Magnetic properties of ultra thin epitaxial Fe films on GaAs(001)

Abstract

The magnetic properties of epitaxial Fe films on GaAs in the range of the first few monolayers have been the subject of a considerable number of investigations in recent years. The absence of magnetic signatures at room temperature has been attributed to the existence of a magnetic ''dead'' layer as well as superparamagnetism. By examining the temperature dependence of the magnetic linear dichroism of the Fe core level photoelectrons, we found that these ''non-ferromagnetic'' layers had in fact a Curie temperature, T{sub c}, substantially lower than room temperature, e.g., a T{sub c} of about 240K for thin films of a nominal thickness of 0.9 nm. The values of Curie temperature were sensitive to the initial GaAs substrate conditions and the thickness of the Fe over-layer with a layer of thickness of 1.25 nm showing a T{sub c} above room temperature. The data suggest that the ultrathin Fe films on GaAs(001) are ferromagnetic, although a weaker exchange interaction in the films lead to a substantial reduction in Curie temperature.