Fe3O4 Thin Films Research Articles

Confirmation of spatial coexistence of magneto-electric coupling in Bi0.7Dy0.3FeO3 thin films integrated with Si/ZnO film for MEMS and memory applications

Spatial presence of ferroelectric and magnetic domain structure of the multiferroic dysprosium (Dy)-modified BiFeO3 (Bi0.7Dy0.3FeO3 or BDFO) deposited on ZnO at the macroscopic level is investigated in this paper. BDFO thin film is deposited on Si/ZnO using pulsed laser deposition (PLD) technique. Magnetic properties are observed by saturated magnetic hysteresis at room temperature. Ferroelectric hysteresis loop (P–E) is used to compare the response of magnetic field on ferroelectric properties at room temperature of BDFO and BDFO/ZnO thin films. The changes in ferroelectric hysteresis loops with magnetic field ensures about the magnetoelectric (M–E) coupling in BDFO/ZnO films. A well-saturated ferroelectric hysteresis loop with remarkable improvement in remanent polarization (∼1.72μC/cm2) is observed. The obtained results confirm the coexistence of ferromagnetic and ferroelectric ordering with significant coupling at room temperature. The coupling behavior and magnetic transition are also verified using multimode atomic force microscope by applying bias between sample and MFM tip. The leakage current density is measured in the order of 10−5A/cm2. Integration of BDFO films with ZnO piezoelectric thin film suggests in principle its potential in applications of micro electro mechanical systems (MEMS) as well as in memory devices and in strong history dependent systems.

Electrostatic force microscopy analysis of Bi0.7Dy0.3FeO3 thin films prepared by pulsed laser deposition integrated with ZnO films for microelectromechanical systems and memory applications

In this paper, we report the charge trapping phenomena in zinc oxide (n-ZnO) and Bi0.7Dy0.3FeO3(BDFO)/ZnO thin films deposited onp-type <100> conducting Si substrate. The significant change in contrast above the protrusions of ZnO verifies the possibility of heavy accumulation of injected holes in there. The ZnO and BDFO/ZnO films were characterized by the electrostatic force microscopy (EFM) to understand the phase dependence phenomenon on the bias supporting electron tunnelling. The EFM has an important role in the analysis of electrical transport mechanism characterization and electric charge distribution of local surface in nanoscale devices. It was observed that in BDFO/ZnO, the contrast of EFM images remains constant with the bias switching and that primarily indicates availability of trap sites to host electrons. The change in contrast over the protrusions of ZnO suggests that mobility of the electrical charge carriers may be through the grain boundary. The formation of these hole-trapped sites may be assumed by bond breaking phenomenon.

Investigation of defects dependence of local piezoelectric response on Fe, La-modified (Pb,Sr)TiO3 thin films: A piezoresponse force microscopy study

In this study, undoped-(Pb,Sr)TiO3 and Fe3+, La3+ co-doped (Pb,Sr)TiO3 thin films were investigated at the nanoscale level by piezoresponse force microscopy (PFM), in order to evaluate the impact of doping-induced damages on the ferroelectric and piezoelectric properties. Detailed investigations with nanoscale resolution have revealed occurrence of abnormal domains in writing pattern under forward and reverse bias for (Pb,Sr,La)(Ti,Fe)O3 thin films. Further piezoresponse hysteresis loop measurements show that fully switchable loops were observed under high voltage mediated by defect dipoles and by “ferroelectric-like” polar defects clusters. They have been discussed taking into account charged defect formation with both local changes in the dipole moment and local symmetry breaking effects. In addition, the domain writing and its retention behavior of the undoped-PST and (Pb,Sr,La)(Ti,Fe)O3 thin films were investigated. Undoped-PST films exhibited better stability for both positive and negative domains for a relatively long time in comparison to that observed for (Pb,Sr,La)(Ti,Fe)O3 films.

Ni: Fe2O3, Mg: Fe2O3 and Fe2O3 thin films gas sensor application

Iron oxide is a widely used sensitive material for gas sensor applications. They have fascinated much attention in the field of gas sensing and detecting under atmospheric conditions and at 200 °C temperature due to their low cost in production; simplicity and fast of their use; large number of detectable gases. Iron oxide gas sensors constitute investigated for hazardous gases used in various fields.The morphological structure (particle size, pore size, etc.), optical, magnetic and electrical properties of Ni:Fe2O3, Mg:Fe2O3 and Fe2O3 thin films which grown by Spray pyrolysis (SP) have been investigated. XRD, Raman and AFM techniques have been used for structural analysis. AFM measurements have been provided very useful information about surface topography. I-V (Van der Pauw) technique has been used for response of gas sensor. These devices offer a wide variety of advantages over traditional analytical instruments such as low cost, short response time, easy manufacturing, and small size.

