Masayoshi Shinohara

Magnetic recording characteristics of sputtered γ-Fe 2 O 3 thin flim disks

A thin film disk of γ-Fe 2 O 3 for high density magnetic recording has been developed. γ-Fe 2 O 3 films were prepared in a serial process from the reactive sputtering of on to α-Fe 2 O 3 reduced to Fe 3 O 4 and oxidized to γ-Fe 2 O 3 . A high coercive force of 700 Oe and a squareness ratio of 0.8 were attained for γ-(Fe 0.955 Ti 0.025 Co 0.02 ) 2 O 3 . Recording characteristics of the disk were evaluated using a Mn-Zn ferrite head. The recording density D 50 reached 1,100 bits/mm (27,900 bpi), and the number of dropout errors at 50 % threshold level was less than 50 per surface. Stability versus temperature change and wear resistance were also evaluated.

Magnetic and R/W properties of CoPt-SiO/sub 2/ granular media

We fabricated Co/sub 80/Pt/sub 20/-SiO/sub 2//Cr granular media by sputtering and studied their structure and their magnetic and read/write (R/W) properties while varying the volume ratio of CoPt to SiO/sub 2/. Transmission electron microscopy (TEM) images revealed that the diameter of CoPt particles increased with an increase in volume ratio. The maximum coercivity (about 2700 Oe) was obtained at 65 vol% of CoPt. On the other hand, at over 40 vol% of CoPt media, the signal to media noise ratio (S/N/sub m/) rapidly decreased with an increase in the volume ratio. This indicates that media with finer grains exhibit low noise. In the same way, the instability of the magnetization was diminished with an increase in volume. This instability is very sensitive to the grain size of CoPt.

Magnetic relaxation in thin film media as a function of orientation ratio

Abstract We investigated the thermal relaxation of isotropic and oriented media having the same K u V/kT via a method combining micromagnetic and Monte Carlo simulations and experiments. Through simulations and experiments, we ascertained that the thermal stability of remanent magnetization increases with increased circumferential orientation. We also confirmed via simulations that written dibit and continuous bits are thermally stabilized by circumferential orientation media.

Magnetic properties and structure of (Co-alloy)-SiO/sub 2/ granular films

We fabricated (Co-alloy)-SiO/sub 2/ granular films by rf-sputtering with composite target and annealing in a high vacuum environment. The coercivity of the films depended on annealing temperature, the Co-alloys volume fraction in the film, and other added elements to cobalt. We found that a (Co/sub 85/Pt/sub 15/)/sub 83/-(SiO/sub 2/)/sub 17/ granular film (Co/sub 85/Pt/sub 15/: 64 vol.%) exhibited about 1600 Oe of coercivity at room temperature. The grains diameter was about 50 nm measured by AFM. X-ray diffraction patterns showed that the Co-alloy grains of most films had an fcc-phase structure. From Henkel-plot analysis, the magnetic exchange interaction between the CoPt grains was found to be weak.

The effect of orientation ratio on the dynamic coercivity of media for >15 Gbit/in/sup 2/ recording

The dynamic coercivity of longitudinal magnetic recording media has been investigated using a spin-stand. Improvement of the media orientation ratio (O.R.) or the in-plane alignment of the anisotropy axes not only results in the improvement of thermal stability at storage times but also in a reduction of the difference between the coercivity at high data rates (<10 ns) and at semi-dc conditions (/spl ges/1 s). Comparison of remanence curves at 1 s and 14.3 ns indicate that the optimum writing current does not increase as significantly as the coercivity.

