Ferrite Films Research Articles

Thermally active nanoparticle clusters enslaved by engineered domain wall traps

The stable assembly of fluctuating nanoparticle clusters on a surface represents a technological challenge of widespread interest for both fundamental and applied research. Here we demonstrate a technique to stably confine in two dimensions clusters of interacting nanoparticles via size-tunable, virtual magnetic traps. We use cylindrical Bloch walls arranged to form a triangular lattice of ferromagnetic domains within an epitaxially grown ferrite garnet film. At each domain, the magnetic stray field generates an effective harmonic potential with a field tunable stiffness. The experiments are combined with theory to show that the magnetic confinement is effectively harmonic and pairwise interactions are of dipolar nature, leading to central, strictly repulsive forces. For clusters of magnetic nanoparticles, the stationary collective states arise from the competition between repulsion, confinement and the tendency to fill the central potential well. Using a numerical simulation model as a quantitative map between the experiments and theory we explore the field-induced crystallization process for larger clusters and unveil the existence of three different dynamical regimes. The present method provides a model platform for investigations of the collective phenomena emerging when strongly confined nanoparticle clusters are forced to move in an idealized, harmonic-like potential.

Electronic structure of nickel ferrite thin films growth on strontium titanate

In this study nickel ferrite thin films have been grown on strontium titanate-100 single crystal substrate by using RF magnetron sputtering. To investigate the electronic structure of nickel ferrite film, X-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy were employed. In the X-ray photoelectron spectra of Fe 3p, the presence of the valence states Fe2+ and Fe3+ was evidenced; also, Ni2+ and Ni3+ were identified in the Ni 3p spectra. The atomic ratio of 2.01 was found, which is agreeing to the nominal atomic ratio. By reflection electron energy loss measurements found a band gap between 1.77 eV. The magnetic properties were analyzed by vibrating sample magnetometry, indicating in-plane easy magnetization.

The ferroelectric response of island-like regions in bismuth ferrite oxide compound

We investigate the piezoelectric and ferroelectric properties in island-like ferroelectric regions of bismuth ferrite oxide films. Samples were synthesized by the simultaneous laser ablation of bismuth, and iron oxide targets. Bismuth content in the deposited films was controlled with the plasma density (Np) that is produced during the ablation of the Bi target. A change in the NpBi alters the Bi incorporation into the films. Relatively homogeneous films deposited at NpBi of 11 × 1012 cm−3 with an effective piezoelectric coefficient (deff) of ~15 pm/V served as the starting point. A reduction of NpBi at 2 × 1012 cm−3 produced films with almost null piezoelectrical response but at 4 × 1012 cm−3 caused the formation of island-like ferroelectric regions with large deff values that spans from 70 to 108 pm/V. The island-like regions presented upright hysteretic phase-switching loops with low coercive voltages and squareness values close to unity. The resulting large deff values were attributed to the reduction of the substrate-clamping effect, the (001)-textured BiFeO3 structure, and the coexistence of secondary phases with the main BiFeO3 phase. The mechanisms for polarization switching and the electromechanical response of the island-like regions are discussed. Finally, some preliminary results of ferroelectric fatigue experiments in island-like regions are presented.

Chemical Vapor Deposition of Cobalt and Nickel Ferrite Thin Films: Investigation of Structure and Pseudocapacitive Properties

AbstractTransition metal ferrites, such as CoFe2O4 (CFO) and NiFe2O4 (NFO), have gained increasing attention as potential materials for supercapacitors. Since chemical vapor deposition (CVD) offers advantages like interface quality to the underlying substrates and the possibility for coverage of 3D substrates, two CVD processes are reported for CFO and NFO. Growth rates amount to 150 to 200 nm h−1 and yield uniform, dense, and phase pure spinel ferrite films according to X‐ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA) and scanning electron microscopy (SEM). Atom probe tomography (APT) and synchrotron X‐ray photoelectron spectroscopy (XPS) give insights into the vertical homogeneity and oxidation states in the CFO films. Cation disorder of CFO is analyzed for the first time from synchrotron‐based XPS. NFO is analyzed via lab‐based XPS. Depositions on conducting Ni and Ti substrates result in electrodes with pseudocapacitive behavior, as evidenced by cyclovoltammetry (CV) experiments. The interfacial capacitances of the electrodes are up to 185 µF cm−2.

