The Optoelectronics industry in Taiwan has recently grown at a very rapid rate with an annual compound growth rate about 35% last five years. One of rapid optoelectronics industry growth came from the growth of optical storage products in Taiwan. For example CD-ROM productive in Taiwan, which did not have any production in 1993, reached 45 millions units (about 47% of world wide market share) in 1999.
DVD products have begun to replace CD products for the current major optical storage application in PC and consumer electronics. We have successfully developed key components needs in DVD application. As the optical storage technologies is continuous to develop in order to keep up with the rapid advances in hard disk storage technology. We are working on the key technologies for the net generation optical storage products, such as HD-DVD and optical write/Magnetic read technologies. In this paper, the current status of DVD and HD-DVD key components and key technologies in Taiwan R&D communities will be reviewed.

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A magneto-optical microscope magnetometer (MOMM) has been developed to grab the domain reversal patterns in real time under applying a magnetic field, as well as, to simultaneously measure the local magnetic properties with 400-nm spatial resolution. Using the system, the domain reversal behavior is revealed to change contrastingly between wall-motion and nucleation dominant with changing the multilayer structure of Co/Pd multilayers. From a quantitative analysis, the reversal ratio of the wall-motion speed over the nucleation rate is a governing parameter for the contrasting domain reversal dynamics. The activation volumes of the wall-motion and nucleation processes are found to be unequal, and the difference is closely related with the domain dynamics. Based on a Monte-Carlo simulation, both the macroscopic magnetic properties and the local magnetic variation are responsible for the contrasting domain reversal behavior.

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X-ray magnetic circular dichroism (X-MCD), i.e. the dependence of the absorption coefficient of circularly polarized X-rays on the projection of the magnetization in a ferromagnetic system onto the photon propagation direction, yields e. g. at L_2,3 edges in transition metals large values up to 50%. In combination with a soft x-ray microscope where Fresnel zone plates as optical elements provide a lateral resolution down at 25nm, X-MCD can be used to image magnetic microstructures. This photon based technique allows for recording images in varying external magnetic fields, it exhibits inherent chemical specificity, a high sensitivity due to the large contrast and allows to distinguish between in-plane and out-of plane contributions. In this report the basic features of this novel technique will be outlined and results obtained with the XM-1 microscope at the ALS (Berkeley/CA) with thermomagnetically written bits in magneto-optical storage systems demonstrate the applicability of this new experimental technique to technological relevant issues.

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Short magnetic in-plane field pulses were used to pull the magnetic spin system of a NiFe film out of its equilibrium state and to initiate coherent magnetisation dynamics. This field induced dynamics was investigated by means of a time-resolved pump-probe experiment, measuring the linear Kerr effect with a balanced photodiode scheme. Precession frequencies of several GHz and relaxation-times in the nanosecond range were observed. Emphasis is on the generation of the short magnetic in-plane field pulses. They were generated using an ultrafast photoconductive switch based on GaAs and launched by a waveguide to the sample. The waveguide and the photoswitch were designed to yield as large as possible magnetic field strengths. The field pulses used in this work had a rise time of 10-60ps, a decay time of 500-700ps and a maximum field strength of 9Oe.

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We report the physical realization of periodic networks of micromagnetic dots, coupled by both the exchange and dipolar interactions. A series of samples with different ratios of exchange to dipolar coupling ρ, were patterned using a focused Ga⁺ ion beam (FIB). The parameter ρ can be controlled by varying the Ga⁺ ion beam fluence. Both static and dynamic studies reveal a transition between exchange and dipolar coupled states as Ga⁺ fluence is increased.

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Femtosecond laser pulse induced magnetization reversal of α-Gd_23.1Fe_71.9Co_5.0 was investigated by time-resolved measurements of the polar Kerr-rotation. The dynamics is found to follow the Bloch-equation via a relaxation time that does not depend on temperature but strongly decreases with increasing excitation density. A minimum value of (190±40)ps was obtained for the highest applicable pump-fluence. Comparing the reversal dynamics to temperature induced variations of magnetization within a single domain state and to the magnetization dynamics measured in remanence, the different contributions of transient temperature and domain formation to the magnetic response are separated.

