Cobalt Ferrite Films Research Articles

Inkjet Printing of Cobalt Ferrite for Hard Ferromagnetic Thick Films Manufacturing

Inkjet printing is a versatile and cheap technique for the fabrication of films, offering unique advantages in terms of scalability, precision, and customization. In recent years, there has been a growing interest in utilizing inkjet printing technology for the deposition of magnetic films with tailored properties. Cobalt ferrite (CoFe2O4) stands out due to its exceptional magnetic properties, including high coercivity, saturation magnetization, and excellent chemical stability. This paper presents a comprehensive study on the inkjet printing of cobalt ferrite magnetic films, focusing on the manufacturing process, especially on the different factors that could lead to stable multilayer depositions to achieve high thicknesses: ink solid loading, drop spacing, substrate temperature, and interlayers drying. Finally, the microstructure of the samples is investigated to identify the occurring defects after sintering between 800 and 1000 °C. The magnetic properties of the films are determined, revealing a maximum coercivity of 1.98 kOe and a magnetic saturation of 78.25 emu cm−3.

Thickness-dependent morphological, structural, and optical properties of cobalt ferrite films

ABSTRACT A facile and prudent approach has been developed to deposit cobalt ferrite (CoFe2O4) films on the surface of the precursor solution by purging ammonia vapors over it. The vigorous technique to control the thickness of the film attributes spectacular characteristics to this approach. The study of CoFe2O4 films has been carried out by using FE-SEM, AFM, XRD, and UV-Visible spectroscopy. FE-SEM micrographs confirm the formation of the thin films composed of nanoparticles. The AFM micrographs indicate an increase in the root mean square roughness value with purged NH3 concentration due to the aggregation of nanoparticles. The observed XRD spectra show a cubic spinel structure of CoFe2O4 films with an increase in crystallite size in the range of 20–45 nm on increasing the NH3 concentration. UV – Visible spectroscopic investigations show a decrease in the band gap energy from 2.84 to 2.37 eV on account of the increased concentration of NH3 vapors.

Tuning optical, dielectric, and electrical properties of Carboxymethyl cellulose (CMC) doped with Cobalt ferrite (CoFe2O4) nanoparticles via laser ablation for flexible electronic devices

Studying a series of Carboxymethyl cellulose (CMC)/Cobalt ferrite (CoFe2O4) films with different content of Cobalt ferrite (CoFe2O4). By using a pulsed laser ablation approach, the CoFe2O4 was implanted into the CMC polymeric material. The synthesized nano-films have been examined via XRD, FESEM, and FTIR besides thermal, electrical, and optical examinations. FESEM illustrations clearly show that size reduction is accelerated by increasing the laser irradiation period to 20 min. The CMC/CoFe2O4 polymeric film with a laser irradiation time of 5 min demonstrates an average grain size ∼1.75 µm, while with t = 20 min it was ∼ 0.25 µm. Thermal behavior demonstrates introducing higher thermal stability with raising cobalt ferrite ratio. Moreover, the activation energy was 151.93 kJ mol−1 for t = 0.0 min, while becomes 167.66 kJ mol−1 at t = 10.0 min, Then it dropped into 160.12 kJ mol−1 at t = 20.0 min. The notable raising in E * firstly is owing to complexation tendency, while the density of the H-bond leads to activation energy dropping at t = 20 min. Optical behavior shows a decline in absorption edge from 5.4 e.V at t = 0.0 min to 4.8 e.V at t = 10, 20 min. The change in dielectric constant (ε′) by increasing frequencies upon cobalt ferrite content variation provokes a great development for the electrical behavior of the studied compositions.

The magnetic properties of Mn-doped cobalt ferrite films prepared by the spin-coating method

The magnetic properties of Mn-doped cobalt ferrite films prepared by the spin-coating method

Structure, magnetic morphology and magnetization correlations in pulsed laser deposited CoFe[formula omitted]O[formula omitted] ([formula omitted]) thin films

The present paper reports a complete study on the correlation between structure, morphology, and magnetic properties of (111)-oriented cobalt ferrite (CoFe2O4) thin films with varying film thickness. The CoFe2O4 (CFO) thin films were deposited on Pt-coated Si substrate by pulsed laser deposition (PLD) at 550 °C. The x-ray diffraction (XRD) data confirms the (111)-oriented growth of the cobalt ferrite films. The in-plane morphology of the films in the field emission scanning electron micrographs ensure the Stranski–Krastanov growth mechanism, and the atomic force micrographs confirms the effect of lattice relaxation on the morphology of the films with varying thickness. The possible cation distributions for the samples were determined from the Raman spectroscopy, which revealed the crystal structure-magnetic property correlations in cobalt ferrite films. The magnetic hysteresis (M−H) loops show a significant spin reorientation by showing the variation between the in-plane (IP) and out-of-plane (OP) magnetization. The presence of a kink on the OP M−H loops and its variation with film thickness clearly establishes the existence of competing magnetic anisotropies in the films. The high coercivity (HC) values observed for OP magnetization of cobalt ferrite films with thicknesses 115 nm and 125 nm may be explored for possible room-temperature (RT) device applications.

