In the patterned master magnetic contact duplication technique, the spacing between master and slave media seriously affects the duplication characteristics. When a slave medium with coercive squareness S^* of 0.43 was duplicated by using a master medium with a pattern width L of 2.5 μm and a magnetic layer thickness of 1 μm, it was found from experiments and simulation that the spacing loss factor K is about 30 dB. The reason for this small value is that the recording demagnetization in the duplication process is very weak. It is shown by simulation that a higher S^* value in slave media is advantageous for the patterned master magnetic contact duplication.

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A finite element read/write simulation was performed by solving the Poisson equation for a two-dimensional model of an antiferromagnetically coupled magnetic medium (AFC medium) and a thin-film-head system. The AFC medium is composed of two recording layers (top recording L1 layer, bottom recording L2 layer) and a thin intervening Ru layer. From a simulation of a di-bit pattern, we found that (1) when the coercive force H_c0 (L1) is smaller than H_c0 (L2), the L1 magnetization just recorded is rewritten by the applied reverse head field, and an extra-bit region appears in L1, (2) the extrabit is consolidated into a di-bit in L2 with increasing time, (3) the effect of the extrabit appears as a distortion in the output waveform, and (4) with increasing time, the output waveform changes so that its polarity becomes opposite to that at t = 0 sec. From the simulation at 423 kFRPI, it was found that (5) when H_c0 (L2) is small or large compared with H_c0 (L1), the thermal stability is improved at a finite small interlayer antiferromagnetic exchange coupling, and (6) for H_c0 (L1) ≈ H_c0 (L2), the thermal stability is improved with much larger interlayer antiferromagnetic exchange coupling.

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The effects of the thickness of Cu underlayer and Sm-Co layer in Sm-Co/Cu film were studied. When the thickness of Cu underlayer was 200 nm, its preferred orientation was (111), and the grain size was as large as 300 nm, owing to the substrate heating during the Sm-Co layer deposition. When the Sm-Co layer thickness was as thin as 10 nm, an SmCo₅ (002) diffraction line was observed in the XRD diagram, and the perpendicular coercivity was about 6.2 kOe. The magnetic properties of the Sm-Co/Cu film did not show any visible changes for 450 days. It was found from XPS depth profiles that Cu element was diffused into the Sm-Co layer from the underlayer, and may be effective in preventing Sm from oxidizing.

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Enhancement of grain isolation in CoPtCr-SiO₂/Ru perpendicular recording media is discussed in relation to SiO₂ the content and grain size of the Ru seed layer. The value of the remanence coercivity obtained by subtracting the thermal agitation effect, H₀, increases significantly with increasing SiO₂ content up to ∼ 11 at%, indicating enhancement of the grain isolation of CoPtCr. TEM images revealed that a single CoPtCr grain grows on a Ru grain in this SiO₂ content region, and experimental results showed that the grain size of the Ru seed layer plays a dominant role in determining the grain size of CoPtCr layer. However, a further increase in SiO₂ content beyond 11 at% results in a growth of multiple CoPtCr grains on a Ru grain, leading to a decrease in H₀. The formation of the multiple CoPtCr grains was remarkable on large Ru grains, suggesting a significant reduction of the diffusion length (mobility) of SiO₂ during film deposition as a result of the increase in SiO₂ content. Both a grain size reduction and an improvement in grain size homogeneity are required for a Ru seed layer to enhance the grain isolation in CoPtCr SiO₂ perpendicular recording media.

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Recently much interest has been aroused by L1₀ ordered FePt thin films due to their large magnetocrystalline anisotropy, which is required for ultra-high-density magnetic recording media. The grain size of pure FePt films is fairly large, which can cause medium noise and a reduction of recording resolution. We prepared FePt and FePt-Al₂O₃ films by the in-situ ordering method, aiming to suppress the growth of grain size by transforming the disordered fcc phase into the L1₀ structure.