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X-ray polarization-contrast images resulting from x-ray magnetic circular dichroism (XMCD) in hard x-ray region have been successfully recorded for the first time. The apparatus used consisted of an x-ray polarizer, double x-ray phase retarders, and a high-spatial-resolution x-ray charge-coupled device (CCD) detector. The sample used was a hexagonal close packed (h.c.p.) cobalt poly-crystal foil of thickness about 4 μm. The x-ray polarization-contrast image resulting from XMCD was observed at a photon energy 10 eV above the cobalt K-absorption edge (7709 eV). The observed contrast in the images was reversed by inversion of a magnetic field. Furthermore, the contrast was reversed again at a photon energy 32 eV above the cobalt K-absorption edge.

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Spin-dependent tunnel magnetoresistance of Co(10nm)/Al₂O₃(2.6nm)/M(tnm)/ NiFe(10nm) with M = Co or CoFe was studied as a function of the thickness of M_t. The thickness (t) of the doped Co or CoFe was varied between 0 and 3 nm. We have experimentally showed that the polarization of tunneling electrons can be varied by modifying the interfacial condition between the insulator and magnetic layers. The enhancement of the tunneling magnetoresistance in samples of Co(10nm)/Al₂O₃(2.6nm)/CoFe(tnm)/NiFe(10nm) is greater than that in samples of Co(10nm)/Al₂O₃(2.6nm)/Co(tnm)/NiFe(10nm) for t between 0.8 and 2.0 nm. The enhanced tunneling magnetoresistance may be attributed to the increase in the effective polarization of the tunnel electrons due to the spin-filtering effect from the additional magnetic layer M. Besides, from the oxidation process study of the Al-O insulator layer on Corning glass, we have shown experimentally that the optimal condition for the oxidation of the Al-O insulator layer in FM/A1-O/FM system can be obtained under the pressure of 5x10^-2 torr for 50% of Ar + 50% of O₂ environment with both natural and plasma oxidations. For optimal oxidation of the Al-O insulator layer in a spin-dependent tunnel system, its thickness should be less than 3 nm

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The effects of annealing on the exchange coupling in NiFe/NiMn bilayers and the properties of NiMn-pinned spin valve are studied. With increasing annealing time and annealing temperature, the exchange coupling field H_ex first increases, followed by a decrease. The evolution of H_ex with annealing is the competing result between nonmagnetic fcc-antiferromagnetic fct phase transition and interfacial diffusion. The exchange coupling between NiFe and NiMn layers is very stable at temperatures from room temperature to about 210 °C. The distribution of blocking temperature T_b is responsible for the thermal stability. For the NiMn-pinned spin valve, a lower annealing temperature is favorable, at the expense of a longer time to obtain a desired exchange coupling field.

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The introduction of the Cr interlayer caused magnetic decoupling in SmCoAlSi / Cr / SmCoAlSi and SmCoAlSi / Cr / SmCoCuTi thin films. High coercivity of 3400∼3840 Oe and extremely fine grain size in this two kinds of films were examined. Magnetic coupling within sublayers was introduced by using different substrate bias among the SmCoAlSi (deposited with substrate bias of -150 V) / SmCoAlSi (deposited with no substrate bias) / SmCoAlSi (deposited with substrate bias of -150 V) triple layers. This multilayer exhibited high coercivity ∼2960 Oe and S* 0.96. SmCoAlSi / SmCoCuTi / SmCoAlSi trilayer improved matching between the magnetic layer and the Cr underlayer, and led to increased in-plane anisotropy, high coercivity 3620 Oe and S* 0.91. The microstructures of these four kinds of media were also examined. Results obtained suggest that it is possible to produce SmCoAlSi-based multilayer media with the combined magnetic properties required for the ultra-high magnetic recording density of ∼20 Gbit/in².

