Papers by Keyword: CoFe₂O₄

Abstract: In this study, the particle sizes of SrFe₁₂O₁₉ in hard/soft SrFe₁₂O₁₉/CoFe₂O₄ nanocomposite magnets made using mechanical alloying and ultrasonic irradiation were investigated. SrFe₁₂O₁₉/CoFe₂O₄ nanocomposites were combined in a ratio of 75:25, with each magnetic material being prepared separately. SrFe₁₂O₁₉ powder was prepared from Fe₂O₃ and SrCO₃ powder by mechanical alloying and ultrasonic irradiation for different times, 0, 3, 6, 9, and 12 h. Varying the ultrasonic time during the preparation of the SrFe₁₂O₁₉ samples resulted in differences in morphological characteristics, crystal structure, particle size, crystal size, microstrain, density, porosity, and magnetic properties. The longer the ultrasonic time, the crystal size and particle size decreases, the density increases, and the porosity reduction which affects the magnetic properties. SrFe₁₂O₁₉ after 12 h ultrasonic process reach M_s value = 61.29 emu/g. CoFe₂O₄ powder was produced from Fe₂O₃ and CoCO₃ powder by mechanical alloying with a 10 h milling time. Furthermore, each SrFe₁₂O₁₉ sample was composited with CoFe₂O₄ powder by ultrasonic irradiation for 1 h and these composite samples also showed different characteristics, where there is an increase in M_r and M_s compared to the single SrFe₁₂O₁₉. The morphology, crystal structure, particle size, and magnetic properties of the samples were measured using scanning electron microscopy, X-ray diffraction, particle size analysis, and PERMAGRAPH. The crystal size and microstrain were calculated using a Williamson–Hall plot, and density and porosity were determined using Archimedes’ law.

Abstract: Herein, the spinel Co_1-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4 and 0.6) powder samples have been prepared by the solid-state reaction method. We have carried out the measurements of crystal structure, element analysis, material characterization, magnetic property and Curie temperature using the X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer, and the first-principles calculations within the framework of the density functional theory (DFT). The EDS measurement indicates that the Co_1-xZn_xFe₂O₄ powder samples have been successfully synthesized and exhibited the cubic spinel structures. Both the lattice constant and crystallite size increase with the Zn concentration due to the larger ionic radius of Zn²⁺ ion than the Co²⁺ ion. The concentration ratio of the Co²⁺ and Co³⁺ ions can be predicted by the distribution of cations between the A and B sites by the XPS measurement. For the magnetic properties, the residual magnetization, coercivity and Curie temperature decrease monotonically as the Zn concentration increases, while the saturation magnetization initially increases and then decreases at the room temperature. For the Co_0.8Zn_0.2Fe₂O₄ sample, the magnetic saturation reaches the maximum value of 62.98 Am²kg^-1, due to a large amount of the Co³⁺ ions. The adequate replacement of Zn ion for the Co site can improve the magnetic properties of spinel Co_1-xZn_xFe₂O₄ powders, and effectively regulates the Curie temperature.

Abstract: Increasing dispersion stability is the main issue in recent research at magnetorheological (MR) fluids. The presentation of nanoparticle addictive in MR fluids is an effective method not only to increase dispersion stability but also increasing performance in MR fluids. In this study, the effect of hard magnetic CoFe₂O₄ nanoparticles addition on rheological properties and dispersion stabilization had been studied. Rheological properties were investigated using a rheometer at room temperature. The result showed that the addition of CoFe₂O₄ nanoparticles 1wt% in particles of MR fluids were improving the shear stress and viscosity of MR fluids. Both MR fluids with and without nanoadditives behaving like a Newtonian fluid at the off-state condition and act like Bingham fluid at the on-state condition. Moreover, MR fluid with CoFe₂O₄ additives had a higher sedimentation ratio than MR fluids without additives.

Abstract: In this study, the synthesis of CoFe₂O₄ by using the fine sediment of the Bengawan Solo River, Trucuk District, Bodjonegoro Regency as raw materials with the coprecipitation method has been successfully carried out. The fine sediment is used as a source of Fe cation in the synthesis of CoFe₂O₄. The XRD confirmation results showed that CoFe₂O₄ is formed at an annealing temperature of 800° C with crystallite sizes ranging from 34.88 to 38.05 nm. Thus, the VSM characterization showed that the magnetic properties of the CoFe₂O₄ nanoparticles depend on the heat treatment of the fine sediments as ore materials. Finally, the obtained CoFe₂O₄ samples can be used as photocatalysts with a maximum reduction rate ratio of 83%.

Abstract: Ferrite materials, especially those containing nickel and cobalt, are popular due to their unique mechanical and magnetic properties. Single phase NiFe₂O₄ and CoFe₂O₄ nanopowders obtained by different methods were used for sintering studies. Chemical sol-gel self-propagating combustion method, co-precipitation technology combined with hydrothermal synthesis or spray-drying method, and high frequency plasma chemical synthesis have been used to synthesize ferrite nanopowders. Relatively dense (95-99%) materials with high saturation magnetization (M_S = 80-84 emu/g for CoFe₂O₄ and M_S = 46-48 emu/g for NiFe₂O₄) were obtained at 1100-1200 °C temperatures.

