To understand the origin of the soft magnetic properties of Fe-Co system films with a high saturation magnetic flux density (B_s), structural analysis was performed by conducting detailed X-ray diffraction (XRD) measurements and transmission electron microscope (TEM) observations in a wide range of film thicknesses and Al₂O₃ compositions. An initial growth layer with small grains, a continuous columnar structure, and alternation of the crystal orientation according to the film thickness are important for obtaining good soft magnetic properties in a wide range of film thicknesses. These features can be obtained by using a combination of an Al₂O₃ additive of about 1−3 at% and a thin underlayer. The mechanism of the soft magnetic properties of Fe-Co system films seems to be partially explained by the existence of an initial growth layer with good soft magnetic properties and the exchange-coupling effect with the initial growth layer.

View full abstract

An eddy current testing (ECT) coil system including a double-D coil as a pickup coil and a ring coil as an axisymmetric excitation coil was modeled. (Despite the frequent use of a double-D coil in ECT probes as an excitation coil, we employed it as a pickup coil). A double-D coil made from two semicircular wires connected in counter-series was placed within a ring coil in such a way that the coils were coaxial and co-planar. The structure of the coil system makes it insensitive, in principle, to a magnetic field with an axisymmetric distribution and sensitive to any unbalanced field. The method presented here is based on the numerical calculation of the well-known expression for the vector potential due to a ring coil, developed by Dodd and Deeds. Using this method, the induced voltage in the double-D coil due to flaw-eddy current interaction was numerically evaluated on numerous grids placed over the surface of an aluminum plate. In this way we plotted the measured voltage versus the radial distance between the centers of the probe and the flaw. By investigating the plot we can characterize the flaw. The experimental results agree very well with the results of numerical calculation.

View full abstract

Magnetic contact duplication is proposed as a method for forming phase servo patterns on hard disks. In a phase servo pattern, the magnetic field used for duplication is applied diagonally across the master pattern. This work clarifies the influence of the master pattern angle θ against hard magnetization direction of the slave medium on the magnetic duplication characteristics. In the case where θ= 30°, the output signal voltage decreases and the half-value width of the signal becomes broad compared with that for θ= 0°; that is, the magnetic duplication characteristics deteriorate as θ increases. Even if the duplication field is made strong for large θ, the magnetic duplication characteristics are not improved.

View full abstract

Bilayered Fe₆₅Co₃₅ (=FeCo)/Co films were prepared by facing targets sputtering with 4πM_s∼24 kG. Soft magnetic properties were induced in the FeCo films by the presence of a Co underlayer. H_c decreased rapidly when the Co underlayer was 2 nm or more. The films showed well-defined in-plane uniaxial anisotropy, with typical values of H_ce = 10 Oe and H_ch = 3 Oe, respectively. The high-frequency characteristics of the films show that they can work at 0.8 GHz with real permeability as high as 250. Reduced roughness was achieved by a inserting Co layer between the glass substrate and the FeCo layer.

View full abstract

A cylindrical magnetic storage system was investigated and developed, using perpendicular double-layered media with several CoPtCr-SiO₂ recording layers and inclined-pad-type heads with a single-pole-type (SPT) writer designed for use with cylindrical media. The fabricated head was capable of stable flight over a rotating cylindrical medium. The inclined-pad-type head had almost the same linear velocity dependence of its flying characteristics as in the theoretical design, and is thought to be a potentially valuable component of cylindrical magnetic storage systems. Composite recording layers of CoPtCr-SiO₂/Ru/Pt/Ta deposited on a rotating cylindrical substrate with a soft magnetic underlayer (SUL) had coercivities of 3.9 kOe (medium #A) and 5.9 kOe (medium #B), controlled by varying the SiO₂ content, and a squareness ratio of around 1. These properties were almost the same as those of composite recording layers deposited on conventional disk substrates with SULs. The fundamental read/write characteristics of CoPtCr-SiO₂/CoZrNb perpendicular double-layered cylindrical media were measured and a D₅₀ value of around 310 kFCI was obtained using medium #B and an SPT writer attached to the inclined-pad-type head. A reduction of the flying height and protective layer thickness is indispensable for further increasing the areal recording density while maintaining sufficient overwrite capability.

