The diffraction limited spot size in optical recording can be decreased by use of the Solid Immersion Lens (SIL). The simplest form of the SIL utilizes a hemispherical lens with the rays of a focused bean entering along its radii to form a spot at the flat surface of the hemisphere. The spot size is decreased from that in free space by a factor 1/n, where n is the refractive index. If an optical disk is placed close enough to the SIL, this reduced spot size is obtained at the disk. In this case the effective numerical aperture of the lens can be greater than one.
   The SIL is used in optical recording in two different ways. In the first example the SIL is mounted on a floating head which maintains the air gap automatically to be of the order of 100 nm. This method is now being developed for a removable disk drive with over 10 Gigabytes storage by TeraStor. A second technique, demonstrated by Sony, uses an effective numerical aperture less than one with a relatively large air gap of the order of 50 micrometers. This method gives relatively low spherical aberration and is suitable for use with multilayer systems.

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  Magnetic recording has been the dominant data storage technology for many years, and presently delivers higher bit density at lower cost than magneto-optic data storage. The trend of ever-increasing bit density for magnetic recording is now, however, encountering some fundamental physical barriers. We examine here these barriers and conclude that a change in magnetic recording paradigm, probably including the use of patterned media, will be required to carry magnetic data storage to and beyond 100 Gbit/ in².

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  The magneto-optical Kerr spectra of several transition-metal-An alloys are investigated theoretically, on the basis of relativistic energy-band theory in the framework of the local-spin-density-functional theory. Calculated Kerr spectra are presented for the artificial compounds FeAu and MnAu, and also for the ordered XAu₄ (X = V, Cr, Mn) compounds. The theoretical Kerr spectra of FeAu correspond in shape to the experimental spectra, but the calculated Kerr effect is bigger than the experimental one. For the XAu₄ compounds a modest Kerr angle of −0.4° to −0.5° at, 1.7eV is predicted. The XAu₄ compounds are predicted to display a huge Kerr anisotropy, which is purely a magnetocrystalline anisotropy effect.

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  Thin epitaxial and polycrystalline Mn_xPt_1-x films with 0 ≤ x ≤ 0.38 were prepared by molecular beam epitaxy on (001) SrTiO₃ substrates. RHEED patterns confirm the epitaxial growth of the epilayers on the monocrystalline substrate. X-ray diffraction measurements reveal an anomalous structural strain-induced phase transition from the AuCu₃ to the AuCu structure. The Curie temperature of strained epilayers is enhanced compared to polycrystalline films, while the magnetization is reduced. Magnetization curves for epitaxial films of (001) and (111) orientations are shown. Magneto-optical spectra of (001) oriented MnPt₃ films show a remarkably large Kerr rotation of −0.82° at 1.1 eV.

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  The magneto-optical Kerr effect in Co₂₂Ag₇₈ granular thin films which exhibit a perpendicular magnetic aniostropy is studied using a Kerr spectroscope at photon energy of 1.4-6.8 eV. The observed shift of both the positive peak at 5-6 eV of Kerr rotation angle and the negative peak at 4-5 eV of the Kerr ellipticity toward lower energies with increasing annealing temperature suggests the change in electronic structures of fine Co particles / the change of the shape of the particles compared with that of previously reported of FCC Co.

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  A Type I thermo-magnetic recording medium having a blocking temperature of ≈220°C is characterised optically and magneto-optically with a view to optimising its readotlt properties. The medium consists of a dispersion of single domain cobalt particles prepared by the thermal disassociation of sputtered films of cobalt nitride.

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  The structure and magnetic properties of Fe in Rare-Earth-Transition Metal multilayars were investigated utilizing EXAFS and MCD effect. The Fe structure gradually relaxed with increasing Fe thickness up to 2.3 um, and abruptly changed from the amorphous to bcc structures above 2.3 nm. The MCD signals were hardly seen when the Fe layer thickness is below 2.0 nm. On the other hand, the MCD signals were clearly seen for the multilayers with the thicker Fe layer. Consequently, we speculate that the 3d band structure of amorphous Fe is different from that of bcc Fe.

