Ferrite Films Research Articles

Coexistence of the electric polarization and conductive current in the bismuth–neodymium ferrite garnet films

The Nd1Bi2Fe5O12/Nd2Bi1Fe4Ga1O12 polycrystalline films on the glass substrate and the Nd0.5Bi2.5Fe5O12 epitaxial films on the single-crystal gadolinium gallium garnet substrate have been investigated by impedance and dielectric spectroscopy. The inductive contribution to the impedance and two relaxation channels related to ferroelectric domains and migration polarization have been established. The magnetocapacitance and magnetoimpedance have been determined. The conductive and polarization currents and the phase difference between them for the films of two types have been determined. The critical temperatures of the polarization disappearance and hysteresis I–V have been found. A model of the polarization caused by the piezoelectric effect and flexoelectric interaction has been proposed. I–V hysteresis is explained by the presence of ferroelectric domains near the interface and is associated with the hysteresis of the electric polarization.

Ferrimagnetic insulators for spintronics: Beyond garnets

Ferrimagnetic insulators have gained much attention as material platforms with efficient magnetization dynamics. To date, epitaxial iron garnet thin films are the most widely used materials in the emerging field of “insulator spintronics.” However, further advances in this field require overcoming the disadvantages of garnets—e.g., their complex structure, high growth temperature, incompatibility with other crystalline materials, and relatively weak perpendicular magnetic anisotropy. In this Perspective, we make the case that epitaxial thin films of spinel ferrites and hexagonal ferrites are viable materials for insulator spintronics with complementary advantages over the oft-used garnets. Specifically, spinel ferrites have a simpler structure, can crystallize at lower temperatures, and are more amenable to coherent integration with various materials; hexagonal ferrites possess enormous perpendicular anisotropy of bulk origin, in contrast to garnets where the strength of anisotropy is restricted by interfacial strain. The expanded repertoire of materials for insulator spintronics will enable new physical insights and potential applications, beyond what is currently possible with garnets.

Propagation of Hybrid Surface Waves in Ferrite Anisotropic Plasma Planar Structures

This manuscript presents a theoretical analysis of hybrid surface wave propagation at the ferrite–anisotropic plasma planar interface. Maxwell’s equations in differential forms and impedance boundary conditions are used to solve the problem. The influence of the plasma frequency, cyclotron frequency, and the different permittivities of ferrite films on the dispersion curve are analyzed. Moreover, the propagation length, normalized phase speed, and normalized field distribution are also analyzed. The presented work may have potential applications in surface waveguide control, optical sensing, and wave propagation in the terahertz frequency range such as measurement of electron bunches, remote sensing, material characterization, medical and biological imaging.

Insight into magnetic properties in zinc ferrite thin films by tuning oxygen content

In this investigation ZnFe2O4 thin films were fabricated by RF magnetron sputtering and the magnetic behavior was examined under the influence of the growth conditions in three types of atmospheres, using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and vibrating sample magnetometry (VSM). XPS revealed that films under an Ar/O2 ratio 1:2 and 2:1 have Fe/Zn atomic ratios similar to the Fe/Zn stoichiometric composition; while the films deposited in pure Ar atmosphere, showed a formation of Fe ions (Fe0) reduced by Ar ion sputtering. VSM revealed an enhancing of the saturation magnetization for the ZFO in thin films unlike the samples in bulk, suggesting that Fe ions migrate to A sites and the interaction JAB dominates the magnetic properties instead of JBB interaction.

Magnetic and electrical transport properties of Ru doped cobalt ferrite thin films with perpendicular magnetic anisotropy

Epitaxial ferrimagnetic thin films of (Co, Ru) Fe2O4 were grown on MgO (001) substrate using pulsed laser deposition technique. Ruthenium substitution in cobalt ferrite has increased the conductivity by orders of magnitude, but it has a minimal effect on magnetic properties. The film has a high coercivity and perpendicular magnetic anisotropy (PMA), where the magnetic easy axis points perpendicular to the film surface. We report the magnetic and electrical transport properties here. The temperature variation of resistivity showed different conduction mechanisms at high and low-temperature regimes. Room temperature Hall measurement reveals “n” type carrier with a carrier concentration of 4×1020/cm3. The film showed negative MR and a linear decrement with the magnetic field without any saturation.

