CoFe2O4 Research Articles

LaFeO3-CoFe2O4 bi-magnetic composite thin films prepared using an all-in-one synthesis technique

Bi-phasic composite films are generally grown as multilayers that result in layer-by-layer morphology with each layer having a distinct chemical composition. In this work, we report an all-in-one chemical synthesis technique combined with spin-coating to prepare single-layer bi-magnetic LaFeO3 (LFO)-CoFe2O4 (CFO) composite thin films with both phases co-existing in the same layer. The films have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the magnetic properties have been probed using dc magnetometry at room and low temperature. The unique synthesis technique followed ensures homogeneity of the two phases on the nanoscale with grain sizes ~10 nm for CFO and few tens of nm for LFO, as observed from TEM images. XRD confirms the presence of only the desired LFO and CFO phases in the films without any undesired secondary phases. Magnetic hysteresis loops reveal a coercivity of ~0.2 T at room temperature that increases by nearly one order of magnitude at T = 5 K. The all-in-one synthesis technique reported here can be used to prepare different bi-phasic composites in the form of single-layer two-dimensional films as well as zero-dimensional nanoparticles by a suitable modification of the precursors, solvents, and chelating agents.

Self‐assembled patterned CoFe2O4‐SrRuO3 electrodes: Enhanced functional properties by polar nano‐regions reorientation

AbstractEpitaxial CoFe2O4 (CFO) and SrRuO3 (SRO) nanopillar heterostructures were deposited on Pb(Mg1/3Nb2/3)0.70Ti0.30O3 (PMN‐30PT) single crystal substrates by switch pulsed laser deposition (SPLD). Since the CFO nanopillars are insulating, and the SRO matrix conductive, this self‐assembled nanopillar heterostructure served as a patterned electrode on PMN‐PT, which then enhances the dielectric and piezoelectric constant of the substrate. Cross‐sectional electron microscopy images revealed the formation of a nanopillar heterostructure layer with CFO nanopillars within a SRO matrix. AFM and XRD revealed good topography and epitaxy, indicating a high quality SRO‐CFO self‐assembled nanopillar structure. Using a SRO‐CFO thin film patterned electrode, PMN‐PT was found to have a notably higher (30%) dielectric constant with increasing electric field and enhanced transverse broadening in reciprocal spacing mapping (RSM) scans.

CoFe2O4/N-doped reduced graphene oxide aerogels for high-performance microwave absorption

Nowadays, to solve electromagnetic radiation issues, an urgent demand is to develop high-performance microwave wave absorption materials with lightweight, broad bandwidth and strong absorbing capacity. In this work, by embedding CoFe2O4 (CFO) nanoparticle into N-doped reduced graphene oxide (N-rGO) aerogels, a unique CFO/N-rGO aerogel microwave wave absorber with a 3D porous architecture is synthesized via a facile solvothermal method and lyophilization technique. Impressively, the as-synthesized N-rGO aerogels exhibit typical ferromagnetic behavior. The electromagnetic parameters of CFO/N-rGO aerogels can be immensely improved by tuning the additive amount of CoFe2O4 nanoparticle. An optimal microwave absorption performance is achieved when the mass ratio of graphene oxide (GO) to CoFe2O4 is 1:2. Here, a strong reflection loss (RL) reaches −60.4 dB at 14.4 GHz with a thickness of 2.1 mm and a low filler loading ratio of 20 wt%. Further, the effective absorption bandwidth (RL < −10 dB) can be up to 6.48 GHz (11.44–17.92 GHz) with a thickness of 2.2 mm. Notably, at only 3 mm, its effective absorption bandwidth can completely cover X-band. The superior microwave wave absorption performance of as-synthesized CFO/N-rGO aerogels is attributed to the specific surface morphology and porous structures, leading to the multiple scattering and reflecting, interfacial polarization and optimal impedance matching. This work not only provides a deep insight on tuning microwave absorption performance of ferrite/N-rGO aerogels, but also offers a new route to design high-performance magnetic/dielectric absorbers.

Multi-walled carbon nanotubes-CoFe2 O4 nanoparticles as a reusable novel peroxymonosulfate activator for degradation of Reactive Black 5.

