Akihiko Takeo

High performance CoPtCrO single layered perpendicular media with no recording demagnetization

High coercivity CoPtCrO single layered perpendicular medium has been newly developed in order to solve the recording demagnetization problem, and exhibited the excellent recording characteristics with ring type head; the areal recording density being higher than 11 Gbit/inch/sup 2/. The high Pt content and the segregation structure with thick oxygen-rich boundaries led this perpendicular medium to high coercivity, steep hysteresis slope at Hc, and high squareness at the same time. These features were found to be primary factors for both high SNR and suppressed recording demagnetization.

Precise noise characterization of perpendicular recording media

Perpendicular recording is one of the technology candidates to extend the areal density growth trend with the superior thermal stability and the high recording resolution. As we have experienced with longitudinal recording, noise originating from perpendicular recording also has a strong impact on the channel performance. In this study, the noise characteristics of the readout waveforms of a tri-layer perpendicular media and single-pole write/MR read heads were investigated using precise time-domain analysis. Waveform fluctuations were obtained by subtracting the ensemble-averaged signal from each measured noise-contaminated waveform. The time-domain analysis makes clear the dominant type of transition-related noise such as transition jitter, pulse breathing or dc noise, etc. It was revealed that the noise from perpendicularly recording medium concentrates at the center of written transitions. The dominant transition noise source was found to be the transition position jitter. The level of transition jitt...

Low noise FeAlSi soft magnetic under-layer for CoPtCrO double-layered perpendicular recording media

FeAlSi multi-layered structure successfully reduced the noise compared with a mono-layered film. Optical surface analyzer also revealed that the films did not show any clear magnetic domains of spike noise source in the whole disk. TEM image of low noise film showed wide grain boundaries between 200 to 500 nm diameter FeAlSi grain clusters. The coercivities of films were significantly reduced when they were laminated. Along with the cluster isolation effect, the interlayer magnetic coupling of the multi-layered FeAlSi films also effectively reduce the noise. Double-layered perpendicular medium with a CoPtCrO recording layer and a multi-layered FeAlSi soft under-layer showed 25.8 dB SNR at 400 kBPI and 0.36 /spl mu/m read truck width, and 2.5/spl times/10/sup -7/ BER on a spin stand was achieved.

A new design to suppress recording demagnetization for perpendicular recording

Perpendicular recording is expected to be a high areal density recording system because of strong thermal stability potential and highly efficient writing process. However large demagnetizing fields in uniformly magnetized areas cause recording demagnetization and signal decrease with time. We propose a new recording design to suppress recording demagnetization for perpendicular magnetic recording, using high nucleation field media. A CoPtCrO perpendicular medium with high nucleation field successfully demonstrated the low noise performance. It shows less recording demagnetization and strong thermal stability. CoPtCrO perpendicular medium exhibited good BER performance with ring head recording.

Quantitative MFM study on partial erasure behavior of longitudinal recording

In this paper, we propose a new MFM (magnetic force microscopy) method to analyze the probability and size of partial erasure (PE). An analysis classifying the linear and nonlinear partial erasure is also proposed. It was realized that the nonlinear PE is correlated with the inter-granular magnetic coupling in thin film media. The isolation of the magnetic coupling was found effective to reduce the nonlinear PE.

Analysis of Effective Field Gradient in Microwave-Assisted Magnetic Recording

Microwave-assisted magnetic recording (MAMR) is one of the promising techniques for future high recording density hard disk drives. In this paper, we estimate the effective field gradient in MAMR using the relation between recorded transition length πa and field gradient by dynamic write process simulation. The effective field gradients reach 600 and 700 Oe/nm on each optimum field generation layer (FGL)-position and FGL oscillation frequency when the microwave field strength (c - Hac) are 700 and 950 Oe, respectively. These results indicate extremely high linear density would be possible by MAMR.

Technique to obtain head-medium magnetic spacing in a disk drive

A technique is presented to determine the head-medium magnetic spacing utilizing square wave recording spectral measurements. Because spectral analysis does not give a unique separation of the spacing and the transition parameter, the transition parameter is first determined at low densities using time domain transition noise analysis. The total noise power versus density is utilized to determine the transition parameter variation with density due to record process nonlinearities. Spectral fitting gives both the spacing and the giant magnetoresistance gap length. It is shown this technique is robust by analysis of data on perpendicular media with both inductive and single pole heads.

Dynamic read/write performance characterization of perpendicular recording

Double-layer perpendicular recording media employing high squareness magnetic properties have been developed and tested with single-pole perpendicular heads. Dynamic performance tests revealed that double-layer perpendicular media exhibited high output signal, high resolution, and superior write performance at the same time. Signal decay tests also indicated superior thermal stability. Drive integration test with a 42 kTPI (1654 track/mm) system showed comparable tracking servo performance to conventional systems.

Flat Surface Percolated Perpendicular Media With Metal Pinning Sites

The percolated perpendicular media with nonmagnetic metal pinning sites was newly developed by sputtering Ag in the deposition of [Pt/Co] multilayer. By adding Ag to this media, an approximately twofold increase in the coercivity could be achieved while keeping strong intergranular coupling and Ag is expected to function as pinning sites. The media surface was sufficiently flat to be able to fly a read/write head and this percolated media exhibited an excellent performance recordable at 750 k flux change per inch. This is the first report of such high linear density recording with the flat surface percolated perpendicular media and, with a view to further improvement, the relationship between pinning site and magnetic domain wall is discussed.

Multi-Level Read/Write Signaling Using Pulse Width Modulation for High Density Perpendicular Magnetic Recording

In this letter, we propose a novel read/write (R/W) signal processing method by 3-ary amplitude shift keying for high density perpendicular magnetic recording. We also provide a 3B2T modulation to generate 3-ary signal, which will be converted to a pulse width modulation (PWM) signal, and then recorded on magnetic media. The PWM signal can be simply demodulated to derive the 3-ary signal through a low-pass filter at readback side. The demodulated signal in the presence of intersymbol interference is detected by the Viterbi algorithm as partial response signal. Nonbinary low-density parity-check codes over GF(8) are applied as error correcting codes in our evaluation. Our simulation result shows the proposed R/W method has +4% more user bit density gain than conventional binary recording.