Berlin 2005 – scientific programme

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MA: Magnetismus

MA 24: Oberfl
ächenmagnetismus

MA 24.5: Talk

Tuesday, March 8, 2005, 11:30–11:45, TU A060

Bias dependence of the spin polarized tunneling current between a ferromagnetic tip and antiferromagnetic surfaces — •U. Schlickum, C. L. Gao, W. Wulfhekel, J. Henk, P. Bruno, and J. Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle

In spin-polarized scanning tunneling microscopy (Sp-STM) measurements the spin dependent tunneling current is used to image magnetic structures on the nanometer scale. Spin sensitivity is achieved by the tunneling magnetoresistance effect, i.e. the tunneling current depends on the relative orientation of the magnetization of the tip and sample spin. Besides the possibility to image magnetic structures, this technique allows the investigation of the spin dependent tunneling through a well defined tunneling barrier (vacuum gap). In our contribution, we present Sp-STM measurements performed on ultra-thin antiferromagnetic Mn and Cr films on Fe(001). Both systems show a layer-wise antiferromagnetic order at the surfaces [1, 2]. We found that the size and the sign of the spin contrast, i.e. the difference in the tunneling current between oppositely spin polarized layers, depends on the bias voltage. For Cr, a strong increase of the spin contrast close to a spin polarized surface state was measured. For Mn, we observed, however, a rather complex dependence which can be explained with model calculations based on ab-initio band structures.

[1] U. Schlickum, N. Janke-Gilman, W. Wulfhekel, and J. Kirschner, Phys. Rev. Lett. 92, 107203 (2004). [2] D. T. Pierce, J. Unguris, R. J. Celotta, and M. D. Stiles, J. Magn. Magn. Mater. 200, 290 (1999).