Jaekyong Cho

Magnetooptic Spatial Light Modulator for Volumetric Digital Recording System

A novel reflective magnetooptic spatial light modulator has been fabricated and its dynamic switching testing was investigated. Improvements by a factor of three in pixel switching sensitivity and power consumption could be achieved by the use of a wedge-shaped drive line, compared to the use of a conventional reflective magnetooptic spatial light modulator. Simpler fabrication processes by a factor of two could also be achieved by the use of a drive line which covers most of the surface of the pixel, a non-rectangular channel and a unpatterned insulator layer.

Effects of groove depth and patterned permalloy film on magnetization switching of LPE-garnet pixels for use in magneto-optic spatial light modulators

Effects of pixel groove depth and patterned permalloy assist film for the magnetization switching of LPE-garnet film were studied experimentally. The results showed that the magnetization field to switch a structured pixel could be reduced by controlling the pixel groove depth. It was also found that the permalloy assist film creates a unique pair-domain pattern within a single garnet pixel, which is useful for realizing a new type of magneto-optic spatial light modulator with high resistivity to noise.

Large Kerr rotation in ordered CrPt3 films

CrPt3 films have been prepared by depositing Cr/Pt multilayers using a magnetron sputterer followed by heat treatment. Small and wide angle x-ray diffraction diagrams, magnetic hysteresis loops, and Kerr rotation angle spectra of the films have been investigated. The films had AuCu3 type ordered alloy structure and strong and weak preferred orientation of {111} and {100} planes parallel to the film surface. It was found that CrPt3 films showed the perpendicular magnetic anisotropy to the film surface, large coercivity of 3.7 kOe, and maximum Kerr rotation angle of 0.65 degrees at about 1100 nm. The origin of the large Kerr rotation was discussed.

FERROMAGNETIC (LASR)MNO3 FILMS DEPOSITED BY RF SPUTTERING

We prepared polycrystalline films of perovskite-type lanthanum manganese oxide La1-xSrxMnO3 (0≤x≤1) by RF diode sputtering, and investigated their structural, magnetic and magneto-optical properties. Crystalline films were easily grown during sputtering at relatively low substrate temperature (≥170°C). The films as crystallized in situ were poorer in crystallinity, and much smaller in saturation magnetization compared to bulk samples. By annealing the films in O2 atmosphere above 900°C, the saturation magnetization increased and approached the values of bulk samples. Magnetization was aligned perpendicular to the film plane when the film with x=0.21 (which was sputter-deposited in mixed gas of Ar:O2=9:1 on a GGG substate at 500°C) was annealed in air at 800°C. Faraday rotation F and ellipticity X increased at higher photon (hv) energy range. F of the film annealed in O2 atmosphere at 900°C formed a peak at hv=2.9 eV, reaching -2.6×104 deg/cm. X of the film reached -5.0×104 deg/cm at hv=3.1 eV. The lanthanum manganese oxide film is a candidate for magneto-optical recording media using Kerr effect at short wavelength.

Structural and Magneto-Optical Properties of Bi-Substituted Garnet Films Prepared by Pyrolysis from Organic Solution

Bi1.5Dy1.5Fe4AlO12 films were prepared by pyrolysis from acetylacetonic solution of metal nitrates. The solution was chemically stable and had good wettabiiity on glass substrates without any surface pretreatment. Film structure and the shape of the Faraday rotation hysteresis loop markedly depended on drying conditions, especially on the initial temperature Ti of the drying process. The best Ti was 130°C. The crystallized film dried at Ti=130°C had crystalline grains uniform in size (diameter ~0.5 µm) and exhibited Faraday rotation hysteresis loops with an excellent squareness and a large coercive force (1.7 kOe).

New drive line shape for reflective magnetooptic spatial light modulator

A new drive line for a reflective magnetooptic spatial light modulator was designed using three-dimensional electromagnetic field simulation and its prototype device was fabricated. The new reflective magnetooptic spatial light modulator using a wedge-shaped conductor has a simple fabrication process and could achieve almost 100% window efficiency and one-third the driving current, compared to the conventional reflective magnetooptic spatial light modulator.

Structural, morphological, and mechanical properties of amorphous carbon and carbon nitride thin films deposited by reactive and ion beam assisted laser ablation

Amorphous carbon nitride thin films have been prepared on Si (100) wafers by nitrogen ion beam assisted Nd:YAG laser ablation techniques. Amorphous carbon and carbon nitride films have also been prepared by the conventional laser ablation techniques for comparison. Raman spectroscopy and spectroscopic ellipsometry have been performed for the films to analyze structural properties, atomic force microscopy to observe surface morphologies, and scratch, acoustic emission, and Vicker hardness test to examine mechanical properties. The amorphous carbon nitride films deposited by the ion beam assisted laser ablation techniques had generally better mechanical properties compared to the amorphous carbon films and amorphous carbon nitride films deposited in N2 atmosphere. The amorphous carbon nitride films deposited at optimum ion beam current of 10 mA and laser power density of 1.7 × 109 W/cm2 showed excellent mechanical properties: root mean square surface roughness of 0.33 nm, friction coefficient of 0.02–0.08, the first crack and critical load of 11.5 and 19.3 N respectively, and Vicker hardness of 2300 [Hv]. It is considered that the films have high potential for protective coatings for microelectronic devices such as magnetic data storage media and heads.

Magnetic and magneto-resistive properties of Bi-doped (LaCa)MnO3

Bi-doped lanthanum manganites with chemical compositions of BixLa0.67 − xCa0.33MnO3 (x = 0, 0.04, 0.1, 0.2) have been prepared by the standard ceramic process. The crystallinity and microstructures of the samples have been investigated by x-ray diffractometry and optical microscopy, respectively. The magnetic and magneto-resistive properties of the samples have been measured by vibrating sample magnetometery and van der Pauw method, respectively, at the temperatures ranging 100 K–300 K with applied magnetic field of 0.4–0.5 T. Good crystallinity and high Curie temperature (275 K) have been obtained for the Bi-doped samples with small dosage (x = 0.04, 0.1) even they were sintered at 1200°C, which is about 200°C lower than normal sintering temperature of undoped sample. The Bi-doped samples with the small dosage showed lower relative electrical resistivity and higher magneto-resistive ratio compared to the undoped sample in the most temperatures measured. The Bi-doped samples also exhibited large magneto-resistive ratio (maximum of 15% for x = 0.1) at room temperature even under a weak magnetic field of 0.4 T.

Flat-surface magneto-optic spatial light modulator

In this paper, for the first time, we report the flat-surface magneto-optic spatial light modulators without the artificially isolation of pixels and external bias coil.

Compensation of Cross Talk Error for Optical Voltage Sensors

This paper discusses the errors associated with electric field cross talk for optical voltage sensors in a three-phase electric system and provides a solution to compensate the errors. For many practical conductor configurations, the electric field cross talk may cause errors unacceptable for the accuracy requirements of the sensors. We devised a real time compensation method for the cross talk and built an electronic circuits based on it. The mechanism of the compensation and the corresponding error reduction were discussed.