Zero Field Magnetic Amplifying Magneto-optical System (ZF-MAMMOS) is realized by using an exchange-coupled tri-layer. The recorded mark with any length appears as the expanded domain with the size of collapse diameter in the readout. layer without external magnetic field. As the ZF-MAMMOS has a resolution of 1/10 of a laser beam spot, this corresponds to 40 nm using a 405 nm laser diode and an objective lens of NA, 0.9. An AlSiN enhance/cooling layer was arranged for overwriting, and a GdFeCo recording assist layer was developed for high recording field sensitivity. As a result, the durability of overwriting is improved and the recording with ±140 Oe is achieved. This result also indicates that it is possible to realize a heat assisted magnetic recording with a very small recording field.

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The resonance frequency of ferromagnetic particles with surface anisotropy was investigated by micromagnetic simulation. Two kinds of calculations were done: those with Aharoni surface anisotropy and those with Néel-Brown surface anisotropy. In Aharoni surface anisotropy, the relationship between the resonance frequency and particle size D was in agreement with Shilov's theory. In Néel-Brown surface anisotropy, the resonance frequency was proportional to 1/b, where b was the length of the short axis.

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We analyzed the head noise in CPP-GMR heads to clarify the effect of shape anisotropy on spin-torque noise through an experiment and calculations. We fabricated two types of CPP-GMR heads with a current-screen layer (a nano-oxide layer with a confined current path), using two different track widths (50 nm and 90 nm) and the same stripe height (100 nm). The measured and calculated noise of a 50-nm-wide-track head is larger than that of a 90-nm one when the sensing bias voltage is 120 mV and the peak asymmetry is the same. This behavior is explained by considering that the shape anisotropy field enhances the tilt of the magnetization, especially at the edge of the track in the free layer, and that this magnetization configuration increases spin torque. Accordingly, we clarified that spin torque noise is sensitive to a head-internal field such as a shape magnetic anisotropy field, and that controlling the shape anisotropy field is important for reducing the spin-torque noise.

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occupy different sites, depending on the substitution rate. Since the coercivity is easily decreased even by small amount of substitution, Co²⁺ and Sn⁴⁺ ions may prefer the 2b and 4f₂ sites, which is considered as the cause of uniaxial anisotropy, at x < 0.8.

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The dysprosium substituted yttrium iron garnet (Dy:YIG) film was investigated because of high magnetstriction for operating voltage driven type magneto-optic spatial light modulators (V-MOSLMs). The fabricated Dy:YIG film had magnetostriction of 3.5 ppm, soft magnetic property, transmittance of 47 % and faraday rotation of -2.7 deg./μm at 532 nm wavelength. Furthermore, a reflection type one dimensional magneto photonic crystal (1D-MPC) by using the Dy:YIG film as a defect layer was fabricated for enhancement of Kerr rotation. In the case of the defect layer of 147 nm thick, a Kerr rotation angle was 15 times higher than the single layer at localized wavelength.

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This paper describes detailed studies of the effects of size distribution on the easy axis alignment of L1₀-FePt nanoparticles synthesized by the recently developed “SiO₂-nanoreactor” method (Appl. Phys. Lett. 87 032503 (2005)). The steady state orientation of the easy axis of the L1₀-FePt nanoparticles of the L1₀-FePt/polystytene composite, which had been prepared at 60°C under an external field of 50 kOe, was analyzed with particular emphasis on the effects of size distribution. Analyzes that did not take account of size distribution resulted in very limited success. To quantitatively estimate the effects of size distribution, the size dependency of particle magnetization, which originates not only in changes in particle volume but also in the size dependency of saturation magnetization, was considered. Such analyzes of the rocking curve of the L1₀-FePt/polystytene composite, which had been measured by using the (002) diffraction peak of the L1₀-FePt, resulted in quantitative determination of the steady-state orientation of the easy axis of the L1₀-FePt nanoparticles. It was revealed that about 50% of the L1₀-FePt nanoparticles have angles of less than 13 degrees between the magnetic easy axis and the external magnetic field.

