UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-22 2:00
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Conference: Bucharest University Faculty of Physics 2003 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
GMR nanostructures obtained using Thermionic Vacuum Arc


Authors:
G. Musa, I. Mustata, M. Blideran, V. Zaroschi


Affiliation:
National Institute for Laser, Plasma and Radiation Physics Bucharest


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Keywords:


Abstract:
The present tendency to miniaturize the devices of all kind started a strong competition between different technologies in order to reveal the most suitable way to obtained thin films, which exhibits the GiantMagnetoResistance effect. The GiantMagnetoResistance effect it is defined as the decrease of a structure resistance when a magnetic field is applied on it. There are two main types of GMR thin film depositions, namely the sandwich type and the granular one. A GMR sandwich structure is grown from alternating ultra thin layers of magnetic materials. The most critical parameters of this thin film layers is the thickness of the nonmagnetic layer. The nonmagnetic layer thickness determines the ferromagnetic or anti-ferromagnetic coupling between the two ferromagnetic layers situated on the both sides of the separating nonmagnetic film. The desired coupling in the absence of the magnetic field is the anti-ferromagnetic one. The probability for an electron to be scattered when it passes into a ferromagnetic conductor depends on the direction of its spin and the direction of the magnetic moment of the layer. When the electron spin direction is anti-parallel with the magnetic moments the collision cross-section, is much greater than in the case of the parallel alignment. This determines the parallel spin electrons to travel trough, practically without collisions and to create an electrical shortcut circuit, which lowers the total resistance of the layer in the case of ferromagnetic alignment of the magnetic moments. The ferromagnetic alignment can be assured by an externally magnetic field. The subject of this paper is the granular type of structure when the magnetic metal, as Co, Fe, Ni, is introduce as clusters into a conductive metal sea, Cu, Ag, Au. The critical parameters in this case are the dimension of these clusters and the distance between them and the mechanism is similar to the case of alternating layers. Thermionic Vacuum Arc method proved out to be very well suited for the metallic GMR structure deposition. It uses an electron beam emitted by an externally heated cathode and accelerated by the high anodic voltage. The electron beam can evaporate the anode materials as neutral pure particles and facilitate their deposition on the substrate when the electron energy and current intensity are not too high. If we increase the anodic voltage up to a certain value, the evaporation rate increases as much as to allow an electrical discharge to be ignited in the evaporated pure material. This discharge is maintained even when the discharge currents are as low as some hundreds milliamps but can burn only in the presence of the externally heating cathode source. In a vacuum chamber with the minimum pressure of 10(-6) torr we mounted two independent group of deposition one for cobalt and the other for copper or silver. Each group has its proper filament and anode source, and between them an electrical screen was mounted trying to minimize the reciprocal influence of the two plasmas. The obtained data show that TVA discharge could be considered as a good candidate for GMR film depositions because of the high purity of the film and high compactness and density. We obtained GMR effect as high as 3 to 33% at the ambient temperature and many times without post-deposition thermal treatment. The deposition rate is relatively high. The treated probes showed very rapid wing variations that are for short magnetic field domains of variation, which could be very good for magnetic sensitive gauges production. A very important characteristic of this method is that the energy of ions can be controlled by modifying the high anode voltage or the cathode heating.