金属酸化物および金属単体のナノ構造制御による磁気特性と光機能の創出

抄録

Magnetic and optical functionalities ascribable to nanostructure and sub-nanostructure of elemental metals and metal oxides are described. It is known that localized surface plasmon resonance takes place in a nano-structured metal and induces enhanced electric fields around the metal, which can interact strongly with incident light. This phenomenon can be applied to a random laser system comprising metal nanoparticles and fluorescent species. It is demonstrated that the threshold of laser oscillation can be controlled by tuning the separation between a metal nanoparticle and a fluorescent molecule. Also, a drastic change of magnetic and magneto-optical properties based on the modification of sub-nanostructure of metal oxides is exemplified. ZnFe₂O₄, the stable phase of which adopts the normal spinel structure and is antiferromagnetic with a Néel temperature as low as 10 K, can be ferrimagnetic with large magnetization and transition temperature higher than room temperature when a random spinel structure is achieved. EuTiO₃, the stable phase of which is antiferromagnetic, can be converted to a ferromagnet by lattice volume expansion or amorphization of the crystalline compound. The mechanism is explained in terms of the sub-nanostructure.