CoPt-TiO₂ granular-type media with extremely thin Ru intermediate layer were prepared on a highly oiiented high-B_s FeCo soft underlayer (SUL) pinned by an IrMn antiferromagnetic layer. Although the increase of the IrMn antiferromagnetic layer thickness deteriorates the crystal orientation of the media, the magnetic properties of the recording layer were little changed. On the other hand, the H_ch (H_c in the hard axis direction) of the SUL were greatly decreased and the H_ex (exchange coupling field) of the SUL was largely increased. The H_ex of about 10 Oe is effective for the magnetic domain control of the SUL. The recording performance was measured by using a SPT head. The S/N increased as the IrMn layer thickness was increased. This improvement of the recording performance seems to be responsible for the magnetic domain control by the IrMn antiferromagnetic layer. Moreover, enough effect was obtained by H_ex of about 10 Oe under environment of conventional spin stand measurement system.

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  Microwave-assisted magnetic recording (MAMR) has been proposed as one of the candidates to achieve a higher area1 recording density over 1.0 Tbit/inch². MAMR needs a device to generate strong oscillating magnetic field to induce magnetic resonance in a recording medium. Its oscillating frequency is needed over 20 GHz, implying that eddy current might influence the dynamic magnetization behaviors of the field generating layer (FGL). In this paper, the influences of eddy current on the dynamic behaviors of the oscillator proposed by J-G. Zhu are discussed. The eddy current field in the FGL acts on the magnetizations to inhibit the rotation of precession, resulting in a slight increase in the oscillating frequency. However, the strength of the eddy current field is very small less than 20 A/m. Thus, it is concluded that eddy current field little influences the dynamic behaviors of the FGL.

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  The relationship among the sputtering conditions, composition, microstructure, and magnetic properties of Co-Si-O granular film deposited using various metal-oxide composite targets was investigated. The raw materials of the sintered targets were (a) (Co)-(SiO₂), (b) (Co)-(Si)-(Co₃O₄), and (c) (Co)-(Si)-(CoO) retaining the same nominal composition of (Co)-7.7mol%(SiO₂), Co_79.9Si_6.7O_13.4 (at%). It was found that; (1) in the case of Ar gas pressure (P_Ar) of 0.6-4.0 Pa, the discharge voltage with targets (b) and (c) was lower than that with target (a), (2) the oxygen content of the film became larger with increasing P_Ar from 0.6-8.0 Pa, (3) each granular film deposited by using the three targets with the same sputtering conditions showed nearly the same film composition, phase, microstructure and magnetic properties. This indicates that it is possible to control oxygen content and O/Si ratio in the granular film at the same time by increasing the amount of raw material of oxide in the composite target. Moreover, it is indispensable for formation of SiO₂ phase in the films to choose at least two kinds of raw materials including Si or O.

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  A new method for measuring track edge noise in perpendicular magnetic recording is proposed. Extraction signals were initially recorded at both edges of a write track to reduce the stray field from background magnetization, which deforms the bias field of the read head. The extraction signals also made the track edge noise clear. The linear density of the extraction signal was optimized to produce a smaller stray field and transition noise. By using the proposed method, the source of the track edge noise was determined to be the erase band formed near the recorded track edges.

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  The magnetization process of Nd-Fe-B bonded magnets prepared by the Hydrogenation-Disproportionation-Desorption-Recombination(HDDR) process was studied by observing magnetic domain structures using spin-polarized scanning electron microscopy (spin SEM). The positional relationship between the grain boundaries and the magnetic domain walls is clearly imaged. The result revealed that these magnets contain grains with a multi-domain structure in the thermally demagnetized state. The domain wall motions in grains with multi-domains are dominant in weak magnetic fields in the initial magnetization process, whereas fraction of the grains with a single domain increases with further increasing the magnetic field. The coercivity variations in these grains were also visualized.

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  Spin-torque-induced RF oscillations in MgO-based magnetic tunnel junctions (MTJs) were investigated at two different in-plane angles of applied magnetic field. The RF spectra with the magnetic field applied in the hard axis direction of the MTJ showed a simple Lorentzian-type peak structure, while those measured in the easy axis direction had a complicated peak structure. It was found by analyzing Lorentzian-type RF spectra that the linewidth decreased linearly as the injected dc current was increased. The linear decrease of the linewidth indicates the reduction of effective damping in the magnetization dynamics due to spin-transfer-torque. The RF output power measured with the magnetic field in the hard axis direction was 32 nW, which was larger than that measured with the magnetic field in the easy axis direction.

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  Radio-controlled watches that automatically adjust the time by using standard frequency and time signals becoming popular with consumers. To evaluate the receiving sensitivity of the antenna, we calculated the antenna output voltage by combining a magnetic field simulation and a circuit simulation. The output voltage of an antenna in a metal case is much smaller than that of an antenna in a non-conductive material case, because the leakage field induces an eddy current in the metal case. We present an example in which the sub-core increased the output voltage suppressing the leakage field. This effect of the sub-core depends on the size and arrangement of the sub-core in an antenna system, and thus optimization is essential. It is important to evaluate the quality factor (Q factor) of antennas, because the Q factor has a close relation to the receiving sensitivity. However, we show that an antenna with a higher Q factor might not always have a higher output voltage.

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  We report the results of a study undertaken to determine properties of magnetite particles that disipate heat only through Néel relaxation. The magnetite samples we considered for the heat dissipation studies were found to dissipate heat through both Néel and Brownian relaxations. The relative contributions of both relaxations on magnetic heat dissipation were investigated by analyzing the physical, magnetic, and heating characteristics of magnetite particles with various average diameters dispersed in low and high viscosity media. The results suggested that the size of magnetite particles that dissipated heat through Néel relaxation was around 12 nm and this agreed well with theoretical predictions.

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