DETERMINATION OF ANOMALOUS SUPEREXCHANGE IN MNCL2 AND ITS GRAPHITE-INTERCALATION COMPOUND

The low-temperature magnetic structure of MnCl2 graphite intercalation compound has been studied by neutron diffraction. Magnetic peaks occur at wave vectors incommensurate with the MnCl2 and graphene sublattices. The in-plane spin configuration is explained by an exchange Hamiltonian that includes three shells of nearest neighbors in the plane. The nearest-neighbor exchange is ferromagnetic but anomalously weak, and the magnetic behavior is dominated instead by the antiferromagnetic third-neighbor interaction. The exchange parameters are used to explain the spin configuration of bulk MnCl2 after adding an interplanar coupling.