As use of the Internet expands and broadband network operations increase remarkably, so too methods of using pictures, sounds and other media contents are beginning to change dramatically. These contents, which are conventionally transmitted by broadcasting, CATV, and packaging, can now be taken from networks as communications and broadcasting fusion.
Broadcasting is becoming increasingly digitized, thus broadening the range of new services it can provide such as multi-channel, Hi-Vision, data broadcasting, and storage-type broadcasting. With its rich media contents, broadcasters now see broadband as a new business opportunity, and several attempts to exploit it have already been made.
Furthermore, there has been impressive progress in storage technology. For instance, the “Blu-ray Disk, ” a large-capacity optical disk, can store up to 13 hours of regular-definition television programs and up to two hours of Hi-Vision programs. If this technology is applied to professional use recording devices, these optical disks can be used for all operations including archive management at broadcasting stations. As the hard disk, which was originally developed as a memory device for computers, becomes ever more powerful and cheaper to produce, it is becoming possible to use it as a video storage device.
Contents are the key for expansion of broadband use. In the flow of contents from production and distribution to storage and reproduction, the role of the storage device will continue to grow. This paper describes the prospects of broadband applications and mounting expectations for storage devices.

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In diluted magnetic semiconductors (DMSs), extended sp-carriers strongly couple with localized d-electrons of transition metal ions. This sp-d exchange interaction causes interesting magneto-optical phenomena of DMSs. Large Faraday effect of Cd_1-xMn_xTe can be used for an integration of magneto-optical waveguide with semiconductor optical devices. The sp-d exchange interaction can be used for the manipulation of the motion of Mn²⁺ in Cd_1-xMn_xTe by ultrafast laser pulses. We also discuss magneto-optical properties of new DMSs.

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Experimental observations of linear and nonlinear magneto-optical phenomena in magnetically ordered nanostructured materials and thin films are discussed. Films of ferromagnetic nanoparticles of CoNbTa in SiO₂ matrix with a various relation of metal and dielectric phases were studied by means of static and dynamic magneto-optical techniques with subpicosecond temporal resolution. The optical second harmonic generation was investigated in ferromagnetic-semiconductor heterostructures MnAs/Si (111). The observed changes in the second-harmonic intensity were odd in magnetisation. Second and third harmonic optical spectra were studied in epitaxial magnetic thin films in the spectral range of 1.7-3.2 eV and 2.4-4.2 eV, respectively. No significant increase of the intensity of the nonlinear spectra was found above the bandgap near 3.2 eV where linear absorption increases by two orders of magnitude.

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The full-potential linearized augmented-planewaves (FLAPW) method is often regarded as a benchmark-setting approach among the electronic structure methods. Here we present ab initio calculations of polar magneto-optical Kerr effect spectra using the FLAPW method. A comparison to a different electronic structure method, the augmented spherical waves (ASW) scheme, demonstrates the independence of the results on a particular numerical procedure. The materials studied here include transition metals and their alloys, viz. Fe, Ni, Co, CoPt, and FeAu, the uranium compounds US, URhAl, and UCu₂P₂, and the transition-metal oxide CrO₂.

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The recent development of Magneto-Optical (MO) devices has been reported. Variable types of MO devices are used in the current optical networks. For the next generation systems, the polarization control device and dispersion control device using Magneto-Optical effects will be needed.

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Quadratic or second-order magneto-optic effects in reflection significantly affect magneto-optic vector magnetometry and magneto-optic ellipsometry measurements. Theoretical formulae for the magneto-optic effects in uniaxial crystals as a function of crystal rotation have been derived including quadratic terms in a permittivity tensor. Anisotropy phenomena of the quadratic MO effects enable to distinguish among main crystal symmetries. Method for measurement and evaluation of the quadratic MO parameters has been proposed.

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This paper reports on experimental results which evidence particles size effects on Faraday rotation induced in ferrofluids. The four ferrofluid samples studied here are all issued from the same initial ferrofluid. Using a separation phase method their diameter size distributions are centered around four different values, their volume fraction of particles being adjusted to the same level. Optical and magneto-optical measurements on theses samples show that using small diameters provides a large increase of the factor of merit of this material.

