Naoki Honda

Preparation of ordered Fe-Pt thin films for perpendicular magnetic recording media

Abstract A new preparation method of ordered Fe–Pt thin films with perpendicular magnetic anisotropy was studied. Low-temperature ordering phenomenon was found at high Ar sputter-gas pressures. Extremely large perpendicular magnetic anisotropy was obtained for a thin film using a glass substrate. Extending the method, further improvements of the Fe–Pt film have been made in terms of domain size. A very fine domain pattern was successfully observed, suggesting that the new Fe–Pt film will be expected to be a future ultrahigh density recording medium.

Studies of the perpendicular magnetization mode in Co-Cr sputtered films

The extremely high resolution properties in a perpendicular magnetic recording system were studied with a recently developed Co-Cr film medium. Bitter technique was used to observe magnetization distribution in the medium, and the transition of magnetization was directly observed on the top and the bottom surfaces of the film. It was proved that an ideal perpendicular magnetization mode, having a very narrow transition width, takes place even in a high recording density over 40 kBPI. From the angular variation of H c and the micro-structure of the Co-Cr film, it was concluded that the high recording resolution of the film results from the fine columnar particles which show the rotational mechanism of magnetization reversal accompanied by a perpendicular magnetocrystalline anisotropy. The Co-Cr film was also found to be superior in perpendicular anisotropy to any other Co-M films studied here in.

Magnetization reversal process in polycrystalline ordered Fe–Pt(001) thin films

Magnetization reversal processes in Fe–Pt(001) thin films prepared by a high-pressure sputter deposition method were studied. Samples were classified in four types of domain patterns. Type I, with maze-like domain patterns, has a mixing mode of nucleation and wall motion for magnetization reversal. While, type II, with large island domain patterns, shows wall motion in its magnetization reversal. Type III has small island domain patterns, and type IV has fine discrete domain patterns showing rotational modes with inclined M–H loops. Type IV is expected to be one of the candidates for future ultrahigh-density magnetic recording media with high resolution and low noise.

Overview of latest work on perpendicular recording media

Recent works on perpendicular recording media were reviewed, Co-Cr alloy films are still under improvment and show a recording ability of 20 Gbit/in/sup 2/ and beyond. New perpendicular recording media that have high perpendicular anisotropy have been developed. These would be candidate media for ultrahigh density recording beyond 100 Gbit/in/sup 2/.

Design consideration of ultrahigh-density perpendicular magnetic recording media

Design consideration of double-layered perpendicular magnetic recording media for ultrahigh-density recording was studied based on a micromagnetic model. It was found that the introduction of an appropriate exchange coupling between grains remarkably improves the recording resolution of the media. The essential role of the exchange coupling could be understood that it increases the perpendicular M-H loop slope, which has the same contribution to the resolution as the head field gradient. Large values for the product of the M-H loop slope parameter and the head field gradient are expected to result in small transition widths less than 10 nm. Consideration of thermal stability of the media including effects of the demagnetizing field and the M-H loop slope suggested that Co-Cr based media would meet the magnetic properties for recording of 200 Gb/in/sup 2/ but may not for higher densities. Media with higher anisotropy fields like Fe-Pt would be the candidate.

Fe-Pt perpendicular double-layered media with high recording resolution

Abstract Design and preparation of a new Fe–Pt perpendicular double-layered medium are discussed. The Fe–Pt perpendicular medium with enhanced wall-pinning in a laterally exchange-coupled state showed high recording resolution and high thermal stability. An ultra-high reproducing resolution is expected to be verified for the medium if a narrower shield gap reproducing head would be used.

Co-Pt-TiO/sub 2/ composite film for perpendicular magnetic recording medium

A new type of oxide composite film was proposed as perpendicular magnetic recording medium. The storage layer is composed of Co-Pt and Ti-oxide. By transmission electron microscopy (TEM) observation, the film exhibited a well isolated fine granular structure with small and uniform Co-Pt grains surrounded by TiO/sub 2/. More sufficient segregation by TiO/sub 2/ was realized from the beginning of the layer growth compared with other oxide addition film, resulting in a magnetically weak coupled structure. This film has a relatively large magnetic anisotropy constant (K/sub u/) and saturation magnetization (M/sub s/) of more than 5/spl times/10/sup 6/ erg/cm/sup 3/ and about 800 emu/cm/sup 3/, respectively. The structure was brought about by a high sputtering gas pressure of Co-Pt-TiO/sub 2/ film deposition.

Low noise Co/Pd multilayer media for perpendicular magnetic recording

Read-write tests and magnetic force microscopy (MFM) observations have been performed for Co/Pd multilayer perpendicular magnetic recording media. For a Co/Pd multilayer medium with a nucleation field (H/sub n/) of/spl sim/1.5 kOe and a small slope at coercivity (Hc), no reversed magnetic domains between the transitions were observed and a low medium noise was also obtained. Moreover, a negligible time decay in magnetization was detected at the remanent state as well as in signals at both low and high recording densities.

High density recording on ultra-thin Fe-Pt perpendicular composite media

Ultra-thin Fe-Pt films of perpendicular composite media were studied. It was found that a preparation condition at a temperature of 375/spl deg/C and introduction of an exchange-decoupling layer between the Fe-Pt layer and the soft-magnetic underlayer led to reduction of the initial growth layer of the Fe-Pt film. A 5 nm thick Fe-Pt medium exhibited a high SNR and a high recording resolution with high thermal stability.

Gbit/in/sup 2/ perpendicular recording using double layer medium and MIG head

Perpendicular recording has been studied using ring heads for read and write. It was confirmed that an areal recording density of 1 Gbit/in/sup 2/ could be achieved by using a MIG type ring head for recording and a narrow gap ring head for reproduction combined with a single layer Co-Cr system alloy medium with a thin soft magnetic backlayer. Improvement in overwrite properties with the backlayer and noise reduction by increasing the Cr content are discussed. It is concluded that it would be possible to realize a 10 Gbit/in/sup 2/ recording system by perpendicular recording by using a high resolution MR head without any fundamental changes in the medium.