Magnetic Properties Of CoFe2O4 Nanoparticles Research Articles

Influence of pH and fuels on the combustion synthesis, structural, morphological, electrical and magnetic properties of CoFe2O4 nanoparticles

Nanocrystalline spinel cobalt ferrite particles are synthesized by simple combustion method using aspartic acid and glycine as fuels. The single phase cubic structure of CoFe2O4 is revealed through X-ray diffraction analysis (XRD). Further the Rietveld refinement confirms the formation of inverse spinel structure of CoFe2O4. The characteristic functional groups of Co–O and Fe–O are identified from Fourier Transform Infrared (FT-IR) analysis. Uniform distribution of of nearly spherical particles with the size range of 40–80nm is identified through field emission scanning electron microscope (FESEM) images. The calculated DC conductivity is 1.469×10−7 and 2.214×10−8Scm−1, for CoFe2O4 synthesized using aspartic acid and glycine, respectively. The dielectric behavior obeys the Maxwell–Wagner interfacial polarization. The ferromagnetic behavior of CoFe2O4 is identified using VSM analysis and the calculated coercivity is 27Oe and saturation magnetization is 68emu/g.

Charge transfer mediated magnetic response of cobalt ferrite nanoparticles

Herein, we have performed rational surface modification of CoFe2O4 nanoparticles (NPs) to tune its room temperature ferrimagnetic properties by using different non-ionic surfactants. The NPs have been prepared by surfactant-assisted chemical co-precipitation technique with a narrow size distribution. For our study, we have chosen four non-ionic surfactants of triton X and tween group having different chain-lengths. Interestingly, we have found that surfactant co-ordinated magnetic NPs show a maximum of ~94% increase in coercivity along with a considerable decrease in magnetization as compared to the bare one. Systematic investigation reveals that both the nature and number of surfactant׳s head group and chain-length of its alkyl tail group have a remarkable impact on the magnetic properties of CoFe2O4 NPs. We believe that the tuned magnetic response of CoFe2O4 NPs depending on the nature of the surface binding ligand would open up many new opportunities as well as enhance their beneficial activities toward diverse application fields.

Tuning the magnetic properties of Co-ferrite nanoparticles through the 1,2-hexadecanediol concentration in the reaction mixture.

This work reports on the effect of the 1,2-hexadecanediol content on the structural and magnetic properties of CoFe2O4 nanoparticles synthesized by thermal decomposition of metal-organic precursors in 1-octadecene. Although pseudo-spherical particles having an average size of about 8 nm and similar stoichiometry have been observed in all studied samples, a high level of variability in the crystal quality and, in turn, in the magnetic properties has been found as a function of the amount of 1,2-hexadecanediol added to the reaction mixture. The magnetic study reveals that samples progress from glassy magnetic behavior to bulk-like, ferrimagnetic order as the crystal quality improves. The analysis of the reaction mixtures by Fourier transform infrared spectroscopy at various stages of the reaction shows the key role of the 1,2-hexadecanediol in favoring the decomposition of the metal-organic precursor, formation of an intermediate Co(2+)Fe(3+)-oleate complex and, finally, the nucleation of nanoparticles at lower temperatures.

Superspin glass behavior of self-interacting CoFe2O4 nanoparticles

Low-temperature magnetic properties of CoFe2O4 nanoparticles (3–16nm) have been investigated by AC and DC magnetic measurements. The saturation magnetization (MS) of ultra-small CoFe2O4 nanoparticles (3–9nm) sharply increases at low temperature (10K) compared to room temperature (RT) MS value. For example, the increment in MS value for 3nm CoFe2O4 nanoparticle is 22emu/g and is null for 12nm and larger sized nanoparticles. A similar trend of increment in MS is also seen in ultra-small size Fe3O4 and MnFe2O4 nanoparticles. However, the MS enhancement in ultra-small CoFe2O4 nanoparticles is found much higher as compared to Fe3O4 and MnFe2O4 nanoparticles. The ultra-small sized nanoparticles arrange with a high packing density to induce a strong exchange as well as dipolar interactions, which renders the enhanced low temperature MS with superspin glass (SSG) state. The exchange coupling strongly depends on magnetic anisotropy energy, which increases in the order Mn2+<Fe2+<Co2+ and thus the ultra-small CoFe2O4 nanoparticles show a large enhancement of MS at low temperature due to strong exchange coupling. A noticeable enhancement of spin glass temperature (Tg) for ultra-small sized CoFe2O4 nanoparticles also confirms the presence of strong exchange coupling in this case. Fitting of the ac susceptibility χ′(T, f) data to a power-law scaling and Vogel–Fulcher model shows a satisfactory fit and the dynamic critical exponent takes value between 8.9 and 11.9 which are in a range typical for the spin-glass systems. Memory behavior in ultra-small CoFe2O4 nanoparticles suggest that the frequency dependent blocking process of ultra-small sized nanoparticles can be better described by power law model, while the interaction regime present in the 12nm and above sized nanoparticles is ascribed to a Vogel–Fulcher model.

