Magnetization induced second harmonic generation (MSHG) is a new nonlinear magneto-optical technique that combines interface sensitivity with huge magneto-optical effects. These effects are due to the simultaneous breaking of inversion symmetry (at. interfaces) and time-reversal symmetry (by the magnetization). The higher-order nonlinear optical tensor is also responsible for the appearance of essentially new magneto-optical effects that have no equivalent in the linear case.
  Because most magnetically ordered materials are centrosymmetric in their bulk form, MSHG is a particularly useful probe to study the magnetic properties of the interfaces in magnetic multilayer systems, that are used for recording as well as sensor materials.
  In this paper, I will give a brief introduction and overview of this novel nonlinear magneto-optical technique, and discuss some recent advances in this field. In particular the possibilities to probe in-situ the magnetic and structural (changes in the) interface properties of magnetic multilayer sensor and recording materials will be illustrated.

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  We have fabricated micronic and submicronic dot arrays patterned from ultrathin films Au/Co/Au in order to study their magnetic properties using polar magnetooptical Kerr effect (PMOKE). Kerr microscopy observation of the magnetization reversal inside the dots reveals a wide distribution of nucleation energy barriers in the continuous film after processing. This is observed in the dot arrays because of the blocking of the domain wall propagation at the dot boundaries. Polar Kerr effect measurements have been performed in the specular beam and at the different diffraction orders. The Kerr rotation depends on the surface occupied by the dots, and differences on the diffracted beams are observed in the Kerr rotation between the "s" and "p" incident polarizations. Such observations have stimulated the elaboration of a theory of the magnetooptical far field Fraunhofer diffraction by a regular array of magnetic dots, which qualitatively explains the experimental results.

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  Lorentz electron microscopy in a highly modified transmission electron microscope has been used to study the magnetisation reversal process in films of interest as magneto-optic storage media. Domain structures, mainly in CoNi/Pt multilayers, have been observed under a range of applied field conditions. Whilst domain propagation under increasing fields and the approach to saturation have both been investigated, the focus has been on the early stages of domain growth where time-dependent effects are prominent. Close agreement between experimental observations and micromagnetic modelling has been achieved allowing values of the domain wall energy to be extracted.

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  We have combined a Magnetic Force/Atomic Force Microscope (MFM/AFM) with a Magneto-optic (MO) microscope. This instrument combines the high spatial resolution of the MFM/AFM and its capability to correlate magnetic structure with the structure of the sample surface with the real-time imaging capability and large field of view of the MO microscope. Using this instrument, we studied nucleation and displacement of domain walls (DW) in amorphous TbFe alloy films and Co/Pd multilayer films. We found that in Co/Pd multilayer film with 20 Co/Pd layer pairs and 16 nm total thickness, nucleation of domains during sample remagnetizations occurs repeatedly in the same points, and that displacement of domain walls is unidirectional. The high topographic resolution of the AFM allowed us to show that domains nucleate at small defects (1-2 nm in depth) on the sample surface. The unidirectional displacement of the domain walls was found to correlate with the anisotropic structure of the sample surface. We observed reversible bending of domain wall segments pinned to defects and irreversible, jump-like displacement of domain wall segments in an applied magnetic field. The maximum reversible displacement of domain walls was 50-100 nm and the length of the segments which reversibly curved in the field was about 150 nm. Measurement of the change in radius of curvature of a DW segment in response to an applied field allowed estimation of the DW energy density and local self-demagnetizing field of the film acting on the DW. The irreversible displacement of a DW was not a continuous process. The 200 - 400 nm long DW segments exhibited jump-like motion over distances of 100-150 nm.

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  We present a scanning near-field optical microscope (SNOM) which is optimized for quantitative determination of magneto-optic effects. Faraday rotation can be measured in transmission mode while a reflection mode SNOM enables us to determine the Kerr rotation on opaque samples. The local Faraday rotation of rare-earth doped ferrimagnetic garnets is presented as well as the local Kerr rotation of a Co/Pt sample with thermomagnetically written magnetic domains. A quantitative determination of magneto-optic effects is achieved by employing a phase-modulating lock-in technique. This allows the investigation of the fine structure of domain walls which is illustrated on the garnet samples. The angular resolution of the local Faraday and Kerr rotation is limited by the degree and stability of the polarization at the fiber tip and amounts to approximately 0.1° for the samples presented.

