A second example is provided by the family of hexagonal rare earth manganites (h- R MnO 3 with R =Ho-Lu, Y), which have a structural phase transition at around 1300 K consisting primarily of a tilting of the MnO 5 bipyramids. While the tilting itself has zero polarization, it couples to a polar corrugation of the R -ion layers which yields a polarisation of ~6 μC/cm. Since the ferroelectricity is not the primary order parameter it is described as improper. The multiferroic phase is reached at ~100K when a triangular antiferromagnetic order due to spin frustration arises.