THE PHASE DIAGRAM OF NEW ORGANIC SUPERCONDUCTOR BETS SALTS WITH A MIXED HALIDE GALLIUM ANION

1996年，研究了一系列具有三斜晶胞和四重准堆积排列的有机超导体(=双(乙二硫基)四硫富瓦烯)的晶体结构、电阻率和磁化率。其电阻率行为与阴离子的大小有关。通过交换卤素原子(X，Y)和z值可以系统地考察超导行为。研究了lambda-bets_2GaCl3F和lambda-bets_2GaBrzCl_&lt；4-z&gt；(0&lt；z&lt；1.5)的磁化率。虽然lambda-bets_2GaX_zy_&lt；4-z&gt；的电阻率行为与所谓的10K级kappa型BEDT-TTf超导体非常相似，但在超导态附近的绝缘基态是非磁性的。从理论上指出，这种非磁性相有可能存在于自旋能隙相和反铁磁相的交界处。今年，用^1H-核磁共振对这一非磁性相进行了精确的研究。^1H-核磁共振没有表现出kappa-(Et)_2[CuN(CN)_2]Cl中观察到的二阶矩的突然增加。在λ-(Bts)_2GaCl_&lt；2.5&gt；BR_&lt；1.5&gt；中，在25K到2K的温度范围内没有观察到形成磁有序的特征的1/T_1发散现象，因此该相不是反铁磁相，而是非磁相。Lambda‘-BETS3GaBr4具有改进的Lambda型结构，在50K以下表现出窄禁带半导体行为。在50K以下，Lambda’-BETS3GaBr4转变为绝缘相。在60K以下，观察到平行于H和垂直于H的各向异性的磁化率降低。这种相变似乎是反铁磁性的。与高温无机超导体相比，有机分子的高温反铁磁相变是非常罕见和有趣的。

In 1996, crystal structures, electrical resistivities and magnetic susceptibilities of a series of organic superconductors with tetrahedral mixed halide gallium anions, lambda-BETS2GaXzY4-z (X,Y=F,Cl, Br ; 0<z<4) having triclinic unit cells and fourfold quasi-stacking arrangement of BETS (=bis (ethylene-dithio) tetraselenafulvalene) molecules were examined. The resistivity behavior dependedon the size of anion. The superconducting behavior could be examined systematically by exchanging the halogen atoms (X,Y) and the z-value. The magnetic susceptibilities were studied on lambda-BETS_2GaCl_3F and lambda-BETS_2GaBr_zCl_<4-z> (0<z<1.5). Although the resistivity behaviors of lambda-BETS_2GaX_zY_<4-z> resemble closely those of so-called 10K-class kappa-type BEDT-TTF superconductors, the insulating ground state near the superconducting state is non-magnetic. Theoretically this non-magnetic phase is pointed out that it has the possibility of exsisting on the borderline of spin-gap phase and antiferromagnetic phase. This year this non-magnetic phase was examined precisely by ^1H-NMR.^1H-NMR did not exhibit the abrupt increase of 2nd moment, which was observed in kappa-(ET)_2[CuN(CN)_2]Cl. In lambda-(BETS)_2GaCl_<2.5>Br_<1.5> the divergence of 1/T_1 which is characteristicin forming the magnetic orderness was not observed within the temperature range from 25K to 2K.So this phase is considered not as antiferromagnetic phase but as non-magnetic phase. lambda'-BETS3GaBr4 has a modified lambda-type structure and it shows narrow-gap semiconducting behavior down to 50K.lambda'-BETS3GaBr4 transforms to the insulating phase below 50 K.The decrease of magnetic susceptibilities with the anisotropies parallel to H and perpendicular to H was observed below 60 K.This phase transition seems to be antiferromagnetic. Such a high temperature antiferromagnetic phase transition of organic molecules is very rare and very interesting, compared with high-temperature inorganic superconductors.