title: Polarization curling and flux closures in multiferroic tunnel junctions.
abstract: Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La,Sr)MnO3ferroelectric tunnel junctions, the polarization in active PbTiO3layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Jonathan J P
authors.initials: JJP
authors.lastname: Peters
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Geanina
authors.initials: G
authors.lastname: Apachitei
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Beanland
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Marin
authors.initials: M
authors.lastname: Alexe
authors.affiliation: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK.
authors.forename: Ana M
authors.identifier: http://orcid.org/0000-0002-8230-6059
authors.initials: AM
authors.lastname: Sanchez