Ken-ichi Itoh

Detecting dynamic signals of ideally ordered nanohole patterned disk media fabricated using nanoimprint lithography

The authors have fabricated ideally ordered alumina nanohole patterned disk media via anodic oxidation and nanoimprint lithography with a thermoplastic resist. The ordered arrays of alumina nanoholes with 100nm pitch, filled with Co by electrodeposition, were created over a macroscopically large area on a hard-disk substrate using these industrially applicable nanofabrication technologies. Stable flight of a perpendicular magnetic head above the media and perpendicular magnetic anisotropy of the Co nanopillars enable high-speed dynamic magnetic recording and playback. Dynamic periodic signals that matched the nanopillar periodicity were clearly observed after writing bit patterns, showing alternate reversal of magnetization of the nanopillars.

Controlled filling of Permalloy into one-end-opened carbon nanotubes

Controlled filling of Permalloy into a one-end-opened carbon nanotube (∼40 nm in inner diameter, 900 nm in length) array embedded in an anodic aluminium oxide film was achieved by an electrochemical route. Thanks to the electron-microscopically transparent carbon nanotubes, the time course of the electrochemical deposition process was readily visualized by means of transmission electron microscopy, revealing that Permalloy filling started from the pore bottom of the carbon nanotubes. This novel bottom-up filling opens a route to controllable filling of materials of interest into carbon nanotubes with one open end. The magnetic properties of the controlled filled carbon nanotubes in the array were studied. Interestingly, even in the case of isolated Permalloy nanoparticles inside the carbon nanotubes in the array, prominent magnetic anisotropy with an easy magnetization direction along the carbon nanotube axis was observed. In addition to the Permalloy-filled carbon nanotube array as embedded in the anodic aluminium oxide film, individual carbon nanotubes filled with Permalloy were also obtained.

Longitudinal recording on a rigid disk using Ba-ferrite powder

We propose a new concept for a Ba-ferrite coated disk, in which the Ba-ferrite particles are longitudinally oriented and to which acicular Co-γFe 2 O 3 powder is also added, to achieve high density recording and low noise characteristics for rigid disk applications. By using a ring head, longitudinal orientation was found to be effective in obtaining an increased output and a symmetrical waveform. Acicular powder is added to reduce pinholes upon longitudinal orientation. Although the critical bit density, D 50 , decreases slightly, practical recording density, judged from the degree of peak shift, is larger for longitudinal orientation than for perpendicular orientation. The new disk has great promise for applications of more than 40 kFRPI, without any change to conventional disk drives and ring-shaped heads.

Magnetic behavior in an ordered Co nanorod array

The magnetization reversal process of an ordered Co nanorod array is shown using the images obtained from successive in-field magnetic force microscope (MFM) measurements. The magnetization reversal model is discussed according to local and whole magnetization reversal properties measured by the polar magneto-optical Kerr effect (PMOKE) and an alternating gradient magnetometer (AGM), respectively. Additionally, the dipolar field was probed using in-field MFM measurements. By removing the effect of the dipolar field, an intrinsic switching field distribution (SFD) is shown in a map with a hexagonal array. A detailed study of the dipolar field in ordered nanorod arrays with various diameters and pitches was carried out by numerical calculations.

Magnetic head field over the air-bearing surface as visualized by the projection of a patterned electron beam

We have developed a technique to provide a way to map a two-dimensional magnetic field distribution over an air-bearing surface of a recording head. This technique is based on modified transmission electron microscopy (TEM) and the computer processing of TEM images distorted by the head field. The technique makes it possible to study the field distribution at various distances from the air-bearing surface of the head.

Dynamic Write/Read Characteristics of Alumina Nanohole Patterned Media With a Soft Underlayer Measured With a Perpendicular Magnetic Head

We present dynamic write/read characteristics of alumina nanohole patterned media having a soft magnetic underlayer (SUL), which offer good flyability of a perpendicular magnetic head with a flight height of 10 nm. Increase in the head-field gradient in the recording layer owing to the SUL was confirmed by measurements of signal-to-noise ratio and isolated magnetic transition width. The writability of the magnetic nanopillars was clearly demonstrated by visualization of the recorded patterns with a magnetic force microscope

Improvement of Magnetic Recording Characteristics by Narrowing the Array Pitch of Nanohole Patterned Media

Dynamic magnetic recording properties of Co-filled nanohole arrays were successfully investigated as perpendicular magnetic media via a flying giant-magnetoresistive head. By narrowing the Co nanopillar pitch, we observed suppression of the magnetic transition width and increase of the signal-to-noise ratio. The dynamic signals reflect magnetic field variation caused by the nanopillar arrangement on the tens of nanometers scale. These characteristics and the signal behavior suggest their possible application to ultrahigh-density magnetic recording.

New 3.5′′ Magneto-Optical Disk System: 1.3 GB GIGAMO –Technology, Design Concept and Reliability–

We have developed and commercialized a new-generation 3.5?? magneto-optical (MO) disk system, the GIGAMO, which marks the worlds first utilization of magnetically induced super resolution (MSR) to realize 1.3 GB capacity and the high performance of up to 5.9 MB/s data transfer rate. The system design and the format are optimized, especially for the purpose of achieving complete downward compatibility with former 3.5?? MO families from 128 MB to 640 MB media. The improvement of media characteristics and intelligent firmware development of the drive system enable us to ensure usage at various temperature and repeated write/read cycles.

Selenium Alloy Film For New Erasable Optical Disk Media

Selenium film alloyed with indium and antimony has good characteristics for erasable optical disk media. Depending on the conditions of the irradiation directed to the film, it exibits two different reflectances and geometrical deformations,.and the change between these two states is reversible. The mechanism of the reversible changes is different from amorphous-to-crystalline phase transition. Both states are definitely crystalline, which have been confirmed by transmission electron microscope analysis. The film has a good durability of write-erase cycles and is chemically stable. The disk sample has been confirmed to be capable of writing and erasing at a speed of 600 rpm. The resolution is sufficient to record a bit of 1 pm length on the disk. Carrier-to-noise ratio is fairly good. This film also has a potential for higher signal transfer rates.

In-field magnetic force microscope study of dipolar interaction in an ideally ordered Co nanorod array fabricated using nanoimprint lithography

We have performed experimental studies and numerical calculations on the dipolar interaction in an ideally ordered hexagonal nanorod array. The dipolar field in an ordered Co nanorod array was measured using an in-field magnetic force microscope (MFM) with a controlled applied field. The average dipolar fields of neighboring nanorods acting on a center nanorod were calculated by approximating the monopole with a magnetic charge m=MSS on the end of each nanorod. The largest dipolar field obtained from numerical calculation is agreement with that from in-field MFM measurements.