Investigation of the magnetic interaction of small permalloy particles

Permalloy island arrays and undulated lines were systematically studied by MFM to clarify the effect of neighbor magnetic interaction. The islands are 860 nm × 320 nm and 35 nm thick, single domains and patterned to have preferential interaction along the easy and hard axes. The switching field for easy axis interaction is relatively high, i.e., 370 Oe with a 32 Oe spread; while the hard axis interaction produces a switching field of 130 Oe and a slightly wider distribution of over 40 Oe. A third array is comprised of undulated lines with connected segments. Magnetic charges accumulate at the ends of each segment, and yield the strongest possible interaction along the easy axis. In this case all segments on one line simultaneously switch at a specific field. The switching field increases linearly from 150 Oe with the number of segments up to a maximum number of 50, and approaches a constant field of 290 Oe. The results favorably compare with the prediction for parallel rotation of the Jacobs-Bean chain of spheres model.