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A medium formation technique for fabricating high purity Co₉₀Pt₁₀ magnetic thin film with uniform grain size was developed, whereby the signal-to-medium-noise ratio (S/Nm) can be improved. In this technique, a Co₉₀Pt₁₀ (CP) island layer is deposited as a nucleation site layer (NSL) on SiO₂/Si disk substrate with adherent gas. After the deposition, a heat treatment is sequentially carried out in order to remove the adherent gas. High purity films can be produced by the removal of adherent gas. A Cr film and a Co₉₀Pt₁₀ magnetic film are successively deposited after the heat treatment (HT). In the deposition of Cr film, the fabricated Co₉₀Pt₁₀ island forces nucleation of Cr grain to start from the Co₉₀Pt₁₀ island and thus eliminates simultaneous nucleation from many points on the region without the Co₉₀Pt₁₀ island. The resulting Cr film as a underlayer is composed of a monolayer of closely packed Cr grains with uniform grain size. In this medium formation, nucleation of Co₉₀Pt₁₀ grain to magnetic layer to start from the Cr grain to underlayer is created. Therefore, Co₉₀Pt₁₀ magnetic thin film with uniform grain size is produced. The fabrication of high purity Co₉₀Pt₁₀ magnetic film with uniform grain size has been achieved by the deposition of NSL and removal of adherent gas. As a result, it is indicated that the use of this technique results in increase of S/Nm at 304.4 kFCI of 25%.

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Thermal stability of CoPtCrO granular thin films with perpendicular magnetic anisotropy is investigated. Magnetization decay with time M(t) exhibits almost a linear dependence with ln(t), similar to that for longitudinal recording media. In comparison with amorphous rare earth-transition metal alloys media which shows a non-linear decay with ln(t), the differences in magnetization reversal process and energy barrier distribution are discussed. From magnetic viscosity measurements, activation volume is determined and shows a minimum of about 2x10^-18 cm³ for CoPtCrO at fields near its coercivity, leading to a coupled region of 10 nm average diameter. Also recording performance is investigated using a conventional merged GMR head and magnetic force microscope. The linear recording density dependence of signal amplitude reveals that the 50% rolloff density D₅₀ is about 300 kfci.

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In this work we report on experimental analysis and numerical simulations of the time decay of magnetization in the films of amorphous TbFeCo alloys. It is shown that experimental results can be explained on the basis of an incoherent thermally activated subnetwork magnetization reversal model. Thermally activated reversal of transition metal subnetwork and associated compensating reversal of the antiferromagnetically coupled rare-earth subnetwork may result in effective stabilization of the net film magnetization. The unique combination of a small activation diameter Da = 5-6nm and high thermal stability parameter k∼250 makes TbFeCo amorphous films an excellent candidate for perpendicular recording medium at over 100 Gbit/in² areal recording density.

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Epitaxial CrPt₃ and Mn_0.2Cr_0.8Pt₃ films were grown by MBE system and the structure and the magnetic and magneto-optical properties of these films have been investigated. RHEED observation suggests that the CrPt₃(111) film epitaxially grows on MgO(111) and forms Cu₃Au type ordered structure. The easy axis of magnetization of CrPt₃ on MgO(11) lies in the film plana although the CrPt₃ on fused quartz substrate exhibits large perpendicular ansotropy (K_u = 1.5 × 10⁶ erg/cm³). The perpendicular magnetic anisotropy of Mn_0.2Cr_0.8Pt₃ is induced when the 30 nm Pt buffer layer is inserted at the interface between the alloy layer and the MgO(111).