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Hard/soft-stacked perpendicular recording media were proposed in order to improve recording writability without notable changes in thermal stability and noise performance. The advantage theoretically expected for hard/soft-stacked media was confirmed experimentally. The media consist of a magnetically hard CoPtCr-SiO₂ layer underneath a soft NiFe-SiO₂ layer. The total thickness of the two layers was set to be smaller than the coherent length of magnetization; the thickness of the CoPtCr-SiO₂ layer was fixed at 10 nm, and that of NiFe-SiO₂ layer varied from 0 to 4 nm. TEM images revealed that NiFe/CoPtCr stacked grains were well isolated by SiO₂ at grain boundaries, similarly to the isolation of single CoPtCr-SiO₂ media. No change was observed in the slope of the hysteresis loop by stacking the NiFe-SiO₂ layer, suggesting there was no significant change in the intergranular coupling of magnetization. The switching field decreased as NiFe-SiO₂ thickness increased, but no significant change was observed in ratio of the magnetic anisotropy energy to thermal energy, K_uV_act/kT. We successfully demonstrated that the hard/soft-stacked media show a better recording writability with no notable change in signal-to media noise ratio or thermal stability.

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MR head and double-layered medium used for perpendicular magnetic recording interact strongly each other. In order to investigate the influences of the interaction on MR head read characteristics, we perform micromagnetic simulations considering the interaction between head and medium. The output of shielded MR head are larger than those of non-shielded MR head due to reducing the demagnetization field in the free layer. However, the interaction between shield and soft under layer causes decrease in the signal output and the widening of reproduced wave form, which might result in degradation of resolution.

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An experiment was carried out to examine the effect of composition, heat treatment, and nitrogenation conditions on the magnetic properties of Sm-Fe-Co-Ti-Zr nitrides with TbCu₇-type structure. The optimum preparation conditions of the compounds were as follows: composition {Sm₁₀(Fe_0.9Co_0.1)_89.2Ti_0.3Zr_0.5}_83.5N_16.5; roller velocity 52m/s; heat treatment 700°C × 60 min in high-purity Ar gas; and nitrogenation condition 420°C × 15 h in high-purity N₂ gas. Typical magnetic properties of the obtained powders were as follows: J_r = 0.96 T, H_cJ = 811.7 kA/m, (BH)_max = 141 kJ/m³ (17.7 MGOe), and T_c = 504°C. Recoil loops of the hysteresis curve and X-ray analysis showed that the sample was an exchange spring magnet. The value of (BH)_max of the bonded magnet prepared from {Sm₁₀(Fe_0.9Co_0.1)_89.2Ti_0.3Zr_0.5}_83.5N_16.5 powder was 102 kJ/m³ (12.8 MGOe) when the density of the bonded magnet was 6.06 Mg/m³. The reversible temperature coefficient of J_r was α(J_r)_ave. = −0.05 %/°C, and the temperature coefficient of H_cJ in the range from 25°C to 125°C obtained by linear extrapolation was α(H_cJ) = −0.46 %/°C

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Physical properties of SrRu_1-xMn_xO₃ (0 ≤ x ≤ 0.5) show complex changes at about x=0.2∼0.3. The crystal structure changes from the orthorhombic of SrRuO₃ to the tetragonal of SrRu_0.5Mn_0.5O₃. The electrical conductivity shows a metallic behavior at x=0.0∼0.15, a band-gap type semiconductive behavior at x=0.4, and a hopping type semiconductive behavior at x=0.5. The samples between x=0.2 and 0.3 are mixtures of the two phases, and the conduction shows semiconductive behavior in low temperature and metallic behavior in high-temperature. Itinerant ferromagnetism disappears at about x=0.3. This system's MI transition occurs when the structure changes from orthorhombic to tetragonal by Mn doping into the Ru site.

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The magnetocrystalline anisotropy energy of Fe₁₆N₂ is calculated by the band model. The approximate energy bands of this material are formulated by Deegan's prescription and the formulas of Slater and Koster inclusive of the spin-orbit interaction and the exchange splitting, which is consistent with the experimental and calculated results of the magnetization. The anisotropy constants, K₁ and K₂, are evaluated through a comparison of the electronic energies with the magnetization parallel to the [001], [100], and [101] directions. The calculated anisotropy constants obtained with the exchange splitting 0.109 Ry are much the same as the experimental ones. However, the calculated results obtained by using an exchange splitting greater than 0.117 Ry do not agree with the experimental ones in the approximate number of electrons for Fe₁₆N₂. The calculated constant K_u for Fe₁₆C₂ inclusive of the exchange splitting 0.109 Ry agrees well with the experimental one.

