Magnetic Field Modulation Recording Research Articles

Towards 100 Gb/in<sup>2</sup> MO storage using a blue laser, high-NA far-field optics and domain-exoansion media

A Magneto-Optical recording technology is described for storage densities of 50-100 Gb/in2 and data rates of 100-200 Mb/s. A sliding optical head which forms a key component for this recording technology has been developed. The head incorporates a thin-film coil for high data rate Magnetic Field Modulation recording and a dual lens objective with a Numerical Aperture of 0.85. To limit head-disc interface problems due to heating by the laser a cover layer of a few tens of μm is applied to the disc. Cover layer requirements are discussed and MFM recording results obtained with a NA=0.6 version of the sliding head and TbFeCo media with a thin cover layer are presented.

High density magneto-optical recording using solid immersion lens with magnetic field modulation

A near field optical technique based on combined supersphere solid immersion lens (SIL) with magnetic field modulation (MFM) recording is described. A better resolution is achieved by using SIL with MFM recording in comparison with light intensity modulation. A recorded mark as small as 0.3 /spl mu/m/spl times/0.2 /spl mu/m could successfully be detected. These marks were readout by the SIL head with a typical signal to noise ratio value of 36 dB. The present study demonstrates the capability to achieve a very high areal density beyond 20 Gb/in/sup 2/.

A Study of Asymmetry Compensation for Partial-Response Maximum-Likelihood Detection in Optical Recording Media

The partial-response maximum-likelihood (PRML) detection technique is effective for high-density recording media. In the field of magnetooptical recording media, it is mainly adopted in a magnetic field modulation recording system. For a light intensity modulation (LIM) recording system, however, signal asymmetry caused by the deviation from the optimum recording conditions easily deteriorates the PRML detection procedure. In this paper, we propose an “adaptive reference level technique”, which can greatly improve the write power tolerance. It is expected to suppress the influence of the signal asymmetry in the LIM recording system.

Magnetic Field Modulation Recording Characteristics of a TbFeCo/Ultra-Thin DyFeCo Double Layer

We studied the magnetic field sensitivity in a double layer which was composed of a TbFeCo recording layer with low Tb content and a high-Tc RE-rich DyFeCo ultrathin layer. The Tb14Fe82Co4/Dy30Fe35Co35 double layer has better magnetic field sensitivity than a TbFeCo single recording layer. We concluded that the high C/N of the double layer disk was caused by the large MS of the recording layer and suppression of micro-domain nucleation by the ultra-thin DyFeCo layer.

Magnetic domain formation in Tb/sub 23/Fe/sub 77/ thin film on a moving magneto-optical disk with magnetic field modulation recording

In this paper, the magnetic domain formation process on a moving disk for Tb/sub 23/Fe/sub 77/ magneto-optical recording thin film under the magnetic field modulation recording was investigated by a new simulation method. The simulation results showed that the convex prior edge of the domain was instantly formed and pinned when the magnetic field changed from low state to high state. Then, the domain boundary was lengthened opposite to the disk moving direction without changing the width during the high state of the applied magnetic field. As the magnetic field changed from high state to low state, the concave posterior edge of the domain was simultaneously formed and pinned, and the domain became a closed chevron shape. Both edges closely resemble the Curie temperature contour. There existed a threshold applied magnetic field strength, and the domain could not be formed when the applied field strength was below the threshold value, The value of the threshold field was approximately the same as the demagnetizing field around Tc, but reversed in polarity, and it increased with the laser power. The domain width increased as the applied field increased above the threshold value, and it rapidly became saturated when the applied field was about 30 Oe greater than the threshold value, There also existed a threshold laser power, below which the domain could not be formed. The threshold power was 3.3 mW for Tb/sub 23/Fe/sub 77/. The domain width increased monotonically with the laser power for high applied magnetic field, and it increased (then decreased) with the laser power when the applied magnetic field was closed to the threshold value.

