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AM: Magnetismus

AM 11: Magnetowiderstand II

AM 11.4: Talk

Wednesday, March 28, 2001, 14:45–15:00, S 5.4

Magneto-tunneling through a vacuum barrier — •Haifeng Ding, W. Wulfhekel, C. Chen, and J. Kirschner — Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle

Utilizing spin-polarized scanning tunneling microscopy (Sp-STM), we studied the magneto-tunneling effect through a vacuum barrier. A strong dependence of the magneto-tunneling resistance (TMR) between a ferromagnetic tip and a Co(0001) surface on the thickness of the vacuum barrier is found. At wide tunneling barriers (≈1nm) the magneto-tunneling effect shows almost no dependence of the barrier width. At narrower tunneling barriers the magneto-tunneling effect, however, drops dramatically and nearly vanishes at tunneling resistance of about 0.5 MΩ. A similar drop is also found for tunneling into Fe films deposited on Co(0001). Several mechanisms are discussed that may explain this effect. Further, nonmagnetic noble metal films (Au) are deposited on top of the Co(0001) surface to study the magneto-tunneling effect in the presence of a nonmagnetic metal spacer. The TMR effect remains for thin Au covered layer, however, decreases with the Au film thickness. The experimental setup allows to study the magneto-tunneling effect without impurity scattering inside the barrier.