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Large area patterning of self-assembled alumina nanobumps, with hexagonally close-packed order, has been used to create ordered array of bit pattern magnetic media. We have studied the magnetic properties of perpendicular magnetic TbCo alloy and Co/Pt multilayers deposited on self assembled alumina nanobumps. Measurement of reversal field as a function of field intensity, as well as magnetic force microscopy images confirm the weakness of exchange coupling between bits in the case of Co/Pt multilayer while stronger coupling is observed in the case of TbCo alloys.