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A simple method was developed for using the resolution of a magnetic field sensor with a finite-length thin magnetic core in order to assess its ability to detect a tiny magnetic dipole source. The values of the total linkage magnetic flux to the core in a uniform magnetic field and in a dipole magnetic field are compared to determine the detectability of a tiny magnetic dipole source. For a given geometry of cores and a dipole source, the magnetic flux densities in a thin core are calculated numerically by means of a FEM package. For a given fluxgate magnetometer with the resolution characterized in the uniform magnetic field, one can tell whether or not it is possible for the magnetometer to detect a given tiny magnetized sphere within the limit of allowable access to the target.

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It is generally desirable that material properties should remain constant in magnetic materials used for transformers and other electrical machinery and apparatus. However, the relative permeability of thermosensitive magnetic material depends on the temperature. Recent years have seen the development of various thermosensitive magnetic materials, whose relative permeability changes linearly over a wide range of temperatures. We designed a contactless temperature sensor system using one of these thermosensitive magnetic materials.

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This paper presents a method for calculating the characteristics of a magnetic gear on the basis of reluctance network analysis (RNA). The magnetic gear has inner and outer permanent magnet rotors, and has ferromagnetic stator pole-pieces arranged between the two rotors. The inner and outer rotors rotate in opposite directions with a certain gear ratio determined by the number of pole-pairs of the rotors. This magnetic gear has a higher performance than others because all the rotor magnets always contribute to the transmission of torque. The steady-state characteristics of the magnetic gear are calculated by RNA, and are then compared to the results obtained by the finite element method (FEM). Finally, the dynamic behavior of the magnetic gear is simulated by RNA.

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EIE-core variable inductors have useful features in that they are easy to scale up because they are made from a laminated silicon steel sheet, and their output current is almost sinusoidal without an air gap or a low pass filter. Hence, practical applications of EIE-core variable inductors as voltage regulators in electric power systems are expected. A highly accurate numerical calculation based on reluctance network analysis (RNA) was introduced in previous papers. Various characteristics including eddy current loss on the laminated silicon steel can be estimated using RNA. This paper proposes a method of reducing eddy current loss in variable inductors. The cutting plane of the EIE-core due to the reduced eddy current loss is determined based on the flux distribution calculated by RNA. An over 10% reduction in iron loss is demonstrated to be possible based on the proposed method.

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This paper proposes a cable-less magnetic actuator that exhibits a very high thrusting force and is capable of being adapted to propel a robot within a pipe. The actuator is moved by the difference in frictional force between the forward and backward supporting force of flexible materials. The actuator contains a mechanical inverter that directly transforms dc power from button batteries into ac power. The mechanical dc-ac inverter incorporates a double one-degree-of-freedom-model that switches under electromagnetic force. A prototype actuator containing a mechanical dc-ac inverter was fabricated, and is able to move through a pipe with an inner diameter of 8 mm. When powered by a 10-battery pack of button batteries, the actuator displayed speeds of 17.3 mm/s moving straight upward and 20.4 mm/s moving horizontally. This cable-less actuator has many possible applications, including inspection and maintenance of pipes.

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We have developed a hybrid flux-locked loop (FLL) system that is composed of a digital FLL and an analog FLL. The digital FLL achieves a wide dynamic range with the double-counter method for flux-quanta counting. The analog FLL on the hybrid system achieves a wide bandwidth using a differentiator. The frequency characteristics simulation revealed that the hybrid FLL system behaves like a low-pass filter in the digital part and a high-pass filter in the analog part. We carried out characteristic evaluations and a demonstration of MCG measurement using a prototype hybrid FLL system. It not only achieved great stability against high-frequency magnetic-flux noise but also enabled measurement of high-frequency magnetic-flux signals. This paper discusses the effectiveness of the hybrid FLL system.

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The measurement of magnetic field around a peripheral nerve is a possible technique for peripheral nerve diagnosis. It seems to be sensitive in comparison to skin potential measurement, which is widely used as a diagnostic tool, called nerve conduction study, as the permeability is almost homogeneous in the body. The normal component of the magnetic field around a nerve after stimulation has two pairs of peaks of in-and out-magnetic fluxes typically. However the conduction velocity or the intensity of the component of the field at those peaks may change if the nerve is injured and some fibers are lost. As nerve fiber loss is often observed in diabetic patients, the magnetic field around a diabetic sural nerve after electric stimulation was executed. Much variety of the velocity and the intensity of the peaks was observed between diabetic nerves than controls. In several cases, slower conduction and higher peak intensity ratio of conduction side to stimulation side were observed. The analysis of magnetic field seemed to be a possible method for fiber loss diagnosis.

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