Co-based amorphous powder was produced by a new atomization process “Spinning Water Atomization Process(SWAP)”, having both rapid super-cooling rate and mass production potential. The composition of the alloys was((Co_0.95Fe_0.05)_1-xCr_x)₇₅Si₁₅B₁₀ (x=0, 0.025, 0.05, 0.075). The powders obtained were in the amorphous state at particlesize up to 500 μm and exhibited good magnetic softness. The coercive force of powders was about 27.1-53.3 A/m.Furthermore, Co-based amorphous powder cores with glass binders were also fabricated by pressing and annealingmethods. For the core pressed at 2 GPa in room temperature and annealed at 763 K ×15 min. in air, the initialpermeability up to 100 kHz was about 110 and the core loss at 100 kHz for Bm=0.05 T was 85 kW/m³. Comparedwith Fe-based amorphous powder core, the former was 30 % higher and the latter was 40 % lower.

View full abstract

In order to clarify the origin of coercivity enhancement of Nd-Fe-B sintered magnets by the Grain BoundaryDiffusion Process (GBDP), microstructural observations were performed and the coercivities of magnets processed with various rare-earth oxides were investigated. Microstructural analysis using FE-EPMA revealed that Dy supplied from the magnet surface diffused into whole magnets with a thickness of 2 mm. At the center of a magnet, the Dy distribution width around a grain boundary is almost comparable to the width of the Nd-rich grain boundary phase.When rare-earth (R) oxides whose R provide higher anisotropy in R₂Fe₁₄B than that of Nd₂Fe₁₄B, are used for GBDP, the magnets showed higher coercivity than that of the control, and vice versa. Although the diffusion depth of Dy into the Nd₂Fe₁₄B grains was unclear at the center of the magnet, the relationship between the kinds of rare-earth elements used for GBDP and the resultant coercivities strongly suggests that the rare-earth elements supplied from the surface of the magnets and absorbed along the grain boundary phase may diffuse into very thin portions of the Nd₂Fe₁₄B grain surface.

View full abstract

This describes the presents development of a polishing technique for creating a nanometer-level mirror plane on the surface of planar-shaped and irregular-shape acrylic resin using MCF(magnetic compound fluid) paste and the new polishing machine manufactured by FDK. We found a relationship between the condition of the resin surface, the light transmittance, and the visibility, and clarified that the roughness of the acrylic resin surface is improved from the micron level (Ra 0.6 μm, Ry 4.5 μm) to the nanometer level (Ra 0.01 μm, Ry 0.09 μm) by using this method.

View full abstract

We developed a very sensitive high-frequency carrier-type magnetic field sensor with a sub-pT resolution using a resonating transmission line. Meander-type sensor elements using amorphous CoNbZr films were fabricated. We obtained a magnetic field resolution of 7.4 x 10^-13 T/Hz^1/2 at 501 kHz. The detectable magnetic field was limited bythe noise caused by nonlinear magnetic excitation. We analyzed the quality factor of the resonance for enhancementof the signal-to-noise ratio.

View full abstract

EPS (Electric Power Steering) enables an increase in automotive fuel efficiency by 3-5% and contributes to the protection of the environment by eliminating the oil medium used in conventional hydraulic power steering. For this reason a sharp increase in demand for EPS is expected. Permanent magnet motors are generally used for EPS but a reduction of cogging torque in these motors is one of the challenges we face to ensure safe and comfortable vehicle handling. In this paper, magnetic field analysis was conducted on brushless motors with radially oriented ring magnets to find effective ways to reduce cogging. Through the investigation of the relationship between coercive force distribution and magnetizing waveform, it was confirmed that the following methods were effective in reducing the cogging torque.
(1) Optimization of the skew magnetization angle according to the coercive force distribution along the axial direction of the magnet.
(2) Control of the magnetizing intensity along of the circumferential direction of the magnet.

View full abstract