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The thickness dependent magnetic domain structures in FePt/MgO(100) L1₀ ordered alloy thin films are investigated by Magnetic Force Microscopy (MFM), for as-deposited and AC-demagnetized states. Truncated stripe domains and bubbles are observed for as-deposited states. However, very regular maze patterns, with a tendency of aligning along the [110] direction for thickness greater than 1000 Å are observed for AC-demagnetized states. Unreversed domains with edges parallel to the [110] direction appeared in the remanent states for thickness greater than 1000 Å. The preferential alignment of the domains along the [110] direction are attributed to the groove-like surface morphology running along the [110] direction as revealed by Atomic Force Microscopy (AFM).

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In this work thin silver oxide layers (AgO_x) were prepared by reactive sputtering of a silver target in oxygen containing atmosphere. We report a gradual composition change of the deposited layers with increasing oxygen concentration from Ag over Ag₂O to AgO and furthermore that dispersed silver clusters are present even up to high O₂ concentrations. Raman- along with IR-spectroscopy and ellipsometric measurements reveal specified compounds at defined oxygen concentrations. Optical transmission and reflection measurements as a function of temperature show that these compounds exhibit phase transitions (i.e. AgO decomposes to Ag₂O and finally to Ag), connected to considerable refractive index changes. This work was done with respect to super-Resolution Near-Field Structures where these effects are exploited to realize ultra high optical data storage in combination with magneto-optical and phase change recording materials.

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We constructed an equipment for measuring rapid changes in reflectivity of optical recording materials on test pieces during recording laser irradiation, which is very important in a development of these kinds of materials, with a time resolution less than 10 ns. Using this equipment, we examined the metal/GeS₂ systems in the performance as recording materials for Write Once Read Many (WORM) optical disks. Seven kinds of metals were tested. Differences in the profiles of the reflectivity changes during the laser irradiation were clearly elucidated depending on the metal layer materials. In/GeS₂ and Sn-Bi/GeS₂ (Sn-Bi:Sn-57wt%Bi eutectic alloy) samples showed the most rapid decreases in the reflectivity with low laser power absorbed in the samples. These results suggest that In/GeS₂ and Sn-Bi/GeS₂ are promising for the WORM optical recording material with high sensitivity and high recording speed.

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The preparation of CaS films by magnetron sputtering with the requisite properties for optical recording is studied. Sputtering targets are produced from pressed powders permitting rapid investigation of the optimum dopant concentration of the rare earth ions Eu and Sm. The problem of negative ion re-sputtering is addressed but low sputtering rates remain a problem.

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The process of domain transcription and wall motion in magneto-optical recording media for MAMMOS and DWDD is investigated by micromagnetic computer simulation. The result of calculation agrees with experiment semiquantitatively, which shows the effectiveness of the micromagnetic simulation in the development of these devices.

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Flexural and torsional motions have been investigated in low field anisotropic giant magnetostrictive (GMS) single domain state (SDS) exchange-coupled Tb/Fe/Fe multilayers (ECML). The magnetoelastic (ME) coefficient b^γ,2 and susceptibility db/dH depend strongly on the ECML structures, compositions, sputtering deposition parameters and post-deposition heat treatments. Due to a well defined but low uniaxial anisotropy associated with the SDS induced by a bias field during the film deposition, a Spin Reorientation Transition (SRT) with quasi-static and resonant bi-stability properties is clearly achieved near the saturation field along the hard axis. Harmonic and subharmonic excitations of first and higher-orders (linear and non-linear excitations) of flexural and torsional oscillations modes with huge amplitudes have been stimulated from the SRT in agreement with our theoretical model. The corresponding very large dynamical ME susceptibility gives the possibility to control GMS micro-electromechanical systems (MEMS) with a strong reduction of the excitation field.

