The effect of head field gradients and thermal gradients in heat assisted magnetic recording is investigated. When recording at a constant temperature, or in a constant external field, clear correlations between the recording performance and the head field gradient or thermal gradient can be found. Thermally assisted recording with a write head is much more complex and higher gradients do not necessarily translate into higher SNR.

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  This paper addresses the effect of a shield for the ring head to improve high track density. We analyzed the shape and the position of the shield with the finite-element method and checked the effect of the shield using a three-dimensional magnetic recording simulator in which a curing magnetic reversal model and self-consistent magnetic calculations were combined with the finite-element method. In this analysis, all components of the fringing field of the shield head were reduced, especially for the 30-degree components, which refers to the orientation angle of obliquely oriented metal evaporated tapes. We calculated the side erase band (SEB) from recorded magnetization on DC erased obliquely oriented metal evaporated tapes and found an optimal shield shape and position with respect to the head/media spacing. The well designed shield head was advantageous in having an SEB that was less than half that of a conventional head, was effective for achieving high track density in a tape storage system.

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  Magnetic printing characteristics using a perpendicular anisotropic master medium (PAMM) with various patterns were numerically analyzed. The recording field distribution of PAMM and the magnetization distribution of the recording layer were analyzed by micromagnetic simulation. As a result, the recording field of dot a pattern was about 1 kOe higher than those of line and checker patterns under the same printing field. The magnetic printing with PAMM was found to be applicable to any pattern. When the bit length was not more than 100 nm, the optimum printing field for the dot pattern was 1-2 kOe lower than those of line and checker patterns. The optimum printing field varied according to pattern and bit length.

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  We measured perpendicular magnetic recording media with a static tester to analyze the read-write characteristics (SN ratio, ATE, and recording margin) of future bit patterned media (BPM). We clarified that the measured current of a granular-type perpendicular magnetic recording medium's reproduction waveform at half pulse width, T₅₀, and the magnetization transfer parameters, were small. The read-write resolving power is thought to improve and reproduce a steep magnetization transition through contact recording. Furthermore, we measured the BPM samples and ascertained that the actual measured values conformed to those calculated qualitatively. In addition, we found the dot pitch from a reproduction wave did not depend on the dot size, and it was almost the designed value, and we confirmed that the standard deviation was around 6% of the dot pitch at dot lengths longer than 40 nm.

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  We previously reported that an advanced preparation method was applied to the synthesis of a radially anisotropic composite bonded magnet with a continuously controlled direction of anisotropy for inner and outer rotor magnets. The preformed magnets were extruded and compressed into ring-shaped magnets by using self-recoverability based on the incomplete three-dimensional (3-D) network molecular structure at an elevated temperature. In this study, an investigation of the thermomechanical behavior of the self-recoverability of the magnets together with their magnetic properties was carried out in order to apply them to small motors as various specific shapes. As a result, the (BH) max of a magnet attained a typical value of 165 kJ/m³, and no deterioration of magnetic properties was detected throughout the preparation process even if the magnets were miniaturized at weights ranging from 38 to 400 mg. The reduction in size is attributed to the optimized incomplete 3-D network molecular structure.

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  We have investigated the dynamics of a vortex core trapped in a single layered Fe₁₉Ni₁₈ disk. The large amplitude excitation of the vortex core translational mode causes a shift in the resonance frequency. We can explainthe self-bistable mode where the position and amplitude of a dynamic vortex core determines the translational mode effect on the dynamic change of the gradient of the potential well. The phenomenological model that describes the self-bistability also provides an explanation for the asymmetrical spectrum shape. The self-bistability to tune the resonance using the input current would be extremely useful for high-frequency devices. This work also opens up a rich new area of study in the field of nano-scale magnets.

