Study on Mechanism of Interaction in Organic Radical Ferromagnets

本文从两个方面总结了本研究的主要成果；压力对真正有机磁性晶体分子间相互作用的影响及低维系统中多体量子海森堡自旋的协同现象。通过同时测量磁化率和热容，我们发现首次报道的有机铁磁体p-NPNN（对硝基苯基硝基氮氧化物）的居里温度随静水压力而降低。在7kbar下，减少幅度高达45%。然而，我们最近在高达10kbar的高压下进行的实验表明，随着压力的增加，有机反铁磁体的转变温度会增加。这些结果与压力作用下通过不同分子轨道的动力学和电位交换相互作用的竞争有关。压力作用下晶格维数的降低也反映在化合物的磁性热容的变化上。利用不同的硫酰自由基晶体衍生物对低维系统中量子统计量的定量检验进行了研究。我们测量了p-CDTV(3-（4-氯苯-1,5-二甲基-6-硫氧基）的场依赖性和温度依赖性，得到了一维量子铁磁体的自由能、零极限下的热容和磁化率的临界指标与理论结果非常吻合。交错磁化率是反铁磁体的一个虚拟的本征量，利用TOV（1,3,5-三苯基-6-氧overdazyl）的二维量子Heisenberg - Heisenberg反铁磁体中的倾斜弱铁磁体，估计了交错磁化率。揭示了反铁磁磁化率测量中晶格维从二维到三维的交叉现象。将二维反铁磁体中交错磁化率与自旋相关长度之间的标度关系与本研究结果进行比较，明确了交叉效应特征。少

The main results of the present research are summarized in two ways ; pressure effects on intermolecular interactions in genuine organic magnetic crystals and cooperative phenomena in many-body quantum Heisenberg spins in low-dimensional systems. We found that the Curie temperature of the first reported organic ferromagnet p-NPNN (para-nitrophenyl nitronyl nitroxide) decreases with hydrostatic pressures by the simultaneous measurements of magnetic susceptibility and heat capacity. The reduction amounts as much as 45% under 7kbar. Recent our experiments in the higher pressures up to 10kbar, however, have revealed the transition temperature turns to increase as the pressure induced enhancement of the Neel temperature of organic antiferromagnets.These results are relevant to competition between the kinetic and the potential exchange interactions via various molecular orbitals under the pressure.The reduction of the lattice dimensionality under pressure is also found to be reflected on the … More change of the magnetic heat capacity of this compound.Quantitative check of quantum statistics in low-dimensional systems is exanined using various crystalline derivatives of verdazyl radical. We measured field and temperature dependence of p-CDTV (3-(4-chlorophenyl-1,5-dimethyl-6-thioxoverdazyl) and got an excellent agreement with the theoretical results for the free energy for one-dimensional quantum ferromagnet, as well as the critical indices of heat capacity and magnetic susceptibility at the limit of zero degree. The staggered susceptibility, which is a fictitious but intrinsic quantity for antiferromagnets, is estimated in a two-demensional quantum Heisen berg Heisenberg antiferromagnet of TOV (1,3,5-triphenyl-6-oxoverdazyl), by making use of the canted weak ferromagnets in this system. The latticedimensional crossover from two to three in antiferromagnetic susceptibility measurements has been revealed. The scaling relation between the staggered susceptibility and the spin correlation length in two-dimensional antiferro-magnet is compared with the present result to make clear the crossover effect feature detected here. Less