Atsuyuki Watada

Cobalt‐titanium substituted barium ferrite films for magneto‐optical memory

We have studied Faraday rotation and magnetic properties of Co‐Ti substituted barium ferrite films with perpendicular anisotropy, which were prepared by targets‐facing‐type sputtering method on (111) oriented GGG substrates. Faraday rotation (θF) of 500–830 nm was measured by using the Faraday modulation method. It was found that θF increased proportionally to the content of cobalt in the wavelength range 700–830 nm. In the BaFe10.42Co0.78Ti0.8O19 film, Faraday rotation and magnetic properties were as follows: θF=0.75 deg/μm at 780 nm, anisotropy field: Hk=5.2 kOe, coercive force: Hc=800 Oe, Curie temperature: TC=380 °C. Thermomagnetic recording was achieved on this film by using a 780‐nm laser diode. As a result, 2.0‐μm bit patterns were observed by Faraday effect.

Magneto-optical properties and thermomagnetic recording of M-type Ba-ferrites

Abstract Thermomagnetic recording by Ar laser was achieved on a Ba-ferrite perpendicular film. The Faraday rotation of a Co-Ti substituted Ba-ferrite single crystal was 0.83° / μm at λ = 0.78 μm .

Structural Analysis of Ag–In–Sb–Te Phase-Change Material

The Ag–In–Sb–Te system is widely used for phase-change discs such as compact disc rewritable (CD-RW) and rewritable digital versatile disc (DVD+RW). To clarify the effect of Ag and In in the Ag–In–Sb–Te system, we studied the local structure of Ag–In–Sb–Te phase-change material by extended X-ray absorption fine structure (EXAFS). The results suggest that the existence of Ag contributes to the thermal stability of amorphous marks and existence of In contributes to high-speed phase-change.

Ba-Ferrite Magneto-optical Recording Media

We have studied on the application of Ba-ferrite(BaFe12O19) to magneto-optical recording. It was found that CoTi substituted Ba-ferrite(BaCoxTixFe12-2xO19) films on GGG single crystals had Faraday rotation of 0.9deg/ µ m(λ=780nm) and Curie temperature of 320°C at X=0.9. And CoTi substituted Ba-ferrite films with the perpendicular magnetic anisotropy were obtained on glass substrate by using (111) orientated NiZn-ferrite(NixZn1-xFe2O4) films for under layer. From these results, Ba-ferrite magneto-optical recording medium which constitution is glass substrate, NiZn-ferrite under layer, CoTi substituted Ba-ferrite magnetic layer and stripe-shaped metal reflective layer for the guide tracks, is proposed from the optimization of each layer.

In-Sb Phase-Change Material for 16× Rewritable Digital Versatile Disk

We investigated Sb-based In-Sb as a material for high-speed recording that is capable of maintaining a highly stable amorphous phase. The crystalline phase of In-Sb is unstable at approximately its eutectic composition. After an aging test, InSb was segregated, and its reflectivity was reduced. For an Sb-rich In-Sb, we confirmed that its crystalline phase is stable and its crystallization speed is high. We demonstrated the feasibility of 16× digital versatile disk (DVD) recording using 2T-period multiple-pulse strategy.

Multiple reflection effect on Co substituted Ba-Ferrite for magneto-optical recording media

We have studied the enhancement by mutiple reflection effect on Faraday rotation of Co-Ti-substituted BaM film which should be designed as thin as possible to reduce the laser power for magneto-optical recording and background noise caused by polycrystalline boundary. The sample constitution which is used in the experiment is Au reflective layer/Co-Ti-BaM magnetic layer/ Ni-Zn-ferrite under layer/quartz glass substrate. The multiple reflection effect was examined from the wavelength dependence of reflectivity and rotation. As the result, some enhanced peaks of the rotation of reflected light were observed. And the wavelengths at which they appeared exactly agreed with those at which, the reflectivity had bottoms. It was found that the Faraday rotation in infrared region was enhanced several times larger by multiple reflection.

The preparation of Co-Ti substituted Ba-ferrite films

Abstract Co-Ti substituted Ba-ferrite (BaCo x Ti x Fe 12-2 x O 19 ; x =0, 0.75, 1.0) films have been deposited by a sputtering method on GGG single crystals with (111) orientation and on (111) oriented polycrystalline NiZn-ferrite films. The films deposited on both substrates had a polycrystalline structure with a magnetoplumbite phase (M phase). They exhibited c -axis orientation perpendicular to the film plane above the substrate temperature threshold ( T cry ) at which the crystallization of Ba-ferrite films occurs. T cry ) increased from 520°C ( x =0) to 650°C ( x =1.0) proportionally to the content of Co-Ti substitution. The Δθ 50 of the (008) plane of Co-Ti substituted Ba-ferrite films deposited on GGG single crystals was about 3.0° and about 2.5° for the simple Ba-ferrite films. On the other hand, the degree of c -axis orientation of Ba-ferrite films deposited on NiZn-ferrite films strongly depended on the (111) orientation of the NiZn-ferrite films. The Δθ 50 of the (008) plane of Co-Ti substituted Ba-ferrite films deposited on NiZn-ferrite films was about 4.5°.

Selective Excitation of a Symmetric Interference Plasmon Mode in Two Close Planar SiO2/Si Interfaces Observed by Electron Energy-Loss Spectroscopy

We have studied the effects of the SiO2/Si interface parallel to an electron beam on transmission electron energy-loss spectra of a SiO2 area for poly-Si/SiO2/Si samples. The dependence of the energy-loss spectra on the distance from the interface to the probe position and on the distance between two interfaces was investigated. Spectra obtained from the center of the thick (150 nm) SiO2 layer had no peak in the energy region of 4–10 eV. However, a peak at about 7 eV was observed in the spectra obtained at a position of 7.5 nm from the SiO2/Si interface for the same specimen. This peak was assigned to a SiO2/Si interface plasmon excitation. For the thin (15 nm) oxide poly-Si/SiO2/Si sample, on the other hand, the peak appeared at 8.7 eV. Furthermore, this peak shifts to higher energies as the oxide thickness decreases. This peak was assigned to an excitation of a symmetric interference plasmon mode in two close planar SiO2/Si interfaces.

X-ray absorption fine structure of V2O5 and LixV2O5

Vanadium K-edge XAFS measurements of five compounds were carried out. The compounds studied were crystalline V2O5 and four types of LixV2O5 with different insertion levels x, which show different EMFs (2.0–3.4 V). The EXAFS data analysis shows no remarkable difference in the V—O distances in the five compounds, showing that the structure of the VO5 square pyramids changes only slightly as lithium atoms are intercalated into the V2O5. In the XANES spectra, three peaks are observed for crystalline V2O5 and LixV2O5 (3.4 V). When the EMF is decreased, the intensity difference between the first and second peaks disappears and the third peak shifts to lower energy. The XANES data were analysed using full multiple-scattering calculations. In the calculated spectra the intensity of the first peak increases as the V2O5 intercalates lithium atoms.

Preparation of TbFeCo Films by Two Source Magnetron Sputtering

The magnetic and magneto-optical properties of TbFeCo films formed on glass substrates by two-source (FeCo and Tb) magnetron sputtering, while varying the RF input power, Ar gas pressure, and subtrate rotation speed, are reported. By independent variation of the input power for the two sources, many different film compositions were obtained. The film Ms, perpendicular anisotropic energy K¿ and Kerr rotation angle ¿K were all fairly stable for substrate rotation speeds of 20 rpm or above, below this all three values increased as the speed was decreased.