Longlong Chen

The increase of the light transparency induced by a magnetic field for the colloid film based on α–FeOOH nanoparticles

α–FeOOH nanoparticles are spherical and weakly magnetic. The size of the particles is about 8 nm, so they are regarded as Rayleigh scatterers. Aqueous colloids based on these particles exhibit magnetically enhanced transmission of light; the relative transmission coefficient reaches almost 1.3 when H = 500 Oe. Since the magnetic interaction between the particles is too weak to form chain-like aggregates, the enhancing effect is mainly attributed to the variation of the absorption cross-sections of the colloidal system in relation to the coupling of magnetic and dielectric properties of the particles. Along the direction of the external magnetic field, the absorption cross-section of the colloid decreases so that the transmitted light parallel to the field direction is enhanced and increases with the field. The results of this investigation indicate that there could be potential applications for weakly magnetic colloids based on non-cubical nanocrystals.

Investigation into loss in ferrofluid magnetization

Ferrofluids containing γ-Fe2O3/Ni2O3 nanoparticles (not chemically treated) were synthesized using water and mixed water–glycerol as carrier liquid and the ferrofluid viscosity was modified by varying the glycerol content in the carrier liquid. The apparent magnetization of the ferrofluids decreased with increasing glycerol content. The loss in magnetization is described by the ratio of effective magnetic volume fraction to physical volume fraction of nanoparticles in the ferrofluids as a characteristic parameter. We ascribe the loss to the formation of “dead aggregates” having a ring-like structure of closed magnetic flux rather than to any chemical reaction. Such dead aggregates exist in zero magnetic field and do not contribute to the magnetization in the low or high field regime, so that the effective magnetic volume fraction in the ferrofluids decrease. An increase in carrier liquid viscosity is similar to a weakening of the thermal effect, so the number of dead aggregates increases and the magnetiza...

Preparation of Composite Nanoparticles of Fe-Zn Bioxide Using Surface Modification and Their Subsequent Characterization

During the liquid-phase synthesis of γ-Fe₂O₃ nanoparticles using a chemically induced transition in FeCl₂ solution (400 mL, 0.25 M), the surface modification of the particles was undertaken by adding ZnCl₂ solution, in an attempt to prepare composite nanoparticles. The magnetization, morphology, chemical composition, and crystal structure of the product were characterized using a vibrating sample magnetometer, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The experimental results showed that when the concentration of ZnCl₂ solution did not exceed 2 M (50 mL), the γ-Fe₂O₃-ZnFe₂O₄ bioxide composite nanoparticles coated by FeCl₃ · 6H₂O could be prepared. These particles were nearly spherical and their average size was about 11 nm; specific saturation magnetization was about 48 Am²/kg. The molar, mass, and volume percentages of every composition phase, as well as the average density of the composite nanoparticles, were estimated from the characterization results. A particle model with a core that is γ-Fe₂O₃ covered with ZnFe₂O₄ is proposed.

The magneto-optical behaviors modulated by unaggregated system for γ-Fe2O3–ZnFe2O4 binary ferrofluids

Under an external magnetic field, when circularly polarized light was transmitted through binary ferrofluids based on strongly magnetic γ-Fe2O3 and weakly magnetic ZnFe2O4 nanoparticles, the birefringence Δn and dichroism Δk arising from the chains of γ-Fe2O3 particles system were modulated and decreased by the unchained ZnFe2O4 particles. In our experiments, we used two types of ZnFe2O4 nanoparticles: one consisted of ZnFe2O4(1) particles with higher moments, and the other consisted of ZnFe2O4(2) particles with lower moments. Comparing the birefringence and dichroism of the γ-Fe2O3–ZnFe2O4(1) and γ-Fe2O3–ZnFe2O4(2) binary ferrofluids, it was found that the modulating action of the ZnFe2O4(2) particle system with lower moments was larger than that of the ZnFe2O4(1) particle system with higher moments. Using a model for a bi-dispersed system based on chained and unchained particles, the behavior of the modulating action was explained by an additional effective relative magnetic permeability, which depends ...

Transformation of ferrihydrite to goethite and then to maghemite in a mixed FeCl2/NaOH solution

Ferrihydrite (Fe5O7(OH)·4H2O) is poorly crystalline hydrated ferric oxyhydroxide. Using a treatment in a mixed FeCl2/NaOH solution, we attempted to prepare magnetic nanoscale particles from ferrihydrite. During the treatment, the concentration of FeCl2 was fixed at 0.1 M, and the concentration of NaOH was varied from 0.09 to 0.26 M. The as-prepared products were characterized using X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The experimental results showed that under the FeCl2/NaOH solution treatment, the ferrihydrite transformed into nanoscale γ-Fe2O3 via an α-FeO(OH) intermediate phase. The as-prepared products contained rod-type α-FeO(OH), sphere-type γ-Fe2O3, and flake-type γ-Fe2O3 particles. A mechanism for a coupling of the aggregation and the transition was proposed to interpret the formation of highly crystalline nanoscale particles from the poorly crystalline smaller particles.

The extrinsic hysteresis behavior of dilute binary ferrofluids

Abstract.We report on the magnetization behavior of dilute binary ferrofluids based on

The dependence of Ni-Fe bioxide composites nanoparticles on the FeCl 2 solution used

\gamma

Characterization and magnetism of Co-modified γ-Fe2O3 core–shell nanoparticles by enhancement using NaOH

- Fe2O3/Ni2O3 composite nanoparticles (A particles), with diameter about 11nm, and ferrihydrite ( Fe5O7(OH)·4H2O nanoparticles (B particles), with diameter about 6 nm. The results show that for the binary ferrofluids with A-particle volume fraction

Magneto-optical effect in a system of colloidal particle having anisotropic dielectric property

\phi_{A}

Large magneto-optical birefringence of colloidal suspensions of α-FeOOH goethite nanocrystallites

= 0.2 % and B-particle volume fractions