Spin-1/2 Heisenberg antiferromagnets on anisotropic triangular lattice, [Pd(dmit)2] salts -: How do they release frustration?

A series of [Pd(dmit)(2)] salts have been characterized as spin-1/2 Heisenberg antiferromagnets on the anisotropic triangular lattice, in which the spin frustration provides some substantial effects. We have found that they release the frustration in three different ways. One is the appearance of metallic state observed under pressure or uniaxial strain. In the insulating state at ambient pressure, a novel temperature-induced crossover from a frustrated paramagnet to in antiferromagnetically correlated state is observed, where the lattice anisotropy plays a crucial role at low temperatures. A novel phase transition accompanied by charge separation is found only in the Et2Me2Sb salt, which leads to a non-magnetic ground state with all electrons paired. (c) 2005 Elsevier Ltd. All rights reserved.