A study of band edge phenomena in ridge waveguide magnetophotonic crystals is presented. Normal mode analysis is used to examine the near-band edge and Bragg center-wavelength group velocities and their relation to the polarization. Large polarization departures from the input are observed in Bragg gratings patterned by focused-ion-beam milling on liquid-phase-epitaxial (LPE) (Bi,Lu)_(2.8±0.1)Fe_(4.6±0.2)O_(12.4±0.3) films on (111) gadolinium gallium garnet (GGG) substrates. Transfer matrix analysis of the spectral response in the photonic crystals allows the determination of the phase of the elliptically polarized normal modes from measured transmittances and polarization rotation. Unlike non-birefringent Faraday rotators a non-linear-relation exists between polarization rotation and the normal mode phase difference. Large phase differences between right- and left-elliptically polarized normal modes and optical slow-down are found near the band edges and at the resonant cavity center-wavelength. Standing-wave photon trapping and optical slow-down are analyzed and compared for these systems.

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Simulations of heat assisted recording using electron beams as a heat source were carried out. A heat flow model was combined with a micromagnetic model to calculate the recording process. The influence of underlayers on the thermal properties of the system is discussed. The results demonstrate the feasibility of heating a medium sufficiently using a low power electron beam source, allowing the use of materials with a higher uniaxial anisotropy. Additional heating of the recording layer may be achieved by patterning the medium into discrete tracks, providing access to materials with Curie temperatures of around 600 K.

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A magneto optic spatial light modulator (MO-SLM) for multiple-tone expression was fabricated by using in-plane magnetization of garnet film. By using Al substituted Bi:YIG film, magnetization curve was modified to suitable for multiple tone expression. Changing a driving current from 0 to 28 mA, we were able to change brightness of pixels in the line.

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Time evolution of magnetization during a cooling process in thermally assisted magnetization reversal of rectangular MRAM cell has been numerically investigated by taking account of not only temperature variations of material parameters but also a thermal fluctuation effect. The rectangular MRAM cell with 100×150×20 nm³ in size is assumed, where the shape anisotropy dominates the switching property. The threshold amplitude of magnetic field required for a successful thermally assisted switching is decreased as the exchange stiffness constant is changed from 1×10^-6 to 1×10^-7 erg/cm. The time for the magnetization to relax into the bias field direction can be reduced by increasing the bias field amplitude. To switch the magnetization within 1 ns, it is found that the bias field should be larger than 165 Oe. An exchange coupling field in a ferromagnetic bilayer system is considered to be available for producing such a large bias field required for a faster switching in thermally assisted MRAMs.

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Polarization modulation technique has been applied for magneto-optical (MO) imaging to measure MO values quantitatively. In this paper, we report on a real-time MO imaging using the polarization modulation method with a liquid crystal modulator. Measurements of MO images and hysteresis Kerr loop of patterned Bi,Ga substituted yttrium iron garnet film were demonstrated by using the technique. A frame rate of 1 s was achieved in this experiment.

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A magneto-optic spatial light modulator (MOSLM) driven by an electric field was fabricated, which is multiferroic device with magneto-optical garnet layer and piezoelectric PZT one. To control the direction of magnetization of the garnet layer, a stress field induced by PZT film was applied to the garnet layer. With an external magnetic field, the pixels of the MOSLM were switched. The driving current required for the magnetization switching was remarkably reduced to 500 nA, whose value was less than 1% of a driving current of the conventional current-driven MOSLM.

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Magneto-optical garnets stand out because they exhibit a high Faraday rotation and low optical losses in the near infrared region. In this spectral range garnets are the only materials discussed in optical communications to realize nonreciprocal devices such as optical isolators. Such isolators are necessary to prevent reflected light caused by e.g. cable splices from irregularly entering optical components and hence to reduce the noise signal. Nowadays one wants to integrate such macroscopic optical components on a single chip leading to integrated optics. In order to achieve this, it is necessary to understand the principle growth mechanism, so that one can deposit high quality thin films of the optical active materials.
We deposited Bi₃Fe₅O₁₂ on (100), (110) and (111) Gd₃Ga₅O₁₂ and on SiO₂ by Pulsed Laser Deposition. Here we want to give details on the growth and preferential growth direction of the films. Our investigations have been carried out by utilizing an Environmental Scanning Electron Microscopy, Energy Dispersive X-ray Analysis, Rutherford Backscattering Spectroscopy, and X-ray Diffraction. We also report on the Faraday rotation of the films, which has been determined in a special setup polarization microscope.