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Thin MnBi films have been grown by molecular beam-epitaxy technique in combination with an alloying process. The formation of MnBi is driven by an enhanced intermixing due to diffusion close to the eutectic temperature where Bi becomes liquid. The growth process of MnBi was investigated in detail by preparing a wedge-shaped thin film. Highly c-axis oriented nano-particles of MnBi are formed in a Bi matrix. The particles show two magnetic phases with magnetic moments of 744 kA/m and 113 kA/m and coercivities of 20 kOe and 7 kOe, respectively. They have a large magnetic energy product of 171 kJ/m³. The magneto-optical Kerr rotation in the visible spectral range is determined.

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Measurements and analysis of spectroscopic reflection ellipsometry and magneto-optical polar and longitudinal complex Kerr effect are reported on a natural (111) fece of a high quality NiFe₂O₄ single-crystal. The experimental reflection data is expressed in terms of the permittivity tensor. This information is employed in modeling experimental polar Kerr spectra of a NiFe₂O₄ film and a satisfactory agreement has been achieved. These results demonstrate the importance of the spectroscope magneto-optic reflection ellipsometry in the diagnostics of magnetic oxide films with thicknesses in the range 10¹ to 10² nm.

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Diffraction anomalies arising as a consequence of surface structure are shown to be capable of producing enhancement in magneto-optic effects. The magneto-optic behaviour of structured magnetic surfaces is studied in the presence of two anomalies :- (a) where orders pass-off grating horizons and (b) where surface plasmon resonances occur.

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We have studied the magnetization behaviour of Co deposited on step bunched vicinal Si(111) misoriented 4° towards (11-2) using two complementary magneto-optical techniques : magnetization induced second harmonic generation (MSHG) and linear magneto-optical Kerr effect (MOKE). MSHG rotational anisotropy measurements have shown clear step induced contributions thereby allowing accurate determination of the direction of the steps. MOKE measurements exhibited a uniaxial anistropy with the hard axis perpendicular to the step edges and an interesting bulk magnetization behaviour for intermediate angles which is shown to be due to the flipping of the magnetization of the material.

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A new method is developed to simulate how a magnetic domain is stabilized in magneto optical recording. Based on the method in which dynamics of a domain wall is estimated from the calculation of force on the wall, the wall is assumed as the zero thickness line in arbitrary shapes. With this method the deformation processes of arbitrary domain shapes including not only circular and crescent ones can be treated. The deformation processes of the crescent-shape initial domains are performed under the uniform temperature and the uniform bias field.

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Magnetic and magneto-optical properties were measured at room temperature in the Mn-diffused surface layer of a CdGeP₂ single crystal. The magnetization curve measured using VSM clearly shows a ferromagnetic hysteresis loop with H_c=0.4 kOe superposed on the diamagnetic component. The ferromagnetic Curie temperature was determined as 320 K from the magnetization vs. temperature curve. The magneto-optical Kerr effect was measured between 1.2 and 4 eV. The peak Kerr ellipticity of 0.14 deg appeared around 1.75 eV.

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In magneto-optical technology, the interest for magnetic coupled layers has increased in the last decade with the development of new methods like the Magnetic Super Resolution (MSR) and the Magnetic Amplification of Magneto-Optical System (MAMMOS), allowing improvement in recording density. In this framework, hysteresis loops of a GdFeCo/TbFeCo bilayered structure are studied. For the rare-earth transition metal (RE-TM) alloys in the infrared and visible light wavelength, the Kerr and Faraday rotations are predominantly due to the transition metal magnetization. Experimental results show that the relation between the sign of the rotation and the transition metal (TM) magnetization direction is not so obvious but depends on several parameters like the material thicknesses and the optical and magneto-optical constants. The experimental investigation of the structure is complemented by optical simulations where great variations on the rotation order of magnitude and rotation sign are also obtained. The analytical model of the system shows that these variations are due to the interferences occurring in the layered structure.

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A sequence of magnetic-optical ternary DyFeCo and quaternary SmDyFeCo films have been prepared by r.f. magnetron sputtering method. The magnetic, magneto-optical and temperature property of quaternary SmDyFeCo films was investigated compared with the ternary DyFeCo films. The results show that SmDyFeCo films have good reproducibility. The writing/erasing cycles of the SmDyFeCo films was estimated over 10⁶ times.

