Ken Tamanoi

Very High-Density Recording on Exchange-Coupled Trilayer Magnetically Induced Super Resolution Media without Special Initializing Magnet.

We obtained a high carrier-to-noise ratio (CNR) of 47 dB and a low jitter of 8% for 0.33 µm mark length ( 0.66 µm mark pitch) on exchange-coupled trilayer magnetically induced super resolution (MSR) media. This media is composed of a readout layer, an intermediate layer, and a writing layer. The magneto-optical signal is read through an aperture at the focal point between a front mask and a rear mask. The double mask can be formed by applying a readout magnetic field smaller than 300 Oe.

Relationship between Crosstalk and Readout Magnetic Field Direction on Trilayer Magnetically-Induced Super Resolution Media.

Land/groove recording was conducted on the trilayer double-mask MSR media. A CNR of 47 dB was obtained for a mark length of 0.33 µ m and track pitch of 0.7 µ m. The crosstalk was negligibly low when the readout magnetic field was applied in the writing direction. Random jitter was 10%, even when the data were recorded on the adjacent tracks, assuming (1, 7)-RLL encoding. This implies that an areal density of 3.69 Gbits/inch2 is possible. The crosstalk changed drastically depending on the readout magnetic field direction. It was found that the area of the front mask was larger when the readout field was applied in the writing direction, compared to the readout field in the erasing direction. This explains the big difference in crosstalk due to the readout field direction.

Growth of Ce-substituted yttrium iron garnet films by MoO3-K2MoO4-Y2O3 flux and their Faraday rotation spectra

Ce-substituted YIG films are grown using a liquid-phase epitaxy method from MoO3-K2MoO4-Y2O3 pseudoternary flux. The growth rate is found to be less than that in PbO-based flux by 1/100. The films with more Ce3+ ions are grown from melts where CeVO4 is used as a starting cerium material. Ce doping of less than 0.05 (at./f.u.) is attained. Faraday rotation characteristics of the Ce-substituted YIG are observed in the grown films.

Faraday Effects of Tetrahedrally Coordinated Co 3+ in Magnetic Garnets

Effects of the spin-orbit interaction (SO) and S<inf>4</inf> low-symmetry crystal field on the Faraday rotation spectra (FRS) of tetrahedral Co³⁺ in magnetic garnets are investigated in the context of crystal field theory. The FRS of magnetic garnets containing tetrahedral Co²⁺ and Co³⁺ are also calculated. In order to explain the observed FRS of tetrahedral Co³⁺, (1) an SO coefficient ¿ in the range from -100 to -160 cm^-1, and (2) a fairly large low-symmetry field, are required.

Rear Aperture Detection on Magnetostatically Coupled Magnetically Induced Superresolution Medium

A magnetically induced superresolution (MSR) medium was developed using magnetostatic coupling. The medium comprises a GdFeCo reading layer, a SiN intermediate layer, and a TbFeCo writing layer. We implemented rear aperture detection (RAD) using a transition metal (TM)-rich reading layer with perpendicular magnetization. We obtained a carrier-to-noise ratio of 45 dB for a mark length of 0.38 µm. Crosstalk was below -40 dB, which is low enough for practical use. By measuring the minor Kerr loop for the sample, on which small domains were written, we clarified that initialization of the reading layer occurs spontaneously, even in the absence of a magnetic field.

Optical Absorption Spectra in Cobalt-Substituted Epitaxial Magnetic Garnet Films Measured with Photothermal Deflection Spectroscopy

Optical absorption spectra were measured at room temperature by means of photothermal deflection spectroscopy (PDS) in Co2+-substituted or Co3+-substituted magnetic garnet films prepared by liquid phase epitaxial technique. We compared the PDS results with theoretical absorption spectra calculated for Co2+ and Co3+ ions using the ligand-field theory. A satisfactory agreement has been obtained between the calculation and the observation especially for the case of Co2+-substituted films.

First surface magneto-optical recording of over 36 Gbit/in2 using domain expansion media

First surface magneto-optical (FSMO) recording offers great potential for high-density recording. We have developed a domain expansion media for FSMO recording that uses a finely structured seed layer. Additionally, we clarified the relationship between drop-out and the recording resolution of this type of media. We realized a clear magnetic domain with continuous marks, a low drop-out, and a signal reproduction of 65 nm using domain expansion media. This domain has drastically improved the recording resolution. This was achieved by forming a finely structured seed layer under the memory layer. This technique enables a recording density of over 36 Gbit/in2.

Magneto-optical effects in Th-substituted yttrium iron garnets

Abstract To investigate the effects of Fe2+ in YIG on the magneto-optical effects, we grow (YTh)3Fe5O12 films using an LPE method, and measure the absorption coefficient and the Faraday rotation (FR). A decrease of FR is observed at around the wavelength of 0.52 μm. In order to make clear the origin, we calculate the electronic states of a divalent iron-oxygen octahedral cluster using the SCF-Xα method. The observed spectra are assigned to the internal transition of an electron from 3d-like e∗g orbit to 4p-like t1u one in Fe2+ on the octahedral site in YIG.

Cotton-Mouton Spectrum in Cobalt-Substituted Magnetic Garnet

Spectra of the Cotton-Mouton effect and Faraday rotation in cobalt-substituted magnetic garnet films were measured at wavelengths between 0.5 and 2.0 ¿m using a piezobirefringent modulator. Experimentally measured spectra were compared with those obtained by theoretical analysis within the framework of the ligand field theory. Satisfactory agreement between experiment and theory was obtained for a reasonable set of parameters.