Hisashi Takano

Investigation of 2 Gb/in/sup 2/ magnetic recording at a track density of 17 kTPI

Developments of magnetic head, recording medium, positioning, and signal processing technologies made it possible to perform magnetic recording at an areal density of 2 Gb/in/sup 2/ on a prototype 3.5-in diameter hard disk drive. A track density of 17 kTPI, which is comparable to or even greater than that used in optical storage systems, is used to minimize the reduction in the physical clearance between the medium and the head. The authors outline the system and its component technologies. The read/write characteristics of the 3.5-in prototype disk system are also reported. >

Submicron-trackwidth inductive/MR composite head

To explore the possibility for ultra-high areal density recording, submicron-trackwidth inductive-write/magnetoresistive-(MR)-read composite heads were fabricated. The focused ion beam etching technique was applied to fabricate a approximately 1- mu m-wide write-track completely aligned to the read-region of the MR sensor. The write head using multilayered Fe-based alloy pole pieces with a saturation magnetization of 2.0 T revealed sufficient writability and excellent frequency response. A shunt-biased MR sensor having a narrow gap-length operated at a high current density over 3*10/sup 7/ A/cm/sup 2/ is developed to reproduce a sufficient signal amplitude at high linear-density regions. Recording tests were carried out on a thin-film medium with a head-medium clearance of 0.05 mu m. The output voltage per micron of trackwidth over 400 mu V with symmetrical pulses, and a -6-dB rolloff density of around 90 kFCI were measured. The design procedure, fabrication method, and recording performances of the submicron-trackwidth inductive/MR composite heads which can attain 2 gigabits recording are discussed. >

Fine Metallic Particles for Magnetic Domain Observations.

Fine domain structures of a ferromagnetic specimen can be visualized by deposition of ultrafine ferromagnetic particles onto its surface. We have applied various ferromagnetic particles, such as Co, Fe, Co–Fe alloy and Permalloy, to observation of high-density recording states of thin-film recording media. These studies have revealed that single-domain particles mainly contribute to the domain pattern contrast, while very small superparamagnetic particles are so insensitive to the leakage field from the recording media that they deteriorate the image quality of the domain patterns. Therefore, suppressing the formation of the superparamagnetic particles is effective in improving the resolution and the image quality of the observed domain patterns. In order to suppress the formation of superparamagnetic particles, we have attempted to synthesize hcp-Co particles with large uniaxial anisotropy by alloying Co with some elements which increase the fcc hcp transformation temperature, but all the Co and Co-alloy particles exhibit a pure high-temperature fcc phase.

Dynamic micromagnetic field measurement by stroboscopic electron beam tomography

A stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads is presented. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of the dynamic magnetic field are calculated using a tomographic reconstruction algorithm. To obtain enough current even in pulsed electron beam operation, a high-brightness Ti/W thermal field emitter is used. This system was successfully applied in measuring the field distributions of a thin-film recording head, with 0.1 mu m spatial resolution and 1 ns time resolution at an operation frequency of 30 MHz. >

Study on the write-field profile and intensity of narrow-track-width SPT head

The effects of the structure of a single-pole-type (SPT) head and the underlayer thickness on the write-field profile and intensity were examined by computer calculation. The results demonstrated the possibility of achieving a strong write field even with a thin underlayer in the case of narrow-track-width SPT. The shorter throat height enhanced the maximum write-field intensity without a great change of the write-field profile. We also proposed a new, tapered SPT head suitable to address the sidewriting issue for drive integration.

Computer simulation of magnetization switching behavior in high-data-rate hard-disk media

We have investigated magnetization switching behavior in high-data-rate hard-disk media by micro-magnetic simulation. We found that the remanence coercivity measured by a short-pulse-field depended on the field-pulse shape. The time integration of external field over the remanent coercivity for a long-pulse-field, namely switching force integration (SFI), was an essential factor for the switching. We also found that the optimum writing field, H/sub w/ must be increased by only 0.4 kA/m per MB/s independent of the linear recording density. Overwrite (OW) value decreased by 1 dB per percentage point of H/sub w/ and did not depend on the data-transfer rate. The recording characteristics at high data transfer rates were not degraded if only a writing field of H/sub w/ was applied to the film. The simulation results were consistent with the results of read/write experiments especially OW characteristics up to 80 MB/s.

Current progress of single-pole-type GMR heads for perpendicular recording

We studied several proposals to address the problems encountered when single-pole-type giant magnetoresistive (SPT-GMR) heads are applied to an actual recording system. The first area of problems was regarding side erasure when there is a head skew. We fabricated a trapezoid-shaped main pole using a focus-ion-beam trimming or using a new wafer-processing technique and examined their write performances and their effects on reducing side erasure. The second area of problems concerned the stray field robustness of SPT-GMR heads when combined with a double-layered perpendicular recording medium. We tried to optimize the robustness and write performance by changing the width of a yoke in the main pole or by positioning a shield above the main pole. The stray field robustness and write performance were adequate in both cases, but a tradeoff relationship exists between both performances.

Noise characteristics of double-layered perpendicular media

Abstract Time-domain analysis of a reproduced waveform shows that the media noise of double–layered perpendicular media consists of transition noise localized around the transitions and DC-erased area noise independent of transition. We used this analysis to develop a waveform model, incorporating media noise, to estimate the bit error rate performance of double-layered perpendicular media. Moreover, we proposed a simple mathematical method for estimating the media noise power using the head/media magnetic parameters and R/W conditions.

Time resolved measurement of dynamic micro-magnetic field by stroboscopic electron beam tomography

Stroboscopic electron-beam tomography has been achieved for time-resolved measurement of the magnetic recording thin-film head. The transition characteristics of magnetic field distributions were compared; the driving current was found to have a temporal resolution of 1 ns. Both the driving current waveforms and the magnetic field distributions are measured by a pulsed electron beam with the same timing pulse gate. This measurement was successfully applied to Ni-Fe and CoTaZr amorphous thin-film disk heads. It was found that the magnetic field distribution change with time is not uniform and that the peak field is a few nanoseconds behind the driving current for Ni-Fe heads. The frequency characteristics of these heads correspond for the magnetic field delay to the driving current. The frequency characteristics of the head whose magnetic field delay is longer are inferior to those of the head whose magnetic field delay is shorter. >

An accurate head-positioning signal for perpendicular recording using a dc-free servo pattern

We devised a dc-free servo pattern for perpendicular recording to prevent distortion of the readback wave form from the servo area. This servo pattern remarkably improves the servo sector error rate, and shows the same linearity of position error signals as does that from a conventional pattern. An experimental 2.5 in hard disk drive (HDD) with a trapezoidal-shaped single pole type (SPT) head shows good following performance within a wide range of yaw angle.