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The magnetoresistance effect in Ni nanowires was investigated. The magnetoresistance ratio at 77 K reached 2400%, far beyond that of ordinary giant magnetoresistance effects. The Ni nanowires exhibit two different types of magnetoresistance effect: large MR with quantized conductance, and small MR without quantized conductance. The results imply that a relation exists between quantized transport and the giant magnetoresistance effect.

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The thermal transformation and magnetic properties of Ni_49.0Mn_27.2Ga_23.8 single crystals were investigated. A martensitic transformation was observed at 172 K during cooling. At this temperature, the strain in the [100] direction under an applied field of 10.1 kOe in a direction parallel to the [100] plane was approximately −8000 ppm. The entropy change in this transformation was estimated as 5.6 J/kg·K by calorimetric measurement. On the other hand, an intermediate phase transformation was observed at 230±2 K. The entropy change was 0.3 J/kg·K. At this temperature, the thermal expansion coefficient was increased, the magnetization in the low-field region was decreased, and the magnetostriction in the [100] direction was increased. The magnetostriction at 232 K was 2.3 times larger in the parallel field and 7.3 times larger at 228 K in the vertical field than the values at room temperature.

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An experiment was carried out to investigate the effect of Mn substitution on Co-Ni spinel ferrite prepared by the chemical coprecititation method without post-annealing. The chemical coprecipitation compositions were chosen according to the formula (CoO)_0.5(NiO)_0.5-y(MnO)_y·n/2(Fe₂O₃), where y varied between 0 and 0.5 and n between 2.0 and 2.5. Optimum magnetic properties were achieved with materials whose composition was (CoO)_0.5(NiO)_0.4(MnO)_0.1·1.125(Fe₂O₃). The typical magnetic and physical properties are saturation magnetization σ_s = 55.5 × 10^-6 Wb·m/kg (44.2 emu/g), coercivity H_cJ = 567.2 kA/m (7.12 kOe), average particle size D = 43 nm, anisotropy constant K₁ = +1.36 × 10⁵ J/m³ (+1.36 × 10⁶ erg/cm³), K₂ = −11.3 × 10⁵ J/m³ (−11.3 × 10⁶ erg/cm³), anisotropy field H_A ≈ 3.56 MA/m (44.7 kOe). The rotational hysteresis integral Rh, which is related to the magnetization mechanism of these fine particles, is 1.62, and it was found that the magnetization mechanism is an incoherent one.

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We observed spin-dependent tunneling in Co₉₀Fe₁₀/AlO_x/Co₉₀Fe₁₀/AlO_x/Co₉₀Fe₁₀ ferromagnetic double tunnel junctions. A middle Co₉₀Fe₁₀ layer, which is inserted between two AlO_x layers, is discontinuous due to the difference in the surface energy of these layers. The average diameter of Co₉₀Fe₁₀ particles was estimated to be 2.0-4.5 nm from cross-sectional transmission electron microscopy (TEM) images. At low temperature (< 50 K), a Coulomb gap is observed in current-voltage (I-V) curves, and the tunnel magnetoresistance (TMR) ratio within the gap enhances significantly with decreasing temperature, which indicates that the dominant electron transport is inelastic co-tunneling within the Coulomb gap. These observations in a ferromagnetic tunnel junction with 2-dimensional magnetic nano-particle layer insertion accord well with theoretical predictions by Takahashi and Maekawa [Phys. Rev. Lett. 80, 1758 (1998)].

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We investigate the magnetoresistance of a magnetoresistive element consisting of a nonmagnetic semiconductor, four electrodes, and a metallic shunt, with varying locations of the voltage electrodes. The optimum location of the voltage electrodes is estimated from MR ratios calculated by using the finite element method. The MR ratio of 6.9%, which was obtained at an applied magnetic field of 0.005 T for an MR element with asymmetrical voltage electrodes separated by a distance of 25 nm, is higher than that for the MR element with symmetrical electrodes. In order to improve the MR ratio at a low applied field, a flux-guide-type MR element is proposed in this study. An MR ratio of 124% at an applied field of 0.005 T was obtained for a flux-guide-type element with asymmetrical electrodes.

