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 Foil Al2O3 on Al substrate

Porous Anodic Alumina (PAA) - Al2O3• Powerful template for the fabrication of n

ano-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 5-300 nm in diameter, 0.1-300 um in thickness

• Pore density as high as 108-1011 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.

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Electrodeposition• A thin Au layer was sputtered on o

ne side of the porous alumina templates

• The pure Co, Pt, and Co/Pt magne

tic barcode nanowires were grown,

respectively, in a single electrolyte

with a pH of 3.0 containing 0.3 M C

oSO4, 0.03 M K2PtCl6, and 0.485 M

H3BO3 by using a pulsed-electrode

position technique. (alternative con

stant potentials of -1000mV to dep

osit cobalt segments and -350mV t

o 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.