Ferrofluid Material Research Articles

Magnetically induced interfacial instabilities in a ferrofluid annulus.

We investigate the flow of a viscous ferrofluid annulus surrounded by two nonmagnetic fluids in a Hele-Shaw cell when subjected to an external radial magnetic field. The interfacial pattern formation dynamics of the system is determined by the interplay of magnetic and surface tension forces acting on the inner and outer boundaries of the annulus, favoring the coupling of the disjoint interfaces. Mode-coupling analysis is employed to examine both linear and weakly nonlinear stages of the flow. Linear stability analysis indicates that the trailing and leading annular boundaries are coupled already at the linear regime, revealing that perturbations arising in the outer interface may induce the emergence of deformed structures in the inner boundary. Moreover, second-order weakly nonlinear analysis is utilized to identify key nonlinear morphological features of the ferrofluid annulus. Our theoretical results show that linear, n-fold symmetric annular patterns having rounded edges are replaced by nonlinear polygonal-like shapes, presenting fairly sharp fingers. It is found that, as opposed to the linear patterns, the nonlinear peaky structures reach a stationary state, characterized by a growth saturation process induced by nonlinear effects. Furthermore, the response of the ferrofluid ring to changes in the thickness of the annulus, in the relative strength of magnetic and surface tensions forces, as well as in the magnetic susceptibility of the ferrofluid material, are also discussed.

Plasmonic sensor for magnetic field detection with chalcogenide glass and ferrofluid materials under thermal variation in near infrared

In this paper, surface plasmon resonance based magnetic field sensor is simulated and analyzed in near infrared wavelength region (1557 nm) . The magnetic fluid is a colloidal material that can transform into different states depending on the strength of the external magnetic field (H). The structure of the sensor consists of chalcogenide (Ge 28 Sb 12 Se 60 ) prism, silver layer, graphene monolayer, and a magnetic fluid (ferrofluid) film. Analysis is carried out using temperature-dependent complex refractive index of graphene (as per Kubo formulation) and silver layer (as per phonon-electron and electron-electron scatterings) along with the thermo-optic effect in prism and ferrofluid media. Angular interrogation method has been used. An extremely fine detection limit of 0.0037 mT at room temperature can be achieved. As large magnitude of figure-of-merit (FOM) as 1.7263 (mT) −1 can be achieved with the proposed magnetic field sensor. High refractive index of Ge 28 Sb 12 Se 60 glass is helpful in ascertaining high spatial resolution while the non-linearity in Ge 28 Sb 12 Se 60 may not be an issue as a low power laser source is required for the practical implementation of the proposed magnetic field sensor scheme. • Chalcogenide glass and ferrofluid materials have been used in plasmonic sensor for magnetic field measurement. • Angular interrogation method is applied while utilizing graphene layer that acts as a protective layer atop Ag layer. • Effect of temperature in near infrared (1557 nm) is studied for sensing performance enhancement. • Proposed probe provides significantly large sensitivity and fine detection limit of magnetic field detection.

The magnetic switch manufacturing by using ferrofluid and ferrofluid doped copper nanoparticles

In this work, a magnetic switch was prepared using two typesof ferrofluid materials, the pure ferrofluid and ferrofluid doped with copper nanoparticles (10 nm). The critical magnetic field (Hc) and the state of magnetic saturation (Hs) were studied using three types of laser sources. The main parameters of the magnetic switch measured using pure ferrofluid and He-Ne Laser source were Hc(0.5 mv, 0.4 G), Hs (8.5 mv, 3 G). For the ferrofluid doped with copper nanoparticles were Hc (1 mv, 4 G), Hs (15 mv, 9.6 G), Using green semiconductor laser for the Pure ferrofluid were Hc (0.5 mv, 0.3 G) Hs (15 mv, 2.9 G). While the ferrofluid doped with copper nanoparticles were Hc (0.5 mv, 1 G), Hs (12 mv, 2.8 G) and by using the violet semiconductor laser the pure ferrofluid parameters were Hc(0.5 mv, 0.5 G), Hs (15 mv, 3.5 G) while the ferrofluid doped with coppernanoparticles are Hc (0.5 mv,1 G), Hs (15 mv, 3.3 G).

