Dresden 2006 – scientific programme

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MA: Magnetismus

MA 3: Spin-Dependent Transport Phenomena I

MA 3.7: Talk

Monday, March 27, 2006, 11:45–12:00, HSZ 103

How many crystalline interface layers are necessary to create high TMR? — •Christian Heiliger, Peter Zahn, and Ingrid Mertig — Martin Luther University, FB Physik, FG Theorie, D-06099 Halle, Germany

Recent experiments [1-3] based on epitaxially grown Fe/MgO/Fe samples shed light on the subject of tunneling magnetoresistance (TMR). First of all, the obtained TMR ratios exceed the predictions by Julliere’s model. Second, the measured bias voltage characteristic shows features which could be related to the electronic structure of the system. The high crystallinity of the samples [1-3] seemed to be the reason. New experiments [5], however, demonstrate that even amorphous electrodes attached to a crystalline MgO barrier show a TMR of more than 230%. The question that is addressed in this talk is: How many crystalline metal layers close to the interface are necessary to obtain high TMR?

A screened Korringa-Kohn-Rostoker (KKR) method based on density functional theory was applied to calculate the electronic and magnetic structure of the different junctions self-consistently. The Landauer conductance of planar junctions was calculated using the Baranger-Stone scheme by means of Green’s functions in the limit of coherent tunneling.

The results demonstrate that only a few crystalline ferromagnetic layers cause a significant spin-polarisation and TMR.

[1] J. Faure-Vincent et al., Appl. Phys. Lett. 82, 4507 (2003)

[2] S. Yuasa et al., Nature Materials 3, 868 (2004)

[3] S.S.P. Parkin et al., Nature Materials 3, 862 (2004)

[4] K. Tsunekawa et al., Appl. Phys. Lett. 87, 072503 (2005)