  PbTiO3-based nano-scale dots and tubes have received a great deal of
attention owing to their potential applications to nonvolatile memories and
multi-functional devices. As for the size effect of 180o stripe domains in
ferroelectric thin films, there have been extensive reports on the
thickness-dependent domain periodicity. All these studies have revealed that
the domain periodicity of 180o stripe domains scales with the film thickness
(d) according to the classical Landau-Lifshitz-Kittel (LLK) scaling law down to
the thickness of ~2 nm. In the case of PbTiO3 nanodots, however, we obtained a
quite striking correlation that for the thickness less than a certain critical
value, dc (~35 nm), the domain width even increases with decreasing thickness
of the nanodot, which surprisingly indicates a negative value in the LLK
scaling-law exponent. On the basis of theoretical considerations of dc, we
attribute this anomalous domain periodicity to the presence of a
nonferroelectric surface layer, in addition to the finite lateral-size effect
of a ferroelectric nanodot.