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Co₂MnX (X = Si,Ge) thin films epitaxially grown by the ion beam sputtering (IBS) method were investigated. Co₂MnGe films grown on MgO(001) substrates at temperatures from 400°C to 600°C were epitaxial and showed the same saturation magnetization as the bulk value. To improve the high surface flatness of these thin films, the roughness as a function of substrate temperature was investigated for 500 Å and 1000 Å film thicknesses. Smaller thickness and lower substrate temperature improved the surface flatness but decreased the saturation magnetization. The tunnel magnetoresistance (TMR) effect of junctions using 500 Å Co₂MnSi film deposited on a Ta buffer layer at 500°C was 0.4%.

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We theoretically study the temperature dependence of TMR in half-metallic manganite tunnel junctions. By performing numerical simulation based on linear response theory, it is shown that the effects of spin fluctuations on TMR are small and that the MR ratio remains at high temperatures near bulk T_C. We deduce that the disappearance of the MR ratio at temperatures far below T_C in experiments originates from a change in the interface electronic structure and magnetism.

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We investigated the influences of an underlayer on the soft magnetic properties and microstructure of FeCo electrodeposited thin films. Bcc crystallites with preferable (110) orientation contributes to the reduction of the coercivity for FeCo electrodeposited thin films, and the existence of the crystallites with bcc (211) orientation caused an increase of the coercivity. FeCo electrodeposited thin films with ruthenium underlayers had an uniform microstructure and a low coercivity from the initial growth layer to the surface in the film with the thickness above 1 μm.

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The output voltage of an eddy current displacement sensor depends on the quality factor Q = ωL/R of the coil. Therefore, impedance analysis of the coil is important for output voltage analysis. Theoretical analysis of coils has been performed by C. V. Dodd, A. Reatti, and others. However, the quality factor of a coil cannot be calculated by using their theory. This paper presents theoretical, numerical, and experimental analyses of a coil for an eddy current displacement sensor. The impedance characteristics are analyzed by combining three theories: Dodd's theory, Reatti's theory, and the finite element method (FEM). As a result, the calculated value of the quality factor using the technique of complementing Dodd's theory with FEM is found to be accurate within seven percent. This technique is effective from the viewpoints of calculation time and accuracy. The calculation times of the three methods are also discussed in this paper.

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We are considering development of a highly sensitive force distribution sensor using an amorphous ribbon. First, we measured the tensile stress characteristics of amorphous ribbons. The effect on the force sensitivity characteristic of various compositions of amorphous ribbons was examined in order to determine the optimum composition for an amorphous ribbon. The existence of anisotropy in the quenching and casting of the amorphous ribbon was confirmed. A force distribution sensor was then constructed and its basic behavior and sensitivity characteristics were confirmed by experiment.

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A method for detecting current-induced magnetic fields by magnetic force microscopy (MFM) was proposed and demonstrated, as one candidate for quantitative current evaluation in fine structures with high spatial resolution. Our system consisted of a conventional MFM and a feedback system for elimination of electrostatic force. To determine the spatial resolution of our system, we fabricated a pair of 0.5-μm-wide Au wires with a 0.2 μm separation. In these wires, ac currents flowed in parallel. From a calculation of a magnetic field around the Au wires, we confirmed that magnetic field gradients existed on both sides of the current paths. Since the characteristics of the magnetic force signals on both sides of the current paths were clearly identified, we concluded that the spatial resolution of our system was better than 0.2 μm. The linear dependences of the peak amplitudes on the ac current values were also confirmed.

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This paper deals with the velocity dependency of an eddy current sensor for measuring the rail joint gap using two air coils for ordinary railways. The sensor is able to detect the flux change due to the eddy current between the sensor and the rail. It is demonstrated that the sensor does not depend on the velocity in conditions where the exciting frequency is more than 50 kHz. The key points of this paper are as follows: (1) the principle of the measurement using a rail joint gap sensor composed of a detecting coil under an exciting coil; (2) the velocity dependency of the output voltage on a non-joint gap turn disk with an exciting frequency between 500 Hz and 1 MHz, and a velocity between 0.65 and 50 m/s (2.34 and 180 km/h); (3) the velocity dependency of the output voltage on a turn disk using two imitated joint gaps.

