  We fabricated epitaxial thin films of hexagonal DyMnO3, which otherwise form
in a bulk perovskite structure, via deposition on Pt(111)//Al2O3 (0001) and
YSZ(111) substrates: each of which has in-plane hexagonal symmetry. The
polarization hysteresis loop demonstrated the existence of ferroelectricity in
our hexagonal DyMnO3 films at least below 70 K. The observed 2.2 uC/cm^2
remnant polarization at 25 K corresponded to a polarization enhancement by a
factor of 10 compared to that of the bulk orthorhombic DyMnO3. Interestingly,
this system showed an antiferroelectric-like feature in its hysteresis loop.
Our hexagonal DyMnO3 films showed an antiferromagnetic Neel temperature around
60 K and a spin reorientation transition around 40 K. We also found a clear
hysteresis in the temperature dependence of the magnetization, which was
measured after zero-field-cooling and field-cooling. This hysteresis may well
have been of spin glass origin, which was likely to arise from the geometric
frustration of antiferromagnetically-coupled Mn spins with an edge-sharing
triangular lattice.
