Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 103: Spintronics incl. quantum dynamics (MA with HL/TT)

HL 103.5: Talk

Friday, March 20, 2015, 10:45–11:00, EB 202

Tricky details of tunnel magnetoresistance — •Christian Franz, Michael Czerner, and Christian Heiliger — I. Physikalisches Institut, Justus Liebig University, Giessen, Germany

The basic mechanism responsible for the large TMR in coherent tunnel junctions has already been clarified in the first publications [1,2]. These predictions initiated a broad investigation continuing for more than a decade. Nevertheless, the quantitative understanding of TMR is still incomplete. In particular, the agreement between experiments and calculations remains deficient. The reason for these shortcomings is a complicated interplay of many effects, several of which are not yet fully understood.

We contribute by investigating several effects in great detail using advanced ab initio methods [3]. In particular, we discuss the effects of disorder, several interface resonance states and bulk states of different materials. These effects are illustrated by the example of Fe_1−xCo_x alloys as ferromagnetic layers [4] which show substitutional disorder for finite concentrations, a complicated concentration dependence of the interface resonance states and variety of bulk states which become available via band filling.

[1] W.H. Butler, X.-G. Zhang, T.C. Schulthess, J.M. MacLaren, Phys. Rev. B 63, 054416 (2001)

[2] J. Mathon, A. Umerski, Phys. Rev. B 63, 220403 (2001).

[3] C. Franz, M. Czerner, C. Heiliger, J. Phys.: Condens. Matter 25, 425301 (2013).

[4] C. Franz, M. Czerner, C. Heiliger, Phys. Rev. B 88, 094421 (2013).