Magnetic Order In Ybmno3 Studied By Neutron Diffraction And Mossbauer Spectroscopy

The magnetic ordering of the hexagonal multiferroic compound YbMnO3 has been studied between 100 and 1.5 K by combining neutron powder diffraction, Yb-170 Mossbauer spectroscopy, and magnetization measurements. The Yb moments of the two crystallographic sites order at two different temperatures: the 4b site together with the Mn moments (at T-N similar or equal to 85 K) and the 2a site well below (at 3.5 K). The temperature dependences of the Mn and Yb moments are explained within a molecular-field model, showing that the 4b and 2a sites order via Yb-Mn and Yb-Yb interactions, respectively. A simple picture taking into account the local Mn environment of the rare-earth R (4b) ion is proposed to couple R and Mn orders in hexagonal RMnO3 manganites. The nature and symmetry of the R-Mn interactions yielding the R order are discussed.