Groupe de Physique Statistique

The magnetic properties of Fe grown in FeIr(100) superlattices are investigated by 57Fe Mössbauer spectrometry. Series of superlattices with 3 to 8 57Fe and/or 56Fe atomic planes and Ir thicknesses from 2 to 30 Å were prepared by molecular beam epitaxy. For the series with 4 Fe atomic planes with body-centered tetragonal (bet) structure, the occurrence of a sizeable magnetic moment in the two central Fe layers above a critical volume threshold is evidenced, whilst the Fe in contact with Ir keep weakly magnetic. For series with more than 4 Fe planes, the transition from the bet to the bcc structure results in new magnetic sites. The arrangement along the growth direction is detailed showing a magnetic dissymmetry between the Ir/Fe and Fe/Ir interfaces. Moreover, magnetic relaxation effects and spin wave softening are observed, likely due to small magnetic correlations from plane to plane.