Strain-Driven Nanoscale Phase Competition near the Antipolar-Nonpolar Phase Boundary in Bi0.7La0.3FeO3 Thin Films.

Complex-oxide materials tuned to be near phase boundaries via chemistry/composition, temperature, pressure, etc. are known to exhibit large susceptibilities. Here, we observe a strain-driven nanoscale phase competition in epitaxially constrained Bi0.7La0.3FeO3 thin films near the antipolar-nonpolar phase boundary and explore the evolution of the structural, dielectric, (anti)ferroelectric, and magnetic properties with strain. We find that compressive and tensile strains can stabilize an antipolar PbZrO3-like Pbam phase and a nonpolar Pnma orthorhombic phase, respectively. Heterostructures grown with little to no strain exhibit a self-assembled nanoscale mixture of the two orthorhombic phases, wherein the relative fraction of each phase can be modified with film thickness. Subsequent investigation of the dielectric and (anti)ferroelectric properties reveals an electric-field-driven phase transformation from the nonpolar phase to the antipolar phase. X-ray linear dichroism reveals that the antiferromagnetic-spin axes can be effectively modified by the strain-induced phase transition. This evolution of antiferromagnetic-spin axes can be leveraged in exchange coupling between the antiferromagnetic Bi0.7La0.3FeO3 and a ferromagnetic Co0.9Fe0.1 layer to tune the ferromagnetic easy axis of the Co0.9Fe0.1. These results demonstrate that besides chemical alloying, epitaxial strain is an alternative and effective way to modify subtle phase relations and tune physical properties in rare earth-alloyed BiFeO3. Furthermore, the observation of antiferroelectric-antiferromagnetic properties in the Pbam Bi0.7La0.3FeO3 phase could be of significant scientific interest and great potential in magnetoelectric devices because of its dual antiferroic nature.

Optical Properties of Fe3O4 Thin Films Prepared from the Iron Sand by Spin Coating Method

Research on magnetic oxide is growing very rapidly. This magnetic oxide can be found in nature that is in iron sand. One of the beaches in Sumatera Barat containing iron sand is Tiram Beach, Padang Pariaman District, Sumatera Barat. The content of iron sand is generally in the form of magnetic minerals such as magnetite, hematite, and maghemit. Magnetite has superior properties that can be developed into thin films. The purpose of this research is to investigate the optical properties of transmittance, absorbance, reflectance and energy gap from Fe3O4 thin films. This type of research is an experimental research. The iron sand obtained from nature is first purified using a permanent magnet, then made in nanoparticle size using HEM-E3D with milling time for 30 hours. After that, the process of making thin film with sol-gel spin coating method. In this research, variation of rotation speed from spin coating is 1000 rpm, 2000 rpm and 3000 rpm. Based on XRD results indicated that the iron sand of Tiram beach contains magnetite minerals and the SEM results show that the thickness of the thin films formed is 25μm, 24μm and 11μm. The characterization tool used for characterizing optical properties is the UV-VIS Spectrophotometer. So it can be concluded that the greater the speed of rotation the thickness of the thin layer will be smaller, resulting in the transmittance and reflectance will be greater, while the absorbance will be smaller. Energy gap obtained from this research is 3,75eV, 3,75eV and 3,74eV. So the average energy gap obtained is 3,75eV.

Analysis of Crystal Structure of Fe3O4 Thin Films Based on Iron Sand Growth by Spin Coating Method

Recently, iron sand used as one of base materials in the steel industry. However, the content of iron sand can be used as starting materials in sensor technology in the form of thin films. In this paper, we report the analysis of crystal structure of magnetite thin film based on iron sand from Tiram’s Beach. The magnetic content of sand separated by a permanent magnet, then it was milled at 30 hours milling time. In order to increase the purity of magnetite, it washed after milling using aquades under magnetic separation by a magnet permanent. The thin film has been prepared using iron (III) nitrate by sol–gel technique. The precursor is resulted by dissolving magnetite in oxalic acid and nitric acid. Then, solution of iron (III) nitrate dissolved in ethylene glycol was applied on glass substrates by spin coating. The X-Ray Diffraction is operated thin film characterization. The structure of magnetite has been studied based on X-Ray Peaks that correspond to magnetite content of thin films.