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Dependence on γ-Fe and Cu thickness of magneto-optical Kerr effect for [γ-Fe/Cu] epitaxial multilayers grown by MBE method has been investigated. The sub-valleys of the polar Kerr rotation spectrum and the thickness-dependent shift of them are observed. The sub-valley around 2.7eV could be attributed to the magneto-optical transition from the majority spin Δ₂ band to the QWS's majority spin Δ₁ band in the γ-Fe layer. In addition, the Cu thickness-dependent shift might arise from the shift of the QWS in the γ-Fe layer by the change of the electron property of γ-Fe accompanied with the change of Cu thickness.

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Nonlinear (at the second harmonic frequency of the incident light) optical reflection by two-dimensional hexagonal magnetic bubbles (cylindrical magnetic domains) lattice is theoretically studied. Because the period of this magnetic bubble lattice is comparable with the wavelengths of the fundamental and the second harmonic radiation, it would be possible to observe diffraction at the second harmonic frequency. A polarization analysis of nonlinear diffracted radiation is performed.

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The non-linearities arising in the magneto-optical recording write channel are described. Their occurrence result in distortions that are damaging to the information circulating across the channel. For high speed data recording it is imperative to have a precise view of the transmission characteristics of a signal sent across the channel. When the non-linearity is weak, it is possible to perform Volterra series expansions to model the time response and port it to the frequency domain where non-linear distortions are derived from basic principles and applied to a general time dependent recording write channel.

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Faraday rotation spectra were measured in single crystals of SrTiO₃ between 1.7 and 3.2 eV at room temperature and at 20 K. The rotation showed a monotonous increase as the absorption edge was approached. In a single crystal with thickness of 0.5 mm, it took a value as large as 7.7° at 400 nm for magnetic field of 1 T. The center of dispersion of the magneto-optical spectrum was determined to be 4.19 eV. This value agreed with the peak energy position (=4.2 eV) of the imaginary part of dielectric function, ε₂ deduced from the reflectivity spectrum meas red between 0.5 and 20 eV.

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We have succeeded in preparing good quality epitaxial CoCrPt thin films on different substrates (Al₂O₃, LaAlO₃, SrTiO₃ and MgO) with the c-axis perpendicular to the substrate plane and magnetic properties were investigated. Magneto-optical spectra of the CoCrPt films prepared under different conditions were measured at room temperature between 1.2 and 6 eV, to investigate the physical properties of these films from the fundamental point of view.

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The magnetic properties of Co/Pt films can be modified and even controlled by ion beam irradiation. For example, the coercivity and magnetic anisotropy of a 1.4nm thick Co layer are reduced with increasing the Ga⁺ ion dose. Images of the demagnetized states and remanent hysteresis loops are obtained for arrays of dots or tracks patterned by the focused ion beam technique. 20 nm wide sharp non-magnetic irradiated lines separate the magnetic dots or the tracks, the size of the dots or the width of the tracks varying from 1.8 μm down to 70 nm. The efficiency of the dipolar interaction is studied, and the use of such dot arrays for magnetic or magneto-optical recorrding discussed.

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We present theoretical model of magnetooptical binary grating with cylindrical microdots, where the anisotropy of permittivity is induced by external magnetic field. Rigorous coupled wave method is applied to grating multilayer with periodical ordering. In particular, Kerr rotation versus grating fill factor dependence is studied and obtained results are compared to experimental ones.

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Optical storage is the leading technology for removable storage media. In order to follow the roadmap of other computer components, an annual capacity growth of 30% to 60% is needed. In the past, this was reached by decreasing the wavelength and increasing the numerical aperture; however, the next generation of DVR will approach practical limits with a numerical aperture of 0.85 and a wavelength of 405 nanometers. In order to reach capacities in the range of terabytes, volume recording is needed. We show that minor changes in the architecture of optical pick up can allow multilayer recording of a few hundred layers. New media are needed but solutions are foreseen for Read Only and Write Once media. Magneto-optic and Phase-change rewritable media offer a poor modulation to absorption ratio; therefore, multilayer rewritable media is still a challenge.

