This paper reports the design principle of a preamplifier using Gilbert cell^1 for MO application. This preamplifier accomplishes signal normalization, channel balancing, signal differentiation, high bandwidth, and low noise.

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An error rate characterization method in a large scale CD-ROM production is presented.

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The SNR and BER of a digital holographic memory using a Ce-SBN single crystal were measured, and their relationship to the number of multiplexed pages was determined. The SNR was 8.0 and the BER was 6.0×10^<-6> in the case of single-page recording, but the SNR fell to 4.9 and the BER rose to 2.0×10^<-4> in the case of 10-page multiplexing. A 1.3 kbyte data file of a color picture that was compressed by a JPEG technique could be recorded and reconstructed with no error by using a Hamming (7,4) ECC.

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This paper gives formulas for calculating the diffraction efficiency of reflection-type gratings recorded in a photorefractive medium. The analysis uses coupled-wave theory for photorefractive bologram gratings, taking into account the photorefractive phase shift and fringe curvature. General solutions for signal and reference waves were derived in a closed-form expression. The optimum media parameters and recording conditions for high diffraction efficiency were obtained using the derived formulas. Diffraction efficiency for wavelength mismatch from the Bragg condition was quantified by the formulas. The experimental results for wavelength selectivity were in good agreement with the analysis. Two successive wavelength-multiplexed holograms are recorded and reconstructed.

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Memory characteristics of NiFeCo/Cu/Co system deposited on 4°tilt-cut Si (111) substratc have been investigated. With a Cu (50A) underlayer on 4° tilt-cut Si (111) substrate, NiFeCo/Cu/Co multilayers developed in-plane uniaxial magnetic anisotropy and they showed perfectly square R-H curves, which represent the possibility of a MRAM application. In large scale test MRAM cells consisting of [NiFeCo (60A)/Cu (40A)/Co (30A)/Cu (40A)]_5 multilayers, 400 μV voltage difference between the two magnetoresistive states was obtained with 2 A of word current at 1 mA of fixed sense current, which has been believed to show high potentials of NiFeCo/Cu/Co system in a MRAM application

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Ni65Co35 (λ s=0) thin film was prepared by RF magnetron sputtering method and themagnetoresistance (MR) ratios were measured by four-point probe method. MR properties as functions of certain sputtering parameters such as sputtering Ar pressure, bias voltage, subtrate temperature were investigated. The maximum MR ratio we obtained was 4.4%. In addition, the annealing kinetics of Ni65Co35 thin film was studied, and the thermal activation energy was obtained.

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A series of Co_xAg_<1-x> (0&le;x&le;100 at. %) granular films were prepared using ion-beam cosputtering technique at different substrate temperature. Systematical investigations have been made on the giant magnetoresistance (GMR) effect and characterization of microstructures in these thin granular films. The magnetoresistance ratio strongly depends on cobalt concentration, substrate temperatures, and annealing treatment. The optimal value of GMR was observed in Co_<22>Ag_<78> sample prepared at the temperature of 300 K. The microstructures of as-deposited and annealed samples were characterized by a variety of structural techniques. For Co_<22>Ag_<78> sample, Real time observation, in situ, of TEM together with FMR spectra indicates that the size and shapes of cobalt granules evolve primarily along the film plane during annealing process. Also, the results of FMR provide that the cobalt granules are still single domain particles after annealed up to 700 K.

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Soft magnetic properties and microstructural evolution of FeTaNC films were investigated, and compared with FeTaN and FeTaC films. Effects of substrate species (glass vs. CaTiO_3) on the magnetic properties were also investigated. Co-addition of N and C significantly enhance the grain refinements and soft magnetism compared with N or C addition only. Good soft magnetic characteristics of coercivity of 0.17 Oe, permeability of 4000 (5 MHz). and saturation flux density of 17 kG can be obtained in the FeTaNC in the relatively wide process window. While these values appears to be similar to those of FeTaN on glass substrate, most distinctive difference between FeTaNC and FeTaN (or C) is in the effects of substrate. Whereas FeTaNC films show good magnetic charactcristics for both glass and CaTiO_3 substrates, FeTaN (or C) films shows significant degradation on the CaTiO_3 substrate.

