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.     

Anomalous ferroelectric and magnetic behavior in BPFO-NZFO multiferroic nano-composites

Multiferroic nano-composites (1-x) Bi_.9Pr_.1FeO₃ (BPFO) –x Ni_.5Zn_.5Fe₂O₄ (NZFO) for x?=?0.0, 0.1, 0.2, 0.3 and 1.0 were synthesized by sol-gel auto-combustion method. Detailed investigations were made on the structural, morphological, ferroelectric, magnetic and dielectric properties of these nano-composites. The X-ray Diffraction pattern confirms the co-existence of perovskite BPFO and spinel NZFO phases without any impurity. The average particle size of as prepared BPFO and NZFO nanoparticles is nearly equal to 110?nm and 35?nm respectively which have been confirmed by the XRD and Transmission Electron Microscopy analysis. Structural and surface morphology are studied by Scanning Electron Microscopy. The dielectric properties of the composites are also studied at room temperature. The magnetic hysteresis loop has been studied to know the magnetic response of samples to the applied magnetic field of ±?1?T at room temperature. The saturation and remnant magnetization are found to increase with increase in NZFO weight percentage in the composite. The saturation magnetization values are 8.57?emu/g, 16.71?emu/g, 24.41?emu/g and remnant magnetization values are 0.78?emu/g, 1.23?emu/g, 1.58?emu/g for BPFO-NZFO 1, 2, 3 composite samples respectively. An anomalous ferroelectric behavior of BPFO-NZFO 1 composite sample was observed which can be understand with the help of observed results in dielectric and morphology of the samples. The incorporation of BPFO and NZFO enhances the multiferroic properties in the present composite materials which are quite promising from application point of view.     

Synthesis and Characterization of Magnetite/Polyvinyl Alcohol Core–Shell Composite Nanoparticles

Magnetite (Fe₃O₄)/polyvinyl alcohol (PVA) core–shell composite nanoparticles were successfully synthesized using a coprecipitation of ferrous and ferric chloride followed by coating with PVA. The resulting nanoparticles were characterized using X‐ray diffraction, Fourier Transform Infrared Spectroscopy, Transmission Electron Microscopy, X‐ray photo electron spectroscopy, Zeta potential measurements, UV–Vis spectroscopy, Thermogravimetric Analysis, and Vibrating Sample Magnetometry (VSM). The average particle size was 13 nm. The presence of characteristic functional groups of PVA around the core of magnetite nanoparticles was confirmed by FTIR spectroscopy while the amount of PVA (%) bound to it was estimated by TGA analysis. Zeta potential measurements made by dispersing dilute sonicated samples in a Phosphate Buffer Saline (PBS pH 7.4) confirmed that the particles were negatively charged. The stability and retention of the coating material PVA in PBS (pH7.4) over a period of time were substantiated by UV–Vis spectroscopy. Room‐temperature magnetic measurements were made with a VSM which demonstrated the superparamagnetic nature of the particles with higher saturation magnetization of 56.41 emu/g. Furthermore, in vitro cytocompatibility testing of Fe₃O₄/PVA core–shell composite nanoparticles was carried out on human cervix cancer cells. This confirmed a 97% cell viability with no significant cytotoxicity and thereby substantiated their biocompatibility.     

PVA assisted coprecipitation synthesis and characterization of MgFe2O4 nanoparticles

Single phase magnesium ferrite (MgFe₂O₄) nanoparticles were prepared by the coprecipitation method followed by calcination at 700 °C for 1 h. The effects of polyvinyl alcohol (PVA) agent on the structural, microstructure, magnetic properties and AC magnetically induced heating characteristics of MgFe₂O₄ nanoparticles were investigated. The structure and cation distributions investigated by X-ray diffraction method showed single phase MgFe₂O₄ powders had partially inverse spinel structure in which the inversion coefficient increased by adding more PVA. The small particle size and narrow size distribution of the coprecipitated MgFe₂O₄ powders characterized by scanning electron microscopy were achieved using PVA agent. Magnetic properties of MgFe₂O₄ nanoparticles studied by vibrating sample magnetometry showed ferrimagnetic characteristics with the highest saturation magnetization and coercivity of 24.6 emu/g and 17 Oe, respectively. The coprecipitated MgFe₂O₄ nanoparticles assisted by PVA exhibited the lower AC heating temperature of 5.6 °C and specific loss power of 2.4 W/g in comparison with 6.1 °C and 2.7 W/g for the powders coprecipitated without using PVA.     

