Hiroki Kurisu

Fabrication of high-permeability ferrite by spark-plasma-sintering method

Abstract Using spark-plasma-sintering (SPS) method, Mn–Zn ferrite platelet cores with few vacancies were successfully fabricated. Laminated cores composed of Mn–Zn or Ni–Zn–Cu ferrites and permalloy layers were also prepared by the SPS method. The laminated cores had large saturation magnetic flux density and high permeability at high frequencies. These soft magnetic cores may be available as the magnetic cores of a magnetic head used in a card reader or the soft magnetic substrates of the perpendicular recording hard disks.

Electronic structure and thermoelectric properties of clathrate compounds Ba8AlxGe46−x

Thermoelectric properties of Al-substituted Ge clathrate compounds Ba8AlxGe46−x were investigated experimentally and theoretically. Polycrystalline Ba8AlxGe46−x (x=12–18) was synthesized by using an arc melting and a spark plasma sintering technique. The obtained samples show the n-type behavior and the carrier concentration decreases with increasing amount of Al composition from x=12 to 16. The reasonably large power factors was obtained: 900–1000 μW/cm K2 around 900 K. Theoretically electronic structure of Ba8Al16Ge30 was calculated by means of a first-principles method and then thermoelectric properties were analyzed on the basis of the result of the calculated electronic structure. The calculated thermoelectric properties agree with the experimental results very well in the wide range of temperature between room temperature and 900 K.

Co-Cr films prepared by sputtering using electron cyclotron resonance microwave plasma

The sputtering deposition using an electron cyclotron resonance (ECR) microwave plasma was tried to use in the fabrication of the Co–Cr perpendicular magnetic recording media. As the Ar sputtering gas pressure increased from 4×10−2 to 8×10−2 Pa, the Co(002) x‐ray diffraction peak intensity increased and the half‐value width of the rocking curve Δθ50 decreased. This result implies that Co–Cr films with high perpendicular orientation and good crystallinity are achieved at high Ar gas pressure. The Co–Cr films deposited at a target to substrate distance of 230 mm had a good preferred crystal orientation (Δθ50 less than 4°), high perpendicular magnetic anisotropy (Hk higher than 4 kOe), and high perpendicular coercivity over 1400 Oe even though the Co–Cr thickness is as small as about 50 nm, and no underlayers were introduced. Thus, the ECR sputtering has high potential in the deposition of the Co–Cr films for ultrahigh density recording media.

Recording characteristics of Co‐γFe2O3 perpendicular magnetic recording media

The recording characteristics of Co‐γFe2O3 perpendicular magnetic recording hard disk media were investigated. Sliding contact recording was performed to evaluate the intrinsic high‐density recording performance of the media with using a metal‐in‐gap‐type ring head. The half‐voltage density D50 of 176 kFRPI and low‐density reproduced voltage Ep of 143 nVp‐p/[turn μm (m/s)] were obtained for the optimal medium whose Co‐γFe2O3 layer thickness was 0.13 μm and perpendicular coercivity was 1800 Oe. The pass wear durability test was performed at 2 m/s, or at a disk rotation of 830 rpm. The reproduced voltage did not decrease with time, and scratches and damage were not observed on the tested track even after 18 000 000 passes. The Co‐γFe2O3 medium is one of the candidates for ultrahigh‐density recording media because of its specific advantages; superior high density recording performance and hardness tolerable for sliding contact use.

Fabrication of ultrathin Ni-Zn ferrite films using electron cyclotron resonance sputtering method

Well-crystallized Ni–Zn ferrite (Ni0.4Zn0.6Fe2O4) highly oriented ultrathin films were obtained at a substrate temperature of 200 °C by a reactive sputtering method utilizing electron cyclotron resonance microwave plasma, which is very effective to crystallize oxide or nitride materials without heat treatment. Thin films of Ni–Zn ferrite deposited on a MgO (100) underlayer showed an intense X-ray-diffraction peak of (400) from the Ni–Zn ferrite as compared to similar films deposited directly onto thermally oxidized Si substrates. A 1.5-nm-thick Ni–Zn ferrite film, which corresponds to twice the lattice constant for bulk Ni–Zn ferrite, crystallized on a MgO (100) underlayer.