Analysis of magnesium ferrite and nickel doped magnesium ferrite thin films grown by Spray Pyrolysis

The magnetic magnesium ferrite (MgFe2O4) with a partially inverse spinel structure has been prepared by the classic ceramic method, which have practical application in information storage systems, magnetocaloric refrigeration and magnetic diagnostics. Nickel-magnesium ferrites (Ni:MgxFe3-xO4 or Mg(1-x)NixFe2O4; 0 ≤ x < 1) are magnetic materials of technological significance due to low electrical conductivity, low magnetic coercivity and low eddy current deceives. Magnesium plays an important role in the electrical and magnetic properties of Mg(1-x)NixFe2O4. Thin films were synthesized on different substrates with Spray Pyrolysis (SP) technique. The thin films were analyzed through Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and UV–Vis double beam spectrophotometer and for magnetic properties of films were used Vibrating-sample magnetometer (VSM) technique. In this study, the film is doped with material having magnetic properties and non-magnetic material. The change in the magnetic properties of the film will be examined as a result of the doping. As a result, the magnetic hysteresis curve of the film was changed by doping. Investigation of magnetic properties is very important for magnetic device applications such as magnetic recording, in magnetic sensor technology and room temperature giant magnetoresistance (GMR) applications.

An all-inorganic, fully dense, stretchable ceramic magnetic film.

There is widespread interest in new materials-based approaches for introducing flexibility to electromagnetic devices, such as displays, human–machine interfaces, smart textiles, and biomedical implants. From fabrication to application, incorporating ceramic components is particularly challenging due to their extreme stiffness. Here, we introduce a new approach for designing flexible ceramic films and demonstrate it by fabricating fully dense, pre-wrinkled magnetic cobalt ferrite films composed of tiled nanoplatelets. The method relies on the colloidal engineering of metalized graphene nanosheets, which are cast and compressed into wrinkled composite films with accurate control of composition and morphology. Removal of the graphene template by thermal oxidation yields free-standing cobalt ferrite films that can be stretched up to 200% and bent to radii of 2.5 mm while maintaining their magnetic properties. Magnetization retention of 73% is documented after 150% linear mechanical stretching over 100 cycles. The significant stretchability and flexibility in this hard magnetic material is achieved at near full metal oxide crystal density without addition of significant void space or a polymeric elastomer matrix.

Cobalt metal doped magnesium ferrite and zinc ferrite thin films grown by Spray Pyrolysis

The transition metal doped magnesium ferrite and zinc ferrite as the most common form of iron oxide become an especially important photoanode material for photoelectrochemical water splitting, due to its comparatively small band gap (Eg = 2.0 eV) that can absorb visible light and its perfect chemical stability in watery solutions. Spinel ferrites have the general formula of AFe2O4 (where A2+:Fe, Co, Ni, Zn, etc.). Thin films were synthesized on different substrates by Spray Pyrolysis (SP) technique. The technique of SP is easier, cheaper and faster than other method. Spinel ferrites, AFe2O4, are technologically important group of materials due to their optical, magnetic, and electrical properties. Among the different spinel ferrites, magnesium ferrite have unique properties. The effects of doped cobalt metal on the thin films were analyzed through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD) and UV–Vis double beam spectrophotometer and for electrical properties of films were used Van der Pauw technique.

