Structural, electronic, and magnetic properties of Metal-Doped TiO2 and TiO2-delta.

L. A. ERRICO; M. RENTERÍA; M. WEISSMANN

Angra Do Reis

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

PUC, UFF, UERJ (Brasil)

Integrating spin functionality into otherwise nonmagnetic materials has become ahighly desirable goal in the last years. For example, dilute magnetic impurities insemiconductors produce novel materials appealing for spintronics [1, 2] . This is a rapidlydeveloping research area because the electron spin may play a separate role, in additionto the usual charge degree of freedom. For their practical applications, ferromagneticsemiconductors are required to have a high Curie temperature (TC). While most of thedilute magnetic semiconductors (DMS) have a TC much lower than room temperature,room temperature ferromagnetism has been observed in Co- and Fe-doped TiO2 thinfilms with both the anatase and rutile phase [3-5] . These results have motivated intensiveexperimental and theoretical studies on the structural and electronic properties of thesematerials [6] , but the origin of ferromagnetism and its high Tc is still controversial.In this work we study the structural, electronic, and magnetic properties of dopedrutile TiO2 for different impurity concentrations, considering different distributions of theimpurities in the host lattice. Calculations were performed with ab initio methods,assuming that the magnetic impurities substitutionally replace the Ti ions. Our resultsshow 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-xO2the magnetic ions align ferromagnetically, while in MnxTi1-xO2 and FexTi1-xO2 theantiferromagnetic alignment is energetically favorable.We have also studied the effect of oxygen vacancies. Their presence decreases theenergy required to introduce the impurities in the host lattice and reciprocally, thepresence of impurities is related to a higher vacancy concentration. Therefore, the pairsimpurity-nearest neighbor oxygen vacancy seem to be the energetically preferredstructures and to produce the highest local magnetic moments. Ni and even Cu impuritiesacquire magnetic moments in this environment.[1] H. Ohno, Science 281, 951 (1998).[2] T. Fukumura et al., Appl. Surf. Sci. 223, 62 (2004).[3] Y. Matsumoto et al., Science 291, 854 (2001)[4] W. K. Park et al., J. Appl. Phys. 91, 8093 (2002).