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Very high uniaxial anisotropy K_u as well as a moderate Curie temperature is required for magnetic materials by heat assisted magnetic recording (HAMR). Crystalline structure and magnetic properties of Fe-Ni-Pt thin films deposited on quarts glass substrates have been investigated in order to obtain optimum composition for the HAMR. L1₀ phase is found in Fe_60-xNi_xPt₄₀ (x = 0 to 24) with c-axis aligned in the perpendicular direction to the film plane. As Ni content x increases, the quality of (001) orientation is improved, while the order parameter S is gradually degraded. As a result, K_u in the perpendicular direction to the film plane is decreased from 3 x 10⁷ erg/cm³ for Fe₆₀Pt₄₀ to 1 x 10⁷ erg/cm³ for Fe₄₅Ni₁₅Pt₄₀ film. The Curie temperature measured is decreased with Ni content to 320°C for Fe₄₅Ni₁₅Pt₄₀. Thermal simulation on the Fe-Ni-Pt disk assuming the similar film structure as current perpendicular recording media has revealed that the temperature rise above 350°C is available by the laser irradiation with a power of 2 mW and pulse width of 2 ns. Therefore, Fe-Ni-Pt can be a candidate material with high anisotropy and optimum Curie temperature suitable for the HAMR.

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This paper describes the techniques which can be used to control the magnetic and magneto-optical hybrid recording properties of sputtered amorphous SmCoCu/Co thin films. SmCoCu/Co films with high coercivity are interesting for various applications including high density hybrid recording. In this work, SmCoCu/Co films on glass substrates have been systematically prepared at different substrate temperatures. The results show that the uniaxial anisotropy perpendicular to the film plane and the magneto-optical Kerr rotation are dependent upon the annealing time, substrate bias and heating used during deposition. A procedure for optimizing the magnetic and magneto-optical properties of SmCoCu/Co for magneto-optical and hybrid recording applications is outlined. With proper composition and suitable sputtering condition, these thin films have excellent magneto-optical and perpendicular characteristics.

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Thermomagnetic recording process was simulated using Huth’s model for the magnetic field modulation (MFM) recording on a TbFeCo medium. This study focused on the effects of introduction of a field gradient layer, reduction of the laser spot size, and application of laser pulsed MFM method. By using GdFeCo layer, field gradient of 3.7 Oe/nm was confirmed to be applied in the recording layer. This field gradient contributes to the decrease of recorded mark elongation and the suppression of the collapse of the marks, which are two major problems to record marks smaller than 100 nm. For the reduction of the laser spot size, the mark elongation was confirmed to decrease, however the improvement of the stability of small sized marks was insufficient. By applying laser pulsed MFM method, the simulation showed the improvement of recording characteristic of small sized marks.

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We developed high quality Bi substituted Lu iron garnet (Bi,Lu)₃(Fe,Ga)₅O₁₂ films with in-plane magnetization to use for magneto-optical imaging (MOI). These films were grown on 1-inch (100) orientated Gd₃Ga₅0₁₂ substrates by liquid phase epitaxy (LPE) using PbO-B₂O₃ flux. In particular, in order to reduce defect density in the film, we optimized the melt composition and growth temperature. We could almost remove defects caused by adhesion of fine garnet crystallites by increasing the amount of flux. The in-plane magnetization was obtained by controlling the stress-induced anisotropy caused by the lattice misfit between film and substrate. These high quality Bi garnet films had the Faraday rotation coefficient θ_F of -690∼-810 deg/mm at 633nm, the saturation magnetization 4⊥M_s of 30mT and the perpendicular saturating field H_s of 120mT at room temperature.

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A magneto-optical hybrid recording is one of the effective approaches to achieve high density in magnetic recording. In hybrid recording, the most important issue, specifically, is the magnetic head device with the near-field optics for heat assisted recording. In this study, we proposed a Near-field Optical Advanced Hybrid (NOAH) head for high efficiency of optics in hybrid recording. The head slider was designed using a transparent material for achieving a high efficiency of optical light. The shape and material of the plasmon antenna was studied by using the Finite Difference Time Domain (FDTD) method. According to these results, an antenna was designed and fabricated on the polished transparent slider. An experimental system was built for the head with a red diode laser and a lens at Numerical Aperture (NA) = 0.8. In a recording experiment, a mark of about 130 nm in diameter was observed on the dyed film by using the fabricated NOAH head.

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Recently, much attention has been focused on so-called “hybrid recording” such as “optically assisted magnetic recording” or “heat assisted magnetic recording”. In other words, hybrid recording is expected to be a most promising storage device beyond 1 Tera bit/inch², ultra high density region. When the domain radius becomes very small in magneto optical recording film, the wall energy is dominant in the total energy of the domain, and then it will shrink and disappear. To write a very small domain, it is necessary to increase the domain wall coercivity to freeze the written domain. We perform three-dimensional Landau-Lifshitz-Gilbert (LLG) simulations for estimating domain shapes and wall structures in coupled granular and continuous (CGC) like films of TbFeCo film/FeNiPt grains. In the results, even when using lower Tc FeNiPt (Tc= 307 °C, Ku= 1.8×10⁷ [erg/cm³] at room temperature) grains than FePt (Tc = 497 °C, Ku = 7.0×10⁷ [erg/cm³] at room temperature) grains, we find a minute magnetic domain of 26 nm diameter, could be made on TbFeCo /FeNiPt bi-layer film. Moreover, the domain wall width, the obstacle in the minute magnetic domain structure of bi-layer film, is narrow. This narrowness advantageously contributes to a high density recording.

