Ferrite Films Research Articles

Connecting electrical current conduction and Urbach energy in doped BiFeO3 thin-films

The present study explores the influence of Co2+ and Mn4+ ions on the optical and electrical properties of bismuth ferrite thin films prepared on indium tin oxide-coated glass substrates. In particular, a correlation between the Urbach energy tails and the current conduction is established. Doping-dependent variations in Urbach energy tail widths, optical bandgap energies and J-V curves of the fabricated films are investigated. The Urbach energy tail width of Co-doped BiFeO3 is found to increase by 36%, while that of Mn-doped one is found to reduce by 15%. The optical bandgap of Co-doped and Mn-doped BiFeO3 was found to reduce by 44% and 40% respectively compared to undoped BiFeO3. A correlation between the induced defect states and the optical parameters has been observed. Analysis of J - V characteristics reveals the dependence of the current conduction upon the valence state of the dopant. In particular, the dark current density decreased by almost one order of magnitude with Mn-doping and increased by more than one order with Co-doping. A defect-dependent space-charge-limited conduction (SCLC) mechanism is proposed to understand the J - V curve in the Co-doped and Mn-doped BFO samples. A direct variation of the leakage current density with the Urbach energy suggests that Urbach energy studies could be considered as an alternative indicator of the leakage current density in thin-film BiFeO3-based devices.

Structural and magnetic properties of NiCuZn ferrite films deposited using sputtering

Structural and magnetic properties of NiCuZn ferrite films deposited using sputtering

Effect of Elastic Resonances of Substrate on Ferromagnetic Resonance in Yttrium Iron Garnet Films

The problem of excitation of ferromagnetic resonance in a thin ferrite film with magnetoelastic properties located on a thick elastic substrate is considered. A model is proposed for the excitation of elastic modes in the substrate due to the propagation of a periodic boundary regime created by magnetic oscillations in the film. The conditions for stationary oscillations are used to obtain the frequency response characteristics of ferromagnetic resonance, which exhibit strong oscillations due to the excitation of high-order elastic modes over the thickness of the substrate.

Robust Ferrimagnetism and Switchable Magnetic Anisotropy in High‐Entropy Ferrite Film

AbstractFerrimagnetic insulator materials are the enabling technology for the development of next‐generation magnetic devices with low power consumption, high operation speed, and high miniaturization capability. To achieve a high‐density memory device, a combined realization of robust saturation magnetization (Ms), controllable magnetic anisotropy, and high resistivity (ρ) are highly demanded. Despite significant efforts that have been made recently, simultaneously achieving significant enhancements in these properties in a soft magnetic insulator material still remains a great challenge, severely limiting their practical application. Herein, a high‐entropy strategy in an ultra‐thin spinel ferrite (CrMnFeCoNi)3O4 film is reported that exhibits concurrently a superior saturation magnetization (MS = 1198 emu cm−3), low coercivity (HC = 90 Oe), and excellent resistivity (ρ = 1233 Ω cm), as well as switchable magnetic anisotropy. The comprehensive lattice probing and microstructure analysis studies reveal that such desirable ferromagnetic properties originate from the high‐quality structurally ordered but compositionally disordered single‐crystal epitaxial structure. The switchable magnetic anisotropy demonstrated in the high‐entropy ferrite film can be attributed to the new antiferromagnetic rock‐salt phase. This work unveils the critical benefits of the high‐entropy strategy for magnetic oxide thin films, which opens up new opportunities for the development of high‐performance magnetic materials.