View full abstract

In perpendicular magnetic recording, track edge noise, write fringing, and transition curvature are crucial issues that need to be addressed in order to increase track density. In particular, it is thought that the transition curvature at the written track edges broadens readback pulse width through the azimuth loss effect, but quantitative discussion of this phenomenon has not been sufficient. In this paper we extract transition lines observed in MFM images, and examine the influence of the transition curvature on the readback pulse width and transition jitter. Our findings show that this influence is not very large, and that deterioration of the writing resolution or broadening of the transition width at the track edges is more significant.

View full abstract

To enhance the write performance of a CF-SPT head, a smaller main pole of Co-Ni-Fe and a finer coil were fabricated by using the electrodeposition method. Fine coils with 2.5 μm pitch were obtained by the damascene process. The magnetic domain structure of the 15-μm-high and 20-μm-wide main poles could be controlled by changing their taper angles. A head with a favorable domain except at its tip exhibited stable write performance and no pole erasure. Thus, it was concluded that a control of the magnetic domain was necessary for write heads.

View full abstract

Current-perpendicular-to-plane giant-magnetoresistance spinvalve with Cu-AlO_x NOL (nano-oxide layer) spacer has attracted much attention for its relatively high RA and high MR ratio, which are due to the current-confined metal path in the oxide insulator. To clarify the mechanism for the formation of an NOL, we studied the surface structure of an inhomogeneous AlO_x layer on Cu by in-situ conductive-AFM observations in various oxidation conditions. The current intensity images obtained show that different Cu metal paths appear at a Cu surface surrounded by AlO_x grains, where the AlO_x structure of each NOL is different. The AlO_x structure, i. e., the NOL structure, can be controlled by pre-annealing of the Al layer before oxidation. It was found that a thin Al layer on Cu (111) was changed remarkably to fine particles by annealing. The fine particles moved from the Cu (111) terrace to the terrace edge. Therefore, the Al movement from a terrace, where a metal path appears, is caused by a decrease in the Cu surface energy.

View full abstract

We studied a magnetic recording head for a cylindrical perpendicular magnetic storage system with regard to its stability when a slider is flying over a rotating 1-inch-diameter cylindrical medium. We also designed an inclined-pad-type slider for the cylindrical magnetic storage system. This slider has an inclined pad formed on its leading edge and a trailing pad formed on its trailing edge, to generate an air-bearing force. The inclined pad is protruded in the thickness direction of the slider relative to the trailing pad. A waveform of an acoustic-emission (AE) sensor and an envelope of a reproduced signal were obtained from the combination of the cylindrical perpendicular medium and fabricated this slider. These waveforms did not show any large pulse and thermal asperity associated with contact. These results confirm the flying stability of the inclined-pad-type slider.

View full abstract

Polycrystalline and single crystalline thin films of Co₂(Cr_1-xFe_x)Al (x = 0.6, 1) full-Heusler alloys with different disordering were prepared on thermally oxidized Si and MgO(001) substrates, respectively, by the dc magnetron sputtering method. The magnetic tunnel junctions with a polycrystalline and single crystalline B2 type Co₂FeAl (x =1) electrode demonstrate TMR of 70% and 75% at 5 K, respectively, which is larger than that of 65% at 5 K for Co₇₅Fe₂₅, indicating that the spin polarization for Co₂FeAl is larger than that for Co₇₅Fe₂₅. The TMR for Co₂FeAl with both the A2 and the B2, which is controlled by substrate heating, is almost the same, whereas for Co₂(Cr_0.4Fe_0.6)Al the TMR increases with increasing the degree of ordering, corresponding to the first-principles calculations.

View full abstract

To develop a new versatile technique for determining the interfacial spin polarization of ferromagnetic materials, we examined Andreev reflection measurements by using superconducting NbN junctions. In this article, we report measurements and analysis of spin polarization of La_0.7Sr_0.3MnO₃ film at the interface. We found that the spin polarization of La_0.7Sr_0.3MnO₃ film strongly depends on the cooling condition of La_0.7Sr_0.3MnO₃ film after deposition. The maximum spin polarization of La_0.7Sr_0.3MnO₃ film was 0.77 ± 0.02.