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  The magneto-optical activity in the range from 1.4 to 6.8 eV for hcp Co₃Pt films deposited onto Al₂O₃(0001) with different degree of the ordering is presented. An increasing chemical ordering, evidenced by X-ray and electron diffraction measurements, is accompanied by a change in the magneto-optical spectra in a characteristic peak at around 3.2 eV, which does not occur for the case of the fcc Co, and hcp Co. The strong perpendicular magnetic anisotropy in such films is related to the ordered state of the hcp structure.

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  Co₅₀Pt₅₀ alloy films were grown by the molecular beam epitaxy (MBE) method onto MgO(111) or (001) substrates at temperatures in the range of 40 to 500 °C. X-ray diffraction measurement demonstrated that the films grown onto the (111) substrates at 300 °C had L1₁ (CuPt type) ordered structure, whereas those grown onto the (111) substrates at 500 °C and onto the (001) substrates at 300 °C formed L1₀ (CuAu type) ordered structures. The (111) oriented L1₁ and the (001) oriented L1₀ CoPt alloy films showed large perpendicular magnetic anisotropies of 1.75 × 10⁶ J/m³ and 1.8 × 10⁶ J/m³, respectively. The magneto-optical Kerr spectra for the (001) and (111) oriented L1₀ CoPt alloy films are similar. The (111) oriented L1₁ CoPt film showed Kerr spectra quite different from those of the L1₀ CoPt films. The θ_K did not show a peak in the high energy region.

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  A study of magnetic and magneto-optical properties of Fe_100-xPt_x (0≦x≦60) alloy thin films as functions of composition and substrate deposition temperature in conjunction with structure is carried out. It is found that the coercivities for both perpendicular and in-plane magnetization curves become very large for the mixed phase of fcc and fct. For Fe₅₀Pt₅₀ thin films, the perpendicular magnetic anisotropy constant Ku is found to increase with increasing deposition temperature (Ts) and becomes nearly constant (5×10⁷erg/cc) at Ts beyond 250°C. Also, the Ku of Fe₅₀Pt₅₀ films increases with the intensity ratio of I₍₀₀₁₎/I₍₀₀₂₎, being closely related with the tetragonality (c/a). These results indicate that the evolution of Ku is due to the occurrence of the fct phase. The magneto-optical polar Kerr rotation and Kerr ellipticity are found to exhibit different behaviors with tetragonality. In particular, the Kerr rotation and Kerr ellipticity at photon energies from 1.5∼2.5eV are found to be sensitive to the tetragonality (c/a).

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  The magnetic and magneto-optical properties of TbFeCo/(Pt, Pd) multilayer films prepared by sputter-deposition are discussed in conjunction with the multilayer structure. The effect of polarized Pt on the polar Kerr spectra is significant at ultraviolet photon energies. A drastic increase in the magnetic moment and ω σ_xy” spectra for the TbFeCo/(Pt, Pd) multilayers indicate the existence of interfacial Fe-Pt and Fe-Pd alloys.

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  Magneto-optic polar Kerr spectroscopic and magnetization studies on the oxide multilayers NiO/α-Fe₂O₃ prepared by pulsed laser deposition on quartz substrates are reported. The spectra are consistent with the hypothesis that a layer of spinel ferrite NiFe₂O₄ is formed at the interfaces. The line width in the MO Kerr spectra are typical for the ferrimagnetic spinels containing exclusively ferric ions. The formulae which explain the role of the interface and propagation effects on the observed MO response in reflection and transmission are provided.

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  Strontium ferrite (SrFe₁₂O₁₉) thin films are deposited using a large area laser ablation system capable of uniform deposition over 2-inch diameter. As deposited amorphous films are crystallized when annealed at temperatures ≥ 650 °C. The films deposited at low oxygen pressures (P_O2 = 1 and 10 mTorr) when annealed at T_A = 700 °C, exhibit high degree of c-axis orientation normal to the film plane and hence a perpendicular anisotropy K_U ∼ 2.5 x 10⁶ erg/cc. These films consist of well-oriented hexagonal platelets with grain sizes ∼700-1500 nm. With intcreasing P_O2, the c-axis orientation degrades and films become more isotropic with the grain sizes decreasing to ∼ 80 nm at 80 mTorr. The grain sizes can also be reduced by substitution of rare-earth elements such as Dy or Ho retaining the high perpendicular anisotropy. The magneto-optic polar Kerr spectra exhibits large Kerr activities in the energy ranges of 3 - 6 eV which could be interesting for the future application potential of this material.

