Magnetic force microscope (MFM) tips are prepared by coating Si tips of 5, 4, and 3 nm radiuses with Co films by varying the thickness in a range between 5 and 80 nm. The effects of base-Si tip radius and coating thickness on the MFM spatial resolution are investigated. With increasing the thickness from 5 to 20 nm, the resolutions of MFM tips prepared by using Si tips of 5, 4, and 3 nm radiuses improve from 10.2 to 7.7 nm, from 12.1 to 7.3 nm, and from 12.1 to 6.6 nm, respectively. This is due to an increase of signal detection sensitivity related with the coating thickness. With further increasing the thickness, the resolution declines due to an increase of tip radius. The resolution is affected by both the detection sensitivity and the tip radius. A higher resolution is obtained by using a sharper base-Si tip. Magnetic bits of a perpendicular medium recorded at 1900 kFCI (bit length: 13.4 nm) are distinguishable in the MFM image observed by using a tip prepared by coating Si tip of 3 nm radius with 20-nm-thick Co film. An MFM tip prepared by coating sharp base-tip with Co film of optimized thickness is useful to investigate the magnetization structure of future recording media.

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  A technique of light energy transfer for thermally assisted magnetic recording must be the crucial breakthrough not only to confine an optical near-field spot onto a medium efficiently but also to prevent the temperature from rising in a HDD recording head. A waveguide with a plasmon antenna is investigated using a finite-difference time-domain simulation. For the results, an optical near-field antenna with an apex radius of 12 nm and a protruding structure can confine a light down to 8.5 nm full width at half maximum in intensity, even on a continuous medium. Matching the wavenumber of the incident light to that of a surface plasmon polariton by adjusting the incident angle is a useful technique to transfer energy. The efficiency of light delivery with the plasmon waveguide is 60% greater than the efficiency without the plasmon waveguide.

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  All-optical magnetic recording by applying circularly polarized light is a promising new technology for ultra-fast speed recording. This technique can control the direction of magnetization without any applied magnetic field. It is, however, unsuitable for creating small magnetic domains for high density recording, because optical spot size is restricted to the diffraction limit. Previously, we proposed methods to generate a localized circularly polarized light by localized surface plasmon antennas (LSPA), and to utilize a surface plasmon polariton waveguide (SPPW) for high efficiency in energy propagation. This study investigates a new antenna array that combines plasmon cross antenna and high efficient SPPW. The circular polarization is evaluated by the degree of circularity C and power intensity of electric field I. The circularly polarized light of 5 nm in diameter is located at the center of the LSPA, which keeps the C value at 0.8. It is revealed that the confined circular polarization can be generated by the LSPA with SPPW.

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  To study thermally assisted magnetic recording focusing on surface plasmon effect as well as thermal diffusion effect, a 90-femto-second laser pulse impinged upon surface plasmon antennas on Co₅₅Pt₃₀Cr₁₅-SiO₂ granular film. It is important to use a femto-second laser pulse to analyze those effects, because the effects can be degraded by the thermal diffusion during the laser pulse duration if a longer laser pulse is applied. A SiN dielectric inter-layer was fabricated to keep an accurate distance between the antennas and the granular film. Written magnetic domains caused by surface plasmon effect were clearly observed by a magnetic force microscope. The minimum domain corresponded to 166 nm × 120 nm in size even though the laser spot diameter was about 50 μm. The surface plasmon effect was evaluated by the Finite-Difference Time-Domain method, and the thermal diffusion effect was also calculated to study thermally assisted magnetic recording.

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  Magnetic and fluorescence properties of Ce:YAIG (Ce_yY_3-yAl_5-xFe_xO₁₂) nanocrystals synthesized by co-precipitation and annealed at 1273 K for 4 hours have been investigated. The structural characterization by X-ray diffraction shows that the samples with 0 ≤ x ≤ 5.0 and 0 ≤ y ≤ 0.2 are in the garnet phase. With increasing x from 0 to 5.0 while y maintained at 0.06, ｔhe lattice constant gradually increases from 12.04 nm to 12.40 nm. When y is increased with x fixed at 3.0, only garnet peaks are observed for 0 ≤ y ≤ 0.15, while CeO₂ appears to be present besides the garnet when 0.15 ≤ y ≤ 0.2. The saturation magnetization of Ce:YAIG is found to increase from 2.21 emu/g for y = 0 to 4.35 emu/g for y = 0.06 at x = 3.0. With increasing x from 0 to 3.0 at y=0.06, the fluorescent peak observed at ～520 nm gradually diminishes, indicating that the fluorescence of Ce:YAIG is not only dependent on the presence of Ce³⁺ at the dodecahedral sites but also sensitively on the ratio of Al³⁺ to Fe³⁺ at the octahedral and tetrahedral sites in the garnet.