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We have been developing an electron beam recorder (EBR) for high-density optical disk mastering, and use it for read-only memory (ROM) and rewritable (RW) substrate mastering. We confirmed a 4.4% jitter value at 25 GB ROM disk. The reproducing characteristics of the high-density optical disk were dominated by the signal-to-noise ratio and the cross-talk. We fabricated an RW substrate with a 320-nm track pitch and confirmed a 5.4% jitter value for a data bit length of 112 nm after 100 direct-over-write and crosswrite cycles.

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To achieve ultra high-density Magneto-optical (MO) recording, it is necessary to increase the domain wall coercivity (H_W) to freeze the shape of a written domain. TbFeCo film is fabricated on FePt crystalline film, which has large crystalline magnetic anisotropy, to increase the H_W of TbFeCo film by the exchange coupling effect. The TbFeCo film is rare earth (RE) dominant ranging from room temperature (T_room) to Curie temperature (T_c). The FePt is deposited as multilayers and then it is subjected to vacuum annealing at 400°C for 2 hours. The TbFeCo/FePt film shows higher H_W, coercivity (H_c), and the thermal stability than those characteristics of the single TbFeCo film. Those characteristics can be attributed to the exchange coupling between magnetic moments of Fe and Co in TbFeCo and FePt films.

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Non-stoichiometric spinel ferrite films are proposed in this work as write-once recording layers for high density optical storage with blue laser sources. Two types of ferrite films has been studied: mixed Co-Cu ferrites and γ-Fe₂O₃ which are anionic deficient and cationic deficient phases respectively. For Co-Cu ferrites films, the minimal writing powers leading to “readable” bits were 15 and 4 mW for red and blue laser spots respectively. Writing is realized by local oxidation of the film by laser heating. The readout signal takes benefit of the resulting changes in optical properties and bump formation on media surface.γ-Fe₂O₃ films can be locally transformed into α-Fe₂O₃ by blue spot irradiation without any topographical modification of the film surface. The transformed domains can be optically read because of different optical indices for γ and α phases in the blue spectral region. Writing sensitivity of γ-Fe₂O₃ film can be improved by adding 10 nm thick absorptive Ti layer. 5 mW is then enough to write bits at 488 nm. For this type of structure, small bumps are however formed on the written domains.

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Perpendicular magnetic anisotropy of sputtered Gd-Fe thin films has been investigated by means of X-ray diffraction, energy-dispersive X-ray spectroscopy, conversion electron MOssbauer spectra and magnetisation. The results show that the as-deposited film is already formed in a nanocrystalline state with a perpendicular magnetic anisotropy. The hyperfine field distribution implies a coexistence of two magnetic phases with respective average<B_hf>value of 31 T and 18 T. The high hyperfine field phase corresponds to Fe-rich nanoparticle and the low hyperfine field one is related to an amorphous Gd-Fe state. As the annealing temperature is increased, the separation of these two phases becomes more evident. The Fe-spin orientation and the perpendicular magnetic anisotropy constant (K_⊥) have been estimated. For the as-deposited film, K_⊥equals to 8.5×10⁴J/m³. It is enhanced as the temperature is decreased and annealing temperature is increased. The observed perpendicular anisotropy has been attributed to the surface contribution.

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Fe/FeSi/Si/FeSi/Fe epitaxial structures with combined spacers are prepared using co-evaporation. Combined spacers consist of Fe_0.5Si_0.5grown at elevated temperature and nominally pure Si. The thickness of each part of the combined spacers is varied from 0 to 20Å. Magnetic properties are examined with longitudinal MAKE hysteresis and Brillouin light scattering. Inserting Fe_0.5Si_0.5layers at the bottom interface increases antiferromagnetic coupling due to the suppression of ferromagnetic coupling. Interlayer exchange coupling for combined spacers exceeds 8 erg/cm². The dominant role of the insulating-type part of the combined spacer consisting of nominally pure Si spacers for strong antiferromagnetic coupling is demonstrated.

