Toshitaka Fujii

Bio: Toshitaka Fujii is an academic researcher from Toyohashi University of Technology. The author has contributed to research in topics: Amorphous solid & Magneto. The author has an hindex of 6, co-authored 20 publications receiving 770 citations.

One-dimensional magnetophotonic crystals

Abstract: Two types of one-dimensional photonic crystals composed of magnetic and dielectric materials (magnetophotonic crystals) driven, respectively, by Kerr (reflection) and Faraday (transmission) modes were constructed. Their optical and magneto-optical (MO) properties were studied in detail to confirm our theoretical results showing the large Kerr and Faraday effects of the media originating in the localization of light. For the Kerr-mode operation, films with (SiO2/SiN)×k/Co/(SiN/SiO2)×k (k: number of layers) structures were fabricated, while for the Faraday-mode operation, films with (SiO2/Ta2O5)×k/Bi:DyIG/(Ta2O5/SiO2)×k structures were formed. Excellent agreement between the theoretical and experimental results was obtained, where large enhancement in both Kerr and Faraday rotations appeared originating in the localization of light in the vicinity of the magnetic layers. Since the localized state of light can be controlled artificially, the one-dimensional magnetophotonic crystals will impact for various MO...

Magneto-optical properties of one-dimensional photonic crystals composed of magnetic and dielectric layers

Abstract: The magneto-optical (MO) Faraday effect of one-dimensional photonic crystals (1D-PCs) composed of Bi-substituted yttrium–iron–garnet films and dielectric films such as SiO2 and TiO2 films were studied theoretically. Because of considerable localization of light, these media exhibit a very large MO effect. For instance, when the film structure is chosen to be appropriate for supporting the localization of light, the 1D-PC films can possess a huge Faraday rotation angle reaching to −28 deg/μm at λ=1.15 μm. The analysis reveals that the MO characteristics of the 1D-PC films are almost governed by the degree of localization of light, which can be controlled by varying the number of reflection layers in the films.

A theoretical analysis of magneto-optical Faraday effect of YIG films with random multilayer structures

Abstract: The magneto-optical (MO) Faraday effect of Bi-substituted yttrium iron garnet (Bi:YIG) films with random multilayer structures is analyzed using the random matrix approach, and the Faraday rotation angles (θF) are examined in comparison with those of periodic multilayer films. The films consist of Bi:YIG films and SiO2 dielectric films, which are stacked randomly (periodically) so as to form the random (periodic) multilayer structures. Similarly to the case of MO Kerr effect, a considerable enhancement in θF takes place when the film structure meets the nonreflection condition of light. In particular, θF of the film reaches a maximum of 1.4°/μm at λ=1.15 μm, with the fraction of Bi:YIG layers in the random multilayer film is 41%. This value is about seven times larger than that of a single Bi:YIG film (θF=0.2°/μm), and cannot be attained with periodic multilayer films.

Love‐type surface‐acoustic waves propagating in amorphous iron‐boron films with multilayer structure

Abstract: The propagation of Love‐type surface‐acoustic waves (SAWs) in a multilayer structure was investigated. The structures consisted of rf‐sputtered iron‐boron (FeB) amorphous magnetic films stacked alternatively to SiOx insulating layers i.e., FeB‐(SiOx−FeB)×n (where n denotes the stacking number) onto a soft glass substrate. The phase of waves was controlled over a wide range by a magnetic field applied in the film plane, through change in the strength of magnetoelastic coupling between the magnetic moment of the FeB film and SAW propagating in the substrate. The transducers for the Love‐type SAW excitation were constructed by combining the interdigital electrodes and ZnO films, prepared by sputtering in an oblique electrode arrangement. The controllable phase shift (ΔΦ) under a magnetic field increases linearly with n, when the total FeB film thickness DM is kept constant (DM=1.5 μm). The ΔΦ of a device with n=8 is about 2300°/cm within the magnetic field smaller than about 120 Oe.

Optimum geometrical structure of highly magnetostrictive multilayer films for horizontally polarized high frequency magneto‐surface‐acoustic‐wave propagation

Abstract: Optimum geometrical structure of highly magnetostrictive multilayer films for the propagation of horizontally polarized magneto‐surface‐acoustic‐wave (Love‐type MSAW) was determined theoretically. The multilayered medium is composed of highly magnetostrictive alloy films and insulating films which are stacked alternately on a glass substrate. The analysis revealed that outstanding magnetoacoustic quantities comparable to those of an ideal nonconductive medium can be realized with the conductive multilayer films whose geometrical parameters meet the following conditions: DM/DL≥1, DM/DI≥10, and N∼20, where N is the number of insulating layers having the whole thickness of DI, and DM is the whole thickness of magnetic layers. DL is a limiting thickness of the magnetic film with a single‐layer structure, above which the magnetoacoustic quantities are considerably deteriorated due to the micro‐eddy current losses.

Photonic crystals

Abstract: The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

The Past, Present, and Future of Ferrites

Abstract: Ferrites—ceramic ferromagnetic materials—have been considered as highly important electronic materials for more than half a century. During this time, the characteristics of commercial ferrite materials, both soft and hard ferrites, have come to approach theoretical values. The quality of commercial ferrites has been improved through accumulated scientific knowledge and advanced technology. This article provides a comprehensive survey of the historical development of the science and technology of ferrite materials as well as applications of the ferrites. The article also offers a forecast of the future of ferrites in terms of their chemistry.

Enhanced magneto-optical effects in magnetoplasmonic crystals

Abstract: Plasmonics allows light to be localized on length scales much shorter than its wavelength, which makes it possible to integrate photonics and electronics on the nanoscale. Magneto-optical materials are appealing for applications in plasmonics because they open up the possibility of using external magnetic fields in plasmonic devices. Here, we fabricate a new magneto-optical material, a magnetoplasmonic crystal, that consists of a nanostructured noble-metal film on top of a ferromagnetic dielectric, and we demonstrate an enhanced Kerr effect with this material. Such magnetoplasmonic crystals could have applications in telecommunications, magnetic field sensing and all-optical magnetic data storage.

Magnetoelectric and multiferroic media

Abstract: The last decade has witnessed a significant growth of research into materials with coupled magnetic and electric properties. Reviewed here are the main types and mechanisms of magnetoelectric interactions and conditions of their origin. Special attention is given to potentially practical materials that display magnetoelectric properties at room temperature. Example applications of magnetoelectric materials and multiferroics in information and energy saving technologies are discussed.