrons. The NMR data, both static (the spectra) and dynamic (the spin-lattice relaxation), indicate the freezing of Mn2+ moments into a short-range or an incommensurate long-range antiferromagnetic order below T MI.

New radical cation salts based on 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP), viz., κ-(BDH-TTP)4CuCl4·(H2O)n (1) and κ-(BDH-TTP)2[CuCl4]0.67· ·(H2O)0.33 (2), were synthesized and structurally characterized. Single crystals were prepared by the electrochemical oxidation of BDH-TTP under galvanostatic conditions. The X-ray diffraction study showed that the salts have layered structures characterized by the presence of κ-type BDH-TTP conducting layers. These layers alternate with the complex anions composed of [CuCl4]2− units and water molecules. Both salts exhibit the temperature dependence of the metallic conductivity down to 4.2 K. Spin-spin antiferromagnetic correlations in the Cu2+ subsystem were observed in the crystals of 2.

The surfaces of a ten years aged crystal and a freshly prepared κ-(BEDT-TTF)2Cu(NCS)2 crystal were compared by scanning tunneling microscopy (STM). The molecularly-resolved STM images of the bc plane of the crystals agree with each other and with the electronic contrast obtained by new density functional theory (DFT) based simulations. Even after ten years STM images of the molecular stacking of BEDT-TTF display a variation in brightness at the positions of different molecules. We attribute this symmetry breaking concerning the brightness in the STM images of the otherwise equivalent BEDT-TTF dimers to the electronic states of a relaxed surface.

The first polymorph, κ″-(ET)2Cu[N(CN)2]Cl, of the well known Mott insulator κ-(ET)2Cu[N(CN)2]Cl has been prepared and its crystal and electronic structures have been examined. The polymorph has monoclinic symmetry in contrast with the orthorhombic one of the isostructural κ-salts of the family (ET)2Cu[N(CN)2]X (X=Cl, Br, I). The monoclinic phase exhibits a layered structure in which the conducting layers are packed in a κ-type arrangement and the anion sheets consist of polymeric zigzag chains formed by Cu[N(CN)2]Cl units. The main structural differences with the orthorhombic κ-salts are that the anion sheets are disordered and the ET molecules are less planar. The new polymorph shows metallic type resistivity down to 4.2 K.

Magnetic properties of novel organic conductor (BEDT-TTF) 2 Dy(NO 3 ) 4 were studied by EPR and SQUID magnetometry methods. Two spin subsystems coexist in this compound: hopping local S = 1/2 (BEDT-TTF + ) moments on conducting radical-cation layers with spin contribution to magnetic susceptibility, I epr (300 K) = 6.3 × 10 −4 emu/mol, and strongly localized 4f 9 -electrons J = 15/2 (Dy 3+ ), χ p (300 K) = 4 × 10 −2 emu/mol, in the core of individual anions. The phase transition was detected in both EPR at T = 197 K, and transport properties at T = 220 K, but not in static magnetic susceptibility χ p ( T ) measured by SQUID. The transition is attributed to the electronic metal–insulator phase transition induced by a fine rearrangement of Dy(NO 3 ) 4 − anions. Interlayer (π–f) or intralayer (f–f) exchange interactions have not been found within 2–350 K. However, the local moments of Dy 3+ contribute to the magnetic anisotropy of the compound and dipole–dipole spin relaxation on BEDT-TTF layers.

New multicomponent radical cation salts derived from bis(ethylenedithio)tetrathiafulvalene (ET) were prepared: bis(ethylenedithio)tetrathiafulvalene dicyanamide dihydrate α″-(ET)2N(CN)2·2H2O and bis-(ethylenedithio)tetrathiafulvalene nitrate α‴-(ET)6(NO3)3·2C2H5O2N3 containing two biuret molecules (C2H5O2N3). The crystal structures of the compounds were determined, and their conducting properties were examined. Both salts have layered structures in which radical cation layers alternate with nonconducting anionic layers. The radical cation layers in the salts α″-(ET)2N(CN)2·2H2O and α‴-(ET)6(NO3)3·2C2H5O2N3 are packed in the α″ and α‴ fashion, respectively. Anionic layers consist of polymeric chains formed by hydrogen bonding between [N(CN)2]− anions and water molecules in α″-(ET)2N(CN)2·2H2O or between NO−3 anions and biuret molecules in α‴-(ET)6(NO3)3·2C2H5O2N3. Both salts show semiconductor conductivity.

