Ultrahigh vacuum scanning tunneling microscopy/magnickel oxide filmsnetic force microscopy study of ultrathin iron films grown on polycrystalline nickel oxide films

Abstract

The thickness dependence of the topographic and magnetic structure of ultrathin Fe films grown on polycrystalline NiO films under ultrahigh vacuum ~UHV! conditions was studied to investigate the growth mechanism of the ferromagnetic film and the corresponding magnetic interaction with the antiferromagnetic substrate. Externally prepared NiO films of 60 nm thickness were cleaned by heating in UHV. Ultrathin layers of Fe in the range of 1–27 nm were deposited on top of the NiO film and were analyzed at specific coverages. Iron grows as a polycrystalline film with the grains increasing in size with the thickness. The contours of the underlying NiO crystallites were evident at low coverages but gradually disappeared as the Fe grains coalesced at thicker coverages. Magnetic force microscopy images of the 1 nm thick film show randomly oriented magnetic grains with an average domain size of 30 nm. With an increase in film thickness the size of the domains grows to about 200 nm at 15 nm of iron. At a film thickness of 19 nm cross-tie domain walls become visible, indicating the crossover of some parts of the film from random magnetic grains into continuous domains with in-plane magnetization. A further increase in the film thickness leads to larger in-plane domains, while there are some areas with localized grains on the surface.