Structural, Optical and Magnetic Properties of Diamagnetic Cd2+ Incorporated Cobalt Ferrite Thin Films Deposited by Spray Pyrolysis

Structural, Optical and Magnetic Properties of Diamagnetic Cd2+ Incorporated Cobalt Ferrite Thin Films Deposited by Spray Pyrolysis

A Novel Trace-Level Ammonia Gas Sensing Based on Flexible PAni-CoFe2O4 Nanocomposite Film at Room Temperature.

In this study, we developed a new chemi-resistive, flexible and selective ammonia (NH3) gas sensor. The sensor was prepared by depositing thin film of polyaniline-cobalt ferrite (PAni-CoFe2O4) nanocomposite on flexible polyethylene terephthalate (PET) through an in situ chemical oxidative polymerization method. The prepared PAni-CoFe2O4 nanocomposite and flexible PET-PAni-CoFe2O4 sensor were evaluated for their thermal stability, surface morphology and materials composition. The response to NH3 gas of the developed sensor was examined thoroughly in the range of 1–50 ppm at room temperature. The sensor with 50 wt% CoFe2O4 NPs content showed an optimum selectivity to NH3 molecules, with a 118.3% response towards 50 ppm in 24.3 s response time. Furthermore, the sensor showed good reproducibility, ultra-low detection limit (25 ppb) and excellent flexibility. In addition, the relative humidity effect on the sensor performance was investigated. Consequently, the flexible PET-PAni-CoFe2O4 sensor is a promising candidate for trace-level on-site sensing of NH3 in wearable electronic or portable devices.

Control of Magnetic Properties of Barium Ferrite Thin Films With Unusual Valence Fe

Thin films of BaFe1-xMxO3 (M = Hf, Zr, and Ce; 0.0 ≤ x ≤ 0.75) were fabricated using pulsed laser deposition and their magnetic properties were investigated. X-ray diffraction analysis indicated that oxygen-deficient BaFeOx (x < 3.0) with a monoclinic structure was formed when the deposition was conducted using a non-substituted target (x = 0.0). The as-grown BaFeOx films were converted into fully oxidized BaFeO3 with a perovskite structure by low-temperature oxidation in an ozone atmosphere. In contrast, the as-deposited films of Hf, Zr, and Ce-substituted films exhibited a perovskite structure, and their crystallinity did not change after low-temperature ozone annealing. The magnetic transition temperature Tc of the BaFeO3 film was 115 K, whereas the substituted BaFeO3 films showed ferromagnetic behavior even at 300 K. These results can be attributed to the weakening of the antiferromagnetic super-exchange coupling among Fe ions owing to the lattice expansion in the substituted BaFeO3. In addition, the magnetization of the films was found to increase with the decreasing ionic ratio of Fe4+/Fe3+, suggesting that the inherent carrier-induced ferromagnetic interaction is dominant in the films.

High temperature treatment of epitaxial nickel ferrite thin films: The way to bulk-like magnetic properties

An appropriate choice of growth conditions has made feasible fabrication of thin epitaxial NiFe2O4 / SrTiO3 films with parameters close to those of bulk nickel ferrite. Spin waves with a damping parameter as low as 10-2 and a very narrow ferromagnetic resonance line were observed in the samples subjected to post-growth high temperature annealing in oxygen. The analysis of electron and X-ray diffraction has shown substantial improvement of the crystalline quality of the annealed films. X-ray absorption spectroscopy and X-ray magnetic circular dichroism data simulation have revealed that the films exhibit a completely inverted spinel structure characterized by the maximal possible net magnetic moment.

Design of ultra-compact TE mode ring optical isolator using a cobalt ferrite film for silicon photonic integrated circuits

In this study, we present the design of an integrated transverse electric mode isolator realized by the epitaxial growth of a cobalt ferrite (CFO) film on a silicon micro-ring resonator structure. Exploiting the large magneto-optical activity of CFO along with the good characteristics of resonator structures, we numerically demonstrated isolator designs with ultra-compact sizes. The use of ring resonator structures with the reduced size is appealing because of lower insertion loss values. The nonreciprocal phase shift was maximized by optimizing the ring cross-section and was further studied in terms of the ring radius employing a transformation optics theory. Finally, we analyzed the optical isolator characteristics in terms of ring size and ring-waveguide power coupling ratio. The computed results pointed out that decreasing the ring size improves the device performance and can ease the device design and fabrication process.

