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

Magnetic properties of ultrathin fee 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 ellips ometry, in line with previous studies of Fe/Co/Cu(100) and Fe/Ni/Cu(100). T hese magnetic states are closely related to the film structure. Above 10 mo nolayers (ML), the iron films are homogeneously magnetized and adopt the bc c phase. Very thin films up to 2.5 ML are homogeneously magnetized as well but show an fee structure in conjunction with a (4 X 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/N i film interface. The surface magnetization is apparently correlated with a n enlarged atomic volume at the surface and a (2 X 1) surface reconstructio n. Additionally, the magnetic Ni substrate induces ferromagnetic order in t he Fe film at the Fe/Ni interface. The coupling of the two ferromagnetic po rtions of the film shows a strong temperature dependence. This is attribute d to the temperature dependence of the bilinear and biquadratic exchange co upling. At low temperature an antiferromagnetic coupling between the two fe rromagnetic portions is observed. With increasing temperature this is follo wed by a canted spin arrangement and finally a ferromagnetic coupling. [S01 63-1829(99)07041-1].