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A study of magnetic and magneto-optical properties of (Co_100-xFe_x)₅₀Pt₅₀ (0 ≤ x ≤ 100) alloy thin films in conjunction with the structure is carried out. The intrinsic perpendicular magnetic anisotropy constant K_u measured at room temperature increases with order parameter, and decreases with tetragonality c/a. This result is at variance with the calculation based on the first principle analysis at the order parameter S=1. The K_u increases with S for all the compositions. The polar Kerr rotation of (Co_100-xFe_x)₅₀Pt₅₀ thin films is enhanced for photon energies over 1.5-3.5eV and 4-6.8eV with increasing Fe content. On the other hand, the polar Kerr ellipticity exhibits a rather complicated change with Fe content.

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Ferromagnetic EuO films were epitaxially grown on MgO substrate. The Curie temperature Tc of the obtained film was 69K. Spectra of magneto-optical polar Kerr rotation and Kerr ellipticity were measured from the substrate side of the MgO/EuO/Ag structure using the photoelastic modulator technique for photon energies between 1.2 and 4 eV under the magnetic field of 1T. Huge magneto-optical effect was obtained. A few spectral structures were observed for photon energies between 1.2 and 2.6eV, which undergo strong temperature dependence.

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Thermomagnetic recording process for various TbFeCo films on PMMA has been simulated in the case of the irradiation of the laser spot with 1.0 and 0.2 μm by using a modified Huth’s equation. In the case of TM-rich alloy, it is found that the domains smaller than 0.1 μm in diameter are formed at temperature below the Curie point because of the large demagnetizing energy, which results from the large magnetization. On the other hand, the large temperature gradient makes it difficult to stabilize the small size domain in RE-rich film.

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We have calculated the light intensity distributions inside the multilayer thin film stacks of a MO disk at different incident angles for both s and p polarization waves by use of matrix method. The results show that the difference of the light intensity distributions between s and p waves is obvious especially at higher incident angles, while the difference of the Joule losses between s and p waves in the recording layer is rather small for the light rays at different incident angles. For high NA case, the light intensity distribution for a converged beam can be regarded as the summation of the results of s waves and p waves of a set of plane waves.

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Magneto-optical Bi-YIG particles are prepared by different coprecipitation procedures. The crystallite size of the particle increases with the heat treatment temperature. In spite of a similar crystallite size, the saturation magnetization is considerably different by the coprecipitation procedure. The Faraday rotation of the composite film with the mixture of epoxy and the Bi-YIG particles linearly increases with the saturation magnetization for the film with crystallites smaller than 30 nm, while that for the film with larger crystallites deviates from the linearity and exhibits a decrease in the Faraday rotation. These results can be interpreted based on the scattering of the probing light due to the morphology of the composite film. The presence of a magneto-optically inactive surface region of the crystallite is also discussed.

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It is shown by theoretical arguments that thermally-assisted recording using conventional optical means for heating the medium locally gives only moderate improvements over conventional recording. These improvements are comparable with those of perpendicular recording over oriented longitudinal recording. When bits are cooled down immediately after writing and not heated again, large improvements in areal density and signal-to-noise ratio are possible. However, writing becomes extremely difficult in the region of small switching times where thermally-assisted recording allows large grainsize reductions.

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TbFeCo perpendicular magnetic recording media were developed by employing a NiP underlayer to control the magnetic properties of TbFeCo magnetic layer. With the NiP underlayer the magnetization reversal changed from the wall motion to the rotation mode. Dynamic write-read characteristics of a single-layer medium were examined using a conventional merge-type GMR head with a write core width of 1 μm that was designed for longitudinal magnetic recording. A clear magnetic pattern of 450 kFCI, high media SNR and acceptable overwrite properties were obtained. It was shown the thermal stability of the TbFeCo medium is good enough for practical applications. A double-layer medium with a soft-magnetic backlayer exhibited a practical overwritability for a narrow track pitch of 0.4μm.

