Low temperature magneto-transport properties in bilayered magnetic anti-dot mircoarrays

Magneto-transport study on the photolithographically-patterned anti-dot micro-arrays of cobalt upper-layer over a uniform thin nickel under-layer has been carried out. Circular anti-dots in rhomboidal symmetry were fabricated. The magnetoresistance (MR) curves were recorded for magnetically-easy and -hard axes of the bilayer structure at various temperatures. In addition to anisotropic MR, at low temperatures, the MR data shows anomalous behavior with several kinks and plateau regions, indicating complex reversal phenomena. Further, decrease in temperature results in increase of MR average peak height, double splitting of MR peaks and broadening of MR peaks. Additionally, the exchange bias behavior was found in the transverse MR curve; while no significant exchange effect was seen in the longitudinal MR curve. Using energy dispersive spectrum and X-ray absorption spectra taken at Co L3,2-edge, the presence of CoO layer over the bilayer structure was detected; while the Ni under-layer remained deoxidized.