Crossover from 2D to 3D magnetic disorder in sub-mono-atomic ferromagnetic layers

We present transport and magnetoresistance (MR) measurements performed on quench condensed ultrathin films of Gd evaporated on an amorphous Ge or Sb layer. These films show a large negative MR accompanied by a hysteretic superimposed structure. When the film is coated by an overlayer of Ge or Sb the magnitude of the MR increases and the hysteretic structure disappears. We speculate that the findings are a result of a crossover from a 2D magnetic disorder in the uncoated layers of Gd to a 3D magnetic disorder as the Gd film is coated by a semiconducting layer.