Finite size effect on Sm3+ doped Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) ferrite nanoparticles

Samarium doped Mn–Zn ferrite nanoparticles of composition Mn_0.5Zn_0.5Sm_xFe_2−xO₄ (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques for their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter and lattice strain increases with the increase in Sm³⁺ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm³⁺ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced by EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetism for x=0, 0.1 the samples with saturation magnetization of 23.95 emu/g for Mn_0.5Zn_0.5Fe₂O₄ sample which increases with rise in Sm³⁺ ions content. The results are explained and correlated with the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.     

Structure and magnetic properties of multi-morphological CoFe2O4/CoFe nanocomposites by one-step hydrothermal synthesis

Multi-morphological CoFe₂O₄/CoFe nanocomposites have been synthesized using a facile hydrothermal process. The effects of hydrazine hydrate amount during hydrothermal reaction on the structure and magnetic property of the specimens were studied. With increasing hydrazine hydrate amount, the CoFe₂O₄ transformed to CoFe and the morphology of the specimen changed from granular particles to faceted particles. The saturation magnetization monotonically increased and the coercivity monotonically decreased with increasing hydrazine hydrate amount. The magnetic interactions, determining the magnetic properties of the composites, result from the dominant dipole coupling and relative weak exchange coupling between CoFe₂O₄ and CoFe nanoparticles. The CoFe₂O₄/CoFe nanocomposite prepared with 2?mL hydrazine hydrate exhibited the optimal magnetic properties, with the saturation magnetization of 81?emu/g and coercivity of 636?Oe.     

Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites

CoFe₂O₄ (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe₂O₄ nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe₂O₄ nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe₂O₄ (10%) nanocomposites is higher than that obtained for PS/CoFe₂O₄ (30%).     

Synthesis of MnFe2O4 nanocrystals by wet-milling under atmospheric conditions

This work reports an original method for synthesis of well-crystallized manganese ferrite (MnFe₂O₄) nanoparticles via a high energy wet milling technique under atmospheric conditions, starting from metallic Mn and Fe powders in the presence of distilled water. The effects of milling conditions on the formation and magnetic properties of MnFe₂O₄ nanoparticles were investigated in detail. Fully stoichiometric MnFe₂O₄ nanocrystals with an average crystallite size of 14.5 nm were produced after 24 h of milling. As-synthesized MnFe₂O₄ nanocrystals were found to show soft magnetic behavior at room temperature with saturation magnetization of 53 emu/g. Due to reduced thermal effects, the saturation magnetization increased to 68 emu/g at 5 K. Results show that this method is simple and efficient for the mass production of MnFe₂O₄ nanoparticles.     

Synthesis and characterization of CaFe2O4 nanoparticles via co-precipitation and auto-combustion methods

In this paper, the techniques for the synthesis of CaFe₂O₄ nanoparticles using the auto-combustion and co-precipitation methods are discussed. The effects of both methods on the microstructure and magnetic properties of the CaFe₂O₄ nanoparticles were compared. The CaFe₂O₄ powder was obtained after drying the synthesized sample via co-precipitation overnight in an oven at 80 °C. For auto-combustion method, the sol that was initially formed was gradually converted into a gel, which was then combusted at 250 °C. Finally, the CaFe₂O₄ nanoparticles were calcined at 550 °C. The different synthesis methods produced nanoparticles with different physical and magnetic properties in order to find an optimum size to be utilized for drug delivery applications. The results of the X-ray diffraction showed that both processes produced nanocrystals with an orthorhombic crystalline structure. It was noted from the measurements made with a transmission electron microscope (TEM) that the synthesis using the co-precipitation method produced nanoparticles with a size of about 10–20 nm, which was comparable with the size that was obtained when the auto-combustion method was used. The magnetic properties were investigated using a vibrating sample magnetometer (VSM), where the magnetic saturation (M_s) of CaFe₂O₄ for the sample synthesized using the co-precipitation method was 47.279 emu/g, which was higher than the magnetic saturation (M_s) of 31.10 emu/g obtained when the auto-combustion method was used. The hysteresis loops (Hc) for the samples were 17.380 G and 6.1672 G, respectively. Additionally, the elaborate properties mentioned above, such as the size and superparamagnetic properties of the synthesized CaFe₂O₄ nanoparticle size, were the characteristics required for drug delivery because the targeted therapy required nanoparticles with good magnetic properties, a suitable size, and which were non-toxic in order to have a potential application in targeted drug delivery systems.     