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Thermally-assisted magnetic recording experiments on high-coercivity, perpendicular anisotropy, multilayer Co/Pt media are reported. High performance writability is demonstrated on media that could not be written at ambient temperature. Simulations help to clarify the physical phenomena involved in the thermally-assisted writing process.

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A Magneto-Optical recording technology is described for storage densities of 50-100 Gb/in² and data rates of 100-200 Mb/s. A sliding optical head which forms a key component for this recording technology has been developed. The head incorporates a thin-film coil for high data rate Magnetic Field Modulation recording and a dual lens objective with a Numerical Aperture of 0.85. To limit head-disc interface problems due to heating by the laser a cover layer of a few tens of μm is applied to the disc. Cover layer requirements are discussed and MFM recording results obtained with a NA=0.6 version of the sliding head and TbFeCo media with a thin cover layer are presented.

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A new MO (magneto-optical) disk has been developed as a new memory for digital still cameras, named “iD (image/intelligent disk) PHOTO”. Advantage of the iD PHOTO disk is a larger recording capacity of 730 MB, than those of semiconductor memories on current digital still cameras. The field modulation method for recording and Center Aperture Detection (CAD) type magnetic super resolution for reproducing are employed to achieve this capacity.
This disk is designed considering mobile use. For the first point, high field sensitive CAD media is realized so as to reduce electric power consumption. By the addition of the capping layer, the recording field has been reduced to be smaller than 100Oe. For the second point, as well as the mechanical stability, write/read characteristic is enhanced in broad environmental temperature range. More than ±12% read power margin is obtained on each temperature area from -5°C to + 60°C.

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Various technique to reproduce magneto optical signals from high-density recorded patterns are reported, for example DWDD, MAMMOS, CAD, etc. In this paper we propose a method with NA 0.85 lens and a 405 nm laser. We search the feasibility of conventional MO media by laser-pulsed magnetic field modulation (LP-MFM) method having a target of high-density 20Gbit/inch². We had the method of UV irradiation to suppress the media noise, thermal control layer to prevent the decay of the Kerr rotation angle, and optical phase shift method to reduce the cross-talk. And we could be making sure the feasibility of 20Gbit/inch² observing a low error rate of less than 10^-5 at the bit length of 0.13 μm.

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Laser-assisted magnetic recording is an interesting method for narrowing a track pitch; in particular, crosstalk canceling in laser-assisted magnetic readout has a unique feature that it enables us to reproduce a narrower track than an assisting laser spot size. Shorter wavelength of the assisting laser promises the higher track density, accordingly. In this paper, we have demonstrated the crosstalk evaluation by using a blue laser for the assisting beam and obtained as high track density as 85ktpi.

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A new type of front aperture detection using magneto-static coupling was studied. Recording marks were copied by magneto-static coupling instead of exchange coupling. To enlarge readout power margin, a TM rich switching layer having low Curie temperature was employed between cut-off layer and writing layer. Both high resolution and low readout field requirement that was less than 100 Oe could be achieved. Margins of both readout power and field were wide enough.

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The spatial resolution of the copy process (the copy window) of a magnetic domain from the recording layer into the readout layer of a MAMMOS disk is investigated as a function of laser power. This copy window is measured experimentally and calculated with a model of the copy process. The calculations show that higher disk speeds appear to be better concerning the power margins which apply for the MAMMOS process.

