Doped CoFe2O4 Research Articles

Effect of Zr, Sm and Gd Doped CoFe2O4 on Structural, Spectral and Magnetic Properties

In this work, cobalt composite nano ferrites with chemical formula CoZr0.05-xRExFe1.95O4 (x = 0 and 0.025 and RE = Sm, Gd) were prepared using sol-gel synthesis method and studied structural, optical and magnetic properties of them. The Rietveld assessment of XRD data validated the emergence of a single-phase cubic spinel configuration for all compounds. SEM has been used to study the surface morphology of the compounds. Energy gap has been estimated and the values are 2 eV, 1.8 eV and 1.6 eV for CoZr0.05Fe2O4, CoZr0.025Sm0.025 Fe1.95O4, and CoZr0.025Gd0.025 Fe1.95O4 compounds respectively. FTIR and Raman spectra confirmed the structure with the appearance of standard modes. The RE replacement in CoFe2O4 ferrites has an intense impact on magnetic properties. With the substitution of Sm3+ and Gd3+ ions in cobalt-zirconium ferrite, there is a reduction in saturation magnetization (55 emu g−1 of CoZr0.05Fe2O4 reduced to 25 emu g−1 for Gd3+ and to 29 emu gm−1 for Sm3+) as the size of crystallites decreases. A decrease in crystallite size correlates with an increase in the number of spin disorder occurrences in rare Earth-substituted cobalt-zirconium ferrite nanoparticles Further, the decrease in coercivity (2440 Oe of CoZr0.05Fe2O4 reduced to 720 Oe for Gd3+ and to 29 Oe for Sm3+ with rare Earth element doping is due to the crystallite size and large lattice distortion showed an enhancement of magnetocrystalline anisotropy field which effects a shift of resonance frequencies from higher frequencies which is good for the memory storage devices.

A New Class of Multifunctional CoDyzFe2−zO4 Magnetic Nanomaterials: Influence of Structural, Morphological, Optical, Magnetic, Antibacterial, and Photocatalytic Traits

Here we focus on preparing recoverable Dy doped CoFe2O4 photocatalysts for the removal of the malachite green pollutant (MGP) in natural Sunlight. XRD results demonstrate development of the spinel symmetry with no impurities phases. The FESEM analysis revealed spherical grains with definite grain boundaries and agglomerated behavior. We found that our synthesized photocatalysts behaves as an excellent magnetic nanomaterial by observing the saturation magnetization of 77.79 emu g−1. Out of all photocatalysts, CoDy0.03Fe1.97O4 nanophotocatalyst exhibit the high zone of inhibition (ZOI) for Staphylococcus aureus and Escherichia coli. It makes the prepared nanomaterials highly suitable for the biological purposes. The effectiveness of photocatalytic degradation activity of prepared specimens is significantly impacted by the addition of dysprosium ions. During a 150 min of reaction period, CoDy0.03Fe1.97O4 has a higher degradation percentage around 95.36% as compared to CoFe2O4 (86.09%). The prepared doped and undoped CoFe2O4 nanomaterials displayed the least decline in the degradation percentage of MGP after four reuse cycles and this might be attributable to the weight loss during the recovery. Therefore, the nanomaterials suggested a reliable and durable photocatalyst for degradation process. Hence the prepared magnetically recoverable and multifunctional photocatalysts are reliable for the water remediation and biological usages.

Exploring the supercapacitive potential of Sm3+ doped CoFe2O4 nanoparticles: Enhanced magnetic and dielectric properties

This study investigates the impact of Sm3+ substitution on the structural, electrical, magnetic, and electrochemical properties of CoFe2O4 nanoparticles prepared via a combined solid-state reaction and mechanical milling approach. Rietveld refinement analysis confirms the presence of single-phase cubic spinel structures within the Fd3m space group for both CoFe2O4 (CF) and Co0.95Sm0.05Fe2O4 (SmCF). Field emission scanning electron microscopy and energy dispersive spectroscopy are employed to validate the microstructure and elemental composition. Tauc plot analysis reveals a decrease in the band gap from 2.24 eV for CF to 2.07 eV for SmCF. Hysteresis loop measurements demonstrate an enhancement in saturation magnetization, remanent magnetization, and magnetic moment for SmCF, indicating improved magnetic properties. Furthermore, a substantial increase in magneto-crystalline anisotropy is observed with Sm³⁺ doping. Frequency-dependent dielectric properties are investigated using Havriliak–Negami fitting, confirming the presence of Cole-Cole dispersion. A direct correlation between the dielectric constant and temperature is identified, suggesting higher temperatures lead to elevated values. Notably, the incorporation of Sm³⁺ results in a significant enhancement in specific capacitance, positioning SmCF as a promising candidate for energy storage applications, particularly in supercapacitors.

