Invited Paper TF+EM-MoM1
Nanostructured Magnetic Thin Film Heterostructures: Fabrication, Exchange Interactions and Tailored Anisotropies

Monday, October 18, 2010, 8:20 am, Room Ruidoso

Ultrathin metallic heterostructures show richness in magnetic behavior driven, in part, by exchange, interface, proximity, size and dimensionality effects. One of the most widely studied and technologically important, but still not well-understood, magnetic behavior is the phenomenon of exchange bias (EB) observed in ferromagnetic (FM)/antiferromagnetic(AFM) structures. In this talk, I will first discuss epitaxial growth of such MnPd/Fe bilayers with tailored AFM spin-lattices (compensated and uncompensated) at the interface exhibiting in-plane EB and (Co_xÅPt_yÅ)_n/IrMn multilayers with perpendicular EB. Assymetric magnetization reversals in exchange-biased Fe/MnPd bilayers were confirmed by photoemission electron microscopy (PEEM) with x-ray magnetic circular dichroism (XMCD) for magnetic contrast. Further, the element-specific magnetic structure of the Mn₅₂Pd₄₈/Fe bilayer was investigated with atomic-layer depth sensitivity at the antiferromagnet/ferromagnet interface by soft-XMCD and magnetic reflectivity (XMR). A complex magnetic interfacial configuration, consisting of a 2-monolayer-thick induced ferromagnetic region, and pinned uncompensated Mn moments that reach far deeper (~13 Å), both in the antiferromagnet, were found. These epitaxial EB samples also show in-plane reorientation transitions, determined by the competition between the interface exchange coupling and the intrinsic uniaxial energies, and is driven by the temperature, as well as the thickness of MnPd and Fe layers. Complementing these results, work on multilayers show that perpendicular EB arise from a complex interplay between unidirectional anisotropy at the terminating FM/AFM interface, the perpendicular anisotropy of the FM/nonmagnet(NM) multilayer stack and the overall magnetostatic energy of the structure. Finally, we have developed and implemented nanoimprint lithography (NIL) to fabricate wire and particle arrays of exchange biased elements at the 300nm length scale. A mask transfer NIL process has also been developed to grow epitaxial structures. The role of size and dimensionality as well as competing anisotropies, introduced by particle shape, on EB heterostructured elements has been studied. Details will be presented.