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Magnetic Co/Pd superlattices have been sputter deposited using special triple concentric ring magnetron cathode. Magnetic layer properties are investigated as function of argon/krypton sputter gas pressure and of Co layer thickness showing maximum coercivity at 0.2 nm Co thickness. Coercivity is approximately linear function of sputter pressure with highest value of 7 kOe at 40μbar Kr. Special software to control sputter time and power allow deposition times of less than 0.1 s for an individual layer of the superlattice. Power ratio dependent co-sputtering of two cathodes enables preparation of stoichiometrically varying TbFeCo layers giving therefore a tool for efficient investigations of magnetic properties on layer composition.

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This paper describes the details of a new co-sputtering device (Multi-Source Trio) designed for the SPRINTER 750 sputtering system for MO production (MiniDisk, 3.5″ or smaller formats). Focussing on TbFeCo films we present data for changing the magnetic properties of the film by adjusting the sputter power level on the individual targets with different elemental composition. Special emphasis is placed on the composition uniformity throughout the disk which has been shown to be better than 0.2%.

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Bi₃Fe₅O₁₂ thin films have been deposited onto single crystal Gd₃Ga₅O₁₂O (111) substrates by the technique of pulsed laser deposition. X-ray diffraction patterns and cross section transmission electron micrographs show epitaxial growth and a flat interface between film and substrate. The magnetic-optic Faraday rotation is high, with a peak value of 22deg/μm at 560nm. The films have been used to visualize at low temperature the out of plane flux density distribution at the surface of a patterned high Tc superconducting thin film

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A PtCo multilayer magneto-optic recording medium is deposited on a nano-structured 2D sinusoidal grating substrate to study the concept of plasmon enhancement of magneto-optic readout and other phenomena associated with this type of surface. Comparison is made with the magneto-optic behaviour of a simple cobalt film deposited on the same structured substrate and PtCo multilayers in the Kretschmann-Raether configuration.

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Films of the potential electron trapping optical memory medium CaS: Eu, Sm produced from optimally composed sputtering targets, are themselves optimized by postdeposition thermal processing in a sulfur atmosphere. X-ray diffraction studies and a variety of spectroscopic techniques are used to study the development of crystalline structure and the deployment of the active Eu and Sm species within the CaS host lattice.

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To predict the performance of optical read channels readout waveforms generated using linear superposition techniques are often used. The readout waveform is, however, often degraded by non-linear components particularly at high storage densities. In this paper the origins of such non-linearities are explained and their effects on read channel performance investigated. It is found that channel bit error rate can be properly optimised only if the signal non-linearity is taken into account.

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We present a new direct method of“ stereo-microscope” for three dimensional structure analysis of thin films, with which one can realize three-dimensional atomic arrangement directly by eyes. The azimuthal shifts of forward focusing peaks in photoelectron angular distribution pattern obtained with left and right helicity light are the same as the parallax in stereo-view. Taking advantage of this phenomenon of circular dichroism in photoelectron angular distribution, one can realize a stereoscope of atomic arrangement. A display-type spherical-mirror analyzer can obtain stereoscopic photographs directly on the screen without any computer-aided conversion process. Some recent results are described.

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X-ray magnetic circular dichroism (X-MCD) was used as magnetic contrast mechanism to image at high lateral resolution the domain structure in thin magnetostrictive Terfenol-D layered systems both with full field magnetic X-ray transmission microscopy (M-TXM) at the Advanced Light Source (ALS) in Berkeley CA (USA) and a new photoemission electron microscope (PEEM) at the Swiss Light Source SLS in Villigen (Switzerland). The switching behavior of the magnetic domain structure could be studied with the transmission X-ray microscope at the ALS by recording the evolution of magnetic domains in external magnetic fields. A spin reorientation from out-of-plane to in-plane was observed both after tempering the as-grown amorphous system at elevated temperatures and with decreasing thickness. The coupling mechanism to an adjacent Co layer could be observed due the inherent element-specificity of X-MCD by images taken at the Fe and Co sites, resp. The complementary of x-ray-in/x-ray-out and x-ray-in/electron-out microscopies to image magnetic microstructures could be demonstrated

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Abstract- X-ray polarization-contrast images arising from x-ray magnetic linear dichroism (XMLD) in hard xray spectral range have been recorded in an iron-rich metal-particulate (MP) magnetic recording medium for the first time employing an interesting optical system: polarization switching optics. The contrast of 0.06/0 between 90-degree magnetic domains, which were made artificially on the sample, was clearly observed at photon energy of 1 eV above the iron K-absorption edge.

