Long range and short range magnetic order in orthorhombic LiMnO2

The magnetic properties of orthorhombic LiMnO2 have been investigated in detail for the first time. The susceptibility data show several features including a Curie-Weiss regime from 600 to 800 K with theta(p) = -1056(13) K and mu(eff) = 4.82 mu(B)/Mn3+, a broad maximum at 360 K, and a field-cooled (FC), zero field cooled (ZFC) divergence below 100 K. The broad maximum indicates two-dimensional rather than one-dimensional short-range spin correlations. A Neel temperature for a transition to three-dimensional long-range order is seen at 261.5 K from both neutron diffraction and the magnetic heat capacity behavior as determined from the susceptibility data. The magnetic structure has been solved from neutron diffraction data and has a propagation vector of k = (1/2 1/2 1/2) and an ordered magnetic moment of 3.69(4) mu(B)/Mn3+ with a preferred direction parallel to the b axis. The neutron scattering data also provide evidence for two-dimensional short-range correlations above T-c at 271 K in the form of a feature with a Warren line shape. The long- and short-range order are discussed in terms of the crystal structure which is of the ordered NaCl type distorted by the presence of the Jahn-Teller ion, Mn3+. (C) 1997 Academic Press.