Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 40: Poster II: Bio- and Molecular Magnetism (1-9); Magnetic Coupling Phenomena/Exchange Bias (10-15); Magnetic Particlicles and Clusters (16-29); Micro and Nanostructured Magnetic Materials (30-51); Multiferroics (52-64); Spin Injection in Heterostructures (65-67); Spin-Dyn./Spin-Torque (68-93); Spindependent Transport (94-108)
MA 40.105: Poster
Freitag, 27. März 2009, 11:00–14:00, P1A
Tunnel magnetoresistance in Al2O3 – MgO composite magnetic tunnel junctions — •Oliver Schebaum, Volker Drewello, Alexander Auge, Andy Thomas, and Günter Reiss — Bielefeld University, Germany
In the recent years TMR ratios of up to 500% at room temperature (RT) have been observed for magnetic tunnel junctions with MgO tunnel barriers, while the TMR ratio of Al2O3 based MTJs seems to be limited to 70% to 80%. This has been explained by coherent tunneling in the crystalline FM/MgO/FM systems. With our investigation we wanted to find out, if also an increased spin polarization could be the reason for this high TMR ratios. We therefore investigated MTJs with MgO, Al2O3 and MgO – Al2O3 composite tunnel barriers and Co-Fe-B magnetic electrodes. The samples have been prepared by DC and RF magnetron sputtering and optical UV lithography. The characteristics of these tunnel junctions have been investigated for different annealing temperatures by transport measurements. The highest observed TMR ratio for the composite barrier MTJs is 74% at room temperature. The prepared reference MTJs with an MgO tunnel barrier exhibit a maximum TMR ratio of 176% at room temperature. The highest observed TMR ratio for the composite tunnel barrier MTJs is in the range of the highest reported values for amorphous single layer Al2O3 tunnel barriers, but still much lower than the observed and reported values for MgO based MTJs. This gives evidence that the high tunnel magnetoresistance ratios obtained in MgO based tunnel junctions might be attributed to coherent tunneling.