Cobalt ferrite nanoparticles were prepared by co-precipitation method and were heat treated at 100 oC, 200 oC, 400 oC and 600 oC for 2 h to increase the particle size. Phase purity of samples was confirmed by X-ray diffraction. Scherrer formula calculations showed crystallite size varied from 12 to 24 nm when heated from 100 oC to 600 oC. Transmission electron microscopy reveals a uniform and narrow particle size distribution about 12 nm for as-prepared cobalt ferrite particles. Room temperature saturation magnetization was found to vary from 40.8 to 67.0 emu/g as the particle size increased from12 nm to 24 nm. Increase in saturation magnetization with increase in particle size was attributed to the presence of magnetic inert layer on the surface of nanoparticles. Inert layer thickness calculated at 10 K and 300 K was 6 Å and 11 Å respectively. The dielectric properties ε’, tanδ, Z and θ have been studied as a function of frequency and particles size. For the 12 nm grain size, the dielectric constant is one order higher than that of bulk cobalt ferrite. Increase in the grain size showed an increase in the dielectric constant. The increase in the conductivity with grain size is mainly due to the grain size effects. The present study shows that the dielectric properties can be tailor-made to suit the requirement of a particular application by controlling the grain size.

A systematic study was carried out to determine the effects of composition and grain size on the structural, optical and magnetic properties of pure ZnO and vanadium-doped ZnO nanocrystalline powders and films in the 0.0 at.% V - 6 at.% V range. The powders and films were synthesized via a sol-gel approach, where ethanolamine was used to increase the viscosity of the precursor solutions and promote the adhesion of the films onto quartz substrates. Powder X-ray diffraction confirmed the formation of ZnO (host oxide) after annealing of the precursors in air. The average grain size in the thin films ranged from 11 nm to 23 nm when the samples were annealed in air for one hour between 450ºC and 550ºC. UV-vis and photoluminescence confirmed the formation of the host oxide. Also, the photoluminescence intensity was found to be strongly dependent on the amount vanadium. Furthermore, it was found that the vanadium concentration and the annealing temperature play an important role in the ferromagnetic behavior of the material.

Pt/Pb(Zr0.4Ti0.6)O3 (PZT)/Pt capacitors were prepared by the sol-gel technique and their electric properties were analyzed. The asymmetry of polarization-electric field (P-E) and capacitor-voltage (C-V) curves exhibits existence of an interface layer (dead-layer) between top Pt electrode and PZT thin film. By conducting temperature dependant measurement, the Pt/PZT/Pt capacitor was confirmed to be Schottky emission conduction. In addition, barrier height of PZT contact calculated 0.67eV. On basic a series capacitors model and Schottky contact of Pt/PZT interface, the thickness and the dielectric constant of this dead-layer were estimated to be 6.4 nm and 170, respectively. Moreover, the dielectric constant of 900 was obtained for the real PZT ferroelectric layer. The existence of the dead-layer was also confirmed by the high resolution transmission electron microscopy (HR-TEM) observation and the energy dispersive X-ray (EDX) analysis on PZT ferroelectric layer in the Pt/PZT/Pt structure. Based on EDX analysis result, a 10-nm layer at Pt/PZT contact was suggested to be the dead-layer.

This study reports on the structural and magnetic characterizations of free-standing bismuth ferrite, BiFeO3, nanoparticles synthesized in polyol medium. Fine tuning of the ferrite magnetic properties was achieved by adding an excess bismuth species or doping with cobalt ions, coupled with thermal annealing. Crystalline Bi1-yCoyFeO3 powders (where ‘y’ ranges from 0.00 to 0.10) were produced after annealing the precursors for one hour at 700οC. The average crystallite size was calculated to be approximately 22 nm. We found that the synthesis under stoichiometric excess of Bi species (up to 10 at.%) promoted a more complete crystallization of the material, i.e., no precursor phases remained. Furthermore, both the saturation magnetization and the coercivity of the synthesized powders were strongly influenced by the concentration of Co. They increased from 0.13 emu/g and 19 Oe to 3.5 emu/g and 1183 Oe for pure BiFeO3 and 10 at.% Co-doped BiFeO3, respectively.