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  Co thin films were prepared on SrTiO₃(100), SrTiO₃(110), and SrTiO₃(111) single-crystal substrates by ultra-high vacuum molecular beam epitaxy. The film structure and the magnetic properties were investigated. Co epitaxial thin films are obtained on these SrTiO₃ substrates at elevated temperatures with different film orientations. The nucleation of Co thin film on SrTiO₃ substrate varies depending on the substrate orientation and the substrate temperature. Co(100)_fcc single-crystal films are obtained on SrTiO₃(100) substrates. On SrTiO₃(110) substrates, Co epitaxial thin films with Co(110)_fcc, Co(111)_fcc and/or Co(0001)_hcp, and Co(100)_fcc planes parallel to the substrate surface are formed. Thin films consisting of Co(111)_fcc and Co(0001)_hcp crystals epitaxially grow on SrTiO₃(111) substrates. 0.4-0.5% reductions in lattice spacing normal to the substrate surface are observed for Co thin films prepared at a substrate temperature of 300°C. The film strain decreases with increasing the substrate temperature. The in-plane magnetization properties of Co thin films are influenced by the magnetocrystalline anisotropy and the shape anisotropy caused by the roughness of Co islands which form the Co thin films.

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  The Magnetic structure of magnetic multilayers composed of a full Heusler Co₂MnSi(CMS) alloy and Cr was calculated by using first-principles band calculation. We found that the magnetic moments of Co and Cr were parallel, while those of Mn and Cr were anti-parallel in CMS/Cr/CMS multilayers. By comparing the calculated results with those in Fe/Cr/Fe multilayers, it could be argued that the magnetic structure calculated for Co, Mn, and Cr atoms is crucial for the biquadratic coupling observed in these multilayers.

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  A magnetic tunnel junction (MTJ) spin-filter device of Pt/Co ferrite/MgO/Co demonstrated -19.8 % tunnel magnetoresistance (TMR) and 27.5% spin-filter efficiency at 10 K. By increasing the bias voltage, the TMR at 10 K first increased and then decreased, exhibiting a maximum at 0.17 V. This anomalous dependence of TMR on bias was interpreted as tunneling via the spin-down conduction band in the Co ferrite. At room temperature (RT), the tunneling mechanism was thought to originate from hopping in the defect states due to structural and chemical defects in the Co ferrite. To achieve higher spin-filter effect at RT, it is important to reduce the defects in the Co ferrite barrier.

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  We successfully fabricated L2₁-ordered Mn₂VAl Heusler thin films and evaluated their ferrimagnetic properties by soft x-ray magnetic circular dichroism (XMCD). The buffer layers and annealing temperatures were varied to prepare the Mn₂VAl films. We discovered that Mn₂VAl could be ordered in an L2₁ phase well when it was deposited directly onto an MgO (001) single crystalline substrate. The maximum values of L2₁ and B2 long-range order parameters we obtained were about 0.5 for both phases for samples without a buffer layer, when substrates were heated at 500°C or 600°C. The saturation magnetization (M_s) for these samples was roughly 150 emu/cc. This is rather small compared to that expected from the ideal Slater-Pauling behavior, which might be due to the suppressed degree of L2₁ or B2 ordering. Ferrimagnetism in the Mn₂VAl, ferrimagnetic coupling between Mn and V moments was clearly observed by using the XMCD technique in well-ordered L2₁-Mn₂VAl film as has been predicted in theoretical investigations.

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  This paper describes the experimental investigation of relatively weak magnetic noise at low frequencies, which was caused by the fluctuation of air currents through ducts in a magnetically shielded room (MSR). The noises were measured by SQUID magnetometers in the MSR installed on an active microtremor isolation system. First, the paper clarifies that magnetic noise depended only on air fluctuation at frequencies less than 10 Hz, whereas on both air fluctuation and mechanical vibration via floor at frequencies from 10 to 30 Hz. Second, the major contributor to magnetic noise at low frequencies was identified by evaluating the coherence coefficients between magnetic noises, vibrations of the MSR, and sound pressure inside and outside the MSR. The deformations of the wall and those of the ceiling in directions perpendicular to their planes due to air-fluctuation mainly contributed to magnetic noises. Third, by measurement, we inferred that the peak frequencies of the sound pressure resulting in magnetic noise were generated by the air duct.

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  The high sensitivity detection of magnetic fields was demonstrated using the oscillatory domain-wall displacing method for a GMR sensor. A micro-wire with a width of 30 μm and a length of 200 μm of a spin valve film, Al (20 nm)/MnIr (20 nm)/CoFe (3 nm)/Cu (2.2 nm)/CoFeB (10 nm), was fabricated as a magnetic sensor device. The domain walls in the free layer, whose easy axis was perpendicular to the wire, were oscillatorily displaced by an alternating magnetic field produced by a current with 140 kHz through the micro-wire. The oscillatory wall displacement reduced the influence of wall coercivity and the linear relationship between the external field with 1 kHz and an output signal for the sensor circuit was obtained down to 10^-3 Oe.

