Magnetic Fluid Thin Film Research Articles

Optical relaxation properties of magnetic fluids under externally magnetic fields

The relaxation behavior (including the rising and falling relaxation processes) of the transmitted light after the magnetic fluid thin films under longitudinal and transverse magnetic fields is investigated, respectively. The physical mechanisms of the two different relaxation processes are discussed. The experimental data of the rising and falling relaxation processes are fitted by using two exponential functions to achieve the rising and falling response times. The relationship between the response time and the strength of applied magnetic field, the concentration of magnetic fluid is studied experimentally. The modulation depth of the transmitted light is researched quantificationally and the deepest modulation depth is obtained with Sample 3 (with volume fraction of 5.62%) in our experiments.

Temperature Dependence of the Optical Transmission of aMagnetic Fluid with an Applied Magnetic Field

The physical origin of the temperature dependence of the optical transmission of a magnetic fluid under an applied magnetic field is studied in this paper When a magnetic field is applied parallel to the plane of a magnetic fluid thin film, magnetic chains form in the same direction as the magnetic field, which suppresses the optical transmission. We observed that the optical transmission could be tuned by varying the ambient temperature of the magnetic fluid thin film. The design and the experimental results are also analyzed.

Melting of mesoscopic lattices of magnetic fluid thin film subjected to perpendicular fields

Applying a magnetic field on the magnetic fluid thin film perpendicularly, leads a phase separation that is concentrated in particles separating from a dilute phase. The concentrated phase forms cylindrical columns that construct two-dimensional lattices. This kind of artificial lattice is a novel mesoscopic system and has been explored with optical microscope, CCD, and digital imaging analysis. We explore the ordering evolution of the two-dimensional extraordinary lattice by varying the applied field. The ordering of these lattices is analyzed in terms of translational and bond-orientation correlation functions to address the two-dimensional melting.

Dynamic formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields

The application of a low-frequency oscillating magnetic field perpendicular to a magnetic fluid thin film leads to the separation of a phase that is concentrated in particles from a dilute phase. The concentrated phase forms cylindrical columns that construct two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for potential optical applications. We investigate the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields.

Ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields

Applying an oscillating magnetic field perpendicularly on the high-quality magnetic fluid thin film, the phase separation of particles in the liquid matrix will occur. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. The ordered structure of magnetic fluid thin films is the basis for the potential optical application. We explore the dynamical ordering formation of columnar lattices in magnetic fluid thin films subjected to oscillating perpendicular magnetic fields in this study.

On the origin of a structural grating in a magnetic fluid thin film under electric and magnetic fields

On the origin of a structural grating in a magnetic fluid thin film under electric and magnetic fields

Effect of initial states on the phase diagram of the structural pattern in magnetic fluid films under perpendicular magnetic field

When a magnetic fluid thin film is subjected to a magnetic field perpendicular to the plane of the film, a portion of magnetic particles is condensed out from the initially monodispersed magnetic fluid and forms magnetic columns. These columns evolve from a disordered column phase to a two-dimensional ordered structural pattern as the field strength reaches some critical value, Hh. The structural pattern formative process of the ordered structures that follows depends on the condition of the disordered column phase. In the letter, the effect of the initial disordered column phase, which can be altered by changing the initial field strength, Hi, on the formative process of the ordered structures is studied, and a phase diagram on the H–Hi plane is constructed. With an initial field strength that exceeds Hh, the structural pattern formative process goes through a plateau, a transition phase, and another plateau. On the other hand, if the initial field strength is less than Hh, the columns in the disordered column phase split and new columns emerge in the magnetic fluid film as the field strength increases. Finally, the structural pattern reaches a plateau. In both processes, the distance between columns in the structural patterns converges to that of a pseudostatic case.

Novel properties and applications in magnetic fluids

In this review, we will report a series of investigations on the homemade homogeneous magnetic fluids. The most spectacular property discussed in our research is the ordered structure of the magnetic columns formed in the magnetic fluid thin film under the influence of the external magnetic field, either perpendicular or parallel to the film surface. It is worth noting that the ordered structure can be manipulated by changing the control parameters. This reveals the variability of the ordered structure. With the ordered structures, some significant magneto-optical characteristics such as magnetochromatics, birefringence, and field-dependent transmittance are generated. These optical properties form the groundwork for further development of related optical devices by using the homogeneous magnetic fluid films.

