Influence of calcination rate on morphologies and magnetic properties of MnFe2O4 nanofibers

In the present study, we succesfully synthesized electrospun MnFe₂O₄ nanofibers (NFs) from poly(N-vinylpyrrolidone)/manganese(II) nitrate composite by electrospinning and then as-spun NFs were calcined 450 °C for 2 h in air atmosphere to remove the polymer matrix and fabricate inorganic MnFe₂O₄ nanofibers. In order to investigate the sintering behavior of MnFe₂O₄ nanofibers in air atmosphere, the synthesized as-spun nanofibers were calcined with different calcination rates. Thus the effect of calcination rate on structure and morphology of nanofibers were discussed clearly. The structural, magnetic, morphological, spectroscopic and thermal characterizations were also done by XRD, VSM, TEM, SEM, FTIR and TG analysis. In the presence of slow calcination rate, only peaks of MnFe₂O₄ could be observed on other hand in the presence of rapid calcination rate, formation of an impurity was observed. Scanning electron microscope images revealed that MnFe₂O₄ nanorods possess a broader range size distribution with higher particle size. Also, magnetic properties were both size and shape dependent.     

Effects of annealing on the structural and magnetic properties of flame spray pyrolyzed MnFe2O4 nanoparticles

In this study, manganese ferrite (MnFe₂O₄) nanoparticles were produced through flame spray pyrolysis (FSP). To investigate the effects of heat treatment, the nanoparticles were annealed between 400 and 650°C for 4 h in air in a comparative manner. The structural, chemical, morphological, and magnetic properties of the nanoparticles were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), dynamic light scattering (DLS), and vibrating sample magnetometry (VSM), respectively. The XRD results showed that the nanoparticles synthesized by the FSP method exhibited the MnFe₂O₄ spinel ferrite structure. The annealing process led to the decomposition of MnFe₂O₄ into various phases. According to the morphological analysis, the as-synthesized particles were hemispherical–cubic in shape and had an average particle size of less than 100 nm. In addition, the chemical bond structures of the nanoparticles were confirmed in detail by XPS elemental analysis. The highest saturation magnetization was recorded as 33.50 emu/g for the as-produced nanoparticles. The saturation magnetization of the nanoparticles decreased with increasing annealing temperature, while coercivity increased.     

Structural,spectral, dielectric and photocatalytic studies of Zr-Ni doped MnFe2O4 co-precipitated nanoparticles

In this study the Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles fabricated by co-precipitation technique were investigated. Thermo-gravimetric analysis (TGA) exhibited the annealing temperature of the nanoparticles ~990 °C. Cubic spinel structure of Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. Crystallite size was calculated by XRD data and found in the range of 32–58 nm. Photocatalytic activity of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄/graphene nanocomposites was tested by degrading methylene blue (MB) under visible light irradiation. The MB was almost completely degraded in the presence of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄-graphene nanocomposites under visible light irradiation. Dielectric parameters were also investigated in the frequency range 1×10⁶–3×10⁹ Hz. An overall decrease in the values of dielectric constant, dielectric loss and tangent loss was observed on account of the substitution of Zr and Ni with Mn and Fe cations.     

Magnetic properties and self-heat behaviors of core@shell structured MnFe2O4@Fe3O4 magnetic nanoparticles

In this work, a facile solvothermal synthesis of MnFe₂O₄ nanoparticles is followed by an easy and reproducible process to envelop the synthesized MnFe₂O₄ nanoparticles with iron oxide nanoparticles using ethanol and ethylene glycol as solvents. All prepared MnFe₂O₄ nanoparticles show a homogenous distribution of spherical particles with an average particle size between 12 and 16 nm. The encapsulation process of MnFe₂O₄ nanoparticles does not affect their homogenous distribution with a very thin layer of Fe₃O₄ on the shell structure. The magnetic properties showed a superparamagnetic character with enhanced magnetic properties of MnFe₂O₄@Fe₃O₄ compared to pure MnFe₂O₄, which has been verified by magnetization and electron spin resonance. The heating efficiency of the prepared samples was evaluated in terms of the specific loss power using the calorimetric method. The synthesized MnFe₂O₄ nanoparticles show a significantly high value of about 72 W/g, which got doubled in the core@shell structure and reached 140 W/g at 189 kHz and 10kA/m of the magnetic field.     