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Conventional planetary gears are used for heavy industrial applications, such as in the main engines of airplanes and power shovels. This gear system can be used for accelerators by installing an outring gear in the case of exchanging input and output. But a magnetic planetary gear can be used as an accelerator while driving the outring gear.
This paper presents a performance characteristics test for magnetic planetary and differential gears for accelerators. It is shown that the gear ratio of such accelerators is larger than that of ordinary accelerators. The reason for this is that an outring gear is driven differently from a planetary gear.
We deduce the best conditions for driving planetary and differential gears. For example, the sun gear speed Na of the output is 1050 rpm when the planetary gear speed Nb of the input is 50 rpm and the differential outring gear speed Nc is 200 rpm. Magnetic planetary and differential gears can be used for wind power generators and industrial clutches.

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In this paper, we examine the magnetic properties of 5-leg core for 3-phase transformer, which has a divided structure. Each magnetic property was examined in comparing the magnetic flux density, the magnetic field strength, and the iron loss under the condition of each divided structure mutually. It is known that the iron loss can be expressed by the relationship between the magnetic flux density and the magnetic field strength vector. The two-dimensional vector magnetic properties can be used to express this relationship as a vector. In the analysis, we have used the E&SS modeling, which can express the two-dimensional vector magnetic properties.

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Recently, along with high-end products, users have come to demand steel plates with high quality and high added value manufactured by a continuous steel plate process. In the factory, a continuous thin steel plate subjected to iron and steel processes is supported by a series of rollers during processes such as rolling. In the plating process, the steel plate is conveyed 20-50 m in the vertical direction for drying, during which time it is not supported by rollers or other mechanisms. Therefore, plating nonuniformity due to the generation of vibration and other factors prevents an increase in productivity. To solve this problem, we developed a noncontact guide system for high-speed traveling steel plates in which electromagnetic forces are applied at the edges of the steel plates. The control performance in replacing the electromagnet with a permanent magnet, moreover thus eliminating the running cost, was examined, and the efficacy of the proposed system was verified by experiments.

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The purpose of this study was to examine the effectiveness of active seat suspension when it is applied to small cars, and to survey the problems associated with its practical use. A small active seat suspension, which is easy to install, was designed and manufactured for one-seat electric automobiles. In a realistic driving test, a test road was prepared in which the concavity and convexity of an actual road surface were simulated by using hard rubber. Our aim was to examine the vibration isolation effect for the driver's seat, using disturbance cancellation control. We examined the control performance with respect to the variation of the parameters for the frequency and the driver's weight. We performed experiments in several conditions, and compared the results of control performance with passive control, feedback control, feedforward control, and disturbance cancellation control. As a result, we confirmed the suppressive effect of the disturbance cancellation control.

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Thin steel plates are used in various industrial products such as automobiles. We proposed a magnetic levitation control system, and its realization has been confirmed through a digital control experiment. However, when only levitation control is applied to the steel plate, it has no horizontal restraining force on the direction of travel. Therefore, we installed electromagnetic actuators in order to control the horizontal movement of the levitated sheet steel. Electromagnetic control forces of the actuators are applied horizontally to the levitated sheet steel. This paper aims at reporting the effect of suppressing the elastic vibration of the steel beam in the electromagnetic field.

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Application of a magnetic actuator to a capsule endoscope is proposed. Capsule-type magnetic actuators were fabricated and their motion properties were investigated in a silicone tube and in the intestine of a pig. The dummy capsule is 11 mm in diameter and 40 mm in length. This magnetic actuator is composed of a permanent magnet inside the dummy capsule and spiral structures outside it. The permanent magnet is magnetized in the direction of the diameter. When a rotational magnetic field is applied, the magnetic actuator rotates and moves wirelessly. The velocity of capsules with top spirals was examined in a silicone tube. In addition, a motion test was conducted in the intestine of a pig. The actuator can pass through the small and the large intestines over distances of 450 mm and 400 mm, respectively, in less than 150 s. The capsule can pass out of the bag-shaped section of the large intestine. This result shows that the actuator has the potential to be used in the guidance system of a capsule endoscope.

