Structural, electronic, and magnetic properties of metal-doped TiO2 and TiO2-ƒÔ

L. A. ERRICO, M. RENTERÍA, Y M. WEISSMANN.

Angra do Reis, Brasil

Congreso; XII Latin American Congress of Surface Science and its Applications (XII CLACSA); 2005

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Integrating spin functionality into otherwise nonmagnetic materials has become a highly desirable goal in the last years. For example, dilute magnetic impurities in semiconductors produce novel materials appealing for spintronics1, 2. This is a rapidly developing research area because the electron spin may play a separate role, in addition to the usual charge degree of freedom. For their practical applications, ferromagnetic semiconductors are required to have a high Curie temperature (TC). While most of the dilute magnetic semiconductors (DMS) have a TC much lower than room temperature, room temperature ferromagnetism has been observed in Co- and Fe-doped TiO2 thin films with both the anatase and rutile phase3-5. These results have motivated intensive experimental and theoretical studies on the structural and electronic properties of these materials6, but the origin of ferromagnetism and its high Tc is still controversial. In this work we study the structural, electronic, and magnetic properties of doped rutile TiO2 for different impurity concentrations, considering different distributions of the impurities in the host lattice. Calculations were performed with ab initio methods, assuming that the magnetic impurities substitutionally replace the Ti ions. Our results show that a local magnetic moment appears in the cases of  Mn, Fe, and Co impurities, but not in the case of Ni and Cu impurities. They also show that in the system CoxTi1-xO2 the magnetic ions align ferromagnetically, while in MnxTi1-xO2 and FexTi1-xO2 the antiferromagnetic alignment is energetically favorable. We have also studied the effect of oxygen vacancies. Their presence decreases the energy required to introduce the impurities in the host lattice and reciprocally, the presence of impurities is related to a higher vacancy concentration. Therefore, the pairs impurity-nearest neighbor oxygen vacancy seem to be the energetically preferred structures and to produce the highest local magnetic moments. Ni and even Cu impurities acquire magnetic moments in this environment.