Antiferromagnetic coupling in fcc Fe overlayers on Ni/Cu(100)

Abstract

Magnetic properties of ultrathin fcc Fe overlayers on Ni/Cu(100) have been determined to study the influence of a magnetic interface. Three regions of different magnetic behavior are distinguished by magneto-optic Kerr ellipsometry, in line with previous studies of Fe/Co/Cu(100) and Fe/Ni/Cu(100). These magnetic states are closely related to the film structure. Above 10 monolayers (ML), the iron films are homogeneously magnetized and adopt the bcc phase. Very thin films up to 2.5 ML are homogeneously magnetized as well but show an fcc structure in conjunction with a $(4\ifmmode\times\else\texttimes\fi{}1)$ reconstruction. The most complex magnetic properties characterize Fe films between 5 and 10 ML. In this thickness range the iron films are not homogeneously magnetized. Instead ferromagnetism is only observed at the Fe film surface and the Fe/Ni film interface. The surface magnetization is apparently correlated with an enlarged atomic volume at the surface and a $(2\ifmmode\times\else\texttimes\fi{}1)$ surface reconstruction. Additionally, the magnetic Ni substrate induces ferromagnetic order in the Fe film at the Fe/Ni interface. The coupling of the two ferromagnetic portions of the film shows a strong temperature dependence. This is attributed to the temperature dependence of the bilinear and biquadratic exchange coupling. At low temperature an antiferromagnetic coupling between the two ferromagnetic portions is observed. With increasing temperature this is followed by a canted spin arrangement and finally a ferromagnetic coupling.