γ-Fe2O3 Nanocrystals Research Articles

Comparative study on the synthesis of γ-Fe2O3 and Fe3O4 nanocrystals using high-temperature solution-phase technique

Comparative study on the synthesis of γ-Fe2O3 and Fe3O4 nanocrystals using high-temperature solution-phase technique

Magnetic Behavior of γ-Fe2O3 Nanocrystals Dispersed in Colloidal Silica Particles

The magnetic properties of composites that consisted of γ-Fe2O3 nanocrystals (4−10 nm) dispersed in submicrometer spherical silica particles at different packing fractions have been studied. The spherical composites were prepared by aerosol pyrolysis of a methanol solution containing tetraethoxysilane and iron nitrate and further annealing in a conventional furnace. Hysteresis loops registered at room temperature indicated that all composites exhibited superparamagnetic behavior. Studies of the thermal evolution of magnetization indicated that these composites could be considered as an adequate experimental system to determine the influence of particle size and interparticle interactions on the magnetic properties. It was observed that the blocking temperature strongly depends on particle size. Also, we have found that interparticle interactions cause frustration of the moments, and we have determined a dependence of the effective anisotropy with the particle size probably associated with the existence of...

Cigar-shaped ferrite nanocrystals: Orientation of the easy magnetic axes

Mesoscopic structures made of cigar-shaped γ-Fe2O3 nanocrystals with an average length of 325 nm and aspect ratio of 7 are described. The structures were prepared starting from an aqueous solution to which a magnetic field parallel to the substrate could be applied during the evaporation process. If a magnetic field was applied, the nanocrystals rotated their long axis along the magnetic field direction to form ribbons, whereas without a field the nanocrystals remained deposited on the substrate with a random orientation. The orientation of the nanocrystals is responsible for the anisotropy of the ribbons as evidenced by the hysteresis loops.

Soft x-ray imaging and spectroscopy of single nanocrystals

Resonant photoemission electron microscopy (PEEM) at the Fe L3,2 absorption edge was utilized to image single γ-Fe2O3 nanocrystals of 10 nm average diameter (∼20 000 Fe atoms) and to record soft x-ray absorption spectra of individual particles. Within the spectral resolution of the experiment, no damage to the individual nanoparticles occurs during repeated, prolonged exposure to the intense x-ray beam. Furthermore, no differences in the position or shape of the soft x-ray absorption spectrum of a single nanocrystal and the ensemble are observed within the experimental resolution. PEEM contrast images and soft x-ray absorption spectra, however, show strong intensity variations between different particles reflecting the size distribution of the sample. This proof-of-principle experiment successfully demonstrates the applicability of x-ray spectromicroscopy to the study of nanoscale systems on a hitherto unachieved length scale.

Fabrication and Characterization of the Plate-Shaped γ-Fe2O3 Nanocrystals

Plate-shaped γ-Fe2O3 nanocrystals have been successfully prepared in a water system by a simple reduction−oxidation method at room temperature and under ambient pressure. The reactions contain two steps: first, Fe(II) is reduced into Fe atoms by γ-ray irradiation in nitrogen atmosphere; then, Fe atoms are oxidized into γ-Fe2O3 in air. XRD, TEM, EDXA, XPS, and Mössbauer spectrum were used to characterize the final product. The magnetic characterization showed that the γ-Fe2O3 nanocrystals have a specific saturation magnetization of 83 emu/g and a coercivity of 320 Oe (25.5 kA/m). A possible formation mechanism of the plate-shaped γ-Fe2O3 nanocrystals was suggested.

High Bulk Modulus of Nanocrystal γ-Fe2O3 with Chemical Dodecyl Benzene Sulfonic Decoration Under High Pressure

Structural transformation in γ-Fe2O3 nanocrystals (about 10 nm) with dodecyl benzene sulfonic (DBS) coated is studied by using high-pressure energy dispersive x-ray diffraction of synchrotron radiation and high-resolution transmission electron microscopy (HRTEM). Relative to the bulk crystal, the transition pressure showed a decrease while the compressibility increases significantly up to 375 (±9 GPa). HRTEM picture confirmed that there is surface cladding surrounding nanocrystals due to DBS, which formed new special boundaries between nanocrystals and should be different from the ordinary grain boundaries. The experimental results imply that the surface layers of γ-Fe2O3 nanocrystals have strong effect on the compressibility.