Morphology and magnetic properties of submonolayer Gd films

We report on scanning tunneling microscopy (STM) measurements on ultrathin Gd films in the thickness range 0.5 less than or equal to d(Gd) less than or equal to 10 ML [1 monolayer (ML) = 2.89 Angstrom] grown on a Y (0001) buffer layer at substrate temperatures T-s = 473 K and T-s = 573 K. The magnetic properties were investigated on these films capped with a 100-Angstrom Y later with the transverse magneto-optical Ken effect. A ferromagnetic signal was found down to the sub-ML regime d(Gd) approximate to 0.5 ML for T-s = 473 K In this regime, the STM images show a lateral growth of ML thick Gd islands of hexagonal shape. The depression of the Curie temperature T-C follows a power law Delta T-C proportional to d(Gd)(-lambda) with Gd an exponent lambda approximate to 1 up to d(Gd) approximate to 3 - 5 ML, where lambda changes to lambda = 1.6. This transition is also observed in the same thickness range for the exponent beta of the magnetization M.