Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 27: Spinabh
ängiger Transport II

MA 27.11: Talk

Thursday, March 11, 2004, 17:45–18:00, H22

Disorder effects on tunneling magnetoresistance — •Michael Wimmer und Klaus Richter — Institut fü Theoretische Physik, Universität Regensburg

Spin-dependent transport phenomena have gathered a lot of interest in the past decade. Among those is the tunneling magnetoresistance effect (TMR). Nowadays Al₂O₃-based tunnel junctions show a significant TMR effect. However, recent experiments on Fe/GaAs-based junctions found an effect much less than expected from simple models. It was suggested that spin-flip scattering may explain the low value of the TMR. (S. Kreuzer et al., Appl. Phys. Lett. 80, 4582 (2002) )

We study the effects of disorder on the TMR in a phenomenological model that we solve numerically using a recursive Green’s function technique. This model includes a position-dependent effective mass, spin-conserving and spin-flip scattering.

We investigate the effect of disorder at the interfaces and find that disorder tends to decrease the TMR effect. Surprisingly, the decrease is almost identical for spin-conserving and spin-flip scattering.

Additionally we compute the magnetic field dependence of the conductance of a tunnel junction in the presence of impurities.