Spatially-Resolved Study of the Electronic Transport and Resistive Switching in Polycrystalline Bismuth Ferrite

Ferroelectric materials attract much attention for applications in resistive memory devices due to the large current difference between insulating and conductive states and the ability of carefully controlling electronic transport via the polarization set-up. Bismuth ferrite films are of special interest due to the combination of high spontaneous polarization and antiferromagnetism, implying the possibility to provide multiple physical mechanisms for data storage and operations. Macroscopic conductivity measurements are often hampered to unambiguously characterize the electric transport, because of the strong influence of the diverse material microstructure. Here, we studied the electronic transport and resistive switching phenomena in polycrystalline bismuth ferrite using advanced conductive atomic force microscopy (CAFM) at different temperatures and electric fields. The new approach to the CAFM spectroscopy and corresponding data analysis are proposed, which allow deep insight into the material band structure at high lateral resolution. Contrary to many studies via macroscopic methods, postulating electromigration of the oxygen vacancies, we demonstrate resistive switching in bismuth ferrite to be caused by the pure electronic processes of trapping/releasing electrons and injection of the electrons by the scanning probe microscopy tip. The electronic transport was shown to be comprehensively described by the combination of the space charge limited current model, while a Schottky barrier at the interface is less important due to the presence of the built-in subsurface charge.

High remanence ratio of aluminum substituted hexagonal barium ferrite films for self-biased microwave devices

A high remanence ratio of hexagonal barium ferrite film is urgently needed for self-biased microwave devices. In this work, the aluminum-substituted hexagonal barium ferrite films (BaFe(12−x)AlxO19) with different substituting concentrations (x = 0, 1.5, 2, 2.5, 3) were deposited on the Al2O3 substrate by pulsed laser deposition method using self-sintered BaFe(12−x)AlxO19 target. Firstly, the targets with different Al concentrations were sintered by the solid phase method and exhibited high dense, uniform microstructure, and high purity. Then, the influence of the Al ions concentration on the crystal structure, morphology, and magnetic and microwave properties of BaFe(12−x)AlxO19 films was studied in detail. Structural characterizations confirm that the Al prefers to substitute for 2a, 4f2 and 2b sites and promotes the grain (formed as single-domain) orientation growth, which results in a decrease in the saturation magnetization, an increase of remanence ratio and anisotropy field. Consequently, a high remanence ratio of 95 % was obtained for BaFe(12−x)AlxO19 film at x = 3, and also displays a high anisotropy field (27.7 kOe), a low saturation magnetization (1758 G) and an appropriate ferromagnetic resonance linewidth (～436 Oe), which can be applied in self-biased devices.

Excitation by shot circuited coaxial transducer of magnetostatic modes in rectangular yttrium iron garnet film

The purpose of this work is the study of design of new short-circuited coaxial transducer with thin linear jumper, that circuits on one side of the grounded coaxial cylinder, located above the rectangular iron-yttrium garnet (YIG) film, in homogeneous constant magnetic field with rectangular film along its length or width. The thin linear jumper is directed parallel to the width of the YIG film. Methods. In the CST Microwave Studio environment, an electrodynamic analysis of the model was carried out using the finite element method. To study the efficiency of modes excitation in a ferrite film at different distances between the coaxial transducer and the surface of the YIG film, the frequency dependences of the inverse losses S11 of the model were calculated. Results. 1. The identification of modes in a homogeneous static magnetic field H , directed parallel to the plane of a rectangular YIG film along its width (z-axis) was carried out. 2. The identification of modes in a homogeneous static magnetic field H directed parallel to the plane of the rectangular YIG film along its length (y-axis) was carried out. 3. A comparison of modes spectra was made at H, directed parallel to the plane of the YIG film along its width (z-axis) and length (y-axis). Conclusion. In this paper short-circuited transducer with a thin linear jumper, circuited on one side of the grounded coaxial cylinder, is investigated. By the electrodynamic method distributions of high-frequency magnetic field of the excited magnetostatic modes were calculated and their identification was carried out for two directions of homogeneous static magnetic field H: along width and along length of rectangular YIG film. The dependence of number of excited modes on the distance between a short-circuited transducer and rectangular YIG was also studied. A comparison of modes spectra is carried out at H, directed parallel to the plane of the YIG film along its width and length. With this rotation of vector, the band of effectively excitable modes shifts from 4.6...4.9 GHz to 4.5...4.75 GHz. However, the excitation of these modes in the case of the vector H, directed along the width of YIG film (z-axis), is much more effective in the band 4.65...4.9 GHz than in the case when this vector is directed along the length of YIG film (y-axis). At the same time, excitation of these modes in the case of the vector H, directed along the length of YIG film (y-axis) is effective in the band 4.4...4.6 GHz.