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  Magnetic domain patterns and their dynamics in 500 Å thick Fe₁__xTb_x amorphous magnetron-sputtered films with 0.16 < x < 0.35 have been studied experimentally. All films possess a strong perpendicular anisotropy (PMA) with the anisotropy constant K_U ≈ 3·10⁶ erg/cm³ . For the observation of the magnetic domains a Kerr microscopic technique was used. The Kerrmicroscopical observations showed that the domain patterns are strongly dependent on the film composition. It was also seen that the deviation of the composition from the compensation point (x ≈ 0.23) plays a decisive role in the pattern appearance. The time dependence of the integral Kerr amplitude gives the temporal evolution of the remagnetization process. In order to describe the experimental observations a micromagnetic model was developed showing good agreement with the experimental results.

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  We proposed the multi-wavelength read-out (MWR) method for achieving both high signal to noise ratio and large memory density of MO recording. The double MO layered disk was optimized for MWR and fabricated by sputtering. Recorded data were reproduced by using lasers of 680 and 780 nm in wavelength. It was proved that the recorded data for each MO layer were independently deduced by using MWR method without changing a optical focus point.

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  A magnetic amplifying magneto-optical system (MAMMOS) which can expand a size of a small domain is one of the most promising candidates for ultra high density MO storage. Since the MAMMOS read-out consists of both domain expansion and collapse processes, it is important to understand the behavior of the aperture of the read-out layer in order to optimize laser power to achieve higher resolution. This paper reports on the aperture state and the read-out response, when an alternating magnetic field is applied. It is shown that domain expansion and collapse processes occur many times for every 0.4 μ m sized domain and that the shape of the read-out signal is very square. Additionally the number of times that the domain expands and collapses decreases by lowering laser power, which means that the aperture area becomes restricted. It was also confirmed that both expansion and collapse times are much faster than the transient time of the circuit with a band width of 20 MHz, and it is independent of the read-out velocity.

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  In this paper we propose a new method to reproduce signals from high-density recorded patterns irrespective of the resolution of the readout optical system. The basic mechanism of this method, that is, domain wall displacement due to the temperature gradient, was confirmed by direct observation through a polarizing microscope. A clear readout waveform and a CNR of 39.5dB were obtained for a mark length of 0.1μm with this method.

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  A new type of magnetic expansion readout (Center Aperture Rear Expansion Detection) has been reported for the trilayer CAD-MSR disk with a TM-rich GdFe intermediate layer. The copied magnetic domain in the aperture of the readout layer expands restrictedly into the expansion region where the temperature is higher than that of the aperture. The expansion region corresponds to the rear mask for MSR. This disk has an advantage for readout because readout under low DC field and DC laser is possible.

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  For high density MO recording, a new method named MAMMOS using a magnetic domain expansion effect has been proposed[1]. In the readout process, recording domains marked in the recording layer are copied into the readout layer, and expanded to obtain a higher signal level. At first, this effect was confirmed by the magnetic field modulation (MFM) readout method[1]. Herein, however, we propose another scheme using a light intensity modulation (LIM) readout method, with which the readout laser power is modulated to control the expansion process. In a disk with an in-plane magnetizing film for the readout layer, the fundamental function of this LIM MAMMOS has been experimentally confirmed.

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  We have developed Light intensity Modulation Direct Over Write (LIMDOW) Magneto Optical (MO) media whose structure gives CNR higher by 2dB than the conventional LIMDOW. In addition, cross-write characteristic has been improved by tuning of magnetic layers parameter. The LIMDOW media with 1.9Gbit/inch² of recording density is realized by these improvements without using any techniques such as PRML in λ =680nm and NA=0.55.

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  The Magneto-Optical (MO) technologies for 5Gbit/inch² are combined and the performance is examined. Using an optical system of a 640nm laser and a NA0.6 objective lens, the thin substrate, land/groove recording, magnetically induced super resolution and laser pumped magnetic field modulation recording are employed for high density recording.

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  Influence of interference layer that is located between substrate and magnetic layer was studied in FAD structure. The Kerr ellipticity of reflection light could be decreased by using larger thickness than that of minimum reflectivity. This lead to crosstalk reduction in L&G recording that is strongly affected by the Kerr ellipticity. The crosstalk was decreased by 5dB on O.65μm effective track pitch, while CNR was not affected by the thickness.

