Recent progress of the bit patterned media fabricated by ion irradiation method is reviewed. High energy ion irradiation is a useful method to modify the magnetic properties and this technique can be used to fabricate high density bit patterned media which is a promising candidate to overcome the limit of the areal density of the conventional recording media. In order to achieve magnetic patterned structure having the feature size less than 50 nm by the ion irradiation technique, the materials whose magnetic order is easily suppressed by low dose ion irradiation are necessary. One of the candidate is L1₂ phase CrPt₃, and the control of the magnetic order of CrPt₃ by the ion irradiation and the fabrication of CrPt₃ bit patterned medium are discussed.

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The structure and magnetic properties of Fe-Pt/Fe films have been investigated to confirm exchange coupling behavior. Intermediated layer of Cu was inserted between FePt layer and Fe layer. It was found that the switching field (H_sw) was decreased with decreasing the thickness of Cu layer, indicating that the distance of the exchange coupling between FePt layer and Fe layer was less than 1 nm. The magnetic properties of FePt/Fe films were remarkably changed by the thickness of each layer. With increasing the thickness of Fe layer, the saturation magnetization (M_s) increased but the coercivity (H_c) decreased. From the magnetic force microscope observation, it was revealed that a remarkable difference was exist between FePt thin film and FePt/Fe thin film.

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Magnetoresistance (MR) effects and electroric structure were investigated for granular films employing Co₂FeAl_0.5Si_0.5 (CFAS) alloy. CFAS-MgO granular films showed a maximum MR ratio of approximately 4.8 %. It was however recognized that the surface of CFAS granules was slightly oxidized due to the low formation energy of MgO matrix. By utilizing MgF₂ matrix, the MR ratio increased to approximately 6.5 %. After annealing at 200°C, the MR ratio increased slightly. It was thought that the L2₁ ordered structure was not obtained due to the low annealing temperature. Further annealing at high temperature is required to obtain L2₁ ordered CFAS granules.

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The spin transfer switching in the TbCoFe / CoFeB / Cu / GdFeCo current perpendicular to plane (CPP) giant magnetoresistance (GMR) structures were studied. The GMR junction exhibited 0.1 % MR ratio, and current induced magnetization switching of the GdFeCo free layer was confirmed by a 100 msec pulse current. The difference of the critical current density between J_c⁺ (anti-parallel (AP) to parallel (P)) and J_c^- (P to AP) was estimated to be 15.3 × 10⁷ A/cm², and thus the average current density to be 7.7 × 10⁷ A/cm². It was confirmed that the sign of the interlayer coupling between GdFeCo and TbCoFe / CoFeB depended on the relative direction of the transition metal (TM) - moments of GdFeCo free layer and TbCoFe / CoFeB pin layer, which means the coupling is dominated by the exchange coupling through Cu spacer.

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To evaluate magnetization process of pixels in magneto-optic spatial light modulators (MOSLMs) with one-dimensional magnetophotonic crystals (MPCs), a magneto-optic microscope composed of optical parametric oscillator (OPO) wavelength variable laser system was developed. The observation results show that the microscope is effective for accurate determination of magneto-optic rotation angle of samples exhibiting strong wavelength dependence, such as the case of MPCs, because of the very narrow wavelength width of the OPO laser system. The magnetization process of the MPC pixels was found to be unique, where tiny magnetic clusters change their direction almost irrespectively to each other, and the resultant pixel exhibit gray-scale color depending on the number of magnetic clusters whose magnetization switched its direction.

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Recording simulation at 5 Tbit/in² was studied for bit patterned media with inclined anisotropy. Magnetic dot was modeled as 7.5×10×5 nm³ with saturation magnetization of 1000 emu/cm³ and average anisotropy field of 22 kOe, and the dots were arranged with 10 and 12.5 nm in down- and cross-track periods, respectively, on a soft magnetic underlayer. The magnetic anisotropy of the dots was set at 30 degrees from longitudinal direction. Maximum filed of around 15 kOe was obtained for a shielded planar head with a pole size of 10×45 nm² in spite of relatively large head-medium spacing of 6 nm. Recording with the head revealed large write shift margins of around 5 nm in down- and cross-track directions. On track recording simulation indicated tolerances of around 4 % in anisotropy field dispersion and 4 degrees in orientation dispersion.

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Signal recording processes were simulated using micromagnetic calculation for microwave assisted magnetic recording in perpendicular magnetic media. Strong magnetostatic field caused by the large saturation magnetization of the media tends to deteriorate recorded bit patterns resulting in low signal to noise ratio for the play back signal. The moderate exchange interaction fields were shown to improve recording characteristics and increase signal to noise ratio even for the large saturation magnetization media. The influence of thermal fluctuation fields on recording characteristics was also discussed and the influence was negligible for the media assumed in this study.

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Co-Pt dot arrays were prepared by ion milling etching using a self-assembled diblock copolymer mask. Two samples with different diameter of 24 nm and 38 nm, and similar size dispersion of 13-14 % were fabricated. The Co-Pt dots were indicated to have damaged portion, which has reversible magnetic propertiy, from the difference between the dc-demagnetization (DCD) curve and the hysteresis curve. It is estimated that the depth of the damaged portion is about 3 nm from the sidewall surface of the dot. The Switching Field Distribution (SFD) was roughly estimated by fitting the DCD curve. The DCD curve was successfully fitted by two SFD curves with high and low H_c's. The SFD curves at high-H_c are supposed to reflect the intrinsic SFD of the dots, and they show similar SFD of 12-15 % in spite of difference in the dot size.

