In a hard disk drive (HDD), a postprocessor is used for correcting the random error in a PRML (Partial Response Maximum Likelihood) channel. However, the postprocessor needs an error-detecting code, such as a single parity check code, and the code rate decreases. This paper proposes an erasure correction by Reed-Solomon (RS) code using Squared-Distance-Increase (SDI) instead of a postprocessor. This system does not need any error detecting code. The performance is obtained by computer simulation and is compared with that of the error correction system using a postprocessor. The results show that the proposed system provides an SNR improvement of about 2.6dB compared with the system using a postprocessor in a perpendicular magnetic recording channel with random and burst errors.

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The anisotropy constants K₁ and (K₂-K₃) of anisotropic Nd-Fe-B magnet powders prepared by the modified HDDR process were obtained from torque measurements in magnetic fields of up to 7.2 MA/m. A value of K₁=5.2×10⁶ J/m³ was obtained by Fourier analysis of an unsaturated torque curve. In the case of quasi-single crystal powders, K₁ was 5.9×10⁶ J/m³, which was closer to the results for Nd₂Fe₁₄B sintered magnets. The magnitude of the anisotropy field H_A distribution in each direction for 2 kinds of anisotropic and isotropic Nd-Fe-B magnet powders prepared by the HDDR process was also determined by Flanders and Shtrikman's method. In powders prepared by the modified HDDR process, the quantity of particles with higher H_A was greater than in those prepared by the ordinary HDDR process in the easy direction, and the angular distribution of H_A was sharp. The easy-axis distribution of particles was less than ±20° for anisotropic powders. In the case of isotropic powders, the easy axes were equally distributed in all directions. The results of experiments showed that Flanders and Shtrikman's method was appropriate for determining the magnitude of H_A and the angular distributions of permanent magnets with high anisotropy.

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Magnetic structures and magnetization processes in a permalloy wire-based honeycomb network were investigated by means of magnetic-force microscopy (MFM) and magnetoresistance measurement. The MFM measurements show that the remanent magnetic structures are governed by a magnetic interaction similar to the ice-rule, which provides a direct analogy between the present honeycomb network and an Ising system on a kagomé lattice. The magnetoresistance measurements reveal that the magnetic interaction at the vertexes also dominates the magnetization processes in the network. With a decrease in the exchange energy at the vertices, the ice-rule-type interaction disappears, causing a transition of the magnetization distribution in the network.

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We demonstrate micromagnetic calculations of magnetic domain walls in nanocontacts with various dimensions H-shaped samples, and estimate the domain wall widths, which are important for domain wall scattering at nanocontacts. It is necessary to calculate the domain wall widths, since the lengths and widths of nanocontacts are varied, as are their exchange stiffness constants. The domain wall width monotonically increases as the contact width increases. Low exchange stiffness at a nanocontact leads to small domain wall width. The contact shape can be changed by changing the contact angle in order to confine the domain wall at a nanocontact: the domain wall width increases as the contact angle increases. These results imply that large domain wall scattering occurs only for nanocontacts with small effective exchange coupling between two magnetic materials.

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Gold nanowires were produced inside a transmission electron microscope (TEM) for an in-situ study of conductance quantization. In particular, G₀/2 quantization was investigated, where G₀ is the quantization unit corresponding to a resistance of 12.9 kΩ. The probability of observing G₀/2 quantization was increased by increasing the applied magnetic field, decreasing the bias voltage, and decreasing the stretching speed of wires.

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We successfully grew Co₂Cr_1-xFe_xAl full Heusler films (0 ≤ x ≤ 1) with the L2₁ structure onto GaAs(001) substrates by achieving stoichiometry in an ultrahigh-vacuum molecular beam epitaxy chamber. The films develop epitaxial crystallinity with the relationship of Co₂Cr_1-xFe_xAl(001)‹110›||GaAs(001)‹110›, which induces very strong uniaxial magnetocrystalline anisotropy, except for x = 0. For x = 1, in particular, the film is almost a single phase and its magnetic moment per formula unit exhibits Slater-Pauling behavior. Films of this type were used to fabricate magnetic tunnel junctions with 8.8% and 4.9% tunnel magnetoresistance (TMR) ratios at room temperature for x = 1 with an Al-O tunnel barrier and x = 0.6 with a MgO barrier, respectively. The TMR ratio can be further enhanced by both realizing an L2₁ single phase and eliminating lattice distortion.

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Magnetic microstructure and anisotropic magnetoresistance (AMR) were simultaneously investigated for a permalloy film with dimensions of 2 mm × 100 μm × 35 nm by means of Lorentz microscopy. The ripple contrast of the magnetic domain in which the average magnetization is parallel to the external field was fainter than that of the domain with anti-parallel magnetization. The difference of the resistivity of these domains was experimentally confirmed.

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To develop micromagnetic devices for microwave applications, it is necessary to develop magnetic films with a ferromagnetic resonance (FMR) frequency higher than 1 GHz. For this purpose, it is essential that such films should have both high saturation magnetization and large magnetic anisotropy. In the present study, an exchange-coupled multilayer film, consisting of Fe₈₉Si₁₁(at.%) with a saturation magnetization of 19 kG and Mn₈₀Ir₂₀(at.%), was fabricated and characterized. From the experimental results, the Mn-Ir/Fe-Si exchange energy J_ex was estimated to be about 0.1 erg/cm². The [Mn-Ir (10 nm)/Fe-Si (7.2 nm)]₂₁/Mn-Ir (10 nm)/Fe-Si (3.6 nm) multilayer film exhibited FMR at around 6 GHz. In addition, μ' was estimated 40-80, and μ” was nearly equal to zero at low frequencies (f < 4.5 GHz). The exchange bias magnetic field was decreased by thermal process. If the decrease of the FMR frequency due to thermal process is allowed by 10 % of as deposited film, the maximum process temperature must be lowered by 250 °C.

