Miki Hara

COMPUTER SIMULATION OF THIN-FILM MEDIA NOISE USING AN AUTOCORRELATION FUNCTION ALONG THE TRACK DIRECTION

The causes of thin‐film media noise are discussed by deriving a formula which shows a direct relationship between the noise spectrum and the magnetization configuration of a thin‐film medium. This formula is derived by Fourier‐transforming the autocorrelation function of jMx‐Mz along the track direction, where Mx and Mz are the longitudinal and vertical components of magnetization, respectively. Noise and signal spectra are computed by means of this formula. The computed noise spectra are the maximum for a relatively long wavelength. Their form and intensity are shown to be strongly affected by the anisotropy constant and the axis orientation of easy magnetization.

Computer simulation of coercive force and thermal viscosity in perpendicular recording media

In this study, H/sub c/ and the temporal change of H/sub c/ have been analyzed by using micro-magnetic simulation including incoherent magnetization rotation in a grain.

Effect of grain size, cluster size, and crystallographic orientation upon simulation of longitudinal recording media

Simulations of hexagonal magnetic particles with uniform exchange energy and random c-axis in-plane orientation do not reproduce real media magnetic properties. Simulation software was thus modified to model four experimentally observed Co-alloy microstructures, to distinguish the effects of grain size, cluster size, exchange decoupling, and cluster substructure; and to more accurately model real media behavior. Results include: (1) Clusters of isolated uniaxial particles act like single grains having the cluster size. Exchange decoupling on a size scale smaller than the crystallographic grain size has little effect upon hysteresis loops or media noise. (2) The magnetic properties of clustered bicrystal and randomly oriented media depend on the exchange interactions within and between clusters of grains. Media hysteresis loops and recorded tracks are well simulated using exchange energies within randomly oriented or bicrystal grain clusters up to ten times larger than those used in the standard model.

Computer simulation of ultrahigh-density perpendicular magnetic recording

The possibility of ultrahigh-density recording higher than 10 Gb/in.2 with perpendicular magnetic recording is investigated by computer simulation for a ring-type head and single-layer medium combination. A nucleation model is used as a media model because it incorporates a nucleation site, which causes irreversible magnetization switching. Fundamental read–write characteristics are found to be entirely different from those of longitudinal recording. Recorded magnetization strongly depends on head field strength; the maximum magnetization appears around the head field strength of media coercivity, and beyond this the recorded magnetization decreases abruptly. Spacing loss in the recording process also depends on head field strength and recording density. However, saturation recording can be attained even at an ultrahigh recording density of 600 kFCI with a spacing of 30 nm. Also, a higher signal-to-noise ratio than in longitudinal recording can be obtained by introducing weak intergrain exchange interacti...

High-density perpendicular recording media with large grain separation

The possibility of 300-500 Gbit/in/sup 2/ perpendicular recording using granular recording media has been investigated through micromagnetic simulation based on the Langevin equation. Writability and thermal stability in 10 years were obtained changing media parameters such as the grain size D, the grain separation d, and the thickness of the recording layer t/sub mag/ for proper combination of the grain saturation magnetization M/sub s-grain/ and the grain perpendicular anisotropy energy K/sub u-grain/. It was found that high-density recording is realized under the large grain separation, the large grain saturation magnetization, and the large grain anisotropy energy. The read/write calculation using ordered medium with D of 4.2 nm, d of 2.3 nm, t/sub mag/ of 12.0 nm, M/sub s-grain/ of 1313 emu/cm/sup 3/, and K/sub u-grain/ of 7.0 Merg/cm/sup 3/ confirmed the possibility of 1303 kFCI and 1954 kFCI perpendicular recording, leading to 325 and 488 Gbit/in/sup 2/ with 250 kTPI (track pitch of 102 nm).

M?H Loop Slope and Recording Properties of Perpendicular Media

The slopes of the M–H loop of perpendicular magnetic recording media were estimated by micro-magnetic simulation for various inter-grain exchange couplings, grain aspect ratios and inter-grain spacings. The slope of the M–H loop depends not only on inter-grain exchange coupling but also on grain aspect ratio and inter-grain spacing. The simulation revealed that the required head field decreases with increasing inter-grain exchange coupling. The optimum value of the slope was slightly larger than 1.0 for compromising resolution and SNR by changing the inter-grain exchange coupling. The simulation results also indicated that the inter-grain spacing improves both resolution and SNR.

Write-field gradient effect on transition width in perpendicular recording media

Perpendicular magnetic recording (PMR) system using a single-pole writer and a double-layered perpendicular recording medium with a soft underlayer (SUL) is a promising candidate for high recording densities of over 100 Gb/in/sup 2/. The relationships between medium characteristics and recording performance have been studied. In this paper, we have clarified the dependency of the write-field gradient on the transition width using by a micromagnetic modeling. Also, the dependence of medium parameters is also discussed in the paper.

A technique for capturing the transition curvature and analysis of the write head characteristics

Transition shift as a function of cross-track position and the remanent magnetization profile was obtained using a spin-stand with a reference clock head. This measurement method captures the written patterns from a GMR readback waveform in high resolution, and is useful for precise study of the head/media characteristics. Tracks recorded using a high Ms head or a high Hc disk revealed flat transition patterns across the track and showed good on-track performance. The write field affected the transition curvature, and the off-track margin could be improved by controlling the write current.

Recorded magnetization analysis by computer simulation

A new method is proposed for accurately differentiating between an effective recorded-track area and an erase band by making a correlative evaluation of the magnetic-pole density distribution. At each end of an effective track, there is an area where a magnetization transition phase-shift occurs. This phase-shift area causes interference between consecutive bits at high-density recording, and reduce the effective track width. Also, an erase band is formed just outside the effective track. Simulation showed that the phase-shift area and the erase band are affected by the recording field distribution and narrowing the gap length, and reducing the recording magnetic field can effectively reduce these areas.

Exchange interaction energy in magnetic recording simulation

Based on a phenomenological theory, micromagnetic simulations and experiments are used to evaluate an improved function for the exchange interaction between magnetic particles in perpendicular recording media. Assuming diluted spin layers in the particle boundary and a gradual rather than abrupt rotation of magnetization between grain cores, the exchange energy is better described by an even power series of θ, rather than a cosine function. The conventional cosine function does not have a restoring torque near θ = π and adjacent grains tend to align strictly antiparallel. In contrast, using a power series of θ, adjacent grains tend to align at a small angle away from θ = π. This gives rise to a small in-plane magnetization component and therefore a distinct peak in in-plane susceptibility is observed around H = 0. From magnetization measurements of a real medium, a peak is observed around H = 0, which matches with an assumption of 2 or 3 spin layers. In some situations, the exchange interaction between di...