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  The possibility of modifying solid state properties under ion beam irradiation is a well documented phenomenon. It stands as a very common technique in semiconductor technology. We have used it to design magnetic patterns on ultra-thin films. The local magnetization can be modified without changing such essential characteristics of the films as the perpendicular anisotropy and surface roughness. We report magnetooptical imaging experiments in such magnetically patterned samples: dipolarly coupled dot arrays obtained using a Ga⁺ Focused Ion Beam (FIB) and a comb-like array obtained with a non focused He⁺ ion beam irradiation through a mask fabricated by electron beam lithography.

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  The perpendicular magnetic anisotropy of both amorphous Tb-Fe and crystalline fcc Pt-rich Co-Pt alloys is enhanced by increasing growth temperature, up to the onset of significant bulk atomic mobility (approximately one third of the melting temperature). High growth temperature also stabilizes these materials against subsequent annealing which tends to eliminate the anisotropy. The dependence on growth temperature can be fit with a two-level systems analysis in which the low energy surface state during growth is anisotropic. The source of this low energy state is suggested to be related to surface segregation for the Co-Pt alloys. The anisotropy for both materials shows very little dependence on substrate type, sample thickness, or details of the deposition such as sputtering or e-beam evaporation. Coercivity on the other hand is extremely dependent on microstructure and hence on details of preparation, substrate type, thickness, and crystallographic orientation. For α-Tb-Fe, the dominant mechanism appears to be domain wall pinning by microstructural defects in the bulk of the film, such as columnar microstructure.

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  A series of epitaxial films with nominal composition Co₃Pt were grown over a range of growth temperatures from 450 K to 950 K. With increasing growth temperature the crystalline structure of the films varies, and there is an associated variation of the perpendicular magnetic anisotropy constant. A study has been made of the magnetic domain structures which evolve in the series of films under different magnetizing conditions. Quantitative measurements have been made of characteristic domain widths determined from MFM measurements, and it has been found that the widths are directly proportional to the perpendicular anisotropy constants.

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  The field-induced magnetization reversal mechanism in CoNi/Pt multilayers was studied by magnetooptical magnetometry and microscopy. Nucleation or domain wall dominated types of reversal were discussed as a function of the multilayer microstructure and thickness. The preparation conditions and characteristics of the best multilayer structure for magnetooptical recording are determined.

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  Local structural anisotropy was estimated using extended X-ray absorption fine structure (EXAFS) spectroscopy for Dy/Fe multilayers prepared by sputtering and vacuum deposition methods. Fourier transformed Fe-EXAFS indicated a difference in the atomic coordination between in-plane and out-of-plane. Both the structural anisotropy and the perpendicular magnetic anisotropy change depending on the bilayer period and the preparation methods. The variation of the structural anisotropy was found corresponds closely to that of the perpendicular magnetic anisotropy

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  After reviewing the state of the art of the preparation and the properties of MnBi thin films, we report on the first successful epitaxial growth of MnBi single crystalline films with very high magnetic energy products and coercivity fields up to 20 kOe. The best films have been grown by molecular beam epitaxy on buffered BaF₂ substrates. The epitaxy on GaAs substrates will also be discussed.

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  The Epitaxial growth of MnBi films has been studied by means of molecular beam epitaxy (MBE) technique. Single crystals of MgO (001) and Al₂O₃ (00.1) were employed as substrates. Without any buffer layers, MnBi thin films grown on these substrates were polycrystalline. We then prepared MnBi films using either a Au or a Cu layer as a buffer on the substrates. Using Au buffer layers (10.2)-oriented MnBi films were obtained, yet the magnetic property of these films are poor. On the other hand, using Cu (111) buffer layers MnBi films with a sufficient flatness and better magnetic property were obtained, although some trace of (10.2)-orientated grains was observed.

