Nanodomains in multiferroic hexagonal RMnO3 films (R = Y,Dy,Ho,Er)

A homogeneous distribution of ferroelectric nanoinclusions was observed by optical second harmonic generation in epitaxial films of hexagonal RMnO3 (R = Y, Dy, Ho, Er) grown on ZrO2(Y2O3) substrates. The inclusions correspond to secondary orientations in the c-axis-oriented films. Their volume density is in the range of 10(-3) and their occurrence is independent of growth technique and film thickness in the range of 20-1000 nm. The inclusions behave as preferentially polarized ferroelectric nanodomains whereas the epitaxial film is in a ferroelectric single-domain state. In addition, the antiferromagnetic phase exhibits nanodomains of < 100 nm which is three orders of magnitude below the extension of bulk antiferromagnetic domains in RMnO3. Indications for a polarization-induced magnetic order different from that of the bulk are discussed.