Uniaxial Films Research Articles

Analysis of angular-selective performances of obliquely deposited birefringent thin film

A slanted columnar TiO2 sculptured anisotropic thin film is prepared using the glancing angle deposition (GLAD) technique. We extend the inference regarding the optical properties of a uniaxial birefringent film based on theoretical analysis to include the more general case of a multilayer biaxial birefringent thin film, the optic axis of which is in the incident plane. We also investigate in detail the symmetrical angularselective transmittance performances of TiO2 biaxial anisotropic thin films for light incident at the same angle but coming from opposite sides of the surface normal. The tilted nanocolumn microstructures of the birefringent thin films induce optical anisotropy. The transmisson spectra for the p-polarized wave of TiO2 biaxial anisotropic thin film measured in the experiment almost overlap at the symmetrical oblique incidence at the ±0 angles, which validates our theoretical derivation.

Theory of magnetic domains in uniaxial thin films

For uniaxial thin films, properties of magnetic domains are usually described within the Kittel model, which assumes that domain walls are much thinner than the domains. In this work we present a simple model that includes a proper description of the magnetostatic energy of domains and domain walls and also takes into account the interaction between both surfaces of the film. Our model describes the behaviour of domain and wall widths as a function of film thickness, and is especially well suited for the strong-stripe phase. We prove the existence of a critical value of magneto-crystalline anisotropy above which stripe domains exist for any film thickness and justify our model by comparison with exact results. The model is in good agreement with experimental data for hcp cobalt.

Simulating the Emission Properties of Luminescent Dyes within One-Dimensional Uniaxial Liquid Crystal Microcavities

We have developed a simulation method which is capable of simulating the emissive properties of luminescent dyes inside uniaxial anistropic thin film microcavities[1]. The method uses plane wave decomposition of the electric field of a dipole antenna in a uniaxial medium and a scattering matrix formalism to account for interference and reflection from the various interfaces in the device. We apply this method to simulate the excitation of waveguide modes in a slab waveguide formed by reorientation of a liquid crystal. We investigate the emission both outside the device and into waveguided modes inside the liquid crystal device.

Magnetic anisotropy in epitaxial Mn5Ge3films

High crystalline quality Mn 5 Ge 3 films with thicknesses ranging 4–200 nm have been grown on Ge(111) substrates by solid phase epitaxy. The basal hexagonal plane of Mn 5 Ge 3 is in epitaxy with the Ge(111) plane. Magnetic properties of the films have been investigated as a function of the film thickness and the magnetization curves have been analyzed using a theory that includes a description of magnetic domains in uniaxial thin films. The results clearly indicate the existence of a critical thickness below which the magnetic stripe phase disappears. We have determined the value of this thickness to lie between 10 and 25 nm from the analysis of experimental magnetization curves and the theoretical fit of the in-plane remanent magnetization. Although analogies can be drawn between the behavior observed in our system and that of hcp Co, we have shown that the critical thickness is considerably smaller in Mn 5 Ge 3 ; this has the potential to open new fields of applications for Mn 5 Ge 3 thin films in magnetic recording and spintronics.

Magneto-Optic Fraunhofer Diffraction on 2D Magnetic Domain Patterns

Magneto-optical Fraunhofer diffraction on phase 2D domain patterns with Cmm6 and Pab2 symmetry in uniaxial iron garnet films was studied. Domain patterns contain more than 100 elementary cells and have high spatial homogeneity. The diffraction patterns contain up to 10 or more orders of peaks. Possibilities of space-time modulation of optical radiation and multiplication of the modulation frequency both under change of diffraction order as well as amplitude of magnetic bias field strength were shown.

Bifurcation magnetic resonance in films magnetized along hard magnetization axis

We study low-frequency ferromagnetic resonance in a thin film magnetized along the hard magnetization axis performing an analysis of magnetization precession dynamics equations and numerical simulation. Two types of films are considered: polycrystalline uniaxial films and single-crystal films with cubic magnetic anisotropy. An additional (bifurcation) resonance initiated by the bistability, i.e. appearance of two closely spaced equilibrium magnetization states is registered. The modification of dynamic modes provoked by variation of the frequency, amplitude, and magnetic bias value of the ac field is studied. Both steady and chaotic magnetization precession modes are registered in the bifurcation resonance range.

