Ferroelectricity in finite-dimensional systems continues to arouse interest, motivated by predictions of vortex polarization states and the utility of ferroelectric nanomaterials in memory devices, actuators and other applications. Critical to these areas of research are the nanoscale polarization structure and scaling limit of ferroelectric order, which are determined here in individual nanocrystals comprising a single ferroelectric domain. Maps of ferroelectric structural distortions obtained from aberration-corrected transmission electron microscopy, combined with holographic polarization imaging, indicate the persistence of a linearly ordered and monodomain polarization state at nanometre dimensions. Room-temperature polarization switching is demonstrated down to ~5 nm dimensions. Ferroelectric coherence is facilitated in part by control of particle morphology, which along with electrostatic boundary conditions is found to determine the spatial extent of cooperative ferroelectric distortions. This work points the way to multi-Tbit/in(2) memories and provides a glimpse of the structural and electrical manifestations of ferroelectricity down to its ultimate limits.

Methods have been developed for the shape-selective synthesis of ferroelectric LiNbO 3 nanoparticles. Decomposition of the single-source precursor, LiNb(O-Et) 6 , in the absence of surfactants, can reproducibly lead to either cube-or sphere-like nanoparticles. X-Ray diffraction shows that the LiNbO 3 nanoparticles are rhombohedral (R3c). Sample properties were examined by piezoresponse force microscopy (PFM) and Raman where both sets of nanoparticles exhibit ferroelectricity. The longitudinal piezoelectric coefficients, d 33 , varied with shape where the largest value was exhibited in the nanocubes (17 pm V 21 for the cubes versus 12 pm V 21 for spheres).

The magnetoelectric effect that occurs in multiferroic materials is fully described by the magnetoelectric coupling coefficient induced either electrically or magnetically. This is rather well understood in bulk multiferroics, but it is not known whether the magnetoelectric coupling properties are retained at nanometre length scales in nanostructured multiferroics. The main challenges are related to measurement difficulties of the coupling at nanoscale, as well as the fabrication of suitable nano-multiferroic samples. Addressing these issues is an important prerequisite for the implementation of multiferroics in future nanoscale devices and sensors. In this paper we report on the local measurement of the magnetoelectric coefficient in bilayered ceramic nanocomposites from the variation in the longitudinal piezoelectric coefficient of the electrostrictive layer in the presence of a magnetic field. The experimental data were analyzed using a theoretical relationship linking the piezoelectric coefficient to the magneto-electric coupling coefficient. Our results confirm the presence of a measurable magnetoelectric coupling in bilayered nanocomposites constructed by a perovskite as the electrostrictive phase and two different ferrites (cubic spinel and hexagonal) as the magnetic phases. The reported experimental values as well as our theoretical approach are both in good agreement with previously published data for bulk and nanostructure magnetoelectric multiferroics.

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Highly uniform bilayered perovskite-spinel hybrid nanostructures were deposited on glass and LaNiO3-buffered (100) silicon substrates at almost-ambient temperatures via the liquid-phase deposition (LPD) method. Field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) evidenced that the perovskite and spinel layers are constructed by arrays of densely packed nanoparticles with uniform sizes. The bilayered nanocomposites exhibit both piezoelectricity and ferrimagnetism at room temperature. The value of the static piezoelectric coefficient of the PbTiO3 (PTO) film was 14.1 pm/V, whereas the values of the saturation magnetization were 234.4 and 223.2 emu/cm3 for the PbTiO3−Co0.32Fe2.68O4 (CFO) and PbTiO3−Ni0.66Fe2.34O4 (NFO), respectively. The coercivity of the nanocomposite decreased by 12.11% for the PTO−CFO, whereas, for the PTO−NFO, it increased by 20%, with respect to the coercivity values of the pristine ferrite films, which is the result of a magnetoelectric coupling between the two dissimilar layers in the nanocomposite. Additional evidence about a stress-induced magnetoelectric coupling in these bilayered structures was provided by Raman spectroscopy, which showed that, under a magnetic field, the vibrational modes of the nanocomposite are altered by the deformation of the top ferrite layer. In turn, this will generate a stress at the shared interface, thereby leading to a shift toward higher wavenumbers of the Raman bands of both the perovskite and spinel phases.

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Highly ordered spinel ferrite M x Fe 3Àx O 4 (M ¼ Ni, Co, Zn) nanotube arrays were synthesized in anodic aluminium oxide (AAO) templates with a pore size of 200 nm by combining a liquid phase deposition (LPD) method with a template-assisted route. The morphology of the transition metal ferrite nanotubes was characterized by electron microscopy (FE-SEM; TEM, SAED and HRTEM) and atomic force microscopy (AFM), whereas their chemical composition was determined by inductive coupling plasma (ICP). The phase purity was studied by X-ray diffraction (XRD) and the magnetic properties of the nanotubes were measured by SQUID measurements. Unlike the deposition of thin film structures, nanotube arrays form within the pores of the AAO templates in a much shorter time due to the attractive interactions between the positively charged AAO and the negatively charged metal complex species formed in the treatment solution. The as-deposited nanotubes are amorphous in nature and can be converted into polycrystalline metal ferrites via a post-synthesis heat treatment which induce the dehydroxylation, crystallization and formation of the spinel structure. The resulting nanotubes are uniform with smooth surfaces and open ends and their wall thickness can be varied from 4 to 26 nm by increasing the deposition time from 1 to 4 h. Significant differences in the magnetic properties of the ferrite nanotubes have been observed and these differences seem to result from the chemical composition, the wall thickness and the annealing temperature of the spinel ferrite nanotubes.

The microstructure and the ferroelectric properties of mirrorlike polycrystalline PbTiO3 thin films were studied as a function of the film thickness. Highly uniform PbTiO3 films were deposited onto LaNiO3-buffered (100) Si substrates by liquid phase deposition at temperatures as low as 45 °C. The as-deposited films are amorphous and can be easily converted into single phase PbTiO3 thin films upon a heat treatment at 750 °C in air for 6 h. X-ray diffraction patterns of the films have shown that they are chemically pure and adopt a tetragonal structure with the value of the lattice volume slightly smaller than that of the bulk material, indicating the presence of a compressive stress. This was furthermore confirmed by Raman spectroscopy by monitoring the variation of the positions of the soft optical phonon modes with the thickness of the films compared to that of those measured from a powdered sample. The E(1TO) and E(2TO) phonon modes undergo an upward shift and this shift decreases with increasing as the films get thicker indicating the presence of a compressive stress which decreases with increasing the film thickness. Piezoelectric force microscopy (PFM) and PFM bit-lithography experiments performed at room temperature allowed not only the visualization of the ferroelectric domain structure but also control the orientation of dipoles with an external electric field, thereby confirming the high quality of the films. The PbTiO3 films are formed by 180° ferroelectric domains and the static value of the piezoelectric coefficient d33 was found to increase with the film thickness, presumably as a result of the reduction of the stress and the substrate-induced clamping effect.