Structural and magnetic properties of CoFe2O4 thin films grown on isostructural lattice-matched substrates

Epitaxial thin films of cobalt ferrite (CoFe2O4) are grown on two isostructural substrates, (001)-oriented MgGa2O4 and ZnGa2O4, using pulsed laser deposition. The substrates have a lattice mismatch of 1.26% and 0.70% with bulk CoFe2O4 (CFO) crystal. We have systematically investigated the structural and magnetic properties of the epitaxial CFO films on these substrates. X-ray diffraction and transmission electron microscopy result analysis reveal that the films deposited on spinel ZnGa2O4 are essentially free of defects and are under a small compressive strain, while films on MgGa2O4 show partial strain relaxation along with defect formation. Room temperature magnetization data indicate that CFO grown on ZnGa2O4 substrates have a bulk-like saturation magnetization of 420 emu/cc and a uniaxial substrate-induced anisotropy value of −22.9× 106 erg/cm3 with an anisotropy field as low as 60 kOe.

Structural and magnetic properties comparison between cobalt ferrite films obtained by different deposit method

We presented a comparison of the structural, morphological, and magnetic properties between films of cobalt ferrite oxide (CFO), these were deposited with pulsed laser deposition (PLD) and spin-coating (SC) technique. In CFO films obtained by PLD method, a preferential orientation is clearly observed in (004) planes, with a large grain size distribution associated with the splashing effect. For the CFO films obtained by SC method have a homogeneous microstructural distribution with grain size around 50 nm. Additionally, Raman spectra deconvolution was used to estimate the cation distribution in CFO films. Magnetic measurement of CFO films obtained by SC shows a coercive field increment, and which that can be due to a reinforcement in magnetocrystalline anisotropy due to the homogeneous microstructure, whereas for CFO films obtained by PLD, it shows a coercive field decrement due to the splashing effect.

Cobalt and titanium co-doped zinc ferrite film photoanode with boosted interfacial photoelectrocatalytic activity for efficient degradation of tetracycline via the covalency competition in the Zn-O-Fe backbone

• The co-doping of Co and Ti in the ZFO leads to its lattice expansion. • LB-CoTiZFO film shows higher PEC activities than LB-ZFO film in TC degradation. • Surface rearrangement occurs in the LB-CoTiZFO film under the PEC circumstances. • Fe-O bond breakage caused by the covalency competition leads to boosted PEC activity. For efficient removal of the residual tetracycline (TC) in the aquatic environment, a novel cobalt (Co) and titanium (Ti) co-doped zinc ferrite (CoTiZFO) film was prepared via the Langmuir-Blodgett (LB) method in this study. With the co-doping of Co and Ti, the interfacial photoelectrocatalytic (PEC) activities for degradation of TC by the LB-assembled CoTiZFO (LB-CoTiZFO) films were significantly improved. As the applied voltage was 0.6 V in a two-electrode system, the five-layered LB-CoTiZFO (LB-CoTiZFO-5) films exhibited the optimal TC degradation rate and mineralization rate, which were accordingly 92.85% ± 1.45% and 81.92% ± 0.26%. In the same case, the kinetic rate constant ( k ) for PEC degradation of TC by the LB-CoTiZFO-5 films is equivalent to 3.3-fold of that by the films without the co-doping of Co and Ti. Under the PEC circumstances, the Co 3+ and Ti 4+ in the LB-CoTiZFO-5 film would be reduced to Co 2+ and Ti 3+ , while the Fe 2+ was oxidized to Fe 3+ , which results in the surface rearrangement of the LB-CoTiZFO-5 film. In addition, the Density Functional Theory (DFT) calculation results manifest the covalency competition in the Zn-O-Fe backbone can lead to the Fe-O bond breakage, the bare Fe metals with unpaired valence electrons will diffuse to the Helmholtz layer and serve as active sites, which endows the LB-CoTiZFO-5 films with boosted interfacial PEC activities. Therefore, the LB-CoTiZFO-5 film photoanode shows great prospective in efficient PEC degradation of TC.

Magnetoelastic constant of thin films determined by a four-point bending apparatus

We have developed a method to variably induce lattice strains and to quantitatively evaluate the induced magnetic anisotropy. Both tensile and compressive strains were introduced into epitaxial films of cobalt ferrite (CFO) grown on a single crystal MgO(001) substrate using a four-point bending apparatus made of a plastic material fabricated by a 3D printer. The change in magnetic anisotropy due to bending strain can be measured quantitatively by using the conventional magneto-torque meter. The strain-induced magnetic anisotropy increased with the tensile strain and decreased with the compressive strain as expected from a phenomenological magnetoelastic theory. The magnetoelastic constant obtained from the changes in bending strains shows quantitatively good agreement with that of the CFO films with a uniaxial epitaxial strain. This signifies that the magnetoelastic constant can be evaluated by measuring only one film sample with strains applied by using the bending apparatus.