Complementary study of anisotropic ion conduction in (110)-oriented Ca-doped BiFeO3 films using electrochromism and impedance spectroscopy

Oxygen vacancies are ubiquitous in oxides, and taking advantage of their mobility is the cornerstone for a variety of future applications. The visualization and quantification of collective defect flow based on electrochromism is a powerful approach to explore oxygen kinetics and electrochemical reaction even in cases that electronic conduction is considerably mixed, but whether or not the measured kinetic properties harmonize with those obtained by the conventional impedance spectroscopy remains veiled. Here, we identify complementary relationships between the two methods by investigating the oxygen vacancy transport in Ca 30%-doped bismuth ferrite thin films epitaxially grown on SrTiO3 (110) substrates. We find that the activation energy of ionic hopping is 0.78 (or 0.92 eV) for the application of an electric bias along [001] (or [11¯0]) due to the grain elongation along [001]. We anneal the films in an N2 gas environment at high temperatures to suppress the electronic contribution for access to standard impedance spectroscopy. The oxygen kinetic properties obtained from the two methods are consistent with each other, complementarily revealing the collective phase evolution as well as the ionic impedance of the bulk, grain boundary, and interfacial regions. These comparative works provide useful insights into ionic defect conduction in oxides in an intuitive and quantitative manner.

Influence of Gd doping and thickness variation on structural, morphological and optical properties of nanocrystalline bismuth ferrite thin films via sol–gel technology

Influence of Gd doping and thickness variation on structural, morphological and optical properties of nanocrystalline bismuth ferrite thin films via sol–gel technology

Anneal temperature dependence of resistive switching and photoelectric properties of Bismuth ferrite thin film prepared via sol–gel method

Enhancement on resistive switching characteristics of Bismuth ferrite (BFO) has attracted persistent interest in the past decades due to the inimitable interior structure. In the work, the amorphous and the polycrystalline Bismuth ferrite thin films have been successfully prepared via sol–gel method. We utilize X-ray diffraction, Transmission Electron Microscope and absorption spectrum to characterize the internal structure and calculate the band gap of Bismuth ferrite thin film samples. By comparing the current–voltage (I-V) characteristics between the amorphous and the polycrystalline sample, we investigate the amorphous sample has better resistive switching performance (switching ratio is 104) than that of polycrystalline (101) bismuth ferrite thin film devices. However, the polycrystalline Bismuth ferrite sample exhibits favorable switchable photovoltaic response and good stability. Additionally, we discuss the conduction mechanism via the double logarithm fitting of amorphous Bismuth ferrite sample. The article also indicates that resistive switching property is closely related with the defects such as oxygen vacancies. The article deepens the comprehension of resistive switching properties of amorphous and polycrystalline Bismuth ferrite thin film which would have further potential applications in advanced electronic devices such as new resistive memory.

Immobilization of diastase on PVA- CoFe2O4 nanocomposite film for improving stability and recycling

Enzyme immobilization on a suitable support is one of the strategies used to improve enzyme stability and recovery. In present communication, PVA-CoF2O4 nanocomposite film has been used as a support to develop highly active, stable and magnetically separable immobilized diastase. For preparing magnetically separable support, first Cobalt ferrite nanoparticles have been prepared by using co-precipitation method. Prepared nanoparticles have been dispersed in polyvinyl alcohol (PVA) solution to get a PVA-CoFe2O4 film. The detail characterization of cobalt ferrite nanoparticles and PVA-CoFe2O4 film has been carried out. Enzyme diastase has been immobilized on the PVA-CoFe2O4 film and the catalyst activity of immobilized enzyme has been tested in hydrolysis of starch to maltose. The stability of immobilized diastase has found to be higher than free enzyme. Reusability study of the immobilized diastase has been carried out. Improved stability and reusability of immobilised diastase offer the promising applicability as magnetically separable biocatalyst for industry.

Study the electrical and magnetic properties of Ferrite Ni1-x ZnxFe2O4 films and their potential use in the magnetic core of transformers

Membranes (Ni1-x ZnxFe2O4) were prepared by chemical precipitation method and with different weight ratios of values (x = 0, 0.3, 0.5, 0.7, 0.9), the electrical properties of the prepared samples were studied with the presence of a magnetic field of magnitude (0.45T), the result (Hall Effect) The majority of charge carriers are electrons, while the results of magnetic tests showed that the prepared films of different weights are of a type (soft Ferrite) The membranes behaved as a ferromagnetic material. The results indicate that the membranes can be used in the fields of microwave frequencies and in the transformers inside the magnetic core due to the smallness of the hysterical loop.