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In this paper, to calculate site attenuation of anechoic chamber, we applied the FI method that was used Maxwell's relations with the integration form. First, in order to examine the influence of the cell size on the site attenuation calculation, we compared with the difference between the calculations values of a 30MHz tuned dipole antenna and a shortened dipole antenna using 40MHz tuned dipole antenna at the frequency of 30MHz. As a result, it was necessary for the 30MHz tuned dipole antenna to be 50 divisions to the wavelength of 30MHz, but, for the shortened dipole antenna to be 300 divisions to the wavelength. In order to examine this cause, we calculated the electric field in the antenna surroundings by the moment method (NEC2), and found that the change of the electric field distribution around the shortened dipole antenna was steeper than that around the tuned dipole antenna. Therefore, it is thought that the difference of the electric field distribution with this antenna was the cause mentioned above. The best size of the cell was presumed from the examination mentioned above, and we calculated the site attenuations of an open area test site and an anechoic chamber by the FI method. As for the open area test site, the calculation value by the FI method agreed with that by the moment method within 0.4dB. As for the anechoic chamber, the calculation value by the FI method was corresponding to the actual measurement value within 0.5dB by setting the cell size of 2cm. Therefore, it was confirmed that the FI method is effective for the calculation of site attenuation on the anechoic chamber.

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Inductively coupled plasma (ICP) is widely used as an ionization or excitation source for elemental analysis. It is one of the most powerful tools because of its excellent sensitivity. Recent years, target of elemental analysis has been shifted to smaller samples such as nano-particles, biocells, etc. But conventional ICP is not suitable for these targets because it consumes large amount sample solution. To analyze small amount samples efficiently, we have developed and studied a microplasma source for elemental analysis. In this study, dc power supply was used to generate microplasma at first, but the analytical figure of merit was not enough high. The probable reason was plasma temperature and electron number density were lower than that of Ar-ICP. To improve the analytical performances, several types of power supplies are tested. It includes dc biased RF and dc biased pulse power supply. In order to evaluate the analytical performance of merit, the emission intensity from some typical elements and the fundamental plasma properties are measured. The excitation temperature of RF driven microplasma increases by 400 K at 30 W of RF input power. And the lower limit of halogens detection improves about 35% with pulse operation compared to dc.

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The plasma generated by focusing Nd:YAG laser beam in liquid is studied to clarify the physical properties of liquid laser plasma. Little is known about laser-produced plasma in liquid. The ultra pure water dissolved NaCl up to 24 % is used as a test liquid. The electron density is measured by Mach-Zender interferometer. Dense plasma with electron density of the order of 10²⁵-10²⁶ m^-3 is observed. The electron density is highest at the focal spot while it decreases with distance from there. The several spectral lines in plasma luminescence are observed in the wavelength of 240 nm to 850 nm. The electron temperature is calculated from light intensity ratio of Hydrogen atom. The electron temperature is measured to be about 5000 K.

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For obtaining three-dimensional properties of streamer discharges we propose a new stereographical method in which streamers are observed simultaneously from three angles of 0°, 90°, and 225°. Two photographs taken from 0° and 90° individually provide the horizontal and depth coordinates of each streamer channel, as well as the vertical coordinate obtained from the both photographs, while the other taken from 225° yields clues for specifying identical streamer channels from the former two photographs. This method enables to maintain the absolute error of the depth coordinate low, differently from typical stereogram. Using the observation method we have demonstrated the evaluation of the propagating velocity and several branching characteristics of streamer channels.

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The current of the barrier discharge usually contains many pulse currents. These pulse currents are due to occurrence of the many micro discharges, which are observed as filamentary micro discharges. However, the atmospheric pressure glow discharge or the atmospheric pressure Townsend discharge does not contain such pulse currents, and the discharges are homogeneous. We have been developing an electric circuit simulation method of the filamentary barrier discharge. Here we improved the simulation program so as to be a more realistic one, and also we extended the simulation program to a new one which is also available to the atmospheric pressure glow and the Townsend discharges. The electric circuit simulation models are introduced in this paper, together with the examples of current and voltage on the three types of barrier discharge modes.

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This paper presents results of magnet characteristic analysis of a concentration type hybrid surface magnetic motor by using the finite element method. This motor has a structure combined neodymium magnets and ferrite magnets. We investigated optimal thickness of the magnets and their effectiveness.

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Nitrogen with internal energy for long period supplies primary electron which leads to breakdown in the space. However, it is not elucidated about primary electron supply process. Accordingly, we changed the cathode surface area and the volume between electrodes to analyze the primary electron supply processes under high pressure nitrogen gas. It was confirmed that the number of primary electron depended on the surface area of cathode. In the next stage, experiment was carried out in N₂/SF₆ and N₂/CF₃I to confirm the effect by electron attachment reaction and quenching reaction of activated species. The decrease rate of primary electron number supplied by activated species is higher in N₂/CF₃I than in N₂/SF₆. In addition, dependence of the number of primary electron on the pressure and the interval time changed remarkably in case of N₂/CF₃I. Thus, it was confirmed that the breakdown probability changed depending on the number of primary electron supplied.

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