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  Co_xPt_1-x (x≈0.25) alloy films with saturated remanence ratio were prepared directly on glass substrates by sputtering a Co-Pt composite target. Their thermal magnetic recording performances were investigated. The optical and magneto-optical (MO) spectra of CO_xPt_1-x (x≈0.25) alloy films were measured and the corresponding MO Voigt parameters were deduced. The experimental results showed that write & crase of static signals could be easily realized in sputtered CoPt alloy films using moderate recording power. Using the measured complex refractive indexes and the deduced MO Voigt parameters, the thickness dependence of Kerr rotation or CoPt alloy films was calculated, which could agree well with the experimental results.

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  Co₇₅Pt₂₅ films deposited onto Al₂O₃(0001), Al₂O₃(11-20) and, MgO(111) substrates at substrate deposition temperatures from 230 to 450°C exhibit a large perpendicular magnetic anisotropy ( > 1.0 × 10⁷ erg/cm³ at room temperature). X-ray diffraction analyses reveal the presence of the hcp CO₃Pt ordered state in these films. A close correlation between the ordered state and the large perpendicular anisotropy is found for films deposited at 380°C and above. Magneto-optical spectra show a characteristic peak for the film with ordered structure in a photon energy range from 2 to 4 eV in both of Kerr rotation and ellipticity. Magneto-optical properties of Co-Pt alloys above 5 eV are studied for the first time, where high positive Kerr rotation is observed.

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  MnPt₃/Co multilayer films were grown by the molecular-beam epitaxy (MBE) onto MgO(111) substrates at a temperature of 300 °C. Small angle XRD measurements demonstrated that the samples had multilayered structure with sharp MnPt₃/Co interfaces. The appearance of superlattice lines due to Cu₃Au structure confirmed a partial formation of the ordered phase in the MnPt₃ layers. The [MnPt₃(1.9 nm)/Co(0.4 nm)]₂₀ multilayer showed a preferential magnetization perpendicular to the film plane and a 100% perpendicular remanence. The Kerr spectrum of the multilayer had a negative peak of -0.24 deg around 1.4 eV and showed a enhancement in the high energy region. This result implies the existence of the ordered phase in the MnPt₃ layer and alloying layer of Co and Pt at the MnPt₃/Co interface.

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  Co/Pt/Ni/Pt/ multilayers have been prepared by rf sputtering to study the effect of Ni layer thickness on the magnetic and magneto-optical properties. The magnetization and the Faraday rotation have been interpreted in terms of the properties of Ni layers in Ni/Pt and a good agreement is obtained. The squareness of the loop of Co 5 Å/Pt 15 Å increases form 0.7 to 1.0 with the addition of very thin Ni layers (≤ 5 Å). For Ni layers thinner than about 10 Å, the effective anisotropy increases due to the contributions from the surface anisotropy in thin Ni layers and the reduction in 2πM². For thicker Ni layers this surface anisotropy is negligible and hence the loop shows in-plane character. In Ni/Pt multilayers, Ni layers thinner than 10Å are non magnetic at room temperature, but in the present system exchange coupling from Co layers lead to an relative increase in the Curie temperature.

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  Due to the ferrimagnetism of rare earth-transition metal alloys (RE-TM) the magnetic states of exchange-coupled double layers (ECDL) may present by increasing the temperature, strong modifications depending not only on the external field applied along the normal to the layers, but mainly on the type of the ECDL which can change from a type 1 with interlayer macroscopic antiparallel coupling to a type 2 with parallel coupling. The present work analyzes the temperature-induced magnetization states and processes in ECDL from perpendicular anisotropy TbFeCo film 1 and DyFeCo film 2. The films compositions were adjusted for T_CP1 < T_CP2 ∼ RT in order to well separate two temperature ranges for the types 1 (A) and 2 (P) which displays strong magnetooptical (MO) hysteresis changes as observed from Faraday rotation measurements. Direct and indirect (or multisteps) magnetic transitions are detected under increasing magnetic field depending on the temperature and ECDL type. For T < T_CP2 MO minor loops, shifted from zero field position by a bias field H_b induced by the interlayer exchange interaction, is observed. This bias field, associated with the creation of an interfacial wall σ_w, increases with T up to huge values (H_b > 10 kOe) near T_CP2 and vanisbes for T > T_CP2 where the bilayer has changed towards a type 2P

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  The activation energies for the structural relaxations in Tb₂₂Fe₇₈ and (Tb_0.22Fe_0.78)₉₈Si₂ were estimated to be 137-197kJmol^-1 and 142-194kJmol^-1, respectively. These structural relaxations are attributed to the Fe atom diffusion. The distribution of the activation energies in Tb₂₂Fe_0.78 is wider than that in (Tb_0.22Fe_0.78)₉₈Si₂. The addition of Si improves the thermal stability at low temperatures, corresponding to the temperatures in the pulse-heated areas of magneto-optical recording amorphous media.

