Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4).. We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600 °C for 2 h in Ar gas forming arrays of cobalt ferrite nanowires inside the AAT. The morphology of the ferrite before and after annealing was observed using a field-emission scanning electron microscope. The crystallographic structure of the nanowires was analyzed using x-ray diffraction and transmission electron microscopy. The magnetization was measured by a superconducting quantum interference device. The coercivity of the annealed ferrite in the form of nanowires is significantly larger than that of the separate ferrite nanoparticles in the pores. This effect is due to the clustering of nanoparticles when the organic solvent is removed by high-temperature annealing as well as an improvement in the crystallininty of the ferrite by reduction of defects. The Faraday spectra of the nanowires were measured before and after annealing. A significant peak was observed at 725 nm. The nanowire/AAT composite material had a Verdet constant of 0.1 min/ (Oe cm) at the peak. It is important to mention that not only the properties but also the form of the material—a regular array of pillars—may be important for microelectronic or information storage applications.
J. Appl. Phys.
J. Appl. Phys. 97, 10F306 (2005)