A new method of fabricating patterned media was developed. Circumferential magnetic patterned media were prepared on 2.5-inch-diameter glass plates. A Ni master disk contraining spiral patterns with 60-250-nm-wide lands and a 400-nm-wide groove was pressed against a resist film on a CoPt or CoCrPt film to transfer the spiral patterns. A diblock copolymer solution was cast into the obtained grooves, and then annealed to prepare self-assembling dot structures aligned along the grooves. According to the dot patterns, lower magnetic films were patterned by ion milling to yield patterned media with a 40-nm diameter. The coercive forces and squareness ratios of the patterned media were greater than those of continuous media. Single magnetic domains with an almost perpendicular orientation were confirmed in each magnetic dot.

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A SiO₂-added CoPtCr magnetic layer was employed in perpendicular recording media. The microstructure, magnetic properties, and recording performance of these media are discussed. The addition of SiO₂ to CoPtCr is very effective for enhancing a well-isolated fine grain structure without disturbing the epitaxial growth of CoPtCr grains on a Ru underlayer. Very fine grains with a size of ∼7 nm, are realized, surrounded by grain boundaries which consist mainly of silicon oxide. The media show a large perpendicular anisotropy K_u of ∼3.6 ×10⁶ erg/cm³ and a K_uV/kT value of more than 80, even at a CoPtCr-SiO₂ thickness of 12nm, resulting in a high coercivity H_c of 4.3 kOe and high squareness M_r/M_s of 0.9. The CoPtCr-SiO₂ medium has a very small signal decay of 0.4%/decade at this thickness, and exhibits excellent SNR performance together with high thermal stability at very low thickness, indicating a great potential for use in high-density perpendicular recording media.

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NdFeB thin films with perpendicular c-axis orientation texture have been studied as promising candidates for ultrahigh-density recording media because of their high magneto crystalline anisotropy and large saturation magnetization. Films with composition of Nd₁₈Fe₇₆B₆ and a thickness of 15 nm exhibited perpendicular coercivity as high as 6.0 kOe. The grain size for this film is about 70 nm, as evaluated by SEM surface images. It was found that an increase in B percentage can decrease the grain size to 20 nm with B content up to 15 at.%. The perpendicular coercivity, nucleation field, and grain size for NdFeB films with 12.3 at.% of B and a thickness of 15 nm are 5 kOe, -2.5 kOe, and about 40 nm, respectively.

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A guideline for selecting materials to be used in CoCr-based perpendicular media with high squareness and normalized coercivity was investigated by taking the effects of thermal agitation and intergranular exchange coupling into consideration. The main results are as follows: (1) The current media have a low maximum value of H_c/H_k ^grain of 0.35, which is considered to be due to the effects of thermal agitation for K_u ^grain V_act/kT <150, and intergranular exchange coupling for K_u ^grain V_act/kT > 200. (2) Media with low 4πM_s/H_k^grain and large α tend to show a low positive H_n/H_k^grain. (3) Media with large 4πM_s/H_k^grain and large α tend to show a low effective nucleation field H_n^eff. On the other hand, some media that have low α, with a value of about 1, show positive H_n^eff. The behavior of H_n^eff is considered to be caused by thermal agitation. (4) To realize a medium with S = 1 and α as low as possible, the selection of a material with 4πM_s/H_k ^grain = 0.2-0.3 (for α = 1.6) is promising. This medium is expected to show values of K_u ^grain V_act/kT of 150-200, and of H_c/H_k ^grain of 0.22-0.28. To realize a medium with high H_c/H_k ^grain, 4πM_s/H_k ^grain = 0.6-0.7 (for α = 1.3) is promising. This medium is expected to show values of K_u ^grain V_act/kT of 150, and of H_c/H_k ^grain of 0.35.

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The effect of boron doping on the magnetic and recording performance was examined in [Co (0.4 nm)/Pt (1 nm)]₉ superlattice media, and ways of reducing media noise while maintaining a large perpendicular anisotropy K_u were discussed. The boron was doped only in the Co layer. The K_u was found to decrease as the boron content increased beyond 15 vol.%, while maintaining a large value of 5.7×10⁶ erg/cm³ even at 30 vol.% in the Co layer. Moreover, the addition of boron was found to reduce the strength of intergranular exchange coupling, probably owing to the reduction of the exchange stiffness, resulting in an improvement of the signal-to-medium-noise ratio, SN_mR. It was also shown that the use of an NiAl seed layer for Co/Pt superlattice media enhances grain segregation, resulting in an improvement of SN_mR. However, no significant improvement in SN_mR was achieved by the boron doping for [Co (0.4 nm)/Pt (1 nm)]₉ media with an NiAl seed layer.

