Dresden 2006 – wissenschaftliches Programm

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MA: Magnetismus

MA 35: Magnetic Thin Films V

MA 35.2: Vortrag

Freitag, 31. März 2006, 11:00–11:15, HSZ 03

The relevance of dipolar coupling for the stability of ferromagnetism in ultrathin films — •Roland Meier, Frank Bensch, Wolfgang Kipferl, Joseph Biberger, Dieter Weiss, and Günther Bayreuther — Institut für Experimentelle und Angewandte Physik, Universitätsstraße 31, 93040 Regensburg

It has been rigorously shown by Mermin and Wagner [1] that ferromagnetic order cannot exist in two-dimensional systems at any temperature T > 0 provided the magnetic interactions are short-range and isotropic. However, it is empirically known that even single atomic layers can have a Curie temperature above 200 K. These contradictory facts are reconciled if we note that real ferromagnetic films are never free from magnetic anisotropy and are subject to long-range dipolar interaction. In order to investigate the relevance of dipolar interactions, the Curie temperature Tc was measured for ultrathin Fe(001) films (about 3 atomic layers) epitaxially grown on GaAs(001) and in arrays of sub-micrometer circular dots and parallel stripes prepared by electron beam lithography and ion etching. It is found that Tc decreases drastically with decreasing thickness, with decreasing dot diameter and with increasing dot separation. A quantitative analysis of the results provides convincing evidence that indeed the long-range dipolar coupling strongly enhances the stability of ferromagnetic order against thermal spin excitations in ultrathin epitaxial films magnetized in the film plane.

[1] N.D. Mermin and H. Wagner, Phys. Rev. Lett. 17 (1966) 1133