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  Effect of in-plane anisotropy of amorphous HoFe thin films on the magnetic phase transition was investigated by measurements of temperature dependence of magnetization. We found that the coherent in-plane anisotropy induces ferrimagnetic phase as perpendicular one does. Such a “coherent anisotropy” is important to stabilize ferrimagnetic phase of rare earth-transition metal films for magneto-optical storage.

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  A mean- field theory is developed to research the temperature dependence of the amorphous SmTbFeCo thin films. It is shown that with available Sm substitution of Tb, the composition temperature T_comp decreases, Curie temperatureT_C remains unchanged, Kerr angle becomes larger, the saturation magnetization Ms at room temperature increases. Therefore, LRE-HRE-TM amorphous films can be used as the high density magneto-optical media in a wide range of temperature. However, the Sm substitution of TM does not improve the magneto-optical performance.

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  Cubic spinel ferrite films containing cobalt, copper and manganese were prepared by the rf sputtering from targets formed by intimate mixtures of ferrite powders. Additional heat-treatments at temperatures of about 450°C introduce cation vacancies which have positive influence on the magneto-optical properties of films. Figure of merit shows maxima at 600, 850 and 1500 nm which classifies these films to promissing materials for magneto-optical recording.

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  Single crystalline {Y₃}[Fe₂] (Fe₃) O₁₂ and {Y_3-x Bi_-x}[Fe₂] (Fe₃) O₁₂ (x ≅ 1.10) garnet thin films were deposited on either (111)-oriented gadolinium gallium garnet Gd₃Ga₅O₁₂ (GGG) or (111)-Ca-Zr substituted GGG using the ion beam sputtering method. The preparation consists of two main steps : i) deposition of amorphous films ii) post-annealing for crystallization in oxygen atmosphere. Using electron microprobe analysis, the Y/Fe content ratio. R, was determined. The lattice constant of the films was deduced from X-ray diffraction studies using Cu-Kα wavelengths. Only the (444) and (888) reflection peaks were observed and for all the films studied, the [111] orientation of the single crystalline films was deduced. We find first that the angular position of the reflections lines of the magnetic layer is quasi independent of the nature of the substrate for the pure YIG films. It is concluded that only films deposited on GGG substrates are epitaxially grown. Bi-YIG films deposited on large lattice parameter substrates were found also epitixially grown. The YIG film composition is explained by the presence of Y³⁺ ions in the octahedral [a] site when R<0.6 and by a point-defect structure model including an oxygen vacancy and a small amount of Fe²⁺ ions in the dodecahedral {c}site when R<0.6.

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  Optical and magneto-optical properties of several single and layered Co-, Ti- and Al-substituted hexaferrite thin films prepared by the sol-gel method were investigated. The Faraday coefficient exhibits pronounced extrema in the infrared and visible part of the spectra. Broad maxima of the figure of merit at 700 to 900 and 1400 to 1800 nm regions show that some of the materials could be considered as the candidates for magneto-optical recording materials at interesting laser wavelngths of 800 and 1500 nm.

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  The evolution of the magnetization distribution with the temperature is investigated in a wide range (0-500K) in bilayers F₁/F₂ corresponding to a TbFeCo or DyFeCo layer F₁ with perpendicular anisotropy exchange-coupled with a planar layer (F₂) with low (GdFe and GdFeCo) or large (GdCo) in-plane anisotropy. The temperature dependences of the magnetic parameters (magnetization, uniaxial anisotropy, exchange constant) are first determined in the layers F₁ and F₂ from the mean field theory. In a second step the evolutions with the temperature of the magnetization distributions are obtained from a micromagnetic model using a non-continuous model of the magnetization. A re-orientation of the magnetization from in-plane to normal to the film F₂ is stimulated at a switching temperature T_S2 which depends strongly on the magnetic parameters (magnetization, effective anisotropy) of the planar layer. The extension of the analysis from ECDL (F₁/F₂) to ECTL (F₁/F₂/F₃) with two in-plane magnetic layers F₂ and F₃ shows the possibility to induce sequential phase transitions at different switching temperatures T_S2 and T_S3 with a dynamic expansion of the transition in the capping layer F₃ when T_S3>T_S2.