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The combination of Magnetic Amplifying Magneto-Optical System (MAMMOS) media, a blue laser and a high NA objective lens has been investigated using simulations and experiments. This paper describes the experimental and simulated results of domain copying phenomena for the MAMMOS media using a 413nm blue laser and an objective lens with a numerical aperture (NA) of 0.9. Without an external magnetic field, the readout laser was irradiated onto the MAMMOS media. Since the phenomena were related to Rear Aperture Detection phenomena, the signal amplitude simulation assumed temperature dependence of the Kerr rotation, the aperture thermal properties and the Gaussian laser beam profile. This paper also presents the analysis of expansive and shrinking forces per unit wall area concerning the MAMMOS readout using the blue laser and the high NA objective lens.

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Readout characteristics were improved for Rear Expansion Detection (RED) magneto-optical media. Readout field margin of more than 60 Oe was obtained for marks written with light intensity modulation (LIM) and that of more than 100 Oe was obtained for marks written with laser pulse magnetic field modulation (LP-MFM). Retainable ghost signal appeared in tri-layer RED media was reduced by inserting an additional layer. Optimized RED media exhibited CNR of 44 dB at mark length of 0.2 μm.

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A new type of MAMMOS (Magnetic amplifying magneto-optical system), which operates under the DC magnetic field in reproducing process, was proposed and evaluated. In this system, the CNR of 43 dB was obtained for 0.25 μm packed domains by applying 10 kA/m of DC magnetic field. Compared with conventional CAD (Center aperture detection)−MSR (Magnetically induced super resolution) disk, it was shown that the CNR for domain size below 0.4 μm was greatly improved.

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Dependences of domain wall and interface wall on temperature have been simulated for the Domain Wall Displacement Detection, and the front process and the rear process have been considered. For the front process, abrupt decrease of the exchange-coupling contributes to small jitter of the wall displacement of the displacement layer. There exists magnitude of external magnetic field where the front process can arise and the rear process can not in the displacement/switching/memory structure. For the rear process, the control layer disturbs that the interface wall spreads to the displacement layer, as a result, critical mark length for the ghost can be elongated in the displacement/control/switching/memory structure.

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Simulation for the Domain Wall Displacement Detection has been studied Temperature dependence of the Gilbert's damping factor is inversely proportional to that of the net magnetization. Motion of the magnetization in the wall is similar to that for single domain due to large driving field Wall coercivity is might be small enough not to affect wall velocity. Average wall velocity is estimated to be 50m/sec for linear velocity of 3m/sec. The external magnetic field of ±200Oe considerably influences the wall velocity.

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With a combination of a high numerical aperture (NA) lens and a short wavelength laser, ultra high density over 100Gbit/in² recording can be achieved by the Magnetic AMplifiying Magneto Optical System (MAMMOS). In MAMMOS, after the expansion of copied domain in the reading layer and getting high level read out signal, the domain should be collapsed for reading out next information. Then, the velocity of the expansion and shrinking of the domains is one of the most important parameters which corresponds to the high speed performance of MAMMOS. We have developed a new stroboscopic observation system by using an image intensifier with a high speed shutter as fast as 200ps for observing domain dynamics. By using the system, the domain shrinking processes are observed and the results are shown.

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Super-resolution readout was established by using a non-magnetic readout layer on a magneto-optical disk. The readout layer was composed of AgOx and separated from a recording layer at a near-field coupling distance as well as a super-resolution near-field structure (Super-RENS) disk. A laser-generated Ag cluster works as a scattering center in the readout layer to reproduce a Kerr rotation angle of a recorded mark. As a result, by using the AgOx readout layer, marks of about 200-nm size could be read out beyond the diffraction limit

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As a result of applying super-resolution near-field structure to a magneto-optical disk with a non-magnetic mask layer such as a silver oxide light scattering center type mask layer, we could retrieve the signals of below 200-nm mark length. With the improved antimony transparent aperture type mask layer, in this work, we could get the polarized magneto-optical signals as well that we had not been able to obtain by using the previous antimony mask layer. This was well agreed with computer simulation result. Another optimization, such as magnetic layer thickness, dielectric materials and so on, was also investigated for a better magneto-optical disk of super-resolution near-field structure with a silver oxide light scattering center type mask layer.

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