Cobalt ferrite nanoparticles: Achieving the superparamagnetic limit by chemical reduction (original) (raw)
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International Journal for Innovation Education and Research, 2021
In this study we report on the synthesis and characterization of cobalt ferrite (CoFe2O4) nanoparticles (NPs), synthesized by chemical co-precipitation in alkaline medium. Two samples were synthesized at two different temperatures, 35 and 90 oC. Both samples were characterized by Transmission Electron Microscopy (TEM), x-ray diffraction (XRD), and room-temperature (RT) magnetization. Two samples showed superparamagnetic behavior (SPM) at RT. TEM reveals morphological mean diameter increasing 5.8 nm to 10.4 nm, with the increase of the co-precipitation temperature. XRD confirm the inverse cubic spinel structure. The RT magnetization curves were analyzed by the first-order Langevin function averaged out by a lognormal distribution function of magnetic moments. This analysis showed saturation magnetization and magnetic moment increases from 60.2 to 74.8 emu/g and from 3.9 x 103 to 8.2 x 103 mB, respectively.
IEEE Transactions on Magnetics, 2000
Cobalt ferrite (CoFe 2 O 4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe 2 O 4 nanoparticles with coercive magnetic flux density (H c) in the range 5.5-31.9 kA/m and M s in the range 47.9-84.9 A.m 2 Kg-1. At a grain size of ~54±2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in H c. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe 2 O 4 synthesis. The magnetic trends reported will aid in the optimization of functional CoFe 2 O 4 nanoparticles.
Finite size and surface effects on the magnetic properties of cobalt ferrite nanoparticles
Journal of Nanoparticle Research, 2011
Cobalt ferrite, CoFe 2 O 4 , nanoparticles in the size range 2-15 nm have been prepared using a non-aqueous solvothermal method. The magnetic studies indicate a superparamagnetic behavior, showing an increase in the blocking temperatures (ranging from 215 to more than 340 K) with the particle size, D TEM . Fitting M versus H isotherms to the saturation approach law, the anisotropy constant, K, and the saturation magnetization, M S , are obtained. For all the samples, it is observed that decreasing the temperature gives rise to an increase in both magnetic properties. These increases are enhanced at low temperatures (below *160 K) and they are related to surface effects (disordered magnetic moments at the surface). The fit of the saturation magnetization to the T 2 law gives larger values of the Bloch constant than expected for the bulk, increasing with decreasing the particle size (larger specific surface area). The saturation magnetization shows a linear dependence with the reciprocal particle size, 1/D TEM , and a thickness of 3.7 to 5.1 Å was obtained for the non-magnetic or disordered layer at the surface using the dead layer theory. The hysteresis loops show a complex behavior at low temperatures (T B 160 K), observing a large hysteresis at magnetic fields H [ *1000 Oe compared to smaller ones (H B *1000 Oe). From the temperature dependence of the ac magnetic susceptibility, it can be concluded that the nanoparticles are in magnetic interaction with large values of the interaction parameter T 0 , as deduced by assuming a Vogel-Fulcher dependence of the superparamagnetic relaxation time. Another evidence of the presence of magnetic interactions is the almost nearly constant value below certain temperatures, lower than the blocking temperature T b , observed in the FC magnetization curves.
Superparamagnetic Cobalt Ferrite Nanoparticles: Effect of Temperature and Base Concentration
Journal of Superconductivity and Novel Magnetism, 2014
Cobalt ferrite nanoparticles were coprecipitated in air medium using NH 3 , and the effects of temperature and base concentration on the properties were studied. X-ray diffraction (XRD) technique and Fourier transform infrared spectroscopy were used to investigate the structural properties of the samples. Particle sizes and shapes were determined by a transmission electron microscope (TEM). Magnetic measurements were done using vibrating sample magnetometer at room temperature. The proper reaction temperature was found to be 80°C for the synthesis of superparamagnetic cobalt ferrite nanoparticles. The effect of base concentration on the properties of the superparamagnetic nanoparticles was investigated under this temperature. The magnetization values of cobalt ferrite nanoparticles increased as the base concentration increased and reached to a value of 32.4 emu/g with zero coercivity. The particle sizes (d XRD , d TEM , and d VSM ) of cobalt ferrite nanoparticles were calculated from XRD patterns, TEM images, and magnetic data, respectively. It was observed that the d TEM and d VSM are similar to each other, and the d XRD are bigger than those with the similar trend of increase with the increase of base concentration.