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  To obtain a high S/N magneto-optical disk with a flat underlayer, the motion of the domain wall and the recording noise on various TbFeCo disks were investigated while varying compensation temperature and underlayer surface roughness. In disks with a rough underlayer, the recording noise decreased with increasing compensation temperature. In disks with a flat underlayer, we found that a rare-earth-rich TbFeCo disk had a large recording noise because of a strong contracting force acting on a domain wall. The relationship between the TbFeCo composition, the domain size and the contracting and expanding forces acting on the domain wall in the disks with a flat underlayer can be explained using Huth’s theory. In the disks with a rough underlayer, however, the dependence of these forces on composition and domain size could not be explained using Huth’s theory. A possible cause of this difference in the domain wall motions of the disks with flat and rough underlayers is that a disk with a flat underlayer has few domain wall pinning sites than a disk with a rough underlayer.

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  Thermomagnetic recording process has been simulated for transition metal(TM)-rich and rare earth(RE)-rich TbFeCo films assuming heam spot size of 1 and 0.1 micron, where very simple temperature dependence is assumed for the wall energy. For the TM-rich Tb₁₈(Fe₇₈Co₂₂)₈₂ film, domains smaller than 0.1 micron can be written owing to the large stray field. On the other hand, for the RE-rich Tb_25.6(Fe₇₈Co₂₂)_74.4 film, small domains cannot be written due to the large effective field which, originating from the wall energy and its spatial gradient, forces to shrink the domain.

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  We, who have three different manufacturing lines of Magneto-Optical disk, have started up manufacturing 2.6 Giga Byte / 130 mm Light Intensity Modulation Direct Overwrite Magneto-Optical (LIMDOW-MO) disk which an International Standard ; ISO / IEC 14517 specifies. We have checked the conformity of the specifications of those three LIMDOW-MO disks. Even though the three LIMDOW-MO disks have been made with the three different manufacturing lines, their characteristics have conformed to each other.

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  CoPt alloy films with perpendicular magnetic anisotropy and saturated remanence ratio were prepared on glass substrates with and without Pt underlayer by sputtering a composite target. The influences of Pt underlayer and its preparation conditions on the magnetic and magneto-optical properties or CoPt alloy films were investigated. It was found that the introduction of Pt underlayers could improve the magnetic properties of CoPt alloy films but the Pt underlayers must be prepared at low sputtering pressure (<2 Pa) or high sputtering pressure while the substrates were heated so that the underlayers and further the alloy films had good f.c.c. (111) crystalline orientation.

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  The magnetization and the Kerr rotation of Gd-, Dy- and Pr-Co amorphous films with various composition are measured. Based on the molecular field theory, the temperature dependence of the saturation magnetization is analyzed, and the subnetwork magnetizations are calculated. Assuming that the saturation Kerr rotation consists of two parts, each of which is proportional to the corresponding subnetwork magnetization, the proportional constants called Kerr rotation constants are determined from the compositional dependence of the Kerr rotation. The Kerr rotation constants for Co, Gd, and Dy are about −0.2, 0, and 0.08 [deg/T], respectively, and they depend only slightly on the wavelength between 400 [nm] and 1000 [nm]. The constant for Pr, on the other hand, increases quickly with increasing wavelength from a value of −1.4 [deg/T] at 400 [nm] to −0.3 [deg/T] at 1000 [nm].

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  A method for pinning magnetic domains with prescribed shapes has been developed for the magneto-optical (MO) thin film material Dy_x(FeCo)_1-x. The pinning array of holes on the substrate was fabricated using electron beam lithography. The thin film of Dy_x(FeCo)_1-x sandwiched between SiN layers was deposited onto a patterned polymethyl methacrylate (PMMA) layer. The pinned domains acquire the shape of the holes, while the sharpness of their boundaries depends on the size of the holes. The stability of the pinned domains is affected by the sample’s magnetization. In our experiments, the minimum stable domain size pinned within the hole array was found to be around 30 nm in diameter.

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  The Partial-Response Maximum-Likelihood (PRML) signal detection method is well known as an effective way to improve the recording density of a magneto-optical (MO) disk system. We have developed a PRML simulator to evaluate various PRML systems for MO recording. This report presents the performance evaluations of various PRML systems based on computer simulations to find bit error rate (BER) characteristics. Calculation of BER was made under the condition that the wave front aberration caused by tilt of the disk and defocus of the optical head is given to the readout beam.