View full abstract

Thin films of ordered double perovskite Sr₂FeMoO₆ were sputter-deposited on Ba_0.4Sr_0.6TiO₃-buffered SrTiO₃ substrates, and their surface properties were examined by atomic force microscopy (AFM) and X-ray photoemission spectroscopy (XPS). The Mo 3d spectra of Sr₂FeMoO₆ films showed a multiple peak structure, which originated from the unusual electronic state of metallic Sr₂FeMoO₆. Systematic XPS studies of the air-exposed surface of Sr₂FeMoO₆ film indicated that the surface native barrier was an insulating SrMoO₄. In addition, a TMR junction with the native barrier was fabricated using a convention photolithographic technique, and an MR ratio of 10 % was observed at 4.2 K.

View full abstract

Co₂V_0.67Fe_0.33Al full-Heulser alloy films were fabricated on an MgO (100) single crystalline substrate by using two different heat treatments: substrate heating and post-annealing. Ultra-high-vacuum dc magnetron sputtering was used to prepare the sample. The L2₁ structure was obtained when the substrate temperature (T_s) was 500°C. For the same sample, the magnetic moment per formula unit showed the highest value of 2.4 μB at 5 K. There were small differences between the samples fabricated by substrate heating and post-annealing in terms of their structural and magnetic properties. A magnetic tunnel junction (MTJ) using Co₂V_0.67Fe_0.33Al as a bottom electrode was fabricated. A larger tunnel magnetoresistance (TMR) was obtained by substrate heating than post-annealing with a maximum value of 28% at RT and 50% at 5 K when the Co₂V_0.67Fe_0.33Al was sputtered at T_s = 500°C. We found that there is an intimate relationship between the lattice constant of Co₂V_0.67Fe_0.33Al and the TMR.

View full abstract

Co-Zn-Ti substituted M-type barium ferrites of BaCo_xTi_xFe_12-2xO₁₉ (x = 1−3 ) and BaCo_1.1Zn_yTi_1.1+yFe_9.8-2yO₁₉ (y = 0−1.0) were prepared by a powder metallurgy method. Their characteristics were examined by using an X-ray diffractometer, a vibration sample magnetometer (VSM), a vector impedance analyzer, and a scanning electron microscope. When Fe ions of BaFe₁₂O₁₉ were replaced with Co-Ti ions, the magnetic anisotropy and coercivity decreased. As a result, the initial permeability increased to 27 for a sample with x = 1.15. Zn-Ti ions were also substituted for Fe ions in BaCo_1.1Ti_1.1Fe_9.8O₁₉. When the amount of substitution (y) was 0.4 in BaCo_1.1Zn_yTi_1.1+yFe_9.8-2yO₁₉ (y = 0−1.0), the initial permeability at 10 MHz had a very high value of about 40. The reason for this may be that the coercivity becomes small as a result of the growth of the crystal particles and the decrease in the anisotropic magnetic field.

View full abstract

It is important to understand leakage magnetic fields surrounding magnetic machines and devices for facilitation of development and evaluating the environmental effects of the magnetic field level to determine whether it conforms to the EMC guideline. The magnetic projection method is a measurement technique that can detect a leakage magnetic field by means of a simple probe. The principles of 2-D magnetic field measurement and reconstruction have been previously reported. This paper proposes the principles of a spherical magnetic projection method, and reports on an experiment carried out to observe the overall leakage magnetic field around a sample object. As a result, it is shown that the projection method can easily measure and visualize a magnetic field on a spherical surface with good accuracy.

