NMR Evidence for Antiferromagnetic Transition in the Single-Component Molecular System, [Cu(tmdt)$_{2}$]

The magnetic state of the single-component molecular compound, [Cu(tmdt)$_{2}$], is investigated by means of $^{1}$H-NMR. An abrupt spectral broadening below 13 K and a sharp peak in nuclear spin-lattice relaxation rate, $T_{1}^{-1}$, at 13 K are observed as clear manifestations of a second-order antiferromagnetic transition, which is consistent with the previously reported magnetic susceptibility and EPR measurement. The ordered moment is estimated at $0.22-0.45$ ${\mu}_{\rm B}$/molecule. The temperature-dependence of $T_{1}^{-1}$ above the transition temperature indicates one-dimensional spin dynamics and supports that the spins are on the central part of the molecule differently from other isostructural compounds.