Impact of Zn doping on the dielectric and magnetic properties of CoFe2O4 nanoparticles

Owing to its unique magnetic, dielectric, electrical and catalytic properties, ferrite nanostructure materials gain vital importance in high frequency, memory, imaging, sensor, energy and biomedical applications. Doping is one of the strategies to manipulate the spinel ferrite structure, which could alter the physico-chemical properties. In the present work, Co_1-xZn_xFe₂O₄ ($x$ = 0, 0.1, 0.2, 0.3, and 0.4 wt%) nanoparticles were prepared by sol-gel auto-combustion method and its structural, morphological, vibrational, optical, electrical and magnetic properties were studied. The structural analysis affirms the single-phase cubic spinel structure of CoFe₂O₄. The crystallite size, lattice constant, unit cell, X-ray density, dislocation density and hopping length were significantly varied with Zn doping. The Fe–O stretching vibration was estimated by FTIR and Raman spectra. TEM micrographs show the agglomerated particles and it size varies between 10 and 56 nm. The Hall effect measurement shows the switching of charge carriers from n to p type. The dielectric constant (ε′) varies from 0.2 × 10³ to 1.2 × 10³ for different Zn doping. The VSM analysis shows relatively high saturation magnetization of 57 and 69 emu/g for ZC 0.1 and ZC 0.2 samples, respectively than that of undoped sample. All the prepared samples exhibit soft magnetic behaviour. Hence, it can be realized that the lower concentration of Zn ion doping significantly alters the magnetic properties of CoFe₂O₄ through variation in the cationic distribution and exchange interaction between the Co and Fe sites of the inverse spinel structure of CoFe₂O_4.     

Effect of bimetallic (Ni and Co) substitution on magnetic properties of MnFe2O4 nanoparticles

Nickel and cobalt substituted manganese ferrite nanoparticles (NPs) with the chemical composition Ni_xCo_xMn_1–2xFe₂O₄ (0.0≤x≤0.5) NPs were synthesized by one-pot microwave combustion route. The effect of co-substitution (Ni, Co) on structural, morphological and magnetic properties of MnFe₂O₄ NPs was investigated using XRD, FT-IR, SEM, VSM and Mössbauer spectroscopic techniques. The cation distribution of all products were also calculated. Both XRD and FT-IR analyses confirmed the synthesis of single phase spinel cubic product for all the substitutions. Lattice constant decreases with the increase in concentration of both Co and Ni in the products. From ⁵⁷Fe Mössbauer spectroscopy data, the variations in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values with Mn²⁺, Ni²⁺ and Co²⁺ substitution have been determined. While the Mössbauer spectra collected at room temperature for the all samples are composed of magnetic sextets, the superparamagnetic doublet is also formed for MnFe₂O₄ and Ni_0.2Co_0.2Mn_0.6Fe₂O₄ NPs. The magnetization and Mössbauer measurements verify that MnFe₂O₄ and Ni_0.2Co_0.2Mn_0.6Fe₂O₄ NPs have superparamagnetic character. The saturation and remanence magnetizations, magnetic moment and coercive field were determined for all the samples. Room temperature VSM measurements reveals saturation magnetization value close to the bulk one. It has been observed that the saturation magnetization and coercive field increase with respect to the Ni and Co concentrations.     