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  A cluster growth model based on Direct Simulation Monte Carlo (DSMC) is introduced to examine the effect of experimental conditions in cluster beam deposition process. We simulate the behavior of cluster and inert gas in the flight path in the equipment for cluster beam deposition under different experimental conditions, which are flight path length, ratio of the material gas to the inert gas, and temperature of the outer wall of the equipment. Several size distributions of the cluster under various conditions are obtained by this model. The results of the present simulation show that the size distribution strongly depends on the experimental conditions. In other words, the size distribution of cluster can be controlled by changing the experimental conditions.

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  A remarkable photoinduced disaccommodation (DA) of magnetic permeability μ is observed in yttrium iron garnet (YIG) single crystal with very low contents of Ca: these double peaks of DA are around 125 K(0.46eV) and 200 K (0.60 eV) with correlative onset of the irreversible decrease of real part of permeability μ'_ insensitive to demagnetization at lower temperature than 250K. In addition, we observed the lowest temperature peak of DA is strongly frequency dependent and at 1 kHz it is cancelled by the accommodation (A) phenomenon. For these observations, we propose that the pinning center may be due to a photoinduced structure change around oxygen defects.

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  Ultrafast laser techniques are employed to study optically induced modulation in an exchange biased ferromagnetic (FM) antiferromagnetic (AF) thin bilayer film (NiFe/NiO). We have discovered that by photoexciting the FM/AF interface with femtosecond laser pulses, significant modulation in the unidirectional exchange bias field (H_ex) can be induced on an ultrashort timescale, which leads to large coherent magnetization rotation in the permalloy film on a timescale of 100 psec. Theoretical considerations are offered from total magnetic energy arguments while the temporal details observed experimentally are well described by Landau-Liftshitz-Gilbert equations.

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  The definition and measurement of the fluctuation field and activation volume is reviewed. The activation volume is shown to have a simple physical interpretation only when the energy barrier is linear with the field. Calculations are presented which demonstrate that the activation volume is dependent on the measurement time. The use of the activation volume in simulations of M-O media and in the characterisation of the stability of conventionally recorded information is discussed.

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  Films of the half-metallic Heusler alloy, PtMnSb, are observed to exhibit optical transmittance that is a nonlinear function of the incident radiation intensity. This behaviour probably originates in a strong temperature dependence of the refractive index (i.e. the diagonal elements of the permittivity tensor [ε] rather than from the small third order susceptibility, χ³.

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  In the half-metallic Heusler alloy PtMnSb the magneto-optic interaction is so large that effects quadratic in the magnetization M are not only readily observed but must be separated from first-order effects linear in M when determining the magneto-optic constant Q = (Q₁+iQ₂). Measurements taken in any Kerr configuration record simultaneously behaviour arising from both linear and non-linear (M²) effects. In the transverse configuration separation of the effects is relatively straightforward and unambiguous evaluation of Q is shown to be possible.

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  Time-resolved photo-induced nonlinear magneto-optical Kerr effect measurements are introduced as a promising tool for studying magnetization dynamics on the femtosecond time-scale at a gallium arsenide surface. A circularly polarized, ultrashort pump pulse induces a spin polarization in the sample - that is, a transient magnetization that can be temporally resolved by measuring the magnetically-induced second harmonic generated by a delayed probe pulse. Furthermore, measuring the sum frequency generation due to the coherent interaction of pump and probe pulses can lead to such temporal information as well. First results tend to show that a rapid spin relaxation occurs in a time shorter than the pulse duration of our experiment - i.e. less than ca. 50 femtoseconds.

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  We adopted mark position recording in order to cancel ghost signals which appear in domain wall displacement detection. We obtained a jitter of 6.8 % at a linear velocity of 1.5 m / sec for a bit length of 0.15 μm and a track pitch of 0.85 μm using a conventional optical pickup. We confirmed that readout and recording power tolerances are ± 22 % and ± 24 %, respectively, at an areal density of 5.0 Gbit / inch².

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  MAMMOS (Magneto Optical Amplifying Magneto Optical System) is one solution to amplify extremely small magneto-optical signal reproduced from a very tiny domain which is recorded as a high areal density. Especially, in the case of MAMMOS with alternative external readout field, the enhanced signal reaches to the saturated signal level, even if the small domain size is 0.1 μm in length which is one tenth compared to the laser spot size. The domain expansion phenomena suddenly happen beyond a critical readout power or external field, that is, it is independent of the domain size. The critical phenomena depend on the critical magneto-static coupling between the expansion layer and the recording layer.