Spray pyrolysis-derived robust ferroelectric BiFeO3 thin films.

Scalable and low-cost synthesis of high-quality ferroic films is critical for the development of advanced electronic devices and sensors. Here, we employ solution-based spray pyrolysis to fabricate bismuth ferrite thin films on glass substrates and explore the impact of annealing conditions to attain functional thin films of superior quality and switchable polarization. Optimised thin films display polycrystalline nanostructured grains with the highest X-ray diffraction intensity along the (110) orientation and a mixed Fe2+/3+ valence suggesting the presence of oxygen vacancies. The optimized films show a complex ferroelectric domain microstructure and exhibit robust nanoscale polarization switching in the range of several volts. Domains are found to scale with the sizes of nanocrystalline grains, which points to the role of surface-energy-related mechanisms affecting the domain patterns. Our results demonstrate the potential of spray pyrolysis for the fabrication of high-quality ferroelectric thin films and provide new opportunities for the development of low-cost scalable advanced electronic devices.

Manganese doped two-dimensional zinc ferrite thin films as chemiresistive trimethylamine gas sensors.

Trimethylamine (TMA) is highly toxic and can have lethal effects on living organisms. Detecting the presence of TMA in air is very important because, if the TMA level exceeds the OSHA (Occupational Safety and Health Administration) limit, it may harm the environment and endanger human life. Doping is an appropriate flexible way to change the electrical structures of metal oxide semiconductors (MOSs) and improve their ability to detect toxic gases. In this work, Mn-doped zinc ferrite thin film nanorods with agglomerated morphology were fabricated by a spray pyrolysis technique. For the first time, a comprehensive investigation was done on the gas sensing capabilities of Mn-doped ZnFe2O4 thin films. The findings showed that ZFM1 had the best gas sensing characteristics, with high sensitivity (S = 6.24), good selectivity, and quick recovery, towards 10 ppm TMA at ambient temperature. The alternate Mn-ZF sites are responsible for the rapid recovery because they can significantly increase the concentration of oxygen vacancies in the ZF crystal. 0.1 Mn doped ZnFe2O4 (ZFM1) thin film exhibits greatly enhanced gas sensing properties towards TMA, because of its high surface-to-volume ratio and rough surface with a small nanorod structure. The sensor's response to 10 ppm TMA was measured 13 weeks later for stability testing. The stability test results show that the coated ZFM1 film works well as a TMA gas sensor. This work shows that ZF thin films are effective in detecting TMA in the atmosphere.

Coupling oxygen vacancy gradient distribution and flexoelectric effects for enhanced photovoltaic performance in bismuth ferrite films

Coupling oxygen vacancy gradient distribution and flexoelectricity for the enhancement of ferroelectric photovoltaic effects.

Flow cell for operando X-ray photon-in-photon-out studies on photo-electrochemical thin film devices.