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Recently, for the high recording density technology that aims at recording density of 1Tbit/inch², heat assisted hybrid recording has been suggested. Near-field optics is one of the important factors for the hybrid recording to shrink an optical spot to a diameter of 50 nm or below. In this study, we analyzed a double layered plasmon antenna for hybrid recording by Finite Difference Time Domain (FDTD). The double layered plasmon antenna was designed on the resonance wavelength which itself depends on the materials and the shape of the antenna. The results of the calculation showed high power intensity and focused optical spot at the nanosize level.

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We study the optical properties of a photonic crystal interfaced with a uniform medium with the negative dielectric constant or with another photonic crystal. We show that, at such an interface, non-propagating surface states may arise. These states result in a sharp feature in the transmission and reflection spectra of the system. We also show that interfacing magnetic and non-magnetic photonic crystals gives rise to giant Faraday and Kerr effects.

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Cu substitution raises the degree of (001) crystal orientation perpendicular to the film surface for FeCuPt prepared by Rapid Thermal Annealing (RTA). To increase areal packing density of FeCuPt grains, a SiO₂ Substrate having self-organized nano-pores was used as a nano-template. The highly ordered structure of the mesophase thin film is formed by the ordering of self-assembled triblock copolymer micelles, and after annealing at about 600 °C, 8 nm nano-pore arrays formed where there had been micells. Ar-etched SiO₂ substrate with self organized nano-pores is effective in increasing the areal packing density and decreasing the size of FeCuPt grains prepared by RTA. An average grain diameter, standard deviation of diameter and areal packing density of FeCuPt grains were 5.9 nm, 1.3 nm and 0.57 (about 3 times the non Cu substituted case), respectively. We observed (001) peak and almost no peak at (111) by x-ray diffraction, where the degree of (001) crystal orientation I(001) / I(111) > 3 means a high rate of ordering orientation, which gives us reliable evidence of ordered FeCuPt grains.

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We have proposed, simulated, fabricated and experimentally demonstrated monolithically integrable semiconductor active waveguide optical isolators based on the nonreciprocal loss at an optical telecommunication wavelength range of 1530-1560nm. The semiconductor active waveguide optical isolators are composed of semiconductor optical amplifier (SOA) waveguides and ferromagnetic metals. In transverse electric (TE) mode semiconductor active waveguide optical isolators composed of InGaAsP SOA waveguides and Fe thin films, we demonstrated 14.7dB/mm optical isolation at the wavelength of 1550nm and 10dB/mm isolation over entire wavelength range of 1530-1560nm. In transverse magnetic (TM) mode semiconductor active waveguide optical isolators, we used epitaxially grown MnAs thin films as top ferromagnetic electrodes, and demonstrated stable electrode performance and 8.8dB/mm optical isolation. Based on these demonstrations, we can realize monolithic integration of optical isolators with edge-emitting semiconductor laser diodes and polarization insensitive semiconductor active optical isolators. We also discussed the problems and solutions of our semiconductor active waveguide optical isolators at present stage.

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Methodology and selected applications of magneto-optical (MO) spectroscopic scatterometry (MOSS) are presented on various types of magnetic gratings made by lithographic patterning. Three types of theoretical models with different levels of accuracy are described in detail: a rigorous one, an analytical approximation, and a model mostly appropriate for real structures affected by line-edge roughness (LER). The MOSS approach, based on explaining diffracted MO Kerr effect measurements by simulations employing the mentioned models, is demonstrated as a technique highly sensitive to nanoscale features such as native oxide overlayers, as well as capable of determining the LER characteristic quantitatively. Further possibilities to study unsaturated magnetic structures and compositions of magnetic materials including imperfect deposition or aging processes are suggested.

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The Sold Immersion Mirror(SIM) is a device capable of producing the small light spot required for Heat Assisted Magnetic Recording(HAMR). HAMR is a hard disk technology that incorporates a laser for heating a subwavelength sized region of the recording media. Here we measure the effects of comatic aberration on the focused spot of the SIM and compare the results with a recently published model and ray optics.

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We present a design of on-chip optical circulator that is ultra-compact, with a footprint on a single-wavelength scale, using rotating non-reciprocal states in a two-dimensional magneto-optical photonic crystal. Both analytic theory and detailed finite difference time domain simulations are presented to illustrate the operating principle of the device.

