Muon spin relaxation studies on magnetic properties of organic conductors Pd(dmit)2 salts and α-(BETS)2I3

Magnetic properties of organic conductors β'-Et2Me2Sb[Pd(dmit)2]2 (Et = C2H5, Me = CH3), P21/m crystal of EtMe3P[Pd(dmit)2]2 and α-(BETS)2I3 were investigated by muon spin relaxation (μSR) method. It has been suggested that Et2Me2Sb[Pd(dmit)2]2 exhibits a charge separation phase below ∼70 K and that EtMe3P[Pd(dmit)2]2 exhibits a spin-Peierls-like state below ∼25 K although it has a quasi two-dimensional structure. Our zero-field μSR results indicate that these Pd(dmit)2 salts show quite similar behavior to an organic spin-Peierls system although changes in the μSR time spectra of the EtMe3P salt was ambiguous. For α-(BETS)2I3, a metal-insulator transition is expected to occur at TMI ∼ 50 K. We observed a slight enhancement of the muon spin relaxation below TMI and it gradually became remarkable at lower temperatures. The present result may reveal the existence of a spin-singlet ground state showing similar temperature dependence of the muon spin relaxation rate to that in the Pd(dmit)2 salts. However, the possibility that the relaxation in this system originates from magnetic fluctuations is also still conceivable.