The areal density of high density hard disk drives is reaching 1 Tbit/inch², in which very short bit lengths are close to 15 nm, although they should be around 10 nm. Many challenges must be resolved to achieve such short bit length recording. Read head resolution is one major issue, because shield-to-shield spacing, or a shield gap, is not easy to narrow to 10 nm. This study revealed the required read resolution for bit patterned media recording. Reciprocity with sensitivity functions calculated with finite element method (FEM) was studied to investigate read-back pulse, roll-off performance, and cross-track interference. We found that a narrow shield gap length of less than 20 nm was required in order to attain 5 Tbit/inch².

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  Magnetic force microscope (MFM) tips are prepared by coating Si tips of 4 nm radius with 80-nm-thick FePd-alloy films at room temperature followed by annealing at temperatures ranging between 200 and 600 °C. The effects of annealing temperature on the spatial resolution and the switching field of MFM tip are investigated. It has been shown that an MFM tip with resolution bellow 10 nm and switching field of 1.5 kOe can be prepared by FePd-alloy film coating. The resolution is nearly constant at 8.8 ± 0.3 nm for tips annealed at temperatures lower 550 °C, while it deteriorates to 9.4 ± 0.3 nm by 600 °C annealing. The variation of spatial resolution is related with an increase in surface roughness of film-coated tip caused upon annealing. The switching field is shown to depend on the degree of L1₀ ordering in FePd film. It increases from 0.25 to 1.5 kOe by increasing the annealing temperature from 200 to 600 °C, where the order degree in FePd film increases from 0 to 0.84.

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  The Effect of saturation magnetization and interlayer exchange coupling on the time-evolutional magnetization reversal process in exchange-coupled composite (ECC) media with high coercivity was investigated by utilizing micromagnetic simulation. In order to apply magnetic field, we used magnetic printing. As a result, the magnetization reversal time of the hard layer became shorter as the saturation magnetization of soft layer increased because the magnetostatic field generated from the soft layer increased. Thus, as the saturation magnetization of both layers increased, magnetization reversal occured for the weaker interlayer exchange field.

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  The influence of Pt concentration, an underlayer and CoPt thickness on the domain structure of CoPt films was investigated. The domain structure changed from maze domains to irregular and large domains as films became thinner. The average domain size increased as Pt concentration increased for films that were less than 10 nm thick, and the average domain size of films with an underlayer was larger than that without one.

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  This paper proposes our newly measurement method of the GHz range near field from a coplanar waveguide (CPW) using a Ni‐Fe coated magnetic force microscope tip and amplitude modulation of the line current. Cantilever resonance frequency modulation of approximately 25 kHz supplies the CPW with current and carrier frequencies up to 1.0 GHz. The CPW has a signal line width of 3 μm and a ground line width of 50 μm. The RF magnetic near field was evaluated from the difference in the oscillation amplitudes of the tip with and without Ni-Fe coating for a carrier frequency range up to 1.0 GHz, and became maximum near the center of gap on the CPW. This result also suggests that this method may be applicable to high resolution measurements of the magnetic near field distribution near RF power lines and ground lines, which have downsized for microscale radio frequency integrated circuit (RFIC) chips.

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  Eddy current testing (ECT) is one of the most representative nondestructive methods of testing metallic materials, parts, and structures. The operating principle underlying ECT is based on the two major properties of magnetic fields. The first is that alternating a magnetic field induces eddy current in all of the conducting materials. Thereby, input impedance of the magnetic field source, i.e., the electric source, depends on the eddy current path. The second is that the magnetic field distribution not only depends on the exciting but also the reactive magnetic fields caused by the eddy currents in targets. The former and latter are impedance sensing and magnetic flux sensing types.   
This paper is concerned with improving the sensibility of impedance sensing. The sensibility of ECT can be improved in two steps. The first is achieved by selecting the optimum exciting frequency. We employed a natural parallel resonant frequency in the ECT coil. The second is achieved by increasing the sharpness of the resonance curve on impedance versus frequency characteristics by changing the coil connections. Thus, we succeeded in developing an ECT sensor that had up to four times greater sensibility than the conventional one.

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  This paper describes the numerical circuit analysis of a magnetic oscillation direct current/alternating current (dc-ac) power converter using a magnetic control device called a bridge-connected magnetic circuit. The converter can supply electric power to an ac-voltage source such as a line electric power source and can control the output electric power by using the small dc-current that flows through the control winding of the bridge-connected magnetic circuit. A simulation model of the bridge-connected magnetic circuit and a simulation circuit of the dc-ac converter based on a general purpose circuit simulation program called “SPICE” are proposed for the quantitative analysis of the dc-ac converter. The fundamental characteristics of the dc-ac converter were calculated using SPICE. Comparisons between the simulation results and the experimental ones are presented in this paper.

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  This paper describes the fundamental characteristics of an improved magnetic oscillation direct current/alternating current (dc-ac) power converter with sinusoidal output. The converter can supply electric power to an ac-voltage source such as a line electric power source, according to the law of equal ampere-turns. The magnetic oscillation noise current is, however, contained in the output current of the converter due to magnetic oscillations. This paper presents an improved magnetic oscillation dc-ac power converter that is designed to reduce the noise in magnetic oscillation including from a line electric power source. A simple common mode choke was added to the ac-voltage source side of the converter. The effect the choke had in removing noise is also described.

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  Many engineers have recently been developing battery chargers that have employed contactless power transmission techniques for consumer products. These have contributed to improving the convenience of charging batteries. We investigated methods of electromagnetic induction for transmission from several different types. The efficiency of power transmission was dependent on the quality factors of two coils and the coupling coefficient between them. Previous reports indicated that copper clad aluminum wire (CCAW) and magnetic-plated wire (MPW) can improve quality factors. We need to select these materials appropriately according to our individual needs in order to achieve highly efficient power transmission systems. Therefore, we examined the performance of three materials for power transmission coils in this research and found a method of selecting materials to construct a highly efficient system of transmission with a broad range of coupling coefficients.

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  Several manufacturers have recently marketed ultra-compact electric vehicles. We propose the use of active seat suspension to improve the ride comfort on bad roads as a high value-added product. Ultra-compact electric vehicles can be installed with actuators for active seat suspension with a voice coil motor. The main purpose of this study was to inspect the utility and effectiveness of active seat suspension. Ultra-compact vehicles are different from standard cars in that they are frequently driven on narrow roads with poor surfaces. There are numerous barriers and small obstacles on poor road on a road surfaces and adverse effects on ride comfort in vehicles are expected during comparatively low-speed runs. We tested ride comfort with two different control techniques including sliding mode control on undulating and gravel roads. The results indicated that acceleration was reduced over undulating and gravel roads when sliding mode control was applied, and vibration was suppressed when the driver's weight changed.

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  Technology to achieve, contactless power transmission that can improve the utility of power feeding has recently attracted a great deal of attention. We researched electromagnetic induction as a method of contactless power transmission. This method is based on simple and standard technology. We propose a method that uses two coils on the secondary side, which we called the LC-Booster method. This method consists of using an LC-resonator and pick-up coil connected to the load, and it has the advantage of sequential matching by changing the coupling coefficient between the LC-resonator and pick-up coil. This paper reports the effect of additional capacitance connected to the pick-up coil to aim for a more effective LC-Booster method.

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