Magnetization processes of recording layer and soft magnetic back layer in double layered perpendicular magnetic recording media can be divided and evaluated ferromagnetic Hall effect. Anomalous Hall effect and planar Hall effect in double layered film can be evaluated taking into account of the symmetry of those characteristics for the applied magnetic field. Magnetization component of anomalous Hall effect that has a point symmetry is only detected in Co-Cr-Ta single layer. Magnetization component of planar Hall effect that has a symmetric with respect to the vertical axis is simultaneously detected with a component of anomalous Hall effect in Ni-Fe single layer.
Thermomagnetic recording process for various TbFeCo films has been simulated in the case of the irradiation of the laser with the spot diameter of 1.0, 0.6, and 0.2μm by using Huth's equation modified by assuming the domain wall of 20 nm. In the case of TM-rich film, it is found that the domain having a diameter of 60 nm was formed at temperature below Curie point because of the large demagnetizing energy which resulted from the large magnetization. On the other hand, the large temperature gradient made it difficult to stabilize the small size domain in RE-rich film. The smallest size of written domain was 40nm, which was observed for the films with compensation composition irradiated by 0.2μm laser spot.
A new type of MAMMOS(Magnetic AMplifying Magneto-Optical System)was proposed. This method needs only a DC magnetic field for expanding and erasing the magnetic domains and RE(Rare-Earth)-rich GdFeCo was used for readout layer. In this system, 43dB of CNR was obtained for 0.25μm packed domains by applying 10kA/m of DC magnetic field. Compared with the conventional CAD(Center Aperture Detection)disk, CNR for the domains smaller than 0.4μm was improved. This method exhibited a high readout resolution in spite of an AC field-free method.
In magnetic recording technology, thermal instability of recorded bits becomes a serious obstacle toward high storage density. In this paper, the thermal stability in both longitudinal and perpendicular recording media is discussed and compared. The magnetization decay is found to be reduced by the presence of the stabilizing thin layer present in the ferrimagnetic structure. Interaction between grains which is related to media noise, has also been investigated from isothermal remanence measurements. The change of V_a with H is broader in the case of SFM and granular media than in TbFeCo and also shows different minimum values.
The field dependence of the activation volume(V_A)is determined for longitudinal recording media by several different methods. For two methods, which use the irreversible magnetisation, V_A is found to increase for larger reversing fields up to the coercivity(H_C). The V_A as determined from the time dependence of the total magnetisation including the reversible magnetisation, yields the opposite behavior : V_A is found to be much larger at low fields and found to decrease for larger reversing fields up to H_C. The difference between the methods is found to be attributed to the large difference between the total magnetisation and irreversible magnetisation, which is particularly large for small reversing fields. Around H_C however, the different methods yield comparable results.
Image Production characteristics and selection method of the image production layer in the "multilayered waveguide holographic read-only memory(MWH-ROM)" were investigated. Information recorded in different layers of the MWH-ROM was reconstructed without any crosstalk effects from other layers by adjusting the position of the read-out beam. Optical coupling state between the read-out beam and the optical waveguide can be judged by analyzing the emission patten from the MWH-ROM. Furthermore, comprehensive method of judging the coupling state by analyzing the radiant intensity from the multilayered waveguide was also investigated.
A newly developed phase-change material, Sn-added Ge-Sb-Te, shows superior crystallization characteristics. The laser-crystallization time of the Ge-Sn-Sb-Te quaternary film was kept less than 50ns even in the case that the film thickness was reduced to 5nm. An experimental rewritable dual-layer optical disk was prepared with a Ge-Sn-Sb-Te quaternary film(6nm)and a Ge-Sb-Te ternary film(12nm)as the first and second memory layers, respectively, for achieving a specification corresponding to 27GB of capacity and 33Mbps of recording data rate utilizing a blue-violet optics(λ:405 nm, NA:0.65). More than 50 dB of C/N and more than 30dB of erasability were successfully obtained for the both layers with available recording laser powers of 8 and 11 mWs for the first and the second layers, respectively.