Study on Mechanism of Interaction in Organic Radical Ferromagnets

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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