Birefringence In Magnetic Fluids Research Articles

Optical fiber magnetic field sensor based on birefringence in liquid core optical waveguide

An optical fiber magnetic field sensor based on the birefringence of magnetic fluid is proposed by filling the magnetic fluid into a hollow-core waveguide. The birefringence characteristics of magnetic fluids with different concentrations tuned by magnetic field were investigated under different magnetic fields when the filled hollow-core waveguide is placed in a Sagnac loop. As the magnetic field increases, the internal chain-like structure of the magnetic fluid increases, resulting in changes in birefringence. The experimental results show that the device has a highly linear response to the variation of magnetic field intensity in the range of 0–300 Oe with the maximum sensitivity of 29.2 pm/Oe and resolution of 0.68 Oe. The proposed magnetic field sensor has such advantages as ease of fabrication, simple structure, low cost and it is expected to find potential applications in the magnetic field measurement with high accuracy, optical fiber gyroscopes, magneto-optic modulators and so on. Due to the external field tunability, the device also provides a promising technology for microfluidics research.

Theoretical Analysis and Experimental Measurement of Birefringence Properties in Magnetic Fluid Subjected to Magnetic Field

In this paper, the birefringence properties of the magnetic fluid exposed to magnetic field at 300 K were studied by simulation and experimental measurement. In addition, the arrangement of magnetic particles in the magnetic fluid was simulated using Monte Carlo method, and was verified by the experiment. It was concluded that the change of birefringence is influenced by the anisotropy of the magnetic fluid microstructure in the magnetic field. In addition, the sensitivities of the birefringence in simulation and measurement were $1.2245\times 10^{\mathrm {\mathbf {-5}}}$ /Gs and $4.4\times 10^{\mathrm {\mathbf {-6}}}$ /Gs, respectively, when the magnetic field intensity was in the insensitive interval of 0–300 Gs. In summary, the birefringence of magnetic fluid would increase with the increasing magnetic field intensity, and vice versa. This research on the birefringence characteristics of magnetic fluid could be used in the optical sensing technology.

Birefringence Measurement for Magnetic Fluid Film Using Optical Fiber System

Birefringence was a significant parameter of an optical material in optical area. Compared with the traditional birefringence measurement method, a novel birefringence measurement method of magnetic fluid using optical fiber was proposed in this letter. The measurement error induced by the alignment and the optical loss over the space optical path was effectively reduced. Moreover, it was stability, strong resistance to disturbance, easy assembly, and achievement. Simulation and experiment were carried out to prove the effective of the novel measurement system, and the magnetic fluid birefringence induced by an external magnetic field was measured. In addition, the birefringence of magnetic fluid was from 0 to 1.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> in the range of 0-600 Gs. In addition, when the magnetic field was from 0 to 200 Gs, the sensitivity of magnetic fluid birefringence was 1.25 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> /Gs; when the magnetic field was from 200 to 500 Gs, the sensitivity downgraded to 0.26 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> /Gs. It has a great potential for the application of magnetic fluid birefringence in the optical sensing area.

On the theory of birefringence in magnetic fluids

The influence of homogeneous correlations between the positions and orientations of ferroparticles on the effect of light birefringence in magnetic fluids has been studied. It has been demonstrated that, for typical magnetic fluids, the optical effects associated with the homogeneous correlations can be stronger than the effects caused by elongated primary aggregates formed at the stage of ferrofluid synthesis, as well as heterogeneous chains resulting from magnetic attraction between the largest particles of a magnetic fluid.

环境温度对纳米磁流体场诱导光学双折射的影响

The relationship between the birefringence of Fe3O4 magnetic fluids and the ambient temperature(in the range of 20~80 ℃)at several different magnetic field strengths(lies in 0~200 mT)are investigated.The results show that similar dependence of birefringence on magnetic field strength and temperature happens for magnetic fluids with different concentrations.Moreover,the birefringence of the magnetic fluid is inversely proportional to the ambient temperature at fixed magnetic strength and proportional to the magnetic field strength at fixed ambient temperature.In a given temperature and magnetic field strength,the birefringence of the magnetic fluid with high concentration is larger than that with low concentration.The phenomena and results are analyzed carefully and the physical mechanism is clarified in detail.

Birefringence of maghemite-based magnetic fluid in the highly concentrated regime

The transmitted light intensity of a series of ionic magnetic fluid samples based on maghemite nanoparticles was investigated using the typical birefringence experimental setup. The field dependence of the transmitted light intensity evolves from a peak-like profile to a typical second-order Langevin profile as the nanoparticle volume fraction reduces from 2.4% to 0.9% volume fraction. The onset of the peak-like profile as the nanoparticle volume fraction increases is accounted for by two points, namely the transmitted light first scales with a sine function and second the birefringence signal appears in the argument of the sine function. The observed negative differential transmitted light is explained as one brings the above-mentioned sine dependence into the nowadays used model for the analysis of birefringence in magnetic fluids.