The effects of surface spin on magnetic properties of weak magnetic ZnLa0.02Fe1.98O4 nanoparticles

In order to prominently investigate the effects of the surface spin on the magnetic properties, the weak magnetic ZnLa_0.02Fe_1.98O₄ nanoparticles were chosen as studying objects which benefit to reduce as possibly the effects of interparticle dipolar interaction and crystalline anisotropy energies. By annealing the undiluted and diluted ZnLa_0.02Fe_1.98O₄ nanoparticles at different temperatures, we observed the rich variations of magnetic ordering states (superparamagnetism, weak ferromagnetism, and paramagnetism). The magnetic properties can be well understood by considering the effects of the surface spin of the magnetic nanoparticles. Our results indicate that in the nano-sized magnets with weak magnetism, the surface spin plays a crucial rule in the magnetic properties.     

A comparative study of electric properties of nano-structured and bulk Mn-Mg spinel ferrite

A series of nano-sized particles of Mn_1−xMg_xFe₂O₄ (x = 0.0, 0.1, 0.2 and 0.25) have been synthesized by co-precipitation method. The effect of Mg-substitution on structural and dielectric properties is reported in this paper. X-ray diffraction analysis for both nanosize and bulk samples revealed the nanocrystalline nature in the prepared ferrite samples. The crystallite size increases from 3-6 nm in nanosamples to 63.9-85.5 nm in bulk samples. The dielectric properties for all the samples have been studied as a function of frequency in the range 10-10⁵ Hz at different temperatures. Dielectric properties such as dielectric constant (?′) dielectric loss (?″), dielectric loss tangent (tan δ) and ac conductivity have been studied for the investigated samples as a function of frequency. The data indicated that, the dielectric constant and the loss factor values of our former are ten orders of magnitude than those of the later. The low dielectric behavior makes ferrite materials useful in high frequency applications.     

The role of Co ion substitution in SnFe2O4 spinel ferrite nanoparticles: Study of structural,vibrational, magnetic and optical properties

In order to accurately investigate the effect of cobalt substitutions in tin ferrite (SnFe₂O₄) properties, we prepared Co_xSn_1-xFe₂O₄ nanoparticles for different Co concentrations, x?=?0.0, 0.25, 0.50, 0.75, and 1.00 using a simple co-precipitation method. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and diffuse reflectance spectra (DRS) are used to study of structural, magnetic, morphology, and optical properties. The XRD and FTIR results confirmed the formation of cubic spinel structure. The lattice parameter and unit cell volume of tin ferrite nanoparticles were found to increase by entering and increasing Co⁺² content in 0.25, and then significantly decrease for higher contents. In accordance with the XRD results, a slight shift in main band υ₁ (${\mathit{Fe}}_{\mathrm{tetra}}^{+3}?O)$ to lower wavenumber and then to higher wavenumber were observed in the IR spectra of Co content x?<?0.25 and x?>?0.25, respectively. In turn to, saturation magnetization, remanent magnetization and anisotropy constant of SnFe₂O₄ nanoparticles were gradually increased for x?=?0.50 and then decreased for x?>?0.50.     

Growth,microstructure and magnetic properties of bixbyite structure ScFeO3: A comparative study between bulk and thin film

The growth, microstructure and magnetic property of both bulk and thin film types of ScFeO₃ are studied. Results show that the mono-phase bixbyite structure bulk ScFeO₃ can be obtained with sintering temperature above 1400 °C. The bulk ScFeO₃ shows dominant antiferromagnetic property with an antiferromagnetic Neel temperature T_N about -26 K. The epitaxial type of ScFeO₃ thin film with bixbyite structure can be well grown on the SrTiO₃(111) substrate. The magnetic property of ScFeO₃ thin film is significantly different from that of bulk material which shows notable room temperature ferromagnetism with a saturation field below 0.4 T. The saturation magnetization M_S, remanent magnetization M_r, coercivity H_c and of ScFeO₃ film increase with decreasing temperature with maximum values of M_S = 5.1 emu/cc, M_r = 1.5 emu/cc, and H_c = 29 mT at 5 K. The ferromagnetism of ScFeO₃ thin film should be caused by the interface mismatch strain at film/substrate interface. This further proves that ferromagnetism of ScFeO₃ can be stabilized with microstructure engineering including strain, which enable multifunctional properties of this material.     