Enhancement of the Seebeck coefficient in ferrofluid based thermoelectric materials: A numerical study

It has been demonstrated that the thermocells, which contain ionically stabilized magnetic nanoparticles (ferrofluids) dispersed in aqueous electrolytes, show enhanced Seebeck coefficient. We have addressed this issue by deriving an analytic expression that relates the Seebeck coefficient to the chemical potential and its temperature derivative taking into account the nanoparticle’s intrinsic characteristics, i.e. magnetization and magnetic anisotropy. Mesoscopic scale modelling with the implementation of the Monte Carlo Metropolis algorithm has been performed on diluted assemblies of γ-Fe 2 O 3 and CoFe 2 O 4 nanoparticles – commonly used ferrofluid materials with different magnetic anisotropies and particle concentrations - to calculate the particle Seebeck coefficient at different temperatures. Importantly, our numerical results show enhancement of the Seebeck coefficient with the increase of the magnetic particle anisotropy and particle concentrations with a maximum that shifts to higher temperatures as the anisotropy increases. Our findings suggest that by tailoring the magnetic particle anisotropy, enhanced thermoelectric signal can be achieved in ferrofluid based thermoelectric materials.

A Dumb-Bell Shaped Damper with Magnetic Absorber using Ferrofluids

Damping devices are made up of ferrofluids which aid in strong magnetization and contribute greatly to minimizing magnetic vibrations. The most important and traditional applications of damping devices are used by ferrofluids and Nano magnetic materials. The combined effect of damping devices and ferrofluid materials show improved vibration minimization ratio. Here, it is observed that the basic damping device with ferrofluid materials consists of isolators, dampers, and absorbers. Moreover, novel dynamic isolation with absorption techniques is introduced in this paper. To obtain improved performance and efficiency of damping devices the use of isolators and vibration absorbers is suggested.

A Dumb-Bell Shaped Damper with Magnetic Absorber using Ferrofluids

Damping devices are made up of ferrofluids which aid in strong magnetization and contribute greatly to minimizing magnetic vibrations. The most important and traditional applications of damping devices are used by ferrofluids and Nano magnetic materials. The combined effect of damping devices and ferrofluid materials show improved vibration minimization ratio. Here, it is observed that the basic damping device with ferrofluid materials consists of isolators, dampers, and absorbers. Moreover, novel dynamic isolation with absorption techniques is introduced in this paper. To obtain improved performance and efficiency of damping devices the use of isolators and vibration absorbers is suggested.

Spheroidal and conical shapes of ferrofluid-filled capsules in magnetic fields

We investigate the deformation of soft spherical elastic capsules filled with a ferrofluid in external uniform magnetic fields at fixed volume by a combination of numerical and analytical approaches. We develop a numerical iterative solution strategy based on nonlinear elastic shape equations to calculate the stretched capsule shape numerically and a coupled finite element and boundary element method to solve the corresponding magnetostatic problem, and employ analytical linear response theory, approximative energy minimization, and slender-body theory. The observed deformation behavior is qualitatively similar to the deformation of ferrofluid droplets in uniform magnetic fields. Homogeneous magnetic fields elongate the capsule, and a discontinuous shape transition from a spheroidal shape to a conical shape takes place at a critical field strength. We investigate how capsule elasticity modifies this hysteretic shape transition. We show that conical capsule shapes are possible but involve diverging stretch factors at the tips, which gives rise to rupture for real capsule materials. In a slender-body approximation we find that the critical susceptibility above which conical shapes occur for ferrofluid capsules is the same as for droplets. At small fields capsules remain spheroidal, and we characterize the deformation of spheroidal capsules both analytically and numerically. Finally, we determine whether wrinkling of a spheroidal capsule occurs during elongation in a magnetic field and how it modifies the stretching behavior. We find the nontrivial dependence between the extent of the wrinkled region and capsule elongation. Our results can be helpful in order to quantitatively determine capsule or ferrofluid material properties from magnetic deformation experiments. All results also apply to elastic capsules filled with a dielectric liquid in an external uniform electric field.

