Magnetic properties of Fe/bct Mn superlattices grown by molecular beam epitaxy

Fe/body-centered-tetragonal (bct) Mn superlattices on (001)-oriented Ge substrates have been prepared by molecular beam epitaxy (MBE). X-ray measurements confirm the high quality of the samples, which all show increased lattice spacing in growth direction compared with bulk bcc Fe. RHEED reflection position analysis proves a different growth behavior of the Fe/Mn and Mn/Fe interfaces. Magnetic measurements show a long period of the oscillatory exchange coupling, but no two-monolayer oscillation. Moreover, all samples show a dramatic reduction of the saturation magnetization (M-S), up to 50%, with increasing Mn layer thickness, probably due to the formation of an antiferromagnetic alloy at the Mn/Fe interface. A giant magnetoresistance (GMR) effect is observed for strong antiferromagnetically coupled Fe layers, which depends on the Mn layer thickness in the superlattice. None of the samples exhibited a ferro- or ferrimagnetic state of bet Mn.