NMR evidence for antiferromagnetic transition in the single-component molecular system [Cu(tmdt)2

Abstract

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