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The Ar gas pressure P_Ar, the thicknesses of Co and Pd layers, and the number of layers were optimized in Co/Pd multilayers for perpendicular magnetic recording media. A high squareness ratio S and high coercivity H_c were obtained in a [Co (0.2 nm)/Pd (0.6 nm)]₂₀ film prepared at P_Ar of 30 mTorr. The relationship between the surface roughness R_a and H_c was examined. It was concluded that the top region of the multilayers exhibited higher H_c, while the bottom region revealed degraded H_c. Large R_a and smaller grain size are essential for attaining high H_c in Co/Pd multilayers.

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The inclination of the magnetization characteristic around the coercivity, λ(=(dM/dH)_H=Hc), of a perpendicular magnetic recording medium is regarded attributable to magnetic interactions among magnetic grains in the medium. Magnetic interactions in [Co/Pd]n multilayer films with strong perpendicular magnetic anisotropy and different λ were studied using ferromagnetic Hall effect measurement, which detects the behavior of the perpendicular magnetization component even when an inclined magnetic field is applied. Specimens with high λ at H_c revealed a sharper and larger positive peak in the ΔV curves an evaluation index for magnetic interaction using the Hall effect than whose with low λ, indicating the dominance of strong exchange interaction among the particles.

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To reduce the spike noise caused by stray magnetic fields, we investigated layered stacking soft-magnetic underlayers (SULs) with interlayer magnetic coupling. To reduce SUL noise as well, nanocrystalline or amorphous materials are used in the large part of the soft-magnetic layer. Through investigation of material problems in ferromagnetic (FM)/nonmagnetic (NM) stacked SULs and antiferromagnetic (AFM)/ferromagnetic (FM) stacked SULs, the following points were clarified: (1) In the case of FM/NM stacked layers using Ru as the NM layer and CoZrNb as the FM layer, when the layer structure of CoZrNb (150 nm)/Ru (0.6 nm)/CoZrNb (150 nm) was adopted, the M-H loop was shifted due to RKKY interlayer exchange coupling. The value of the interlayer exchange coupling constant J was derived at a small value of 0.015 erg/cm². (2) In the above layer structure, by sputtering the Ru layer under At + O₂ atmosphere, or by introducing a Co₇₀Fe₃₀ layer which has high saturation magnetization M_s, between the Ru layer and CoZrNb layer, the value of H_ex and J were enhanced. The J value shows prospects of enhancement over one digit if appropriate materials and process are introduced. (3) In AFM/FM stacked SULs, the unidirectional anisotropy constant J_k between the AFM and FM layers was reduced by increasing the thickness of the FM layer. The principal problem is how to suppress the reduction of J_k by controlling the soft magnetic properties of the FM layer.

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CoZrNb films stacked with non-magnetic interlayer films (Ru, Cu, or C) were deposited on 2.5-inch φglass disks, for use as soft underlayers (SUL) of perpendicular recording media, and the effect of interlayer coupling on their domain structure was investigated. CoZrNb films stacked with a thin Ru interlayer show anti-ferromagnetic interlayer coupling dependent on the thickness of the Ru layer. The anti-ferromagnetic coupling field, H_u, was ∼24 Oe for CoZrNb (50 nm)/Ru (1.8 nm)/CoZrNb (50 nm) film, for instance, and the value of H_u is nearly proportional to the inverse of the CoZrNb thickness. Domain observation by the Bitter method indicates that a single-domain state was successfully realized over a whole disk by the anti-ferromagnetic interlayer coupling, when the thickness of the CoZrNb layer was less than 50 nm (number of stacked layers: 2-4, total SUL thickness: 100-200 nm). Weak noise due to a stray field from the CoZrNb layer was detected by observation using a read head, even in single-domain disks, and is probably due to magnetization ripples in the CoZrNb layer. However, the stray field was no longer detected in disks annealed in an applied magnetic field, perhaps because of the reduction of the magnetization ripple. The anti-ferromagnetic interlayer coupling was found to be effective for realizing a single-domain SUL layer.

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To reduce the grain size and media noise in a typical CoCrPtB/CrMo longitudinal medium, Cr₈₅Ti₁₅ and W_XCr_100-X (X = 0, 25, 50, 75, 100) seedlayers were introduced and exposed to oxygen. The purpose of using a Cr-based seedlayer is to introduce a nucleation site for CrMo grains, and the purpose of exposing the seedlayer to oxygen is to enhance the nucleation site. The main results were as follows: (1) Results of AES and RHEED analysis suggest that a W₁₀₀ seedlayer, which has a very high melting point, forms a layer-like film with very small and dense island grains, due to its high free surface energy and low mobility. On the other hand, W₅₀Cr₅₀ and Cr₁₀₀ seedlayers, which have lower melting points than the W₁₀₀ seedlayer, form island film. (2) The media grain size and the media noise are reduced by the use of W_XCr_100-X (X = 0, 25, 50) seedlayers, which form island film and have higher melting points than the CrMo underlayer. (3) The media grain size and the media noise are further reduced by exposure of the seedlayer to oxygen when CrTi₁₅ or W_XCr_100-X (X = 50, 75) seedlayers, which form island film and have a strong affinity for oxygen, are used. (4) To effectively reduce the media grain size and improve the media signal-to-noise ratio by exposing the seedlayer to oxygen, it is essential to utilize a very thin Cr-based seedlayer with a high melting point and a strong affinity for oxygen and which forms an island-like film, such as a W₅₀Cr₅₀ seedlayer.