Dynamic birefringence in magnetic fluids with allowance for mechanical and magnetic degrees of freedom of the particles

Dynamic field-induced birefringence in magnetic fluids is studied with the aid of the generalized Fokker–Planck equation that takes into account both internal (magnetic) and external (mechanical) orientational motions of the particles. The solution found accounts for the variety of cases and unites several former models.

Experimental evidence of monomer contribution to the static magnetic birefringence in magnetic fluids

Manganese–ferrite and nickel–ferrite ionic magnetic fluids (MFs) were investigated using static magnetic birefringence (SMB). Transmission electron microscopy (TEM) was used to obtain the particle diameter polydispersity profile of the MF samples. The model used in the present study to fit the SMB data includes the field dependence of the magnetic permeability associated to the magnetic structures (incoherent monomer and dimer) and allowed estimation of the magnetic surface anisotropy. The combined analysis of the SMB and TEM data support the contribution of incoherent monomer to the SMB signal in MFs and allows the estimation of its characteristic diameter. It was found that the incoherent monomer diameter is sensitive to the nanoparticle nature. Finally, the surface anisotropy depends upon the nanoparticle diameter and falls within the range of 0.1–1.5 erg/cm2.

Zero-field birefringence in magnetic fluids: Temperature, particle size, and concentration dependence

The temperature, particle size, and particle concentration dependence of the zero-field birefringence were investigated using γ-Fe2O3 and MnFe2O4 ionic magnetic fluids in the range of 290–350 K. Upon heating a sample from below its characteristic temperature Tc, which depends upon the particle size and particle concentration, the zero-field birefringence goes critically down to zero. The experimental data are successfully explained when the following two points are considered in the model describing magnetic birefringence in magnetic fluids. First, dimers rather than monomers are responsible for the zero-field birefringence. Second, thermal disruption of the dimer structure follows a critical behavior. A theory for the zero-field birefringence is developed using classical statistics to evaluate the orientational order tensor component Szz. Finally, the zero birefringence signal at zero field, as found in magnetic fluids containing surfactant on the particle surface, is discussed within the dimer model.

A scaling model for the optical anisotropy in magnetic fluids: dichroism and birefringence

A simple scaling model for dichroism and birefringence in magnetic fluids is proposed. This scaling is based on two physically measured quantities, i.e. the initial slope of the optical anistropy curve with magnetic field, and the saturation value of dichroism or birefringence. Using this model, the isothermal dichroism and birefringence are superimposed into a single function. This model is discussed and compared with one similar to that proposed for the magnetization of a superparamagnetic particle system.

Interaction effects on magneto-optical birefringence in magnetic fluids

Measurements of the magneto-optical birefringence (Δn) and the magnetisation curves in magnetite fluids are reported. The variation of Δn with H2, which is not linear at low fields, is found to arise from particle interactions. Also the effect of magnetic filtration on magnetisation curves and birefringence is studied.

Carrier and chain formation dependence of birefringence in magnetic fluids

Measurements of the birefringence in Fe 3O 4 magnetic fluids were undertaken in the temperature range 190–313 K in magnetic fields up to 0.7 kOe. Our results show that the birefringence increases with temperature exhibiting a maximum near the melting point, T m, of the liquid carrier (kerosene, decalin and Isopar M). For T > T m the birefringence follows a generalized Curie-Weiss law yielding positive ordering temperatures for the three samples. Moreover, our results show that the birefringence behaves irreversibly with temperature, in the decalin based sample. The results also show that the magnitude of the birefringence and the shape of the maximum change with the applied magnetic fields.

Temperature and Concentration Dependence of Magnetic Birefringence of Magnetic Fluids

It was found experimentally that the magnetic birefringence of magnetic fluid thin films obeys a Curie-Weiss like law for all kinds of magnetic fluids except for a water-based one. The birefringence can be described by θ( T , H )=θ a f ( H )/[ T - T a + f ( H )], where θ( T , H ), H and T are the phase difference, the applied field and the temperature of the film, respectively, and θ a is a positive constant. T a and f(H) are also found to be expressed empirically by T a = T 0 +κ ln c , f ( H )=1-exp [-α( c ) H ], respectively, where c is a volume fraction of the colloidal particles, T 0 , κ are positive constants and α( c ) is a function of c . Taking the empirical expression of θ into consideration, the free energy of the magnetic fluid is discussed using Landau's phase transition theory.