The magnetic properties of new radical cation salts (BEDT-TTF)2[CuMn(dca)4] (I) and (BEDT-TTF)2[Mn(dca)3] (II) [where BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene and dca = N(CN2)] are investigated using superconducting quantum interference device (SQUID) magnetometry and electron paramagnetic resonance (EPR) spectroscopy. It is established that, at temperatures below 25 K, both salts are characterized by antiferromagnetic deviations from the paramagnetic behavior. The Weiss constants for compounds I and II are determined to be −5 and −10 K, respectively. The corresponding correlations in the structure of compound I are short-range correlations and do not lead to a change in the effective spin equal to 5/2. It is found that the widths of the EPR lines attributed to the BEDT-TTF conducting sublattice correlate with the widths of the EPR lines associated with the magnetic sublattice of the Mn(dca)3− counterion in the structure of salt II. This correlation suggests that the antiferromagnetic ordering in the magnetic sublattice of compound II affects the spin-lattice relaxation in the BEDT-TTF sublattice. The dependence of the magnetic moment on the magnetic field for compound II at a temperature of 2 K is typical of weakly frustrated uniaxial antiferromagnets and exhibits a kink in a magnetic field of 20 kOe, which corresponds to spin-flop transitions.

Single crystals of the κ-(BEDT-TTF)2Cu[N(CN)2]Cl radical cation salt possessing metallic properties and showing a superconducting transition with Tc=11.5 K at ambient pressure were first prepared.

New radical cation salts based on 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) with copper(II) metal complex anions, β-(BDA-TTP)4Cu2Cl6 and (BDA-TTP)2CuCl4, were synthesized and structurally characterized. Single crystals were prepared by electrochemical oxidation of BDA-TTP under galvanostatic conditions. X-ray diffraction study demonstrated that the salts have a layered structure, in which the conducting BDA-TTP layers alternate with the [Cu2Cl6]2− or [CuCl4]2− anions. Both salts show the semiconductor-type temperature dependence of the conductivity.

Two different β′′-type crystals have been obtained in the syntheses of the title salts. The crystals show metallic behavior of conductivity and paramagnetic response from the metal complex anions.

Two new radical cation salts of the non-TTF containing donor BDH-TTP with the thiocyanatomercurate anions were synthesized. The κ-(BDH-TTP)4[Hg(SCN)4]·C6H5NO2 (1) and α′-(BDH-TTP)6[Hg(SCN)3][Hg(SCN)4] (2) salts were characterized by single crystal X-ray diffraction, electrical resistance measurements and electronic band structure calculations. Both salts have a layered structure in which the BDH-TTP layers of κ- or α′-type alternate with anionic sheets. The anionic layers of 1 contain the counterion [Hg(SCN)4]2− and the nitrobenzene molecule which are statistically disordered. Salt 2 contains two different layers (although both of the α′-type) of the organic donors, a somewhat unusual fact in organic conductors. The anion layers of 2 consist of polymeric chains built up from a combination of the two different anions, [Hg(SCN)3]1− and [Hg(SCN)4]2−. Salt 1 shows a metallic behavior down to helium temperatures whereas salt 2 exhibits two-phase transitions in the temperature range 295–8 K.

Comparative studies of the interlayer magnetoresistance of the layered organic conductor α-(BEDT-TTF) 2 KHg(SCN)4 as a function of the magnetic field orientation have been performed on different samples. The results obtained on the high quality crystal reveal a well defined three-dimensional Fermi surface and provide an evaluation of the interlayer transfer integral, t⊥? 0.04 meV. The lower quality crystal exhibits a very different behavior which is most likely caused by the breakdown of the three-dimensional coherence, when the scattering rate τ -1 exceeds the interlayer hopping rate ∼t⊥/∞.

We report the polarized reflectance spectra (650–6500 cm −1 ) as well FT-NIR Raman spectra of β″-(BEDT-TTF) 3 (NO 3 ) 2 and δ-(BEDT-TTF) 2 (NO 3 ) 0.9 (NO 2 ) 0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal–insulator transition at T = 20–27 K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.

