Magnetic properties of Co-Pt alloy nanowire arrays in anodic alumina templates

Microstructure and magnetic properties of ferromagnetic Co9Pt nanowire arrays electrodeposited into self-assembled anodic alumina templates have been investigated. X-ray diffraction shows that as-prepared Co-Pt nanowires are of FCC polycrystalline structure. The nanowires with diameter d<80nm are mainly of (111) preferred orientation along the wire axis. For a specific diameter, the coercivity and the remanent ratio with the external magnetic field parallel to the nanowire axis, i.e., the parallel geometry, are larger than those of the perpendicular geometry. With temperature increasing from 90 to 600K, above two physical quantities in the perpendicular geometry decrease monotonically, while those of the parallel geometry change little. The dependence of the coercivity and the remanent ratio on temperature and the nanowire diameter can be explained after the shape and the magnetocrystalline anisotropies, and the dipolar magnetic interaction are considered. For the parallel and perpendicular geometries, the coercivity decreases with increasing diameter d as a linear scale of 1/d2 and approaches each other in the two geometries for large d. The degradation of coercivity in Co-Pt nanowires with increasing diameter is suggested to come from the curling mode of magnetization reversal process