Surface morphology and X-ray photoelectron spectroscopy of BiFeO3 thin films deposited on top of Ta2O5/Si layers

In this study a comparison of the topography of BiFeO3 (BFO) thin films deposited on tantalum pentoxide substrates of different thicknesses is provided. The Ta2O5 substrates had a roughness increasing with the film thickness. The relationship between substrates of different topography but the same composition with the quality of the growing bismuth ferrite film is estimated. For the first time the topography estimation of BFO on Ta2O5 is presented. The difference in temperature expansion coefficients leads to intensive evaporation of bismuth ferrite from the surface during annealing. XPS analysis is provided for asdeposited and annealed BFO layers.

Nanoporous manganese ferrite films by anodising electroplated Fe-Mn alloys for bifunctional oxygen electrodes.

An electroplating-anodising method based on a facile and scalable electrochemical process was used to fabricate manganese ferrite porous oxide films for use as precious-metal-free oxygen reduction/evolution reaction (ORR/OER) electrodes. Porous oxide films of spinel manganese ferrites (MnxFe3-xO4) were formed on electroplated Fe-Mn films. The MnxFe3-xO4 porous oxide formed on microcracks in the Fe-Mn films constituted a nanoporous/microcrack hierarchical structure (NP/MC), which provided a large electrode surface area for ORR/OER. The electrochemically active surface area of the NP/MC on Fe-36 at% Mn was 33.3 cm2, which is nine times that of the nanoporous structure on Fe (3.67 cm2). The onset potential of the NP/MC on Fe-15 at% Mn and Fe-36 at% Mn was 0.88 V vs. RHE (overpotential, ∼350 mV) for the ORR at -0.1 mA cm-2. The OER onset potentials at 10 mA cm-2 were 1.79 V on Fe-15 at% Mn (∼560 mV) and 1.74 V on Fe-36 at% Mn (∼510 mV). The OER and ORR activities of the MnxFe3-xO4 porous oxides are better than those of spinel iron oxide (∼510 and ∼640 mV for the ORR and OER, respectively) because of the good intrinsic activity of MnxFe3-xO4 and greater surface area of the NP/MC. The ORR activities of the MnxFe3-xO4 porous oxides decreased to about 30% during ORR durability testing for 7.5 h, and the same level of activity was retained after 24 h of use. The MnxFe3-xO4 porous oxides retained a high level of activity during OER durability testing for 8 h.

Crack resistance of bismuth ferrite films obtained on a flexible substrate

Ultrathin BiOx and FeOx layers were obtained by Atomic Layer Deposition (ALD) on the surface of a flexible Kapton substrate (poly (4,4’-oxydiphenylene-pyromellitimide)) at a temperature of 250 °C. The layer thickness was 50 - 100 nm. Surface morphology, electrical polarization, and mechanical properties were investigated by Atomic Force Microscope, Piezoelectric Force Microscopy and Force Modulation Microscopy. Chemical analysis was performed by X-ray Photoelectron Spectroscopy, where the formation of Bi2O3 and Fe2O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. With a small increase in the Bi content of the film, the BFO / Kapton structure becomes more crack resistant. Modification of the Kapton surface with bismuth and iron oxides showed that such a composition exhibits multiferroic behavior.

Growth and Characterization of Ultrathin Cobalt Ferrite Films on Pt(111)

Growth and Characterization of Ultrathin Cobalt Ferrite Films on Pt(111)

Effects of Scandium Doping on Structural and Magnetic Properties of Cobalt Ferrite Thin Films

Structural and magnetic properties of Sc-substituted cobalt ferrites were studied by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and vibrating-sample magnetometry. The ScSUBx/SUBCoFeSUB2-x/SUBO₄ (x ≤ 0.3) specimens prepared as thin films by a sol-gel deposition method were polycrystalline having cubic spinel structure with a small increase in the lattice constant compared to CoFe₂O₄. The Raman spectral analyses suggested that the Sc-doped specimens have higher tetrahedral CoSUP2+/SUP population than that of pristine CoFe₂O₄. The magnetic hysteresis curves of the ScSUBx/SUBCoFeSUB2-x/SUBO₄ specimens indicated that the saturation and remanent magnetization decrease proportionally with the increase of Sc composition (x). The decrease in the ferrimagnetic parameters is understandable in terms of the octahedral substitution of non-magnetic ScSUP3+/SUP ions. However, the octahedral ScSUP3+/SUP ions caused an increase of the coercivity.

