Many researchers have investigated the magnetic properties of magnetic cores in order to reduce iron losses in power-electronic systems. Wide bandgap power-semiconductor devices (silicon carbide (SiC) and gallium nitride (GaN)) with high-speed switching characteristics have been studied. Here, we examine the iron losses and magnetic B-H loop properties of magnetic materials under excitation with a GaN inverter at high carrier frequencies on the order of MHz. We find that the magnetic B-H loops include minor loops due to the magnetic materials even at such high carrier frequencies. We show that the iron losses increase at high carrier frequencies due to distortions of the voltage waveform.

  We prepared single crystals of six typical hexaferrites (M-type, W-type, X-type, Y-type, Z-type, and U-type) in order to investigate their formation, crystal size, and magnetic properties. In addition, we also investigated the conditions of single-crystal formation at several flux concentrations and cooling rates. We found that the growth of single crystals on the MY-line (Y- and Z-type) became more significant than that on the MS-line (W-type) under a slow-cooling condition. In contrast, the single crystals on the MS-line appeared with a relatively high cooling rate of 10°C/h., where the single crystals did not grow large. By using the self-flux method, we succeeded in synthesizing single crystals with a more complex structure with a possibility of being M₂Y₇ on the MY-line and investigating the magnetic properties.

  All-optical magnetic recording with circularly polarized light has attracted attention for ultra-high-speed magnetic recording. To obtain high-density magnetic recording, localized light over the diffraction limit is required. Nanoantennas have been designed to generate localized circularly polarized light for high-density all-optical magnetic recording system. The amplitude and phase of the localized light depend on the incident wavelength, shapes, and materials of antennas. To realize these practical systems, the antenna shape must be robust against fabrication errors. Therefore, we propose an antenna shape with high robustness against these errors. Furthermore, a control method for the amplitude and phase of localized light is proposed.

  A method for the power loss analysis for ferrite is required and is expected to lead to the development of low-loss ferrites. In the present paper, the magnetic field intensity in ferrite was decomposed into four components for the analysis. When the time derivative of the magnetic induction, dB/dt, is low, the magnetic field intensity is composed of only two components, H_u and H_h, which yield the magnetic flux and the hysteresis loss, respectively. At high-dB/dt excitations, magnetic field intensities, H_v and H_f, appear in addition to H_u and H_h, where H_v lowers the permeability and H_f causes the dynamic magnetic loss, respectively. The temperature characteristics of H_u, H_h, H_v and H_f differ, which implies that the hysteresis and dynamic magnetic losses are caused by different physical mechanisms. The function tables for H_u (B, B_m), H_h (B, B_m), H_v (B, dB/dt, B_m) and H_f (B, dB/dt, B_m) were obtained from measurements conducted at ferrite core temperatures of 20, 40, and 60 °C, where B_m is the maximum magnetic flux density. The tables were used to simulate the magnetic field intensity for the excitation when a sinusoidal waveform voltage was applied to a ferrite inductor. The simulation results show good agreement with the experimental results.