Computer modelling of spatial temperature gradient dependence of magnetic field modulation in magneto-optic recording

Reduced spatial temperature gradient at the recording edge of magnetic field modulation (MFM) recording has been reported to be another important aspect affecting the C/N ratio of MFM recording. Possible means to improve thermal features in MFM recording are studied in this paper by computer simulation. The results obtained show that neither a higher writing laser power nor a lower thermal conductivity of MO layer can significantly increase the spatial temperature gradient. Simulation results indicate that dual modulation is a promising method to improve writing edge temperature gradient, especially when high power laser is used. A backward expanding process of the writing edge is noticed and discussed in this paper also.

New Disc Format for Land/Groove Recording on Magnetically Induced Super-Resolution Disc

We developed a new disc format for land/groove recording. The new disc had grooves wobbled on one side to obtain address information. We examined characteristics of signals reproduced from the wobbled grooves and a suitable groove shape for a double-layered magnetically induced super-resolution disc. By the use of the new disc format, good signal quality of address information is obtained on both lands and grooves. At a groove shape with 40 nm depth and 0.7 µm track pitch, a CNR of 47 dB and a crosstalk of -32 dB were obtained at the recorded mark length of 0.55 µm in magnetic field modulation recording.

LAND/GROOVE RECORDING SCHEME ON MSR MEDIA

Land/groove recording properties on a magnetically induced super-resolution (MSR) disk has been investigated. We prepared an exchange coupled type of MSR disk with double magnetic layers and examined the read/write characterisitics for various track pitches with magnetic field modulation recording. As the results, a track pitch of 0.65 μm was available for practical use from the point of view on crosstalk and crosswrite properties. We have also developed a new groove format in order to obtain address information on both lands and grooves.

磁界変調記録と磁気超解像を用いた高密度光磁気ディスク

磁界変調記録と磁気超解像を用いた高密度光磁気ディスク

Coaxing the Maximum Performance out of an Ordinary Structured MO Disk

An ordinary structured magneto-optical disk was improved and optimized to achieve high areal recording density using the magnetic field modulation recording technique. After studying film material/thickness, groove geometry, and birefringence in a poly-carbonate substrate, a track pitch of 0.85 µm with a linear recording density of 0.31 µm/bit is determined to be a good combination for a wavelength of 690 nm and an objective lens with a numerical aperture of 0.55, which results in an areal density of 3.8 bit/µm2 or 2.4 Gbit/inch2.

High density recording with a super resolution magneto-optical disk using magnetic field modulation method

We have improved the recording magnetic field sensitivity of a magnetic super resolution (MSR) disk consisting of double magnetic layers and examined the magnetic field modulation recording properties. An areal density of 2.2 Gbit/in 2 was obtained with a currently available condition. The experimental optical pickup system had a 680 nm wavelength laser diode and an objective lens of a 0.55 numerical aperture. The MSR disk had 0.7μm-width lands and grooves. The crosstalk values between the land and its adjacent grooves were less than −28 dB. The areal density in the improved MSR disk was accomplished by recording in both lands and grooves and using mark edge recording with a (1,7) run-length-limited coding. Also, if a signaling technique called ‘PRML’ is used, an areal density of 3.1 Gbit/in 2 could be realized.

Thermal stability of sputtered GdDyFeCo films with trilayer structure

The thermal stability of GdDyFeCo films with trilayer structure has been studied by annealing in vacuum up to 300/spl deg/C. In GdDyFeCo films sputtered on glass, the coercivity is reduced after annealing, which is thought to be due to a structural relegation caused by annealing. The saturation magnetization tends to increase upon annealing, in particular for rare-earth rich composition because of the increase of effective magnetic moment, making the compensation temperature (Tcomp) shift higher. The films with Tcomp between room temperature and 100/spl deg/C show superior thermal stability, because their magnetic properties, especially Tcomp, change little after annealing. Overwrite repetition tests using magnetic field modulation recording also indicate that the disks with the Tcomp between room temperature and 100/spl deg/C have superior overwrite durability. Small adjustments of the GdDy content seem to be effective in improving the thermal stability of GdDyFeCo films. The best Tcomp of the GdDyFeCo films is between room temperature and 100/spl deg/C, and the optimum Dy:Gd ratio is between 45/55 and 70/30.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magneto-optical Disk for Magnetic Field Modulation Recording Method with Multi-Pulsed Laser Irradiation

