Synthesis and magnetic properties of highly arrayed nickel-phosphate nanotubes

In this study, nanotube arrays of nickel-phosphate have been developed by electroless deposition into sub-micro to nanometer sized pores of the porous alumina templates by hypophosphite electrolytic solution composed of NiSO4, NaH2PO2, NaC2H3O2 and Na3C6H5O7 at 80-100 °C and pH = 3-6. The dimension of the formed nanotubes has 1 μm in length, 200-300 nm in diameter and 80-150 nm in thickness of tube walls. Transmission electron microscopy examination of the nanotubes clearly show amorphous hallow structure with a average grain size of ∼5nm. The hysteresis loops of the nanotube arrays show a coercive field of about 200 Oe under treatment in 95%N2/5%H2 atmosphere at 500 °C as the magnetic field was applied along parallel and perpendicular to tube axis. The nanotube arrays also exhibit an anisotropic magnetic property with easier saturation along the perpendicular direction. However, both coercive field and saturation of remanent magnetization of the nanotube arrays become lower while continually increasing heat treatment temperature up to 900 °C.