Training effect of the exchange bias in sputter deposited Fe3O4 thin films with varying thickness

The training effect property of the exchange bias in the reactively sputtered polycrystalline Fe3O4 thin films of varying thicknesses in the range 25–200 nm are studied. Structural studies by X-ray diffraction, X-ray photoelectron spectroscopy and selected area electron diffraction confirm the formation of single phase Fe3O4. The scanning electron spectroscopy images show that the grains are uniformly distributed. All the samples show clear and consistent exchange bias training behaviour due to the dynamics of the spins at the interface of the ferrimagnetic core and the spin glass-like surface of the grains. The analysis of the training effect data of the exchange bias field HE measured at 2 K by using three different models show that the model based on the relaxation of the frozen and rotatable spin components at the interface gives the best description for all the samples. From this model, it is found that the reversible interface spins relax around 7 times faster than the frozen interface spins at 2 K for all the samples and that their relative relaxation rates are independent of the sample thickness. This constancy show that the relative relaxation rates of the interfacial frozen and rotatable spin components is a material dependent property. The frozen component of the interfacial spins of each sample is found to be dominated at the initial stage of the training. A direct equivalence between the HE and remanence asymmetry ME is observed. Above the spin freezing temperature, the training effect measurements at 75 K show that the HE decreases sharply with successive field cycling as compared to the measurements made at 2 K and the HE vanishes after first few cycles.

Structural, optical, and electrical properties of multi-walled carbon nanotubes/polyaniline/Fe3O4 ternary nanocomposites thin film

Multi-walled carbon nanotubes/polyaniline/magnetite (MWCNTs/PANI/Fe3O4) ternary nanocomposites were synthesized. The ternary nanocomposites were synthesized through two main steps, namely; (i) polymerization of aniline in the presence of a carboxyl functionalized multi-walled carbon nanotubes to form binary MWCNTs/PANI. (ii) Co-precipitation of magnetite on the surface of MWCNTs/PANI binary composites to prepare MWCNTs/PANI/ Fe3O4 ternary composites. MWCNTs/PANI/ Fe3O4 ternary composite thin films were also fabricated via thermal evaporation technique in a vacuum at 1 × 10−4 Pa. The characterization of the prepared ternary nanocomposites either powder or thin films were described by numerous techniques including FT-IR, TGA, TEM, XRD. The magnetic properties were investigated by the vibrating sample magnetometer (VSM). XRD showed the polycrystalline nature of a monoclinic crystal system with space group P21/c of ternary nanocomposites powder and showed nanostructure of thin films as well. Optical properties (transmittance and reflectance) of the thin films with 300 nm thickness in the wavelength range of 300–850 nm were studied. The optical complex dielectric constant, optical conductivity, and optical energy band gaps Egwere calculated. The optical absorption data indicated that MWCNTs/PANI/Fe3O4 thin films have mainly both indirect and direct energy band gaps allowed transitions in the energy range of 2.90–3.41 EV. The dark current-voltage characteristics of the MWCNTs/PANI/ Fe3O4 thin films were non-linear and showed rectification behavior. The Rectification ratio (RR) of the forward and reverse currents at the same voltages (V = ± 3 V) was found to be 5 at room temperature.

Monitoring the Surface Chemistry of Functionalized Nanomaterials with a Microfluidic Electronic Tongue.

Advances in nanomaterials have led to tremendous progress in different areas with the development of high performance and multifunctional platforms. However, a relevant gap remains in providing the mass-production of these nanomaterials with reproducible surfaces. Accordingly, the monitoring of such materials across their entire life cycle becomes mandatory to both industry and academy. In this paper, we use a microfluidic electronic tongue (e-tongue) as a user-friendly and cost-effective method to classify nanomaterials according to their surface chemistry. The chip relies on a new single response e-tongue with association of capacitors in parallel, which consisted of stainless steel microwires coated with SiO2, NiO2, Al2O3, and Fe2O3 thin films. Utilizing impedance spectroscopy and a multidimensional projection technique, the chip was sufficiently sensitive to distinguish silica nanoparticles and multiwalled carbon nanotubes dispersed in water in spite of the very small surface modifications induced by distinct functionalization and oxidation extents, respectively. Flow analyses were made acquiring the analytical readouts in a label-free mode. The device also allowed for multiplex monitoring in an unprecedented way to speed up the tests. Our goal is not to replace the traditional techniques of surface analysis, but rather propose the use of libraries from e-tongue data as benchmark for routine screening of modified nanomaterials in industry and academy.

A review of Fe3O4 thin films: Synthesis, modification and applications

Magnetite (Fe3O4) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe3O4 thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe3O4 thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe3O4 thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe3O4 thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe3O4 thin films will give us some breakthroughs in materials science and technology.

