Increasing the Magnetization of Electrolessly Deposited Ni-B Nanotubes

In this paper, we have deposited continuous and uniform Ni-B nanotubes with a length of 20 m and outer diameter of 400 nm via an electroless deposition method and investigated their magnetic properties. We show that as the pH of the electroless deposition bath increases, the B content of the Ni-B deposit decreases. As the boron content decreases the specific saturation magnetization s increases, with a maximum value of 33.7 J T1 kg1 obtained for a composition of Ni88B12. We have found that the magnetization of the Ni-B nanotubes increases after annealing due to crystallization of amorphous Ni-B, while the nanotube structure is still preserved at high temperatures. A maximum specific saturation magnetization of 46.3 J T1 kg1 was measured after annealing at 500 C for 1 h. Our results are analyzed in comparison to bulk Ni metal with specific saturation magnetization of 55.4 J T1 kg1. The electrolessly deposited nanotubes are shown to have a vortex mode reversal mechanism, which is attributed to the wall thickness in comparison to the outer diameter of the nanotubes.