Magnetoresistive measurement of the exchange constant in varied-thickness permalloy films

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Abstract
A current passed through a thin ferromagnetic stripe, magnetized along the stripe (easy) axis, generates an inhomogeneous magnetic field that opposes exchange forces and fans the magnetization in opposite directions through the film thickness, forming a variable-angle Bloch wall parallel to the film plane. The magnitude of this effect is a strong function of film thickness and is readily detected magnetoresistively in Permalloy films. Comparison of experimental results with micromagnetic predictions allows determination of the exchange constant A. We have extended our previous measurement of A on a single 2800-Å-thick film to three film thicknesses in the range 2000–4000 Å. The overall agreement between theory and experiment is good, and is consistent with a value of A=1.05×10−6 erg/cm±10%, in full agreement with the earlier measurement.