Setsuo Yamamoto

Extremely high bit density recording with single-pole perpendicular head

Since perpendicular magnetic recording is free from recording demagnetization, high-density recording up to the intrinsic limit of a recording medium is possible. This prediction was verified experimentally in a flexible disk system using a single-pole head and a Co-Cr/Ni-Fe double-layer medium. We could record and reproduce signals up to 680KFRPI. The recording bit length at the highest density was of the order of the Co-Cr columnar diameter.

Perpendicular recording by a narrow track single pole head

The feasibility of high track density recording in a perpendicular magnetic recording system has been investigated. The properties of the magnetic field of a single pole type (SPT) head having a narrow track width were studied by using a large scale model of a head and a medium. The y-field gradient of the SPT head near the track edge is steeper than the x-field gradient of a ring head, and it was confirmed by Bitter technique that the recorded track width acculately coincides with the width of the main pole of the SPT head. Perpendicular recording using the SPT head also has superior off-track characteristics and the crosstalk signal is hardly detected even at very narrow track pitches. From a magnetics point of view, no problems exist in narrowing the track width of the SPT head in perpendicular recording. Narrow track recording and reproducing with SPT head of only 6.5 μm in track width could be achieved with sufficient signal to noise ratio in perpendicular flexible disk systems.

First-principles study of type-I and type-VIII Ba8Ga16Sn30 clathrates

We calculated the electronic structures and the thermoelectric properties for type-I and type-VIII Ba8Ga16Sn30 (BGS) clathrates. The band structures show that type-I and type-VIII BGS are indirect semiconductors with band gaps of 0.51 eV and 0.32 eV, respectively. The calculated Seebeck coefficient of n-type type-I BGS is higher than that of n-type type-VIII BGS because of the larger density of states in type-I at the bottom of the conduction band. This is in good agreement with the experimental results. We also calculated the electrical conductivity and thermal conductivity due to charge carriers. Estimated thermoelectric figure of merit, ZT, exceeds 1.0 for both types.

Recording characteristics of perpendicular magnetic rigid disk measured by non-flying single-pole head

A contact recording experiment using perpendicular magnetic hard disks was conducted with a nonflying single-pole-type magnetic head to investigate the practical feasibility of extremely high-density magnetic recording. A single-pole head produces an ideally sharp field distribution because of a strong head-medium magnetic interaction; hence, an isolated magnetization transition in perpendicular magnetic recording becomes much sharper than that in longitudinal recording at a narrower head-medium spacing. A much better durability of hard disks and heads due to a much smoother surface of the disk was also confirmed. >

The effect of magnetic interaction between medium and head on perpendicular magnetic recording characteristics

The high density recording characteristics of perpendicular magnetic recording using a single-pole head are affected by the magnetic interaction between the medium and the head. By decreasing the relative thickness of the Co-Cr layer in the double-layer medium to that of the main-pole of the head, and increasing the saturation magnetization of the Co-Cr layer, the high density recording characteristics are enhanced. When requisite conditions are realized, the reproduced voltage vs. bit density characteristics are improved considerably for a thinner main-pole of the single-pole head.

An analysis of medium noise of Co-Cr double-layer films in perpendicular magnetic recording

Abstract The medium noise in perpendicular magnetic recording is discussed. The perpendicular recording mode was expected to prevent zig-zag walls around transitions, and the experimental result of low transition noise in Co-Cr media confirms this. Also, the main origin of the noise is concluded to be irregular clusters of grains in the film.

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.

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.

High Density Recording with Single Pole Head

The feasibility of high-bit-density recording was investigated experimentally using a perpendicular magnetic recording system employing a single-pole head and a Co-Cr/Ni-Fe double-layer medium. To improve the reproducing sensitivity and resolution, the following were adopted: (a) a newly-developed high-sensitivity single-pole head; (b) a medium with a relatively thin (0.1 ¿m) Co-Cr layer and a thick (0.5 ¿m) Ni-Fe underlayer; and (c) a head-medium spacing of less than 0.03 ¿m. As a result, reproduced signals were detected at up to 680 kFRPI. The recording bit length at the highest density was of the order of the Co-Cr layer columnar grain diameter of the medium. This result proves that recording at densities approaching the intrinsic limit is possible, because the perpendicular recording method is free from recording demagnetization effects at high densities.