The upper critical fields in the direction parallel to superconducting plane, Hc2″, of the layered salts κ-(BEDT-TTF)2X (X=Cu(NCS)2, Cu[N(CN)2]Br) and κ-(BEDT-TTF)4-Hg2.89Br8 far exceed the BCS Pauli paramagnetic limit and show variety of temperature (T) dependence at ambient pressure. We extended the studies of the Hc2″(T) diagrams for all main κ-(BEDT-TTF)2X superconductors by applying pressure. Emphasis is placed on the behaviour at low T and in high magnetic fields. The origin of the exceeding the BCS Pauli paramagnetic limit is discussed. The dependence of Hc2″ on the field direction within the plane is also presented.

The new molecular conductors with some rare-earth metal-complex anions (ET)5[M(NCS)6NO3]·C2H5OH (M=Dy (1), Y (2), Ho (3)) and (TMTSF)3[Y(NO3)5]·2C6H5Cl (4) as well as a new low-temperature modification of tetra-n-buthylammonium dysprosium(III) complex, (Bu4N)3[Dy(NCS)4(NO3)2] (5) used for the preparation of salt 1 were synthesized and studied by X-ray crystallography at 295 and 110 K. Salts 1–3 have a layered crystal structure with a new packing type of the radical cation layers, called an ω-type. Electronic structure calculations for the compounds 1–3 showed that the paired ET molecules have a positive charge +1 and the single ET molecules are neutral. The directions of the TMTSF stacks in the neighboring organic layers of 4 are practically perpendicular so that salt 4 can be regarded as a precursor of 2D conductors formed by mutually perpendicular directions of conductivity.

A new room-temperature metallic modification of the well known radical cation salt (ET)2[KHg(SCN)4] has been prepared by electrochemical oxidation of ET. Its crystal and electronic structure have been examined at 110 K. The salt has a layered structure in which the conducting layers are characterized by the δ-type packing.

The low-temperature charge-density-wave (CDW) state in the layered organic metals $\alpha $-(BEDT-TTF)$_2$MHg(SCN)$_4$ has been studied by means of the Shubnikov -- de Haas and de Haas -- van Alphen effects. In addition to the dominant alpha-frequency, which is also observed in the normal state, both the magnetoresistance and magnetic torque possess a slowly oscillating component. These slow oscillations provide a firm evidence for the CDW-induced reconstruction of the original cylindrical Fermi surface. The alpha-oscillations of the interlayer magnetoresistance exhibit an anomalous phase inversion in the CDW state, whereas the de Haas -- van Alphen signal maintains the normal phase. We argue that the anomaly may be attributed to the magnetic-breakdown origin of the alpha-oscillations in the CDW state. A theoretical model illustrating the possibility of a phase inversion in the oscillating interlayer conductivity in the presence of a spatially fluctuating magnetic breakdown gap is proposed., Comment: 19 pages, 4 figures; submitted to Low Temperature Physics, special issue "New Trends of Fermiology" dedicated to the 60-th anniversary of the Lifshitz-Kosevich theory

A new radical cation (ET) 5 [Dy(NCS) 6 NO 3 ]·C 2 H 5 OH salt was prepared by electrochemical oxidation of ET in a chlorobenzene–ethanol solution. Its crystal structure and conducting properties were examined. The salt has a layered crystal structure with a basically new packing type of the radical cation layer, which was called an ω-type. Resistance studies reveal a semiconducting nature of this salt.

We report on the inter-layer oscillatory conductance of the two-dimensional organic superconductor (BEDO-TTF)2ReO4H2O measured in static and pulsed magnetic fields of up to 15 and 52 T, respectively. In agreement with previous in-plane studies, two Shubnikov-de Haas oscillation series linked to the two electron and the hole orbits are observed. The influence of the magnitude and orientation of the magnetic field with respect to the conducting plane is studied in the framework of the conventional two- and three-dimensional Lifshits-Kosevich (LK) model. Deviations of the data from this model are observed in low fields strongly tilted with respect to the normal to the conducting plane. In this latter case, the observed behaviour is consistent with an unexplained lowering of the cyclotron effective mass. At high magnetic field, the oscillatory data could have been compatible with the occurrence of a magnetic breakdown orbit built from the hole and electron orbits. However, the increase of the cyclotron effective mass, linked to the electron orbits, as the magnetic field increases above ∼12 T is consistent with a field-induced phase transition. In the lower field range, where the conventional LK model holds, the analysis of the angle dependence of the oscillations amplitude suggests significant renormalisation of the effective Lande factor.

