Molecular Alloy with Diluted Magnetic MomentsMolecular Kondo System

[Ni1–xCux(tmdt)2] (tmdt = trimethylenetetrathiafulvalenedithiolate) was prepared for realizing molecular Kondo systems. Magnetic moments (S = 1/2) are considered to exist at the central {CuS4} parts of Cu­(tmdt)2 molecules. The χT-versus-T curve of the system with x ≈ 0.15 showed a broad peak at ∼10 K. The decrease in the χT value below 10 K is consistent with a singlet ground state, as expected for a Kondo system. However, in the system with x ≈ 0.27, the χT value decreased when the temperature was lowered to 2 K, indicating antiferromagnetic interactions between magnetic moments through π–d interactions. Although the susceptibility anomaly suggested that the π–d interactions become important at T < 20 K, the observed resistivity (ρobs) showed no resistivity minimum characteristic of a Kondo system down to 4.2 K. However, the differential resistivity Δρ­(T) = ρobs – ρL(T) showed a logarithmic resistivity increase at 8–20 K with decreasing temperature, where ρL(T) is a fitted function of ρobs obtained at T > 50 K that is considered to represent approximately the temperature dependence of the resistivity without spin scattering of the conduction electrons.