Magnetostatic interactions between sub-micrometer patterned magnetic elements

Abstract

We have investigated the effect of the magnetostatic interaction field between submicrometer patterned magnetic elements in arrays (/spl sim/10/sup 8/ elements) using Alternating Gradient Force Magnetometry. Single layer NiFe elements were studied over a range of width (0.12 to 0.48 /spl mu/m), length to width aspect ratio (1.5 to 4) and thickness (30 /spl Aring/ to 60 /spl Aring/). The arrays were patterned using e-beam lithography in a rectangular lattice with bit separation equal to element width. Effective interaction fields were obtained using a novel application of /spl Delta/M plots to these patterned arrays. The /spl Delta/M plot is derived by subtracting remanent magnetization curves that had initial states of full magnetization from those that were initially demagnetized. Interaction fields were quantified using H/sub int/=/spl Delta/M//spl chi//sub irr/, where /spl Delta/M is the difference in these remanent loops and /spl chi//sub irr/ is the derivative of the remanent magnetization with respect to field. We found H/sub int/ to increase with element aspect ratio, thickness and inverse width. For structures with the largest aspect ratio, thickness and smallest width, H/sub int//spl ap/6 Oe. We calculated the actual dipolar interaction fields using micromagnetic simulation and used these fields in a simple 2-d Ising model to simulate the experiment. We found H/sub int/ that is a good measure of the difference in interaction fields tending to magnetize or demagnetize the sample.