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 μm 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 σ_s increases, with a maximum value of 33.7 J T^-1 kg^-1 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 T^-1 kg^-1 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 T^-1 kg^-1. 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.