Influence of sample width on the magnetoresistance and planar Hall effect of Co/Cu multilayers

Abstract

We have studied Co/Cu multilayers to understand the effect of the sample's width on their magnetoresistance (MR). By keeping constant both the length and the thickness and exploring the widths within the range of usual magnetic domain sizes in those nanostructures, we were able to observe effects on the MR curve, as well as infer linked changes in the magnetization process. Associating MR and Planar Hall Effect (PHE) measurements, coupled to an analysis of the MR plots' symmetry, we were able to establish that, apart from the expected antiferromagnetic coupling, reducing the width forces the magnetization to stay aligned to the current channel, thus inducing more symmetric, closer to model Giant Magnetoresistance (GMR). Also, the sample edges might contribute by adding extra coupling through magnetostatic interaction. The added effects result in a counter-intuitive trend that goes from the near ideal wide samples through intermediate sizes with fairly abrupt changes in MR, and finally to the closer to bell-shaped ideal GMR at narrow widths.

Anomalous anisotropic magnetoresistance in single-crystalline Co/SrTiO3(001) heterostructures*

“…However, the sign of transverse AMR is changed from positive at 300 K to negative at 5 K for the Co[110] Hall bar, but the transverse AMR is always positive for the Co[100] Hall bar. These results of the transverse AMR never appear in Co, [47,48] Fe/GaAs, [33] or Co x Fe 1−x /MgO, [34] which only show the positive behaviors. The different temperature-dependent behaviors of the longitudinal and transverse AMR for two Hall bars enlighten us to consider the contribution of crystal symmetries.…”

Current trends in planar Hall effect sensors: evolution, optimization, and applications

“…Briefly, PHE is studied with a varied width, for larger magnitude, a hysteresis free accompanied by a single domain model is acquired. While, for smaller width, a remarkable hysteresis behavior is introduced to the sensor profile and magnetization reversal occurs as one step [190,206,207]. Moreover, a tilting angle of the cross junction by 45º can raise the sensor sensitivity by 30% [189].…”