Abstract: Cobalt and nickel ferrites powders are synthesized by the co-precipitation technology, combined with the spray-drying method. The crystallite size, specific surface area (SSA), magnetic properties of synthesized products are investigated. All the synthesized ferrites are nanocrystalline single phase materials with crystallite size of 5-6 nm, the SSA of 80-85 m²/g and the calculated particle size of 13-15 nm. After spray-drying granules of the size up to 10 μm are obtained. After thermal treatment at 550 and 950 °C SSA decreases to 40-50 m²/g and 20-22 m²/g, respectively. The saturation magnetization at these temperatures increase from 17 to 40 emu/g for NiFe₂O₄ and from 51 to 77 emu/g for CoFe₂O₄. By the pressure-less sintering method the dense material forms at 1100 °C for CoFe₂O₄ and 1200-1300 °C for NiFe₂O₄.

Abstract: Cobalt ferrite (CoFe₂O₄) nanoparticles were successfully synthesized by utilized sol gel method with controlled pH and temperature solution during reflux process in order to obtain monodispersed nanoparticles with high magnetic properties. The obtained cobalt ferrite particles are oval with the size vary from 100 nm to 220 nm. The Co˗O and Fe˗O bonds are formed as confirmed by FTIR measurement. The sample has high quality crystal with spinel structure as indicated by similar XRD pattern of the sample and the JCPDS (00-001-1121) data without impurity peaks. From the Vibrating Sample Magnetometer (VSM) measurement, magnetic remnant around 0.2303 emu/cc and coercive field around 2.7039 kOe are obtained.

Abstract: In this study, we report the synthesis and characterization studies of amine functionalized CoFe₂O₄ and NiFe₂O₄ nanoparticles (NPs). The synthesis process was accomplished by refluxing metal chloride precursors in ethylene glycol in presence of sodium acetate and ethanolamine. The average crystallite sizes of the synthesized particles are found to be in the range of 8-10 nm. The synthesized particles are characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) technique, FTIR, Raman and UV-visible spectroscopy for crystal structure, average size, surface area, phase and functional group determination. The surface morphology and elemental composition were studied by Scanning electron microscope (SEM) and X-ray fluorescence (XRF) respectively. Magnetic behavior upto fields of 3T at room temperature measured in PPMS magnetometer showed the superparamagnetic behavior of these particles. Analysis of cytotoxicity was carried out by examining their effect on cell viability of human peripheral blood lymphocytes so as to assess biocompatibility for various biomedical applications.

Abstract: The present work aims to study the magnetic properties of nanoferrita cobalt obtained by combustion reaction. The structural feature as well as the magnetic behavior when in the presence of a magnet and magnetic measurements was investigated. The resulting samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), magnetic behavior when in the presence of a magnet and magnetic measurements. The results indicated the phase single the spinel ferrite CoFe₂O₄, with high intensity of diffraction peaks indicating that the samples are crystalline and nanoparticle formation. The characteristic bands of spinel were observed for nanoferritas CoFe₂O₄. The ferrite nanoparticles were strongly attracted when in presence the magnet presenting a saturation magnetization of 58.0 emu/g, coercivity of 1.14 kOe.

Abstract: Magnetic nanoparticles of cobalt ferrite (CoFe₂O₄) have been synthesized by co-precipitation method with various synthesis temperatures, concentration of NaOH and stirring duration. The results showed that nanoparticles have well crystallized structure with various grain sizes which depend on synthesis parameters. The grain size increased with increasing synthesis temperature, decreasing concentration of NaOH and decreasing stirring duration. Magnetic characterization of CoFe₂O₄ nanoparticles measured by Vibrating Sample Magnetometer (VSM) showed that coercive field was decrease with the decreasing of particle size. The saturation and remnant magnetization showed increasing when crystallinity increased. However, it also depends on presence of α-Fe₂O₃ phases and their grain size. Based on magnetic characterization analysis, sample with parameter of synthesis temperature 80^°C, concentration of NaOH 5 M and stirring duration 120 minutes have been selected to be modified using polyethylene glycol (PEG)-4000. XRD and TEM analysis showed that surface modification with PEG-4000 could increase the crystallinity of nanoparticles, decrease agglomeration and control the shape to more spherical. VSM analysis showed that modification PEG-4000 could decrease the saturation magnetization which is due to the existence of α-FeO(OH) and γ-FeO(OH) phases from bonds at interface of CoFe₂O₄ as confirmed by XRD and Furrier Transform Infra Red (FTIR) analysis. Keywords: magnetic nanoparticles, CoFe₂O₄, copresipitation, PEG-4000