Berlin 2005 – wissenschaftliches Programm
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MA: Magnetismus
MA 23: Spinabh
ängiger Transport III
MA 23.6: Vortrag
Dienstag, 8. März 2005, 11:45–12:00, TU H1028
Scanning laser microscopy studies of tunneling magnetoresistance in artificial La2/3Ca1/3MnO3 grain boundaries — •T. Nachtrab1, M. Wagenknecht1, H. Eitel1, M. Zaiser1, R. Kleiner1, D. Koelle1, J.-B. Philipp2, and R. Gross2 — 1Physikalisches Institut - Experimentalphysik II, Universität Tübingen, 72076 Tübingen — 2Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching
It is widely believed that an artificial grain boundary (GB) in a manganite film, made e.g. by growing the film on a bicrystal substrate, can act as a tunneling barrier for the spin polarized current below TCurie. However, the TMR effect in these devices can be strongly influenced by the formation of magnetic microdomains along the GB.
By means of low temperature scanning laser microscopy (LTSLM), we imaged the tunneling conductance distribution along the GB in a La2/3Ca1/3MnO3 film grown on a 24∘ bicrystal SrTiO3 substrate. Our images can be interpreted as a map of the relative orientations of adjacent microdomains at both sides of the GB. Careful ramping of the applied magnetic field enables us to directly observe the growth of the magnetic microdomains at low temperature (T ≈ 10 K). In addition, due to the spatial resolution of the LTSLM (≈ 2 µm), we are able to reconstruct the T dependence of the GB resistance, RGB. It increases with T up to Tmax ≈ 130 K and then decreases. However, it remains at a relatively high level even above TCurie (≈ 220 K). This gives strong evidence that the GB behaves as a barrier also in the paramagnetic phase of the manganite film suggesting a tunneling transport mechanism.