In this study, CoFe2 O4 nanoparticles supported on multi-walled carbon nanotubes (MWCNTs), as novel peroxymonosulfate (PMS) activator, were synthesized for degradation of Reactive Black 5 (RB5). The results showed that the maximum removal efficiencies of RB5 (100%), chemical oxygen demand (83.12%), and total organic carbon (65.5%) could happen at pH of 7, catalyst dosage of 100mg/L, PMS dosage of 2mM, RB5 concentration of 50mg/L, and time of 30min. The results of the temperature effect showed that the activation energy (Ea =20.92kJ/mol) for the synthesized catalyst is much lower compared to other studies. The PMS/MWCNTs-CoFe2 O4 system had higher decolorization efficiency and kinetic rates compared to other adsorption and oxidation systems. Quenching experiments proved that RB5 was degraded by sulfate and hydroxyl radicals. The MWCNTs-CoFe2 O4 catalyst showed suitable stability and reusability even after five consecutive catalytic reactions. The continuous treatment of RB5 in real water resources was performed using catalyst packed in a column reactor, and its results showed the high efficiency of the column in the catalytic treatment of the dye at long reaction time. Based on the proposed degradation pathway, the azo bands and the naphthalene structure of RB5 are oxidized to compounds with low molecular weight. PRACTITIONER POINTS: MWCNTs-CoFe2 O4 was used as a novel recyclable catalyst for the activation of peroxymonosulfate and dye degradation. The rate of dye degradation and peroxymonosulfate activation by MWCNTs-CoFe2 O4 was much higher than that of the catalysts alone. Radical , with contribution percentage of 73.20%, was the main agent for degradation of Reactive Black 5 dye. MWCNTs-CoFe2 O4 in the dye degradation process showed excellent stability and reusability, lower activation energy, and easier separation. The dye degradation products were identified by gas chromatography and UV-vis spectrophotometric analyses, and their degradation pathway was suggested.

Proximity effect tuned magnetic properties in composites of carbon nanotubes and nanoparticles of CoFe2O4

The saturation magnetization of composites of carbon nanotubes and CoFe2O4 (CFO) magnetic nanoparticles synthesized through a novel one-step process in the presence of a surfactant (sodium dodecyl-benzene-sulfonate) show significant increase, to 208 emu/g. This value of saturation magnetization of the composite is a factor of 3.3 higher than pristine CFO nanoparticles. This is the first time such a remarkable magnetic behavior of CFO/ carbon nanotubes composite is presented. The increased magnetism is attributed to the proximity effect between uniformly distributed ferromagnetic CFO nanoparticles on the surface of carbon nanotubes and hybridization of the π-electronic states of carbon and the 3d-bands of CFO. Scanning electron microscopy images confirm uniform and dense distribution of CFO nanoparticles on carbon nanotubes. Magnetic force microscopy images confirm the formation of uniformly distributed magnetic stripe domains. The sample was characterized at ambient using X-ray diffraction, Raman Spectroscopy, atomic force microscopy, scanning electron microscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy. Magnetic properties were characterized by magnetic force microscopy and magnetometry using vibrating sample magnetometer.

Liquid Phase Synthesis and Morphological Observation of BaTiO₃-CoFe₂O₄ Nanocomposite Films.

A novel and inexpensive fabrication method of multiferroic nanocomposite films via liquid-phase formation is demonstrated in this work. Well-aligned anodized TiO₂ nanotube arrays on a Ti substrate were used as the core template. The anodized TiO₂ nanotube arrays were then hydrothermally treated in Ba(OH)₂ aqueous solution to form BaTiO₃ (BTO) nanotube arrays. The average pore diameter and thickness of the BTO nanotube arrays obtained were approximately 50~70 nm and 2~4 μm, respectively. The BTO nanotube arrays were then dip-coated with CoFe₂O₄ (CFO) sol with the assistance of vaccum impregnation equipment to enable the penetration of CFO sol into the tubular pores of the BTO nanotube arrays. The good distribution of CFO in the BTO nanotube arrays was confirmed by electron microscopy accompanied with elemental analysis. The good crystallinity of CFO and BTO in the nanocomposite was confirmed by X-ray diffraction, and the nanocomposite film exhibited anisotropic ferrimagnetic properties upon an in plane and out-plane applied magnetic field.

