  Thin films of TbMnO3 have been grown on SrTiO3 substrates. The films grow
under compressive strain and are only partially clamped to the substrate. This
produces remarkable changes in the magnetic properties and, unlike the bulk
material, the films display ferromagnetic interactions below the ordering
temperature of ~40K. X-ray photoemission measurements in the films show that
the Mn-3s splitting is 0.3eV larger than that of the bulk. Ab initio embedded
cluster calculations yield Mn-3s splittings that are in agreement with the
experiment and reveal that the larger observed values are due to a larger
ionicity of the films.