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This contribution is motivated by the idea of the development of a 2D magnetic field detector. A potential application is in material evaluation - micro-crack detection using stray field sensing. Another motivation is the general study of interactions betwtween individual magnetic elements which can act as magnetic tunnel junction (NITJ) electrodes in MRAM (magnetic random access memory) array or magneto-static logic elements. The structure is studied by magneto-optic (MO) methods including MO diffraction measurement awl Kerr microscopy. At the end of this paper will be presented a comparison of experimental data obtained by Kerr microscopy with micro-magnetic simulation based on the lattice spin Hamiltonian

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A short overview of the present state of the magneto-optical imaging of magnetic flux structures in superconductors and magnetic materials is given. Modern applications of the technique use ferrimagnetic garnet films with in-plane anisotropy as magneto-optical indicators. Advantages and limitations of the technique are reviewed and its possible further development is discussed.

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Using the magneto-optic Kerr effect and atomic force microscopy (AFM) we investigate nanoscale ferromagnetic entities directly patterned in thin superparamagnetic films of Fe-Cr by means of interfering laser beams. We demonstrate, for the first time, that a contact mode of AFM with a non-magnetic tip can be suitably modified to visualize in great detail the response to external fields of even a single nano-ferromagnetic entity in a patterned array. This new approach for magnetic imaging, which we consider to be a magnetostrictive response (MSR) technique, having a lateral resolution typical of AFM, is used to show the strong dependence of the magnetic response of these nanoscale entities to prior magnetization direction. The observed MSR effects provide further insight into the magnetic microstructural aspects of the laser patterned entities and explains qualitatively the information obtained by means of Kerr magnetometry and magnetic force microscopy.

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Abstract- The ultimate speed limit of thermo-magnetic writing is investigated by time-resolved measurements of femtosecond laser pulse induced magnetization reversal in amorphous Gd_23.1Fe_71.9Co_5.0. We prove the resulting reversal dynamics to be governed by the product of two independent processes-the temperature induced changes of the magnetization magnitude times the magnetic field driven reversal of its orientation. Based on this factorization, purely magnetic reversal times are derived from the data. These times show no variation with temperature, but tremendously decrease from several tens of nanoseconds down to only a few picoseconds with increasing excitation density. A minimum reversal time of about 2 ps is found that indicates the possibility of THz thermo-magnetic writing rates. However, the slow cooling of the heated sample limited the maximum achievable writing rates to the GHz range. Only slight improvement of the cooling rates is found when substrates with almost perfect electronic (gold) or phononic (sapphire) heat conductivity are used as heat sinks.

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In Magnetic Amplifying Magneto Optical System (MAMMOS), a small domain in the recording layer is copied to the readout layer where the domain is expanded to a high level readout signal. After the expansion, the domain should be collapsed for reading out the next information. Therefore, the velocity of expansion and shrinking of the domains is one of the most important parameters which certainly affects the high speed performance of MAMMOS.
We have developed a stroboscopic microscope system for observing domain dynamic phenomena. By using this system, domain shrinking processes are observed under a variety of applied fields and the influence of the in-plane magnetic field on the shrinking speed is also measured.

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A new method is developed to simulate how crescent-shape domains are 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 especially crescent ones were performed under the several conditions. The results show that the rapid quenching of the film temperature plays an important role to write crescent-shape domains and over 50Gb/in² can be recorded.

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In this work, we report on a study of the magnetization reversal of (Ga, Mn) As/GaAs systems. Four 0.5 μm thick Ga_1-χ Mn _χ As layers (χ = 0.017, 0.025, 0.051 and 0.057) grown by low temperature molecular beam epitaxy on GaAs substrate are investigated using magneto-optical Kerr effect (MOKE). Firstly we analyze static magnetic properties and we identify a four-fold in-plane anisotropy. Using a modified Stoner-Wohlfart model, the magnetocrystalline anisotropy constants are estimated. In last part of this paper we study the dynamic effects on the magnetization reversal when increasing the applied field sweep rate.

