Thickness dependence of magnetic coupling strength and thermal stability in a spin-dependent tunnel junction

Abstract

The change of magnetic coupling strength between two ferromagnetic layers, separated by an insulating barrier, was investigated as a function of the barrier thickness (TB) and thermal annealing temperatures. The magnetic junctions consist of Ta/CoFe/AlOx/NiFe/Ta layers with three different nominal thickness of T-B = 1.3, 1.6, and 2.0 nm. Isothermal magnetization at room temperature revealed that, while the junction with a lower T-B showed a higher magnetic coupling strength, thermal annealing at T = 225 degreesC increased (and diminished) the coupling strength of the junctions with TB = 1.3 and 1.6 nm (and 2.0 nm), respectively. This observation was utilized to understand consistently the magneto-resistance behavior and specific junction resistance of the junctions as a function of thermal annealing temperature. This study demonstrated that the physical properties of a magnetic tunnel junction, such as magneto-resistance ratio, specific junction resistance and their thermal stability, were substantially influenced by the insulating barrier structure as well as the interface quality between the layers. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.