Remarkable improvement of ferroelectric properties and leakage current in BiFeO3 thin films by nd modification

Ferroelectric and leakage properties are important for ferroelectric applications. Pure and Nd-doped (x=0.05-0.20) BiFeO3 thin films were fabricated by sol-gel method on FTO substrates. The phase structure, surface morphology, leakage current, ferroelectric properties, and optical properties of BiFeO3 - based thin films were investigated. The substitution of Nd3+ ions for the Bi3+ site converts the structure from rhombohedral to coexisting tetragonal and orthorhombic. Nd doping improves the crystallinity of BiFeO3 thin films. The leakage current of Nd-doped BiFeO3 decreases by two to three orders of magnitude compared with that of pure BiFeO3. Among the samples, 15% Nd-doped BiFeO3 exhibits the strongest ferroelectric polarization of 17.96 μC/cm2. Furthermore, the absorption edges of Bi1-x Nd x FeO3 thin films show a slight red-shift after Nd doping.

Electronic structure of Cr doped Fe3O4 thin films by X-ray absorption near-edge structure spectroscopy

Present study reports the electronic structures of Cr doped Fe3O4 (Fe3-xCrxO4 (0 ≤ x ≤ 3) grown on MgO (100) substrates in the form of thin films fabricated by a plasma–oxygen assisted Molecular Beam Epitaxy (MBE). X-ray absorption near-edge structure (XANES) spectra at Cr & Fe L-, and O K-edges were used to understand the electronic structure: changes in the bonding nature, valence states, and site occupancies. Cr doping in Fe3O4 results in the change of charge transfer, crystal structure, and selective occupation of ions in octahedral and tetrahedral sites. Such change modifies the electrical and magnetic properties due to the covalency of Cr ions. The physical and chemical properties of ferrites are strongly dependent on the lattice site, ion size of dopant, and magnetic nature present at different structural symmetry of the spinel structure.

Assessing the scalability of low conductivity substrates for photo-electrodes via modelling of resistive losses.

When scaling up photo-electrochemical processes to larger areas than conventionally studied in the laboratory, substrate performance must be taken into consideration and in this work, a methodology to assess this via an uncomplicated 2 dimensional model is outlined. It highlights that for F-doped SnO2 (FTO), which is ubiquitously used for metal oxide photoanodes, substrate performance becomes significant for moderately sized electrodes (5 cm) under no solar concentration for state of the art Fe2O3 thin films. It is demonstrated that when the process is intensified via solar concentration, current losses become quickly limiting. Methodologies to reduce the impact of substrate ohmic losses are discussed and a new strategy is proposed. Due to the nature of the photo-electrode current-potential relationship, operation at a higher potential where the photo-current saturates (before the dark current is observed) will lead to a minimum in current loss due to substrate performance. Crucially, this work outlines an additional challenge in scaling up photo-electrodes based on low conductivity substrates, and establishes that such challenges are not insurmountable.

Substrate-Dependent Structure, Magnetic, and Ferroelectric Properties of Multiferroic Bi0.9Ba0.1FeO3 Thin Film

The structure characteristic of substrate is a key parameter to modify the structure of as-grown thin film and tune physical properties for oxide thin film materials. Three various substrates are selected to identify the change of structure as well as ferroelectric and magnetic properties of the fabricated Bi0.9Ba0.1FeO3 thin film. XRD and TEM combined with AFM were used to confirm the detailed structure and epitaxial growth of Bi0.9Ba0.1FeO3 thin film on different substrates. Correspondingly, the changes of the ferroelectric and magnetic properties were investigated. It is found that the lattice mismatch between substrate and thin film significantly promotes the structure distortion of Bi0.9Ba0.1FeO3 thin film inducing the change of ferroelectric and magnetic properties. Our results further reveal that the structure characteristic of substrate plays a major role in determining the structure of epitaxial thin film and the enhancement of physical properties, which sheds light to understanding the effect of lattice mismatch in many other functional oxide thin films as well.

Photoelectrochemical properties of hematite thin films grown via a two-step electrochemical deposition method

In this study, Fe2O3 thin films were deposited via one-step and two-step electrochemical deposition methods. The one-step method used a constant growth potential, and the two-step method used two continuous growth potentials during the deposition. The morphological, electrical, and structural properties of the thin films and the relationships of each property with the photoelectrochemical properties of the thin films from the two methods were analyzed and compared. We determined that the samples grown by the two-step method have better photoelectrochemical properties than those grown by the one-step method. In this study, we attempted to determine the optimum growth potentials for the one-step and two-step methods and the growth durations of the first and second stages in the two-step method in terms of the photoelectrochemical properties. The sample formed at −0.05V for 30s in the first step and −0.25V for 2min 30s in the second step in the two-step method has the highest photocurrent density value of 0.28mA/cm2 (at 0.5V vs. SCE), which is higher than that of the samples grown by the one-step method.