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  Switching field reduction and applied field dependence of the switching field of 2 to 4-layer exchange coupled composite (ECC) dots were studied. The analysis was performed based on a simple spin-model. For 2-layer ECC dots, minimum switching field normalized by the averaged anisotropy field, h^*, was obtained for zero anisotropy for the soft layer. For 3-layer ECC dots, smaller values of h^* were obtained for a small anisotropy field, H_k, of the second layer, and minimum h^* of 0.46 was obtained. Smallest applied field angle dependence of the switching field was also obtained for the structure with the smallest h^*. For 4-layer ECC dots, smaller h^* values were obtained for a small H_k of the third layer regardless of H_k of the second layer. The smallest h^* value of 0.42 was obtained which is smaller by only 7 % from that for 3-layer ECC dots. It was concluded that 3-layer ECC dots with a small H_k (around 0.2 times of the hard layer) for the second layer is the best choice for practical applications.

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  The recording density limit of shingled magnetic recording (SMR) and ion-irradiated bit patterned media (BPM) are studied for the perpendicular continuous thin film media and exchange-coupled composite (ECC) media. Under the comprehensive consideration of writability and thermal stability, the source of the noise is investigated, and the signal to noise ratio (SNR) is analyzed versus the recording density. In SMR with density of 0.6-1.2Tb/in², under the same thermal stability, ECC media shows 1-3dB increase in SNR than the conventional continuous media. The noise of BPM recording is compressed in the ion irradiated region between bits and influences SNR greatly.

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  Spin-wave stiffness constant, D, and the Curie temperature, Tc, were evaluated from the magnetization measurements in order to investigate the exchange interaction between Fe and Co in a wide range of concentrations for {(Fe_xCo_1-x)_0.75Si_0.05B_0.2}₉₆Nb₄ amorphous ribbons. It was found that Tc showed a maximum in the middle concentration range of x, although the spontaneous magnetization, M_s, increased with increasing Fe concentration x. The behavior of the concentration dependence of Tc was well explained by the product of D and M_s, that is, simply by the mean field approximation based on the Heisenberg model.

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  The crystal structure and electromagnetic properties of soft magnetic hexagonal ferrites for high frequency devices, and the practical use of Y- and Z-type ferrites are discussed. These X- and U-type ferrites were successfully synthesized, and their electromagnetic properties were investigated. Soft magnetic hexagonal ferrites are promising for high frequency magnetic materials because of their greater anisotropy field and higher resonance frequency. High initial permeability and resonance frequency are required for magnetic materials. When the average grain size decreases, the Q value increases in samples of Y- and Z-type ferrites. The permeability of Co₂Z ferrite was analyzed using two different magnetizing mechanisms. When the grain size decreased, the magnetization mechanism changed from domain wall motion to spin rotation magnetization. These ferrites have great practical potential for inductors, antennas, electromagnetic compatibility/electromagnetic interference (EMC/EMI) filters and wave absorbers. New markets for ferrites should open up when a low temperature ceramic co-firing (LTCC) process is established.

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  The purpose of this study was to clarify the role of pre-existing dislocations on the mechanical and magnetic properties of neutron-irradiated steels. Magnetic domain observation of electron-irradiated well-annealed iron revealed that irradiation defects actually disturbed domain wall movement. Pre-deformed pure iron and iron-based alloys were neutron-irradiated, and their hardness and magnetic hysteresis loops were measured. Decreasing behaviors in coercivity suggest the domain walls moved more easily after irradiation. Also, the role of pre-existing dislocation is discussed by taking into consideration the change in hardness.

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  We investigated reduction in an eddy current loss for a power coupler in an electrodeless discharged lamp with our previously proposed analysis method for plasma in the lamp. We confirmed that a large eddy current flow was observed at the top of an Al stage in the power coupler and the loss was reduced by a decrease in the height of the Al stage. This result suggests that a decrease in the height is effective to reduce wasted power losses and implies the possibility of an improvement in the lamp efficiency. We also confirmed that upward-moving and moderate-elongation of the ferrite core in the power coupler is effective to reduce the wasted loss. In order to verify the result, we evaluated the lamp efficiency of a lamp with a modified power coupler. Resultantly, the lamp efficiency was increased by approximately 3 lm/W (lumen per Watt). Therefore, we can conclude that reducing the eddy current loss in the power coupler is one of the important factors to obtain high lamp efficiency.