We present detailed studies of the B-T-P phase diagram of α-(BEDT-TTF) 2 KHg(SCN) 4 by means of magnetic torque and magnetoresistance measurements. The phase diagram for magnetic field oriented almost perpendicular to the highly conducting layers closely resembles that expected for a charge-density-wave (CDW) system with an imperfectly nested Fermi surface. The influence of pressure can be readily understood as deteriorating the nesting conditions and thus enhancing the role of the orbital effect of magnetic field. At field strongly tilted from the normal to the layers, both the torque and magnetoresistance display a number of irreversible features that may be associated with a series of first-order phase transitions. This behaviour is not understood within the existing CDW theories.

Magnetic quantum oscillations of a quasi-two-dimensional metal κ-(BETS)2C(CN)3 have been investigated at ambient pressure as well as under pressure up to 9 kbar in magnetic fields up to 25 T. At ambient pressure both Shubnikov–de Haas and de Haas–van Alphen effects were studied. In addition to the previously observed frequencies, a new low frequency Fλ(θ)=Fλ0/cos(θ) has been found at tilted fields with Fλ0=120 T. This frequency strongly interferes with the magnetic-breakdown frequency Fβ, giving rise to additional peaks in the Fourier spectrum, Fβ−λ and Fβ+λ.

In this paper, we report on the magnetic properties of the organic conductor κ-(BETS) 2 FeCl 4 , which were studied with a novel Faraday magnetometer in the temperature range from 0.6 to 40 K and under magnetic fields up to 7 T. Above 1 K, κ-(BETS) 2 FeCl 4 exhibits a Curie–Weiss behavior with an average Curie–Weiss temperature of about −1.5 K. Slightly anisotropic Curie–Weiss laws have been obtained for the field directions parallel and perpendicular to the conducting ac -layer. Below 1 K, spin-flop transitions have been observed in low magnetic fields (0.7 T) for the field direction perpendicular to the conducting layer, which indicates that the system is in an antiferromagnetically ordered state with the easy axis normal to the conducting layer. The Neel temperature is near 1 K.

The behavior of the de Haas-van Alphen oscillations in the organic quasi-two-dimensional metal α-(BETS)2NH4Hg(SCN)4 is comprehensively studied as a function of the angle between the magnetic-field direction and the normal to the conducting layers in it. The angular dependence of the oscillation amplitude has minima at angles of ±40° and ±62°, which are caused by the spin zero effect. The positions of these minima suggest that the electron-phonon and electron-electron interactions in this metal are significantly weakened.

De Haas--van Alphen and Shubnikov--de Haas oscillations in the organic superconductor $\ensuremath{\kappa}\ensuremath{-}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F}{)}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Br}$ have been studied at different orientations of the magnetic field with respect to the conducting layers. In addition to the previously reported magnetic breakdown frequency ${F}_{\ensuremath{\beta}}(\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{})\ensuremath{\simeq}3790$ T, a frequency of $\ensuremath{\simeq}530$ T has been detected. This frequency is attributed to the classical $\ensuremath{\alpha}$ orbit enclosing $\ensuremath{\simeq}14%$ of the Brillouin zone cross-section area, confirming earlier extended H\"uckel model band structure calculations. The angular dependence of the $\ensuremath{\beta}$ oscillation amplitude exhibits pronounced spin-splitting zeros. At certain field orientations, distinct beating of the $\ensuremath{\beta}$ orbit dHvA oscillations is found, originating most likely from a very slight ``warping'' of the Fermi surface in the least conducting direction. In contrast, SdH oscillations, detected simultaneously at the same conditions, show no sign of beating.

The crystal structures and physical properties of the BEDT-TTF, BEDO-TTF and BBDT-TTF chlorides are discussed. Most of the discussion concerns two hydrated BEDO-TTF chlorides which are stable organic metals down to 1.3 K but have different types of conducting layers and different counter-ions networks.

The effect of the first-order phase transition occurring around 220K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)2ReO4·H2O has been studied. The crystal structure at 170K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO4− anions. This rotation leads to changes in the S…S and S…O intermolecular contacts within the BEDO-TTF donor layers, nevertheless the band structure is remained practically unchanged. Possible changes in the crystal structure which can occur at room temperature depending on the experimental conditions are considered. It seems very likely that the (BEDO-TTF)2ReO4·H2O crystal loses its water molecules in the vacuum and hence changes its crystal structure.