View full abstract

A wireless multi-position detecting system using three LC resonant magnetic markers was developed and demonstrated. The markers were given individual resonant frequencies of 183 kHz, 487 kHz, and 730 kHz, respectively. The new measuring technique described in this paper was applied to the system in order to reduce the acquisition time: the markers were excited by a superposed wave corresponding to the resonant frequencies, while the voltage signals induced through the pickup coils are separated into each frequency spectrum by FFT analysis. Regardless of the number of markers, the necessary voltage amplitude of each frequency spectrum can be obtained easily at the same time. Thus, our proposed system can detect multiple markers at a time. All the positional accuracies of the three markers are less than 5 mm within 100 mm of the pickup coil array.

View full abstract

A Rayleigh wave propagating on a structural steel plate generates a magnetic field by means of the inverse effect of magnetostriction, which makes the magnetic flux a circuit through the air from the surface of the specimen. Thus, a field is observed as an electromotive force induced in a sensing coil. The amount of flux depends on two type of stress: compressive stress due to Rayleigh waves and residual stress due to the manufacturing process. In this paper, an instrument for measuring these stresses is proposed and the electromotive forces induced by Rayleigh waves are measured in two strainless plates, as-received and heat-treated. The magnetic field dependence of the electromotive forces shows a clear difference between the two specimens.

View full abstract

Magnetic field optical sensors based on the Faraday effect using (TbY)IG single crystals with a striped magnetic domain structure are proposed. It is assumed that the magnetization perpendicular to the striped magnetic domains in (TbY)IG crystals occurs through a rotation of the magnetization, giving rise to a linear magnetization curve like that of Isoperm. This assumption is confirmed by optical measurements. The characteristics of a reflection- type sensor using these crystals were measured at a wavelength of 1.3 μm. The obtained sensitivity was 5.5 × 10^-3 %/A/m, and a good linearity of the sensor output was obtained over a wide dynamic range between 2 A/m to 10² A/m. A noise-equivalent magnetic field of 2.1 × 10^-1 A/m was also obtained. The experimental results are explained well by the proposed magnetization process model.

View full abstract

A switched reluctance generator (SRG) has desirable features including simple construction, high reliability, and low cost. Furthermore, it is suitable for use as an ultra-high-speed generator because its rotor is made of iron steel without any windings or permanent magnets. However, the SRG system is complicated, because it requires detection of the rotor position angle and excitation power for the excitation circuit of the stator winding. For this reason, it has not been used in practical applications. We previously proposed a new reluctance generator (RG) that has permanent magnets in the stator yoke. The experimental results obtained with a trial single-phase RG show that the proposed RG has very simple construction and high performance. However, the single-phase RG has the disadvantages of large leakage flux and cogging torque. In this paper, we evaluate a three-phase RG with permanent magnets buried in the stator core by simulation and experiments.

View full abstract

This paper describes a robust design for a capacitance-drive-type linear electromagnetic solenoid (LES) using a quality engineering method and an exclusive dynamic analysis simulator. Reducing the variation in the performance significant by restrains the rise time of the current in the electromagnetic coil. In addition, the current should be kept above a specified level for a certain period. For this purpose, it is important to increase the inductance of the electromagnetic coil. In other words, it is necessary to increase the winding diameter and reduce the number of turns in order to reduce the variation in the performance. The validity of this robust design has been verified by experiments with actual solenoids. Consequently, it provides a high yield ratio.

View full abstract

In this research, we examined whether magnetic fields exerted any influence on the nervous system of the nematode C. elegans. Both during exposure to magnetic fields and after exposure to magnetic fields, we examined the influence of magnetic fields by observation of the behavior of the worm in response to certain chemicals. After exposure to magnetic fields (60 Hz, 0.5 T) for one hour, some achievement rates for the volatile attractant Diacetyl of the worm decreased in comparison with the nonexposure group. Moreover, some breakthrough rates for CuSO₄, a chemical that the worm avoids, increased in comparison with the nonexposure group. In particular, the breakthrough rate for CuSO₄ of the worm during exposure to magnetic fields increased greatly in comparison with the breakthrough rate of the worm after exposure to magnetic fields. These results suggest that the parts of the worm’s nervous system that relate to DA and CuSO₄ are influenced by magnetic fields, and that there are more effects on the nervous system during than after exposure to magnetic fields.

View full abstract