Effect of aspect ratio on microstructure and magnetic properties of spinel CoFe₂O₄ nanowire arrays

Cobalt ferrite (CoFe₂O₄) nanowire arrays with different diameters were prepared in porous anodic aluminum oxide (AAO) template by a sol-gel template method with the assistance of organic solvent and surfactant. The morphology was studied by scanning electron and transmission electron microscopy. A polycrystalline phase of spinel type structure was ascertained by X-ray diffraction (XRD) patterns. A magnetic test was performed using a physical property measurement system (PPMS), showing the uniaxial anisotropy with easy axis along the nanowire with an aspect ratio larger than 1000. A coercivity reduction from about 1500 Oe to about 800 Oe has been observed, while the diameter increases from 20 nm to 50 nm in this experiment. The cause of this has been discussed.