Cobalt Ferrite/Barium Titanate nanotube arrays were obtained in anodic aluminum oxide templates (AAO) of 100 nm pore diameter by a two step sol-gel process. Each phase was grown in several wetting – drying cycles starting from the cobalt ferrite layers with the barium titanate on top. As-dried composite structures were sintered at 700 C. The composite nanotubes showed a fine polycrystalline microstructure with an average grain size of 5 nm. The formation of both spinel and perovskite structures was verified by High Resolution Transmission Electron Microscopy (HR-TEM) on isolated nanotubes. The growing rate by layer was found to be lower for the BaTiO3 on top of CoFe2O4 than the later on top of the AAO. Wall sizes were estimated by Z-contrast as 9.8 nm for one layer of CoFe2O4 and 6.6 nm for six layers of BaTiO3. Magnetic properties were studied by VSM. Samples showed ferromagnetic behavior with low coercive values. By means of a finite element model the deformation and stress on the piezoelectric phase was estimated and used to simulate the magnetization reversal under stress in the composite nanotubes, using an updated micromagnetic framework to include the magnetostriction effect. Simulation results showed that a curling mode is expected with opposite vortex states at the end of the nanotubes. The change in the vortex domain structure under voltage driven applied stress is presented and discussed.

Perovskite-type transition metal oxides have great potential as storage material in resistive random-access memory (RRAM) devices. Typical non-volatile memory cells are realized in metal-insulator-metal (MIM) stacks with insulator thicknesses of few nanometers. We report on the investigation of single-crystal SrTiO3 to understand the role of volume and interface real structure for the electrical conductivity in such materials. Conductivity in SrTiO3 single crystals was established by a reducing high vacuum (HV) annealing introducing charged oxygen vacancies acting as donor centers. Titanium electrodes are evaporated on both crystal faces to obtain an MIM element.

Nanocomposites formed by ferrimagnetic and ferroelectric materials are multiferroic material in which magnetoelectric coupling occurs via piezoelectricity and magnetostriction phenomena. These nanocomposites have a variety of applications in tunable microwave devices using electric control of spin wave propagation or new magnetic memories in which the magnetic response is controlled by electric field.

In this work, transparent and homogeneous thin films of barium titanate interleaved with cobalt ferrite were prepared by sol–gel method using dip-coating process. Films of pure barium titanate and cobalt ferrite were also prepared for comparison. The nanocomposite films were deposited onto clean quartz substrates, where a coating of each material was deposited interleaved, where the cobalt ferrite film formed the last layer. The films were dried in air after each dipping and heated at 900 oC for 1 hour to convert the amorphous films into crystalline ones. The samples were characterized by low angle X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) and UV-Vis spectroscopy.

Recently, high K materials play an important role in microelectronic devices such as capacitors, memory devices, and microwave devices. Now a days ferroelectric barium strontium titanate [BaxSr1-xTiO3, (BST)] thin film is being actively investigated for applications in dynamic random access memories (DRAM), field effect transistor (FET), and tunable devices because of its properties such as high dielectric constant, low leakage current, low dielectric loss, and high dielectric breakdown strength. Several approaches have been used to optimize the dielectric and electrical properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found that inserting a ZrO2 layer in between two BST layers results in a significant reduction in dielectric constant, loss tangent, and leakage current in the multilayer thin films. Also it is shown that the properties of multilayer structure are found to depend strongly on the sublayer thicknesses. In this work the effect of ZrO2 layer thickness on the dielectric, ferroelectric as well as electrical properties of BST/ZrO2/BST multilayer structure is studied. The multilayer Ba0.8Sr0.2TiO3/ZrO2/Ba0.8Sr0.2TiO3 film is deposited by a sol-gel process on the platinized Si substrate. The thickness of the middle ZrO2 layer is varied while keeping the top and bottom BST layer thickness as fixed. It is observed that the dielectric constant, dielectric loss tangent, and leakage current of the multilayer films reduce with the increase of ZrO2 layer thickness and hence suitable for memory device applications. The ferroelectric properties of the multilayer film also decrease with the ZrO2 layer thickness.

