In unison magnetization reversal in a magnetoelastic bilayer structure

Abstract

Due to the magnetostriction effect, a magnetic material changes its dimensions when it is magnetized. In this work, we show how in a magnetostrictive bilayer structure comprising two materials with magnetostriction constants of opposite signs, the magnetic switching is affected by magnetoelastic coupling. While the layer with positive magnetostriction tries to elongate in the direction of the applied magnetic field, the layer with negative magnetostriction tries to contract. In the studied bilayers, the mechanical influence of each magnetostrictive layer on the other is of the opposite sign because of their opposite magnetostrictive constants. Since magnetoelasticity is not an interfacial interaction but an intrinsic property of magnetic materials, the mechanical strain promoted by the applied magnetic field affects the layers as a whole. The net effect is a simultaneous reversal of magnetization of the two layers regardless of their thicknesses. This behavior has been studied in bilayers with different thickness ratios comprising Ni90Fe10, negative magnetostriction and Fe70Ga30, positive magnetostriction. These results demonstrate the possibility of using this physical mechanism to beat the critical limit thickness imposed by interfacial interactions in magnetically coupled multilayers in such a way that the magnetization reversal is made in unison regardless of the layer thickness.