Selective sensing of oxidizing gases on Co-Ni-Zn ferrite: Mechanism and response characteristics

Studies demonstrate the selective gas sensing characteristics of Co-Ni-Zn ferrite thick film towards oxidizing gases over reducing gases. The Co0.3Ni0.3Zn0.4Fe2O4 ferrite was prepared by combustion method and characterized for its phase purity, nanodimension and valence state by analytical techniques, includes X-ray diffraction, Raman spectroscopy, Transmission Electron Microscopy and X-ray photoelectron spectroscopy, respectively. The Co0.3Ni0.3Zn0.4Fe2O4 gas sensor was fabricated in the form of thick film by screen printing method, and the response of film towards selected oxidizing gases and the reducing gases were investigated. It was found that Co0.3Ni0.3Zn0.4Fe2O4 thick film is highly active towards oxidizing gases at 200 °C, whereas almost negligible response was observed for reducing gases at all temperatures ranging from RT to 300 °C. The Oxygen adsorption - desorption mechanism is proposed for sensing of NO2 and Cl2 gases, and stated to be favored by n to p type conductivity transition on the surface of sensor film at 200 °C.

The role of FeCo and FeCoCr nanowires array on the formation of single phase bi-magnets

Nanowire (NWs) arrays of FeCo and FeCoCr were prepared by AC pulsed electrodeposition embedded into an alumina template. They were then employed as an underlayer to provide the dot array of cobalt ferrite thin films. Highly ordered arrays of NWs with the diameter of 30 nm and length of 10 µm were fabricated and then annealed in various environments. The cobalt ferrite thin films were deposited by the sputtering approach with the almost constant thickness of 70 nm as the hard magnetic phase. The combination of FeCo and cobalt ferrite could provide an exchange spring magnet with the magnetic coupling feature. X-ray diffraction (XRD) patterns of the NW arrays indicated the formation of the body centered cubic (bcc) FeCo phase with [110] texture. Field emission electron microscopy (FESM) equipped by EDS also characterized the morphological features and elemental composition. Magnetization and coercivity of NWs were examined using the vibrating sample magnetometer. The maximum coercivity of NWs array is 2950 Oe which is related to H2 annealing FeCo NWs array. The magnetization reversal process of the as-deposited and annealed FeCo and FeCoCr NWs arrays was performed by angular dependence coercivity and squareness. Further, FORC diagrams indicated an interacting single domain behavior for as-deposited FeCo NWs and a weakly-interacting single domain state for the annealed samples. The morphological and structural features of cobalt ferrite were also studied by XRD, FE-SEM and AFM techniques. It was found that the cobalt ferrite dot array with a uniform chemical composition and structure was formed. The inter-diffusion of atoms between underlayer and thin films was confirmed by EDS. The maximum coercivity of the nanocompsite was 5800 Oe that is obtained for FeCoCr underlayer with argon annealing. The VSM analysis showed that sufficient exchange coupling was formed by using the FeCoCr underlayer in hydrogen annealing, while argon annealing provided a kink in the hysteresis loops. The obtained nanocomposites could be, therefore, considered as the potential candidate for use in the exchange spring magnet.