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  The results of two-dimensional dynamic calculations performed to simulate the domain transcription process in the readout layer of a magnetostatically coupled dual-layer magneto-optical recording medium and those of one-dimensional calculations made to clarify the nature of the domain wall in the readout layer are given. Detailed time-dependent magnetization behaviors in the readout layer are obtained in the former calculation showing the effect of various parameters such as the atmosphere temperature, stray fields from the recording layer and external fields, on domain transcription. The coercivity of the readout layer is realized by introducing dispersion into the magnitude of the anisotropy constant among computing cells, and the Landau-Lifshitz-Gilbert equation is solved numerically. The magnetization structures in a straight-line wall both in equilibrium and in motion are calculated in the latter calculation.

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  The write and readout properties of MAMMOS disks were investigated at 780 nm. The size of domains and readout signals from these domains written at various writing laser powers with the light intensity modulation for the two disks which have different thickness of memory layer were investigated. Smaller domains at threshold writing laser power for the disk with thin memory layer than those of the disk with thick memory layer were observed. A saturation amplitude of the readout signals amplified by the bias magnetic field was observed from various sizes of written domains. The tolerance of the readout laser power and the bias magnetic field for the disk with thick memory layer was larger than those of the disk with thin memory layer.

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  MAMMOS (Magnetic AMplifying Magneto-Optical System) is one of the highest density readout methods for storage media. The signal is directly amplified on the medium and its amplitude is just the same as that from a long domain. Even at a 0.04 μm domain, the signal was large enough. At a 0.2 μm packed domain, CNR was more than 50 dB and BER was in the 10^-4 range. By employing a MAMMOS readout with magnetic field modulation (MFM-MAMMOS), the signals have both very high resolution and large amplitude characteristics.

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  A new magnetic expansion phenomenon has been observed on a magneto-static coupled type MAMMOS medium with an in-plane magnetization readout layer using DC laser power and a DC magnetic field in the readout process. On this new media, it is possible to resolve 0.22 μ m domains and to obtain a clear signal with this unique expansion phenomenon.

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  We investigated reproduced signal waveforms of domain recorded with light intensity modulation in exchange-coupled multilayer MO films. It was found that particular waveforms with steep leading edge caused by a magnetic domain expansion. When a front edge of a recorded domain reached the unstable area where the wall coercivity of the readout layer was smaller than Hr, it was expanded by Hr parallel to the magnetization direction of the readout layer. When a rear edge of the recorded domain entered in the unstable area, it shrunk and collapsed. It was considered that the domain expansion and the collapse occurred rapidly, and produced the rectangular waveform with steep leading and trailing edges.

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  Advanced Storage MagnetoOptical Disk (AS-MO) is one of the highest density media for removable systems. By employing a read power control method, AS-MO has a capacity of 6 GBytes with wide system margins in a 120 mm single sided disk, and can be used under various conditions. The disk has many advantages for both AV and PC applications.

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  A trilayer double-mask MSR media, which operates by applying a small readout magnetic field, was developed. The media was put to a practical use in a new 3.5-inch MO system, named GIGAMO, with a capacity of 1.3 GB. The GIGAMO system can maintain downward compatibility as it utilizes conventional techniques. Furthermore, it was confirmed that a capacity exceeding 2.4 GB was possible by combining double-mask MSR media and land/groove recording from a bit error rate measurement using a conventional optical head and substrate. The next generation 3.5-inch MO system can also maintain downward compatibility.

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  Feasibility of achieving an areal density over 7 Gbit/in² was examined in a center aperture detection type of magnetically induced super resolution disk. We confirmed land and groove recording with a 0.45 μm track pitch was available with practical margins by the use of a conventional optics which consists of a 640 nm wavelength laser and a 0.6 numerical aperture lens. The available areal density reached to 6.8 Gbit/in² and over 9 Gbyte user-capacity in a 120 mm diameter single side disk can be realized.

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