Exploring the 2D to 3D dimensionality crossover in thin iron films

The temperature dependence of the spontaneous magnetization of epitaxial iron films with a thickness ranging from d=20 to 200 nm has been measured. The films are grown on GaAs (1 0 0) substrates which are covered by a 150 nm thick silver (1 0 0) buffer layer. For three-dimensional BCC iron it was observed already in 1929 that saturation of the spontaneous magnetization for T→0 is perfectly described by a T2 power law. On the other hand, for thin two-dimensional (2D) iron films a T3/2 law has been established in many recent experimental investigations. In our iron films grown on diamagnetic silver, this dimensionality change occurs at a thickness between d=100 and 200 nm. Comparison of the here-observed T3/2 coefficients with those on iron films grown on paramagnetic tungsten (1 1 0) shows that the 2D interactions are ∼20 times larger in the films on tungsten. Recent results on Fe films which are grown directly on GaAs (1 0 0) confirm that the substrate has a very strong effect on the coefficient of the T3/2 function, i.e. on the strength of the magnetic interactions in the films.