Crystal field effect in YbMnO3

In this paper, the IR absorption spectra of YbMnO3 are reported as a function of temperature. In addition to the wide and strong charge transfer band due to manganese in visible, the absorption spectra include sharp lines characteristic for the F-2(7/2) -> F-2(5/2) transition of Yb3+ at around 10 000 cm(-1). The number of lines exceeds the theoretical one for the two Yb3+ sites with C-3 (two third) and C-3v (one third of the sites) point symmetries. Magnetic ordering of the manganese sublattice below T-N at similar to 75 K creates a molecular field that splits the Kramers doublets of the Yb3+ ions in the C-3 site. The splitting varies (at 5 K) from a few up to 30 cm(-1). Despite accounting for this splitting, the number of lines is still too high due to the vibronic coupling. The parameters of the crystal field acting at the Yb3+ sites were predicted using the ab initio methods and the superposition model calculations considering the available structural data. A rather good agreement was obtained with the observed splitting of the F-2(7/2) and F-2(5/2) manifolds. (C) 2007 Elsevier B.V. All rights reserved.