“Ferromagnetism in doped-TiO2 thin films”

S. DUHALDE; M.F. VIGNOLO; C. CHILLIOTE; CLAUDIA E. RODRÍGUEZ TORRES; L.A. ERRICO; A.F. CABRERA; F.H. SÁNCHEZ; M. WEISSMANN

Banff (Canada)

Congreso; Cola05- The 8th International Conference on Laser Ablation; 2005

Dilute magnetic semiconductors (DMS) consist of nonmagnetic semiconducting materials doped with a few atomic percent of impurity magnetic cations. Since the observation of ferromagnetism by Matsumoto et al in Co-doped anatase TiO2 [1], DMS have attracted much attention as well as controversy due to the combination of magnetic and semiconducting properties that makes them good candidates for spintronic device applications [2]. At first, ferromagnetism in Co-doped TiO2 was explained in terms of carrier induced mechanism as in III-V based DMS´s. Other works claimed that ferromagnetism was due to the formation of Co clusters within TiO2 structure. More recently, the idea that vacancies and defects are essential to ferromagnetic order and conductivity is being strongly considered [3]. So far, the precise mechanism is still controversial and is being actively debated in the literature. Evenmore, it is not clear if the mechanism of magnetic state formation is common for all DMS systems or if it is different for each combination of semiconductor host and magnetic dopant. But with no doubt a deep knowledge of the structure of the sample under study is the first step for the interpretation of the experimental results. In order to study the role of dopants and oxygen deficiency in the origin and significance of ferromagnetism, Transition-Metal-doped TiO2 thin films, grown by pulsed laser deposition  (PLD), were studied. XANES and EXAFS have been used to determine the valence state and local environment of cations as a function of growth conditions. The crystallographic structure was determined by x ray diffraction (XRD) and their magnetic properties were measured using a Vibrating Sample Magnetometer. Finally, ab-initio calculations, using full potential linear augmented plane wave (FP -LAPW) method, were performed. Theoretical and experimental results are compared and discussed.At first, ferromagnetism in Co-doped TiO2 was explained in terms of carrier induced mechanism as in III-V based DMS´s. Other works claimed that ferromagnetism was due to the formation of Co clusters within TiO2 structure. More recently, the idea that vacancies and defects are essential to ferromagnetic order and conductivity is being strongly considered [3]. So far, the precise mechanism is still controversial and is being actively debated in the literature. Evenmore, it is not clear if the mechanism of magnetic state formation is common for all DMS systems or if it is different for each combination of semiconductor host and magnetic dopant. But with no doubt a deep knowledge of the structure of the sample under study is the first step for the interpretation of the experimental results. In order to study the role of dopants and oxygen deficiency in the origin and significance of ferromagnetism, Transition-Metal-doped TiO2 thin films, grown by pulsed laser deposition  (PLD), were studied. XANES and EXAFS have been used to determine the valence state and local environment of cations as a function of growth conditions. The crystallographic structure was determined by x ray diffraction (XRD) and their magnetic properties were measured using a Vibrating Sample Magnetometer. Finally, ab-initio calculations, using full potential linear augmented plane wave (FP -LAPW) method, were performed. Theoretical and experimental results are compared and discussed.