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Thermomagnetic recording process was simulated for Tb_χ (Fe₇₈Co₂₂) _100-χ media with the thickness of 40 and 20nm by using Huth's model modified for the MFM recording.In the recording of marks smaller than-200nm, the recorded mark length was found to exhibit larger value than the designed mark. From the analysis of the effective fields acting on the domain wall, the stray field was found to be important factor in the recording of the small size marks.

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Abstract-High-density recording four times that of a current DVD-RAM has been achieved by applying Domain Wall Displacement Detection (DWDD) technology using a conventional optical head which has the same wavelength of 660 nm and NA of 0.6 as the DVD head. It has been confirmed by using a sampled servo and PRML that a recording density of 15 Gbit/inch² with a track pitch of 540nm and bit length of 80 nm has sufficient system margin. This means that a capacity of 3 GB on a two-inch-diameter disk is now available for portable use. If applied to a digitalvideo camera, one hour of MPEG2 video contents can be recorded at a transfer rate of 6 Mbps.

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We have developed a magneto optical disk system, having the recording density of 7.1 Gbit/in², by using zero-field type MAMMOS technology and an in-groove structured disk with a 635 nm laser diode and a 0.60 N.A.objective lens. We demonstrated that the system has enough margins for read/write powers, tilt, detrack anddefocus. On the other hand, the dependence of polarization direction of the incident beam on read/write characteristics was a problem, but was solved by optimizing the groove width.

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In a Magnetic Amplifying Magneto-Optic System (MAMMOS) the InterSymbol Interference (ISI) problem is solved by copying bits from the recording layer to the readout layer through an aperture formed by the lagging thermal profile of the optical spot. The SNR problem is tackled by expanding and -after detection-collapsing of the copied domain with an external magnetic field. The consequence is that the detected MAMMOS peaks are partly in phase with the applied external field and do not contain information about the exact location of the bits in the recording layer. This hampers straightforward clock recovery.
A new clock recovery method where the external field is switched depending on the detected data solves this problem. First experiments with a phase-locked loop (PLL) based on this clock recovery method show a jitter of 10.8% when detecting II marks separated by 19 spaces at linear bit dimensions of 250 nm for a system with a laser spot diameter of 0.66 μm (λ=658 nm; NA=0.6).

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OLYMPUS OPTICAL Co. Ltd., Hitachi Maxell Ltd. and SANYO Electric Co. Ltd. have developed a Magnet-Optical disk system, iD (Intelligent, Image) PHOTO disk as a next generation system for data storage. The iD PHOTO system is based on the AS-MO (Advanced Storage Magneto-Optical disk) and its media has a high capacity of 730 MB in a 50.8mm diameter single-sided disk. The storage capacity exceeds that of a CD (compact disc), while being the world's smallest rewritable optical disk.
Considering its intended role as a portable application, it is important to evaluate its various characteristics under a variety of environmental conditions for its reliability. In this paper, we evaluated the recording and readout characteristics of the iD PHOTO disk under environmental temperatures ranging from -5°C to 60°C and under an accelerating condition. The obtained results proved the iD PHOTO disk to be a suitable recording medium for use as a mobile storage device with a high level of reliability and performance.

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For almost all optical disks, signal decline is mainly due to inter symbol interference (ISI) caused by laser beam spot size or magnetic aperture size. Such 151 does not appear for Zero Field Magnetic Amplifying Magneto-optical System (Zero Field MAMMOS). The limit of the frequency response comes from the frequency range of the MO readout channel. MAMMOS has a resolution for 1/10 of a laser beam corresponding to 0.1μm. Decrease in the carrier level and error of less than 0.1μm is caused by expansion failure. If expansion failure were circumvented, Zero Field MAMMOS would have a possibility of readout with 0.04μm resolution using a laser with wavelength, 650nm and an objective lens of NA, 0.6.

