EPR studies of the 2-D magnetic system in an organic cation radical salt, m-MPYNN+·X−

EPR measurements were carried out on a single crystal of m-N-methylpyridinium nitronyl nitroxide perchlorate which consists of a 2-D bond-alternated hexagonal lattice. Angular dependence of the linewidth ΔHpp shows minimums at the magic angles, and can be well interpreted with the theoretical equation for the 2-D magnetic system, ΔHpp=A(3cos2θ-1)2+B. Temperature dependence of ΔHpp shows an anomaly between 50 K and 100 K, which could be relevant to freezing of the orientational disorder of the perchlorate ion. Angular dependence of the g-value confirms the 2-D character of the magnetic system. Below 50 K, the EPR signal is affected by the demagnetizing effects.