Comparative investigation on the structural,morphological, optical,and magnetic properties of CoFe2O4 nanoparticles

Herein, we report a sustainable production of magnetic cobalt ferrite nanoparticles by conventional (CHM) and microwave heating (MHM) method. Hibiscus rosa-sinensis extract was used as both reducing and stabilizing agent. Using plant extracts to synthesize nanoparticles has been considered as an eco-friendly method, since it avoids noxious chemicals. The plethora of plant extract mediated nanoparticles were compared by techniques, such as XRD, Rietveld, FT-IR, SEM, EDX, UV-Visible DRS, PL and VSM were carried out to analyze and understand their crystallite size, functional groups, morphology, optical and magnetic properties. The crystalline structure of cobalt ferrite nanoparticles revealed the cubic structure and the microwave heating of nanoparticles showed smaller crystallite size compared to the conventional heating, which was then confirmed by XRD analysis. To analyze the presence of functional groups and the phytochemical involvement of the plant extract was confirmed by FT-IR studies. Spherical morphology with less than 100 nm sized particles was confirmed by SEM and EDX analysis confirm the existence of Co, O, and Fe elements present in the samples. UV-Visible DRS studies were carried out to calculate the band gap of the as-synthesized nanoparticles, estimated from the Kubelka-Munk function, as 2.06, and 1.87 eV for CHM and MHM, respectively. Photoluminescence emission spectrum of the nanoparticles showed two different bands at 494 and 620 nm, which explores the optical properties of the nanoparticles, due to the quantum confinement effect. VSM analysis showed better ferromagnetic behavior, which can be used for magnetic applications.     

A sonochemical method for synthesis of Fe3O4 nanoparticles and thermal stable PVA-based magnetic nanocomposite

Fe₃O₄ nanoparticles were synthesized via a simple surfactant-free sonochemical reaction. Room temperature synthesis without using inert atmosphere is the novelty of this work. The effect of different parameters on the morphology of the products was investigated. The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer. Fe₃O₄ nanoparticles exhibit a ferromagnetic behavior with a saturation magnetization of 66 emu/g and a coercivity of 39 Oe at room temperature. For preparation magnetic nanocomposite, Fe₃O₄ nanoparticles were added to the polyvinyl alcohol (PVA). Nanoparticles can enhance the thermal stability and flame retardant property of the PVA matrix.     

Development of Co-doped MnFe2O4 nanoparticles for electrochemical supercapacitors

Transition metal ferrites are the essential components utilized in the latest modern-day technology and these include greater elements whose oxidation states and ionic radii are important for exploring their magnetic, optical, structural, and electrochemical properties. The present investigation was targeted on the preparation, physical and electrochemical characterizations of Co-doped MnFe₂O₄ nanomaterials such as 2 wt% Co-doped MnFe₂O₄, 4 Wt.% Co-doped MnFe₂O₄, and 8 Wt.% Co-doped MnFe₂O₄. More specifically, the study will focus on the techniques which have been employed to raise the specific capacitance of the metal oxides. Electrochemical properties such as cyclic voltammetry (CV), potentiostatic and impedance were used to analyse the super capacitive performance of Co-doped MnFe₂O₄ electrodes. Based on the outcomes, it is determined that 2 wt% of Co-doped MnFe₂O₄ has higher super capacitive behaviour than different samples. Precise capacitance for this nanocomposite from GCD was determined to be 551.39 F/g at a current density of 1 mA/cm². Accordingly, Co-doped MnFe₂O₄ may be utilized as a promising electrode for energy storage applications. It could be believed that this form of composites indicates excellent capability as electrochemical supercapacitors.     

