Co/Pd multilayer films are prepared on fcc-Pd underlayers of (001), (011), and (111) orientations hetero-epitaxially grown on MgO single-crystal substrates at room temperature. The effects of underlayer orientation, Co and Pd layer thicknesses, and repetition number of Co/Pd bi-layer on the structure and the magnetic properties are investigated. fcc-Co/fcc-Pd multilayer films of (001), (011), and (111) orientations epitaxially grow on the Pd underlayers of (001), (011), and (111) orientations, respectively. Flatter and sharper Co/Pd interface is formed in the order of (011) < (111) < (001) orientation. Atomic mixing around the Co/Pd interface is enhanced by deposition of thinner Co and Pd layers, and Co-Pd alloy phase is formed. With increasing the repetition number (decreasing the thicknesses of Co and Pd layers), perpendicular magnetic anisotropy is promoted. Stronger perpendicular anisotropy is observed in the order of film orientation of (001) < (011) < (111). Perpendicular anisotropy of Co/Pd multilayer film is considered to be originated from the two sources; the interface anisotropy and the magnetocrystalline anisotropy associated with Co-Pd lattice shrinkage along the perpendicular direction. In order to enhance the perpendicular anisotropy of Co/Pd multilayer film, it is important to align the film orientation to be (111) and to enhance the lattice distortion along the perpendicular direction.

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CoPt and Co₃Pt alloy thin films are prepared on MgO(111), SrTiO₃(111), and Al₂O₃(0001) single-crystal substrates by varying the substrate temperature in a range from room temperature to 600°C by using an ultra-high vacuum radio-frequency magnetron sputtering system. The formation of metastable ordered phase and the structural thermal stability are briefly investigated. CoPt and Co₃Pt films with the close-packed plane parallel to the substrate surface grow epitaxially on these oxide single-crystal substrates. CoPt epitaxial films are also formed by employing Pt, Pd, Cu, Cr, Ti, and Ru underlayers hetero-epitaxially grown on MgO(111) substrates. The crystal structure is evaluated by considering the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phases of L1₁, B_h, and D0₁₉ are preferentially formed in the CoPt and the Co₃Pt films deposited around 300°C. Metastable ordered phase formation is influenced by the substrate temperature, the film composition, and the underlayer material. With increasing the substrate temperature up to around 300°C, the order degree increases. As the substrate temperature further increases, the order degree decreases. Annealing a disordered film at 300°C does not effectively enhance ordering. The CoPt and the Co₃Pt films which include metastable ordered phases have flat surfaces and show strong perpendicular magnetic anisotropies reflecting the magnetocrystalline anisotropies of ordered crystals.

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Deposition of inclined anisotropy film for bit-patterned media was studied using an oblique incidence collimated sputtering. Pt underlayer increased the inclination angle of magnetic layer more than 5° on a Ta seed layer. Further increase of the angle was obtained by annealing Pt/Ru underlayer resulting an inclination angle of 9.4° for a Co-Cr_15.5 film on the underlayer. The magnetic properties of the Co-Cr_15.5 film with an inclined orientation was estimated comparing measured hysteresis loops with simulated ones, which indicated to have inclined magnetic anisotropy with an anisotropy field of about 4.5kOe and a deflection angle of the anisotropy about the same as that of the crystalline orientation.

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The optimum generalized partial response (GPR) target for barium ferrite (BaFe) tape systems was studied. The shift in perpendicular magnetic recording technology in HDDs to systems employing single-pole-type (SPT) recording heads and media with a soft under layer (SUL) has been accompanied by a change in the read channel design, whereas current magnetic tape recording systems utilize a combination of a ring-type recording head with a single magnetic layer structured medium. Therefore, the read channel performance of current oriented BaFe particulate tape systems needs to be studied to best exploit the potential of this medium. Toward this end, DC-free, DC-full, and DC-suppressed targets were compared. The results show that assuming a GPRML detector with 16 or more states, a traditional DC-free target exhibits the best bit error rate performance for both longitudinally and perpendicularly oriented BaFe media, suggesting that the current read channel designed for longitudinally oriented media can also be utilized for BaFe particulate tape systems.

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The uniform magnetic field of various strength was applied to the perpendicularly and in-plane demagnetized media, and the change in each magnetic cluster state was investigated as the fundamental investigation of the influence of demagnetization method on noise during signal recording on the stacked perpendicular recording media. The results showed that the in-plane demagnetization can achieve lower noise level if the recording field is not very high. In other words, the in-plane demagnetization is an effective way to achieve lower noise in transition area, near track edge of recorded bit, and in high-density bit. In addition, the simulation clarified that this noise reduction can be explained using the idea of sub-domain structure in the in-plane demagnetized media.

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Microwave-assisted magnetic recording (MAMR) has been proposed as a candidate technology to realize areal recording densities of over 2 Tbit/inch². MAMR requires a spin-torque oscillator (STO) to generate a strong high-frequency magnetic field that will induce magnetic resonance in the recording medium. The oscillation characteristics of STOs were previously investigated using a micromagnetic model that neglected the magnetic interaction among the STO, the single-pole-type (SPT) writer, and the recording head. The STO is typically placed in the gap between the main pole and the trailing shield of the SPT writer, so that the STO is inevitably subjected to strong magnetic interaction with the main pole and the trailing shield. We have developed a new simulator, referred to as an integrated MAMR simulator, that takes this interaction into account. The integrated simulator has revealed that the magnetic interaction has a strong influence on the oscillation characteristics.

