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 struct ure with lateral sizes down to 0.2 mu m. 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 st ructuring it into a strip with 0.3 mu m width. The parabolic MR behavior ob served in the hard-axis direction suggests that the magnetization in the tw o magnetic layers rotates toward the opposite directions, which can be expl ained 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 rotati on 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% w as obtained for a strip made of [Co(6 nm)/Cu(4 nm)](2) Co(6 nm). A linear- and hysteresis-free MR response was performed with an alternative field mod ulation under a transverse bias field. (C) 1999 American Institute of Physi cs. [S0021-8979(99)63008-0].