We studied magnetic anisotropy in tetragonal distorted Fe-Co alloys, which are promising as novel hard magnetic materials that are free from of rare-elements, by using first-principles electronic structure calculations. Coherent potential approximation (CPA) and virtual crystal approximation (VCA) were employed to calculate the electronic structure in disordered Fe-Co alloys; CPA and VCA are the most reasonable and simplest approximations to deal with the random distribution of Fe and Co atoms. In comparing the uniaxial anisotropy constant calculated with these approximations, the values obtained from CPA were smaller than those from VCA even though the same compositions were considered. We analyzed Bloch spectral functions that reflected the electronic structure calculated with CPA and VCA to verify this inconsistency. Broadening of the spectral function due to electron scattering in disordered alloys drastically influences its magnetocrystalline anisotropy in Fe_0.5Co_0.5 with an axial ratio of c/a = 1.25 where a giant magnetocrystalline anisotropy is expected. We also discuss the effect of the finite lifetime of electrons due to scattering via the analysis of energy variations within second order perturbation theory in terms of spin-orbit interactions.

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  Electromagnetic interference (EMI) is a serious problem in integrated circuits. The ability to accurately measure low-intensity electromagnetic fields is necessary to overcome this problem. We developed in a previous study a system to make magneto-optical measurements that use short laser pulses and a stroboscopic method to measure magnetic-field waveforms. In this study, we considered the spatial resolution of the system and measured the magnetic field distribution around magnetic heads. The overall results suggest that the system of measurement is capable of measuring EMI if we use a thinner garnet and a higher power laser.

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  Thin steel plates are used in many industrial products, including those of the automobile industry. We propose a system of controlling the magnetic levitation and confirmed its realization by means of a digital control experiment. However, the use of a limited number of electromagnets cannot suppress static deflection or high-order-mode elastic vibration, which are characteristics of flexible magnetic materials. We therefore propose a hybrid system to control levitation of thin steel plates to solve this problem using the magnetic force generated by permanent magnets, which incur no operational costs. In this study, we attempted to determine the optimal gap, placement, and number of permanent magnets to reduce the deflection of thin steel plates under a generated magnetic field. The experiments on deflection were carried out on magnetically levitated thin steel plates to verify how useful the optimal placement of permanent magnets was.

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  Variable inductors, which consist of magnetic core and primary dc and secondary ac windings, can continuously control effective inductance of secondary ac winding by using primary dc current due to the magnetic saturation effect. Variable inductors have advantageous features such as their simple and robust structures, and they are extremely reliable. Therefore, they are suitable in applications as reactive power compensators in electric power systems. A three-phase laminated-core variable inductor was proposed in a previous paper that reduced size and weight more than those in conventional single-phase variable inductors. A novel three-dimensional three-phase variable inductor designed to further reduce size and weight and to improve manufacturing capabilities is presented here. The basic characteristics of the proposed variable inductor were calculated through reluctance network analysis (RNA) and the finite element method (FEM).

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  The development of highly-efficient machines has recently been urgently required from the viewpoint of conserving energy and protecting the environment. Therefore, a method of quantitative analysis that can be used to calculate core loss with a high degree of high accuracy is necessary. This paper presents a novel model for a magnetic circuit that incorporates the Landau-Lifshitz-Gilbert (LLG) equation. The model consists of two elements. The first is a dc hysteresis element given by the LLG equation, and the second is an inductance element that denotes eddy current loss in iron steel sheets. The proposed model can be used to estimate the dynamic behavior of voltage, current, and flux by coupling it with an external model of an electric circuit. The validity of the proposed method was proved by comparing it with cataloged values.

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  In recent years, a quantitative analysis method for electric machines is strongly required, especially iron loss calculation with high accuracy is very important to develop the high-efficiency machines. This paper presents a method for calculating iron loss of electric machines based on magnetic circuit method. The proposed magnetic circuit consists of three elements as follows: a dependent source which expresses dc hysteresis of core material, an inductance which denotes eddy current loss, and a dependent source which represents anomalous eddy current loss. These elements can be simply obtained from dc hysteresis loops and core loss curves of core material. The validity of the proposed method is proved by comparing with measured values.

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