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  In the mark-edge recording system with small marks, it has been difficult to simultaneously optimize an equalizer and recording conditions. So we studied how to optimize these conditions independently in such a system. Then we found out the necessity of compensation for the thermal interference according to not only the length of the preceding space but also to the length of the preceding mark. Therefore we developed Adaptive Themo-Compensation (ATC), which adaptively compensates for the thermal interference depending on the preceding mark length. By ATC, all edge-shifts are suppressed with optimal equalizer within 8.4%_p-p of a 0.27-μ,m detection window and, therefore, highly accurate mark-edge controllability is possible. As a result, wide recording power margin is secured.

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  Barium ferrite films have been grown by pulsed laser deposition on sapphire single crystalline substrates. With oxygen and at high temperatures (more than 700 °C), the films exhibit high orientation following the (001) texture. The anisotropy is always perpendicular, with the possibility of in plane component of the magnetisation with annealing at very high temperature (900 °C). The in plane component was attributed to the interdiffused layer which increases with the temperature and deteriorates the coercivity squareness. The magneto-optic measurements show two large peaks in the UV at 270 nm and 390 nm with +0.28 and -0.15 degree as Kerr rotation respectively. The two peaks correspond to the charge transfer transitions of the complex Fe⁺³-O^-2 in which the Fe⁺³ can be either in tetrahedral or octahedral site. The difference in the peak signs was attrihuted to the antiferromagnetic exchange coupling between the tetrahedral and octahedral sites

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  The purpose of this paper is to clear the practicality of an optical waveguide device for magneto optical disk head. This device is made on the Si substrate with photo-diodes for magneto optical signals detection. An incident light beam to this device is converted into TE and TM modes by its optical coupler, and these mode are separated corresponding to their polarization by its thin film bi-prism. The optical coupler consists of a prism and a resin layer with an edge portion. The edge portion, precisely defined by a photolithography process, produces stable coupling efficiency. This coupler structure also reduces sensitivity of the incident angle and coupling dependence on the polarization direction. In addition, a taper region is made around the thin film bi-prism to obtain high transmission efficiency. These waveguide technologies realize an integrated unit for a Mini-Disc head. As the evaluation results of a pickup, the CNR of 3T signal (resonance bandwidth: 10kHz) is 45dB.

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  Reading dynamics in front aperture detection (FAD) and center aperture detection (CAD) magnetic super resolution (MSR) media is studied using a high speed Kerr microscope system with 10-ns resolution. The effects of disk structure and reading conditions on the reading dynamics are investigated. Readout of 0.2 micron domains is successfully demonstrated using 488 nm wavelength light on CAD MSR media.

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  We have investigated high-density magneto-optical recording on a conventionally structured disk with a diameter of 64 millimeters using magnetic field modulation to achieve a capacity of 650 Mbytes. With the groove conditions optimized, the jitter with cross-talk from adjacent tracks was 7.2% and the recording power margin including overwriting and crosswriting was ±20%. As a result of minimizing cross-talk, a sufficient tilt margin of ±0.82 degree and ±0.63 degree in the radial and tangential direction, respectively, was obtained.

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  We have developed the large capacity Light Intensity Modulation Direct Over Write (LIMDOW) Magneto Optical (MO)media by adding the Magnetically induced Super Resolution (MSR) function to the conventional LIMDOW. We selected the magneto static coupling Center Aperture Detection (CAD) from the various kinds of MSR because of its good suitability to the conventional LIMDOW. This newly developed CAD-LIMDOW realizes high performance of both MSR and DOW function. The recording density of 2.7Gbit/inch² has been obtained with sufficient power margin by using a land/groove substrate at the condition of 680nm wavelength LD and NA=0.55. It means that 3.5Gbit/inch² density is probable by using the optical head with wavelength of 650nm and NA=0.6.

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  The SIL (Solid Immersion Lens) Optical System which attracting attention as future high-density recording, focuses a laser beam to the disk surface without any substrate. We have studied the possibility of compatibility of the SIL optical system with the conventional optical disk system which focuses laser beam through a substrate. It was found that the compatibility with optical disks having 0.6 mm thick substrate can be obtained by setting the SIL refractive index to 1.8, radius to 500 μ m, and SIL height to 708 μ m. Although the dimensional accuracy is very severe in this construction, however, it can obtain a spot with very small aberration for both optical disks for SIL and conventional optical disks by loading/unloading SIL.

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  Ab initio magneto-optical (MO) calculations have been carried out for the cubic perovskite SrRuO₃. The results obtained show a good agreement with the presented experimental optical and MO spectra. Features of the MO spectra are explained in terms of the electronic structure and conductivity tensor.

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