Magnetic Order In The Frustrated Ising Quasi-One Dimensional Compound Naco(Acac)(3)Center Dot Benzene

We report the results of susceptibility, magnetization curve, and specific heat measurements on single crystals of NaCo(acac)(3)center dot benzene, which forms a triangular lattice on the ab-plane with Ising ferromagnetic chains along the c-axis. We found a long-range order below 62 mK by specific heat measurement, a steplike increase in susceptibility at this temperature, and a plateau of one-third of the full moment in the M-H curve at 20 mK. We also observed a spin relaxation that obeys the Arrhenius law in the ordered state. The existence of a partially disordered antiferromagnetic state is discussed on the basis of the results.