Detailed measurements of the interlayer magnetotransport of the organic superconductor $\ensuremath{\kappa}\ensuremath{-}\mathrm{bis}(\mathrm{ethylenedithio}){\mathrm{tetrathiafulvalene}}_{2}\mathrm{Cu}[\mathrm{N}(\mathrm{CN}{)}_{2}]\mathrm{Br}$ have been carried out at ambient pressure as well as under quasihydrostatic pressure up to 12 kbar. Shubnikov--de Haas oscillations at frequencies $\ensuremath{\approx}150, 300$, and 3900 T have been observed at various pressures. The rapid oscillations correspond to 100% of the Brillouin zone cross-section area, revealing a magnetic breakdown orbit in accordance with the theoretically predicted Fermi surface. However, the lower two frequencies do not agree with the theoretical predictions based on the room-temperature crystal structure. In order to interpret the discrepancy, we propose that the Fermi surface undergoes substantial topological changes at a superstructural transition below 200 K. The model appears to be fully consistent with the experimental observations.

Using a variant of the Corbino geometry in pulsed magnetic fields of up to 60 T, we have made direct measurements of the Hall potential in {alpha}-(BEDT-TTF){sub 2}TlHg(SCN){sub 4} within the quantum Hall regime. This method enables the in-plane components of the resistivity tensor, which are normally very difficult to measure, to be investigated and the nonlinear behavior of the sample{close_quote}s I-V characteristics to be studied. It is found that an increasing probability of magnetic breakdown at higher fields leads to a degradation of the quantum Hall effect. {copyright} {ital 1999} {ital The American Physical Society}

Quantum de Haas-van Alphen oscillations and semiclassical angular magnetoresistance oscillations are observed in the quasi-two-dimensional organic metal κ-(BETS)2GaCl4. The behavior of these oscillations attests to the existence of two cylindrical Fermi surface sheets with axes perpendicular to the conducting plane. The cross-sectional areas of these cylinders in the conducting plane are equal to about 20 and 100% of the corresponding cross section of the Brillouin zone. It is shown that the many-particle interaction can be suppressed significantly in this compound.

The α-(BETS) 2 Cu 5 I 6 radical cation salt was obtained by electrocrystallization and its crystal structure has been determined by single crystal X-ray diffraction. The salt has a layered crystal structure and shows an unusual two dimensional polymeric anionic network. Crystal resistance and optical properties were studied. At ambient pressure the electrical conductivity of this salt shows metallic behaviour down to 25-30 K and then an M-I transition takes place. It was found this transition was completely suppressed at pressures above ca. 10 kbar. After release of pressure the salt shows metallic behaviour down to 1.3 K.

The \(\)-(BETS)2C(CN)3 radical cation salt was prepared by electrocrystallization, and its crystal structure was determined by single crystal X-ray diffraction. The electronic structure of \(\)-(BETS)2C(CN)3 was studied by means of the extended Huckel tight binding method. The electrical conductivity of this salt as a function of temperature shows a metallic behaviour down to 1.3 K. Shubnikov-de Haas oscillations reveal both the classical and magnetic breakdown orbits on the Fermi surface typical of the \(\)-type organic conductors. In addition, a low frequency oscillation (250 T) which is not predicted by the band structure calculations has been found in the oscillation spectrum.

Hall voltage versus magnetic field curves were found to be nonlinear and to have temperature-dependent shape in the organic superconductors κ-(BEDT—TTF) 2 Cu[N(CN) 2 ]Cl 1 − x Br x (BEDT—TTF = bis(ethylenedithio)tetrathiafulvalene). Close relation between the shape of the curves and structural anomalies in the salts was disclosed. The nonlinearity is assigned to magnetic ordering, causing or accompanying structural transformation. Changes of the Hall effect field dependence were used together with magnetic viscosity phenomena to plot a phase diagram of the salts. The main lines of the diagram could be traced through all compositions, irrespective of their resistance behavior. The results cast doubt on the decisive role of purely electronic instabilities in phase transformations in the material and are discussed in relation to the origin of magnetic order.