Ferrite Ferrofluids Research Articles

Morphological investigation of monodispersed manganese ferrite nanoparticles by the impedance measurement

Particle size distributions in manganese ferrite ferrofluids are analyzed based on ac susceptibility measurements. The frequency dependence of the complex susceptibility, χ″(ω), of the ferrofluid was measured by the slit-toroid technique. The sample exhibited frequency response due to Néel’s rotational relaxation, from which the particle size was estimated. A modified log-normal distribution is used for fitting the experimental results, which allows proper account of the narrow distributions. The calculated average particle size is in good agreement with transmission electron microscopy result.

Structure of Co-Zn ferrite ferrofluid: A small angle neutron scattering analysis

A hydrothermal synthesis route is used to synthesize nanomagnetic particles of Co0.3Zn0.7Fe2O4 ferrite ferrofluids with particle diameter ranging from 5.5–9 nm. XRD analysis shows the formation of a single phase spinel structure. EDX results confirm the stoichiometric composition of the cations. Small angle neutron scattering technique is used to determine the size and size distribution of Co0.3Zn0.7Fe2O4 ferrofluid. The sizes thus obtained are in the range of 5.4 to 8.4 nm. These results are in agreement with magnetic measurements.

Study of ferrite ferrofluids by small-angle scattering of polarized neutrons

Nanoparticles consisting of a magnetic core (Fe3O4, CoFe2O4 and CuFe2O4) and a hydrophobic shell were prepared by chemical co-precipitation of the inorganic cores and by subsequently modifying the surface with dodecanoic acid. The nanoparticles were then dispersed in cyclohexane to form stable ferrofluids. These dispersions were investigated by small-angle scattering of polarized neutrons and the data were interpreted according to a `pearl-necklace' model, opportunely modified to account for the core–shell structure of the particles. Results of the fitting show that the particles consist of a magnetic core with a mean radius of 40–50 A and an organic shell with a thickness of 7–8 A. These nanoparticles assemble in fractal aggregates when a magnetic field is applied.

Low-field DC-magnetization study of Ho 3+-doped Mn–Zn ferrite ferrofluid

The physical and magnetic properties of magnetic nanoparticles are crucial for their effectiveness and reliability in biomedical applications. In this article, we report the synthesis of a stable Ho-substituted Mn–Zn ferrite ferrofluid and its physical and magnetic properties. Substitution by rare earth metal plays an important role in determining the magneto-crystalline anisotropy in 4f-3d inter-metallic compounds. Ho 3+ substitution not only enhanced the magnetic anisotropy but also produced strong spin frustration at low temperature. The field dependence of blocking temperature shows H 2/3 dependency in the entire range of field, i.e., 10–700 Oe, indicating the emergence of Ising spins characteristics in the present system.

Ferromagnetic resonance line of ferrite ferrofluids at high microwave power

The effects of high microwave power levels upon the ferromagnetic resonance (FMR) lines of liquid and frozen ferrite ferrofluids are investigated. The distortions of the FMR lines at critical microwave power levels give evidence of the onset of instabilities due to non-linear processes.

Ferromagnetic resonance of ferrite ferrofluids at high microwave power levels

The effects of high microwave power level upon the ferromagnetic resonance line of ferrofluids at room temperature are investigated. The distortions of the resonance line with increasing power levels give evidence of an apparent foldover effect attributed to spin-wave instabilities. The critical microwave power to onset the instabilities decreases exponentially with the concentration of magnetic particles in the ferrofluid sample.

Anomalous hysteresis behavior in a cobalt ferrite ferrofluid

The magnetization of cobalt ferrite ferrofluid has been studied at low temperatures in the presence of the carrier fluid. A prominent difference between slow and fast cooled samples was observed. In particular the slow cooled samples display an anomalous increase in magnetization on field reversal. The data is analyzed in terms of the possibilities of both coherent and incoherent spin rotations.

Gd-substituted ferrite ferrofluid: a possible candidate to enhance pyromagnetic coefficient

Physical and magnetic properties of newly synthesized Gd-substituted ferrite ferrofluid is studied. The particle size is derived from X-ray, magnetisation and viscosity measurements. This fluid has low-curie temperature, 348K. The study indicates that it is possible to enhance the pyromagnetic coefficient of the magnetic fluid using Gd.

Experimental investigation of longitudinal magneto-optic effects in four ferrite ferrofluids in visible-near infrared spectrum

We present an extensive experimental work concerning measurement of longitudinal magneto-optic effects (Faraday rotation and circular dichroism) induced in magnetic liquids. Seven ferrofluid samples allow the study of the influence of numerous parameters: magnetic suspension and carrier liquid characteristics, magnetic field strength (up to 10 kOe) and frequency (dc to 50 kHz), light wavelength (400 to 2000 nm) and, temperature (253 to 373 K). These topics, especially the spectral area, have rarely been studied before. Most of the studies show interesting behaviors and aid in the understanding of magneto-induced phenomena. They also contribute to the conception of new optical applications of ferrofluids: 1) a pure Faraday rotator (free of circular dichroism) obtained by a ferrofluid mixing method and 2) a Faraday light modulator working up to 50 kHz.

Synthesis and properties of Mn-Zn ferrite ferrofluids

A Mn-Zn ferrite ferrofluid is produced by chemical synthesis. Two different types of ferrofluids, according to the type of carrier liquid, are synthesized: an aqueous cationic ferrofluid and a surfacted hydrocarbon-based one. Ferrite particles are characterized by using several techniques: X-ray diffraction, transmission electronic microscopy, IR-spectroscopy, thermogravimetry, magnetization measurements and chemical analysis. Particles size depends on the synthesis parameters and can be partly controlled by choosing the type of the coprecipitating base. Increasing of the Zn concentration leads to smaller size of synthesized particles, as well as effects the content of associated water. Magnetization of the ferrofluid significantly decreases when the degree of Zn substitution exceeds 0.5.

Electron magnetic resonance of ferrofluids: Evidence for anisotropic resonance at 77 K in samples cooled in a magnetic field

Evidence is presented from studies of electron magnetic resonance for the formation of linear chains in kerosene based Mn 0.1Fe 0.9Fe 2O 4 (MF1) ferrite ferrofluid cooled in a magnetic field. The resonance field at 77 K was found to depend on the field at which the sample was cooled. More interestingly, the samples cooled in a magnetic field exhibited anisotropy in a resonance field with 180° periodicity, giving evidence for frozen chains.

Electron paramagnetic resonance study of ionic water-based manganese ferrite ferrofluids

Abstract We report for the first time electron paramagnetic resonance linewidth measurements in an ionic water-based ferrofluid. The linewidth broadening is studied as a function of the particle-particle distance. We change the average particle-particle distance from 20 to 89 nm by diluting a concentrated sample with water. Magnetic and electric interactions between adjacent particles are used to explain the experimental data.