Background: Photo-electro-chemical (PEC) water splitting represents a promising technology towards an artificial photosynthetic device but many fundamental electronic processes, which govern long-term stability and energetics, are not yet fully understood. X-ray absorption spectroscopy (XAS), and particularly its high energy resolution fluorescence-detected (HERFD) mode, emerges as a powerful tool to study photo-excited charge carrier behavior under operating conditions. The established thin film device architecture of PEC cells provides a well-defined measurement geometry, but it puts many constraints on conducting operando XAS experiments. It remains a challenge to establish a standardized thin film exchange procedure and concurrently record high-quality photoelectrochemical and X‑ray absorption spectroscopy data that is unperturbed by bubble formation. Here we address and overcome these instrumental limitations for photoelectrochemical operando HERFD-XAS. Methods: We constructed a novel operando photo-electro-chemical cell by computer numerical control milling, guided by the materials' X‑ray and visible light absorption properties to optimize signal detection. To test the cell's functionality, semiconducting thin film photoelectrodes have been fabricated via solution deposition and their photoelectrochemical responses under simulated solar light were studied using a commercial potentiostat in a three-electrode configuration during HERFD-XAS experiments at a synchrotron. Results: We demonstrate the cell's capabilities to measure and control potentiostatically and in open‑circuit, to detect X‑ray signals unperturbed by bubbles and to fluently exchange different thin film samples by collecting high-resolution Fe K-edge spectra of hematite ( α -Fe 2O 3) and ferrite thin film ( MFe 2O 4, M= Zn, Ni) photoelectrodes during water oxidation. Conclusions: Our cell establishes a measurement routine that will provide experimental access of photo-electro-chemical operando HERFD-XAS experiments to a broader scientific community, particularly due to the ease of sample exchange. We believe to enable a broad range of experiments which acquired fundamental insights will spur further photoelectrochemical research and commercialization of water splitting technologies.

Spin Seebeck effect in W-type and Z-type hexagonal ferrite thin films

The spin Seebeck effect was studied in thin films of hexagonal ferrites of W-type SrCo2−xZnxFe16O27 with x = 0, 1, and 2 and Z-type with the composition Sr3Co2Fe24O41. The present data were compared with the previously obtained data on Y-type Ba2Zn2−xCoxFe12O22 with x = 0 and 2. Our work showed that the SSE signal can also be generated in materials with complicated crystal and magnetic structures. Hexaferrites with the magnetic easy plane were selected except for uniaxial W-type with x = 2, for which the highest saturated SSE 0.144 μV/K was observed; however, magnetic field above 1 T must be applied to achieve saturation. For low field application, hexaferrites with easy magnetization in ab-plane are more suitable, namely, Y-type with x = 2 or W-type with x = 1. SSE is suppressed in Co-substituted hexaferrites due to the random distribution of Co among various sites. Therefore, the Co cations interfere with the long-range magnetic ordering and diminish the spin-wave propagation. Additional suppression of SSE might be invoked by the higher magnetic anisotropy of the Co-substituted hexaferrites, which opens a gap in the magnon spectrum and, thus, reduces the contribution of lower energy magnons with longer diffusion length.

Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces

The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, Tmin, rebounding to various maximum temperatures, Tmax, followed by secondary cooling. The negative effect of a low Tmin on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the Ar3, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a Tmin of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when Tmin was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels.

Effect of Oxygen Vacancies and Cationic Inversion on Magnetic Properties of Pulsed Laser Deposited Zinc Ferrite Thin Films

Effect of Oxygen Vacancies and Cationic Inversion on Magnetic Properties of Pulsed Laser Deposited Zinc Ferrite Thin Films

Influence of annealing on structural, morphology, magnetic and optical properties of PLD deposited CuFe2O4 thin films