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In the magnetic contact duplication technique using lithographically patterned master media, when the master media have magnetic films not only in protruding parts but also in dented parts, the depth of the dented parts affects the duplication performance. For master media with a pattern width L of 2.5 μm, both experimental and simulation results show that the magnetization duplicated by using the master medium without magnetic films at the dented parts is reversed at transitions and is almost uniform between transitions, and that the magnetization duplicated by using the master medium with magnetic films at 0.5 μm-deep dented parts is not only reversed at transitions but also changes between transitions. It is inferred from simulation that for master media with L of 0.1 and 0.4 μm, if d is 0.1 and 0.2 μm, respectively, magnetic films at the dented parts have no influence on the duplication performance.

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We analyzed magnetic field distributions of two kinds of write heads, using a modified high-resolution electron beam tomography technique which employs a patterned electron beam. The heads differ in their saturated magnetic flux density of upper poles, overwrite properties, and resolutions. As a result, we confirmed that the write component of the magnetic field affected the overwrite properties and the magnetic component perpendicular to the air bearing surface affected the resolutions.

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A finite element read/write simulation was performed by solving the Poisson equation for a 2D model of antiferromagnetically coupled (AFC) media and a thin-film-head system. AFC media are composed of two recording layers and a thin intervening Ru layer. From the simulation of an isolated transition, it was found that (1) an extra transition appears in the underlayer because of the reversal of the field in writing the main transition, (2) the extra transition disappears at around t = 10^-2 [s]. Furthemore, from simulation at 423 kFRPI, it was found that (3) the reverse field plays an important role in the recording process by creating an antiparallel magnetization alignment in each bit. Finally, it is shown that (4) the thermal stability of the AFC medium is better than that of a conventional single-layer medium by about two orders of magnitude and that of a keepered medium by an order of magnitude in time scale.

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A finite element 2D simulation of recorded magnetization on a slave medium with patterned thin films on a master medium was performed by solving the Poisson equation for the magnetic printing system. As a result, the following conclusions were drawn: (1) The printing field decreases drastically in the central region of two magnetic films as compared with that at the film edges. (2) When the printing field is weak, the magnetization in the central region cannot be switched under the printing field, and the output voltage waveform is severely distorted. (3) When the printing field is too strong, the peak of the output voltage waveform shifts in the film edge direction, although the magnetization can be switched completely. (4) The optimum printing field depends strongly on the distance between the films.

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To estimate the demagnetizing field in the recording layer of a double-layer perpendicular medium as a function of the thickness and permeability of the underlayer, a finite element simulation for an arctangent magnetization was performed by solving the Maxwell equation for a 2D model of a head and double-layer medium system, and compared with the demagnetizing field obtained from an analytical formula. In addition, a recorded magnetization and a demagnetizing field were simulated for an SPT head and double-layer medium system, and compared with those for the arctangent magnetization. As a result, it was found that the demagnetizing field decreases drastically due to the multiple images induced between the head and the underlayer, and that the recorded magnetization becomes asymmetrical as the coercive force of the recording layer decreases.

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The effect of the head field gradient and the variance of coercivity on transition jitter and transition width was studied by means of a calculation using Voronoi cells. In this calculation, reproduced waveform was obtained on the convolution operation of magnetization distribution and head sensitivity function. Reducing the variance of coercivity proved to be effective in reducing transition jitter, as well as steepening the head field gradient. To achieve an areal density of 200 Gbits/inch², a cluster size of 10 nm, a head field gradient of 200 Oe/nm, and a variance of coercivity of 600 Oe are required.

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A cylindrical magnetic storage system was built and preliminary measurements were made. The system is expected to overcome the writing problems at high areal densities caused by a write head skew angle, and is aimed at the realization of 1 Tbit/in², 2 Gbps perpendicular magnetic recording. Cylindrical substrates, sputtering equipment, and a read/write tester for a cylindrical magnetic storage were fabricated. For this preliminary investigation the length and diameter of the cylindrical substrates were 1 inch. Thin films (protective layer, storage layer, seed layer, etc.) were deposited by rotating the cylindrical substrate during the sputtering process. Fundamental read/write characteristics were measured using a merged AMR head with a pico-slider.

