Evidence of defect-induced ferromagnetism in ZnFe2_{2}O4_{4} thin films

X-ray absorption near-edge and grazing incidence X-ray fluorescence spectroscopy are employed to investigate the electronic structure of ZnFe$_{2}$O$_{4}$ thin films. The spectroscopy techniques are used to determine the non-equilibrium cation site occupancy as a function of depth and oxygen pressure during deposition and its effects on the magnetic properties. It is found that low deposition pressures below 10$^{-3}$ mbar cause iron superoccupation of tetrahedral sites without Zn$^{2+}$ inversion, resulting in an ordered magnetic phase with high room temperature magnetic moment.Comment: Accepted for publication in Phys. Rev.

HfO2 based memory devices with rectifying capabilities

We report on the fabrication and characterization of metal/insulator/metal capacitor like devices, with both rectifying and hysteretic features. Devices are formed by two junctions, Ti/HfO2 and Co/HfO2. Each junction exhibits highly repetitive hysteretic I-V curves with a sharp transition from a high to a low resistance state (3–4 orders of magnitude jump). The opposite transition (from low to high) is induced by polarity reversal. The rectifying non-crossing characteristics of the I-V branches denote their potential use as a multifunctional device, acting as a built-in rectifier and memory cell in a single device. Based on the phenomenological model description by Zazpe et al. [Appl. Phys. Lett. 103, 073114 (2013)], we propose a circuital equivalent representation supported on switchable rectifying junctions. By exploring different electrode connections, we disentangle the role of the bulk transport in HfO2 devices.Fil: Quinteros, Cynthia Paula. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Zaspe, R.. CIC nanoGUNE; EspañaFil: Marlasca, F. G.. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; ArgentinaFil: Golmar, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; ArgentinaFil: Casanova, F.. CIC nanoGUNE; España. Fundación Vasca para la Ciencia; EspañaFil: Stoliar, Pablo Alberto. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Centre National de la Recherche Scientifique; Francia. Universite de Nantes; FranciaFil: Hueso, L.. Fundación Vasca para la Ciencia; España. CIC nanoGUNE; EspañaFil: Levy, Pablo Eduardo. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

In situ electrical characterization of palladium-based single electron transistors made by electromigration technique

We report the fabrication of single electron transistors (SETs) by feedback-controlled electromigration of palladium and palladium-nickel alloy nanowires. We have optimized a gradual electromigration process for obtaining devices consisting of three terminals (source, drain and gate electrodes), which are capacitively coupled to a metallic cluster of nanometric dimensions. This metal nanocluster forms into the inter-electrode channel during the electromigration process and constitutes the active element of each device, acting as a quantum dot that rules the electron flow between source and drain electrodes. The charge transport of the as-fabricated devices shows Coulomb blockade characteristics and the source to drain conductance can be modulated by electrostatic gating. We have thus achieved the fabrication and in situ measurement of palladium-based SETs inside a liquid helium cryostat chamber.Fil: Arzubiaga, L.. CIC nanoGUNE; EspañaFil: Golmar, Federico. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llopis, R.. CIC nanoGUNE; EspañaFil: Casanova, F.. CIC nanoGUNE; España. IKERBASQUE; EspañaFil: Hueso, Luis E.. CIC nanoGUNE; España. IKERBASQUE; Españ

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.

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

Room-Temperature Spin Transport in C60-Based Spin Valves

Carbon-based spin valves, composed of a C60 layer sandwiched between two magnetic materials show room temperature spin transport for a fullerene thickness up to 30 nm. This result, interpreted by a multistep tunnelling transport model, represents an advance in the field of carbon spintronics.Fil: Gobbi, Marco. CIC nanoGUNE Consolider; EspañaFil: Golmar, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Industrial; Argentina. CIC nanoGUNE Consolider; EspañaFil: Llopis, Roger. CIC nanoGUNE Consolider; EspañaFil: F. Casanova. CIC nanoGUNE Consolider; España. Basque Foundation for Science; EspañaFil: Hueso, Luis E.. CIC nanoGUNE Consolider; España. Basque Foundation for Science; Españ

C60-based hot-electron magnetic tunnel transistor

A C 60-based magnetic tunnel transistor is presented. The device is based on the collection of spin-filtered hot-electrons at a metal/C 60 interface, and it allows an accurate measurement of the energy level alignment at such interface. A 89% change in the collected current under the application of a magnetic field demonstrates that these devices can be used as sensitive magnetic field sensors compatible with soft electronics.Fil: Gobbi, M.. No especifíca;Fil: Bedoya Pinto, A.. No especifíca;Fil: Golmar, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llopis, R.. No especifíca;Fil: Casanova, F.. No especifíca;Fil: Hueso, L. E.. No especifíca

C60/NiFe combination as a promising platform for molecular spintronics

Spintronics based on ferromagnetic metals and organic semiconductors has attracted great interest in recent years. Molecular-based spintronic devices, such as magnetic tunnel junctions, have been demonstrated with performances competing with those of conventional inorganic devices. Still, there is huge margin for improvement, as many details about the injection of spin-polarized electrons into the molecular layer remain not completely understood. In order to achieve better understanding and control of the physical mechanisms, it is necessary to explore various combinations of ferromagnetic metals and organic semiconductors. In this letter, we study the properties of the combination between the ferromagnetic metal NiFe (commonly known as Permalloy or Py) and the molecular system C60. We produced C60/Py bilayers and characterized them structurally, electrically and magnetically. The C 60 films grow smoothly on both Py and SiO2 substrates, and we estimate that a 5-nm-thick C60 film covers completely the surface underneath without leaving pinholes and can be therefore used in a vertical device, as confirmed by electrical characterization. Furthermore, the C 60 film is robust against the deposition of the top metal electrode, being the intermixing layer of only 1-2 nm at the C60/Py interface. Finally, we show that the magnetic properties of Py are not affected by the deposition sequence, and that a 5-nm-thick Py layer on top of a C60 layer keeps its magnetic properties intact. These results show that the combination between Py and C60 provides a robust template platform for the development of molecular spintronics, and can be used later on for more sophisticated investigations, such as the role of the interfaces in the spin injection.Fil: Gobbi, M.. No especifíca;Fil: Pascual, A.. No especifíca;Fil: Golmar, Federico. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llopis, R.. No especifíca;Fil: Vavassori, P.. No especifíca;Fil: Casanova, F.. No especifíca;Fil: Hueso, L. E.. No especifíca