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To achieve high recording density in a bit-patterned media recording system, the spacing between data bit islands in both the along-track and the across-track directions must be decreased, thus leading to the increase of two-dimensional (2D) interference. One way to reduce the 2D interference is to apply a 2D coding scheme on a data sequence before recording; however, this method usually requires many redundant bits, thus lowering a code rate. Therefore, we propose a novel 2D coding scheme referred to as a recorded-bit patterning (RBP) scheme to mitigate the 2D interference, which requires no redundant bits at the expense of using more buffer memory. Specifically, an input data sequence is first split into three tracks in which will then be rotated to find the best 3-track data pattern based on a look-up table before recording, such that the shifted data tracks yield the least effect of 2D interference in the readback signal. Numerical results indicate that the proposed RBP scheme provides a significant performance improvement if compared to a conventional system (without 2D coding), especially when the recording density is high and/or the position jitter noise is large.

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Bit-patterned medium (BPM) is one of the promising approaches for ultra-high density magnetic recording systems. However, BPM requires precise write synchronization, and exhibits write-errors due to insufficient write field gradient, medium switching field distribution (SFD), demagnetization field from adjacent islands, and island position variation. In this paper, an iterative decoding system using a non-binary low-density parity-check (LDPC) code is considered for a BPM R/W channel with write-errors at an areal recording density of 2Tbit/inch² including the coding rate loss. The performance of the iterative decoding system using the non-binary LDPC code over the Galois field GF(2⁸) is evaluated by computer simulation, and it is compared with the conventional iterative decoding system using a binary LDPC code. The results show that the non-binary LDPC system has a larger write margin than the binary LDPC system.

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The previously-proposed model of the writing process in TDMR is modified based on the Stoner-Wohlfarth reversal mechanism. The BER performance for a neuro-ITI canceller is obtained via computer simulation using the R/W channel model based on the writing process, and it is compared to those for well-known TDMR equalization techniques.

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A removable HDD “iVDR” is an international standardized medium, which has HDD features such as a large capacity and high-speed data transfer, and also is removable and compatible. We discuss the concepts of the hardware-specifications designed by the iVDR Consortium and the history of the international standardization activities for iVDR. We also discuss application expansions through these standardization activities.

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In this study, the influence of Gd composition on current-induced domain wall motion in a Gd-Co ferrimagnetic nanowire was theoretically investigated with taking into account of composition dependence of magnetic properties. As a result, the intrinsic critical density to move domain wall significantly reduces near the compensation composition, which is achieved to be less than 10⁵A/cm². Moreover, the intrinsic critical current density also significantly reduces near a certain Gd composition where the domain wall energies of Bloch and Néel walls are almost the same.

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Holographic data storage (HDS) is a next-generation optical storage that uses the principles of holography. The multiplex holographic recording method is an important factor that affects the recording capacity of this storage. Various multiplex recording methods have been proposed so far. In this study, we focus on shift multiplexing with spherical waves and propose a method of shift multiplex recording that combines the in-plane direction and thickness direction of the recording medium. In conventional shift multiplexing with spherical waves, shift multiplexing is usually carried out with respect to the direction parallel to the plane of the recording medium. By focusing on the fact that shift selectivity is also in the thickness direction, we examined the possibility of a multiplex recording method that combines multiple shift directions. Simulation and experimental verification shows that the proposed method is effective in principle.

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The equivalent circuit of aperture-coupled cavities filled with a lossy dielectric is considered by means of an eigenmode expansion technique founded on the segmentation concept. It is different from a series LCR resonant circuit, and the resistor which symbolizes the dielectric loss is connected to the capacitor in parallel. If the cavities are formed by a short-circuited oversize waveguide, then the input admittance can be represented by the product of a coupling factor to the connected waveguide port and the equivalent admittance of the short-circuited waveguide. The transmission line model is effective even if lossy wall effect and dielectric partially-loading effect are considered. As a result, three-dimensional eigenmode parameters, such as the resonant frequency and the Q-factor, become dispensable and the computational complexity for the cavity simulation in the field of microwave heating is dramatically reduced.

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A novel fabrication approach for the amperometric biosensor composed of carbon nanotubes (CNT), a plasma-polymerized film (PPF), hexamineruthenium(III)chloride (RU), and enzyme glucose oxidase (GOD) is reported. The configuration of the electrochemical electrode is multilayer films which contain sputtered gold, lower acetonitrile PPF, CNT, RU, GOD, and upper acetonitrile PPF, sequentially. First, PPF deposited on Au acts as a permselective membrane and as a scaffold for CNT layer formation. Second, PPF directly deposited on GOD acts as a matrix for enzyme immobilization. To facilitate the electrochemical communication between the CNT layer and GOD, CNT was treated with nitrogen plasma. The electron transfer mediator RU play a role as the mediator, in which the electron caused by enzymatic reaction transports to the electrode. The synergy between the electron transfer mediator and CNT provides benefits in terms of lowering the operational potential and enhancing the sensitivity (current). The optimized glucose biosensor revealed a sensitivity of 3.4µA mM^-1 cm^-2 at +0.4V vs. Ag/AgCl, linear dynamic range of 2.5-19mM, and a response time of 6s.

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