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In this review paper, the results of recent observation and studies of the nonlinear magneto-optical effects in magnetophotonic crystals (MPC) are surveyed. Key point of our interests in nonlinear optics of MPC is extension of nonlinear optical enhancement recently observed in dielectric photonic crystals (PC) to enhancement of intrinsically weak nonlinear magneto-optical effects. These PC mechanisms of strong increase of efficiency of nonlinear optical effects are related to optical field increase due to the light localization and parametric enhancement due to the phase-matching.
Strong magnetization-induced intensity effect in second-harmonic (SHG) and third-harmonic (THG) generation is observed in magnetophotonic microcavities formed from single half-wave magnetic garnet layers, sandwiched between two nonmagnetic dielectric photonic mirrors. Absolute values of magnetization-dependent contributions to the SHG and THG intensity are strongly enhanced due to light localization in microcavity garnet spacer.
Magnetization-induced intensity effects in SHG are observed in two types of MPC: one-dimensional multilayer MPC formed from pairs of alternating quarter-wavelength magnetic garnet and silicon oxide layers and three-dimensional MPC based on synthetic silica opals infiltrated by magnetic garnet. Parametric enhancement of MSHG intensity is due to phase-matching at the bend edge. Pure magnetic component of phase-matched SHG is enhanced by two orders of magnitude in garnet MPC in experimental geometry as nonmagnetic SHG is canceled.
Apart from intensity effects, magnetic impact strongly influences other parameters of the SHG radiation in MPC. Significant magnetization-induced variations of phase and rotation of polarization of the SHG waves are observed and systematically studied in garnet multilayer MPC.

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We have developed the magneto-optic spatial light modulator (MOSLM) with one-dimensional magnetophotonic crystal (1D-MPC). The multilayer structure of SiO₂, Ta₂O₅, and bismuth substituted yttrium iron garnet (Bi:YIG) were deposited by the RF magnetron sputtering to form 1D-MPC. By using 1D-MPCs, The large enhancement in Faraday rotation was obtained in localized light mode, and the fabricated MOSLM showed higher contrast than that of single magnetic film. We confirmed the brightness of the magneto-optical image changed by an external magnetic field.

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Thermally assisted magnetic recording can solve fundamental problems with thermal fluctuation and write capability in magnetic recording. We built a dynamic write-read tester composed of a conventional spin stand and a recently designed magneto-optical (MO) head. We demonstrated the capability of writing small magnetic domains on TbFeCo recording media with a high coercive force (Hc) of 13 kOe by applying a small external field of less than 300 Oe. We also demonstrated a narrow track pitch (Tp) recording of less than 50 nm using the light intensity modulation (LIM) method. Magnetic domains with both mark length (ML) and track pitch of 46 nm, which correspond to an areal recording density of about 300 Gbit/in², were reproduced using a conventional giant magneto resistive (GMR) read head. These results indicate that narrow track pitch recording can be achieved by using thermally assisted magnetic recording.

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Bismuth-substituted yttrium iron garnet (Bi:YIG, Bi_0.5Y_2.5Fe₅O₁₂) films have been deposited with aerosol deposition method. We investigated the deposition rate, crystallinity, magnetic and optical properties dependent on carrier gas flow rate (0.5 L/min ∼ 8 L/min) and annealing temperature. With increasing annealing temperature, the crystallinity of Bi:YIG film was improved and the saturation magnetization increased to reach to 1.1 kG at 800°C. The magneto-optical effect, Faraday rotation, increased to 1.4 deg/μm by annealing at 700°C around the wavelength of 0.5 μm. The optical transmittance of the Bi:YIG film was also improved in visible region.

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A series of our studies on sputter-deposited SmCo₅ thin films exhibiting very high perpendicular magnetic anisotropy is reviewed. Introduction of a Cu underlayer is a key to imparting perpendicular magnetic anisotropy to SmCo₅ thin films. Perpendicular magnetic anisotropy was enhanced by depositing the Sm-Co layer with the alternate lamination of Sm and Co sublayers and by using the Cu/Ti dual underlayer for producing a smooth film surface. As a result, under an optimized condition, the magnetic anisotropy constant was as large as 4.0 x 10⁷ erg/cm³, which is greater by a factor of ten than that of material used for conventional magnetic recording media. Furthermore, we found that high perpendicular magnetic anisotropy was obtained even in very thin films and that the coercivity was controllable in a wide range when the films were prepared using an ultra-high vacuum sputtering system. Microstructural analysis suggested that the Cu-rich region in the initial growth stage of the Sm-Co layer played an important role in generating perpendicular magnetic anisotropy. In addition, we tested SmCo₅ thin films for use in conventional and heat-assisted magnetic recording media.

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