Zinc substitution effect on the structural,spectroscopic and electrical properties of nanocrystalline MnFe2O4 spinel ferrite

This paper reports the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of nanocrystalline Mn_1-xZn_xFe₂O₄. The nanocrystalline Mn–Zn ferrites were synthesized using a solvent-free combustion reaction method. The structural analysis using X-ray diffraction (XRD) pattern reveals the single-phase of all the samples and the Rietveld refined XRD patterns confirmed the cubic-spinel structure. The calculated crystallite size values increase from 8.5 nm to 19.6 nm with the Zn concentration. The surface morphological analysis using field emission scanning electron microscopy and the transmission electron microscopy confirms the nano size of the prepared ferrites. X-ray photoelectron spectroscopy was used to study the ionic state of the atoms present in the samples. Further, the high-resolution Mn 2p, Zn 2p, Fe 2p, and O 1s spectra of Mn_1-xZn_xFe₂O₄ does not result in the appearance of new peaks with Zn content, indicating that the Zn substitution does not change the ionic state of Mn, Zn, Fe, and O present in nanocrystalline Mn_1-xZn_xFe₂O₄. The investigated electrical properties show that the dielectric constant, tan δ and ac conductivity gradually decrease with increasing Zn substitution and the sample Mn_0·2Zn_0·8Fe₂O₄ has the lowest value of conductivity at 303 K. The ac conductivity measured at different temperatures shows the semiconducting nature of the ferrites. The impedance spectra analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. The obtained results suggest that the Zn substituted manganese ferrite nanoparticles can act as a promising candidate for high-frequency electronic devices applications.     

The influence of reactive milling on the structure and magnetic properties of nanocrystalline MnFe2O4

Nanocrystalline manganese ferrites (MnFe₂O₄) have been synthesized by direct milling of metallic manganese (Mn) and iron (Fe) powders in distilled water (H₂O). In order to overcome the limitation of wet milling, dry milling procedure has also been utilized to reduce crystallite size. The effects of milling time on the formation and crystallite size of wet milled MnFe₂O₄ nanoparticles have been investigated. It has been observed that single phase 18.4 nm nanocrystalline MnFe₂O₄ is obtained after 24 h milling at 400 rpm. Further milling caused deformation of the structure as well as increased crystallite size. With the aim of reducing the crystallite size of 18.4 nm, MnFe₂O₄ sample dry milling has been implemented for 2 and 4 h at 300 rpm. As a result, the crystallite size has been reduced to 12.4 and 8.7 nm, respectively. Effects of the crystalline sizes on magnetic properties were also investigated. Magnetization results clearly demonstrated that crystallite size has much more effect on the magnetic properties than average particle size.     

Effect of Ni2+ substitution on structural,magnetic, dielectric and optical properties of mixed spinel CoFe2O4 nanoparticles

Nanoparticles of Co_1−xNi_xFe₂O₄ with x=0.0, 0.10, 0.20, 0.30, 0.40 and 0.50 were synthesized by co-precipitation method. The structural analysis reveals the formation of single phase cubic spinel structure with a narrow size distribution between 13–17 nm. Transmission electron microscope images are in agreement with size of nanoparticles calculated from XRD. The field emission scanning electron microscope images confirmed the presence of nano-sized grains with porous morphology. The X-ray photoelectron spectroscopy analysis confirmed the presence of Fe²⁺ ions with Fe³⁺. Room temperature magnetic measurements showed the strong influence of Ni²⁺ doping on saturation magnetization and coercivity. The saturation magnetization decreases from 91 emu/gm to 44 emu/gm for x=0.0–0.50 samples. Lower magnetic moment of Ni²⁺ (2 µ_B) ions in comparison to that of Co²⁺ (3 µ_B) ions is responsible for this reduction. Similarly, overall coercivity decreased from 1010 Oe to 832 Oe for x=0.0–0.50 samples and depends on crystallite size. Cation distribution has been proposed from XRD analysis and magnetization data. Electron spin resonance spectra suggested the dominancy of superexchange interactions in Co_1−xNi_xFe₂O₄ samples. The optical analysis indicates that Co_1−xNi_xFe₂O₄ is an indirect band gap material and band gap increases with increasing Ni²⁺ concentration. Dispersion behavior with increasing frequency is observed for both dielectric constant and loss tangent. The conduction process predominantly takes place through grain boundary volume. Grain boundary resistance increases with Ni²⁺ ion concentration.     