The authors report magnetic field modulation (MFM) recording characteristics for magneto-optical (MO) disks, whose magnetic sensitivity was improved through sputter-etching treatment of the SiN layer beneath the magnetic layer. The sputter-etching treatment increased weak-field recording noise, as well as reproduced signal amplitude. Jitter caused by such noise can be reduced by the introduction of a new MFM recording method with multi-pulsed laser irradiation. This paper discusses the mechanism for the improvement of such MFM recording characteristics on the sputter-etched MO disks.

Extended Capacity and High Speed Magnetic Field Modulation Recording for 3.5" Magnetooptical Disk

The authors attempted recording by magnetic field modulation overwriting with a flying magnetic head, using a (1,7) RLL code, mark-edge recording, write precompensation, equalization, and the ZCAV format. A flying magnetic head for high-speed magnetooptic recording was developed. It was confirmed that the magnetic head has a magnetic efficiency of 1.38 Oe/mA at a spacing of 18 ?m and a modulation frequency of 8.16 MHz. Under these conditions, a linear recording density of 0.55 ?m/bit and an overwrite power margin in excess of ±25% were achieved. A 3.5 magnetooptic disk drive with a storage capacity greater than 300 MB and a high data transfer rate of 2.7 MB/s at the outermost track was realized.

An analysis of the thermal characteristics of magnetic field modulation method of magneto-optical recording

The thermal characteristics of magnetic field modulation (MFM) recording are analyzed. It is found that the heat accumulation in MFM recording can greatly reduce the temperature gradient at the recording edge, resulting in a reduction of bit boundary regularity. A specially considered dual modulation method is thus proposed and discussed which shows a greatly improved thermal situation.

光磁気磁界変調記録における記録パワーマージンの検討

光磁気磁界変調記録における記録パワーマージンの検討

2元マグネトロンスパッタ法によるGdDy/FeCo膜の磁気特性と磁界変調記録特性

2元マグネトロンスパッタ法によるGdDy/FeCo膜の磁気特性と磁界変調記録特性

Large-Capacity and High-Speed Magnetic Field Modulation Recording for 3.5′′ Magneto-Optical Disk Drive

Recording by magnetic field modulation overwriting with a flying magnetic head and adopting a 1-7 RLL code, mark-edge recording, and ZCAV format, was attempted. A 3.5′′ magneto-optical disk drive with a large storage capacity of greater than 300 MBytes and a high data transfer rate of 2.7 MBytes/s on the outermost track was realized.

The overwriting characteristics of magneto-optical disk by magnetic field modulation method

To achieve a direct overwriting on magnetooptical disk, we investigated the magnetic field modulation recording. Several cylindrical magnetic heads were prepared as magnetic field modulation recording heads and recording characteristics were measured using those heads. It was found that the inductance of a head is the chief source of limiting recording frequency. A C/N of 50 dB was obtained at a modulating frequency of 1 MHz. Former recorded signals (hereafter said to be pre-signals) were completely overwritten when the overwriting laser power was the same as the recording power at the former recording process.

Magneto-Optical Recording Characteristics of TbFeCo Media by Magnetic Field Modulation Method

To determine the most suitable composition for a magnetic field modulation recording, we investigated the static and dynamic recording (optical modulation method) characteristics of a TbFeCo film relative to an external magnetic field. It was made clear that the demagnetizing field is the chief determinant of the external magnetic field intensity and that a medium with a compensation temperature between room temperature and about 100°C is suitable for magnetic field modulation recording. AC/N of 50 dB was obtained by modulating the external magnetic field at 500 kHz. An overwriting on the pre-signal was completely realized up to the frequency of 500 kHz.