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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.108: Poster

Dienstag, 27. März 2007, 15:00–19:00, Poster A

High TMR ratio in Fe/MgO/Fe junctions with even one atomic Fe layer — Christian Heiliger, Martin Gradhand, •Peter Zahn, and Ingrid Mertig — Institut für Physik, Martin-Luther-Universität Halle/Wittenberg, D-06099 Halle, Germany

Recent experiments based on epitaxially grown Fe/MgO/Fe samples shed light on the microscopic origin of tunneling magnetoresistance (TMR). The obtained TMR ratios exceeded the predictions by Julliere’s model by far. A screened Korringa-Kohn-Rostoker (KKR) method based on density-functional theory was applied to calculate the electronic and magnetic structure of the junctions self-consistently. The conductance was calculated in the limit of coherent transport using the Landauer formula by means of Green’s functions.

Positive and negative TMR ratios are obtained as a function of interface structure and even a sign reversal of TMR as a function of bias was found [1]. It will be demonstrated how the structure of the electrodes, and especially the finite thickness of the Fe layers influence the TMR ratio and the corresponding bias voltage dependencies. It will be shown that the leads have just to provide states of Δ₁ symmetry which tunnel most efficiently across the barrier and the spin-filter effect is generated by even one monolayer of Fe [2].

[1] C. Heiliger et al., Phys. Rev. B 72, 180604(R) (2005), C. Heiliger et al., Phys. Rev. B 73, 214441 (2006).

[2] C. Heiliger et al., in preparation (2006).