Takanori Tsutaoka

Bio: Takanori Tsutaoka is an academic researcher from Hiroshima University. The author has contributed to research in topics: Magnetization & Magnetic susceptibility. The author has an hindex of 19, co-authored 113 publications receiving 1977 citations.

Frequency dispersion of complex permeability in Mn–Zn and Ni–Zn spinel ferrites and their composite materials

Abstract: Complex permeability spectra μ*=μ′−iμ″ for two types of spinel ferrites (Ni–Zn ferrite and Mn–Zn ferrite) and their composite materials have been investigated. The contribution of domain-wall and natural resonance to the permeability spectra was estimated by the numerical fitting of actual measurement data to a simple formula. Frequency dispersion type of each component, relaxation or resonance, can be estimated from one of the fitting parameters, damping factor. In sintered Mn–Zn ferrite, domain-wall contribution is dominant and gyromagnetic spin resonance or relaxation-type magnetization rotation is large in Ni–Zn ferrite. However, relaxation character is dominant in both Mn–Zn and Ni–Zn ferrite composite materials. In composite materials, the permeability value can be scaled by the ferrite particle content using a simple model concerning demagnetizing field. This analysis is useful in designing the permeability spectra of ferrite composite materials.

Frequency dispersion and temperature variation of complex permeability of Ni‐Zn ferrite composite materials

Abstract: Permeability spectra in Ni‐Zn ferrite composite materials were studied at the volume loading of ferrite above 30% and at temperatures from 100 to 400 K. The permeability decreased with decreases in the volume loading of ferrite. This decrease was much larger than that expected from the empirical mixing law. This was attributed to the demagnetizing field, generated by the magnetic poles on the surface of the ferrite particles. Simultaneously, the demagnetizing field increased spin resonance frequency. For the sintered ferrite, the primary peak of the permeability was just below the Curie temperature. The peak becomes obscure and disappeared as the volume loading decreased. The temperature dependence of the spin resonance frequency was lower in the ferrite composite material than that in the sintered ferrite. These features were also discussed from the view point of the demagnetizing field.

Negative permeability spectra in Permalloy granular composite materials

Abstract: Complex permeability spectra of Permalloy granular composite materials have been studied in the microwave frequency range. The heat-treated Permalloy particles in the air at several hundreds of °C have a high surface electrical resistance; the eddy current effect in the high frequency permeability spectra can be suppressed in the composite structure containing the percolated particles. A negative permeability has been obtained above 5GHz due to the natural magnetic resonance in the 70vol% particle content composite material. In this content, electrical permittivity spectra show a nonmetallic characteristic. This permeability dispersion can be applied for the left-handed media.

Low frequency plasmonic state and negative permittivity spectra of coagulated Cu granular composite materials in the percolation threshold

Abstract: We have studied the relative complex permittivity (e r = e r′- ie r″) of copper granular composite materials containing coagulated Cu particles in the microwave range as well as the electrical conductivity. The insulator to metal transition was observed at the percolation threshold φ c = 16.0 vol. %. The enhancement of permittivity in the insulating state can be described by the Effective Cluster Model. Above the percolation threshold φ c, it was found that the Cu granular composites show negative permittivity spectra below a characteristic frequency f 0 indicating the low frequency plasmonic state. Characteristic frequency tends to increase with particle content.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Complex hydrides for hydrogen storage.

Abstract: Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Recent Progress in Metal Borohydrides for Hydrogen Storage

Abstract: The prerequisite for widespread use of hydrogen as an energy carrier is the development of new materials that can safely store it at high gravimetric and volumetric densities. Metal borohydrides M(BH4)n (n is the valence of metal M), in particular, have high hydrogen density, and are therefore regarded as one such potential hydrogen storage material. For fuel cell vehicles, the goal for on-board storage systems is to achieve reversible store at high density but moderate temperature and hydrogen pressure. To this end, a large amount of effort has been devoted to improvements in their thermodynamic and kinetic aspects. This review provides an overview of recent research activity on various M(BH4)n, with a focus on the fundamental dehydrogenation and rehydrogenation properties and on providing guidance for material design in terms of tailoring thermodynamics and promoting kinetics for hydrogen storage.