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  The accuracy of heat deposition, which is proportional to magnetic fluid weight density, appears to be a major factor in the quality of magnetic-fluid-based hyperthermia. An innovative giant magnetoresistance (GMR) needle probe is proposed as a means of estimating very-low-concentration magnetic fluid weight density in a low-invasive way. The method of estimation is based on the difference between magnetic flux densities inside and outside a magnetic-fluid-filled area in the body, given that the applied magnetic flux density is uniform. Since, for very-low magnetic fluid weight densities the percentage change in magnetic flux density is in the order of 1/100, it is important that the applied magnetic flux density be at least 1/10th more uniform. For this purpose a Lee-Whiting type coil was designed and fabricated, producing a 0.001% fluctuation from the center of the coil in approximately 35% of the outer coil spacing along the axial direction and 25% of the diameter of the coils in the radial direction. Concentrations as low as 0.03% weight density (a change in magnetic flux density in the order of nanotesla) were estimated by means of a GMR needle probe.

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  In order to realize the integrated magnetic thin film devices, RF inductors have been fabricated using CoFeSiO/SiO₂ multilayer granular film and copper spiral coil. Multilayer granular magnetic films which consist of alternate stacks of nano-sized granular and insulator layers exhibit very sharp ferromagnetic resonant (FMR) peak. Granular and insulator layers of 6 nm and 1 nm are suitable for obtaining a very narrow FMR linewidth. High-resolution transmission electron microscopy (HR-TEM) observation revealed a well-defined multilayer granular structure and a homogeneous CoFe grain size, which seem to be necessary for realizing a very narrow FMR linewidth. There is no thermal deterioration in frequency dependence of permeability of CoFeSiO/SiO₂ films at the temperature range below 350°C. The fabricated inductor had a size of about 670 × 670 μm², including a 3μm thick copper spiral coil, and a magnetic film with three different thicknesses of 100 nm, 200 nm and 500 nm. The slit patterned magnetic film and the division of conductor line are appeared to be useful for reducing a loss resistance of fabricated inductors.

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  It is well-known that the irradiation of ultrasound in aqueous solution results in the generation of pulse power and resultant radicals. The ultrasound creates micro-air bubbles as cavitation, and the collapse of the bubble contributes to the generation of a shock wave, heat, and radicals. We propose that the adiabatic expansion phenomenon by a linear actuator creates an aggressive and effective cavitation in an aquatic medium. The system is composed of a piston-cylinder structure and giant magnetostrictive actuator with huge stress characteristics. First, the mechanical equivalent circuit is examined in order to enhance the generation of cavitation by resonance phenomena. One of the applications we discuss is the sterilization of a bacillus and the inactivation of a virus in a water medium. The experimental results indicate that the sterilization and inactivation occurred due to the pulse power of cavitation phenomena.

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  This paper discusses the stress dependence of magnetizing properties in non-oriented electrical steel sheets (NO). Compression stresses deteriorate the magnetic properties at low flux density, but improve them at high flux density, where magnetization rotations are induced. Tensile stresses reduce magnetizing fields at low flux density, but increase them at high flux density. The stress dependence of NO is affected by the exciting direction, as the rolling direction of NO is easy to magnetize and sensitive to stresses. High-grade types of NO (50A290, etc), which have high Si content and large crystalline grains, are more sensitive to stresses than low grades (50A1300, etc), and the magnetizing fields of high grades at high compression are higher than those of low grades. This stress dependence may depend on magnetization behaviors (domain wall displacement and magnetization rotation) and magnetostriction. Domain wall displacement mainly occurs at lower flux density, and in this case tensile stresses improve magnetic properties and compression deteriorate them because magnetic domains orient the magnetization to <100> and λ100 is positive. However, magnetizations rotate to exciting directions at high flux densities, with the result that the <111> component of magnetization is induced, and in this case compression improves the magnetizing properties, because λ111 is negative, whereas tensile stress deteriorates them. Therefore, stress dependences may be modeled by magnetization behaviors and magnetostriction, and analysis of the magnetic properties using this model of stress dependence may improve NO steels and their applications.