Structural and Magnetic Properties of CoFe2O4 Nanoparticles Synthesized by Starch-Assisted Sol–Gel Auto-Combustion Method in Air, Argon, Nitrogen and Vacuum Atmospheres

In the present work, structural and magnetic properties of CoFe2O4 nanoparticles synthesized by starch-assisted sol–gel auto-combustion method in air, argon, nitrogen and vacuum atmospheres were investigated. The particle size, shape, crystal structure and magnetic properties of synthesized ferrite nanoparticles were investigated by powder X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectrometer, Fourier transform infrared spectroscopy (FTIR) and a vibrating sample magnetometer (VSM). The FE-SEM micrographs indicate the octahedron-like cobalt ferrite nanoparticles formation in air atmosphere; however, spherical nanoparticles were formed in argon, nitrogen and vacuum atmospheres. An infrared spectroscopy study showed the presence of two absorption bands in the frequency range around 560 cm−1 (ν 1) and around 340 cm−1 (ν 2) which indicated the presence of tetrahedral and octahedral group complexes, respectively, within the spinel lattice. Room temperature magnetization measurements showed that the saturation magnetization (M s) and coercivity (H c) were influenced by cobalt ferrite formation atmosphere, i.e., air, argon, nitrogen and vacuum.

Magnetic properties of zinc-substituted cobalt ferric oxide nanoparticles: Correlation with annealing temperature and particle size

Nanocrystalline zinc (Zn)-substituted cobalt ferric oxide (CoFe2O4) was prepared through chemical co-precipitation; the prepared samples were annealed at 600°C, 750°C and 900°C. The crystallite size, microstructure and magnetic properties of the prepared and annealed samples were studied by using X-ray powder diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS) and Vibrating Sample Magnetometry. The structural investigations carried out by XRD reveal that the particle size and lattice constant of single phase spinal structured Zn substituted CoFe2O4 increase with the increase of annealing temperature. The FTIR spectra for the samples measured in the range of 4000–400cm−1 exhibit symmetric stretching mode of vibration of tetrahedral and octahedral sites. Furthermore, Zn substituted CoFe2O4 nanoparticles have the crystallite size in the range ~13–65nm, as confirmed by TEM. The elemental analysis was obtained from EDS. Finally, increased annealing temperature resulting in increased particle size and the impact on magnetic properties of CoFe2O4 nanoparticles is a significant finding of this study.

An investigation on synthesis and magnetic properties of nanoparticles of Cobalt Ferrite coated with SiO2

SiO2-coated Cobalt Ferrite (CoFe2O4) nanoparticles were obtained by the hydrolysis of tetraethylorthosilicate in the presence of CoFe2O4 nanoparticles in co-precipitation. The effects of SiO2coating on the magnetic properties of CoFe2O4 nanoparticles were investigated. The structural, morphological and magnetic properties of as-prepared sample were characterization by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, transmission electron microscopy (TEM), Field emission scanning electron microscopy/energy dispersive x-ray analysis (FESEM-EDAX) and magnetic measurements were investigated using vibrating sample magnetometer (VSM). The morphology analysis confirmed that the obtained composite nanoparticles consisted of CoFe2O4 coated by SiO2. It was shown that the saturation magnetization and coercivity of CoFe2O4 decreased after SiO2 coating, which can be interpreted by the interparticle dipole-dipole interactions related to the magnetic particle volume fraction in the composite nanoparticles.

