Thickness dependence of the magnetic anisotropy of Fe layers separated by Al

Magnetic multilayers of 57Fe with nominal thickness, Tnom, between 0.4 and 1.0 nm separated by 3.0 nm Al spacer layers were prepared by alternate deposition of the constituents in high vacuum. The samples were investigated at 4.2 K in external magnetic field. A fraction of Fe atoms corresponding to about 0.3 nm equivalent Fe-thickness was found to mix into the Al spacer. The extremely strong magnetic anisotropy observed for Tnom < 0.8 nm is attributed to Fe layers of approximately two atomic planes thick. The anisotropy decreases considerably after the building up of the third Fe atomic layer starts at Tnom = 0.8 nm, but full saturation was not achieved even for Tnom = 1 nm and 3 T magnetic field applied perpendicularly to the sample plane.