Nanoporous aluminum oxide templates to tailor magnetic anisotropy of electrodeposited cobalt phosphorus nanowires for hard magnetic micro devices

The production of magnetic nanowires as components for micro-electro-mechanical systems requires not only the development of a deposition process to meet the specific requirements of electrochemical deposition of the metal into nanoscale cavities, but also a detailed understanding of magnetic shape anisotropy. In this study, a fabrication process for cobalt phosphorus nanowires produced by electrochemical deposition into highly ordered anodic aluminum oxide (AAO) templates is presented. The AAO templates are fabricated using a two-step anodization process and are characterized with respect to pore diameter, interpore distance, pore density and porosity. A homogeneous pore structure with pore diameters in the range of the single domain size of cobalt is achieved, providing suitable templates for tailoring the magnetic properties. Cobalt phosphorus nanowires are deposited using pulse reverse electroplating with process parameters specifically adapted for nanoscale cavities. Pause durations of 500 ms and 1000 ms are used to ensure sufficient replenishment of cobalt and phosphorus ions within the nanopores, enabling uniform nanowire growth. Structural characterization by X-ray diffraction reveals a (002) preferred orientation, which corresponds to the easy axis of magnetization in the hexagonal close-packed cobalt lattice. Magnetic measurements demonstrate coercive field strengths of up to 60 kA/m for nanowires with a length of 500 nm. These results show the potential of tailoring the magnetic properties by changing the shape of the CoP in the nanometer scale. • Reproducible fabrication process for AAO-templates with defined pore sizes • Template pore size in cobalt single domain size range • Electrodeposition of CoP nanopillars using controlled pulse parameters • High aspect ratio to enable pronounced shape anisotropy • Tailored crystal and shape anisotropy for magnetic property tuning