Low-temperature solid-phase pyrolysis: A new method for the synthesis of nanocrystalline NiFe2O4 thin films

Nickel ferrite thin films were synthesized by a new method of solid-phase pyrolysis. The effect of the annealing temperature on the films characteristics has been studied. The obtained films were characterized by X-ray diffraction (XRD), thermal and thermogravimetric analysis (TG-DTA), and scanning probe microscopy (SPM). XRD showed a single-phase cubic spinel structure. The average size of NiFe2O4 crystallites was 28, 30, 42, and 53 nm for samples annealed at 500, 600, 700, and 800 °C, respectively. The films thickness is about 40 nm. The SPM data confirm a high-quality of the film surface, formed by nanocrystallites. The obtained films are well organized, which makes the proposed as a promising method of synthesis in the thin films preparation processes employed in a variety of applications.

Spray deposited multimetal Cu-Ni-Zn ferrite for gas sensing application

In this work, nanocrystalline Cu-Ni-Zn ferrite thin films were deposited by the cost-effective spray pyrolysis technique and characterized for structural, elemental, morphological, and gas sensing properties. The XRD confirmed the nanocrystalline nature of the film. The morphology of the sample was found with surface pores as a consequence of porogen activity. The deposited material was found better responding to SO2 gas. The optimal operating temperature of the sensor was found 120 ℃. This operating temperature is much lower than earlier reported SO2 gas sensors. At optimal operating temperature, it showed linear response up to 50 ppm of gas exposure.

Effects of Crystal Structure, Morphology and Ion Diffusion During Annealing on Magnetic Properties of Hexagonal Barium Ferrite Films

Effects of Crystal Structure, Morphology and Ion Diffusion During Annealing on Magnetic Properties of Hexagonal Barium Ferrite Films

Magnetic properties regulation by electric-field for α-Fe2O3/LiTaO3 thin film at room temperature

Ion migration driven by electric-field may cause multiple changes in stoichiometry, defect, and structure, thus provide approach for modulating properties. α-Fe2O3 have attracted tremendous attention as anode materials for lithium ion batteries. The magnetic properties of weakly-ferromagnetic α-Fe2O3/LiTaO3 films can be manipulated non-volatilely at room temperature by the applied room temperature electric-field. The regulation of magnetic properties induced by the room temperature electric-field may relate to the migration effects of lithium ions. A theoretical investigation on the microstructure and magnetic properties before and after the insertion of lithium ion into α-Fe2O3 shows that the insertion of lithium ion induces local structural distortion, charge redistribution and the magnetic moment increase. This study makes a step forward for electric control of magnetism in solid-state ferrite film and provides opportunities for the development of multifunctional structures

Structure and dielectric properties of thin nanocrystalline ZnFe2O4 films

Optically transparent high-quality nanosized crystalline zinc ferrite thin films on different substrates have been synthesized by the decomposition of organic zinc and iron (III) compounds. According to scanning probe microscopy study, the films are 40-50 nm thick and their surface consists of densely spaced uniformly oriented crystallites with morphology depending on the substrate. X-ray diffraction analysis has shown that the films are polycrystalline and ZnFe2O4 has a cubic spinel structure. The dielectric constant lies in the range of 53 ÷ 54. The films are spontaneously polarized with a residual polarization of about 0.59 ÷ 0.69 μC⋅cm−2 , the coercive field is (8 ÷ 12)·104 V/cm.

Diverse physical characteristics of mixed Li–Mg spinel ferrite thin films fabricated by spray pyrolysis technique

Nanocrystalline Li0.5-x/2MgxFe2.5-x/2O4 (0.0≤x ≤ 1.0) thin films have been effectively fabricated by spray pyrolysis technique. These films show monophase cubical construction as appeared in the XRD patterns and also validated by FTIR spectroscopy. The optical energy band gap values were obtained in the range of 1.78–2.52 eV. The excitation wavelengths were found to be in between 400 and 410 nm which attributed to the holes and electron in photoluminescence spectra. VSM results reveal that magnetic parameters lowered with Mg2+-substitution in Li0·5Fe2·5O4. The incorporation of Mg2+-substitution in pristine lithium ferrite thin films promotes the tailoring of the structural, optical and magnetic properties.