Preparation And Properties Of Super Fine Magnetic Nanowire Arrays

In recent years, ultrafine magnetic nanowires have attracted much attention due to their exciting application prospect in high-density perpendicular magnetic recording media. In this work, mesoporous silica nanofibres were synthesized within the pores of anodic aluminum oxide (AAO) template using a simple sol–gel method. The mesoporous Co nanowires were formed in the pores of AAO/SiO₂ composite templates. The ultrafine Ni, Co and Fe-Co, Co-Ni nanowire arrays were fabricated within AAO templates. The morphology, microstructure and magnetic property of the nanowires were studied by SEM, TEM, XRD and VSM. The influence of heat treatment on the microstructure and magnetic properties of the nanowires was also studied.The average diameter of the mesoporous silica nanofibre was about 250 nm and lengths up to several micrometers. The mesoporous silica nanofibres possessed typical mesoporous structures with the diameter of about 6 nm, and the brunauer–emmett–teller (BET) surface area was estimated to be 73.0 m² /g. In addition, TEM results showed that the mesostructure (columned and lamellar structure) of silica mainly depended on the concentration of the surfactant. The mesoporous Co nanowires which formed within the AAO/SiO₂ composite templates were mainly composed of 6 nm Co nanorods. In addition, Magnetic measurements showed that perpendicular coercivity and remanence of the as-deposited mesoporous Co nanowires decreased with the increase of the testing temperature. The ultrafine Ni, Co, Fe-Co, and Co-Ni nanowires with a diameter of 15 nm which were fabricated within the AAO template exhibted polycrystalline features. It was obvious that the ultrafine nanowires had an easy magnetic axis perpendicular to the AAO film, i.e. parallel to the axis of the nanowires due to the shape anisotropy. Meanwhile, it is found that the perpendicular coercivity of Co and Fe-Co nanowires arrays was as high as 2101 Oe and 2600 Oe, respectively, which higher than the previous reported results in the literature. The Co crystal lay along with the direction of the (002) after annealing at 300 and 400℃, and the Co-Ni crystal lay along with the direction of the Co (111) Ni (011) after annealing at 600℃. The perpendicular coercivity (Hc⊥) as high as 2497.4 Oe and squareness (Mr/Ms) of about 0.744 can be obtained in Co nanowires annealing at 600℃. For the annealed Co-Ni and Fe-Co nanowires, the Hc⊥and Mr/Ms reached the maximum when the annealing temperature increases to 400℃(1037.5 Oe and 0.48 for Co-Ni, 3029.35 Oe and 0.92 for Fe-Co, respectively)...