2007
Magnetic nanoparticles of cobalt ferrite have been synthesized by wet chemical method using stable ferric and cobalt salts with oleic acid as the surfactant. X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) confirmed the formation of single phase cobalt ferrite nanoparticles in the range 15-48nm depending on the annealing temperature and time. The size of the particles increases with annealing temperature and time while the coercivity goes through a maximum, peaking at around 28nm. A very large coercivity (10.5kOe) is observed on cooling down to 77K while typical blocking effects are observed below about 260K. The high field moment is observed to be small for smaller particles and approaches the bulk value for large particles.
2021
In this study, crystalline nanoparticles CoFe2O4 with a spinel structure were prepared by hydrothermal methods. The magnetic properties of non-calcined cobalt ferrite formed from nanocrystalline powders. The dependence of the particle size and crystalline structure of obtained nanoparticles in the synthesis conditions was examined and characterized using field emission scanning electron microscope (FESEM), and X-ray diffraction analysis (XRD). The XRD analysis revealed a high degree of crystallinity and confirmed the spinel structure of crystalline nanoparticles CoFe2O4. The FESEM image shows the presence of spherical ferrite particles with an average diameter of about 13-18 nm. The results also show that the formation of cobalt ferrite spinel structures was affected by fabrication conditions. Magnetic hysteresis loop data confirm that the magnetic properties of nanoparticles depend on the synthesis conditions. The material prepared by the hydrothermal route and calcination at 150oC...
Journal of Alloys and Compounds, 2011
Co-substituted ferrite nanoparticles with narrow size distribution have been prepared by coprecipitation method. X-ray diffraction (XRD) showed that the samples have cubic spinel structure of which the lattice constant slightly decreases upon cobalt substitution. The mean crystallite size of the samples was in the range 9.5-11 nm as deduced from the XRD line broadening. Energy dispersive X-ray spectroscopy (EDX) verified the presence of cobalt in the substituted samples. The morphology and size distribution of the nanoparticles were studied using transmission electron microscopy (TEM). Magnetic properties were determined using a vibrating sample magnetometer (VSM). The samples are characterized by a superparamagnetic transition at blocking temperatures T B below room temperature. The coercivity H c at low temperatures follows a simple model of thermal activation of particle's moment over the anisotropy barrier in the temperature range below T B which is in accordance with Kneller's law for ferromagnetic materials. From the blocking temperature and from the thermal decay of the coercivity, the effective anisotropy constant values were determined to be in order of 10 6 erg/cm 3 . The Curie temperature T C and saturation magnetization M s at nanoscale are lower than those of the bulk and decrease with the increase of cobalt content.
Journal of Materials Chemistry, 2001
Fine CoFe 2 O 4 powders with monodisperse, almost equi-axial nanometer-sized particles were synthesised in a polyol medium by forced hydrolysis of ionic Co(II) and Fe(III) salts at 160 ³C. K(Co) XANES and 57 Fe Mo È ssbauer spectroscopy show that the structure of this ferrite is slightly deviated from an inverse spinel structure: 16% of cobalt atoms are in tetrahedral sites. The particles are superparamagnetic above 300 K and ferrimagnetic below this blocking temperature with, at low temperature, strong coercivity, a saturation magnetisation value close to the bulk value and high reduced remanence. The saturation magnetisation measured at 5 K is clearly enhanced with respect to CoFe 2 O 4 nanometer-sized particles previously prepared by other methods. These magnetic characteristics suggest that these particles have a high crystallinity which may result from this novel synthesis route.
In this study, superparamagnetic cobalt ferrite nanoparticles (SCFNs) were synthesized by co-precipitation in one-step. The synthesis parameters; reaction time and stirring rate, were varied separately while the other parameters were fixed constant to investigate the effect of the parameters on the properties of SCFNs. X-ray diffraction analysis and Fourier transform infrared spectroscopy confirmed that synthesized samples are cobalt ferrite. The magnetization consistently increased with the particle size as the reaction time increased and the stirring rate decreased. While the reaction time was effective on the size of the cobalt ferrite nanoparticles, the stirring rate was also found to have influence on the particle size and thus the magnetization of the nano-particles. The critical size of cobalt ferrite nanoparticles for superparamagnetic limit with zero coercivity and remanence was found to be around 7 nm and its maximum magnetization value was 41.0 emu/g. When the size of the SCFNs went over 7 nm, the magnetization increased with a small coercivity of 2-5 Oe, which may offer a potential usage in magnetic hyperthermia applications. It was seen that structural properties, especially the particle sizes and corresponding magnetic properties of SCFNs were considerably affected by the parameters of stirring rate and especially reaction time. Therefore, it is seen that SCFNs with desirable properties can be tailored by changing the synthesis parameters and therefore may have the potential to use in biomedical applications .