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.     

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.     

High-strength superparamagnetic composite fibers

The polymer composites of magnetic nanoparticles can be possibly used in a bulk form by preserving all the novel characteristics of magnetic nanoparticles such as superparamagnetic behavior. By introducing magnetic properties of Fe₃O₄ nanoparticles into polymer fibers, novel magnetic properties combine with the advantages of composite fibers such as light-weight and ease-of-use. Using dry-jet-wet fiber spinning technology, we have successfully fabricated iron oxide/polyacrylonitrile (Fe₃O₄/PAN) composite fibers with 10 wt% nanoparticle in the polymer matrix. Composite fiber with a diameter as small as 15 μm can achieve tensile strength and tensile modulus values as high as 630 MPa and 16 GPa, respectively. Superparamagnetic properties of Fe₃O₄ nanoparticles were preserved in the composite fibers with saturation magnetization at 80 emu/g and coercivity of 165 G.     

Green synthesis of CuFe2O4 nanoparticles mediated by Morus alba L. leaf extract: Crystal structure,grain morphology,particle size,magnetic and catalytic properties in Mannich reaction

Copper ferrite (CuFe₂O₄) is one of the most popular ferrite spinel semiconductors due to its superparamagnetic properties. In this study, CuFe₂O₄ nanoparticles were successfully prepared through green synthesis mediated by Morus alba L. leaf extract. Secondary metabolites, such as alkaloids and saponins, in Morus alba L. leaf extract acted as a weak base provider and as a capping agent in the formation of CuFe₂O₄. The crystal structure, grain morphology, particle size, and magnetic properties of the nanoparticles were investigated. X-ray diffraction (XRD) data confirms the formation of the CuFe₂O₄ phase with a cubic Fd-3ms space group. The nanoparticles mediated by Morus alba L. have a spherical shape with distributed particle sizes at 20–70 nm. In the evaluation of stability, the nanoparticles agglomerate with a zeta potential value of ?21.7 mV and have a soft ferromagnetic nature with H_c, M_r, and M_s values of 175.44 Oe, 1.75 emu/g, and 14.16 emu/g, respectively. The catalytic ability of CuFe₂O₄ nanoparticles in the Mannich reaction showed good catalyst performance with a yield of 83.83% at optimum conditions. Green synthesis using Morus alba L. leaf extract offers a more environmentally friendly and effective method for obtaining CuFe₂O₄ nanoparticles with good characteristics.     

Tuning specific loss power of CoFe2O4 nanoparticles by changing surfactant concentration in a combined co-precipitation and thermal decomposition method

New synthetic approaches of nanoparticles (NPs) can be used for magnetic hyperthermia, destroying malignant cells without damaging healthy tissues. Here, a combination of co-precipitation and thermal decomposition techniques was employed to synthesize monodisperse CoFe₂O₄ NPs. A mixture of oleylamine and oleic acid with different concentrations was utilized as a surfactant, significantly changing magnetic, morphological and structural properties of the NPs. Increasing the surfactant concentration from 1 to 7.5 mmol resulted in maximum and minimum coercivity and saturation magnetization of 420.0 Oe 73.6 emu/g, and 67.2 Oe and 48.3 emu/g, respectively, arising from the prevention of agglomeration and reduction in crystallite size. The first-order reversal curve analysis was employed to clarify the role of the surfactant in magnetic distributions and detailed characteristics. The specific loss power of the NPs was found to be tuned for the different surfactant concentrations, achieving a maximum of 268.5 W/g at 7.5 mmol for CoFe₂O₄ NPs with enhanced superparamagnetic contribution in Néel and Brownian mechanisms. MTT assay of the NPs was also carried out, indicating their low cytotoxicity.     