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  The applications of powder cores to very high power conversion equipment have recently been spreading. Fe-Si alloys are effective in downsizing magnetic cores because they have large degrees of magnetization. However, core loss needs to be further reduced. The relationships between core losses for Fe-3mass%Si powder cores made under various conditions were investigated in this study, i.e., hysteresis losses, classical eddy current losses, and anomalous eddy current losses including the sizes of their particles and crystal grains. We found that hysteresis losses decreased as crystal grains increased in size. We confirmed that not only there were classical eddy current losses generated uniformly in particles, but also anomalous eddy current losses occurred. The anomalous eddy current losses suggested that they were due to domain wall movement, and they decreased with decreasing crystal grain sizes. Their exponents of the frequency dependency of anomalous eddy current losses varied between 1.5 and 2.0 depending on test conditions, and they reflected the change in the number of domains with frequency.

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  We studied effect of magnetoelastic anisotropy and role of defects on domain wall (DW) dynamics and remagnetization process of magnetically-bistable microwires. We manipulated the magnetoelastic anisotropy changing the ratio between the metallic nucleus diameter and glass coating thickness and applying the tensile stresses. Application of stresses resulted in increase of the switching field and decrease of the DW velocity, v. The role of defects existing in magnetically bistable microwires is related with nucleation of new reversed domains. Abrupt jumps on v(H) dependences correlate with defects existing in microwires. Annealing allows considerably increase DW velocity, enhances the magnetic field range of single DW propagation regime and domain wall mobility.

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  The Fe_100-xCo_x alloy thin films with dilute Co concentrations (x < 11) were prepared on GaAs(001) substrates by RF magnetron sputtering, and their dynamic magnetic properties were investigated by ferromagnetic resonance spectroscopy operating at Q-band (35 GHz). The magnetization curves measured by VSM show clear dependence on the in-plane field directions, indicating bcc Fe_100-xCo_x films were epitaxially grown on the substrates. The ferromagnetic resonance linewidths include both intrinsic and extrinsic magnetic damping. The origins of the latter were examined to extract the intrinsic damping. The estimated upper bounds of the Gilbert damping constants, caused by the intrinsic damping, depend on the Co compositions; the damping is accelerated as Co concentration increases in the region with x < 11.

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  A magnetoelectric (ME-) interaction such a multiferroic property as the dielectric permittivity ε_r’ (the real part of the complex permittivity) is changed by magnetic field H, Δε_r’(H), was studied in nano-composite oxide films of the Bi₂O₃-Fe₂O₃-PbTiO₃ system prepared by rf-reactive sputtering. In our past studies, vacuum-evaporated Al film was deposited on the film surface to form the planar capacitor to measure the dielectric properties. However, the temporal change of Δε_r’(H), was occasionally observed. In the present study, we replaced Al-film with sputtered In-Sn-O (ITO) film and succeeded to reduce greatly the thermal instability. Thus we can obtain more precise and reliable data of Δε_r’(H), which enables us to elucidate the mechanism of this phenomenon.

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  Magnetic graphene-ribbon is a candidate for realizing future ultra high density 100 tera bit/inch² class data storage media. Multiple spin state analysis was done based on the density functional theory. A typical model has a super-cell [C₈₀H₇] which keeping bare (radical) carbons on one side zigzag edge, whereas mono hydrogenated carbons on another side. Optimizing atomic configuration, self-consistent calculation demonstrated that a total energy of the highest spin state is more stable than that of the lower one, which origin comes from the exchange coupling between carbons. This analysis suggested a capability of designing magnetic data track utilizing such asymmetric graphene ribbon. In order to increase areal magnetization density, bi-layer and quadric layer model were analyzed. Detailed calculation resulted that also the highest spin state is the most stable one. Increasing layer numbers is an effective way to enhance strong magnetism.