Evidence of multiple states of ordered structures and a phase transition in magnetic fluid films under perpendicular magnetic fields

When a magnetic fluid thin film is subjected to a perpendicular magnetic field H, the particles in the film agglomerate and form particle columns. With the increasing H, the columns evolve from a disordered column phase to the first-level hexagonal structural pattern and finally reach the second-level hexagonal structural pattern through a phase transition. During the transition phase, each column split into two columns. The split of a column may be attributed to the further alignment of the magnetic particles in each column under higher H’s. Hence the dipolar repulsive force in each column becomes dominant and causes the split of a column. The formation of the second-level hexagonal structure reveals that the minimum energy of the equilibrium system of magnetic fluid thin films under perpendicular magnetic fields has multiple local minima when H varies.

Behavior of the magnetic structures of the magnetic fluid film under tilted magnetic fields

The patterns of the magnetic structure of the magnetic fluid thin film under tilted magnetic fields were taken to investigate the behavior of magnetic structures. The tilted angle θ is the angle between the direction of applied magnetic field and the normal line of the film. In our previous work, a nearly perfect ordered hexagonal structure in magnetic fluid thin film was obtained when a perpendicular magnetic field (θ=0) was applied. By increasing θ, each column in the hexagonal structure gradually tilted to reveal a lattice of segments instead of dots on the pattern with an unchanged lattice distance d. As θ exceeding a critical value θc, these segments began to form longer periodic chains with an abrupt increasing of d. Hence, a transition from the magnetic hexagonal structure to a periodic chain structure at θc existed for magnetic fluid thin film in which the θc decreases exponentially as the sweeping rate increases.

An experimental study of light modulator using magnetic fluid for display applications

A new type of light modulator using magnetic fluid has been studied experimentally. The operation principle and design of the modulator are addressed. It is shown that the luminance of the device can be modulated by applying an electric current to the light-reflecting metal electrode. A high contrast ratio was obtained using a magnetic fluid thin film with a saturation magnetization of 196 G and a thickness of around 20 μm. Doubling of the luminance level from a minimum value takes about 200 ms for a driving current of 80 mA.

Magneto-chromatic effects of tunable magnetic fluid grating

The ordered structures in Fe3O4 kerosene-based magnetic fluid films were discovered and the magneto-chromatic effects were also observed under various magnetic fields. In this report, we studied the relationship between the ordered structures and the magneto-chromatic effects theoretically and experimentally. The nearly perfect hexagonal structures with the distance between two columns d in μm range for our magnetic fluid thin films offer a two-dimensional tunable magnetic fluid grating in the visible light region. By using a grating model, the diffraction patterns for visible lights at certain incident angle θ, wavelength λ, and column distance d, were calculated. Experimentally, it was found that the conditions of the observed light around the direction perpendicular to the plane of film coincide with the calculated results. Therefore, the magneto-chromatic effects resulting from the ordered structures of the tunable magnetic fluid grating were confined.

Magnetochromatic effects in magnetic fluid thin films

A homogeneous ferrofluid composition capable of reversiblyforming ordered crystalline two-dimensional hexagonal lattices ofmagnetic particle columns in a thin film under the influence ofexternal magnetic fields has been synthesized. We can manipulatethe spacings between the particles columns by adjusting parameters suchas external magnetic field strength, film thickness, rate of change ofthe field strength, and concentration of magnetic particles in theferrofluid. These spacings between particle columns are of theorder of several micrometers and are capable of diffracting visiblelight to produce monochromatic interference colors. We can changethe resulting colors by altering the lattice spacing to exhibit thefeasibility of generating monochromatic colors.

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.

Magnetic Birefringence and Dichroism in Magnetic Fluid

The magneto-optical effect in magnetic fluids is investigated. The phase difference ? between the ordinary ray and the extraordinary ray transmitted through the magnetic fluid thin film, was found to be described by the functional form ? 1 f(H)/[T-T 1 +f(H)], where H is the magnetic field applied to the magnetic fluid film, T is the absolute temperature of the film, f(H) is a certain increasing function of H, and T 1 and ? 1 are positive constants. The field dependence of the optical transmissivity of magnetic fluid thin films is well described by the cluster model of ferrous colloidal particles in the applied field direction when the aggregation is small. The field dependence of transmissivity is, however, explained neither by the electric absorption of the clusters, nor by the Rayleigh scattering when the cluster becomes larger. The effect of diffraction by linear clusters oriented by the applied field must be taken into account in explaining the optical extinction.