Structural and electrical properties of (1-x)Na0.5Bi0.5TiO3-xCoFe2O4 (x = 0.1, 0.2) multiferroic composite ceramic

Na0.5Bi0.5TiO3 (NBT) and CoFe2O4 (CFO) ceramics were synthesized by sol–gel and metallo – organic chemical solution methods respectively. Structural, electrical, dielectric and magnetic properties of (1-x) NBT-(x) CFO (x = 0.1, 0.2) multiferroic particulate composite prepared by mixing NBT and CFO powders in required stoichiometric concentration were studied. The presence of ferroelectric (NBT) and ferrite (CFO) phases had been confirmed by X-ray diffraction analysis (XRD). Room temperature dielectric behavior was studied with varying frequencies. Ferromagnetic behavior was also confirmed by M−H hysteresis loops. The current–voltage (I–V) characteristics were studied by using Keithley 2611 Source Meter.

Effects of pillar size modulation on the magneto-structural coupling in self-assembled BiFeO3–CoFe2O4 heteroepitaxy

The magneto-structural coupling of BiFeO3 (BFO)–CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated.

Preparation and electromagnetic microwave adsorption performances of porous nanocomposite self-assembled by CoFe2 O4 nanoparticles and diatomite

Preparation and electromagnetic microwave adsorption performances of porous nanocomposite self-assembled by CoFe2 O4 nanoparticles and diatomite

Structural characterization of PZT and CFO/PZT films on (001) SrTiO3 by the pulsed laser deposition (PLD)

In this work, we investigated the structural properties of ferroelectric PbZr0.2Ti0.8O3 (PZT) and ferrimagnetic/ferroelectric [CoFe2O4(CFO)/PZT] bilayers grown on (001)SrTiO3 (STO) substrates with 50 nm thick LaNiO3 bottom electrodes via X-ray diffraction by θ-2θ scan, reciprocal space mapping (RSM), rocking curve, and phi-scan modes. Interestingly, structural properties of the PZT layer exhibited remarkable changes after the top-layer CFO deposition. Both the c- and a-domains exist in the PZT layer by the data acquired and the tetragonality of the PZT decreases after the CFO top-layer deposition.

Fabrication and characterization of micropillar-type multiferroic composite thin films by non-aqueous sol-gel method using ferroelectric pillars

CoFe2O4 (CFO) thin films were deposited on (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT) micropillar films by a non-aqueous sol-gel method. The pitch size of 2–5 μm in the micropillar films used as ferroelectric pillars, and 5 and 15 CFO deposition cycles were examined for high density of CFO nanoparticles. All the CFO films formed by five deposition cycles on BNEuT micropillar films with a pitch size of 2–5 μm were composed of mostly single-phase CFO with a cubic inverse-spinel structure. All the CFO films deposited on the four BNEuT micropillar films were highly dense and had excellent surface flatness, based on surface field-emission scanning electron microscope observations. Based on the structural, magnetic and ferroelectric characteristics, the optimal pitch size for achieving a high density of CFO nanoparticles was 5 μm, and the optimal number of CFO deposition cycles was five.

Fabrication and characterization of micropillar-type multiferroic composite thin films by metal organic chemical vapor deposition using a ferroelectric microplate structure

Using a a-axis-oriented epitaxial (Bi3.25Nd0.65Eu0.10)Ti3O12 (BNEuT) thin films with a microplate-like shape as a ferroelectric pillar material, micropillar-type CoFe2O4 (CFO)/BNEuT(h00)/Nb:TiO2(101) composite multiferroic films were fabricated by metal organic chemical vapor deposition. The deposition time was varied from 90–150 min to examine its effect on the structural, ferroelectric, and ferromagnetic characteristics of the films. All the films exhibit single-phase cobalt ferrite with a cubic inverse-spinel structure. The deposited CFO films have a similar columnar structure with a comparatively good step coverage of 37%–66%. The room-temperature magnetization−magnetic field hysteresis loop of the films showed a clear ferromagnetic hysteresis loop, and coercivity decreased from 1.1 to 0.9 kOe with increasing the deposition time. The room-temperature polarization−electric field hysteresis loop of the films showed a ferroelectric hysteresis loop, and the effect of the leakage current was the smallest for a deposition time of 120 min.

Highly efficient nanostructured CoFe2 O4 thin film electrodes for electrochemical degradation of rhodamine B.