• Successfully produced of CuFe 2 O 4 nanoparticles and prepared thin films which is grown on a glass substrate by pulsed laser deposition (PLD) technique. • The detailed structural properties of films are studied using experimental (XRD, FE-SEM, VSM, and Optical properties). • The magnetization and remanence of prepared samples have decreased with increased annealing substrate temperatures. • As per report the thin films have direct band gap energy; it reduces with increasing annealing temperature, which is due to improve the crystallinity. In this work, copper-ferrite (CuFe 2 O 4 ) nano-crystallite was synthesized by the gel method and deposited on a microscope glass substrate using a pulse laser deposition (PLD) technique at room temperature. The obtained deposited thin films were annealed at four different temperatures (200 °C, 300 °C, 400 °C, and 500 °C) for 4 hours in an air atmosphere. The structural, morphological, thermal, magnetic, and optical properties of the thin film samples were characterized using an X-ray diffractometer (XRD), Field emission scan electron microscopy (FE-SEM), thermogravimetric and differential thermal analysis (TG-DTA), Vibrating sample magnetometer (VSM) and Ultraviolet-Visible spectrophotometer (UV-Vis). X-ray diffraction patterns of the unannealed and annealed films show the presence of the anti-ferromagnetic (α-Fe 2 O 4 ) phase along with the single-cubic spinel structure phase. The grain sizes were found to have low crystalline copper ferrite with a mixture magnetic and hematite crystalline phases. With the decrease of the grain size and increasing of annealing substrate temperatures, the ratio of hematite to magnetite phases increased, and reached to an impure magnetite phase for the 6.35 nm grain. The morphological images obtained by transmission electron microscopy technique showed that the particle size of copper ferrite nanoparticles gradually became smaller from 10 nm to 5 nm. Surface morphology of all fabricated samples investigated by field emission scan electron microscopy technique exhibiting different sizes, almost spherical grains and agglomerates, which may be depending upon preparation method and substrate temperature. The correlation between structure and thermal stability of prepared materials was studied by (TG-DTA). With increasing of annealing substrate temperature from room temperature to 500 °C, the saturation magnetization (M s ) value decreased from 8.79 emu/g to 2.12 emu/g while the coercivity (H c ) value increased from 52.22 Oe to 91.26 Oe. The lowest widening of optical band gap in the copper ferrite film was 1.57 eV. The magnetic and the optical parameters suggested that these films are potential candidates for gas sensor applications.

Boosting solar fuel production of bismuth ferrite thin film by incorporating reduced graphene oxide

In this study, a facile chemical approach was utilized to successfully fabricate a porous bismuth ferrite (BiFeO3, BFO)/reduced graphene oxide (rGO) nanocomposite thin film as a photoanode for photoelectrochemical (PEC) water splitting. The BFO nanoparticles possess a pure rhombohedral distorted perovskite crystal structure and are grafted onto rGO nanosheets. BFO/rGO (BGO) thin film has smaller nanoparticles (around 100 nm) and higher porosity which provides a higher surface area compared to BFO. Moreover, BGO exhibits higher visible absorption, a narrower band gap energy of 1.95 eV, and a lower recombination rate of charge carriers. The BGO photoanode has a maximum photocurrent density of 0.451 mA.cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE) under 100 mW.cm−2 illumination which is 2.5 times more than the BFO photoanode. The applied bias photon-to-current efficiency (ABPE) of BGO nanocomposite film is 0.21%, which is approximately 2.5 times that of BFO. The obtained results reveal an intimate heterostructure between BFO nanoparticles and rGO nanosheets. The charge separation and transfer of BFO are significantly boosted by incorporating the rGO. This study sheds light on the mechanism insights of enhanced PEC water splitting in BFO/rGO thin film, offering a new approach to the design and fabrication of high-efficiency photoanodes.

Polarized neutron reflectometry study on the modulation of resistance and magnetism in resistive switching cobalt ferrite thin films

In this work, the resistive switching and electrical-control of magnetization in Pt/CoFe2O4/Nb:SrTiO3 heterostructures have been investigated. The films exhibit a classic bipolar resistive switching effect with a maximum switch ratio of about 5 × 103 and good anti-fatigue performance. Associated with resistive switching, the saturated magnetization of the thin film at high resistance state is found to be larger than that at low resistance state. Meanwhile, polarized neutron reflectivity of the thin film under different resistance states was in situ measured. The results reveal that the interfacial migration of oxygen vacancies driven by an applied electric field plays an important role in the modulation of resistive and magnetism of CoFe2O4 resistive switching devices.

