Magnetism of a Two-Dimensional Weak-Ferromagnetic Organic Radical Crystal, 1, 3, 5-Triphenyl-6-Oxoverdazyl

抄録

A genuine organic radical crystal 1, 3, 5-triphenyl-6-oxoverdazyl (TOV) has been revealed to be an S=1/2 two-dimensional (2D) weak-ferromagnetic Heisenberg antiferromagnet with the exchange interaction 2J/k_B=-9.0, K by the experiments of magnetic susceptibility, heat capacity, magnetization and electron paramagnetic resonance. The anomalous temperature dependence of the weak ferromagnetism at low temperatures is qualitatively explained by a four-sublattice model with two kinds of Dzyaloshinsky-Moriya (D-M) vectors of opposite sign on the ac-plane. The staggered susceptibility, which is a fictitious but intrinsic quantity for antiferromagnets, is estimated in TOV by making use of the canted weak ferromagnetic moments which dominate below 6, K. Especially the rapid growth of the magnetic susceptibility below 6, K is explained by the staggered susceptibility which makes the crossover effect from 2D Heisenberg to 2D Ising system, triggered by above the D-M anisotropy.