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Fe-Ta-N films with three compositions were prepared by using RF reactive diode sputtering technique, using composite targets with Ar+N_2 mixed gas. The influence of partial nitrogen pressure P_<N2> and annealing temperature T_A on structure and magnetic properties of these films was investigated. The addition of Ta effectively inhibits the formation of Fe_4N phase and improves the thermal stability of Fe-Ta-N films. The addition of Ta and N atoms decreases the grain size and causes some lattice expension in the films

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Metastable Co-Cu thin films were sputter-deposited. The relationship between magnetoresistance of CoCu granular film and vacuum annealing temperature, applied magnetic field, and composition of alloy was studied. Co second phase with fcc structure are precipitated after annealing. Giant magnetoresistance (GMR) effect was observed in the nonmagnetic Cu matrix, its magnitude depends on the quantity and size of Co particles.

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The third element was inserted at the NiFe bulk layer in NiFe/Cu multilayer system. The magnetoresistance value was enhanced to〜6% by inserting NiFeCo or Ni layer. The inserting layer of Co or Fe, however, was not so effective as NiFeCo or Ni layer. The magnetoresistance was enhanced up to 〜4% by inserting monolayer of Co. The magnetoresistance value of (NiFe/Ni/NiFe)/Cu or (NiFe/NiFeCo/NiFe)/Cu in this work is the first report that feasible magnetoresistance can be obtained in NiFe/Cu multilayer at the second peak on Cu or NiFe underlayer.

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A micromagnetic simulation of a SAL biased MR head was done and effects of voids in MR layer and SAL on MR response have been described. Volume of voids was varied from 0 to 10.5%. It was found that the MR response becomes lower value, if volume percent of voids or nonmagnetic elements in the MR layer and SAL becomes larger. When the volume fraction of voids was high MR response showed wiggles in a certain range of applied field. In the case of no void, effects of M_s of SAL, shunt current and M_s of permanent magnets on MR response have been also studied.

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As technology moves to proximity recording and Gb/in^2 areal densities, the in-situ flying height and the flying stability measurement of sliders are becoming critical issues in reliability control and tribology performance design of present disk drives. This paper reports a method, testing system, and results of the drive level slider flying stability measurement with slider itself as transducer. The setup is based on monitoring the capacitance of between slider and disk surface. The flying performance and flying stability of sliders were investigated systematically under different track seeking modes

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The fine magnetic particle model was applied to a single layer perpendicular magnetic film, which is treated as a set of many fine magnetic particles, and simulations performed for both the magnetization process and the recording/reproducing process of a perpendicular magnetic film with a fixed initial layer thickness. Changes in magnetization characteristics, recording/reproducing characteristics and the remnant magnetization state with thickness of the film were investigated. Consequently, it was shown that as the film becomes thin, the effective anisotropic field strength decreases. And it was also shown that the relationship between deformation of recorded pattern due to the demagnetized effect of the demagnetization field at short wavelengths and film thickness is indistinct, but that is distinct at long wavelengths.

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Time decay of magnetic properties in perpendicular magnetic recording media were studied. It was suggested that the magnetization of media with a small energy ratio KT/kT of 50 is expected to be thermally stable under no demagnetizing field but the coercivity would suffer from a large time decay. The magnetization of perpendicular recording media exhibited an appreciable time decay even for films with a large energy ratio of 300. The cause of the decay was suggested to be the small perpendicular squareness due to large demagnetizing field acting in the media. The recording density dependence of the time decay in the output was explained in terms of the change in the demagnetizing field acting in the recorded bit. Use of media with a larger energy ratio and a larger squareness could reduce the time decay

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Responses of MR heads are investigated in high density perpendicular magnetic recording, theoretically and experimentally. The reciprocity theorem is used to analyze the MR head response for perpendicular magnetization in double and single layer media, in comparison with longitudinal media. The analysis shows that the differentiation is well adopted to change the transfer function for perpendicular to the familiar longitudinal response. It was found that the differentiation also improves its high density response. Experiments with a single pole write-head proved the analysis ; a high D_<50> of 270 kFRPI. The obtained SN ratio at 200 kFRPI was superior to a longitudinal media by more than 10 dB.

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