Spin-polarized scanning electron microscopy (spin SEM) is a method to observe magnetic domain structures at a ferromagnetic sample surface. It detects the spin-polarization of the secondary electrons from a ferromagnetic sample and the magnetization vector at the originating point of the secondary electrons is deduced. This principle has brought us several excellent capabilities such as high spatial resolution and magnetization vector analysis. This technique has been applied for various magnetic materials and devices since it was developed thirty years ago, and still has been continuously extending its functions and challenging to open new fields for magnetic domain observation. In this article, recent results of spin SEM are introduced after brief explanation of the principle and the key components of the instrument.

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  Media for heat-assisted magnetic recording (HAMR) are designed with a minimized anisotropy constant ratio K_u / K_bulk by using a model calculation. The design method is improved from the previous rough estimation approach to a statistical estimation of the thermal stability factor of media during writing and rewriting. A comparison is made between HAMR and HAMR combined with shingled magnetic recording. The many relationships between the design parameters and K_u / K_bulk are revealed. The parameters are the thickness of the recording layer, the thermal conductivity of interlayer 1, the light-spot diameter, the heat-spot diameter, the linear velocity, the writing temperature, the grain number per bit, and the standard deviation of the grain size. In certain cases, the limiting factor for obtaining the minimum K_u / K_bulk value is information stability during 10 years of archiving, which relates to improving media preparation to increase K_u / K_bulk. In other cases, the limiting factor is the information stability on the trailing side located 1 bit from the writing position during writing and in the adjacent tracks during rewriting, which relates to examining the media structure to increase the heat-transfer thermal gradients.

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  We have investigated the synthesis conditions, and the magnetic properties of BaFe²⁺₂Fe³⁺₁₆O₂₇ (Fe₂W) and Ba₂Fe²⁺₂Fe³⁺₁₂O₂₂ (Fe₂Y). It is found that Fe₂W can be synthesized at a sintering temperature of 1300°C and Fe₂Y can be synthesized at a sintering temperature of 1000°C. The X-ray diffraction patterns for Fe₂W and Fe₂Y samples are in good agreement with the pattern of BaCo²⁺₂Fe³⁺₁₆O₂₇ (Co₂W) and that of Ba₂Co²⁺₂Fe³⁺₁₂O₂₂ (Co₂Y). It is also found that the Curie temperatures of Fe₂W and Fe₂Y ferrites are 503 and 375°C, respectively.

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  We have shown by micromagnetic simulation that the wavelength of the spin wave (SW) is modulated when the SW propagates across a step between two ferromagnetic films with different thicknesses. Since the wavelength of the SW depends on the film thickness, the thickness difference works as the different medium in Snell’s law. The wavelength modulation obtained by the simulation showed a good agreement with Snell’s law.

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  A new tracking system for a wireless magnetic ribbon type marker has been developed by using high-speed analog-to-digital [A/D] converters and a field programmable gate array (FPGA) module. The quality factor of the resonated marker (ribbon: 38 mm in length and 4 mm in width) was about 130. The standard deviation (position accuracy) was smaller than ～1/10 that of the previous system because the sampling frequency of the A/D converters was more than 100 times higher and because the FPGA operated at high speed. The distance between the driving coil and the pickup coil array was ～820 mm, which was ～2.7 times larger than that in the previously reported system. The profile of the marker we obtained was relatively smooth and reasonable up to a distance of 475 mm from the pickup coil array.

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  A prototype magnetizing fixture was designed based on magnetic flux patterns simulated using the three-dimensional finite-element method of the JMAG software package. Rectangular shaped anisotropic bond magnets with dimensions of 6×12×24 mm were magnetized to multipoles using the prototype and a pulse power source. The result was significant enhancement perpendicular to the surface component of magnetic flux density (B_z) in the hard-axis compared with B_z for conventional simple magnets, of which the front and back surfaces are magnetized to opposite polarities. Moreover, B_z reached the close value for the Halbach arrayed magnet, 0.24 T, with the same body size fabricated for the attainment target. The enhanced B_z was attributed to the cusp field formed by the flux from both side coils. Demonstrations indicated that the cusp field out of the easy-axis could be efficiently enhanced due to focusing of the flux.

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