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This paper investingates what the magnetic characteristics of TbFeCo films would become if Ar and Kr were used as sputtering gases. The sample structure was glass / underlayer SiN_x(u) / TbFeCo / protective layer SiN_x(p), and the top three layers were deposited by magnetron sputtering. When Kr gas was used, the coercive force H_C and effective perpendicular anisotropy K_eff increased. The increase was not dependent on the difference in Curie temperature. The type of sputtering gas used was changed for deposition of the SiN_x(u) and TbFeCo layers. Consequently, H_C increased when TbFeCo was deposited by using Kr gas. Changing the kind of sputtering gas used seldom affected SiN_x(u).

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We calculated the magneto-optical properties of semiconductor-based multilayer structures containing GaAs:MnAs nanoclusters sandwiched by GaAs/AlAs distributed Bragg reflectors (DBRs). Very large magneto-optical Kerr effects (Kerr rotation and ellipticity) are predicted in multilayers with suitable DBR numbers. On the basis of the calculation, we have grown multilayer structures by molecular beam epitaxy, and have demonstrated a large Kerr effect (more than 600 mdeg of Kerr ellipticity) at a designed wavelength of ∼980 nm under a relatively low magnetic field at room temperature. This large magneto-optical effect in III-V semiconductor-based multilayer structures could be used for thin-film-type magneto-optical devices monolithically integrated with semiconductor opto-electronic circuitry.

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To examine the possibility of using segregated master ingots in the HDDR process, Nd-Fe-B HDDR powders were made from ingots with different levels of homogeneity, and their magnetic properties and structures were evaluated. As the ingots were homogenized, their anisotropy deteriorated and the coercive force increased. In addition, improvement of their magnetic properties was attempted by using intermediate Ar (IA) treatments between the HD and DR processes. As a result, the effect of the IA treatments was confirmed clearly, and good magnetic properties of B_r = 1.23 T, H_cJ = 848kA/m, and (BH)_max = 238kJ/m³ were obtained; these are close to those of commercial HDDR powder (MQA-T).

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II-VI diluted magnetic semiconductor (DMS) Zn_1-xCr_xTe films with Cr concentrations up of to x =0.20 were successfully grown. A single-phase Zn_1-xCr_xTe layer was obtained in films grown at relatively low temperatures of around 250°C. Magnetic circular dichroism measurements showed strong mixing between sp-carriers and localized d-spins indicating that Zn_1-xCr_xTe are DMS. For x = 0.20, spontaneous magnetization was confirmed by the Arrott plots. The Curie temperature of x = 0.20 was estimated to be 300 K ± 10K, which is the highest value among the DMSs in which sp-d exchange interaction has been confirmed. In spite of its high Curie temperature, Zn_1-xCr_xTe showed semiconducting electrical transport property. The co-existence of room-temperature ferromagnetism and semiconducting characters will make Zn_1-xCr_xTe a promising material for various spintronic applications.

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When conduction electrons are strongly coupled to core spins, as in double-exchange systems, they acquire a quantum (Berry) phase while moving through a crystal and are affected by a gauge field, with the result that they produce an anomalous Hall effect. We measured the transport properties of CrO₂ as a pure double-exchange ferromagnet, and show that the experimental results for the anomalous Hall effect of CrO₂ are consistent with this Berry phase mechanism caused by topological spin defects. We also discuss the possibility of magnetoresistance resulting from such defects.

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Granular (CO, Fe)-M-O (M = Ti, Nd, Al, and Si) thin films showing giant magnetoresistance (GMR) of 4%−10% at room temperature were successfully prepared by the reactive deposition method using an O₂ beam. The magnetoresistance (MR) ratios at 19 kOe (MR_r (19 kOe)) were found to have roughly a tendency of MR_r (M = Si)<MR_r (Al)<MR_r (Nd)<MR_r (Ti), which corresponds to the order of the estimated relative dielectric constants (ε_r) of amorphous SiO₂, Al₂O₃, Nd₂O₃, and TiO₂. In particular, MR_r(M = Ti, 19 kOe) was found to reach a large value of 9.8 (%). Furthermore, MR_r (H= ∞) value of these films was found to increase abruptly with the decrease in the average diameter of ferromagnetic particles, and is estimated to reach about 15% at room temperature. The phenomenon can be explained by considering that, as the average diameters of ferromagnetic particles decrease, spin-flips of tunnel electrons are suppressed because the energy for inelastic scattering generated at the time of tunneling between particles with different diameters becomes smaller than the minimum magnon energy.

