山口 一弘

山口 一弘 (やまぐち かずひろ)

 

所属 電気・電子系
職名 教授
専門分野 磁気材料工学
学位 工学博士(豊橋技術科学大学)
E-Mail yamaguch@ece.
末尾に”ibaraki-ct.ac.jp”を付けてください。
Link http://researchmap.jp/read0182504
 
 
研究紹介

 ゾル・ゲル法は、ゾルやゲル状態を利用して、低温でセラミックやガラスを合成する方法である。高均一性や低コストから、この方法は、光学材料、電子材料、触媒などの高機能性材料の作製に用いられている。その上、複雑な装置を導入せずとも、薄膜やフィルムなどの形状の作製も可能である。

 我々は、鉄をベースとした強磁性酸化物の作製を行っている。作製にはエチレングリコールに硝酸鉄(Ⅲ)を溶解した溶液のゲル化反応を利用し、これまでに、酸化鉄やイットリウム鉄ガーネットの薄膜を作製した。薄膜は、適当な粘性をもつゲル溶液を基板にスピンコーティングし、乾燥、熱処理を経て形成する。

 

1.マルチフェロイック薄膜の開発

 マルチフェロイックとは、1994年にH.Schmidに名付けられ、強磁性と強誘電性等、複数の秩序パラメータが共存する物質をいう。学術的な観点以外にも、応用上においても高いポテンシャルをもち、アクチュエータ、センサー、エネルギーデバイス等への応用が期待されている。

 加島らは、反応性スパッタ法によってアモルファスのFeベースの酸化物薄膜を作製し、室温以上において、強磁性と強誘電性が共存していることを発見した。我々は、化学的手法としてゾル・ゲル法を用いて、この薄膜を作製し、スパッタ膜と同様に、作製した膜においても磁気電気効果を発見した。現在は、磁気・電気・光間の相互作用を検証するために、透明電極を用いたフィルムキャパシタの作製を行っている。

 

2.磁性半導体の開発

 TiO2やZnO等に遷移金属を添加した半導体は、室温で強磁性を示す。しかしながら、その磁性の起源は明らかではない。我々は、ゾル・ゲル法によりCoを添加したTiO2薄膜を作製し、磁気光学特性から磁性の起源を明らかにしようとしている。

キーワード:ゾル・ゲル合成法、強磁性材料、マルチフェロイック

 

Kazuhiro Yamaguchi

 

Affiliation Electrical and Electronic Engineering Course
Title Professor
Fields of Research Engineering
Degree Dr.of Engineering(Toyohashi University of Technology)
E-Mail yamaguch@ece.
add “ibaraki-ct.ac.jp” to the end,please.
Link http://researchmap.jp/read0182504
 
 
Research

Sol-gel process is colloidal route used to synthesis ceramics and glasses at low temperature with an intermediate state including a sol and/or a gel state. Owing to high homogeneity and low cost in their products, this process is applied to the fabrication of various kinds of materials with functional facilities such as optical as well as electronic materials and catalysts. Furthermore, variety in configuration such as thin film and fiber can be produced without sophisticated apparatus.

 We have been investigated various Fe-based magnetic materials fabricated by sol-gel reaction of a solution of iron(III) nitrate dissolved in ethylene glycol and succeeded in producing ferromagnetic iron oxide films and yttrium iron garnet films on glass substrates. The solution of ferric nitrate and yttrium nitrate etc. dissolved in ethylene glycol kept at 80C begins to lose its fluidity and ultimately becomes a gel. The films are spin-coated on glass substrates and Si-wafers after the solution has an appropriate viscosity, dried and then annealed at various temperatures.

 

1. Development of Multiferroic films

 The new term multiferroic was first used by H.Schmid in 1994. Multiferroics have been defined as materials that exhibit more than one ferroic order parameter such as ferromagnetism and ferroelectricity. Besides scientific interest in their physical properties, multiferroics have potential for applications as actuators, switches, magnetic field sensors or new types of electronic memory devices. For example, magnetic memories controlled by electric field can be energy saving devices.

Kazima et al. founded that amorphous Ti-Fe-Pb-O films prepared by reactive-sputtering had coexistence of ferromagnetism and ferroelectricity above room temperature. We succeed in producing these films by sol-gel synthesis and founded the magnetoelectric effect as well as the sputtered films. Our present challenge is the observation of new phenomena owing to the combined effects of three factors: electricity, magnetism and light. To realize this, we have been investigating fabrication of the film capacitors with a transparent electrode.

 

2. Development of magnetic semiconductors

 Transition metal doped semiconductor oxides such as TiO2 and ZnO have been found to exhibit ferromagnetism at room temperature. However, the magnetic origin of ferromagnetism in these oxides has not been clearly identified. We have been fabricating Co-doped TiO2 films by sol-gel synthesis and revealing the magnetic origin by measuring magneto-optical properties of these films.  

Keyword:sol-gel synthesis, ferromagnetic materials, multiferroic

 

(title) Preparation of cobalt doped Ti oxide films and their magnetic properties  Research Reports of Ibaraki National College of Technology No.45 (2010) [in Japanese]
(author(s)) K. Yamaguchi, E. Hayashi, K. Yayoi and M.Inoue          
(abstract)

In attempt to obtain diluted ferromagnetic semiconductors, we prepared Co-doped TiO2 films on glass substrates by sol-gel synthesis. X-ray diffraction patterns of films with Co low concentration under 5% and high concentration such as 15% were assigned to anatase and rutile TiO2, respectively. All films showed ferromagnetic behavior at room temperature. Their magnetooptical Faraday spectra were quite different from those of cobalt films and clusters. This result suggested that the origin of ferromagnetism is assigned to Co-substituted TiO2. 

 

(title) Preparation of TM-doped ZnO films  Joint Technical Meeting on Metal and Ceramics and Magnetics, IEE Japan. MAG-06-160(2006) [in Japanese]
(author(s)) A. Hayashi, M. Kawamatsu, K. Yayoi and K. Yamaguchi
(abstract)

In an attempt to fabricate diluted ferromagnetic semiconductors, we fabricated Fe-,Co-doped ZnO films on glass substrates by sol-gel method. Fe-doped ZnO showed ferromagnetic behavior at room temperature. However, the origin of ferromagnetism is not assigned to wrutzite but to spinel structure. In addition, Co-doped ZnO films showed paramagnetic behavior at low temperature of 80K. 

 

(title) Magnetic and Magneto-optical Properties of Composite Films of Ferromagnetic Ultrafine Particles Dispersed in Polymethyl Methacrylate  Materials Science Forum Vols.287-288 pp.483-486 (1998)
(author(s)) K. Yamaguchi,T. Sato, Y. Kato, M. Inoue and T. Fuji
(abstract)

Magnetic and magneto-optical properties of composite films of ultrafine fcc cobalt particles dispersed in a transparent PMMA plastic matrix have been investigated. The colloidal solutions suspended by cobalt particles were synthesized by decomposing dicobalt octacarbonyl dissolved in  toluene together with PMMA. The average particle diameter ranging 3.8nm to 15.9nm, was controlled by the solvent concentrations. The Faraday rotation of the films had a unique wavelength dependence. 

 

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