Multiferroicity around Verwey transition in Fe3O4 thin films

We report observation of finite remanent polarization (∼10-80 nC/cm2) and reasonably strong magnetoelectric coupling in thin film of Fe3O4 within a temperature range from ∼40 K to Verwey transition temperature TCO ∼120 K. Both the intrinsic capacitance and remanent ferroelectric polarization decrease by ∼20-60% under 0-50 kOe field within this temperature range. The measurements using conventional techniques do not yield convincing results as the ferroelectric polarization is small and loss is large. However, use of more sophisticated protocol - which eliminates the contribution from loss and nonhysteretic polarization effectively - provides reliable information about remanent polarization and its change under magnetic field around the Verwey transition.

Structural properties and electrical conduction mechanisms of Bi0.9Sm0.05Tb0.05FeO3 Thin Film

Bismuth ferrite BiFeO3 (BFO) is a fascinating multiferroic material, which exhibits strong magnetic and ferroelectric (FE) characteristics simultaneously at room temperature. The present work was aimed at the controlled growth of Bi0.9Sm0.05Tb0.05FeO3 (BSTFO) thin film prepared by hydrothermal method to enhance its magnetic moment as well as the electric properties. In this work, variation of electrical conduction with temperature is explained by employing few, relevant to perovskite oxide materials, conduction mechanisms. Variable-range hopping (VRH) and small-polaron hopping conduction mechanisms are used to analyze the conduction mechanism. Structure, ferromagnetic and dc electrical properties of Bi0.9Sm0.05Tb0.05FeO3thin films grown on SrTiO3 (100) substrates by hydrothermal method are reported. Saturation magnetization and room temperature resistivity values are found to be 160 emu/cm3 and 1.9×105Ωm respectively. Raman spectroscopy study indicates anomalous changes of vibration modes around the Neel’s temperature. The temperature dependent electrical resistivity shows two distinct regions suggesting two different conduction mechanisms which suggest that small polaron and variable-range-hopping conduction mechanisms are operative in 300–160 K and 160–90 K temperature regions respectively. The density of states, for our samples, at the Fermi level is found to be ∼1020eV−1cm−3.

Photoelectrocatalytic activity of immobilized Fe2O3 photoelectrode for degradation of salicylic acid and methyl orange dye under visible light illumination

Fe2O3 thin films have been successfully synthesized by chemical spray pyrolysis technique. The effect of solution quantities onto the photoelectrochemical (PEC), structural, morphological, and optical properties has been studied. Film prepared at 50 ml solution quantity shows the maximum photoelectrochemical performance in 0.1 M NaOH electrolyte. X-ray diffraction studies reveal that the synthesized Fe2O3 thin films are polycrystalline with rhombohedral crystal structure. The surface morphology of Fe2O3 thin films shows that needle-shaped grains have slowly converted into round-shaped grains. The estimated band gap energy of Fe2O3 films varies from 2.02 to 2.15 eV with respect to quantities of spraying solution and it exhibits absorption in visible region. The photoelectrocatalytic degradation process shows better removal efficiency of organic compounds as compared to photocatalytic process for degradation of salicylic acid (SA) using large area (100 cm2) Fe2O3 photoelectrode under visible light illumination. Further, photoelectrocatalytic degradation process have been employed for degradation of colorant organic compound such as methyl orange (MO) dye.

Direct observation of magnetic domain evolution in the vicinity of Verwey transition in Fe3O4 thin films

We report a direct observation of magnetic domain evolution near the Verwey transition (TV) in Fe3O4 films. We found the stripe domains in the Fe3O4/Mg2TiO4 film while the irregular domains in the Fe3O4/MgO film and the similar characters of magnetic domains in the vicinity of TV for both samples: the bigger domain size and the higher contrast of the phase signal below TV and the more disordered domain images at TV. Remarkably, the magnetic behaviors can be well understood and the domain-wall energy and the demagnetizing energy can be calculated from the magnetic domains near TV in the Fe3O4/Mg2TiO4 film. Our work presents a demonstration of the low-temperature magnetic domains and gives a new perspective to understand the Verwey transition in Fe3O4 thin films.