Magnetic interaction in Co-Cr-Pt-Ta-Nb media: utilization of micromagnetic simulation

Difficulties exist in identifying the intergranular exchange coupling constant (h/sub e/) via magnetic properties measurements and TEM observation of actual media. The h/sub e/ was estimated to be 0.13 for CoCr/sub 12/Pt/sub 5/TaNb/CrMo and 0.115 for CoCr/sub 19/Pt/sub 5/TaNb/CrMo via micromagnetic simulation. The other parameters, which are the magnetostatic coupling constant (h/sub m/) and the grain geometry, were obtained from measuring the magnetic properties and observing the microstructure of actual media by TEM. The h/sub m/ is 0.11 for CoCr/sub 12/Pt/sub 5/TaNb and 0.09 for CoCr/sub 19/Pt/sub 5/TaNb. The parameters were ascertained to be suitable by comparing the MFM images of the DC demagnetized state and the medium noise dependence of the linear density between the micromagnetic simulation and the experiments.

Chemical structure and durability of a plasma-polymerized protective layer for thin-film magnetic disks

Plasma-polymerized films deposited using methane, ethane, acetylene, and benzene as a source material, are generally too thick for practical use (1), (2). Using a diphenylethane monomer, a plasma-polymerized film, less than 10 nm thick, and durable enough for commercial applications, was produced. In this paper, the relationship between the chemical structure and the durability of a plasma-polymerized film is discussed. Films were analyzed using Raman, infrared, and Rutherford backscattering spectroscopies. By increasing the sp2 bonding and decreasing the hydrogen concentration in the films, their durability could be increased. Films of less than 10 nm in thickness film were more durable than sputtered carbon films of a comparable thickness. The new film also showed promising tribological characteristics for high-performance magnetic disk-drive applications. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Trlbology Conference In St. Louis, Missouri, October 14–16, 1991

Signal-to-noise ratio and thermal stability issues in extending synthetic ferrimagnetic media technology over 100 Gb/in/sup 2/

Signal-to-noise ratio (SNR) and thermal stability issues are addressed to evaluate synthetic ferrimagnetic media (SFM) for achieving areal densities >100 Gb/in/sup 2/. Thermally stable SFM is obtained at M/sub r//spl delta/ values as low as 0.15 memu/cm/sup 2/, utilizing a higher magnetic anisotropy for the stabilization magnetic layer. The SNR relations for SFM are decided by the effective M/sub r//spl delta/ and coercivity, similar to conventional media. The recording characteristics of a low M/sub r//spl delta/ medium was compared with a higher M/sub r//spl delta/ medium used for the 106-Gb/in/sup 2/ demonstration. Lower medium noise and higher signal resolution of the lower M/sub r//spl delta/ medium indicate an areal density extension to beyond /spl sim/150 Gb/in/sup 2/.

Reproduced output reduction in thin film media by thermal fluctuations

Abstract Demagnetizing fields in recorded bits accelerate thermal decay of data output in magnetic recording media. The spread of the transition area also promotes the reduction of obtained data output. By comparing the time dependencies of data output at several recording densities from spin stand data with the time dependencies of the remanent magnetization in various reverse fields, the demagnetizing fields in the recorded bits for different recording densities were estimated. The difference observed between the time dependence of data output and that of remanent magnetization was experimentally clarified to be due to the increase in the transition length. We describe a method to account for both magnetization decay and transition broadening in the thermal degradation of the output signal.

Relationship between magnetic circumferential orientation and magnetic thermal stability

Magnetic recording media with a capacity exceeding 40Gbt/in2 must have not only high signal-to-noise ratio (S/NJ but also magnetic thermal stability. Hosoe et al. reported that small magnetic grain size distribution in recording media increases thermal stabilii [l]. On the other hand, magnetic circumferential orientation of recording media has been shown to improve magnetic thermal stability [2]. It was found via numerical simulation and experimentation, that circumferentially oriented media have superior thermal stability even if &V/k,T is kept constant. However, in the previous investigation, the remanence-thickness product (M,6) and the coercivity in the circumferential direction (Hc4,) were changed while varying the orientation ratio (OR). From an HDD design point of view, it is necessary to adjust the M,6 and the Hc.dr. to specification values. In this article, we present the thermal stability of media with the same MJ i and H, , , as a function of the OR.