In this work, we report the application of highly efficient electrodeposited cobalt ferrite (CoFe2 O4 ) thin films in electrochemical degradation of rhodamine B. XRD, FTIR and Raman spectroscopic studies confirmed the formation of single phase CoFe2 O4 . SEM analysis revealed a very fine nanorods dispersed uniformly with average size around 30nm. UV-Vis spectrophotometry emphasized that the optical band gap value is 1.6eV. Moreover, the elaborated CoFe2 O4 thin films showed a good efficiency for the electrochemical degradation of an aqueous solution of rhodamine B (RhB) attaining 99% during the first 3min of reaction time. The trapping experiments revealed that the hydroxyl radicals were the main active species leading to the removal of RhB initial concentration of 10mg/L in a very short time. PRACTITIONER POINTS: A simple electrodeposition technique was used to fabricate CoFe2 O4 thin. XRD and FTIR studies revealed the formation of pure cubic spinel phase. Nano-rod like morphology has been successfully synthesized. The rhodamine B aqueous solution has been completely decolorized using the obtained CoFe2 O4 thin films.

Reversible magnetoelectric switching in multiferroic three-dimensional nanocup heterostructure films

Self-assembled nanocomposite films containing ferroelectric and ferromagnetic phases have attracted enormous research interest because they are the most promising candidates for practical multiferroic applications. However, obtaining a genuine magnetoelectric (ME) coupling effect is still challenging in this research area. To substantially improve the ME effect, new heterostructure designs with efficient strain control between two phases are urgently needed. Herein, a novel three-dimensional (3D) nanocup architecture of a heterostructure film is developed. To establish the unique architecture, a heavily Co, Fe-doped ferroelectric Bi3.25La0.75Ti3O12 (BLT) target was used during the growth of BLT thin films via pulsed laser deposition. Consequently, 3D nanocup-structured CoFe2O4 (CFO) particles formed inside the BLT via spontaneous nucleation and agglomeration. The 3D nanocup BLT-CFO film exhibited magnetically controlled reversible dielectric switching, which is direct evidence of strong ME coupling caused by the efficient interfacial strain coupling and low leakage of the novel nanocup architecture. The obtained results strongly suggest that the 3D nanocup heterostructure film significantly improves the ME coupling effect. In addition, we propose a new paradigm in the architecture design of self-assembled nanocomposite films for diverse multifunctional devices.

Structural, Electric and Ferroelectric Properties of Lead Free 50Na0.5Bi0.5TiO3-50CoFe2O4 Multiferroic Particulate Composite

Na0.5Bi0.5TiO3 (NBT) and CoFe2O4 (CFO) powders have been prepared by sol-gel and metallo – organic (MOD) chemical solution methods respectively. The lead-free 50NBT-50CFO multiferroic particulate composite has been prepared by mixing NBT and CFO powders in required stoichiometric concentration. The structural and microstructural properties of ferroelectric (NBT) and ferrite (CFO) phases have been studied by X-ray diffraction and field emission scanning electron microscopy micrographs. The M-H curve of 50NBT-50CFO confirms the ferromagnetic behavior of the composite. The ferroelectric properties are also investigated by measuring polarization vs. electric field (P-E) hysteresis loops. Electrical properties are also studied by Keithley 2611 Source Meter.

Effect of LaNiO3 on the impedance and dielectric properties of CoFe2O4: a high temperature study

In this article, we report the impedance and dielectric properties of the nanocomposites comprising of CoFe2O4 (CFO) and LaNiO3 (LNO) with varying LNO content (0, 5, 10 and 15%) in the temperature range from 35 °C–400 °C. The impedance and modulus spectroscopy show the non-Debye type dielectric relaxation behaviour of the grain and grain boundary separately in pure CFO with an additional relaxation in the composite with 15% LNO, arising from the electrode polarization. Mostly the grain boundary of the composites is affected by the presence of LNO as its activation energy in the composite with 15% LNO is reduced by ~0.2 eV compared to pure CFO, whereas that of the grain remains similar. The dielectric constant increases consistently with increasing LNO content in the composites owing to the Maxwell–Wagner–Sillar type polarization effect between the interfaces of LNO and CFO. The dielectric constant manifests a negative value in both pure CFO and the composite with 15% LNO at all temperatures in the frequency of hundreds of MHz which is explained by the interband transition. The ac conductivity of pure CFO reveals short range and orientational hopping inside the grains and across the grain boundary, respectively. However, in the composite with 15% LNO, the reduced activation energy assists the charge carriers for short range hopping across the grain boundary while the conductivity inside the grain remains unaffected.