Effects of morphology on the electrochemical performance of NiFe2O4 nanoparticles with battery-type behavior

We report the synthesis of NiFe₂O₄ nanoparticles by the complexation EDTA-citrate method under acidic (pH = 3) and basic (pH = 9) conditions. The structural, optical, vibrational, magnetic, and electrochemical properties were studied. The samples have crystallite sizes of 21 nm (pH 3) and 73 nm (pH 9), with rounded particles and layered structures. The ⁵⁷Fe Mössbauer spectra at 12 K showed that both samples had an inverse spinel cation distribution. At 5 K, the sample prepared at pH 9 showed saturation magnetizations of about 50 emu/g. Raman spectra showed typical bands of NiFe₂O₄ phase. The materials were tested as electrodes under alkaline condition. The cyclic voltammetry and charge-discharge experiments indicated a battery-type behavior, with maximun capacities of 65 and 5 C/g (at specific currents of 3 and 10 A/g) for samples prepared at pH 9 and 3, respectively. This work offers a route for obtaining NiFe₂O₄ nanoparticles with different morphologies and sizes tuned by the synthesis conditions.     

Controlled preparation of Fe3O4/P (St-MA) magnetic composite microspheres by DPE method

In this work, controlled radical polymerization based on 1, 1-diphenylethylene (DPE method) was used to prepare magnetic composite microspheres. By this method, Fe₃O₄/P (St-MA) magnetic composite microspheres were prepared via copolymerization of styrene (St) and maleic anhydride (MA) using DPE as radical control agent in the presence of Fe₃O₄ nanoparticles. The structure and properties of the magnetic composite microspheres obtained were characterized by IR, ¹H-NMR, SEC-MALLS, TEM, TGA, VSM, DLS and other instruments. It was found that the DPE method allows the controlled preparation of magnetic composite microspheres, and Fe₃O₄/ P(St-MA) microspheres possess perfect sphere-shaped morphology, homogeneous particle size, carboxylic surface, superparamagnetism with a saturation magnetization of 14.704 emu/g, and magnetic content with a value of 25%.     

Mg0.5Ni0.5Fe2O4 nanoparticles as heating agents for hyperthermia treatment

In the present work, Mg_0.5Ni_0.5Fe₂O₄ nanopowders were prepared by a sol-gel combustion method. The magnetic properties, heat generation ability in an AC magnetic field and cytotoxicity of the mixed ferrite nanopowders were investigated. The results showed that the powders have crystalline spinel structure with a particle size in the range of 20-90 nm. Maximum saturation magnetization (Ms) of 51 emu/g was obtained for the Mg_0.5Ni_0.5Fe₂O₄ nanoparticles calcined at 900°C. The results showed that, the coercivity (Hc) of the Mg_0.5Ni_0.5Fe₂O₄ initially increases up to 700°C and then decreases with increasing temperature, whereas the Ms of the samples continuously increases. The Mg_0.5Ni_0.5Fe₂O₄ sample exhibited a temperature increase up to 45°C during 10 minutes in the exposure of magnetic field of 200 Oe. By increasing the viscosity of ferrofluid, the heat generation ability of nanoparticles reduced up to 9% at magnetic field of 200 Oe. Cell compatibility of the ferrite powders was studied by MTT assay using MG63 cell line proliferation. MTT results showed that calcination temperature of the Mg_0.5Ni_0.5Fe₂O₄ nanoparticles significantly affects the cell compatibility.     

