XAS study of the local environment of impurities in doped TiO2 thin films

In this work we present an X-ray Absorption Spectroscopy characterization of the local environment of the impurity in room temperature ferromagnetic anatase TiO2 thin films doped with Co, Ni, Cu, or Zn, deposited on LaAlO3 substrate by Pulsed Laser Deposition. It was found that there is a considerable amount of impurity atoms substituting Ti in TiO2 anatase, although the presence of metal transition monoxide clusters can not be discarded. From our results we infer that the observed room temperature ferromagnetism of the samples could be assigned to the metal transition atoms replacing Ti in TiO2 anatase.Comment: 4 pages, 3 figures, 1 table, Physica B (in press

Appearance of room temperature ferromagnetism in Cu-doped TiO2−δ_{2-\delta} films

In recent years there has been an intense search for room temperature ferromagnetism in doped dilute semiconductors, which have many potentially applications in spintronics and optoelectronics. We report here the unexpected observation of significant room temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped TiO$_2$ thin films grown by Pulsed Laser Deposition. The magnetic moment, calculated from the magnetization curves, resulted surprisingly large, about 1.5 $\mu_B$ per Cu atom. A large magnetic moment was also obtained from ab initio calculations using the supercell method for TiO$_2$ with Cu impurities, but only if an oxygen vacancy in the nearest-neighbour shell of Cu was present. This result suggests that the role of oxygen vacancies is crucial for the appearance of ferromagnetism. The calculations also predict that Cu doping favours the formation of oxygen vacancies.Comment: 4 pages, 3 figures, published in Phys. Rev. B (Rapid Comm.

Ab initio study of magnetism at the TiO2/LaAlO3 interface

In this paper we study the possible relation between the electronic and magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO3 has a layered structure along the (001) direction with alternating LaO and AlO2 planes, with nominal charges of +1 and -1, respectively. As a consequence of that, an oxygen deficient TiO2 film with anatase structure will grow preferently on the AlO2 surface layer. We have therefore performed ab-initio calculations for superlattices with TiO2/AlO2 interfaces with interfacial oxygen vacancies. Our main results are that vacancies lead to a change in the valence state of neighbour Ti atoms but not necessarily to a magnetic solution and that the appearance of magnetism depends also on structural details, such as second neighbor positions. These results are obtained using both the LSDA and LSDA+U approximations.Comment: Accepted for publication in Journal of Materials Scienc

The global oscillation network group site survey. II. Results

The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile. Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses. The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum

Electric-pulse-induced reversible resistance in doped zinc oxide thin films

Nonvolatile, electric-pulse-induced resistance switching is reported on S and Co doped ZnO thin films deposited on different substrates using magnetron sputtering and laser ablation. Two resistance states were obtained by applying voltage pulses of different polarity. The switching was observed regardless of the substrate, dopant species, or microstructure of the samples. In the Co doped ZnO samples, the two resistance states are remarkably stable and uniform

Ferromagnetism in doped TiO2 thin films prepared by PLD

Transition-Metal-doped TiO2 thin films, with nominal composition Ti₀.₉TM₀₁O₂-δ (TM = Mn, Fe, Co, Ni, Cu), were grown by pulsed laser deposition (PLD), in order to study the role of dopants in the origin and significance of room temperature ferromagnetism in these systems. The crystallographic structures and their magnetic properties were characterized and the experimental results are compared to ab-initio calculations previously reported. The films are ferromagnetic at room temperature in the cases of Fe, Co, Ni and even Cu impurities, but not in the case of Mn doping. Our results support the hypothesis that oxygen vacancies play a key role in the origin of magnetism in doped TiO2 films, and can explain the diversity of magnetic moments observed experimentally for films grown under different conditions.Instituto de Física La Plat

Magnetic and structural study of Cu-doped TiO2 thin films

Transparent pure and Cu-doped (2.5, 5 and 10 at. %) anatase TiO2 thin films were grown by pulsed laser deposition technique on LaAlO3 substrates. The samples were structurally characterized by X-ray absorption spectroscopy and X-ray diffraction. The magnetic properties were measured using a SQUID. All films have a FM-like behaviour. In the case of the Cu-doped samples, the magnetic cycles are almost independent of the Cu concentration. Cu atoms are forming CuO and/or substituting Ti in TiO2. The thermal treatment in air promotes the CuO segregation. Since CuO is antiferromagnetic, the magnetic signals present in the films could be assigned to this Cu substitutionally replacing cations in TiO2.Comment: 11 pages, 3 figures, Surface Science (in press

Manejo del trauma penetrante cervical de Zona II. Hospital Clínico Regional Valdivia. Serie de casos clínicos

El trauma penetrante cervical de zona II, zona comprendida entre el cartílago cricoides y el ángulo de la mandíbula, que presenta signos de compromiso de una estructura vital, requiere exploración quirúrgica inmediata. La principal controversia, se genera sobre el manejo de lesiones de zona II en pacientes hemodinámicamente estables y sin signos que indiquen daño de estructura vital evidente. Existen 2 conductas: exploración quirúrgica de todas las lesiones que atraviesen el músculo platisma o, tratamiento selectivo que implicaría el examen clínico complementado con estudio por imágenes y endoscópicos que descarten lesiones de resorte quirúrgico. El objetivo de este artículo es presentar una serie de casos de trauma penetrante cervical de zona II en la Unidad de Emergencia del Hospital Clínico Regional de Valdivia entre los años 2002 y 2008 y realizar una breve revisión del tema. Se presentan ..

Ferromagnetism in doped TiO2 thin films prepared by PLD

Transition-Metal-doped TiO2 thin films, with nominal composition Ti₀.₉TM₀₁O₂-δ (TM = Mn, Fe, Co, Ni, Cu), were grown by pulsed laser deposition (PLD), in order to study the role of dopants in the origin and significance of room temperature ferromagnetism in these systems. The crystallographic structures and their magnetic properties were characterized and the experimental results are compared to ab-initio calculations previously reported. The films are ferromagnetic at room temperature in the cases of Fe, Co, Ni and even Cu impurities, but not in the case of Mn doping. Our results support the hypothesis that oxygen vacancies play a key role in the origin of magnetism in doped TiO2 films, and can explain the diversity of magnetic moments observed experimentally for films grown under different conditions.Instituto de Física La Plat