Beyond the Effect of Particle Size: Influence of CoFe2O4 Nanoparticle Arrangements on Magnetic Properties

This paper focuses on the magnetic properties of CoFe2O4 nanoparticles, discussing the influence of nanoparticles arrangements obtained by different synthesis methods. Using high thermal decomposition (HTD) and direct micellar (DM) routes, three samples of CoFe2O4 nanoparticles with equal primary particle size (∼5 nm) were prepared. The HTD method allows one to obtain highly crystalline primary nanoparticles coated by oleic acid organized in a self-assembling arrangement (ACoFeHTD). The DM method results to be appropriate to prepare either irregular arrangements (IACoFeDM) or spherical iso-oriented nanoporous assemblies (SACoFeDM) of primary CoFe2O4 nanocrystals. Despite the same particle size, magnetization measurements of the HTD sample show a tendency toward cubic anisotropy (Mr/Ms ≈ 0.7), while in DM samples, a uniaxial anisotropy (Mr/Ms ≈ 0.4) is observed. The comparison between IACoFeDM and SACoFeDM samples indicates that the ordering of nanocrystals at the mesoscopic scale induces an increase of the coercive field (μ0Hc ≈ 1.17 T → μ0Hc ≈ 1.45 T) and of the reduced remanent magnetization (Mr/Ms ≈ 0.4 → Mr/Ms ≈ 0.5). The reason for these differences is discussed. In particular, a detailed study on interparticle interactions is carried out, highlighting the influence of the molecular coating and the formation of spherical iso-oriented assemblies.

Influence of NaBH4 on the size, composition, and magnetic properties of CoFe2O4 nanoparticles synthesized by hydrothermal method

Cobalt ferrite nanoparticles are prepared by varying the concentration of reducing agent NaBH4 by hydrothermal method. Transmission electron microscope observations show that particle size increases from 11.47 to 28.05 nm by increasing the concentration of NaBH4 from 30 to 70 mM. Williamson–Hall analysis on X-ray diffraction patterns show that strain increases in nanoparticles with increase in quantity of NaBH4. Energy dispersive X-ray analysis and Inductive coupled plasma atomic emission spectroscopy indicate large amount of oxygen deficiency which increase with amount of NaBH4. The magnetic hysteresis loops measured at room temperature clearly illustrate the influence of concentration of NaBH4 on magnetic properties of CoFe2O4. Saturation magnetization, coercivity, and anisotropy constant increases with the quantity of NaBH4 and they reach the maximum values of 93 emu/g, 2210 Oe, and 5.28 × 105 J/m3, respectively, with addition of 70 mM NaBH4. Estimation of micromagnetic parameters (exchange length, critical single-domain volume, etc.) suggests that prepared nanoparticles of CoFe2O4 are in single domain and size lies between superparamagnetic to critical single domain. The enhancement of magnetization is attributed to oxygen deficiency. This technique is useful in tuning the size and magnetic properties of cobalt ferrite nanoparticles.

Exchange coupling behavior in bimagnetic CoFe2O4/CoFe2 nanocomposite

In this work we report a study of the magnetic behavior of ferrimagnetic oxide CoFe2O4 and ferrimagnetic oxide/ferromagnetic metal CoFe2O4/CoFe2 nanocomposite. The latter compound is a good system to study hard ferrimagnet/soft ferromagnet exchange coupled. Two steps were followed to synthesize the bimagnetic CoFe2O4/CoFe2 nanocomposite: (i) first, preparation of CoFe2O4 nanoparticles using a simple hydrothermal method, and (ii) second, reduction reaction of cobalt ferrite nanoparticles using activated charcoal in inert atmosphere and high temperature. The phase structures, particle sizes, morphology, and magnetic properties of CoFe2O4 nanoparticles were investigated by X-Ray diffraction (XRD), Mossbauer spectroscopy (MS), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM) with applied field up to 3.0kOe at room temperature and 50K. The mean diameter of CoFe2O4 particles is about 16nm. Mossbauer spectra revealed two sites for Fe3+. One site is related to Fe in an octahedral coordination and the other one to the Fe3+ in a tetrahedral coordination, as expected for a spinel crystal structure of CoFe2O4. TEM measurements of nanocomposite showed the formation of a thin shell of CoFe2 on the cobalt ferrite and indicate that the nanoparticles increase to about 100nm. The magnetization of the nanocomposite showed a hysteresis loop that is characteristic of exchange coupled systems. A maximum energy product (BH)max of 1.22MGOe was achieved at room temperature for CoFe2O4/CoFe2 nanocomposites, which is about 115% higher than the value obtained for CoFe2O4 precursor. The exchange coupling interaction and the enhancement of product (BH)max in nanocomposite CoFe2O4/CoFe2 are discussed.

