Influence of magnetic on ferroelectric ordering inLuMnO3

Abstract

We have studied the influence of antiferromagnetic ordering on the local dielectric moments of the ${\mathrm{MnO}}_5$ and ${\mathrm{LuO}}_7$ polyhedra by measuring neutron powder-diffraction patterns of ${\mathrm{LuMnO}}_3$ at temperatures near $T_N.$ We show that the coupling is weak, because the magnetic exchange coupling is predominantly in the $\mathrm{ab}$ plane of the ${\mathrm{MnO}}_5$ trigonal bipyramids, and the electric dipole moments, originating in the ${\mathrm{LuO}}_7$ polyhedra, are oriented along the hexagonal c axis. Anomalies in the dielectric properties near $T_N$ are thus caused by the geometric constraints between the ${\mathrm{MnO}}_5$ and the ${\mathrm{LuO}}_7$ polyhedra.