Hisashi Kimura

Single-pole/TMR heads for 140-gb/in/sup 2/ perpendicular recording

Single-pole writers and tunneling magnetoresistive (TMR) readers for 140-Gb/in/sup 2/ perpendicular recording were fabricated and their recording performance was tested. Data erasure, which is observed as write instability in a repeated read-write operation, can be suppressed by combining a laminated pole and low throat height. Fe-Co/Ni-Cr laminated film was used to reduce the remanent magnetization of the main pole after patterning. Narrow track writers with a 120-nm-wide trapezoidal pole showed a good write ability of 30 dB or more in overwrite for media with high coercivity of up to 7 kOe. Also, negligibly small skew writing was confirmed. TMR heads with a sensor width of 85 nm and a head resistance of 250 /spl Omega/ showed approximately 30 dB of head signal-to-noise ratio (SNR). A potentially higher SNR with a higher operating voltage was suggested from a measured output versus sensing current curve. Calculations showed that the side reading was suppressed in a side-shielded design. A 10% amplitude width of the microtrack profile of a 100-nm-wide reader was reduced from 198 to 162 nm by applying the side shields.

Fabricating narrow and trapezoidal main poles for single-pole-type heads

We investigated the fabrication processes used for perpendicular recording heads. To solve the problem of side write/erase on adjacent tracks, it is necessary to develop a trapezoidal main pole for single-pole-type heads. We therefore proposed a fabrication process using ion milling and an alumina hard mask for a sputtered film. We successfully made a narrow (120-nm wide) trapezoidal main pole using the process. The beveled angle of the pole depended on both the throat height and the angle at the flare point. When the flare point angle was 90/spl deg/, the beveled angles of the trapezoid were about 10/spl deg/. Evaluation data confirmed that perpendicular recording heads with a trapezoidal main pole solved the side write/erase problem.

Newly developed wraparound shielded pole heads for perpendicular recording

The perpendicular recording system using single-pole heads and perpendicular media is considered as one of the promising technique for increasing the areal recording density of hard disk drives. In this paper we will describe a newly developed shield process around a main pole and the read-write performances of the head.

Nano-granular metal/insulator multilayer for reader shielding materials

We have developed materials with high resistivity and permeability. It consists of multilayered magnetic metal/insulator films such as CoFe/Al/sub 2/O/sub 3/, NiFe/Al/sub 2/O/sub 3/ and NiFe/SiO/sub 2/. The thickness of each layer is around 1 nm. This film consists of metal granules around nm size covered with insulator as evidenced by using transmission electron microscopy (TEM). The multilayer film CoFe/Al/sub 2/O/sub 3/, showed a resistivity of more than 10 m/spl Omega/cm and a coercivity of the hard axis was between 80 and 240 A/m, and saturation magnetization was higher than 0.9 T. The permeability of this film was around 250 up to GHz level. In this study, the film structure offering the highest resistivity and permeability was 20 to 40 layers of CoFe(1.3-1.5 nm)/Al/sub 2/O/sub 3/(1.0-1.2 nm) bilayer. Nano-granular high-resistivity materials are therefore appropriate for using as head shielding material.

Superconducting magnet with tube-type cryostat for magnetically suspended train

In order to develop a compact and light-weight superconducting vehicle magnet for a magnetically suspended high speed train, a superconducting magnet with a tube-type cryostat has been constructed and tested. The shape of the superconducting coil is a rectangle, which has a length of 1.5 m and a width of 0.6 m, and coaxial vessels of the cryostat cover the coil winding. The liquid helium vessel and the outer vacuum vessel of the cryostat have an outside diameter of 8 cm and 14 cm, respectively. The experimental results and the evaluation for the magnet are described.

A superconducting coil indirectly cooled by forced helium flow

Abstract A small superconducting coil is indirectly cooled by a forced flow of helium. The coil, wound from Nb-Ti-Zr multifilament superconducting composite, is 15 mm id, 24 mm od and 30 mm long. The maximum central field is 30.3 kG at 4.2 K. Contact between the cooling tube and the coil is achieved using grease. The experimental results are expressed by a relation of critical current and energizing rate. Typical transient temperatures of the coil and coolant during energizing and after quenching are presented. The analysis shows the design of coils of this type is possible using hysteresis loss and heat conduction analysis.