Interparticle Interactions and Magnetic Anisotropy in Cobalt Ferrite Nanoparticles: Influence of Molecular Coating

Molecular coating of nanoparticles represents probably the most important and, at the same time, critical step to design new nanostructured magnetic materials. The interaction between molecules and surface atoms leads to a strong modification of surface magnetic properties, that are one of the key points in the physics of magnetic nanoparticles. In this paper the magnetic properties of CoFe2O4 nanoparticles (⟨D⟩ ≅ 4–8 nm) coated with oleic acid have been investigated in order to clarify the role of the molecular coating on the interparticle interactions and surface anisotropy. An increase of magnetic anisotropy (i.e., coercive field and anisotropy constant) with particle size is observed in coated nanoparticles, indicating that the magnetic anisotropy is governed mainly by its magneto-crystalline component. The removal of molecular coating induces a strong increase of anisotropy, because of the increase of its surface component, as indicated by the increase of exchange bias field.

Size selected synthesis of CoFe2O4 nanoparticles prepared in a chitosan matrix

In this paper we report the synthesis and magnetic properties of CoFe2O4 nanoparticles. The nanoparticles with sizes ranging from 6 to 20 nm were prepared in a chitosan matrix. Size selection was achieved by introducing a nonionic surfactant Tween-X, where X={20, 60, 80, and 85}. Aqueous dispersions of Tween-X show micelles with increasing hydrodynamic sizes as X increases. Mössbauer spectroscopy measurements at 300 K show superparamagnetic behavior for the small particles, changing gradually to a blocked magnetic regime as the particle size increases. Magnetization measurements at 300 K show increasing values for the ratio Mr/MHmax and coercive fields (Hc).

Effect of Digestion Time on Size and Magnetic Properties of Spinel CoFe2O4 Nanoparticles

We investigate the effect of digestion time on size, distribution, and magnetic properties of CoFe2O4 nanoparticles prepared by the precipitation approach. The average crystalline size increases from 14 to 19 nm as the digestion time is increased from 1 to 120 min. The observed dependence of average particle size with digestion time is in good agreement with Lifshitz, Slyozov, and Wagner theory. Our results suggest that the dissolution of Co2+−Fe3+ complexes form the surface followed by crystallization of spinel oxide through Oswald ripening process. This observation is in sharp contrast to the growth process in Fe3O4 nanoparticles where Oswald ripening is insignificant beyond 5 min due to the electron hopping between Fe2+ and Fe3+ ions. Magnetization measurements show that the saturation magnetization value decreases from 60 to 49 emu/g as the digestion time is increased from 1 to 120 min. Raman and Mossbauer spectroscopic investigations reveal that reduction of magnetization with increasing particle siz...

Magnetic properties of CoFe2O4 nanoparticles synthesized through a block copolymer nanoreactor route

The development of self-assembled magnetic CoFe2O4 nanoparticles within polymer matrices at room temperature is reported. Diblock copolymers consisting of poly (norbornene) and poly (norbornene-dicarboxcylic acid) (NOR/NORCOOH) were synthesized. The self-assembly of the mixed metal oxide within the NORCOOH block was achieved at room temperature by processing the copolymer nanocomposite using wet chemical methods. Morphology and magnetic properties were determined by superconducting quantum interference device magnetometry, transmission electron microscopy, wide angle x-ray diffraction, and Fe57 Mössbauer spectroscopy. The CoFe2O4 nanoparticles are uniformly dispersed within the polymer matrix, and have an average radius of 4.8±1.4 nm. The nanocomposite films are superparamagnetic at room temperature and ferrimagnetic at 5 K.