Tomoyuki Hiroki

Magnetostatic Coupling MSR with In-Plane Magnetization Films

Magnetically induced super resolution (MSR) with double (front and rear) masks was achieved using GdFeCo/GdFe/TbFeCo (readout/intermediate/memory) triple layer films. The duplication of information from the memory layer to the readout layer is done through the magnetostatic coupling. The front mask and the rear mask are formed by in-plane magnetization and by collapsing written domains, respectively, without applying external fields. The transition from in-plane to perpendicular magnetization was made sharper by introducing the intermediate layer. Using this MSR medium and a conventional optical head (λ=780 nm), carrier-to-noise ratio (C/N) of over 45 dB for a mark length of 0.40 µm and crosstalk of -38 dB for a 0.8 µm track pitch were achieved. However, during the readout process, the magnetostatically coupled MSR medium is much more sensitive to the disturbance of external fields than exchange-coupled MSR medium.

Transition from in‐plane to perpendicular magnetization in MSR magneto‐optical disks

Transition from in‐plane to perpendicular magnetization caused by temperature changes have been investigated for double‐layer (GdFeCo/TbFeCo) and triple‐layer (GdFeCo/GdFe/TbFeCo) magneto‐optical recording films. The transition in the GdFeCo layer occurs mainly as a result of change in the demagnetizing energy of the GdFeCo layer having compensation temperature. Such transition occurs more rapidly in the triple‐layer film than that in the double‐layer film. Micromagnetic calculation showed that in the double‐layer film the interface wall penetrates deeply into the GdFeCo readout layer, while in the triple‐layer film the wall is almost completely confined within the GdFe intermediate layer having a large Ms and a low Tc. The triple‐layer film is found to improve the characteristics of magnetically induced super resolution (MSR).

New Inorganic Write-Once Disc Using Low-Cost and Environmentally Friendly Oxynitride Materials for Multilayer Disc System

We have developed a new inorganic write-once disc using low-cost and environmentally friendly recording materials of Si oxynitride and Al oxynitride with high transmittance. Data-to-clock jitters of 5.6% for Layer 1, 5.5% for Layer 2, and 6.3% for Layer 3 of the individual single-layer discs were obtained using a limit equalizer. This newly developed recording material is immensely promising for a multilayer disc system.

A New Inorganic Write-Once Disc using Hydrogen-Containing Dielectric Recording Material for Multi-Layered Blu-ray Disc System

We have developed a completely novel inorganic write-once disc using a hydrogen-containing dielectric recording material. We demonstrate the recording characteristics of a newly developed write-once disc on the basis of the Blu-ray disc format (dual-layered, 4? speed).

Anneal-less domain wall displacement detection of 27 Gbit/in2 land/groove recording using a deep groove substrate and a blue laser

We have studied an anneal-less domain wall displacement detection (DWDD) disk of a land/groove recording on a deep groove substrate using a numerical aperture (NA) 0.65 objective lens and a blue laser diode (LD). The substrates were prepared using a stamper formed by reactive ion etching (RIE) and O2 plasma treatment to realize both steep side-wall angles and smooth surfaces on the substrates. In designing the groove shape, we have clarified three key factors: the groove edge shape, the groove depth and the land width. These factors affected the magnetic film discontinuity at the groove edge and the recording power margin on the land. We have achieved a recording density of 27 Gbit/in2 by optimizing the groove shape.

15-Gbit/in2 recording on a DWDD disc using a land/groove substrate with a red laser enabled by a side-wall annealing process

We developed a side-wall-annealing technique for land/groove substrates. By applying this technique to our Domain Wall Displacement Detection (DWDD) Magneto-Optical (MO) recording stack formed on a land/groove substrate, even with an NA of 0.6 and a wavelength of 660 nm, we realized a density of 15 Gbit/in2 with a sufficiently wide recording tolerance. This density corresponds to a capacity of 4.7 GB mm disc like MiniDisc.