Modeling of the temperature field of a tumor tissue loaded by magnetic nanoparticles

Background: Magnetic hyperthermia is a recent therapy used to treat cancer. It is based on the heating of magnetic nanoparticles under the effect of an alternating magnetic field. A mathematical study was considered the effect of heating magnetic nanoparticles to obtain an increase in the desired temperature while causing minimal damage to surrounding healthy tissue. We investigated the thermal response of different materials. An analytical resolution is proposed to solve the bio-heat transfer problem in a two-zone tissue in spherical geometry with blood perfusion and metabolism. Bio-heat equation is used to predict the temperature rise in terms of characteristics of the different magnetic nanoparticles (MNPs), applied magnetic field, and size of the tissue. Methods: The tumor is selectively loaded with magnetic nanoparticles of which are inside the healthy tissue, which does not contain nanoparticles. Under application of the magnetic field, the tumor will experience a rapid increase in temperature, which causes necrosis of the latter while healthy tissue remains safe. Results: Results of the thermal response of three ferro-fluid materials (fcc Fe Pt), magnetite and maghemite (volume fraction of MNPs p = 0.0001), on the tumor (size r =1[cm]) under application of alternating magnetic field (the strength and frequency of applied AC magnetic field H=10 [kA/m] and f=300 [kHz]) show an increase in temperature at the center, which vary from one material to another. It reaches 51°C for (fcc FePt); for magnetite and maghemite, it reaches 43°C. The simulations show that these nanoparticles provide the necessary power to conduct treatment with hyperthermia. The different parameters show that they have an influence on the temperature we observed, ranging from 45°C up to 51°C for volume fraction of MNPs E† = 0.00006, 0.00008, 0.0001. The strength of applied AC magnetic field varies as H= 5, 10, 15(kA/m) and shows significant variation for the temperature ranging between 42°C and 60°C. For the frequency of applied AC magnetic field varied as f=150,300, 450(kHz), the temperature varies between 44°C and 54°C. Finally, the effects of tumor size are considered, the temperature with parameters of (fcc FePt) MNPs, p=0.0001, H=10 (kA/m), and f=300 (kHz) at the center and at the interface of the tumor for a size of 10 mm radius is 51°C and 48°C, respectively. For a tumor of 5 mm radius, we note that the temperature decreases at 49°C and 47°C, which is due to the effect of blood perfusion. Conclusion: Theoretical evaluation of nanoparticles as warming agents for magnetic hyperthermia is carried out by combining the heat generating model and bio-heat transfer equation. Accordingly, (fcc FePt) MNPs were found to have a heat capacity greater than that of other MNPs such as magnetite. This study shows that each item contributes to a significant change in temperature, which causes us to determine the best to achieve optimal treatment. This therapy proves to be promoted with its ability to eliminate tumor tissue while preserving healthy tissue.

The effects of magnetic nanoparticle properties on magnetic fluid hyperthermia

Magnetic fluid hyperthermia (MFH) is a noninvasive treatment that destroys cancer cells by heating a ferrofluid-impregnated malignant tissue with an ac magnetic field while causing minimal damage to the surrounding healthy tissue. The strength of the magnetic field must be sufficient to induce hyperthermia but it is also limited by the human ability to safely withstand it. The ferrofluid material used for hyperthermia should be one that is readily produced and is nontoxic while providing sufficient heating. We examine six materials that have been considered as candidates for MFH use. Examining the heating produced by nanoparticles of these materials, barium-ferrite and cobalt-ferrite are unable to produce sufficient MFH heating, that from iron-cobalt occurs at a far too rapid rate to be safe, while fcc iron-platinum, magnetite, and maghemite are all capable of producing stable controlled heating. We simulate the heating of ferrofluid-loaded tumors containing nanoparticles of the latter three materials to determine their effects on tumor tissue. These materials are viable MFH candidates since they can produce significant heating at the tumor center yet maintain the surrounding healthy tissue interface at a relatively safe temperature.

