Perforated alumina templates as a tool for engineering of CoPd film magnetic properties

Abstract

Abstract The patterning of the CoPd films was performed by the deposition of the Co/Pd multilayers on the nanoperforated templates of anodic aluminum oxide (AAO). We observed that the morphology of aluminum oxide is represented by the hexagonal packed hemispherical wells with a pore in the middle. The morphology of the patterned films follows the features of the initial templates; the magnetic material is deposited mainly in the regions between the pores and on their perimeter. The Co atoms diffuse into the Pd layer already during the film deposition, and discontinuous interfaces of Co and Pd are formed leading to the creation of the CoPd solid solution. The out-of-plane hysteresis loops of the nanoporous films exhibited high values of the coercive field (HC = 2.0–3.6 kOe) and squareness ratio (Mr/MS = 0.7–0.8). This indicates that the nanoporous films retain the perpendicular magnetic anisotropy observed for continuous film. Deteriorated values of effective anisotropy constant Keff for the porous films with respect to the continuous film are explained by the complex morphology of the nanoporous films, which leads to partial deviation of magnetic moments from the direction normal to the sample plane. On the other hand the increase of the values of the coercive field HC of the nanoporous films in comparison to the continuous films is related to the pinning of the magnetic moments on the nanopores. We observed the transition of the magnetization reversal mechanism from the domain wall motion observed for the continuous film, to coherent rotation mode for the nanoporous films. We show that this approach allows us to tune the coercive field HC and the effective magnetic anisotropy constant Keff of the CoPd film by engineering the pore size of the templates.