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Small bubbles were found in magnetic garnet films with the easy axis perpendicular to the film plane. Their diameter is smaller than that of normal bubbles. They appear after stripe domains have been chopped by a pulsed magnetic field with high intensity after a single chopping. Small bubbles are generated under a limited range of bias field and pulse field conditions. They remain stable within a narrow bias field range, above which they collapse and below which they transit irreversibly into larger elliptical bubbles or stripes. The contrast of the Faraday image of small bubbles is different from that of normal bubbles.

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The interactions between magnetic dipoles induced in feeble magnetic substances were studied. Recently, interactions between such substances and gradient fields, namely, magnetic forces, have been drawing attention. On the other hand, interactions among such substances under magnetic fields have been neglected because of the extremely small dipoles induced in them. However, through elaborate experiments, we confirmed that even feeble magnetic substances interact magnetically. Furthermore, the interactions can be enhanced when their environmental surroundings are selected properly. Utilizing these interactions, feeble magnetic particles can create some ordered structures such as chain-like or triangle lattice alignments. These results indicate that alignments or structures of particles could be controlled by magnetic fields. This phenomenon could be of use in various fields such as material processing.

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The annealing temperature dependence of the tunnel magnetoresistance (TMR) ratio for ferromagnetic tunnel junctions with additional oxidation at the surface of the bottom ferromagnetic layer was measured. A drastic increase of TMR ratio was achieved at high temperature around 375°C. Such a tendency was very similar to the dependence for radical oxidized junctions. The enhancement of the thermal stability would be due to the existence of oxigen on the surface of the bottom ferromagnetic layer.

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The annealing temperature dependence of the tunnel magnetoresistance (TMR) ratio for ferromagnetic tunnel junctions with CoFeO_x inserted in the pinned layer was investigated. A junction with a CoFe/CoFeO_x/CoFe as the pinned layer exhibited TMR ratios of 47 % and 43 % after annealing at 350°C and at 375°C respectively, The reason for the improvement of the thermal stability is related to oxygen diffusion from CoFeO_x layer, and there is a possibility that CoFeO_x plays a role of Mn (in MnIr exchange layer) diffusion barrier.

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The magnetoresistance and magnetic properties of the free layer in a bottom-type spin-valve with an Fe-oxide layer inserted into the synthetic ferrimagnet pinned layer were investigated. The magnetoresistance in a spin-valve with an inserted Fe-oxide layer has a higher MR ratio of 20.0% than that in a spin-valve with an inserted CoFe-oxide or Ru-oxide layer. The free CoFe layer of a spin-valve with an inserted Fe-oxide layer has good magnetic properties. Interlayer coupling is antiferromagnetic because of the flat Cu layer interface. Coercivity is low because of the small grain size. Magnetostriction is near zero.

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Arrays of synthetic antiferromagnetic (SyAF) patterned elements were successfully fabricated with micron to submicron sizes. Their magnetic domain structures and spin-switching fields were investigated by using magnetic force microscopy (MFM) and the magnetic optical Kerr effect (MOKE), respectively. A single-domain structure was observed in Co₉Fe/Ru/Co₉Fe SyAF bits for even a small aspect ratio of 1, while Co₉Fe monolayer bits showed a multi-domain structure for aspect ratios below 2. The spin-switching field of Co₉Fe (6 nm)/Ru (0.45 nm)/Co₉Fe (10 nm) SyAF exhibited independence of element size, while that of Co₉Fe (10 nm) single elements was strongly dependent on element size. These results indicate the predominance of SyAF for ultrahigh-bit-density MRAM devices.

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Ni-Fe wires with widths > 80μm were prepared by a pulsed laser ablation method, in which the wire was formed by making use of re-ablation of the deposited film. The coercivity is found to increase with decreasing wire width in both the length and width directions. The wires become difficult to magnetize with decreasing wire width. These results are explained in terms of the particular structure of the wire, which is composed of fine particles.

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A process for reversing the magnetization of a magnetic wire with a square pad was observed by magnetic force microscopy (MFM) under an external magnetic field. A wire consisting of Ta (1.5 nm)/NiFe (20 nm) was fabricated on a thermally oxidized Si substrate by means of e-beam lithography and lift-off technique. The width and length of the wire were 150 nm and 50 μm, respectively, and the size of the connecting square pad was 0.5×0.5 μm². The direction of the external magnetic field was set parallel to the wire axis or 30 degrees from the wire axis in the substrate plane. The MFM observation was conducted under magnetic fields ranging from -400 Oe to 400 Oe at intervals of about 50 Oe. As the field increased, the domain structure in the pad changed into a closure, and one of the domain walls was pinned at the region between the wire and the pad. The pinned domain wall disappeared when the magnetic field was increased, indicating that the magnetization reversal takes place as a result of the injection of the domain wall into the wire.