Effect of cobalt substitution on the structural, ferroelectric, and magnetic properties of bismuth ferrite thin films

Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrTiO3 and SrRuO3 buffered SrTiO3 substrates using the pulsed laser deposition technique. The effect of structural transformation from rhombohedral to tetragonal phase with increasing cobalt substitution on the magnetic, electrical, and piezo-/ferroelectric properties is investigated. Piezoresponse force microscopy is used to quantify the coercive voltage from the phase hysteresis loops for different thickness films to investigate the semi-empirical Kay–Dunn scaling law with varying cobalt concentrations. For the rhombohedral structure, a reduction of the coercive voltage is observed with increasing substitution of Fe by Co. The coercive voltage of a 10 nm BFCO (x=0.35) film is found to be 0.63 V, which is 67% lower than that of a pure BiFeO3 (BFO) (1.9 V) film of the same thickness. Cobalt substitution also leads to changes in the magnetic and electrical properties due to modification of spin ordering and reduction of the bandgap, respectively. Further, to validate the experimental results, we have performed theoretical calculations using density functional theory. The theoretical results indicate a reduction in unit cell volume and enhancement in net magnetization can be achieved with cobalt substitution, in agreement with experimental results. Partial Co substitution can, thus, provide a pathway to realize BFO-based nonvolatile magnetoelectric devices with reduced operating voltage.

Nonmonotonous temperature fluctuations of the orbital moment and spin-orbit coupling in multiferroic gallium ferrite thin films

Temperature dependent x-ray absorption spectroscopy and x-ray magnetic circular dichroism experiments were performed at the Fe ${L}_{2,3}$ edges to unveil the magnetic orbital moment and spin-orbit coupling (SOC) behavior in thin films of the multiferroic ${\mathrm{Ga}}_{0.6}{\mathrm{Fe}}_{1.4}{\mathrm{O}}_{3}$ (GFO) compound. A thorough analysis of the data evidenced a nonmonotonous behavior for both magnetic orbital moment and SOC with a minimum at approximately 120 K, accompanied with indications of disturbances of the magnetic exchange and electric field dipole. Resonant photoemission spectroscopy experiments performed at the Fe ${L}_{2,3}$ edges rendered an important modification of the crystal field configuration around this temperature value, pointing to a temperature-driven structural trigonal distortion. These instabilities can be compared to those observed in other iron oxides, in particular, during transitions such as the Verwey transition, with the difference that on GFO they do not have any impact on the macroscopic magnetic properties, such as the coercive field and the global magnetization. This work demonstrates that the absence of instabilities in magnetism at the macroscopic scale does not guarantee the absence of fluctuations at the atomic scale. Such atomic-scale fluctuations of the SOC are undoubtedly shown here and have an impact on the spin Hall magnetoresistance response of the films. This point is of importance for prospective applications of GFO in spin-orbitronics.

Tunable Optical and Multiferroic Properties of Zirconium and Dysprosium Substituted Bismuth Ferrite Thin Films.

This work presents optical and multiferroic properties of bismuth ferrite thin films that are affected by zirconium and dysprosium substitution. Non-centrosymmetric BiFeO3,Bi0.95Zr0.05FeO3, and Bi0.95Dy0.05FeO3 thin films were coated on Pt/TiO2/SiO2/Si substrates using the spin coating method. The crystal structure, optical properties, microstructural, ferromagnetic, and ferroelectric properties of doped bismuth ferrite thin films were systematically investigated. From the XRD patterns, all the prepared thin films matched well with the rhombohedral structure with R3c space group with no observed impurity phases. The average crystallite size of the bismuth ferrite thin films were between 35 and 47 nm, and the size depended on the type of dopant. The determined energy band gap values of BiFeO3, Bi0.95Dy0.05FeO3, and Bi0.95Zr0.05FeO3 thin films were 2.32 eV, 2.3 eV, and 2 eV, respectively. Doping of Dy and Zr at the Bi site led to reduced surface roughness. The prepared thin films exhibited enhanced ferromagnetic and ferroelectric properties. The remnant magnetization of Zr-doped BiFeO3 was greater than that of the BiFeO3 and Dy-doped BiFeO3 thin films. From the obtained results, it was concluded that Zr-doped BiFeO3 thin films are suitable for solar cell fabrication.