Room Temperature Ferromagnetism Study of TiO2 Based Magnetic Semiconductors By Pulsed Laser Deposition

Abstract

The engineering applications of spintronics devices utilizing both charge and spin properties of electrons require host materials for spintronics to possess ferromagnetism above room temperature. A research into the unique properties of oxide diluted magnetic semiconductors is one of the most important issues for the spintronics application. In this thesis, room temperature ferromagnetism (RTFM) was found in several TiO2 related films. Through detailed study, the proposed promising host materials for spintronics applications were Ga doped TiO2 and N doped TiO2 systems. The origin of ferromagnetism in these systems was investigated. The ferromagnetism is related with the defect engineering (intentionally creating cation or anion vacancies) and p-p interaction model.

(1) Ga?TiO2 films were deposited by pulsed laser deposition. The ferromagnetism is not associated with the impurities, but with Ti vacancies, a finding that is verified by positron annihilation spectroscopy.

(2) Room temperature ferromagnetism has been experimentally observed in TiO2:N films prepared by pulse laser deposition under N2O atmosphere. The origin of the ferromagnetism is the O substitution with N. Each substituted N has a magnetic moment of approximately 0.9 ?B. The substitution of O also resulted in p-type behavior, accompanied with magnetoresistance and anomalous Hall Effect.