Preparation and magnetic properties of amorphous Co-Pt alloy nanowire arrays

Highly ordered amorphous Co-Pt alloy nanowire arrays are prepared by electrodepositing it into anodized aluminum disks with nanosized pores. SEM and TEM images reveal that the nanowires of array are uniform, well isolated, and parallel to each other. The average length of the Co-Pt alloy nanowires is about 10 mu m and the typical diameter is about 35 nm. Its microstructures and magnetic properties are also investigated by XRD and VSM (vibrating sample magnetometer), respectively. The sample prepared by the electrodeposition shows perpendicular anisotropy, but the as-annealed sample does not show. These different magnetic behaviors before and after annealing can be attributed to their different microstructures. X-ray diffraction evidences show that the sample before annealing is amorphous, but it changes to be polycrystalline after annealing. In the polycrystalline sample, due to the competition of shape anisotropy and magnetocrystal anisotropy, the sample does not display perpendicular anisotropy. But magnetocrystal anisotropy is very small in amorphous sample, therefore, shape anisotropy plays a dominant role which leads to strong perpendicular anisotropy.