Fabrication and magnetic properties of NiFe2O4 nanocrystalline nanotubes

Aligned NiFe2O4 polycrystalline nanotubes have been successfully fabricated inside the nanochannels of porous anodic aluminum oxide (AAO) templates by wetting chemical deposition. A mixture of Fe nitrate and Ni nitrate, which was thermally decomposed at no less than 400 C, was used to yield NiFe2O4 tubes. By varying the deposition conditions and the parameters of the templates, we could tailor the lengths and the outer as well as the inner diameters of the tubes. Transmission electron microscopy (TEM) images reveal that the nanotubes are uniform and well isolated. X-ray diffraction (XRD) and selected area electron diffraction (SAED) demonstrate that the as-obtained nanotubes can be indexed to polycrystalline cubic spinel. The Mo¨ssbauer spectra show that the magnetic hyperfine field is reduced with the decrease of the metrical temperature as well as the decrease of the size of nanoparticles. Introduction