Hideyuki Akimoto

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.

Analysis of thermal magnetic noise in spin-valve GMR heads by using micromagnetic simulation

The size of the sensor in spin-valve GMR heads has been reduced to increase the areal magnetic recording density. Thermal magnetic noise, which arises from thermal fluctuation, becomes the main source of head noise and a limitation on recording density. Insufficient abutted permanent magnetic biasing yields an asymmetrical waveform both for signal output and thermal magnetic noise. This is due to the same mechanism as that of Barkhausen noise. In contrast, it has been found that small Hex, which is the exchange coupling strength between the bottom pinned layer (Pin1) and the antiferromagnetic biasing layer, emphasizes thermal magnetic noise without affecting signal output. In a head with small Hex, the magnetization near the air bearing surface and the top of the Pin2 layer tilts in the direction of the track width and randomly flips in the opposite direction. In synthetic ferrimagnetic heads, thermal magnetic noise chiefly depends on Hex rather than unidirectional anisotropy, Hua. The value of Hua does n...

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.

Rigid disk medium for 20 Gb/in/sup 2/ recording demonstration

A longitudinal medium was developed for 20 Gb/in/sup 2/ recording. This medium has a coercivity of 3380 Oe and M/sub r//spl delta/=0.42 memu/cm/sup 2/. Modulation noise and track edge noise were well suppressed by the decrease in the activation volume. Remanent magnetization is stable; at 338 K, the coefficient of remanence reduction was -0.066 dB/decade in a reverse field of 460 Oe which corresponds to the demagnetizing field in a bit at 430 kFCI. Recording bits of 430 kfci were confirmed by MFM. The BER was 3.45/spl times/10/sup -6/ using a conventional EPR4 channel with a 16/17 code rate at 405 kBPI (430 kFCI). From squeeze measurements, the track pitch was 0.505 /spl mu/m (50.3 ktpi) including a guard band of 0.06 /spl mu/m. 20.4 Gb/in/sup 2/ recording is made possible by the combination of a narrow gap spin-valve head and a low noise medium.

Low noise properties and thermal stability of Co-based thin film media for high density longitudinal recording

Media with excellent signal to noise properties and adequate high temperature thermal stability have been developed for over 20 Gbit/in/sup 2/ recording. The media are fabricated by dc magnetron sputtering onto textured NiP films on Al-Mg substrates. The magnetic layer is a CoCr-based quaternary alloy with (11.0) preferred orientation on a Cr alloy [002] underlayer. The average grain diameter has been reduced to an average of 0.3 memu/cm/sup 2/ consistent with magnetometry measurements.

Amplitude and Phase Distributions of Magnetization in Tunneling Magnetoresistive Heads

We describe a thermal magnetic noise simulation of tunneling magnetoresistive (TMR) heads. We calculate the phase and amplitude distributions of the local noise resistance derived from the magnetization fluctuation of the free layer in the several gigahertz range and consider their relations with the magnetic noise spectrum. The results show that the phase distribution of the noise resistance strongly influences the second or higher resonant peaks in the magnetic noise spectrum of TMR heads. As an example, we show that the second resonant peak appears in the spectrum when the asymmetric magnetic field is applied to the free layer.

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.

Dynamic memory usage analysis of MPI libraries using DMATP-MPI

This paper presents dynamic memory usage of Open MPI by DMATP-MPI dynamic memory usage analysis tool. The DMATP-MPI is developed to reduce memory usage of MPI communication library. The evaluation results show that the memory usage of MPI Init function increases by increasing number of processes, and must be reduced for post peta-scale systems.