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  Co₇₅Pt₂₅ (at. %) alloy thin films are prepared on MgO(111), SrTiO₃(111), and Al₂O₃(0001) single-crystal substrates by varying the substrate temperature from room temperature to 600 °C. Co-Pt epitaxial thin films with the close-packed plane parallel to the substrate surface are grown on these single-crystal substrates. The film structure is determined by considering the order degree and the atomic stacking sequence of close-packed plane. Metastable ordered phases of B_h and D0₁₉ are partially formed in A3 structure for the films grown on these single-crystal substrates at temperatures between 200 and 500 °C. Higher order degrees of 0.17, 0.26, and 0.19 are observed for the films grown at 300, 400, and 300 °C on MgO, SrTiO₃, and Al₂O₃ substrates, respectively. The ordered phase is preferentially formed around 300 °C. The films including the ordered phase show strong perpendicular magnetic properties reflecting the magnetocrystalline anisotropy of ordered crystal.

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  The negative uniaxial magnetocrystalline anisotropy (K_u) was evaluated for various compositions of Co_100−xIr_x thin films with respect to the atomic layer stacking structure. Pure Co film fabricated at a substrate temperature (T_sub) of 600 ℃ was found to have a positive K_u of 6.1×10⁶ erg/cm³. With increasing x, the sign of K_u changed from positive to negative, and the negative K_u took a maximum value of −9.6×10⁶ erg/cm³ at around x = 20 at. % for films fabricated at T_sub = 600 ℃. Adding more Ir decreased the absolute value of the negative K_u which became 0 over x = 50 at. %. X−ray diffraction analysis and scanning transmission electron microscopy revealed that the atomic layer stacking structure of the Co_100−xIr_x films changed from −A−B−A−B− (hcp) to −A−B−C−A−B−C− (fcc) stacking with increasing Ir content. Moreover, Co₈₀Ir₂₀ grains were revealed to consist of 2 kinds of randomly located composition−modulated atomic layers, nearly pure−Co and pure−Ir layers, while Co and Co₅₀Ir₅₀ had disordered structures. In this paper, a new perspective on the atomic layered structure with superlattice diffraction, which is different from the conventional “ordered structure”, is discussed.

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  This paper describes a study of the magnetic behavior of ultrathin Co/Pd multilayers deposited on Ru/Ta buffer layers deposited on untreated Si wafers. The ultrathin Co/Pd multilayer requires atomically smooth surface/interface in order to exhibit ferromagnetic behavior as well as perpendicular magnetic anisotropy. Our structural analysis demonstrates the interfacial intertwining leading to surface roughness. The corresponding hysteresis loops justify the strong correlation between interfacial roughness and magnetic behavior.

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  An FePd/MgO/FePd tri-layer film is prepared on an SrTiO₃(001) single-crystal substrate by employing a two-step method consisting of sputter deposition at 400 ℃ followed by annealing at 600 ℃. An L1₀-FePd(001)single-crystal lower layer with the c-axis perpendicular to the substrate surface is obtained on the SrTiO₃ substrate. An MgO(001) single-crystal layer is formed on the FePd lower layer. An FePd upper layer epitaxially grows on the MgO interlayer. The upper layer consists of L1₀(001) crystal involving a small volume of L1₀(100) crystal with the c-axis parallel to the substrate surface. The order degrees of L1₀(001) crystals in the FePd lower and the upper layersare 0.67 and 0.65, respectively. A very flat surface is realized for the tri-layer film. The tri-layer film shows a perpendicular magnetic anisotropy reflecting the magnetocrystalline anisotropy of L1₀(001) crystal. A formation of fully epitaxial L1₀-FePd/MgO/L1₀-FePd tri-layer film with a perpendicular magnetic anisotropy is demonstrated.

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  FeNi powders were synthesized by reductive reaction of iron nickel chloride below 320℃. Calcium hydride （CaH₂）was used as a reductant. The coercivity of synthesized powders depends on the amount of CaH₂, and the largest coercivity of 54 kA/m was obtained. The (001) diffraction line due to the L1₀ superstructure was observed by anomalous synchrotron X-ray diffraction using synchrotron radiation, indicating the formation of L1₀-FeNi.

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  FePd, FePt, and CoPt alloy epitaxial thin films are prepared on SrTiO₃(001) single-crystal substrates at 600 ℃ by using an ultra-high vacuum radio-frequency magnetron sputtering system. L1₀ ordered phase formation is recognized for these films. The FePd film consists of L1₀(001) single-crystal with the c-axis perpendicular to the substrate surface, whereas the FePt and the CoPt films involve two L1₀(100) variants, whose c-axes are lying in-plane and rotated around the film normal by 90° each other, in addition to L1₀(001) variant. A higher long-range order degree is observed in the order of FePd (0.61) > FePt (0.35) > CoPt (0.16). The FePd film shows a perpendicular magnetic anisotropy, while the FePt and the CoPt films show in-plane magnetic anisotropies. The magnetic property is influenced by the c-axis direction and the order degree.

