We propose a new model calculation using the reversal probability of grain magnetization for heat-assisted magnetic recording (HAMR). Our new model calculation can obtain the bit error rate as a function of the writing field Hw for a given anisotropy constant ratio Ku / Kbulk, which is a new parameter that we introduced. The physical implication of the recording time window proposed in the micromagnetic calculation is discussed using the new model calculation. Although the recording time window is a good guideline for write-error and erasure-after-write (EAW), EAW cannot be determined solely by the recording time window. The influence of EAW is accurately examined. The allowable range of Hw and Ku / Kbulk is also provided for various Curie temperatures Tc. Tc and the heat-transfer thermal gradient are important parameters for reducing Ku / Kbulk.
We investigated synthesis conditions and magnetic properties of Fe-deficient Ca-based hexagonal ferrites, Ca1−xLaxFeyO19−σ (x = 0.1–0.3, y = 2.0–10), and found the formation of M-type ferrite at x = 0.1–0.3 and y = 7.0–9.0 above 1200°C. Samples of y = 2.0–6.0 showed deviation from the initial compositions since molten calcium-rich oxide (possibly CaFe2O4) leaked out from the samples above 1200°C. The X-ray diffraction pattern of Ca0.8La0.2Fe8.0O19−σ sintered at 1250°C demonstrates the single phase of M-type hexagonal ferrite. The saturation magnetization of this sample was 68.0 Am2/kg at room temperature and its Curie temperature was about 400°C, which is slightly lower than that of the Sr-based M-type ferrite (460°C).
In the transport system of a thin-steel-plate production line, the quality of the plate surface deteriorates over time because of contact with rollers. As a solution to this problem, we have proposed the use of electromagnets to control the horizontal displacement of the steel plate. Vertical force to support the steel plate and horizontal force to suppress elastic vibration are applied to the steel plate by using the horizontal electromagnet. Focusing on these forces, we proposed a magnetic levitation system for the steel plate using only electromagnets installed in the horizontal direction. In this paper, the suspension force in the proposed system is analyzed by the finite element method, and the possibility of applying the proposed system for thinner steel plates is considered. Suspension force is effectively generated owing to the thinness of the steel plate. The results, indicate the proposed magnetic levitation system to be effective for thin steel plates. To verify the validity of the analytical conclusion, an electromagnetic suspension experiment has been carried out, and suspension force generated by the electromagnet has been measured. The agreement between the experimental and analytical results, confirmed the validity of the analytical results.