Magnetostatic interactions between sub-micrometer patterned magnetic elements

We have investigated the effect of the magnetostatic interaction field between submicrometer patterned magnetic elements in arrays (~10 ⁸ elements) using Alternating Gradient Force Magnetometry. Single layer NiFe elements were studied over a range of width (0.12 to 0.48 μm), length to width aspect ratio (1.5 to 4) and thickness (30 Å to 60 Å). 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 ΔM plots to these patterned arrays. The ΔM 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_int=ΔM/χ_irr, where ΔM is the difference in these remanent loops and χ_irr is the derivative of the remanent magnetization with respect to field. We found H_int to increase with element aspect ratio, thickness and inverse width. For structures with the largest aspect ratio, thickness and smallest width, H_int≈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_int that is a good measure of the difference in interaction fields tending to magnetize or demagnetize the sample