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  We attempted to synthesize Fe filled carbon nanocapsules with a narrow size distribution and high magnetization by a discharge in ethanol. Most of the particles found in the as-synthesized soot were less than 40 nm in diameter. High-resolution transmission electron microscope measurements revealed that particles had a core − shell structure and their shells are composed with some graphite layers. Occasionally, carbon particle without any cores were found as impurities. Selected area electron diffraction and temperature dependent magnetization indicated that α-Fe and γ-Fe nanoparticles were encapsulated in carbon cages and they were single crystals. Fe₃C also existed in the soot. After the temperature cycle measurement of magnetization went up to 680 ℃, the nanocapsules showed an increase in magnetization at 10 kOe from 77 emu/g to 100 emu/g owing to a phase transition from γ-Fe to α-Fe, however, the graphite shells of some nanocapsules seemed to be deformed. An annealing treatment at 500 ℃ on the as-synthesized soot was able to increase the magnetization at 10 kOe to 92 emu/g without any deformations of graphite shells.

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  Ni single-crystal films of (001) orientation are prepared on Cu(001) buffer layers hetero-epitaxially grown on MgO(001) single-crystal substrates by varying the thickness in a range between 40 and 500 nm. The influence of film thickness on the magnetostriction behavior under in-plane rotating magnetic fields is investigated. A 40-nm-thick film shows a four-fold symmetry in in-plane magnetic anisotropy. The magnetic anisotropy decreases with increasing the thickness and a 500-nm-thick film shows an almost isotropic magnetic property. A triangular output waveform of magnetostriction is observed when the 40-nm-thick film is measured under low magnetic fields. The triangular behavior is related with the motion of magnetic domain walls in the magnetically unsaturated film under rotating magnetic field. With increasing the magnetic field, the film approaches to magnetic saturation and the waveform shifts to a sinusoidal shape. On the contrary, the 500-nm-thick film shows sinusoidal waveforms under low rotating fields. The magnetostriction behavior of Ni(001) single-crystal film is delicately affected by the magnetization structure which depends on the effective in-plane magnetic anisotropy.

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  Spin waves are promising phenomenon for the future spintronic devices. The stable excitation of continuous spin wave is crucial technology for the realization of the signal processing devices. To obtain the basic characteristics of continuously excited spin wave, we fabricated asymmetric transmission antennas on a Ni₈₁Fe₁₉ thin film in order to excite and detect the signal of continuous spin waves. By controlling an external magnetic field and an rf magnetic field, we observed a waveform of propagating spin wave in time domain. We examined the stability of magnetostatic spin wave waveforms by analyzing the time domain signals, and proved that the signals keep clear sinusoidal waveform up to 20μm propagation distance. The monochromaticity of excited wave was investigated by calculating Fourier spectrum, showing a narrower full width half maximum (FWHM) than the previously used pulse excitation method.

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  The dynamics of a spin-torque-oscillator (STO) coupled with a nano-magnet through dipole-dipole interaction was studied numerically by using the macrospin model for the application of the STO as a read head sensor for hard disk drives. We found that the current, which is necessary to induce the oscillation of the free-layer (FL) of the STO, strongly depends on the distance between the FL and the nano-magnet as well as on the relative orientation of the magnetizations between them. It is essential to consider the dynamics of the dipole-coupled nano-magnet to determine the dynamics of the STO. We found that we were able to detect the orientation of the magnetization of a nano-magnet, or a recording-bit, by modulating the oscillation frequency of the STO.

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  Fully-epitaxial NbN/Co₂MnSi bilayer films were grown on MgO(001) single crystalline substrates by a sputter technique. Structural, electric transport and magnetic properties were investigated for the fabricated films. The resulting NbN/Co₂MnSi bilayer films show superconducting critical temperature T_c was of 16.0 K and the saturation magnetization M_s at room temperature was of 790 emu/cm³. The electric resistivity of the fabricated films was also measured under magnetic fields and the upper critical field B_c2 was estimated to beB_c2 > 30 T in the case of the applied magnetic field parallel to the MgO(001) single crystalline substrate. In addition, NbN/Co₂MnSi junctions were made by an electron-beam lithography technique. The enhancement of a zero-bias conductance peak (ZBCP) was observed in differential conductance in the NbN/Co₂MnSi junctions. The ZBCP disappeared above T_c = 16.0 K of superconducting NbN films.

