Spacer dependence effect in synthetic magnetic force microscopy tips

A series of magnetic force microscopy tips with the synthetic structure consisting of two CoCrPt layers separated by a nonmagnetic Ru layer, which have the same magnetic layers but different thickness of the Ru layer, have been fabricated by sputtering. By analyzing the magnetic force microscopy images taken from the magnetic patterns recorded on longitudinal media, the performance of the tips was found to vary with the Ru thickness in an alternate fashion between enhanced and weakened responses. This phenomenon can be explained by the Ru thickness dependence of the exchange coupling between the two ferromagnetic layers and the corresponding frequency response of the trilayer tip. Synthetic tips with superior performances have been obtained after the Ru thickness was optimized.