Improved photocatalytic performance in Ce3+ doped CoFe2O4 nanoparticles by modifying structural, optical, and magnetic properties

In recent research, semiconductive magnetic nanomaterials have gained significant attention for their potential in photocatalytic applications, primarily due to their ease of recoverability. This study focuses on the successful synthesis of CoCexFe2-xO4 nanoparticles, where the variable x (ranging from 0 to 0.20) introduces Ce3+ ions. The inclusion of Ce3+ ions induces noteworthy changes in the structural, optical, microstructural, magnetic, and photocatalytic properties of CoFe2O4 nanoparticles. Various analytical techniques, including x-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, photoluminescence, transmission electron microscopy, vibrating sample magnetometry, and electron paramagnetic resonance spectroscopy, were employed to investigate these effects comprehensively. The research delves into the photocatalytic degradation of rhodamine B under visible light irradiation, exploring the impact of different elemental compositions, catalyst quantities, irradiation durations, and initial rhodamine B concentrations on the decolorization process.

Peroxymonosulfate activation by sulfur doped CoFe2O4 rod for arsanilic acid removal: Performance and arsenic enrichment

For a long time, the low toxicity of arsanilic acid (p-ASA) makes people ignore its potential risk. The highly diffusible and fatal arsenic produced from the decomposition of p-ASA has sounded the alarm for humans. In this study, a rod-like sulfur doped CoFe2O4 (S-CoFe2O4) was successfully prepared to activate peroxymonosulfate (PMS) for the p-ASA removal. By adding 40 mg/L S-CoFe2O4 and 0.02 mM PMS, 10 mg/L p-ASA can be thoroughly degraded within 15 min. The pseudo-first-order reaction rate constant was calculated to be 0.37 min−1, which was 7.4 times that of CoFe2O4/PMS system (0.05 min−1). S-CoFe2O4/PMS system achieved satisfactory p-ASA removal under acidic, neutral, and alkalescent situations. In addition to the superior p-ASA degradation efficiency, S-CoFe2O4/PMS system can synchronously immobilize the released arsenic, and 73% of arsenic was adsorbed on S-CoFe2O4 surface. Catalytic mechanism study showed that divalent metal active site, oxygen vacancy, and sulfite were responsible for the generation of reactive oxygen species (ROSs) involving·OH, O2·-, and 1O2. This study proposes a reliable approach for safely removing p-ASA in water, and broadens the application of cobalt ferrite.

Development of a novel lead free (CoFe1.9Bi0.1O4/BaTi0.89Sn0.11O3/CoFe1.9Bi0.1O4) magnetoelectric composite via new design strategy

A novel lead free ceramic based magnetoelectric (ME) tri-layered composite with new design strategy has been fabricated by using sol-gel synthesized Bi3+ doped CoFe2O4 and Sn4+ doped BaTiO3. Structural, microstructural, magnetostriction, piezoelectric and magnetoelectric properties of the synthesized materials and developed system have been thoroughly investigated. CoFe1.9Bi0.1O4 have shown the improvement of magnetostriction (∼259 ppm) and strain sensitivity (∼323 ×10−9 Oe−1) compared to those of un-doped CoFe2O4 (magnetostriction ∼163 ppm and strain sensitivity ∼99 ×10−9 Oe−1). On the other hand, the piezoelectricity of BaTi0.89Sn0.11O3 has improved to 424 pC/N from a value of 194 pC/N for un-doped BaTiO3. The unique design strategy (where the output signal has been collected directly from the piezoelectric layer) and the simultaneous improvement of both the magnetostriction and piezoelectricity of the corresponding components have helped in achieving high ME coupling in the final device. The achievement of high values of in-plane ME coupling coefficients (αME) (α31) at off-resonance and zero-bias resonance conditions (αME ∼49 and 750 mV.cm−1. Oe−1, respectively) have proven the ability of the fabricated device in various potential applications related to magnetic field sensing and magnetoelectric effect.