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  In order to investigate the Mn solubility in the GaInAs semiconductor alloys in bulk and that in an elastic tetragonal constraint from GaAs substrate, the formation energy and temperature-composition phase diagram of the pseudo-ternary (Ga,In,Mn)As alloys were obtained based on first principles calculations. Results predict a phase separated type phase stability, and the Mn solubility in the pseudo-ternary (Ga,In,Mn)As alloys increases compared to that in the pseudo-binary (Ga,Mn)As and (In,Mn)As alloys, due to an asymmetry of local atomic (Ga and In) alignments surrounding the Mn atoms in the solid solution. For the system under the tetragonal constraint from the substrate, the formation energy of the solid solution becomes lower than that in the bulk, and the phase diagram indicates that the Mn solubility significantly increases.

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  Magnetic force microscope (MFM) tips are prepared by coating three-sided pyramid base Si tips of 4 nm radius with Co film by employing an ultra-high vacuum evaporation system. The effects of film thickness and coating direction on the MFM spatial resolution are investigated. For a thickness of 10 nm, the one-side coated MFM tip has a lower MFM signal detection sensitivity and a lower resolution compared with those of the two- and the three-side coated tips due to that the volume of film coated around the top part of base tip is smaller in the case of one-side coating. With increasing the thickness from 10 to 20 nm, the detection sensitivity increases and the resolution improves regardless the coating direction. As the coating thickness further increases, the resolution deteriorates due to the increases in radius and surface roughness of tip. The MFM tips prepared by coating one-, two-, and three-sides of base tips with 20-nm-thick films show resolutions of 7.7 ± 0.2, 7.3 ± 0.2, and 6.9 ± 0.2 nm, respectively. Higher resolutions are observed in the order of one- < two- < three-side coated tip. The top parts of one-and two-side coated tips are slightly bent toward the film coating directions. The tip bending is interpreted to decrease the resolution. The resolution is influenced by both tip shape and detection sensitivity.

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  We measured the high-resolution magnetic images using an STM-SQUID microscope that combines a high-T_c superconducting quantum interference device (SQUID) with a scanning tunneling microscope (STM). In the STM-SQUID microscope, the STM probe plays the important role of a flux guide and is responsible for tunneling current detection. Therefore, it is essential to investigate the probe itself in order to improve the magnetic image resolution. We optimized the electrochemical polishing condition to realize the fine probe with a tip radius of 50 nm or less. We fabricated the various shaped probes by controlling the voltage during sharpening. The tip radius of 50 nm or less was achieved when the probe tip was sharpened at the applied voltage of 30 V. We then measured the magnetic images of typical magnetic materials, such as a steel sample and nickel thin films, using the probe with a tip radius of 50 nm or less. The magnetic domain structures were observed clearly.

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  The switching field distributions in GMR devices with GdFe free layers of Si/Ru (3 nm)/Cu (75 nm)/Ru (3 nm)/Cu (70 nm)/Ru (13 nm)/TbFeCo (10 nm)/CoFe (1 nm)/Ag (6 nm)/ GdFe (16.5 nm)/Ru (3 nm) were studied by using high-resolution magneto-optical (MO) microscopy. The MO images of patterns with shapes of circles, triangles, squares and hexagonals, and in various sizes with lengths along one side of 200 nm-50 μm and periods of 1-100 μm are studied. The high-resolution MO microscope had a CaF₂ zoom lens that allowed us to obtain a spatial resolution as high as 200 nm. The switching field distributions were measured for the patterns with lengths along one side of 5-50 μm by analyzing the MO images.

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  A simple new system to measure two-dimensional local magnetic properties is presented in this paper. We developed a new transducer that uses two amorphous cores, which enables measurements in a high magnetic induction range up to 1.0 T. Although the experimental results demonstrated the validity of the measurement system, these results contained ～10% error in iron losses. A double-sided excitation structure was examined to reduce the iron losses.

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  A laser-SQUID microscope can measure the local magnetic field induced by laser excitation. We obtained four magnetic images over a polycrystalline Si solar cell sample with a needle probe, playing a role as a flux guide from the sample surface to the SQUID, symmetrically shifted in four directions around the laser spot. Then, we converted the photocurrent density image showing the constant background contrast from the measured four magnetic images, although the magnetic images had the gradually inclined contrast due to the top electrode influence. The fine contrast changes corresponding to the defects were clearly observed in the converted current image.

