Magnetic order and charge separation in 2D distorted triangular lattice systems β′-X[Pd(dmit)2]2

Magnetic properties of organic compounds with two-dimensional distorted triangular lattice structure, β′-X[Pd(dmit)2]2 are investigated by the muon spin relaxation (μSR) method, where X is counter cation. We have previously reported that the X=Me4P salt (1, Me=CH3) shows a very sharp antiferromagnetic (AFM) transition at 39.3 K. We have carried out μSR measurements on other two Pd(dmit)2 salts: the X=Et2Me2P salt (2, Et=C2H5) and the Et2Me2Sb salt (3). In compound 2, an AFM transition at lower TN=15K with a smaller enhancement of the muon spin relaxation is observed, indicating a larger effect of the spin frustration than in 1. The zero-field μSR time spectra of 3 showed an enhancement of the relaxation below ∼80K, but did not show precessions. Recently, it has been suggested that this salt undergoes a phase transition to a charge-separated nonmagentic state. It is expected that the enhancement of the relaxation is related to the spin localization attributable to the charge separation.