Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 18: Spindependent Transport II

MA 18.1: Talk

Wednesday, March 28, 2007, 15:15–15:30, H22

Tunneling magnetoresistance effect with amorphous electrodes — •Martin Gradhand, Christian Heiliger, Peter Zahn, and Ingrid Mertig — Martin Luther University, Institut f. Physik, D06099 Halle, Germany

Structural disorder is often used to explain the discrepancies between experimental [1,2] and theoretical [3,4] results for the tunneling magnetoresistance (TMR). To prove the influence of structural disorder on the TMR ratio experimentally well characterized Fe/MgO/Fe tunnel junctions were investigated theoretically. The screened KKR method based on density functional theory was applied to compute the electronic and magnetic structure self-consistently. The Baranger-Stone scheme based on Green functions was used to calculate the conductance of the planar tunnel junction in the coherent limit of transport. First of all it was shown that amorphous Fe electrodes of finite thickness next to MgO barrier cause a break down of the TMR ratio. Recrystallisation of at least, one monolayer of Fe next to the MgO barrier leads to a recovery of the effect and two crystalline Fe layers cause the same TMR ratio as semi-infinite Fe leads. Structural disorder in the electrodes behind the two crystalline layers does not influence the TMR ratio at all. All results are supported by a detailed theoretical analysis of the transport properties of amorphous and crystalline iron.

[1] S. Ikeda et al., Jpn. J. Appl. Phys. 44, L1442 (2005)

[2] S. Yuasa et al., Appl. Phys. Lett. 89, 042 505 (2006)

[3] J. Mathon and A. Umerski, Phys. Rev. B 63, 220 403 (2001)

[4] W. Butler et al, Phys. Rev. B 63, 054 416 (2001)