Biomedical Engineering Reference
In-Depth Information
external magnetic field. Assuming the SET to have a nanometer size central
island with a single-electron level we find that the interplay on the island
between coherent spin-flip dynamics and Coulomb interactions can make
the Coulomb correlations promote rather than suppress current through the
device.
2.7
Applications: cobalt-doped nickel nanofibers as
magnetic materials
By developing a fuller understanding of their properties, materials science
has produced magnetic materials far more powerful than those available
only a few decades ago. For instance, ferromagnetic metal nanostructures
reveal physical and chemical properties that are characteristic of neither the
atom nor the bulk counterparts. Quantum size effects and the large surface
area of magnetic nanoparticles dramatically change some of the magnetic
properties and exhibit superparamagnetic phenomena and quantum
tunneling of magnetization because each particle might be considered as a
single magnetic domain. Consequently, some metal nanoparticles such as
Fe, Co, and Ni have been given much attention for use in various
applications such as electronic, optical and mechanical devices, magnetic
recoding media, catalysis, superconductors, ferrofluids, magnetic refrigera-
tion systems and contrast enhancement in magnetic resonance imaging
carriers for drug delivery.
Research suggests that the magnetic properties of those materials are
highly dependent on particle shape. For instance, the coercivity of nickel
nanofibers at room temperature was about 100 times the magnitude of the
bulk material. One-dimensional (1D) magnetic nanomaterials are expected
to have interesting properties, as the geometrical dimensions of the material
become comparable to key magnetic length scales, such as the exchange
length or the domain wall width. This has resulted in the fabrication of
nanoscale magnetic logic junctions with ferromagnetic nanowires as
building blocks. Magneto-optical switches have been prepared using
suspensions of ferromagnetic nanowires. Among the 1D nanoshapes,
nanofibers have considerable importance because of their long axial ratio
characteristic, making them good candidates for nanodevices and nano-
membranes.
Electrospinning is the most popular technique utilized in the production
of functional nanofibers because of its simplicity, low cost and high yield.
Metal base nanofibers are produced by the electrospinning of a sol-gel
composed of a metal precursor and an accordant polymer. In the field of
pure metal nanofibers, the electrospinning process has been exploited to
synthesize Co, Cu, Fe and Ni in a nanofibrous shape by calcination of