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We prepared a Sm-Co/Cr film using substrate heating and studied the effect of the Cr underlayer structure on the magnetic properties of the films. The coercivity depends on the relative intensity of the diffraction line from the Cr(200) plane and increases with relative intensity. When the Cr underlayer was prepared under optimized conditions, the coercivity of the film was about 3.4 kOe, even though the Sm-Co layer was as thin as 2.5 nm. We found that substrate heating during deposition was effective in preparing higher-coercivity films with an ultra-thin Sm-Co layer.

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The composition, crystal structure, and magnetic properties of chemically synthesized FePt nano-particles were investigated. The composition of these particles is closely related to the crystal structure. FePt nano-particles with a composition range of 53.3 < Fe (atomic %) < 70 show high coercivity after annealing at 600°C in vacuum, and are transformed from a chemically disordered fcc structure to a chemically ordered L1₀ phase. An annealed film of Fe₆₃Pt₃₇ nano-particles has an out-of-plane coercivity of 11450 Oe. We applied the Langmuir-Blodgett technique for mono-layer fabrication of FePt nano-particles. The obtained mono-layer, with a thickness of 6 nm, has a hexagonal-like close-packed assembly with an are of 12×20cm².

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We studied FePt-fluorocarbon granular thin films for high-density magnetic recording media. The fluorocarbon as matrix in granular film receives significant attention because of the high hardness and low surface roughness and, thus, the potential application in recording media. FePt-fluorocarbon granular were have fabricated by the facing-targets sputtering method with plasma polymerizing reaction. An FePt alloy was deposited on substrate and the fluorocarbon matrix was polymerized at the same time. It was confirmed by TEM observation that a granular structure formed in films fabricated at C₄F₈ partial pressures of 0.10 and 0.20 mTorr. These films, which consisted of fine FePt particles with a size of 5-10 nm, had high coercivities of 4-8 kOe. It was considered that the FePt-fluorocarbon granular films have the potential to be used in high-density recording media.

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The structural, magnetic, and electrical properties of sputtered Zn_xFe_3-xO₄ thin films were investigated. A spinel structure was obtained for samples annealed above 673 K. The magnetization at 10 kOe of a sample sputtered in Ar and annealed at 873 K was 450 emu/cm³. Magnetization decreased in samples annealed above 873 K, as a result of evaporation of Zn and an increase in the thickness of the insulating layer. A MR ratio of about 4.3 % was observed at T = 300 K in a sample sputtered in Ar and O₂ mixed gas, and MR curve was of a granular type. However, because the Zn was completely evaporated at this sample, the MR was associated with the Fe₃O₄ grains and the α-Fe₂O₃ boundary.

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Polycrystalline thin films with an oriented direction of ε-Mn₄N along the (111) axis and η-Mn₃N₂ along the (113) axis were prepared as a single phase by the RF reactive magnetron sputtering method on glass substrates. It was clarified by XPS spectral analysis that nitrogen atoms in Mn-N compounds act as donor atoms in terms of the electrical/magnetic properties of the films. The ε-Mn₄N film was a single-phase perovskite-type crystal with lattice parameter 0.385 nm, and this film had the properties of ferrimagnetism, with 1.1 μ_B per unit cell, and of a metallic film, with electrical conductivity of 1.6×10⁴ Ω^-1m^-1. The η-Mn₃N₂ film was face center tetragonal (a = 0.420 nm, c = 0.413 nm) and had the properties of antiferromagnetism, with 1.4 μ_B per unit cell, and of a semiconductor flm, with electrical conductivity of 4.2×10³ Ω^-1m^-1.

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In our previous papers, it was reported that the dielectric permeability ε_r' is subject to change with magnetic field H, Δε_r'(H) in ferromagnetic nano-composite oxide films with the Bi₂O₃-Fe₂O₃-PbTiO₃ ternary system. In the present study, we first measured the temperature dependence of ε_r' and Δε_r'(H). Both quantities increase rapidly above 50°C, which suggests that softening of the glass network of the dielectric matrix takes place at this temperature to promote the charge displacement giving rise to the dielectric polarization. Next, we measured the magnetic field dependence of the displacement current J_d(H) to confirm whether the permeability change with magnetic field Δε_r'(H) is intrinsic. It was found that J_d(H) is also subject to change in a similar manner to Δε_r'(H), indicating that the charge displacement assisted by H really occurs. Finally, we observed the dielectric polarization induced by applying a small ac magnetic field at room temperature. This is considered to be a new type of electromagnetic effect. To explain the experimental results, we propose a simple model based on magnetization rotation of ferromagnetic nano-clusters dispersed in a dielectric glassy matrix.

