The pressure-temperature phase diagram of the organic superconductor $\kappa -(\mathrm{BEDT}-\mathrm{TTF}{)}_2\mathrm{Cu}[\mathrm{N}\left(\mathrm{CN}{)}_2\right]\mathrm{I}$ determined by resistive measurements is presented. Under a hydrostatic pressure of about 1 kbar an insulating state is transformed into a metallic state, showing superconductivity with a transition temperature $T_{\mathrm{c}}$ up to 8 K. A resistivity maximum develops in the boundary region of insulator-metal transformation and its position gradually shifts to high temperatures with pressure. These properties of the salt are in line with the generic phase diagram for $\kappa$-phase materials, although the salt is located deep in the insulating domain of the phase diagram, contrary to the expectation based on the ionic radius of the halogen atom. We show the relation of the shape of the phase diagram to the degree of structural order in the material.

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 $\kappa \text{−}(\mathrm{ET}{)}_2{\mathrm{Cu}}_2(\mathrm{CN}{)}_3$ ($\kappa \text{−}\mathrm{Cu}$). 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 $\kappa \text{−}(\mathrm{BETS}{)}_2\mathrm{Mn}[\mathrm{N}(\mathrm{CN}{)}_2{]}_3$ ($\kappa \text{−}\mathrm{Mn}$). 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.

Crystals of (ET)₂Mn[N(CN)₂]₃ (1) and (ET)₂CuMn[N(CN)₂]₄ (2) with mono- and first bimetal dicyanamide anions were obtained and their structure, conducting and magnetic properties were investigated. The structure of 2 is not typical for ET radical cation salts and is characterized by the presence of a 3D polymeric anion built into the ET radical cation layers. The crystals of 1 exhibit a semiconducting behavior of conductivity and 2 undergoes a semiconductor I–semiconductor II phase transition at 295–291 K, which is specified by a jump of resistivity and the appearance of a hysteresis in the R(T) curves. The phase transition is accompanied by changes in the charge state of the ET molecules and intermolecular interactions in the crystal. Antiferromagnetic correlations of spins associated with anionic subsystems were found in both salts at temperatures lower than 25 K. Antiferromagnetic ordering in 1 has a long-range character. The effect of the spin frustrated state of localized spins on conducting electrons of ET subsystem was found in 1.

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.

The radical cation salt, ${\text{ET}}_2\text{MnCu}{\left[\text{N}{\left(\text{CN}\right)}_2\right]}_4$, $\left[\text{ET}=\text{bis}\left(\text{ethylenedithio}\right)\text{tetrathiafulvalene}\right]$ with an unusual three-dimensional anionic polymeric network is studied by x-ray diffraction, static susceptibility measurements, and electron spin resonance (ESR) at frequencies between 9 and 420 GHz. The magnetic properties are determined by the alternating two-dimensional layers of the ${\text{Mn}}^{2+}$ ions of the network and the partially charged ET molecules. At ambient temperature the overlap between ${\text{Mn}}^{2+}$ ions and ET molecules is weak and an exchange integral $\left|J_{\text{Mn}-\text{ET}}\right|\approx 4\cdot {10}^{-2}\text{K}$ is estimated from their resolved ESR lines. At lower temperatures, ${\text{ET}}_2\text{MnCu}{\left[\text{N}{\left(\text{CN}\right)}_2\right]}_4$ is not a simple system of weakly interacting paramagnetic ions in spite of the isotropic, Curie-like static susceptibility. There are first-order phase transitions at 292 K and in the range of 120–180 K. One of the lattice constants shows anomalous temperature dependence below 292 K. Anisotropic ESR shifts appear below 150 K, which we explain by demagnetizing fields of the platelike crystals and an exchange-narrowed fine structure. The latter contributes significantly to the shift when the populations of Zeeman levels are altered in high magnetic fields at low temperatures. We estimated the exchange coupling between ${\text{Mn}}^{2+}$ ions within a layer, $J_{\text{Mn-Mn}}\approx -48\text{K}$ and determined the fine structure parameters below 150 K, showing a distortion in the plane of the ${\text{Mn}}^{2+}$ ions.