TN-LCD 광학보상을 위한 Biaxial Film의 이론적 해석

In this paper, we have studied on the optimal design of the optical compensation film for the TN-LCDs. To have wide viewing angle panels, several methods such as multi-domain method, optical path method, and phase compensation method have been proposed. Among these methods, this paper focused on the phase compensation method. In the phase compensation method, the phase retardation generated from the optical birefringence for the off-axis incident is compensated by using optical films with refractive anisotropy. To compensate the phase retardation of the TN-LCDs, we have proposed design concept for the biaxial optical films and analyzed the optical performance for the proposed structures. The calculation of the dynamic motion of the liquid crystals was based on the Ericksen-Leslie theory and the optical performance of the TN-LCD was calculated from the Extended Jones Matrix Method. From the results, we have confirmed that the optical characteristics of the TN-LCDs with the biaxial films have been improved considerably compared with the TN-LCDs compensated by the combination of the uniaxial films.

Control of Magnetic Moment in Uniaxial Anisotropy Magnetic Thin Film Taking Leakage Flux in RF Planar Spiral Inductors with Closed-Magnetic Core into Account

Control of Magnetic Moment in Uniaxial Anisotropy Magnetic Thin Film Taking Leakage Flux in RF Planar Spiral Inductors with Closed-Magnetic Core into Account

Local field anisotropy in Langmuir-Blodgett films of cadmium arachidate

Lorentz tensor and local field tensor components for uniaxial Langmuir-Blodgett films of cadmium arachidate from 3 to 100 nm thick on silver, polymethyl methacrylate, and glass substrates have been experimentally determined using the data on the film refractive index dispersion in the visible range. The constraints from below on the mean value and anisotropy of the molecular polarizability caused by the intermolecular interactions in the film have been established.

Effect of surface anisotropy on the dynamic properties of Néel domain walls in the films with planar anisotropy

This work is devoted to the investigation into the effect of surface magnetic anisotropy on the motion of domain walls in magnetic uniaxial films with an in-plane anisotropy in the range of thicknesses corresponding to the stability of one-dimensional Neel walls. It has been established that the surface anisotropy with a constant K s > 0 (K s < 0) increases (decreases) the velocity of both stationary and nonstationary motion of the domain wall, as well as the period of oscillations of the velocity of nonstationary motion. The magnitude of the critical field as a function of K s has been determined. Effect of surface anisotropy with K s < 0 on the scenario of the dynamic transformation of the domain-wall structure has been revealed.

Collapse of hard-axis behavior in uniaxial Co films

Collapse of hard-axis behavior in uniaxial Co films

Nanoscale phase separation in quasi-uniaxial and biaxial strained multiferroic thin films

Nanoscale phase separation was investigated in epitaxial strained BiFeO3 thin films on LaAlO3 single crystal substrate. In biaxial strained thin films, nanoscale mixtures of the tetragonal-like and rhombohedral-like phases occur with a film thickness above 35 nm. For 10-30 nm ultrathin ones, tetragonal-like single phase is confirmed using synchrotron x-ray and the atomic force microscopy studies. However, nanoscale phase separations are still observed in quasi-uniaxial transmission electron microscopy foil specimens for those ultrathin films, indicating the phase separation emerges in a much smaller thickness in uniaxial constraint films than that in biaxial ones.

Anisotropy of the local field in anisotropic films of conjugated polymers

Using the data on dispersion of refractive indices in the visible region, the experimental values of the components L j of the Lorentz tensor have been obtained for uniaxial (crystalline, oriented on a substrate, and stretched) films of conjugated polymers from nanometer to micrometer thicknesses. The dependence of the components L j on the axial and planar orientations of macromolecules with respect to the optical axis of the film, technology of fabricating the films, and chemical structure of macromolecules has been elucidated. The correlation between the components L j and the measured parameter η has been determined and the analytical dependence L j (η) for films with both types of macromolecular orientation has been established. In the visible region (0 ≤ η ≤ 0.5), the presence of one point (η = 1/3) of isotropization of the tensor L and three points (η = 0, 1/3, and 0.5) of isotropization of the local field tensor f has been revealed. The point η = 1/3 of isotropization of the tensors L and f has been determined. A comparison has been made between the values of L j (η) with predictions of known models of the local field for conjugated polymers.

