A Ni-Zn-Cu ferrite layer with a thickness ranging from sub-mm to micro meter and a Ba ferrite layer with a thickness of sub-mm were prepared by Spark Plasma Sintering (SPS) method. By using this method, dense ferrite samples were sintered with a shorter sintering time of several minutes than the conventional sintering method using a furnace. The 10 microns thick Ni-Zn-Cu ferrite sample with a low coercivity of 4.80 e and the 0.5mm thick Ba ferrite sample with a high coercivity of 2.1 kOe and uniform grain size could be prepared.
In this study, we address problems of the spike noise from soft magnetic layer by utilizing antiferromagnetic coupling. It was found that magnetic domain structures of soft magnetic layers depend on different materials on the basis of domain observation and that exchange bias field H_<ex> was estimated 40Oe by measuring magnetic fields inside HDDs. Through the experiments using IrMn and PtMn as antiferromagnetic layers, it was concluded the spike nosie from media with greater H_<ex> is reduced more effectively. We obtain satisfactory reduction of the spike nosie and control domain walls of soft magnetic layer by cooling under an application of magnetic field.
The soft magnetic properties of NiFe/FeCo/NiFe sandwich films with high saturation magnetization are discussed in relation to the microstructure. Ta/NiFe/FeCo/NiFe/Ta films prepared using the UHV sputtering process show a very sharp fiber texture of bcc-<110> in the FeCo layer. It was revealed that thin NiFe film with a thickness of only 3 nm works effectively as a seed layer of FeCo film to control the microstructure, resulting in a significant reduction of the coercivity. The best thickness of the FeCo layer in order to realize both soft magnetic properties and high saturation magnetization was found to be 〜100 nm. It was fond that [FeCo/NiFe]_4 single pole head using bulk coil showed better overwrite performance than that of CoZrNb head.
BER performance improvement of PRML system in perpendicular magnetic recording is studied. The performance of Viterbi detector is improved by applying an AR model to the estimation of input sequence. The required SNR's to achieve a BER of 10^<-6> are obtained by computer simulation and they are compared with those of conventional system. The results show that PRML system with Viterbi detector using an AR channel model provides a good performance.
A rewritable dual-layer phase-change optical disk with a balanced transmittance structure for the layer located at the laser beam incident side (Layer 0) was developed. In this disk structure, transmittance of the Layer 0 is almost constant whether the layer is recorded or not. This structure was realized by adopting Ge-Sb-Te film-that has appropriate optical constants, and optimizing the thickness of dielectric layers. It is proved that this disk structure is effective for suppressing influence of recording state of the Layer 0 on the layer beneath (Layer 1). Practical performances of the disk with this structure were confirmed for both layers. The feasibility of up to 55GB-capacity was examined for this rewritable dual-layer phase-change optical disk.
A user data capacity of more than 23 Gbytes will be required for a next generation optical disk to store two hours of high definition digital television (HDTV) broadcast signals. It is difficult to realize high-density optical disk mastering using laser beam recorders (LBR) owing to their resolution limits. Therefore, we developed an electron beam recorder (EBR). We evaluated the performance of the EBR for the high-density optical disks.
We have fabricated a high numerical aperture objective lens that consists of only a single-element. This lens has a large working distance and no assembling procedures in comparison to a two-element objective lens already proposed. We have also developed aberration compensation methods for coma and spherical aberration. Especially, spherical aberration is compensated automatically by using a servo circuit. A signal read-out obtained from a high-density optical disk is demonstrated using this single-element objective lens.
We have developed a single objective lens having NA of 0.85. The lens was installed to an optical pickup and was evaluated with phase change disks. The optical and the write-read performance of the lens showed satisfactory results. Possibility of the 25GByes disk system was also confirmed. For this experiments, we have used two different modulation codes that have deferent minimum run length constraint, 2T and 3T. The read back results with the both modulation codes showed sufficient low bit error rate.