Geometrically induced giant magnetoresistance behavior in quarter-micrometer strip pattern

The present article reports a geometrically induced magnetoresistance (MR) behavior observed in magnetic strips consisting of a symmetric layer structure with lateral sizes down to 0.2 μm. The MR ratio was markedly improved from 2.8% for an as-grown film of Co(6 nm)/Cu(6 nm)/Co(6 nm) to 4.6% by structuring it into a strip with 0.3 μm width. The parabolic MR behavior observed in the hard-axis direction suggests that the magnetization in the two magnetic layers rotates toward the opposite directions, which can be explained by the magnetostatic interaction between the surface magnetic charges at the pattern edges. The dependence of MR saturation field on the pattern width agrees well with a theoretical prediction based on a coherent rotation model. The MR ratio was markedly increased by the increase of the layer number and the thickness of the magnetic layer, the highest value of 7.8% was obtained for a strip made of [Co(6nm)/Cu(4nm)]₂Co(6nm). A linear-and hysteresis-free MR response was performed with an alternative field modulation under a transverse bias field.