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This paper describes a study on the effect of structural differences in collagen fibers on the spin-spin (T2) relaxation and the apparent diffusion coefficient (ADC) of water molecules. Two collagen gels were polymerized from a type-I collagen solution with and without a 4.7 T magnetic field. The T2 relaxation time was measured by the Carr-Purcell-Meiboom-Gill (CPMG) sequence. The ADCs were measured using a stimulated echo sequence with motion probing gradient (MPG) pulses. The temperature in the bore was 15 degrees Celsius. The T2 relaxation times of water molecules in the collagen gels with magnetically oriented fibers and randomly oriented fibers were T2 = 0.52 s and T2 = 1.32 s, respectively. The ADCs of water molecules measured with MPG directions parallel and perpendicular to the collagen fibers were ADC = 2.08 × 10^-9 m²/s and ADC = 1.92 × 10^-9 m²/s, respectively. These differences are attributed to a change of collagen fiber structures due to the magnetic orientation.

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To operate a SQUID magnetometer in a magnetically unshielded environment, it is important to ensure that a flux-locked loop (FLL) circuit has a very wide dynamic range without decreasing its resolution. Digital FLL (D-FLL) satisfies these conditions: its dynamic range is expanded by jumping a working point on the SQUID's periodic Φ-V characteristic and counting the number of such events. We propose a double-counter system, which has two counters: one on a one-chip microcontroller and the other on a host computer. We developed a D-FLL system by using a double-counter with general-purpose operational amplifiers, digital-to-analog converters, and a microcontroller. The effectiveness of the double-counter is shown, and a description is given of how the D-FLL system was used to operate a magnetocardiogram (MCG).

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In this study, we investigated whether very-low-frequency (VLF) magnetic fields induce DNA damage or physiological abnormality in bacterial cells containing bacteriophage λ. After exposure to magnetic fields (20 kHz, 1 mT and 20 kHz, 0.5 mT) for about 4 and 8 hours, the prophages shifted to lytic growth more often than control group, and after exposure to an extremely-low-frequency (ELF) magnetic field (60 Hz, 45 mT) for 8 hours, they shifted to lytic growth twice as often as the control group. These results suggest that both VLF (20 kHz, 1 mT and 20 kHz, 0.5 mT) and ELF (60 Hz, 45 mT) magnetic fields induce physiological damage in bacterial cells.

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We investigated the effects of repetitive magnetic stimulation on tumor development processes and immune functions. A circular coil (inner diameter = 15 mm, outer diameter = 75 mm) was used in experiments. The stimulus conditions were as follows: peak magnetic field = 0.25 T (at the center of the coil), frequency = 25 pulses/sec, 1000 pulses/sample/day. Magnetically induced eddy currents in mice = 0.25 T: 0.79−1.54 A/m². B16-BL6 melanoma model mice were exposed to the magnetic stimulation for 16 days from the day after the injection of cancer cells. Tumor growth study revealed a significant decrease in the tumor weight of the stimulated group (56% vs. a sham group, 41% vs. a controls). B16-BL6 cells were also exposed to the magnetic stimulation (1000 pulses/sample). However, magnetically induced eddy currents had no effect on B16-BL6 cell viabilities. Contrary to the cell viability study, proliferation activities of mice spleen cells were up-regulated by the magnetic stimulation. TNF-α production was also activated in the stimulated mice. These results indicate that the immune functions were up-regulated by the magnetic stimulation, resulting in decreased tumor weight in the tumor model mice. And they also show the potential for therapeutic use of magnetic stimulation in cancer treatment.

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Detection of weak magnetic fields induced by electrical currents using magnetic resonance imaging (MRI) is necessary for mapping neuronal activities in the brain. However, such detection is dependent on the signal-to-noise ratio and sensitivity limit of MRI. Evaluation of these factors requires calculation of radiofrequency (RF) electromagnetic fields in the brain. To determine the feasibility of detecting the magnetic fields induced by neuronal activities, we computed brain eddy current distributions induced by RF magnetic fields from a birdcage coil in MRI by simulations based on the finite element method (FEM), and calculated Johnson noise from the head. With commonly used parameters, the noise was 43.2 nV. On the basis of a theory of the signal-to-noise ratio in MRI, we obtained an equation for the theoretical sensitivity limit for detecting weak magnetic fields by using gradient echo phase images. The theoretical sensitivity limits for gray matter and white matter were 26.1 nT and 21.7 nT, respectively.

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