Development of molecular conducting magnets oriented to π-d interaction control

1.研究了自由基离子盐(EDO-TTFBr_2)_2MCl_4(M=Fe，Ga)在压力下的电阻率和磁阻。FeCl4盐的电阻率表现出两个异常，一个来自π-电子层的连续跃迁，另一个异常来自FeCl4层的长程磁有序。对于GaCl4盐，在低场区观察到负的磁阻，表明外加磁场使SDW带隙减小。FeCl4盐的MR出现两次突变，证明了复合π-d自旋系统中存在场致相继跃迁。根据π电子自旋和d电子自旋相互作用的受阻磁结构，可以定性地解释这种盐的磁阻与场的关系。研究了弱铁磁体(BDHTTP)[M(Isoq)2(NCS)4](M=Cr，Fe；Isoq=异喹啉)的磁性。这些盐形成了二维磁片，其中FeLi…S…反铁磁性连接了更多的给体、阳离子和阴离子的磁链S联系。在常压下，在T_N=7.6K时，铬盐和铁盐都发生了弱铁磁转变。加压使M=Cr和Fe在9kbar时的转变温度分别提高到16.6K和11.6K。剩余磁化强度与压力的关系表明，由于外加压力增加了反铁磁相互作用，铬盐的自旋倾斜角减小，而铁盐由于Dzyaloshinsky-Moriya相互作用的增加，使Fe自旋更加倾斜。平均场分析表明，分子间交换相互作用随着压力的增加而增加，其中链间阴离子-阴离子相互作用具有最高的压力敏感性。这一结果与S…的晶体结构随温度的变化一致，表明其在链间阴离子-阴离子的距离处发生了热收缩S联系方式是最值得注意的内链…SS联系。较少

1. The electrical resistivities and magnetoresistances (MR) of a radical ion salt (EDO-TTFBr_2)_2MCl_4 (M=Fe,Ga) are investigated under pressures. The resistivity of the FeCl4 salt shows two anomalies due to the successive transitions of the π-electron layer, and another anomaly coming from the long-range magnetic ordering of the FeCl_4 layer. For the GaCl_4 salt negative MR is observed in the low-field region, suggesting a decrease of the SDW gap by applying the magnetic field. The MR of the FeCl_4 salt shows two abrupt increases, which proves the presence of field-induced successive transitions in the composite π-d spin system. The field dependence of the MR of this salt can be qualitatively explained based on the frustrated magnetic structure of π- and d-electron spins interacting with each other.2. The magnetic properties of weak ferromagnets (BDH-TTP)[M(isoq)_2(NCS)_4] (M = Cr, Fe ; isoq = isoquinoline) is investigated. These salts form two-dimensional magnetic sheets, where ferri … More magnetic chains of donor cation radical and anion are antiferromagnetically connected by S…S contacts. Under ambient pressure, both the Cr and Fe salts undergo a weak ferromagnetic transition at T_N = 7.6 K. The application of pressure elevates the transition temperatures up to 16.6 K and 11.6 K at 9 kbar for M = Cr and Fe, respectively. The pressure dependence of the remanent magnetization indicates that the spin canting angle of the Cr salt is reduced due to the increase of antiferromagnetic interaction by applied pressure, in contrast to the Fe salt where the Fe spins are more canted due to the increase of the Dzyaloshinsky-Moriya interaction. The mean-field analysis reveals that the intermolecular exchange interaction increases as the pressure increases, among which the inter-chain anion-anion interaction has the highest pressure sensitivity. This result is consistent with the temperature dependence of the crystal structure showing the thermal contraction in the distances of inter-chain anion-anion S…S contacts is the most remarkable in intra-chain S…S contacts. Less