ABSTRACT
264More than a decade ago, it was suggested theoretically that room temperature ferromagnetism (FM) could be obtained in various semiconductors such as ZnO, GaAs, GaN, etc. if we dope Mn transition-metal (TM) into these systems. The magnetic ordering in those compounds was thought to be induced by the Ruderman-Kittel-Katsuya-Yosida interaction of localized moments of dopants via 2p holes or 4s electrons. Being excited by this idea, many experimental groups have tried to dope TMs into many oxides such as ZnO, TiO2, SnO2, In2O3, ZrO2, HfO2, etc. aiming to obtain room temperature FM in semiconductors, in order to be able to exploit both charge and spin in same compounds. Indeed, room temperature FM was found; however, the phenomenon is not the same as what theorists proposed. The finding of Coey’s group in 2004 about room temperature FM of pristine HfO2 has given some warning to the magnetism community to be more careful when judging the role of TM dopings. More recently, experimental observations of FM for various oxides such as TiO2, HfO2, In2O3, ZnO, CeO2, Al2O3, and MgO in nanometer materials have confirmed that FM is certainly possible for pristine semiconducting oxides. It is very likely that FM could stem from oxygen vacancies and/or defects that were formed more comfortably at the surface and interfaces.
Research on very thin films and nanoparticles of diluted magnetic semiconducting oxides (DMSO) has shown that downscaling magnetic oxide semiconductors to nanometer size must be a key point, in order to make them ferromagnetic. Exploiting the bright side of nanoworld in the field would help to open a new door for spintronic applications.
The domain of DMSO research still demands a huge of efforts of leading research groups toward higher levels with hope to make it able to approach closer to a realization of spintronic devices based on DMSO materials.