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  This paper describes the fundamental characteristics of a magnetic oscillation dc-ac power converter using a magnetic control device called a bridge-connected magnetic circuit. An ac-voltage source such as a line electric power source is connected in series to an excitation winding of the magnetic oscillation circuit. The converter can supply electric power to the ac-voltage source, and can control its output electric power by means of a small dc current that flows through a winding of a U-form core that composes the bridge-connected magnetic circuit. The characteristics of the converter in controlling the output electric power are described in this paper.

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  We studied an environmental magnetic noise rejection method using independent component analysis (ICA) for a magnetocardiogram (MCG). In the ICA, when the SN ratio of the data is reduced, the accuracy of the noise rejection becomes low and it becomes difficult to reach a decision regarding the contraction dimension. In order to solve these problems, we examined the initial value of the transformation matrix W of the ICA. We proposed an initial value decision procedure for the transformation matrix W, and as a result the accuracy of the noise rejection was improved. Verification was carried out for MCGs with various SN ratios. It was shown that this method was effective for improving noise rejection.

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  Magnetocardiogram (MCG) is a non-invasive method for measuring functional information concerning the electrical activities of the heart. In this study, the exercise-induced MCG and body surface potential map (BSPM) were measured for normal subjects. MCG were measured by a three dimensional second-order gradiometer connected to 39-channel superconducting quantum interface device (SQUID), which can detect magnetic field components perpendicular to the chest wall (Bz) and tangential to the chest wall (Bx, By) simultaneously. Time-frequency analysis (wavelet analysis) was applied to the MCG to not examine the change of power spectrum of QRS complex and ST segment. We found that the frequency component of Bx, By, Bz in MCG with cross-correlation function was different. When I watch a temporal response of the frequency, 2-8Hz components showed a remarkable change. It is thought that frequency components may affect between rest time and after the exercise.

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  We have studied a method of environmental magnetic noise rejection using independent component analysis (ICA) for magnetocardiograms (MCGs). ICA is a useful method of separating the signal from noise. However ICA has various problems in determining numerous parameters and distinguishing signal or noise components from separated components. In many cases, these have been determined from the experiential results, and it has been difficult to determin the optimum parameters. We proposed a method of the distinguishing signal or noise components using the autocorrelation function of electrocardiograms (ECGs) and MCGs. Contraction dimension decisions were used to determin the maximum value of the autocorrelation function. The testing to verify its accuracy was carried out for MCGs with various signal-to-noise ratios. We found that this method was effective for the noise rejection.

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  Functional electrical stimulation (FES) is a therapy used in the rehabilitation of lost-movement functions by applying electrical stimulation to paralyzed extremities. We adapted the implanted direct-feeding method to apply stimulation, in which small implanted stimulators were placed under the skin at a depth of 20 mm, and stimulus energy and signals to control the devices were applied to them with a mounted system using magnetic coupling. This method had two main advantages in that it had no percutaneous points and it provided highly precise stimulation. The sizes of the mounted coil and the implanted coil were quite different so that the coupling between each was extremely low. To retain this disadvantage, the implant coil had a high-aspect ratio ferrite core, which gave the implant coil a magnetic direction for easy feeding and communication. Therefore, the magnetic fluxes from the mounted coil for feeding and communication had to be generated in the same direction inside the mounted coil. We propose a mounted coil that is able to generate such a magnetic flux, and tested and verified the possibility of whole area feeding and communication with it.

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  Hyperthermia is a cancer therapy that necrotizes cancerous tumors with heat. The soft-heating method is one type of hyperthermia implanting small elongated elements inside the body. The heat element consists of thermosensitive ferrite with a metallic ring. The element generates heat induced by a high-frequency magnetic field produced by the exciting coils. The most heat is generated when the element's major axis is parallel to the direction of the magnetic field, but the solenoidal and spiral coils may be excited in a nearly constant direction. It is difficult to heat the elements efficiently with these coils. Therefore, we need a coil construction that can excite the elements efficiently without having to depend on the direction of the heat elements. In this paper, we discuss a multicoil construction we examined to generate multidirectional magnetic fields. Our group advanced a method of reducing induced current that could drive safely even if it was electromagnetically-coupled. We also examined a therapeutic coil model with this method that had strong electromagnetic coupling. As a result, multidirectional magnetic fields could be generated by using the therapeutic model.

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