Magneto-optical absorption in infrared region for magnetic fluid thin film

The magnetic field and wavelength dependences of the optical absorption coefficient, alpha , were measured in the infrared range for magnetic fluids containing Fe/sub 3/O/sub 4/ or MnZn ferrite particles. The absorption in the absence of magnetic fields is due mainly to the magnetic particles themselves. With increasing applied magnetic field, Delta alpha decreases for the ordinary ray and increases for the extraordinary ray. This magnetic field dependence is attributed to the formation of chainlike clusters of a few colloidal particles (microclusters) whose length is much shorter than the wavelength of the infrared ray. In the Mn-Zn ferrite magnetic fluid, Delta alpha for the ordinary and extraordinary rays increases gradually after a magnetic field is applied. The time dependence is caused presumably by growth into macroclusters whose length is comparable with the wavelength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamical properties of magneto-optical effect in magnetic fluid thin films

The dynamical properties of the magneto-optical effects of magnetic fluids thin films were investigated. The thin films, 12 μm thick, of magnetite colloidal particles in water solvents and alkylnaphthalene one were prepared. A pulsed magnetic field H(t) was generated in a single turn coil by discharging a 40-kV capacitor bank. The intensity I(t) of the transmitted light through the two crossed polarizers and the films located in the coil was measured. The relaxation process of the magneto-optical effect can be described in terms of a single relaxation time, τ=3 μs, for a water-based magnetic fluid, while the relaxation time constant for alkylnaphthalene one depends on the field strength. These dynamical properties can be interpreted by the time-dependent Ginzburg–Landau theory by introducing the order parameter of the colloidal particles.

磁性流体の磁気複屈折と二色性

The magneto-optical effect in magnetic fluids is investigated. The phase difference ? between the ordinary ray and the extraordinary ray transmitted through the magnetic fluid thin film, was found to be described by the functional form ? 1 f(H)/[T-T 1 +f(H)], where H is the magnetic field applied to the magnetic fluid film, T is the absolute temperature of the film, f(H) is a certain increasing function of H, and T 1 and ? 1 are positive constants. The field dependence of the optical transmissivity of magnetic fluid thin films is well described by the cluster model of ferrous colloidal particles in the applied field direction when the aggregation is small. The field dependence of transmissivity is, however, explained neither by the electric absorption of the clusters, nor by the Rayleigh scattering when the cluster becomes larger. The effect of diffraction by linear clusters oriented by the applied field must be taken into account in explaining the optical extinction.

Magnetooptical Effects of Magnetic Fluid

Magnetooptical effects of magnetic fluid thin film are experimentally investigated. Thin films made of magnetic fluid exhibit different transmissivities for the light differently polarized relative to the direction of the magnetic field H applied along the film surface. The phase difference θ induced by the magneto-birefringence increases with H . The function θ of H is reduced to a universal function f u ( x ) irrespective of the magnetic fluids' characteristics by scaling transformation. The initial behavior of θ is proportional to H . The same scaling transformation of the magnetization curve leads to fit f u ( x ). The temperature dependence of θ obeys the Curie-Weiss law 1/( T - T 0 ). The formation of linear chain-like cluster of a few colloidal particles explains experimental results of the dichroism and the birefringence fairly well.

Magnetic Fluid's Anomalous Pseudo-Cotton Mouton Effects about 107 Times Larger than That of Nitrobenzene

The magneto-birefringence of magnetic fluid thin films of 12 µm and 25 µm were studied and anomalous phase differences were found when an external magnetic field was applied normal to the direction of light propagation. The order of the phase differences of the films was about 107 times larger than that of nitrobenzene, which is known to show a large Cotton-Mouton effect. We attribute these phenomena theoretically to a rod-like chain formation of the ferrite particles in the magnetic fluid thin films and derive expressions for the phase difference and absorption. There is a definite difference in the H-\\vartheta curves between theory and experiment in the rising gradient near H=0.