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In the ongoing effort to achieve ultra high density Magneto-Optical recording, Laser Pumped Magnetic Field Modulation (LP-MFM) and Magnetic Amplifying Magneto-Optical System (MAMMOS) are considered promising methods. Using LP-MFM, crescent domains are recorded in a recording layer. Micro-magnetic simulations for the MAMMOS readout have already been reported assuming a crescent domain and red laser irradiation. Huth's equation simulations for the MAMMOS readout have also been reported assuming a circular recorded domain and blue laser irradiation. Micro-magnetic simulations for the MAMMOS readout assuming a blue laser irradiation, however, have not so far been reported. This paper presents the analysis of the combination of a 405nm blue laser and the MAMMOS readout from crescent recorded domains using the micro-magnetic simulations. In this work, MAMMOS readout from a crescent recorded domain is shown to be possible even with blue laser irradiation.

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A promising method for overcoming the diffraction limit for reading marks recorded in optical storage disks is the MAMMOS approach. In this paper some results of a computational investigation of the record and readout processes for a MAMMOS-type disk are presented. Strategies for improving written bit shape and regularity are suggested. The LP-MFM method is shown to be suitable for recording shor marks with accurately located edges. A model for the readout process indicates that the domain copy process occurs quickly followed by domain expansion as the readout layer heats up.

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Use of magneto-optical (MO) medium sputtered from an intermetallic compound alloy target has advantages for mass production but may not be suitable for high-density recording due to its poor perpendicular magnetic anisotropy. The relationship between Ms Hc, the product of saturation magnetization Ms and coercivity Hc, and film microstructure is discussed in this paper; we obtained an Ms Hc of 1.3 × 10⁶ erg/cm³ using microcolumnar structure even when the medium was sputtered from an alloy target. By adopting this film for the memory layer in a DWDD system, tiny marks less than 100 nm in size can be reliably written. As a result, high-density recording at 15 Gbit/inch² is achieved.

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MAMMOS (Magnetic Amplifying Magneto Optical System) is a promising technology for high storage densities towards 100 Gb/in² in rewriteable optical recording systems. However, the laser power margin for correct readout is quite small. This small margin is explained by a discussion of the readout process. A method is proposed to significantly improve the resolution and power margin by using different run length constraints for marks and spaces. Detailed simulations and experimental results on power margin versus bit length are presented, demonstrating improvements in power margin by a factor of around 3 (at constant density) and an increase in storage density by about a factor of 2 (at constant power margin).

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A new type center aperture detection (CAD) magnetically induced super-resolution (MSR) disk is described. A magneto-static type CAD disk was already reported last year, and it improves readout stability withou deteriorating the readout characteristics such as readout resolution by using a gadolinium intermediate layer instead of a non-magnetic layer. Our group studied the intermediate layer further, and realized the exchange coupling type CAD disk that has high-resolution and readout stability simultaneously by using GdFeCo intermediate layer. It has large tolerance to the external magnetic field at readout. The tolerance became about three times larger than the magneto-static coupling type CAD reported before.

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The merging of concepts from magnetic and optical recording technology is now considered an important approach for the continuation of the forty-five year upward march of areal density performance in rigid disk drives (RDD) and other recording systems. Hybrid recording has been proposed in many forms, but here we discuss architectures appropriate for the anticipated thrust of RDD toward 1 Tb/in² and beyond. At these extreme areal densities, many novel technologies must be combined for the performance of thermomagnetic recording consistent with the exacting requirements of RDD. The design of media to support this technology at the required densities will demand significant extensions from past trends into realms that accommodate use of elevated temperatures and compatibility with novel sources of near-field (NF) electromagnetic (EM) energy. We report thermomagnetic recording simulations which illustrate how the recording physics are centrally related to the interplay of optical, thermal, and magnetic phenomena

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We present modeling and experimental work on the alignment tolerances between the optical and magnetic head in a hybrid recording system. The experiments were performed using a longitudinal magnetic write head on TeFeCo media. Based on these findings conceptual designs for an integrated transducer are given.

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