Effect of lemon juice on microstructure,phase changes,and magnetic performance of CoFe2O4 nanoparticles and their use on release of anti-cancer drugs

Cobalt ferrite magnetic nanoparticles were synthesized and developed by a modified Pechini method using iron nitrate, cobalt nitrate, ethylene glycol (EG), and sucrose with different volumes of lemon juice (10, 20, 30, 40, 50, 60, and 70 ml) as the source of chelating agent as well as nonmagnetic elements such as Ca and Mg ions. The XRD patterns confirmed that all samples synthesized by different contents of extracted lemon juice had a cubic crystal structure with single-phase spinel. Scanning electron microscopy revealed that cobalt ferrite nanoparticles had a semi-spherical morphology. Also, the vibrating sample magnetometer indicated that the saturation magnetization of CoFe₂O₄ nanoparticles prepared with different values of extracted lemon juice increased from 18.6 emu/g for 10 ml extracted lemon juice to 75.7 emu/g for 50 ml extracted lemon juice, after which the saturation magnetization diminished. Afterwards, the CoFe₂O₄ nanoparticles were coated with polyethylene glycol (PEG) and doxorubicin (DOX) drugs, whereby drug delivery was detected at different pH levels. The CoFe₂O₄-PEG-DOX nanocomposite could release doxorubicin by more than 42% at pH = 5.4 in 75 h.     

Magnetic and morphological characterization of Bi2Fe4O9 nanoparticles synthesized via a new reverse chemical co-precipitation method

Nano-sized Bi₂Fe₄O₉ (BFO) was successfully synthesized using a new reverse chemical co-precipitation method at different pH values of 8–12. These powders were examined by x-ray diffractometery (XRD), thermogravimetrical differential thermal analysis (TG-DTA), field emission scanning electron microscopy (FESEM) and vibrating sample magnetometery (VSM). The XRD analysis showed the formation of pure phase Bi₂Fe₄O₉ at calcination temperature over 700 ℃. The TG-DTA curves indicated the crystallization temperature of 617 ℃ for the Bi₂Fe₄O₉ sample. The FESEM micrographs revealed a precipitates agglomeration, which is related to the nature of the chemical co-precipitation method and free surface energy of nanoparticles. Furthermore, the particle size of the powder samples increased from 43 to 131 nm as the pH value increased from 8 to 12, respectively. Also, the morphological change from nearly cubic to rod-like shape in the nanoparticles was observed by increasing the pH value. The M-H curves of the as-prepared powders confirmed the antiferromagnetic behavior in all samples. Uncompensated spins from the surface led to the appearance of saturation magnetization in the Bi₂Fe₄O₉ nanoparticles. Besides, a decrease in the particles size resulted in more uncompensated spins, thereby improving the saturation and remnant magnetization from M_s = 0.35 emu/g and M_r = 0.010 emu/g for pH = 12 to M_s = 1.15 emu/g and M_r = 0.042 emu/g for pH = 8. Furthermore, as the pH values increase the coercive fields firstly rise up to 196 Oe for pH = 9 and then decrease to 151 for pH = 12.     

Hollow polyaniline/Fe3O4 microsphere composites: Preparation,characterization, and applications in microwave absorption

Hollow polyaniline/Fe₃O₄ microsphere composites with electromagnetic properties were successfully prepared by decorating the surface of hollow polyaniline/sulfonated polystyrene microspheres with various amounts of Fe₃O₄ magnetic nanoparticles using sulfonated polystyrene (SPS) as hard templates and then removing the templates with tetrahydrofuran (THF). The synthesized hollow microsphere composites were characterized by FT-IR, UV/Vis spectrophotometry, SEM, XRD, elemental analysis, TGA, and measurement of their magnetic parameters. Experimental results indicated that the microspheres were well-defined in size (1.50–1.80 μm) and shape, and that they were superparamagnetic with maximum saturation magnetization values of 3.88 emu/g with a 12.37 wt% content of Fe₃O₄ magnetic nanoparticles. Measurements of the electromagnetic parameters of the samples showed that the maximum bandwidth was 8.0 GHz over ?10 dB of reflection loss in the 2–18 GHz range when the Fe₃O₄ content in the hollow polyaniline/Fe₃O₄ microsphere composites was 7.33 wt%.