Influence of Gd content on the structural, Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe2O4 nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 104 erg/cm3, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe2-xGdxO4 magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.

Particulate multiferroic Ba0.99Tb0.02Ti0.99O3 – CoFe1.8Mn0.2O4 composites: Improved dielectric, ferroelectric and magneto-dielectric properties

In present era, the challenge to design materials which unify multiple order parameters has motived the scientific community to work for multiferroic materials. In this work, the multiferroic particulate composites were fabricated from terbium doped BaTiO3 and manganese doped CoFe2O4. Terbium and manganese dopants improved dielectric and magnetic properties in BaTiO3 and CoFe2O4 respectively. Structural study revealed that doped BaTiO3 and CoFe2O4 crystalized into tetragonal and cubic structures, respectively in composites. In multiferroic composites, a dramatic drop in the unit cell volume of magnetic phase resulted in enhanced strain. The improvement in dielectric constant in composites is explained on the basis of bond and hopping lengths. The Curie Weiss Law ascertained that the dielectric peaks are widened. The calculated activation energy from resistivity measurements revealed insulating behavior of composites. The amphoteric nature of terbium and high resistivity of magnetic phase resulted in ferroelectric hysteresis loops which are free from leakage currents. The magneto-crystalline anisotropy was calculated by the Law of Approach to saturation, and was found to be small in composites, due to quenching of orbital angular momenta of the Co2+ ions by the non-magnetic ferroelectric phase. Temperature dependent magnetic study revealed increase in magnetization during zero field cooling as compared to field cooling, confirming magnetization of one sub lattice decreases at slower rate as compared to another sub lattice. The terbium and manganese doping improved the magneto-capacitance of prepared composites, suggesting the use of these composites in magnetoelectric devices.

Gd3+ Doped CoFe2O4 Nanoparticles for Targeted Drug Delivery and Magnetic Resonance Imaging

Nanoparticles of CoGdxFe2 − xO4 (x = 0%, 25%, 50%) synthesized via sol–gel auto combustion technique and encapsulated within a polymer (Eudragit E100) shell containing curcumin by single emulsion solvent evaporation technique were formulated in this study. Testing of synthesized nanoparticles was carried out by using different characterization techniques, to investigate composition, crystallinity, size, morphology, surface charge, functional groups and magnetic properties of the samples. The increased hydrophilicity resulted in sustained drug release of 90.6% and 95% for E1(CoGd0.25Fe1.75O4) and E2(CoGd0.50Fe1.5O4), respectively, over a time span of 24 h. The relaxivities of the best-chosen samples were measured by using a 3T magnetic resonance imaging (MRI) machine, and a high r2/r1 ratio of 43.64 and 23.34 for composition E1(CoGd0.25Fe1.75O4) and E2(CoGd0.50Fe1.5O4) suggests their ability to work as a better T2 contrast agent. Thus, these novel synthesized nanostructures cannot only enable MRI diagnosis but also targeted drug delivery.

Enhancement in DC Electrical Resistivity and Dielectric Behaviour of Ti4+ Doped CoFe2O4 NP’s for Nanoelectronics Application

Inverse spinel structured cobalt ferrite is one of the capable nominee for information storage and also in nanoelectronics devices. The present paper reports the rietveld refined structural, elastic, electrical and dielectric behaviour of titanium doped CoFe2O4 NP’s. The synthesis of Co1+xTixFe2-2xO4 (where, 0.0  x  0.5) nanoparticles was performed using self generated combustion technique. The prepared NP’s were characterized by X-ray diffraction technique (XRD) and Fourier transform infrared spectroscopy (FT-IR) technique to analyze the structural and elastic properties. The analysis of XRD patterns confirms the formation of single phase spinel cubic structure of all the prepared samples. The diffractograms obtained at room temperature were used for Rietveld refinement to determine the lattice constant, oxygen position, average crystallite size etc. parameters. The elastic modules were investigated through vibrational bands in FTIR spectra. The band positions in FT-IR spectra confirmed the octahedral [B] and tetrahedral (A) stretching which evident the ferrite skeleton. The plot of DC electrical resitivity with respect to temperature shows the semiconducting behaviour of the nanoparticles. The activation energy determined through resistivity plots, show decreasing nature with incrementing Ti4+ doping in cobalt ferrite. The dielectric parameters decreased exponentially with increasing frequency and with Ti doping.

