Studies of interlayer exchange coupling in Fe/Cu/Fe ultrathin heterostructures

Abstract

The interlayer exchange coupling has been investigated in trilayer structures where two coupled Fe layers were separated by a modified Cu spacer. The multilayer heterostructures investigated in this article have the following general structure: Fe1/kCu/lXcCu1−c/mCu/Fe2, where XcCu1−c indicates one atomic layer of Cu atoms alloyed with foreign X atoms of concentration c. Fe1 and Fe2 indicate bottom and top ferromagnetic iron layers, respectively. k, l, and m represent the number of atomic layers (AL) yielding a total spacer thickness of (k+l+m) AL. The ultrathin films were grown using a molecular beam epitaxy system. Atoms X (Fe,57Fe,Cr,Ag) were codeposited simultaneously with the Cu atoms to create an alloyed layer. Foreign atoms were introduced in the spacer to study their effect on the direct interlayer exchange coupling between the outside Fe layers mediated by the valence electrons of the Cu spacer. The ferromagnetic resonance, magneto-optical Kerr effect, and Brillouin light scattering techniques were employed to determine the exchange coupling in these structures. Mossbauer spectroscopy was used to identify the magnetic state of the Fe57 atoms in the alloyed Fec57Cu1−c layer. The results have shown that the presence of foreign atoms inside the Cu spacer significantly decreases the bilinear antiferromagnetic coupling between the Fe layers by creating a potential barrier for the valence Cu electrons. More significantly, the exchange coupling showed a very strong dependence on the magnetic state of the foreign atom. For high concentrations of Fe in the spacer, the coupling was found to be ferromagnetic due to partial magnetic ordering of the iron atoms.