Bismuth ferrite thin film coated on polycarbonate surface and its photocatalytic properties in visible light

Bismuth ferrite (BFO) thin film was coated on the surface of polycarbonate (PC) by dip-coating using BFO sol. The photocatalytic properties under visible light and physicochemical properties of BFO coated with a thin film were investigated. The BFO thin film was mainly composed of a mixture of BiFeO3 and Bi24Fe2O39 structures. The BFO absorbed UV and visible light up to 600 nm. The bandgap of the BFO was estimated about 2.3 eV. Formaldehyde was decomposed on the BFO coated on the surface by photocatalysis under visible light LED lamp. In the estimation of antibacterial properties, Pseudomonas aeruginosa and Klebsiella pneumoniae were completely sterilized on the surface coated BFO thin film by visible light irradiation.

BiFeO3-Thiourea/Carbon heterostructure based self-powered white light photodetector

Herein we report the performance of white-light photodetector fabricated by thiourea stabilized bismuth ferrite(BFO-TU) film as a photoactive layer and carbon as a hole collector. The heterojunction BFO/Carbon helps in excitons dissociation and thereby enhanced the device performance. Under the self-powered condition, the device fabricated with a thickness of 1.2 μm exhibited maximum responsivity and detectivity of 2.85 μA/W and 4.06 × 107 Jones respectively for incident light of power 100 mW/cm2. Besides, the device shows excellent stability and repeatability with a high ON/OFF ratio.

Porogen induced formation of mesoporous zinc ferrite thin films and their chemiresistive properties

The semiconducting metal oxides are the most studied chemiresistive sensing materials. Their surface morphology plays an important role in sensing response. The porous nature of the material can significantly enhance their sensing ability. With this aim, ZnFe2O4 thin films were deposited on glass substrates by spray pyrolysis technique. The added NH4Cl porogen made pores in the film. The chemiresistive response of these porogen induced films for SO2 gas and liquid glucose were found better as compared to compact films; which were deposited without porogen. The reaction mechanism and pore formation are explained in the paper.

Профильный анализ пленок ферритов-гранатов методом оптической эмиссионной спектроскопии тлеющего разряда

Annotation.The paper presents the results of experiments on the application of the method of optical emission spectroscopy of a glow discharge for the profile analysis of vacuum-deposited single and two-layer films of multicomponent garnet ferrites of various compositions before and after crystallization annealing. The presence of internal and external transition layers was revealed, and the modification of their elemental composition during crystallization, as well as the different sequence of synthesis of individual components in ferrite-garnet heterostructures, was investigated.

The Significance of Buffer Solutions on Corrosion Processes of Cobalt Ferrite CoFe2O4 Thin Film on Different Substrates.

The spinel ferrite nanoparticles, such as zinc, nickel, and cobalt ferrites have exceptional electronic and magnetic properties. Cobalt ferrite nanomaterial (CoFe2O4) is a hard material that reveals high magnetic, mechanical, and chemical stability. The objective of this research is to predict the corrosion behavior of cobalt ferrite (CoFe2O4) thin films deposited on different substrates (platinum Pt, stainless steel S.S, and copper Cu) in acidic, neutral, and alkaline medium. Cobalt ferrite thin films were deposited on platinum, stainless steel, and copper via electrodeposition-anodization process. After that, corrosion resistance of the prepared nanocrystalline cobalt ferrite on different substrates was investigated in acidic, neutral, and alkaline medium using open circuit potential and potentiodynamic polarization measurements. The crystal structure, crystallite size, microstructure, and magnetic properties of the ferrite films were investigated using a combination of XRD, SEM and VSM. The results of XRD revealed a cubic spinel for the prepared cobalt ferrite CoFe2O4. The average size of crystallites was found to be about 43, 77, and 102 nm precipitated on platinum, stainless steel, and copper respectively. The magnetic properties of which were enhanced by rising the temperature. The sample annealed at 800oC is suitable for practical application as it showed high magnetization saturation and low coercivity. The corrosion resistance of these films depends on the pH of the medium as well as the presence of oxidizing agent. Depending on the obtained corrosion rate, we can recommend that, CoFe2O4 thin film can be used safely in aqueous media in neutral and alkaline atmospheres for Pt and Cu substrates, but it can be used in all pH values for S.S. substrate.