Dresden 2003 – scientific programme

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MA: Magnetismus

MA 7: Spin-Elektronik

MA 7.12: Talk

Monday, March 24, 2003, 18:00–18:15, HSZ/401

Origin of spin polarization in spin polarized tunneling experiments? — •Markus Münzenberg and Jagadeesh Moodera — Francis Bitter Magnet Laboratory, MIT

The origin and sign of spin polarization from transition metal ferromagnets (FM), as measured by spin polarized tunneling technique of Meservey and Tedrow using the Zeeman-split Quasiparticle excitations in a superconducting Al as spin detector has been investigated for nearly three decades, but is still a subject of intense discussion. The question that we take up is not solved in detail yet: Where does the basic polarization arise from and can we get a further insight into the FM states that determine the tunneling current?
Although it is believed that the spin polarization measured in tunneling experiments is widely dominated by 4s states the contribution of the FM-3d states to the tunneling current can be expected. Experiments to enlighten this fundamental aspect have been carried out by carefully controlling the AlOx tunnel barrier thickness (area 50 µm x 50 µm). As a top electrode we evaporated in this case Fe. The spin-polarization spectra (taken at 0.4K and in an applied magnetic field from 2 to 3.3T) for various samples with junction resistance ranging from 1Ω to 1MΩ have been investigated. We observe a decrease of the polarization of the tunneling electrons from 43% to 22%. This is attributed to be due to contribution of states with d-like symmetry to the tunneling current for ultrathin barriers.
R. Meservey and P. M. Tedrow, Phys. Rept., 238, 173 (1994). *Present address: IV. Phys. Inst., Göttingen University