Takuya Uzumaki

The Effect of Ca2PbO4 Addition on Superconductivity in a Bi-Sr-Cu-O System

We examined the effect of Ca2PbO4 addition on superconductivity in a Bi-Sr-Cu-O system. We determined that Ca2PbO4 is formed in Bi-Pb-Sr-Ca-Cu-O at temperatures lower than 750°C on the basis of powder X-ray diffraction and micro-Raman scattering. A high-Tc phase was synthesized by adding Ca2PbO4 to the Bi-Sr-Cu-O system which has a single CuO layer. It seems that the synthesis process of the high-Tc phase is based on a reaction between the low-Tc structure and Ca2+ in the liquid phase which is caused by decomposition of Ca2PbO4 at 822°C.

A magnetic force microscope using CoFe-coated carbon nanotube probes

Ferromagnetic-film-coated carbon nanotube (CNT) probes were employed in a magnetic force microscope (MFM) observation. We succeeded in making a uniform ferromagnetic film on the CNT probes by improving the coating process and selecting materials. The performance of the CoFe-coated CNT probe was evaluated in ultra-high-density perpendicular magnetic storage media with densities from 600 to 1100?k flux changes per inch (FCI). The magnetic domain structure of the magnetic storage media was clearly observed up to 1100?kFCI. The ultimate lateral resolution of the newly developed MFM probes is down to about 10?nm, which exceeds the bit length of a magnetic recording with a density of Tbit?inch?2.

Signal-to-media-noise ratio improvement of CoCrPt-SiO2 granular perpendicular media by stacked Ru underlayer

In this work we have developed a stacked Ru underlayer and have studied its effects on the improvement of recording performances for CoCrPt-SiO2 granular-type dual-layer perpendicular media. The c-axis distribution ΔΘ50 of the 13.2 nm thick stacked Ru underlayer was 4.5°, which was about 33% smaller than that of Ru monounderlayer with the same thickness. The use of stacked Ru underlayer realized that the recording layer of granular-type media consisted of segregated fine-grain structure with oxide grain boundaries. The signal-to-media-noise ratio (SNR) improvement achieved by the use of the stacked Ru underlayer was indicated when it was compared with the use of Ru monounderlayers. Furthermore, the SNR for monopole head of 8.5 dB at 480 kfci and D50 of 356 kfci were obtained by optimizing the structure of stacked Ru underlayer.

Disk substrate deposition techniques for monodisperse chemically synthesized FePt nanoparticle media

Self-assembled FePt nanoparticles hold promise for future ultrahigh-density magnetic recording media because of their high anisotropy and capability to be formed into small and uniform grains. By using a special spin coater, we were able to form a dense array of FePt particles across the entire surface of a 2.5 in. disk substrate. Our method can control the number of layers of FePt nanoparticles. The media deposited with FePt nanoparticles by the spin coater was annealed in a vacuum. We measured read–write properties of the FePt nanoparticle media on a spin stand, and succeeded in detecting a signal of 290 kfci.

CoFe-Coated Carbon Nanotube Probes for Magnetic Force Microscope

CoFe-coated carbon nanotube (CNT) probes have been successfully fabricated by a radio-frequency sputtering method. The sputtering conditions for obtaining a uniform ferromagnetic film on the CNT probe were investigated. The optimal sputtering conditions were determined from the observations using a scanning electron microscope and an atomic force microscope. CNT magnetic force microscope (MFM) probes prepared under optimized conditions provided us clear images with an ultimate lateral resolution of approximately 10 nm.

Fine Tuning of the Sizes of FePt Nanoparticles

Fine tuning of the sizes of FePt nanoparticles has been realized by a simple modification of a solution phase synthesis, which consists of the decomposition of Fe(CO)5 and the reduction of Pt(acac)2. The key method used to control the particle size is the use of surfactants, and only a change in their amount is required to vary the average sizes of the FePt nanoparticles from 2 to above 4 nm. The resultant nanoparticle volume is proportional to the surfactant amount; this makes the synthesis of FePt nanoparticles of desired sizes possible.

Preparation and magnetic properties of Bi‐Pb‐Sr‐Ca‐Cu‐O superconducting ceramics

A high Tc phase (Tc ≂110 K) in Bi‐Pb‐Sr‐Ca‐Cu‐O systems was synthesized by adding Ca2PbOx to the mixture of a low Tc phase (Tc ≂80 K) and a Bi‐Sr‐Cu‐O (Tc ≂10 K). X‐ray powder diffraction measurement suggests that the sintered bulk mainly consists of the high Tc phase. The volume fraction of the high Tc phase was 74% from the measurement of magnetization. The lower critical field Hc1 was 10 Oe at 77.3 K. The critical current density Jc of 3.0×102 A/cm2 was obtained for a repressed sample with a highly oriented microstructure.

Microstructure improvement of thin Ru underlayer for CoCrPt-SiO/sub 2/ granular perpendicular media

The microstructure improvement of the thin Ru layer was discussed in order to achieve excellent recording performance of the granular-type perpendicular media. The recording layers of granular-type media were deposited on different Ru underlayers by rf magnetron sputtering method with a composite-type sputtering target that consists of CoCrPt and SiO/sub 2/. The effects on the improvement of recording performances was analyzed. It was observed that the recording dependences of signal output and media noise are quite different but they show the same recording density dependences of signal-noise ratio (SNR). Realization of thin Ru underlayer for formation of high performance recording layer resulted in the investigation.

Conduction Band Structure of SrTiO3

Shubnikov de Haas(SdH) oscillations have been measured for the semiconducting single domain SrTiO3 with Carrier concentration of 3.4×1018 cm-3 and 5.9×1018 cm-3. From the temperature dependence of the SdH amplitude, the cyclotron mass values are determined for the [001] and [110] magnetic field directions. We have found, from the angular dependence of the SdH oscillation, that there exist several branches of the frequencies among which the highest and lowest branches originate from the Fermi spheres at the Brillouin zone center, and the other ones from the extremal area which is interconnected through the magnetic breakdown tunneling paths. Energy band parameters based on the kp perturbation method are determined.

Magnetization suppression in Co/Pd and CoCrPt by nitrogen ion implantation for bit patterned media fabrication

We propose a bit patterned media fabrication method based on low energy nitrogen ion implantation. Nitrogen ion implantation of fcc-Co/Pd multilayer or hcp-CoCrPt single layer suppresses their magnetizations at room temperature. Ion implantation reduces the Curie temperature from 600 to 400 K (or lower) as a result of lattice expansion and reduced exchange interaction between the magnetic atoms in the magnetic layer. We have made media with magnetic dots of 190 to 30 nm in diameter by nitrogen ion doping through resist patterns. Writing and reading of the signal from individual dots were performed with a commercial perpendicular magnetic recording head.