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Magnetic heterostructures: examples and perspectives

Abstract Artificial magnetic heterostructures and superlattices have received much attention in recent years because of their scientific and technological relevance. Heterostructures consist of different material layers promising jointly to display physical properties different from any of their single layers. Paramagnetic layers sandwiched between ferromagnetic films are an excellent example of a magnetic heterostructure, since together they display an oscillatory exchange coupling as a function of the paramagnetic spacer thickness not present in any single layer. The strength of the exchange coupling and the oscillation period depend on the details of the Fermi surfaces involved, whereas the overall features of the exchange coupling appear universal. More complex couplings are observed for magnetic superlattices with Cr spacer layers. This is due to the intrinsic spin-density wave state of Cr. Extensive experiments with synchrotron and neutron radiation have recently unravelled the Neel state of thin Cr layers and proximity effects between Fe and Cr, elucidating the mutual interdependence of the Cr spin structure and the Fe exchange coupling. In Co/Cr superlattices the structural mismatch between hep Co and bcc Cr adds another complexity, which affects strongly the magnetic anisotropy. Utilizing the different coercivities of Co and Fe layers, spin valve systems can be constructed from Co/Cr/Fe heterostructures. Both the current status and some future perspectives are briefly reviewed here.