Landau Theory of the Magnetic Phases of Hexagonal Rare Earth Manganites

A group theoretical analysis is presented on the magnetic structure of rare earth atoms in the multiferroic hexagonal manganites RMnO$_{3}$ (R=Ho, Er, Tm, Yb, Sc, Y) which exhibit the coexistence of ferroelectricity (T$_{c }\sim $900 K) and antiferromagnetism (T$_{N }\sim $100 K). Using Landau theory, a phenomenological model of the free energy based on four one-dimensional magnetic order parameters has been developed. Coupling of the various order parameters leads to complex magnetic field -- temperature phase diagrams in qualitative agreement with experimental data. \newline \newline References: \newline [1] S. H. Curnoe and I. Munawar, Magnetic Phases of Rare Earth Hexagonal Manganites, Proceedings of The International Conference on Strongly Correlated Electron Systems SCES '05, July 26$^{th}$ - 30$^{th}$, 2005, Vienna, Austria, (accepted on July 29, 2005 to be published in Physica B)\newline [2] Manfred Fiebig. (2005) Revival of the magnetoelectric effect, Journal of Physics D: Applied Physics, 38, R123-R152