Growth and magnetism of ultrathin Fe films on Pd(100) have been studied in
situ by reflection high-energy electron diffraction, scanning tunneling mic
roscope, and magneto-optical Ken effect technique. It is found that the gro
wth at the initial stage is in the layer-by-layer mode and the magnetic hys
teresis loops are detectable only when the Fe films are thicker than 1.3 mo
nolayer (at 300 K) and 0.5 monolayer (at 55 K). [S0163-1829(99)11139-1].