Magnetoelectric 0.2(CoFe2O4)-0.8(Ba0.85Ca0.15 Zr0.1Ti0.9O3) lead free composite for spintronic applications

Lead free (0.2) CoFe2O4 (CFO) – (0.8) Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) composite is prepared by mechanical mixing of CFO and BCZT phases. The constituent phases, CFO and BCZT are prepared by sol-gel technique. XRD data shows characteristic peaks of both magnetic and piezoelectric phases without any secondary phases confirming the formation of the composite. Polarization (P) versus Electric field (E) measurements show a proper ferroelectric loop for BCZT with Pmax ∼ 4.3 μC/cm2 whereas composite shows a leaky behaviour. Room temperature M-H loops show a decrease of magnetization from ∼ 80 emu/g for pure CFO to 17 emu/g for composite. Thus, 0.2 CFO-0.8 BCZT composite shows both electric and magnetic properties at room temperature.

Improved depolarization temperature via the ordered alignment of defect dipoles in (Na0.5Bi0.5)TiO3-BaTiO3 ceramics

The thermally induced depolarization along with the disappearance/loss of macroscopic piezoelectricity is an inevitable issue in ferroelectrics. Motivated from the Landau phenomenological theory, we have developed a strategy to create inner bias field via forming ordered defect dipoles in the NBTBT via CoFe2O4 (CFO) doping and electric poling. It is proposed that the deferred depolarization is related to the formed inner bias field in the CFO-doped NBTBT ceramics. Temperature-dependent dielectric, piezoelectric, strain and ferroelectric behaviors have been measured to evidence the improved thermal stability after CFO doping. It is found that the depolarization temperature of NBTBT-0.02 with a little sacrifice of piezoelectric response is improved to 138 °C, which is 41 °C higher than the pure NBTBT samples. Our study not only provides a feasible paradigm to enhance the ferroelectric order in NBT based materials though defect dipoles, but also inspires further works to promote the depolarization temperature in other ferroelectric materials.

Effect of molar ratio on the microstructure, dielectric and electromagnetic properties of BaTiO3/CoFe2O4 ceramic

BaTiO3/CoFe2O4 (BTO/CFO) composite ceramics were synthesized by conventional solid-phase method, and the effects of different BaTiO3 (BTO) and CoFe2O4 (CFO) contents on the microstructure, magnetoelectric properties were systematically studied. X-rays showed that ferroelectric and ferromagnetic phases can coexist without chemical reaction. The dielectric constant decreased with the decrease of the molar ratio of BTO, and the dielectric constant increased with the increasing of temperature. The dielectric loss decreased first and then increased and finally decreased as a function of frequency, and the dielectric loss increased with the increase of temperature. The composite with the molar ratio of BTO/CFO (3:1) demonstrated better ferroelectric properties that remnant polarization is 0.82 μC cm−2 and the coercive electric field is 10.23 kV cm−1. The best magnetic property was shown in BTO/CFO (1:3).

Characterization of magnetic properties of ultrathin CoFe2O4 films by utilizing magnetic proximity effect

Magnetic spinel oxides, including CoFe2O4 (CFO), have crucial applications in spintronics. They have excellent magnetic properties, such as high spin polarization and high Curie temperature, which enables the operation of spintronic devices at room temperature. Some interesting phenomena have also been discovered for interfaces consisting of spinel oxides and heavy metals. However, the magnetic properties of ultrathin CFO films have not been investigated sufficiently. In this report, a characterization of the magnetic properties of an ultrathin CFO film was performed by using the magnetic proximity effect (MPE) to observe the anomalous Hall effect (AHE) in Pt. The result was consistent with the measurement performed with magneto-optical effects. By fitting AHE with the Langevin function, it was concluded that these ultrathin films (tCFO<3.4 nm) showed superparamagnetism, and the magnetic moment was estimated to be 3000μB. The results provided the novel method to evaluate the magnetic properties of ferromagnetic insulators by using MPE and AHE, thus providing a better understanding of interface magnetism.