UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2010 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Simultaneously thermionic vacuum arc discharges in obtaining feromagnetic thin films


Authors:
I. Jepu (1), C. Porosnicu(1), I. Mustata (1), C. P. Lungu(1), V. Kuncser(2), M. Osiac(3), G. Iacobescu(3), V. Ionescu (4)


Affiliation:
(1)National Institute for Lasers, Plasma and Radiation Physics, Magurele-Bucharest, RO

(2)National Institute of Materials Physics, Bucharest-Magurele, RO

(3)University of Craiova, Faculty of Physics, 200585 Craiova, RO

(4)University of Constanta, Faculty of Physics, Constanta, RO


E-mail


Keywords:
thermionic vacuum,feromagnetic thin films


Abstract:
High quality granular ferromagnetic thin films on glass and silicon wafer substrates were obtained using the original thermionic vacuum arc (TVA) method developed at National Institute for Laser, Plasma and Radiation Physics. The originality of the method used in this experiment consists on the electron beam emitted by an externally heated cathode (a tungsten grounded filament) accelerated by a high anodic voltage. The electron beam evaporates the anode material as neutral pure particles and facilitates their deposition on the substrate when the electron energy and the discharge current intensity are not too high (5-50 eV and 10-100 mA, respectively). The optimization of plasma ignited in pure metal vapors and to the absence of a buffer gas inside the experimental chamber made possible the obtaining of granular ferromagnetic thin film structures. The experimental studies investigate the GMR (Giant Magneto Resistance)/TMR (Tunneling Magnetorezistive), due to their importance in the development of future data storage devices. We report obtaining of 77-200 nm thick Cu/Ni/Fe structures by Thermionic Vacuum Arc (TVA) technique. A new experimental set-up, with three simultaneously discharges, was made to obtain the desired thin film composition. To ignite all of the materials used for deposition, the three cathodes were heated by a current of 50 to 55A, depending on the material’s melting point. The electron beams were focused on three different tungsten coated carbon crucible anodes filled with Fe, Cu and Ni respectively. Depending on the material melting temperature of each anode, a high voltage of 1400V-2800V was applied. The optimal concentration of the thin film structures included 30%-65% Ni, 5%-25% Fe and 10%-40% Cu. The structural and morphological properties of the prepared nanostructured films were analyzed by AFM (Atomic Force Microscopy), XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy). Magneto-Optical Kerr Effect studies were made in order to infer the electrical resistance behavior of the structures when a magnetic field was applied. In order the obtain concluding electrical measurements results, cooper electrodes were deposited using the same method before and after the actual three material thin structure. In this way significant changes in the electrical resistance behavior were noticed and were correlated with TVA plasma parameters used for film preparation.