Magnetocapacitance (MC) effect has attracted much attention due to the fascinating spin phenomena, such as spin capacitance, frequency-dependent spin transport and potential applications as highly-sensitive magnetic sensors, high-frequency devices and energy storage materials. The MC effect observed in magnetic tunneling systems is generally referred to as tunnel magnetocapacitance (TMC). A normal TMC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (iTMC) effect, which was recently observed in Fe/AlO_x/Fe₃O₄ magnetic tunnel junctions (MTJs). The iTMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the iTMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Fröhlich model, combined with the Zhang formula and parabolic barrier approximation, and spin-dependent drift-diffusion model. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports.

This paper describes the trends on research and development of the switching power supplies for point-of-load, whose switching frequencies are increased to make them smaller. Examples of small power magnetic devices and switching power supplies in which those magnetic devices are mounted will be introduced. In addition, it details the recent research trends of ultra-high frequency and ultra-compact switching power supplies, the latest efforts and prospects for novel high-frequency magnetic materials having granular structure and their applications as the high-frequency power magnetic devices for those power supplies.

This paper reviews recent progress on nonreciprocal metamaterials using yttrium iron garnet ferrites in the microwave region and their applications to resonators and leaky wave antennas. By using the nonreciprocal metamaterials, size-free pseudo-traveling wave resonators with arbitrarily tunable phase-gradient of field distribution are realized and implemented to beam scanning antennas. The resonant mechanism of the antennas helps themselves reduce beam squint without loss of beam scanning functionality and gains higher efficiency.

We have developed a vector network analyzer ferromagnetic resonance (VNA-FMR) spectrometer with field modulation detection. This system provides broadband coverage and very high sensitivity to resolve the FMR signal on a ultra-thin (∼ 1 nm thick) magnetic film. This paper first presents the detail of the VNA-FMR spectrometer built in this work, including its operation principle and design guideline, and second various magnetic properties obtained by the VNA-FMR measurement results.

The effect of the negative permeability of the magnetic film on the inductive coupling was quantitatively investigated using a magnetic circuit analysis of two parallel microstrip line (MSLs) with a Co-Zr-Nb film. First, an electromagnetic field simulation was performed to obtain the magnetic flux distribution around the MSLs with the Co-Zr-Nb film. A simple magnetic circuit model considering the negative permeability, based on the simulated magnetic flux distribution, was constructed. The self-inductance of the MSL and the mutual inductance between the MSLs were estimated. Finally, the coupling coefficient of magnetic flux was obtained using the self and the mutual inductances. As a result, it was shown that the inductive coupling could be reduced to almost zero in the certain frequency range above the FMR frequency caused by the negative permeability of the magnetic film. This result indicates the possibility of developing the design guideline of the magnetic films as the crosstalk suppressors.

This paper describes the study on structure and magnetic properties of Fe-B particles with submicron sizes synthesized by chemical preparation in aqueous solutions. The shape and structure of the particles are spherical and amorphous regardless of median size. Both the remanence magnetic ratio and coercivity of the particles are independent of median size and become lower, suggesting the good magnetic softness with the low hysteresis loss. Furthermore, as for the dynamic magnetic properties of the particles, each ferromagnetic resonance (FMR) peak can be observed in the frequency range of approximately 3∼5 GHz and their line-widths are broad. These results demonstrate that these amorphous Fe-B spherical particles with submicron sizes are one of the candidates as soft magnetic materials for next generation high-frequency magnetic devices.

Effective permeability taking account of demagnetization factor is widely used in the field of the magnetic engineering. A development of this effective permeability to complex permeability in the high frequency domain is studied. In comparison with the solution of LLG equation, it shows that the permeability in the low frequency domain and the resonance frequency calculated by using demagnetization factor are almost corresponding to those calculated by LLG equation. However, the good agreement is not seen in the resonance absorption peak width. Furthermore, the measured complex permeability of a Ni-Fe film is compared with the calculations by using demagnetization factor.

This paper presents the equivalent circuit modeling method for magnetic components used in 10 MHz class-E inverters with 2-port measurement by network analyzer. The equivalent circuit parameter extraction procedures from measured S-parameter with S-Z and equivalent circuit transformation is explained. Magnetization characteristics of iron metal composite core and carbonyl iron core are assessed for the parameter extraction. Circuit simulation results of class-E inverters operation with obtained circuit models almost coincide with experimental results.

Spin-wave integrated circuit using magnetic garnet films attract many interests because of their low Joule heating as well as the wide range of tunability of the wavelength. In this circuit, the phase interference of spin waves plays an important role to show functions. Hence, the control of phase and magnitude of spin waves is an essential technique to realize spin-wave integrated circuits. To control the phase and magnitude of spin waves, we fabricated magnonic crystals using metal periodic structures fabricated on magnetic garnet films. Forward volume spin waves propagated through the magnonic crystal and showed a magnonic bandgap. In this paper, the designing of the magnonic crystal using finite integration technique (FIT) and fabrication of samples using etching were also described.

In this report, we focus on the magnetic dipole moment and the charge model to model the magnetic shield case of the capsule endoscope guiding device and use the two to propose a cylinder of ϕ100×25 proposed by Matsuhashi. The area where the magnetic flux density distribution is different was clarified. As a result, it was suggested that the charge model is effective near the magnet (l = 0 to 0.3 m) and the magnetic dipole moment is effective far from the magnet (0.4 m ≤ l).

In designing motors, the magnetic properties of electrical steel sheets in the actual conditions must be obtained. In particular, the stress dependence of iron loss is important. This paper describes a newly developed apparatus to measure the magnetic properties of an electrical steel sheet in applying both in-plane and out-of-plane compressive stress. By using the developed apparatus, the magnetic properties can be measured under the uniform stress condition throughout the evaluation area. According to the measured results, it can be confirmed that the increasing tendency of iron loss depending on the in-plane compressive stress can be decreased by the out-of-plane compressive stress applied at the same time.

Vanadium oxide (VO_x) thin films were grown on c-plane sapphire substrates by metal-organic decomposition (MOD). Their crystallinity and optical characteristics were evaluated by XRD, XPS, AFM, LSM and a spectrophotometer. The crystallinity of the VO_x thin films were improved in adjusting the O reduction by controlling the firing time in N₂ atmosphere and a spin coating rotation speed. As a result, in the optimized VO_x samples under a firing temperature of 580°C after calcining at 300°C with 6000 rpm coating speed, the growth of polycrystalline fine nanoparticles of a single composition was confirmed which has good thermochromic characteristics.

ZnO microparticles show non-liner I-V properties and they are being used in epoxy resin to make ZnO/epoxy composites. The electrical properties of composite materials depend on ZnO microparticles and their amount in the composites. In this paper, we prepared several composite samples with various amounts of ZnO microparticles and measured their electrical and dielectric properties. The diameter of ZnO micropatricles were around 20∼100 µm and they were injected to epoxy resin in different amount from 35% to 43% volume fractions. The electrical properties of our samples showed a good relationship with ZnO microparticles' amount in them. However, further works are needed to understand the effect of ZnO microparticles amount in epoxy composites.