Transport, magnetic and time dependent effects in metal-insulator granular layered films

• Type: Article in International Scientific Journal
• Date: 2001

Authors

sousa, j. b. (Author) FCUP; G.N. Kakazei (Author) Other; pogorelov, y. g. (Author) FCUP; Freitas, PP (Author) Other; Cardoso, S (Author) Other; Lopes, AML (Author) Other; do Azevedo, MMP (Author) Other; Santos, JAM (Author) Other; Snoeck, E (Author) Other

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Authenticus ID: P-000-X3H

Abstract (EN): Series of multilayered Co80Fe20(t)/Al2O3(30 Angstrom) films were prepared by ion-beam sputtering. We report on their structural characterization, static magnetization and tunnel magnetoresistance (TMR) in the current-in-p lane (CIP) and current-perpendicular-to-p lane (CPP) geometries. Co80Fe20 layers in Al2O3 matrix are found discontinuous at thicknesses t less than or equal to 18 Angstrom. In the CIP case, the thickness t can be optimized to give maximum TMR (similar to6.5 % for t = 10 Angstrom) or maximum initial slope of TMR with field (similar to 24 %/kOe for t = 13 Angstrom) at room temperature. Magnetization data show that ferromagnetism onsets at t 13 A, that is magnetic transition precedes electrical one in this system. The temperature dependence of TMR was found quite different for the two geometries: fairly strong in the CIP case and weak in the CPP case. To explain these features we propose a model taking account of significant differences between short-range magnetic correlations within and across the layers. At t < 14 Angstrom, a new phenomenon of slow electric relaxation was found, suggesting formation of highly non-equilibrium electronic states in the process of tunnel transport in such systems. An extension of the Sheng-Abeles model on the case of finite concentrations of charged granules is proposed. Within mean-field approximation, it gives a general picture of this phenomenon.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6