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Electron transport in ferroelectric tunnel junctions (FTJs) with a three-step-like barrier combining a dielectric, ferromagnetic, and ferroelectric was investigated theoretically. A significant enhanced tunneling electroresistance effect was observed as compared to traditional FTJs with a bilayer composite barrier. The spin polarization also could be enhanced in a certain orientation of ferroelectric polarization. A metal/dielectric/ferromagnetic/ferroelectric/metal FTJ with a large ferromagnetic thickness is preferred for the optimal performance. The ferroelectricity in the ferroelectric layer has a weak modulation effect on the spin polarization. This work provides a way to enhance the performance of FTJs and/or to control the spin-polarized electronic transport by structure engineering.

This report is on the observation and theory for strong mechanical strain mediated magneto-electric (ME) coupling in composites of lead zirconate titanate (PZT) and self-biased Y- or W-type hexagonal ferrites. Polycrystalline Y-type (Ni1−xZnx)2 Y, and W-type (Co1−xZnx)2 W, hexagonal ferrites for x = 0–0.4 prepared by ceramic processing techniques showed a large remanent magnetization due to uniaxial or in-plane magneto-crystalline anisotropy. The strength of ME coupling in symmetric trilayer composites of the ferrites and PZT was measured by the ME voltage coefficient (MEVC) at low-frequencies and at longitudinal electromechanical resonance. The bias magnetic field H-dependence of MEVC at low-frequencies in the composites with (Ni, Zn) Y showed hysteresis with its value under self-bias 90% or more of the value for the optimum bias field. In the case of composites with W-type ferrites, the MEVC under zero-external bias was 60%–80% of its value for the optimum bias field. Both types of composites when subjected to an ac magnetic field at the EMR frequency showed an order of magnitude enhancement in the MEVC compared to low-frequencies and the peak value at EMR for zero-bias was 90% of its value under the optimum bias. A model has been developed for the large ME response under the self-bias provided by the remanent magnetization and estimated values of MEVC are in good agreement with the data. The hexaferrite-ferroelectric composites showing ME response without the need for an external magnetic bias are of importance for use as sensors and sensor arrays of magnetic fields.

The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fibers can be assembled into superstructures with the aid of magnetic and electric fields and characterized for possible use in advanced technologies. Chemical-vapor deposition techniques have been shown to be effective for the preparation of heterostructures of ferrites and ferroelectrics. Exotic planar multiferroic structures with potential for enhancing ME coupling strengths are also considered. Scanning probe microscopy techniques are ideal for probing the nature of direct- and converse-ME coupling in individual nanostructures. Magnetoelectric characterization of assemblies of nanocomposites can be done by ME voltage coefficient, magnetic field induced polarization, and magneto-dielectric effects. We conclude with a brief discussion on possible avenues for strengthening the product properties in the nanocomposites.

Theoretical investigations on ferroelectric tunnel junctions (FTJs) with a fixed-thickness composite layer (Pt/MgO/BaTiO3/Pt and Pt/SrTiO3/BaTiO3/Pt) were conducted. It showed that there is an optimal dielectric thickness that can bring the largest tunneling electroresistance (TER) ratio provided that the ferroelectricity does not change with the dielectric thickness. The optimal dielectric thickness is insensitive to ferroelectric polarization in ferroelectric layer and increases linearly with the composite barrier thickness. Considering the size effect of ferroelectricity, the optimal dielectric thickness (unit cells) changes little if the polarization increases slowly with the ferroelectric thickness. Such studies may help to fabricate FTJs with larger TER ratio and put them into practical application.

In this work, we present the results obtained in fabrication and characterization of single-crystalline lead titanate nanowires synthesized by surfactant-free hydrothermal method at 200°C. The as-prepared samples were characterized by means of x-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, x-ray photoelectron spectroscopy (XPS), thermogravimetry and differential thermal analysis, Fourier transformation infrared spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and ultraviolet-visible spectroscopy. The results show that the products have a tetragonal perovskite structure without any other impurity phase, which are made up of a large quantity of nanowires with uniform diameters of about 12nm and lengths reaching up to 5μm, and the growth of nanowires is generally along the [001] direction. XPS result shows that the binding energy of Ti2p(3∕2) core level peak for PbTiO3 nanowires is larger than that of the corresponding ceramics and leads to the larger spin-orbit splitting (Δ[2p(3∕2)−2p(1∕2)]) for Ti2p. Raman studies show that the vibration modes of nanowires redshifted and broadened, which have shorter phonon lifetime compared to that of bulk materials. A blue light emission peaking at about 471nm (2.63eV) is observed at room temperature, oxygen vacancies are responsible for the luminescence in PbTiO3 nanowires. The band gap energy for PbTiO3 nanowires was about 4.15eV.

Sol-gel-derived (Ba0.65,Sr0.35)TiO3 (BST) thin films were etched in CF4∕Ar and CF4∕Ar∕O2 plasmas using magnetically enhanced reactive ion etching technology. Experimental results show that adding appropriate O2 to CF4∕Ar can better the etching effects of BST films for the increase of etching rate and decrease of etched residues. The maximum etching rate is 8.47nm∕min when CF4∕Ar∕O2 gas-mixing ratio is equal to 9∕36∕5. X-ray photoelectron spectroscopy (XPS) data confirm accumulation of reaction products on the etched surface due to low volatility of reaction products such as Ba and Sr fluorides, and these residues could be removed by annealing treatment. The exact peak positions and chemical shifts of the interested elements were deduced by fitting XPS narrow-scan spectra with symmetrical Gaussian-Lorentzian product function for Ba 3d, Sr 3d, and O 1s peaks, meanwhile asymmetrical Gaussian-Lorentzian sum function was used to fit Ti 2p doublet to adjust the multiple splitting and/or shake-up process of tran...