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Fe-Si, Fe-Co, and Fe-Co-Si powders were prepared by the mechanical alloying process, starting with elemental powders. Their magnetic properties and x-ray diffraction patterns were investigated. Two kinds of milling processes were adopted to obtain higher magnetization for (Fe_1.0-xCo_x)₇₅Si₂₅. A magnetization of 184.6 emu/g at 20 kOe was obtained for a sample prepared by milling a mixture of Fe and Co powders for 30 hours, then milling it with Si powder for a further 10 hours.

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This paper describes the use of magnetoelastic ribbon as a remote viscosity and density sensor. Magnetoelastic ribbon was placed in an AC magnetic field generated by an external coil. The vibration of the ribbon could be monitored with a pickup coil and it reached its maximum value at the mechanical resonant frequency based on the magnetostriction effect. We confirmed that the mechanical resonant frequency of the ribbon was proportional to the square root of the product of the viscosity and density of the surrounding liquids. Moreover, we demonstrated that we could measure the viscosity of the liquid when it was very high by dipping only the edge of the ribbon in the liquid. These results suggest that this configuration is a promising candidate for use as a remote viscosity and/or density sensor.

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We propose a new system for sensing the position of a wireless magnetic marker. It consists of a resonating wireless magnetic marker, a driving coil, and differential pickup coils. The differential pickup coils can save the dynamic range about 1/80 that of conventional pickup coils. The marker does not have a battery or electric wires. The system has an accuracy of around 3 mm, and it can be used for highly accurate position sensing without magnetic shielding, because it is free from earth field noise.

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A precision position-detecting system using a wireless LC resonant magnetic marker was developed. The marker consists of an inductor and a capacitor without battery or electric wires, driven wirelessly by electromagnetic induction. The positional accuracy is less than 1 mm within 150 mm of the pickup coil array. The optimal design made it possible to improve the positional accuracy of the system. The system can be used for highly accurate motion-capturing without magnetic shielding because it is free from the earth's field. In addition, it has the potential to capture multi-point motion because it allows the markers to have individual frequency bands.

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Magnetic micro-machines are driven by a magnetic field. They require no power-supply cables, no batteries, and no control systems on the body of the machine. We fabricated a magnetic micro-machine with a planar structure. In the experiment, the micro-machine swam at a speed of 0.1 to 3 mm/s and had Reynolds numbers between 10^-3 and 1. This result indicates that the shape of this micro-machine is suitable for miniature swimming machines.

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A micropump with a spiral-type magnetic micromachine was fabricated. The magnetic micromachine was composed of a permanent magnet and a spiral coil. When a rotating magnetic field was applied, the machine rotated and produced a thrust force in a liquid. However, the machine remained still and pumped the liquid at the point of equilibrium between the thrust force and a force created by the field gradient. We experimentally examined the basic properties of the pump, such as the flow rate and pressure. As a result, we found that the latter two properties can be controlled by adjusting the frequency of the rotating magnetic field. The pump was able to produce a maximum pressure of 116 Pa and a flow rate of several ml/min.

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This paper presents a method for calculating the operating characteristics of permanent magnet (PM) generators based on the reluctance network analysis (RNA) method proposed by the authors. The PM generator used in the discussion has a distributed winding and an overhang structure in which the permanent magnet is longer than the stator's stack in the axial direction. In the analysis, the stator and rotor, gap, and the permanent magnet including the overhang are expressed as a simplified three-dimensional RNA model. The RNA model of the PM generator is combined with an external electric circuit and motion calculation blocks on a general-purpose circuit simulator called “SPICE.” We can readily calculate the characteristics of the PM generator using the combined model, including its transient state. The calculated values agree well with the measured ones.

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In most wire communication systems, communication lines are also used as power lines. Power is supplied to each terminal from a main power supply. The powered terminal needs to separate ac signals and dc supply in its input part connected to the communication lines. The main power supply and terminals need to have high impedance in order to prevent inflow of signals. Similarly, each terminal connected to the communication lines requires high impedance in our system, which consists of low-power switching power supplies. The powering terminal has a dc-dc converter that operates not only as a power supply but also as a transmitter. The powered terminal receives from the powering terminal the power it needs to operate. Each terminal has a new electronic choke. In this paper, the relation between inductors and the input impedance characteristics of the new electronic choke is investigated experimentally.

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A magnetic micromachine capable of trailing a wire was fabricated. The micromachine was constructed of a permanent magnet, a copper tube, and a spiral shape made from a tungsten wire. The magnet was magnetized in the direction of its diameter. When a rotational magnetic field was applied, the machine rotated and moved in silicone oil. Experiments showed that a spiral shape produced the largest thrust force. The micromachine was able to trail a wire in a small waterway created to simulate a blood vessel. These results show that the micromachine has great potential for navigating medical catheters.

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