Exciton and biexciton properties of CuCl microcrystals in an SiO2 matrix prepared by sputtering method

Abstract We investigated the optical properties of the exciton and the biexciton in CuCl microcrystals embedded in an SiO 2 matrix which is prepared by a novel RF-magnetron sputtering combined with an inductively coupled plasma. The exciton absorption bands of Z 3 and Z 1,2 in CuCl microcrystals shift to energies higher than those for the bulk excitons. In the luminescence spectra intensities of the free exciton and the biexciton luminescence bands under wide excitation density range have linear and superlinear dependencies, respectively: the value of power dependence of the biexciton luminescence bands is about 1.4.

Application of titanium materials to vacuum chambers and components

This paper describes the outgassing properties of titanium materials, and development of vacuum chambers and components for practical UHV/XHV systems. The mechano-chemically polished and the chemically polished titanium materials have a smooth surface and a thin (≤ 10 nm) oxide surface layer, which showed extremely low outgassing rate below 10−12 Pams−1 after baking process. In order to fabricate practical vacuum systems welding, metallizing and brazing processes were optimized, and complex shaped vacuum chambers and various vacuum components such as a bellows, valve, electric feedthrough and ceramic duct with titanium sleeve were fabricated. Sufficient mechanical properties and durability were obtained for practical use.

Characterization of CuCl nanocrystals in SiO2 matrix fabricated by inductively coupled plasma-assisted sputtering deposition

We have investigated crystal characteristics and optical properties of CuCl nanocrystals embedded in a SiO2 glass matrix, which is fabricated by a novel rf-magnetron sputtering technique combined with an inductively coupled plasma (ICP). The diffraction spots caused by the (111), (220), and (311) planes of the zinc-blende structure of CuCl crystals evidently appear on the electron diffraction patterns under inductively coupled plasma-assisted magnetron-sputtering deposition. Nanoscale particles with the mean particle radius of 4.0 nm are observed in the transmission-electron-microscope images. These results indicate that CuCl nanoparticles are crystallized with a very high quality. This yields optical properties in samples such as the sharp exciton-absorption bands named Z3 and Z1,2. These bands appear with a blueshift, as compared to the bulk-exciton energies caused by the quantum-size effect for the exciton. Only the free-exciton luminescence-band appears without other luminescence bands caused by an im...

Perpendicular Co-Cr magnetic recording media prepared by sputtering using ECR microwave plasma

Perpendicular Co-Cr media were deposited on polyimide substrates by sputtering using an electron-cyclotron-resonance microwave plasma in an Ar sputtering gas pressure ranging from 3/spl times/10/sup -2/ to 8/spl times/10/sup -2/ Pa at a target to substrate distance from 170 to 230 mm. The accelerating voltage of the ions which bombard the media surface during deposition drastically affects the crystallographic and magnetic properties of Co-Cr films. Co-Cr media (50 nm in thickness) with good preferred crystal orientation (/spl Delta//spl theta//sub 50/ less than 5 degrees), high perpendicular magnetic anisotropy (H/sub k/ higher than 4 kOe), high perpendicular coercivity (H/sub c/spl perp// over 1400 Oe) and no initial layer were successfully deposited when the ion accelerating voltage was reduced less than about 20 V.

Effects of defects and impurities on electronic properties in CoSb/sub 3/

The band structure and the density of states of doped and non-doped CoSb/sub 3/ were computed by using the supercell. The computation has been done by the linear muffin-tin orbital method with non-overlapped-muffin-tin spheres. Based on the computational results, some doping effects were discussed.