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The real parts of the complex permittivity and complex impedance spectra of Mn-Zn-Ti ferrite with Fe-poor composition (FPF:Fe₂O₃ less than 50 mol%) were measured. The relaxation time was estimated by numerical fitting of the permittivity spectra data. The relaxation time of FPF was about 10^-5-10^-6 s, because dielectric relaxation occurred below 1 MHz. The resistance of the grains is separated from that of the grain boundary in the complex impedance spectra. As a result, it was found that the relaxation time is proportional to the resistance of the grains. It is reasonable to suppose that the relaxation time is related to the electrical mobility.
The temperature dependences of the real parts of the complex permittivity and the complex impedance spectra of the same sample were measured. The activation energy of the resistances of the grains was a little larger than that of the relaxation times.

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Ba₃Co₂R_xFe_24-xO₄₁ (R: rare-earth element, x = 0−0.5) samples with Z-type structure were prepared by the conventional ceramic method. A series of Ba₃Co₂R_xFe_24-xO₄₁ samples (R = La, Nd, Gd, Dy, Ho, Yb) were made. The frequency dependence of the initial permeability of all samples was measured in frequency range of 0.01−1.8 GHz. The initial permeability (at 0.1 GHz) of Ba₃Co₂R_0.1Fe_23.9O₄₁ (x = 0.1, R = Gd, Dy, Ho, Yb) samples was higher than of the Co₂Z ferrite without substitution. In particular, the initial permeability of Gd³⁺-substituted Z-type ferrite sample (x = 0.1) was the highest of all samples. The crystal structure of Ba₃Co₂R_xFe_24-xO₄₁ (x = 0.1) was a single phase of the Z-type structure. As a result, rare-earth ions formed a solid solution of Co₂Z ferrite. The measured lattice constant of these samples (x = 0, 0.1) indicates that La ions substituted for Ba ions and Gd, Dy, Ho, and Yb ions substituted for Fe ions. The apparent specific anisotropy field H_A of a Gd³⁺-substituted Z-type ferrite sample (x = 0.1) was the lowest of the Ba₃Co₂R_xFe_24-xO₄₁ samples (x= 0, 0.1). It would therefore appear that the magnetic anisotropy was changed by substitution between Gd ions and Fe ions in Co₂Z ferrites. But verification by other determination is necessary.

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A novel sputtering method using an electron-cyclotron-resonance (ECR) microwave plasma was used to perform reactive sputter-deposition of Ni-Zn ferrite thin films. Ni-Zn spinel ferrite thin films with preferential orientation of (400) and relatively low coercivity of 15 Oe were obtained at a high deposition rate of 14 nm/min. and at temperatures lower than 200°C. To achieve this high deposition rate, the configuration of the ECR sputtering apparatus and processing parameters such as the microwave input power, target voltage, and oxygen partial pressure were carefully optimized. Reactive ECR sputtering is one of the most suitable methods for preparation of ferrite thin films applicable to magnetic devices such as MMICs isolators and circulators.

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Fe-Co and Fe-Co-Al-O films were prepared by RF magnetron sputtering in Ar gas atmosphere. An H_ch (coercivity in the hard axis direction) value of 11 Oe (0.88 kA/m) was obtained for an Fe-Co film by choosing proper sputtering condiition. H_ch was greatly decreased by using Al₂O₃ addition of 1% and a Ni-Fe underlayer of 0.5-12 nm, resulting in a value less than 1 Oe (80 A/m) for a film thickness range from 50 nm to 600 nm. Amorphous Co-Zr-Nb soft magnetic underlayer films are also effective for obtaining H_ch values less than 1 Oe (80 A/m). It is finally concluded that combination of a small amount of Al₂O₃ addition and a soft magnetic underlayer film is essential for obtaining low H_ch with high saturation magnetic flux density of 2.4 T in a wide range of film thicknesses.

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Co-Fe-B films with a thickness of 0.5μm were fabricated by synchronous dual RF magnetron sputtering a while rotating cylindrical electrode. A magnetic thin-film core for GHz applications was obtained with a large anisotropy field H_k and large saturation magnetization 4πM_s, and these permeability characteristics and micro-structures investigated. The as-deposited film, with H_k of 390 Oe were and 4πM_s of 17.6 kG, exhibited high ferromagnetic resonance (FMR) frequencies of up to 6 GHz in permeability characteristics. The film has an amorphous-like structure including atomic ordering within the range of several angstroms, which leads to good soft magnetic properties with an electrical resistivity of 100μ Ω cm. The large H_k of the films fabricated by the sputtering method is effective for attaining higher frequency characteristics with lower FMR loss.

