Thermal Nanoimprint Process for High-Temperature Fabrication of Mesoscale Epitaxial Exchange-Biased Metallic Wire Arrays

A thermal nanoimprint process for the high-temperature (400°C) fabrication of submicron, epitaxial, metallic wire arrays over areas > 1 × 1 cm 2 is reported. Based on a method using an imprinted polymeric bilayer resist template that is transferred to a metallic (molybdenum) mask, this process is enabled by an appropriate undercut profile of the Mo mask. The undercut profile is obtained from a distinctive wedge-shaped profile of the polymeric resist layers by carefully controlling the etch parameters. Using flexible ethylene tetrafluoroethylene imprint molds, we demonstrate defect-free imprinting on MgO substrates. Epitaxial patterning is demonstrated with Fe/MnPd bilayer wire arrays subsequently grown along well-defined crystallographic orientations. X-ray diffraction of the patterned arrays reveals that the MnPd can be grown in two different crystallographic orientations ( c -axis and a -axis normals). The epitaxial nature of the patterned arrays is further confirmed by magnetic measurements that demonstrate the competing effects of intrinsic (magnetocrystalline and exchange) and lithography-induced shape anisotropies on the magnetization reversal characteristics along different directions with respect to the axis of the wire arrays.