We report a drastically different behavior in spin reorientation transition
of ultrathin Co films grown on smooth versus rough Pd(111) single crystal
substrates. The morphology and magnetic anisotropy of epitaxially grown Co
films have been studied with in situ scanning tunneling microscopy (STM) an
d surface magneto-optical Kerr effects. On an atomically flat substrate, a
smooth transition from perpendicular to in-plane magnetization occurs in a
thickness interval of over 1.5 ML, beginning at similar to4.5 ML. In contra
st, rough substrate causes the transition to begin quite earlier at less th
an or equal to3 ML and complete abruptly in less than 1 ML range. Morpholog
y difference of the Co films obtained with STM suggests that on rough subst
rate, nonuniform coverage of Co leads to locally thicker regions triggering
earlier spin reorientation transition. (C) 2001 American Institute of Phys
ics.