Anisotropic magnetoresistance in electrodeposited cobalt antidot arrays

Nanosphere lithography is a simple and accessible technique for nanostructuring of materials. Combined with electrodeposition, it allows the production of compact, ordered antidot networks. In contrast to other lithographic techniques, the resulting nanostructure shows periodicity also along the growth axis. Interesting results are expected for the magnetoresistive behavior of such structures as function of thickness, due to the confinement of electronic routes and the strong shape anisotropy. We were able to electrodeposit cobalt antidot structures of homogeneous and controlled thickness directly over silicon substrates. Room temperature anisotropic magnetoresistance (AMR) as function of thickness and nanosphere diameter are presented, with the magnetic field applied in plane, transverse to the applied current. An overlap of two effects is observed. At fields lower than 2 kOe typical hysteretic AMR peaks appear around the coercive field, and tend to disappear for thicker films. At higher fields, a reversible contribution, caused by the forced magnetization that rotates the spin away from the local current direction, lowers the magnetoresistance, before it reaches its saturation value.