Spin-polarized vacuum tunneling at small gap widths

Max-Planck Institut für Mikrostrukturphysik - Weinberg 2, 06120 Halle, Germany

Corresponding author: wulf@mpi-halle.mpg.de

Received: 17 September 2002
Accepted: 5 June 2003

Abstract

We studied spin-polarized tunneling through a vacuum barrier using spin-polarized scanning tunneling microscopy on . By varying the tip-to-sample distance in a controlled way, the tunneling magnetoresistance, i.e., the tunneling current asymmetry for parallel and antiparallel configuration of tip and sample magnetization, was measured as a function of the gap width. At large gap widths the asymmetry is constant. At gap widths below , a drop of the asymmetry was found in contrast to predictions of the Jullière model. The drop of the current asymmetry in spin-polarized tunneling is found to correlate with drop of the imaginary electron momentum inside the barrier and we compare our experimental results with the predictions of the Slonczewski model.