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.