Simulations of ferrofluid dynamics: Rigid dipoles model versus particles with internal degrees of freedom

For numerical studies of a ferrofluid dynamics we have developed a model which includes internal magnetic degrees of freedom of ferrofluid particles. Contrary to standard models, we take into account that the magnetocrystalline anisotropy of a ferrofluid particle material is finite, so that the particle moment is allowed to rotate with respect to the particle itself. Simulating magnetization relaxation of a ferrofluid after switching off the external field and comparing results with those obtained for rigid dipoles model, we demonstrate that for anisotropy typical for commonly used ferrofluid materials inclusion of ‘magnetic’ degrees of freedom is essential for a correct description of ferrofluid dynamics.

Langevin dynamic simulations of fast remagnetization processes in ferrofluids with internalmagnetic degrees of freedom

In this paper we present a model which allows numerical studies of ferrofluid dynamicstaking into account the internal magnetic degrees of freedom of the ferrofluid particles. Instandard ferrofluid models the magnetic moment of a ferrofluid particle is supposed to befixed with respect to the particle itself, which corresponds to the limit of an infinitelyhigh single-particle magnetic anisotropy. In contrast to this strongly simplifyingassumption, we take into account that in real ferrofluids the magnetic moments offerrofluid particles are allowed to rotate with respect to the particles themselves. Ourmodel results in a system of equations of motion describing both magnetic andmechanical degrees of freedom, where the ‘magnetic’ equations are coupled withthe ‘mechanical’ equations via (i) the interparticle distances determining themagnetodipolar interaction fields and (ii) orientations of the particle anisotropy axes withrespect to their magnetic moments which define the mechanical torque on theparticle.Using our model we have studied the ferrofluid magnetization dynamics for various particleconcentrations, i.e., for various magnetodipolar interaction strengths. In particular, wepresent numerical results (a) the magnetization relaxation of a ferrofluid after the externalfield is switched off and (b) the frequency dependence of the ferrofluid AC susceptibility.Comparing these results with the corresponding dependences obtained for the rigid dipolesmodel, we demonstrate that for magnetic anisotropy values typical for commonlyused ferrofluid materials (like magnetite) the inclusion of ‘magnetic’ degrees offreedom is qualitatively essential to obtain a correct description of the ferrofluiddynamics.

A novel magneto-optic ferrofluid material for sensor applications

The paper presents the synthesis and characterization of a novel ferrofluid magneto-optic material. A quantity of 100 ml was manufactured using the charge stabilized method, which proved to be very inexpensive (£ 0.15 per ml) and with very high Verdet constant of 122.43 × 10 3 rad T −1 m −1. As no linear birefringence was observed, this material is found to be particularly suitable for magneto-optic sensor applications where the presence of electric field is expected, such as detection of mains electrical current.

Pure Faraday rotator: a ferrofluid mixing method

We present a method for obtaining a pure Faraday rotator by using a ferrofluid material. We demonstrate indeed that compatible magnetic liquids can be mixed in suitable proportions so as to cancel the circular dichroism at selected wavelengths in the visible-near-IR spectrum.

A new and high precision achromatic ellipsometer: a two-channel and polarization rotator method

We present a new ellipsometric method that does not use a quarter-wave plate, an optical compensator, or a polarizing component rotating at a fixed velocity. The implemented set-up is very sensitive, even if reflected light is either circular or quasi-circular, i.e. when the apparatus works in the best conditions of accuracy (angle of incidence approximately equal to principal angle). Furthermore, the adjustment is made by rotating the polarizer only (maximum angle of rotation is less than a few tens of degrees), all other polarizing components being fixed. In the automatic set-up, the polarizer azimuth angle is locked on the ellipsometric angle ψ = arctan|rp/rs|. This ellipsometer uses a Wollaston or Foster prism and a highly efficient Faraday modulator, with water multipassed (visible region) or ferrofluid material (near-IR).

An AC magnetic field remote sensor using a ferrofluid material: application to the measurement of off-centring sleeves of HV transmission lines

The authors describe a remote and contactless AC magnetic field sensor using ferrofluid material. A practical application to the detection and measurement of the joints defects of HV cables is shown.