Growth and characterization of ultrathin cobalt ferrite films on Pt(111)

CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523 K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron Mössbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state. Annealing also induced cobalt segregation to the surface of the thicker films. The measured Mössbauer spectra at low temperature were indicative of cobalt ferrite, the both films showing very similar hyperfine patterns. Annealing in oxygen or vacuum affected the cationic distribution, which was closer to that expected for an inverse spinel in the case of annealing in an oxygen atmosphere.

Small magnetless integrated optical isolator using a magnetized cobalt ferrite film

We experimentally demonstrated a silicon optical isolator using a monolithically integrated cobalt ferrite (CFO) film as magneto-optical material, achieving an isolation ratio of 9.6dB near 1550nm wavelength. By virtue of the large Faraday rotation coefficient of CFO, the device has a compact footprint comparing to the current yttrium iron garnet-based isolators. Furthermore, we demonstrated self-biased isolation by the strong remanence of CFO films, eliminating the tedious demand of an external magnet. Cobalt ferrite represents a potential alternative approach to yttrium iron garnets to realize a practical device for on-chip isolation in silicon photonic integrated circuits because of the small footprint.

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001).

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich films with different stoichiometry ( and ) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/FeO bilayers deposited before on Nb-doped SrTiO(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of cations in the low-spin state on octahedral sites for the film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.

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.

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.

Poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite composite films with a self-biased magnetoelectric effect for flexible AC magnetic sensors

With the rapid development of artificial intelligence and wearable devices, flexible magnetic sensors have attracted much attention in recent years. In this work, large self-biased 0–3 type poly(vinylidene fluoride-trifluoroethylene)/cobalt ferrite (P(VDF-TrFE)/CoFe2O4) flexible magnetoelectric (ME) composite films are proposed for the development of AC magnetic sensors. P(VDF-TrFE)/CoFe2O4 composite films with CoFe2O4 nanoparticle mass contents from 5 to 30% are successfully fabricated through the solution casting method. The results show that the nanoparticles are homogeneously dispersed in the P(VDF-TrFE) matrix, and the composite films have both excellent ferroelectric and ferromagnetic properties. The P(VDF-TrFE)/CoFe2O4 composite films all exhibit a large ME effect. The ME coefficient reaches 47.1 mV·cm−1·Oe−1 for the film with a CoFe2O4 nanoparticle mass content of 20% at resonance frequency. Moreover, the composite films have a large self-biased ME effect with a maximum value of 20.4 mV·cm−1·Oe−1, which is mainly due to the high remnant magnetization of CoFe2O4 nanoparticles. To evaluate the composite films for application in magnetic sensors, the response of the ME output voltage to an AC magnetic field without a bias DC magnetic field was measured. The good linear correlation coefficient, sensitivity and repeatability indicate that the proposed 0–3 type P(VDF-TrFE)/CoFe2O4 composite film is a promising material for flexible AC magnetic sensors.

Influence of applied magnetic field and heating on properties of cobalt ferrite films

Cobalt ferrite (CoFe2O4) films were grown in the presence of a magnetic field using a solution method. These films were investigated to understand the effect of applied magnetic field and heating on their morphological, structural, and magnetic properties. Investigations showed that the crystallite size in both the unheated and heated films increases with the application of the magnetic field. The crystalline size is observed to increase from 3.57 to 5.65 nm in the case of unheated films and from 21.49 to 23.0 nm in the case of heated films, with the application of a magnetic field. Along with the crystalline size, the applied magnetic field is found to influence the magnetic properties of the films.

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.

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

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

Effect of Electric and Magnetic States of Substrate on the Deposition of Organic Polymers

The processes of deposition of organic polymers (using lysozyme an example) on substrates with different magnetic and electric states have been studied using a complex of microscopy methods. It is shown that substrates with a well-developed electric relief promote the immobilization of lysozyme. For substrates with a type of freshly cleaved mica, with specific dipole surface structure, the ordering of lysozyme islands in the form of filaments is observed. An effect of lysozyme self-organization with the formation of dendritic structure upon the deposition of cobalt ferrite films on the surface of films is found, which makes such template substrates promising biotropic structures.

Giant Faraday rotation of cobalt ferrite thin films deposited on silicon substrates for silicon photonic nonreciprocal device applications

In this study, crystalline cobalt ferrite thin films with large Faraday rotation (FR) coefficient were deposited on silicon by radiofrequency magnetron sputtering. An (100)-oriented MgO buffer layer was employed to solve the film/substrate discrepancy. A giant FR coefficient of 25 600 deg cm−1 was achieved for a cobalt ferrite film deposited at a substrate temperature (ST) of 600 °C. Moreover, the magnetic easy axis of the films switched from in-plane (IP) to out-of-plane orientation with increasing ST. This switching in the easy axis could be attributed to induced IP stress in the films with high deposition temperatures.