Studies Of Fe,Co And FeCo Alloy Nanowires

In recent years, magnetic nanowires have attracted much attention because they have potential application in high-density magnetic recording media. The expected recording density could be as high as 400 GB/in2. In this work, Fe, Co and FeCo alloy nanowires were formed in the pores of porous anodic aluminum oxide template (AAO) by dc electrochemical deposition. The morphology,structure and magnetic properties of the nanowires were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). And the influence of heat treatment in the air on the structure and magnetic properties of the nanowires were also studied.Porous anodic aluminum oxide template (AAO) was fabricated by two-step anodization. The pores of the template are orderly arranged, have a narrow size distribution, and with an average pore diameter of about 60nm. The Fe Co and FeCo alloy nanowires were formed in the pores of AAO template using electrochemical deposition. The diameter of the nanowires is equal to the pore size of the template. The aspect ratio of the nanowires is over 600. The XRD spectra show that the nanowires have polycrystalline structure. The nanowire show clearly magnetic anisotropy and the easy axis of the nanowires are along the nanowires direction. This is mainly due to shape anisotropy.Fe, Co and FeCo alloy nanowires were heat treated in the air. And the change of the magnetic properties and structure of the nanowires were studied. It's found that the Fe, Co and FeCo alloy nanowires would be oxidized during heat treatment. Fe nanowires would be oxidized to paramagneticα-Fe2O3, and Co nanowires would be oxidized to antiferromagnetic Co3O4, while FeCo alloy nanowires would be oxidized to ferrimagnetic cobalt ferrite respectively. The initial oxidation process was quite rapid, but it slowed down when oxide layer became thicker with the increase of the heat treatment time, which prevent the further diffusion of oxygen atoms.It's found that the coercivity and remanence ratio of the Fe and Co nanowires increased with the heat treatment time. The possible reason should be that the heat treatment lowers the defect and improves the structure of the nanowires. The coercivity and remanence ratio of FeCo alloy nanowires also increased with the increase of the heat treament time, this should be due to the formation of cobalt ferrite with high magneto crystalline anisotropy during the heat treatment process.