Currently, ferroelectric and ferromagnetic particulate composites are receiving a great deal of interest due to their novel applications in microelectronic devices. Their excellent properties such as high relative dielectric constant, low dielectric loss, strong tunability, and ferromagnetism with colossal magnetoresistance can be controlled by manipulating both electric and magnetic fields. Ba0.7Sr0.3TiO3 /La0.67Sr0.33MnO3 (BST/LSMO) composite was prepared with 20:1 wt% by a high temperature solid-state reaction route. The X-ray diffraction (XRD) pattern confirmed the formation and the coexistence of both phases corresponding to BST and LSMO. High resolution field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) revealed a uniform distribution of the grain size throughout the surface of the sample and the presence of all the constituent elements with its esteemed reaction stoichiometry, respectively. In spite of the presence of both phases, only one transition peak was seen (50Hz-5MHz) around 295 K in dielectric measurement suggesting a nonlinear magnetoelectric coupling. The dielectric properties of BST/LSMO composite carried with different magnetic fields (0-1.7 T) show significant change in the BST dielectric behavior at low frequencies. The M-H curves at room temperature (RT) showed a drop in the saturation magnetization compared with pure LSMO is consistent with our composite structures.

We briefly review our data on MOCVD growth problems of sandwich stacked heterostructures based on Bi-Sr-Ca-Cu-O and YBa2Cu3O7 high temperature superconductors. Non-superconducting layers were (Ca, Sr)CuO2, (Ca, Ba)CuO2 and Bi4Ti3O12. Structures were with c-axis normal or inclined with about 45° vs. the surface of the substrate. Film-substrate lattice relationship, growth mechanism and the resulting morphology controlling roughness and uniformity, stability domain of the phases and inter diffusion are all important aspects toward significant progress in the field. Our analysis indicates that requirements are more severe for non-c-axis heterostructures, and suggest some ideas for further improvements.

Undoped Bi2FeCrO6, 5%Ti- and 10%La-doped Bi2FeCrO6 were prepared by a high pressure solid-state sintering method. The phase structure, electrical, ferroelectric and magnetic properties have been investigated. It is shown that undoped Bi2FeCrO6 has a serious leakage current problem, and doping either Ti or La can enhance the resistivity by 2-3 orders of magnitude. Furthermore, both Ti- and La-doped Bi2FeCrO6 show an antiferromagnetic spin order due to disordered B-site cation alignment. Weak ferromagnetism was only observed in undoped Bi2FeCrO6 and the reason is tentatively explained.

Barium strontium titanate solidly mounted resonators were fabricated with patterned and unpatterned acoustic Bragg reflectors on a sapphire substrate. The patterned and unpatterned solidly mounted resonator devices had acoustic Bragg reflectors consisting of Pt/SiO2/Pt/SiO2. The s-parameters of both devices were measured. The results showed that the quality factor increased for the device with the patterned acoustic Bragg reflector structure. The quality factors for the devices with patterned and unpatterned acoustic Bragg reflector structures were 54 and 115 and 28 and 86, respectively at the resonant and antiresonant frequencies. This investigation shows how an unpatterened acoustic Bragg reflector can contribute to the degradation of the overall quality factor of the device.

Two different types of ferroelectric/semiconductor heterostructures, made up of Pb(Zr,Ti)O3/ZnO and BiFeO3/ZnO respectively, were fabricated on Pt(111)/Ti/SiO2/Si(100) by sol-gel process. Obvious diodelike behavior were observed in BiFeO3/ZnO heterostructures when current-voltage characteristics were measured, while Pb(Zr,Ti)O3/ZnO heterostructures exhibited a symmetrical behavior. It is found that Pb(Zr,Ti)O3/ZnO heterostructures showed a large polarization and the remnant polarization was approximately 15μC/cm2. The remnant polarization performed a modulation on the channel resistance. The different properties of two heterostructures might lead to different applications.