Magnetic and Optical Functionalities of Nanostructured Metal Oxides and Metal Elements

Abstract

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.