FERROMAGNETIC AND ANTIFERROMAGNETIC EXCHANGE COUPLING IN ULTRATHIN FE(001)/PD(001)/FE(001) STRUCTURES

A new phase of fcc Pd with an expanded lattice (5%) was grown on Fe(001). This structure is maintained up to 12 monolayers (ML) of Pd and then it undergoes a complex lattice reconstruction. Ultrathin Fe/Pd, Pd/Fe bilayers, and Fe/Pd/Fe trilayers with Pd thicknesses between 4 and 18 ML were studied using ferromagnetic resonance and Brillouin light scattering. The metallic Pd and particularly its lattice-expanded structure is believed to have a strong tendency to become ferromagnetic. This tendency was observed in Fe/Pd/Fe trilayers with Pd thicknesses less than 6 ML. The exchange coupling remains ferromagnetic up to 12 ML of Pd and then it changes to a weak antiferromagnetic coupling. The exchange coupling in the ferromagnetic region exhibits a distinct oscillatory behavior superimposed on a decreasing background.