Study On The Electrochemical Preparation And Properties Of Magnetic Metal Nanowires And Multilayered Nanowires

The magnetic NiFe and NiAg alloy nanowire arrays and NiFe/Cu multilayered nanowire arrays were prepared by electrochemical deposition into the nanoporous anodic alumina oxide (AAO) templates. The morphology, structure and magnetic properties of the nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively.The anodic aluminum oxide membranes were prepared by two-step oxidation in the solution of oxalic acid, and stripped from the aluminum substrate adopting strip against electricity technique. The oxide barrier layer was chemically dissolved from bottom side of the film in phosphoric acid, and the free-standing AAO menbrane was obtained. The alumina nanowires were obtained by etching anodic aluminum oxide films in an aqueous sodium hydroxide solution and a mixed solution of 6wt% H2CrO4 and 1.8wt% H3PO4. A discussion of the possible mechanism for the formation of nanowires was given.Ordered Fe21Ni79 alloy nanowire arrays were prepared by AC electrochemical deposition into the nanoporous anodic alumina oxide (AAO) templates. The nanowires were about 60nm in diameter and 9.7μm in length. The results indicated that the nanowires in an array were very regular, with an aspect ration controllably. Such nanowire arrays were in fcc structure. The hysteresis loops showed that the nanowire arrays had excellent perpendicular magnetic anisotropy with their easy magnetization axis parallel to nanowire arrays, the as-deposited samples had high squareness(Mr/Ms) (about 0.86) and large coercivity (as high as 1203Oe) when the magnetic field was perpendicular to the membranes. which is larger than squareness(Mr/Ms) (about 0.18) and coercivity (as high as 620Oe) when the magnetic field was parallel to the membranes. Annealing can improve the coercivity and the squareness of nanowire arrays. Coercivity as high as 1315Oe was obtained in the samples annealing at 500℃, above 500℃, the coercivity and squareness decrease sharply.Highly ordered Ni₇₉Ag₂₁ alloy nanowire arrays was fabricated successfully by electrodeposition into the pores of a porous anodic aluminum oxide(AAO). the nanowire arrays were regularly arranged, the length of nanowires was 30μm and thediameter of the nanowires was about 90nm,L/D was up to 300. Such nanowire arrays were in fcc structure. The hysteresis loops show that the nanowire arrays were superparamagnetic. Ordered NiFe/Cu multilayered nanowire arrays were prepared by DC electrochemical deposition into the nanoporous anodic alumina oxide (AAO) templates. The nanowires were about 90nm in diameter. and there was evident boundary between every sublayer. The hysteresis loops showed that the nanowire arrays which had 60 ciecles of NiFe(130nm)/Cu(30nm) had excellent perpendicular magnetic anisotropy with their easy magnetization axis parallel to nanowire arrays, the as-deposited samples had high squareness(Mr/Ms) (about 0.90) and large coercivity (as high as 1320Oe) when the magnetic field was perpendicular to the membranes. which was larger than squareness (Mr/Ms) (about 0.25) and coercivity (as high as 700Oe) when the magnetic field was parallel to the membranes.