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  This paper describes a wireless ammonia sensor that employs the resonance frequency change in a curved magnetic ribbon coated with poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT/PSS). As PEDOT/PSS expands due to the sorption of ammonia molecules, the curvature of the ribbon is decreased with increasing ammonia concentration, P_am. The decrease in curvature reduces the mechanical resonance frequency from 105 kHz at P_am = 0% to 89 kHz at P_a= 10%. We also confirmed that the resonance frequency is proportional to the curvature and that the proportional constant is 0.33 kHz/m^-1. Since the mechanical vibration of the ribbon is excited by applying AC and DC fields and is detected by monitoring the voltage induced on a pickup coil, the P_am value around the ribbon can be detected wirelessly.

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  Magnetic force microscope (MFM) tips are prepared by coating Si tips of 4 nm radius with CoPt-alloy films at 300 ℃ varying the thickness in a range between 10 and 200 nm. L1₁ ordered phase formation is recognized for the CoPt film. The influences of coating thickness on the spatial resolution and the switching field of MFM tip are investigated. With increasing the thickness from 10 to 30 nm, the resolution improves from 10.2 to 7.3 nm due to anincrease of signal detection sensitivity related with the remanent magnetization (M_rt) of coated film. As the thickness further increases, the resolution decreases due to an increase of tip radius. The resolution is influenced by both the detection sensitivity and the tip radius. The switching field monotonically increases from 1.7 to 5.8 kOe with increasing the thickness from 10 to 200 nm. High switching fields are obtained, which are interpreted to be reflecting the magnetocrystalline anisotropy of L1₁ ordered phase included in CoPt film. An MFM tip coated with CoPt film including L1₁ ordered phase is useful for the observation of magnetic domain structures of future HDD media and permanent magnets.

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  This paper presents a novel flux barrier type outer rotor interior permanent magnet (IPM) motor that has both rare-earth and ferrite magnets. The proposed IPM motor has two air layers in the outer rotor. The rare-earth magnets are inserted into the first layer, while the ferrite magnets are placed into the second one. The torque of the proposed IPM motor is larger than that of the reference one, although the volume of rare-earth magnets is almost half. Both the magnet and reluctance torques of the proposed IPM motor have been improved. The validity and availability of the proposed IPM motor were proved by experiments and finite element method (FEM).

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  Magnetic gears, which can change torque and speed without any mechanical contacts, have some advantages in comparison with conventional mechanical gears as follows: low vibration and acoustic noise, high reliability, and low maintenance. This paper presents an optimum design method for a surface permanent magnet (SPM) magnetic gear based on reluctance network analysis (RNA). The RNA has desirable features including a simple analytical model, high-speed and accurate calculation, and ease of coupled analysis. The validity of the proposed method is proved by comparing with another method based on finite element analysis (FEA) and experiment.

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  A surface permanent magnet (SPM)-type vernier motor is a synchronous motor that generates large torque at a low speed. In the vernier motor, the number of slots, the pole of the rotating magnetic field on the armature, and the number of field poles on the rotor are constructed based on the vernier principle. In this paper, six magnetic pole combination types of these parameters are investigated by using a 36-slot stator, and the output characteristics, including the pull-out torque, are shown. These characteristics, calculated by torque and current equations, can be analyzed easily by investigating the induced electromotive force E₀ and the synchronous reactance x_s. For the optimal design of the SPM-type vernier motor with a 36-slot stator, it is clarified that one magnetic pole combination (S36-R68-P4, R/P:17) is effective for achieving a motor with high torque, and another magnetic pole combination (S36-R60-P12, R/P:5) is effective for achieving a motor with a high power factor.

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  A switched reluctance (SR) motor has an extremely simple and robust structure, and high heat capability because of no magnet. Therefore, these advantages are suitable for an application of the in-wheel SR motor to electric vehicles. This paper presents an in-wheel SR motor improved torque density. The proposed SR motor has two features for improvement of torque density; the first one is asymmetrical rotor pole structure that torque is improved in only one rotational direction; the second one is the overlap of the excitation to increase effective voltage. In the proposed SR motor, the maximum torque volume ratio is about 38 N・m/L.

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  This paper presents a method for calculating eddy current loss in a permanent magnet (PM) of a surface permanent magnet (SPM) motor based on electric and magnetic networks. First, a reluctance network analysis (RNA) model of the SPM motor and coupling between the RNA model and electric network model are described. Then, the eddy current loss in the magnet of the SPM motor from no load to full load current conditions including and excluding carrier harmonics are calculated by the proposed model. Finally, it is demonstrated that the RNA model can be taken the effect of division of the magnet into consideration to reduce the eddy current loss in the magnet.

