NUCLEAR AND ELECTRONIC RESONANCE APPROACHES TO MAGNETIC AND LATTICE FLUCTUATIONS IN THE 2-CHAIN FAMILY OF ORGANIC-COMPOUNDS (PERYLENE)2[M(S2C2(CN)2)2](M = PT,AU)

In this work we present and analyze the temperature dependence of the H-1 nuclear-spin-lattice relaxation rate and of the magnetic susceptibility of the two-chain organic compound (Per)2[Pt(mnt)2]. [Here, "Per" is perylene; "mnt" stands for maleonitriledithiolate, which is the same as cis-(2,3-dimercapto-2-butenedinitrile).] The analysis confirms the existence of localized spins on the Pt(mnt)2 chains and their dominant influence on the relaxation through an interstack dipolar coupling. A scaling relation of the form T1(-1) proportional-to T-chi-s(T) is found to exist in the entire temperature domain, including the regime of one-dimensional spin-Peierls Pt(mnt)2 lattice fluctuations observed by x-ray experiments below 30 K. The magnetic-field dependence of the relaxation is also found to qualitatively agree with one-dimensional spin diffusion which is cut off in the low-field region. A comparison is made to data obtained for (Per)2[Au(mnt)2], which have a completely different T1(-1) temperature dependence. This is demonstrated to be a characteristic of itinerant electrons. Finally we analyze the existing EPR data on (Per)2[Pt(mnt)2] and show that the observed low-temperature linear temperature profile of the EPR linewidth results from the existence of an exchange coupling between the itinerant and the localized spins of different stacks. Similar conclusions previously made for Per2[Pd(mnt)2] allow one to study such two-chain compounds as realizations of a one-dimensional Kondo lattice. We discussed several puzzling questions raised by the analysis concerning possible mechanisms that can lead to a spin-Peierls distortion.