Low temperature sintering of magnetic Ni0.5Co0.5Fe2O4 ceramics prepared from mechanochemically synthesized nanopowders

The effect of mechanochemichally synthesized nanoceramics Ni_0.5Co_0.5Fe₂O₄ (NCF) on the sintering process was studied. After 60?h of mechanochemichal treatment, the amount of formed ferrite phase reaches to about 70?vol%. From 60–100?h 10% increase in volume fraction of synthesized magnetic phase can be observed. Further increment in process time had no remarkable effect on the NCF phase formation. After 60?h, ceramic nanoparticle formation is directly reflected by TEM image and specific surface area (28?m²/g equivalent to 40?nm in diameter). The coercivity (Hc) shows a drastic diminution from 1996 to about 159?Oe by 60?h process time. Further milling treatment has no observable effect on the values of Hc. Additionally, the magnetization saturation (Ms) increases up to ~13?emu/g by 60?h mechanical milling of powders mixture. Thereafter from 60?h to 100?h, the Ms rapidly increased from 13 to 32?Oe. Finally, with continuing mechanochemichal process up to 130?h the Ms slightly diminished (~29?emu/g). Additionally, compared to synthesized powders the higher values of M_S (65?emu/g) and lower values of H_C (140?Oe) for sintered ceramic were detected. The low sintering temperature (1300?°C) for magnetic NCF sample prepared from nanoparticles may be caused by the high activity of nanoceramics.     

Enhanced sunlight driven photocatalytic activity and electrochemical sensing properties of Ce-doped MnFe2O4 nano magnetic ferrites

This research deals with the facile combustion synthesis of manganese ferrite (MFO) nanoparticle with different cerium concentration and their potential application as an efficient photocatalyst and chemical sensor. The concentration of introduced cerium affects the size, structure, compositional, morphological, optical, photoluminescence and magnetic properties of the ferrite nanoparticle. The X-ray diffraction pattern affirmed the arrangement of cubic spinel structure with the formation of secondary phase CeO₂ as the cerium concentration exceed 3 mol%. SEM micrographs revealed irregular morphology with more number of pores and voids. HRTEM along with SAED pattern revealed the crystalline cubic nature. The optical band gap deduced from UV–Vis-DRS spectra was observed to be in the range 2.3–2.8 eV. PL studies indicated a significant minimization in combination of electrons & holes in MnFe₂O₄ on addition of Ce dopant. VSM investigation demonstrated the soft magnetic nature of the prepared sample with moderate magnetization value. An excellent photocatalytic performance of Cerium doped MFO (3 mol%) towards MB and AR dye degradation was found to be 1.5 and 1.67 times more compared to host matrix under Sunlight irradiation that correlated to reduced band gap, Ce dopant and efficient separation of charge carriers. Cerium doped MFO (3 mol%) have high specific capacitance value of 471.7 and 1546.8 Fg^-1 for NaNO₃ and HCl electrolytes respectively, indicating the pseudo capacitance nature due to which it can be used as a supercapacitor. The synthesized nanoparticles can sense d-Glucose and Paracetamol even at a lower concentration varying from 1 to 10 mM. The synthesized Ce-doped MnFe₂O₄ nanomaterials have great potential to be used in the future production of promising active photocatalysts and sensitive chemical sensors for the identification and degradation of toxic industrial dyes for improved safety in the fields of environment and health care.