Motivation There has been increasing interest in the fabrication and characterization of 1D magnetic nanostructures because of their potential applications in high-density magnetic memory, giant magnetoresistance (GMR) sensors, and magnetoelectronic devices. Because the magnetic properties of magnetic nanowires are highly dependent on their size, shape, and crystallinity, controlled fabrication of these magnetic nanomaterials with uniform size and shape remains an important issue. Magnetic barcode nanowires consisting of alternating structures of ferromagnetic and nonmagnetic materials, such as NiFe/Cu, Ni/Cu, and Co/Cu have been examined.

Experimental Fabrication of porous alumina templates Fabrication of Co/Pt magnetic barcode nanowires by electro-deposition Structural characterization of Co and Pt nanowires

What is porous anodic alumina ? ——————————————————————————————————————— Anodic Oxidation (DC) Electropolished Al FoilAl 2 O 3 on Al substrate

Porous Anodic Alumina (PAA) - Al2O3 Powerful template for the fabrication of nano-devices in fields of electronics, optoelectronics, magnetics, energy storage, photocatalysis, photonics, biosensors, ultra-filtration, and CVD micro-reactor Densely packed arrays of columnar hexagonal cells with straight nanochannels Controllable sizes of nanopores: ranging from nm in diameter, um in thickness Pore density as high as pores/cm2 Aspect ratio (depth divided by width) as high as 1000~3000 Morphology of synthesized materials: nanodot, nanowire/pillar/disk/rod, metal nanohole arrays, and nanotube. ———————————————————————————————————————

Electrodeposition A thin Au layer was sputtered on one side of the porous alumina templates The pure Co, Pt, and Co/Pt magnetic barcode nanowires were grown, respectively, in a single electrolyte with a pH of 3.0 containing 0.3 M CoSO 4, 0.03 M K 2 PtCl 6, and M H 3 BO 3 by using a pulsed-electrodeposition technique. (alternative constant potentials of -1000mV to deposit cobalt segments and -350mV to deposit platinum segments were applied.)

Modulated magnetism in the Co/Pt barcode nanowires corresponding to the aspect ratio change indicates that the magnetic properties of barcode nanowires can be tuned easily by controlling the relative thickness of the cobalt segments in the Co/Pt magnetic barcode nanowires.

Alternatively, we have observed that reactive ion etching (RIE) is a highly effective method for removing the electrode layer under mild conditions. RIE etching was performed at a fixed RF power (200W) and constant vacuum condition (60 mTorr) while flowing argon gas (7 sccm). The porous alumina templates were then dissolved Large amounts of individual free-standing magnetic barcode nanowires of exceptionally high quality (Figure 4a-h) are obtained successfully in a variety of different barcode structures after removing the porous alumina templates.

Conclusion They have demonstrated a massive fabrication of a variety of barcode Co/Pt nanowires by using a simple and highly effective deposition and releasing process. Modulation of magnetism is possible by controlling the aspect ratio and magnetic segment thickness of the barcodes, and further enhancement of ferromagnetism of such 1D barcodes is straightforward via a thermally induced phase transition process. In particular, these free-standing Co/Pt magnetic barcode nanowires and Co/Pt alloy nanowires have potential applications as key building blocks for 1D-based magnetoelectronic devices.