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural, optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe2O4) nanoparticles and europium doped CoFe2O4 (CoFe2−xEuxO4; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe3+) ions by trivalent rare earth europium (RE-Eu3+) ions on the microstructure, optical and magnetic properties of the produced CoFe2O4 nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu2O3 phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ1 and υ2) and tetrahedral A-site (υ3) around 415 cm−1, 470 cm−1 and 600 cm−1 respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu3+ ions within CoFe2O4 host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu3+ added to CoFe2O4 in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe2−xEuxO4, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe2O4 have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu3+ in CoFe2O4 lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe2O4 samples. Substitution of Fe3+ ions in CoFe2O4 nanoparticles with RE-Eu3+ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.

Cobalt Ferrite Nanoparticles: Preparation, characterization and salinized with 3-aminopropyl triethoxysilane

Coprecipitation method was used to prepare pure and doped CoFe2O4 nanoparticles. Ferric and cobalt salts were used as precursors while Sodium Dodecylbenzene Sulfonate was used as surfactant. Surface functionalization of cobalt ferrite nanoparticles (NPs) is a kind of functional materials, which have been widely used in the biotechnology and catalysis. The fabricated cobalt ferrite nanoparticles were functionalized with amino propyl triethoxy silane (APTES) by silanization reaction and both non-coated and organosilane-coated magnetite characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry, Fourier transformed infrared spectroscopy (FTIR), atomic force microscopy (AFM) and filed emission scanning electron microscope (FESEM). Basic groups of amino anchored on the external surface of the coated magnetite were observed. The nanoparticles above have surface with free - NH2 groups which can transport ionic interface with carboxylic groups and act as a transporter of biological molecules, drugs, and metals.

Structural, morphological, enhanced magnetic properties and antibacterial bio-medical activity of rare earth element (REE) cerium (Ce3+) doped CoFe2O4 nanoparticles

Abstract In this present study, we made an attempt for the different concentration of rare earth element (REE) Cerium (Ce3+) doped cobalt ferrite (CoFe2O4) nanoparticles (NPs) were prepared by the simple sol-gel combustion technique. Cerium was successfully substituted into the spinel lattice without any distortion. It was analyzed the effect of Ce3+ ions doping on structural, morphological, magnetic properties and antibacterial activities using the various instrument techniques. Powder XRD and SEM along with EDX studies confirmed the pure phase formation Ce3+ doped CoFe2O4 NPs and spherical shaped agglomerated nanoparticles morphology without any other impurity. The well resolved broad peaks in the XRD pattern clearly indicated the nanosized, single phased, cubic spinal nature of these samples. There was a substantial decrease in the crystallite size on doping with Ce3+. A more in-depth morphological study was facilitated using the TEM and SAED analysis. TEM investigation revealed random shaped, sharp edged nanoparticles with a normally facetted morphology. The presence of distinctive diffractions spots on the SAED pattern indicated the formation of nanoparticles that are highly crystalline in nature. The magnetic response of the Ce3+ doped CoFe2O4 NPs was recorded at room temperature (RT) using the VSM technique. The magnetic properties have been seen to be altered by the addition of Ce3+ in the CoFe2O4 matrix. The decrease in the saturation magnetization (Ms, emu/g) with the increase in Ce3+ content rendered the synthesized sample applicable in field of antenna construction. This change will be also suitable for reducing the size of the antenna. The antibacterial activity of Ce3+ doped CoFe2O4 nanoparticles was found to be enhanced with increase in Ce3+ doping level as it cause a reduction in the grain size.

