Magnetic Switching Behavior of Permalloy Cap Layers on a Self-Assembled Nanosphere Template*

Three different nanosphere lithography methods, Langmuir film deposition, drop casting, and vertical evaporation, are attempted to create densely packed monolayers of 930 nm diameter polystyrene nanospheres. Langmuir film deposition is the most promising option, yielding the largest area of uniform monolayer, up to 1 mm by 0.5 mm. There is a large parameter space to explore with Langmuir film deposition, with nanosphere concentration, substrate lifting, and surfactant chemistry being critical parameters that need to be carefully controlled. A 10 nm Permalloy layer is sputter-coated onto the monolayer of nanospheres. The topography of these films is explored using AFM, MFM, and SEM imaging. The magnetic force images reveal magnetic anisotropy over the surface of the sample, while the SEM images reveal that the nanospheres do not always contact each other. Magneto-optical Kerr effect and First Order Reversal Curve measurements are conducted to investigate the magnetic switching behavior of the permalloy cap layer on top of the nanospheres.