Large Area Patterning of Embedded Magnetic Nanostructures in Complex Oxide Thin Films
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Complex oxide materials exhibit a wide range of functional properties, making them interesting for future use in electronic and spintronic devices. Through nanopatterning of thin film structures, magnetic shape effects can be investigated. A novel patterning method, combining substrate conformal imprint lithography (SCIL) with ion implantation, was used to pattern areas up to 7.5x7.5 mm² of identical ferromagnetic nanoscale lines in thin films of La0.7Sr0.3MnO3 (LSMO) and LaFeO3 (LFO). The pattern had a linewidth of 160 nm and a pitch of 400 nm, and the lines were embedded in a paramagnetic matrix. In order to perform SCIL on square substrates, an adapter was manufactured in order for the samples to fit on a two-inch SCIL wafer chuck. A dual-layer mask of Amonil and PMMA resists with a total thickness of approximately 180 nm was shown to work successfully as an implantation mask for 50 keV Ar+ ions that disrupted the magnetic order of the unprotected areas of the thin film. Investigation of the patterned thin film by atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) shows that the patterning process yields high-quality ferromagnetic nanostructures with clear shape-induced magnetic anisotropy. The nanoscale pattern in the thin film shows a saturation magnetic moment of 3.2 µ_B per Mn, which is somewhat lower than the bulk value of 3.7 µ_B per Mn. Parallel to the nanoscale line pattern, a coercivity of 290 Oe was measured at 50 K, while a coercivity of 125 Oe was measured perpendicular to the line pattern.