Magneto-dielectric studies on multiferroic composites of Pr doped CoFe2O4 and Yb doped PbZrTiO3

Multiferroic composites with remarkable magnetoelectric effect (ME) are unique candidates for multifunctional devices. This study focuses on the structural, dielectric, ferroelectric, magnetic and ME properties of ferromagnetic (Pr doped CoFe2O4) and ferroelectric (Yb doped PbZrTiO3) composites with the general formula x CoPr0.1Fe1.9O4- (1-x) Pb0.95Yb0.05Zr0.52Ti0.48O3 (x = 0.02, 0.05 and 0.1). The individual phases namely Pr doped CoFe2O4 (CFO) and Yb doped PbZrTiO3 (PZT) for the composites were synthesized by sol-gel auto combustion technique. The powder X-ray diffraction technique showed that the Yb doped PZT retains its tetragonal perovskite structure, while as Pr doped CFO possesses cubic spinel structure. The morphological studies showed a uniform distribution of grains of parent phases in the composites. The dielectric studies in the temperature range of 100–750 K at a selected frequency (100 kHz) revealed a diffused phase transition confirming a ferroelectric to paraelectric phase transition. The composites show well-saturated P-E loops. The room temperature magnetic studies exhibit saturated M-H loops, with dilution of magnetic parameters for the composite. A favorable decrease in magneto-crystalline anisotropy calculated by Law of Approach was observed with decreasing ferrite content in the composite. The magneto-dielectric studies at room temperature confirm a negative magnetoelectric coupling in the composite. The Landau free energy approach confirmed a bi-quadratic coupling in the composites.

Sonochemical synthesis of Gd3+ doped CoFe2O4 spinel ferrite nanoparticles and its physical properties

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe2−xGdxO4; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd3+ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe2−xGdxO4 nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd3+ substitution in CoFe2O4 nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd3+ doped cobalt ferrite (CoFe2−xGdxO4; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10−9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd3+ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd3+ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd3+ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd3+ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

Effect of Gd3+ substitution on structural, magnetic, dielectric and optical properties of nanocrystalline CoFe2O4

Nanoparticles of CoGdxFe2−xO4 with x=0.0, 0.03, 0.05, 0.07, 0.10 and 0.15 were synthesized by co-precipitation method. Gd3+ substitution effect on different properties of nanocrystalline CoFe2O4 has been studied. X-ray diffraction and Raman spectroscopy confirmed the formation of single phase cubic mixed spinel structure. Cation distribution has been proposed from Rietveld refined data. Mössbauer spectra at room temperature showed two ferrimagnetic Zeeman sextets with one superparamagnetic doublet. Mössbauer parameters suggested that Gd3+ ions occupy the octahedral site in CoFe2O4. Room temperature magnetic measurements exhibited that the saturation magnetization decreased from 91emu/gm to 54emu/gm for x=0.0 to 0.15 samples. The coercivity decreased from 1120Oe to 340Oe for x=0.0 to 0.07 samples and increased from 400Oe to 590Oe for x=0.10 and 0.15 samples, respectively. Raman analysis showed that the degree of inversion with Gd3+ substitution supporting the variation of coercivity. Electron spin resonance spectra revealed the dominancy of superexchange interactions in these samples. Optical band gap measurement suggested that all samples are indirect band gap materials and band gap has been decreased with Gd3+ substitution. Both dielectric constant and dielectric loss is found to decrease because of the decrease in hopping rate with the Gd3+ substitution for Fe3+ at the octahedral sites. Low dielectric loss suggested the applicability of Gd3+ doped CoFe2O4 nanoparticles for high frequency microwave device applications.

Effect of Annealing Time on the Cation Distribution in Mn Doped CoFe2O4

In this work, the series of CoFe2-xMnxO4 powders were synthesized using the solid state method. The structure and lattice parameter of the samples were determined by the X-ray diffraction (XRD) and Rietveld refinement method. The morphology was confirmed without annealing and with annealing at 500°C for 4 and 100 h, with the samples examined by scanning electron microscopy (SEM). Then, the distribution of migrating cations was analyzed using X-ray absorption spectroscopy (XAS). Also, magnetic properties were examined by a vibrating sample magnetometer (VSM). It can be confirmed from the morphology that the average particle size before and after annealing remained unchanged, and ranged from 0.66 ± 0.20 μm to 0.79 ± 0.26 μm. Furthermore, the distribution of cations was no different after annealing Mn ions at 500°C for 100 h. However, the distribution of cations migrated to their site of preference after annealing Co and Fe ions in the structure. The result of migrations induced a saturated magnetization increase to 42.24 emu/g.

