Abstract
The thickness-dependent Curie temperatureTc(d) of thin ferromagnetic films is calculated within the molecular field approximation(‘Weiss mean field’) of the Heisenberg model. Two higher mean field theoriesare applied to obtain a quantitative improvement of the results: the Oguchicluster method and the ‘constant coupling approximation’ (CCA). Analyticalexpressions are derived from difference equations or eigenvalue problems with anunknown parameter which can be solved numerically. Explicit expressions forTc(d) canbe given if the interaction is restricted to next neighbour monolayers only, for any value of the spinS within the Weissmean field and for S = 1/2 within the CCA. Effects of an enhanced interaction withinthe surface layers are briefly investigated. Calculated values ofTc(d) for EuO are presented within the three models.
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