Ferromagnetic resonance and bistability field in a uniaxial magnetic film

Peculiarities of ferromagnetic resonance (FMR) corresponding to bias along the “hard” magnetic axis of a film with 2D uniaxial anisotropy are studied based on numerical solution of magnetic moment dynamics equations. It is shown that an additional resonance peak is formed in the FMR spectrum in the vicinity of “bistability field” Hb. The dependence of this field on the amplitude of the microwave field and damping parameters is analyzed.

Control of the principal refractive indices in biaxial metal oxide films

We provide both an extensive experimental characterization and a model for metal oxide, slanted columnar thin films fabricated using glancing angle deposition. The model is applicable to slanted posts of any type, deposited at a constant deposition angle, with variable azimuthal substrate rotation. The model is capable of predicting the column tilt, principal refractive indices, and in-plane birefringence under a single unified framework, given knowledge of common material parameters. This paper also establishes a number of additional important results, including the occurrence of negative in-plane birefringence and the occurrence of uniaxial films with nonzero columnar tilt.

Role of dopants on the electro-optic effect in nematic liquid crystals aligned with doped polypyrrole

In order to estimate electro-optical response times, measurements of the transmitted light intensity through positive uniaxial nematic thin films in planar alignment have been performed. Very fast relaxation times were experimentally found for nematic samples aligned with conductive polymers, namely, polypyrrole doped with 5 types of anions having different molecular sizes and geometries. Using undoped polypyrrole alignment layers, slower electro-optical responses were obtained. Given that the improvement in the relaxation times is induced by the presence of the anions in the polypyrrole films, the increasing of the total restoring torque of the nematic molecules to the confining surfaces—responsible for the short relaxation times—is related to the charges accumulated at the nematic-conductive polymer interface.

Low-frequency ferromagnetic resonance in a uniaxial magnetic film

The equations of the precession dynamics of the magnetic moment have been analyzed to study the specific features of the low-frequency ferromagnetic resonance corresponding to magnetic biasing along the hard magnetic axis of a film with an in-plane uniaxial anisotropy. It has been found that the precession trajectories exhibited a complicated hopping behavior and the resonance curve was asymmetric. This behavior and the asymmetry were due to an angular bistability arising from the presence of two symmetric angular positions of equilibrium near the anisotropy field.

Evidence of Rouse-like dynamics in magnetically ratchetting colloidal chains

We study the collective dynamics of an ensemble of paramagnetic particles organized as a 1D chain and driven by an a-thermal ratchet effect on a uniaxial garnet film. The centre of mass of the chain shows diffusive behavior with mean square displacement ∼t, while its end-to-end distance shows anomalous (sub-diffusive) kinetics growing as . We extract the potential of mean force between the particles within the chain by invoking the Pope–Ching equation. We interpret the experimental data using the Rouse model, originally developed for polymers, and experimentally extract all relevant parameters.

Hysteresis loop design by geometry of garnet film element with single domain wall

Numerical modeling and experimental investigation of magnetostatic stable states of two-domain structure in Bi-substituted uniaxial garnet film elements was made. Single domain walls (DW) between two opposite normally magnetized parts in isolated rectangular strip and strip-like bridge are found to exhibit different behavior. DW inside strip (bridge) suffers increasing repulsion (attraction) from nearest edge when shifted from element center. DW position center position is stable in isolated strip but bridge is magnetized spontaneously to one of two saturated states in zero external field. Isolated strip magnetization process occurs reversibly while bridge magnetization reversal occurs by coercive manner. Strip susceptibility and bridge coercive field are entirely defined by magnetostatic barrier created by element boundary stray field in case of constant DW length during magnetization reversal. Variation of strip and bridge boundary shape along DW trajectory gives the opportunity to create additional controllable potential profile due to DW surface energy modulation by DW length. Garnet elements with high Faraday rotation and low light switching field were developed for fine magnetic sensing and optical data processing applications.

Specific features in precession dynamics of magnetization of a uniaxial magnetic film

The precession dynamics of the magnetization of a film with in-plane uniaxial anisotropy in the case of its biasing along the hard magnetization axis has been analyzed by numerically solving the Landau-Lifshitz equations. It has been revealed that the ferromagnetic resonance spectrum near the magnetic anisotropy field exhibits an additional peak, which is associated with the angular bistability due to the presence of two symmetric angular equilibrium positions. The trajectories of precession motion during biasing along the hard magnetization axis differ substantially from the trajectories corresponding to the biasing along the easy axis.