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  One of the hyperthermia therapies is hgh-frequency induction heating type by using nano-mgnetic materials and magnetic implants. A tumor with injected magnetic materials is heated by hysteresis loss and eddy-current loss under high frequency magnetic fields with a few handred kHz. To generate magnetic fields at the deep position of a body, we proposed a double pancake type exciting system with wireless power transmission. Since this system is constituted by two tuned resonant circuits, the characteristic is sensitive to the change of parameters.
  This paper discusses the fluctuations of resonance frequency depending on the change of a distance between the exciting and induced coils and resonance capacitor. As a result, we recognized the fluctuation range of the resonance frequency for a tuned exciting power source.

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  The fine magnetic materials having a high heat generation ability in an AC magnetic field have been studied for use in new thermal coagulation therapy. The fine ferrite powder about La³⁺ added MgFe₂O₄ was prepared by beads milling. The highest heat generation properties of the La³⁺ added MgFe₂O₄ was obtained at milled for 240min using 0.1 mmφbeads. The maximum heat generation ability and hysteresis loss value were obtained for ca. 8.6nm in crystal size. A physical milling method using bead milling was very effective for preparing the nano-sized La³⁺ added MgFe₂O₄ powder.

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  Mg_0.4Cu_0.6Fe₂O₄ ferrite with the highest heat generation ability in AC magnetic field for the Mg_1-XCu_XFe₂O₄ (X=0-1.0) series was prepared by the solid reaction method, and then bead milled to examine the effect of particle size on the heat generation ability. Nanosized Mg_0.4Cu_0.6Fe₂O₄ was obtained by bead milling using 0.3 mm and 0.1 mm diameter ZrO₂ beads. The heat generation ability increased with decreasing particle diameter to ca. 16.1 nm. However, the heat generation ability decreased with decreasing particle diameter below 14.6 nm.

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  We developed a magnetic nanoparticle (MNP) imaging system that uses the second harmonic signal of MNPs. Detecting the second harmonic signal, we could significantly decrease the interference of the excitation field and obtain a clear signal from MNPs. We showed that the present system can detect a 100-μg MNP sample located at a depth of 30 mm from the pickup coil. We also developed a method to accurately estimate the sample position. For this purpose, we measured the contour map of the signal field. From the measurement of the x and y components of the signal field, B_x and B_y, we could estimate the sample depth z. With the estimated z, the contour map of the B_z field was converted to an MNP distribution map using a mathematical technique called singular value decomposition (SVD). We could clearly distinguish two MNP samples separated by Δx = 20 mm and located at z = 20 mm. We also show the robustness of the SVD analysis by demonstrating that the MNP distribution can be accurately estimated even when a ±5 mm error exists in the depth estimation. This simple imaging system will be useful for in-vivo application, especially for sentinel lymph node detection.

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  We present a magnetic noise rejection method using wavelet transformation (WT) and independent component analysis (ICA) for analyzing magnetocardiograms (MCGs). In the ICA, when the signal-to-noise (SN) ratio of the data is low, the accuracy of the noise rejection becomes low and the determination of the contraction dimension becomes difficult. For example, MCG has a very low SN ratio in patients who have a wire surgically fixed in their sternum. To solve this limitation, we have proposed a method to distinguish signal and noise components using Mahalanobis distance and WT as pre-processing for ICA. We carried out a simulation which attached a wire to a normal subject in order to show accuracy improvement of the noise rejection by the proposed method. The SN ratio of measured MCG was the -6dB. The correlation coefficient of waveform after noise rejection with control data (waveform without the wire noise) was calculated. As this result, it became 0.98 high value. The proposed method was effective for the wire noise rejection.

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  Novel multifunctional superparamagnetic and optical nanohybrids are fabricated for biomedical applications. This architecture involves a silica core surrounded by a thin shell of FePt that is further covered with an outer shell of gold. Polyethyleneimine was utilized as a linker to bridge the FePt shell with the gold shell, which allowed 3-nm gold nanoparticle seeds to be loaded and a uniform gold shell to be formed. These gold and FePt doubly coated silica nanoparticles take advantage of the tunable resonance absorption in the visible and near-infrared (NIR) ranges and can be controlled by using an external magnetic field, which makes them very promising candidates for future biomedical applications.

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