Onset of ferromagnetism in Fe epitaxially grown on GaAs(001) (4×2) and (2×6)

Ultrathin Fe films were epitaxially grown at room temperature on GaAs(001) with either predominant (4×2) or (2×6) surface reconstruction. At nominal Fe coverages of tFe⩾2.8 monolayers (ML), a ferromagnetic state is observed below a certain critical temperature, TC. Surprisingly, the magnetic phase t...

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Veröffentlicht in:Journal of applied physics 2001-06, Vol.89 (11), p.7133-7135
Hauptverfasser: Bensch, F., Garreau, G., Moosbühler, R., Bayreuther, G., Beaurepaire, E.
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Sprache:eng
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Zusammenfassung:Ultrathin Fe films were epitaxially grown at room temperature on GaAs(001) with either predominant (4×2) or (2×6) surface reconstruction. At nominal Fe coverages of tFe⩾2.8 monolayers (ML), a ferromagnetic state is observed below a certain critical temperature, TC. Surprisingly, the magnetic phase transition at TC appears even sharper than for Fe films on metallic single-crystal substrates, which were believed to be an excellent representation of two-dimensional (2D) ferromagnets. This may be due to the extremely short lateral length scale of film inhomogeneities. The critical exponent β=0.26 is close to the value expected for 2D XY systems of finite size. For tFe=3.6 ML, TC is close to room temperature. TC decreases steeply with decreasing Fe coverage, with an average slope of 270 K/ML. From a power law extrapolation, TC seems to vanish at tFe=2.5 ML. The onset of ferromagnetism at tFe=2.5 ML is interpreted as a percolation phenomenon during the coalescence process of Fe islands.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.1361258