Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 25: Micro- and Nanostructured Magnetic Materials II
MA 25.1: Vortrag
Mittwoch, 25. März 2009, 14:45–15:00, HSZ 403
Anisotropy of the Curie temperature in ultrathin epitaxial Fe(001) wire arrays — Roland Meier and •Günther Bayreuther — Universität Regensburg, 93040 Regensburg, Germany
According to Mermin and Wagner [1] long-range ferromagnetic order in isotropic 2D systems with short-range magnetic interactions is destroyed by spin fluctuations at any temperature T>0. Curie temperatures, TC, above 200 K in single atomic layers can be understood by considering magnetic anisotropies and long-range dipolar interactions. The relevance of dipolar interaction was verfied in ultrathin Fe(001) dot arrays epitaxially grown on GaAs(001) by variation of dot diameter and dot separation. By assuming that magnetization fluctuations in space and time close to TC are partially suppressed by combined exchange and dipolar interactions in the same way as purely spatial magnetization fluctuations in polycrystalline films ("magnetization ripple"), the result of a Green’s function approach [2] predicts that TC should be higher in a long wire magnetized perpendicular to the wire axis compared to a parallel magnetization and to a circular dot. This was confirmed by exploiting the strong uniaxial interface magnetic anisotropy in Fe/GaAs(001). Compared to the extended film a reduction of TC by 3% was observed for perpendicular magnetization versus 8% for the parallel case; for a dot with the same dimension the reduction was indeed the sum of both, i.e.11%. This means that in epitaxial ultrathin ferromagnetic wires the Curie temperature is indeed anisotropic. [1] N. D. Mermin and H. Wagner, Phys. Rev. Lett 17 (1966) 1133 [2] W. Maass, PhD thesis, University of Regensburg, 1984