Fabrication and temperature dependent magnetic properties of Co-Ni nanotube arrays.

Abstract Parallel arrays of Co-Ni nanotubes with external diameter of 150 nm, wall thickness of 20 nm, and length of about 0.8 μm were successfully fabricated in ion-track etched polycarbonate (PC) templates by electrochemical deposition. The morphology and composition of the nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Temperature dependent magnetic analyses were performed with superconducting quantum interference device (SQUID) magnetometer which indicate that saturation magnetization of the nanotubes follows modified Bloch's law in the range 80–300 K. An abrupt deviation of the experimental curve (increase in magnetization) was observed from the modified Bloch's law below 80 K, which can be attributed to the disordered surface spins in the nanotubes due to the finite size effects. Finally, it was found that coercivity measured at different temperatures follows Kneller's law within the premises of Stoner–Wohlfarth model for ferromagnetic nanostructures. [ABSTRACT FROM AUTHOR]