Role of Mn2+ Doping on Structural, Morphological, and Opto-Magnetic Properties of Spinel Mn x Co1−x Fe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) Nanocatalysts

Spinel MnxCo1−x Fe2O4; x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles were synthesized by ureaassisted auto combustion method using nitrates of Co, Mn and Fe as the starting materials and urea as the fuel. X-ray diffraction (XRD) analysis showed that all composition was found to have a cubic spinel structure. The average crystallite size of the samples was estimated using the Debye-Scherrer formula and was found to be in the range of 22.62 and 36.45 nm. The lattice parameter increased from 8.432 to 8.457 A with increasing the Mn2+ content, which was determined by Rietveld analysis. High-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM) analyses were used to study the morphological variation, and the results showed a nanosized particle-like morphology. Energy-dispersive X-ray (EDX) results showed that the composition of the elements was relevant as expected from the synthesis. The bandgap energy of the pure CoFe2 O 4 was estimated to be 2.33 eV from UV-visible diffuse reflectance spectroscopy (DRS). With the increase of Mn2+ ion, the bandgap energy increased from 2.35 to 2.42 eV. The magnetic properties of the samples were investigated at room temperature by using a vibrating sample magnetometer (VSM). The magnetic hysteresis (M-H) loop confirmed the superparamagnetic nature of pure CoFe2 O 4 and a weak ferromagnetic behavior of Mn2+doped CoFe2 O 4 samples with specific saturation magnetization in the range of 55.16±24 and 66.92 ± 05 emu/g. All compositions of spinel Mn x Co1−x Fe2 O 4 samples were successfully tested as catalyst for the conversion of benzyl alcohol, which has resulted in 62.75 and 92.62 % conversion efficiency of CoFe2 O 4 and Mn0.5Co0.5Fe2 O 4, respectively.

Self-propagating high temperature synthesis, structural morphology and magnetic interactions in rare earth Ho3+ doped CoFe2O4 nanoparticles

Substitution effect of rare earth trivalent Ho3+ ions on the composition, HoxCoFe2−xO4, with x varying from 0.0 to 0.1 in steps of 0.025 using sol–gel auto combustion route has been investigated. Examination of X-ray diffraction (XRD) patterns shows that all the samples consisted of ferrite phases of typical spinel cubic structure, and when Ho3+ ion content was x⩾0.075, orthoferrite–HoFeO3 phase was detected. The micro and nanostructure of the synthesized Ho doped CoFe2O4 ferrites were investigated by scanning and transmission electron microscopy respectively. With increasing doping content of Ho3+ ions, the lattice constant, particle size and bulk density increased, and after an increase to its maximum value, the sample particle size and density dropped down. Cation distribution estimated from XRD patter revealed that the Co2+ and Ho3+ ions prefer to occupy octahedral B-site whereas Fe3+ ions are distributed over tetra- and octa-hedral site. Oxygen positional parameter shows larger values than its ideal value. The analysis of magnetic properties revealed that the saturation magnetization and coercivity of CoFe2O4 increased with the rare earth Ho3+ substitution.

Markedly enhanced coercive field and Congo red adsorption capability of cobalt ferrite induced by the doping of non-magnetic metal ions

In this contribution, a series of CoFe2−xMxO4 (M=Al3+, In3+ and Cu2+) ferrites were synthesized by a facile hydrothermal method. On the premise of spinel structure, the coercive forces and adsorption capabilities of the doped CoFe2O4 ferrites are significantly enhanced. It is first reported that coercive field of magnetic material shows more important influence on the adsorption capacity than that of specific surface area. Water magnetized mechanism was proposed to explain the relation between the coercive field and adsorption capacity. To the best of our knowledge, the CR adsorption value of 605.4mgg−1 may be the best among the reported magnetic adsorbents with spinel structure.