  Detailed structural measurements were conducted on a new perovskite, ScMnO3,
and on orthorhombic LuMnO3. Complementary density functional theory (DFT)
calculations were carried out, and predict that ScMnO3 possesses E-phase
magnetic order at low temperature with displacements of the Mn sites (relative
to the high temperature state) of ~0.07 {\AA}, compared to ~ 0.04 {\AA}
predicted for LuMnO3. However, detailed local, intermediate and long-range
structural measurements by x-ray pair distribution function analysis, single
crystal x-ray diffraction and x-ray absorption spectroscopy, find no local or
long- range distortions on crossing into the low temperature E-phase of the
magnetically ordered state. The measurements place upper limits on any
structural changes to be at most one order of magnitude lower than density
functional theory predictions and suggest that this theoretical approach does
not properly account for the spin-lattice coupling in these oxides and may
possibly predict the incorrect magnetic order at low temperatures. The results
suggest that the electronic contribution to the electrical polarization
dominates and should be properly treated in theoretical models.
