A Study On Templates Synthesis Of Magnetic Nanowire Arrays

A highly ordered nanowire arrays have a potential of extensive application due to their distinct properties resulted from low-dimensional small size and high order arrangement. Magnetic nanowire arrays have received considerable interests because of their potential application in ultra-high-density magnetic recording media. The synthesis and characterization of magnetic nanowire arrays have been investigated in this thesis.Porous anodic aluminum oxide (AAO) templates with highly ordered and controllable pore size have been successfully prepared by a two-step anodization technique. The effect of processing parameters (such as anodization technique proceeding, the voltage, type of electrolyte, temperature, time, quality of aluminum etc.) on the quality of AAO templates has been analyzed. The suitable processing conditions have been obtained to prepare high quality AAO templates with different pore diameter.Highly ordered uniform Fe Ni nanowire arrays have been successfully fabricated in homemade AAO templates by DC electrodeposition method. The composition, morphology, structure of nanowire arrays have been characterized by the X-ray diffraction (XRD) patterns, scanning electron microscope (SEM), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM). The diameters of Fe or Ni nanowires correspond to the pore diameter of the AAO templates and the nanowires are uniform in diameter. The crystal orientation of Fe or Ni nanowires depends on the pore size of AAO templates. The smaller the pore size of AAO templates, the better the crystal orientation of the nanowire arrays. The Fe nanowires arrays fabricated by AAO template with 35nm pore size have obviously preferred orientation along the [200] direction while 200 nm Fe nanowires arrays don't show a preferred orientation. The metal spontaneously grow along the preferred orientation in small pore size AAO template is due to the extrusion and restriction effect of the wall of AAO templates. The magnetic properties of nanowire arrays have been investigated by vibration sample magnetometer (VSM). The magnetic properties of nanawire arrays with different diameters indicate that the nanowire arrays with small diameter have obviously perpendicular anisotropy. A high squareness (up to 98%) isobtained for Fe nanowire arrays with 35nm in diameter, while the nanowire arrays with 200nm in diameter don't have obviously perpendicular anisotropy. The reason of the highly preferred orientation in nanowire with small diameter owes to the shape anisotropy of nanowires.The CoFe2O4 nanowire arrays have been prepared in AAO templates by sol-gel method. The diameter of CoFe2C>4 nanowire is equivalent to the diameter of templates and the nanowires are polycrystalline structures. There is no a preferential magnetic orientation in the nanowire arrays because the nanowire arrays obtained in our experiments are inhomogeneous polycrystalline with the magnetic domain irregularly distributed, resulting in the absence of perpendicular anisotropy.The AAO template is an effective way to fabricate magnetic nanowire arrays. The DC electrodeposition method can be used to prepare highly ordered metal nanowire arrays that their structures and properties can be adjusted by controlling the pore sizes of the AAO templates. The sol-gel method is an appropriate way to prepare polycompound magnetic nanowire arrays.