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Organic magnetic materials were fabricated by the arc discharge method with starting materials of nitrogen gas and triethylamine. After nitrogen gas or gaseous triethylamine was introduced into the chamber, an arc was discharged between carbon electrodes with a purity of 99.99%. The as-made samples were annealed in decreased air from 400°C to 1000°C for 3 hours. The carbonaceous sample prepared in nitrogen gas was a diamagnetic material, while the sample made from triethylamine was a ferromagnetic-like material whose magnetization was around 0.02 emu/g at room temperature. After annealing between 500°C and 600°C, the magnetization of the ferromagnetic-like material increased by around 3 times as much as that of as-made one. However, the spin density, measured by electron spin resonance, decreased with increasing annealing temperature; in particular, it fell rapidly between 500°C and 600°C. Therefore, the linewidth of the ferromagnetic-like carbonaceous material after annealing at 500°C and 600°C was narrower than that of the as-made material, and the intensified spin interaction suggested an increase in the magnetization.

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Stress-magnetization property changes in Co-based amorphous ribbons due to heat treatment were investigated. Co-based amorphous ribbons with a negative magnetostriction constant showed unique magnetization behavior under stress, such a stress-insensitive region and a peculiar magnetization increment. Our interpretation of the appearance of the unique stress-magnetization behavior is that three factors, i. e., an induced anisotropy field due to field annealing, a magnetoelastic anisotropy field under stress, and an exciting magnetic field along the sample axis, are responsible. A simple magnetization rotation process using the three factors shows a tendency for the stress-insensitive region to expand with larger induced magnetic anisotropy as same as the experimental results, however, it did not show any unusual magnetization increment. In interpreting the unique stress-magnetization characteristics, therefore, a transient magnetization process should be considered to be like a magnetic domain ramification and/or its reordering in conjunction with the above three factors.

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A GMR line sensor is a magnetic sensor for visualizing a magnetic field distribution using only a single scan. This sensor is composed of many GMR elements on a line of polyimide file. A multilayer NiFeCo/Cu GMR element with the shape of five multi-arcs is used. Therefore, this sensor has an omnidirectional magnetic sensitivity in plane. The GMR line sensor can detect a horizontal element of the magnetic field. This paper discusses detection of a change of magnetic flux in eddy current testing, using the GMR line sensor. The GMR line sensor can visualize the position of the slit in only a single scan, without depending on its direction.

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In recent years, PCBs (printed-circuit boards) are widely employed to achieve compact, lightweight electrical devices. PCB inspection, however, is not simple because of the complex circuit structures implemented. One nondestructive test used in PCB inspection is to measurement of the electromagnetic fields integral to circuit operation. Estimating the field sources from the measured fields becomes useful and important information not only for checking specification values but also for resolving EMC/EMI problems. The current viewer discussed here enables direct visualization of the current distributions in PCBs.
We designed a vector current viewer that combines two current viewers orthogonally, and we verified its usefulness for visualizing the magnitude, as well as direction, of currents using Lissajous diagrams. For efficient implementation, the present paper proposes a vector current viewer array system incorporating a computer, analog-to-digital converter, and vector current viewer array. A simple prototype of the vector current viewer array system demonstrates its usefulness for visualizing current distribution on planar electric circuits.

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Eddy-current testing (ECT) inspection is an attractive approach for detecting trace damage on as-fabricated printed circuit boards (PCBs). The distinctive features of this approach are its non-contact method and conductive testing by induced eddy currents. We propose several kinds of planar-type probes with a meander exciting coil and discuss detection characteristics.
This paper reports the structure and scanning of a probe that enhances the sensitivity and resolution of inspection. Results show that wiring, soldering points, and damage can be imaged on a two-dimensional plane. Disconnections can be detected on printed wiring with 0.2-mm width.

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This paper presents an eddy-current testing probe (for pipes including weld points) using a meander coil. Simulations clarified distributions of the eddy current by the meander coil and revealed that a probe can generate an effective eddy current for flow detection. Experiments demonstrated that the probe can detect an outer notch with 50 % depth and 10 mm length, which is located near the weld point. Enhancement of detectivity by inserting magnetic material in the detector coil was examined.

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We report experimental results of an eddy current test. When an excitation coil is brought close to a conductor, an eddy current is induced in the conductor. If there is a crack in the conductor, the eddy current will avoid that area, causing variation in the magnetic field generated by the eddy current. We examined how effectively the differential motion method could be used to detect the magnetic field change through the output voltage difference between two coils. We report characteristics of detecting coil output voltage and phase difference characteristics between excitation current and the output voltage and frequency characteristics of the detecting coil output voltage.

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We fabricated a new magnetic thin film sensor using a large Barkhausen effect. The sensor consists of a Ni-Fe thin film stripe, 0.7 mm by 4.6 mm, on a glass substrate and an aluminum thin film search coil of 400 turns on the other side of the substrate. The Ni-Fe thin film is a bi-layer composed of a soft magnetic layer and a semi-hard magnetic layer. The aluminum thin film search coil size is 6 mm by 10 mm; the line width and space are 5 μm. As a result, the sensor generated an induced pulse of about 1.4 mV by the large Barkhausen jump under asymmetrical ac magnetic fields in the frequency range from 1 to 100 Hz.

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