MORPHOLOGY AND MAGNETIC-PROPERTIES OF SUBMONOLAYER GD FILMS

We report on scanning tunneling microscopy (STM) measurements on ultra thin Gd films in the thickness range 0.5 less than or equal to d(Gd) l ess 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 cap ped with a 100-Angstrom Y later with the transverse magneto-optical Ke n 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 ima ges show a lateral growth of ML thick Gd islands of hexagonal shape. T he depression of the Curie temperature T-C follows a power law Delta T -C proportional to d(Gd)(-lambda) with Gd an exponent lambda approxima te to 1 up to d(Gd) approximate to 3 - 5 ML, where lambda changes to l ambda = 1.6. This transition is also observed in the same thickness ra nge for the exponent beta of the magnetization M.