Microstructural origin of switching field distribution in patterned Co∕Pd multilayer nanodots

Abstract

We have identified an important microstructural origin of the switching field distribution (SFD) in patterned Co∕Pd multilayer nanodots. In this study, we patterned a marked array of 115nm Co∕Pd nanodots on 50-nm-thick Si3N4 substrate. We identified the dots with unusually small and large (>2 standard deviations of the mean) switching fields with magnetic force microscopy, followed by microstructural characterization of the same dots with transmission electron microscopy (TEM). From electron diffraction, we found that most nanodots with small switching fields have strong (200) spots, whereas those with large switching fields lack these spots. While bright-field TEM images reveal an average grain size of 7nm, dark-field images of the (200) spots reveal on average, a single grain of >10nm in lateral dimensions. Since we observed a direct correlation between strong (200) reflections and small reversal fields, we conclude that the largest grain in each nanodot, with an in-plane [001] is the likely cause for premature switching, which in turn defines the SFD of this array.