A new and promising pathway towards utilization of FePt nanocubes in high density recording
(Nanowerk News) Films of FePt nanocubes begin to overcome several of the obstacles associated with the development of magnetic data storage media based
on self-oriented magnetic arrays of FePt nanoparticles.
Chemically synthesized FePt nanoparticles have potential for application as magnetic media for data storage. In order to be used as data storage
media, however, they must be deposited on substrates in such a way that their magnetic axes are aligned with respect to one another and with
respect to the substrate, a problem that has yet to be overcome with spherical FePt nanoparticles. Researchers at Seagate Research and the Department of Materials Science and Engineering at Carnegie Mellon University now have successfully synthesized single crystalline FePt nanoparticles with cubic shapes. Their findings will be reported in an article titled "Oriented self-assembly of cubic FePt nanoparticles" in the April 2006 edition of Materials Letter.
"The synthesis and oriented self-assembly of cubic FePt nanoparticles takes us several steps forward towards the ultimate development of magnetic recording media based on monodisperse FePt nanoparticles in the magnetic L10 phase" Nisha Shukla, one of the researchers, told Nanowerk. "Nanoparticles have now been synthesized in a cubic rather than spherical shape. This allows closer packing of particles into self-assembled two dimensional arrays."
"More importantly" Shukla adds, "these deposit on a substrate with crystallographic axes that are oriented with respect to the surface normal. More surprisingly, they assemble with axes that are oriented in the plane with respect to one another. This orientation of nanoparticles has not been achieved before and has always been a challenge for particulate based recording media."
Bright-field TEM (transmission electron microscopy) micrographs of unannealed FePt nanocubes deposited
from a non-polar solvent on a carbon-coated copper TEM grid. The cubes are
roughly 5 nm on a side. The particles in image A form a monolayer. The
particles in image B that are marked in circles have formed a bilayer. The
particles in the first and second layer have their sides aligned and one can
observe an interference pattern between the two. (Source: Seagate Research)
Synthesis and self-assembly of FePt nanoparticles have been
of great interest to the data storage industry as a possible means
for making nanoparticle based magnetic media which can
enable recording densities as high as 1 Tbit/in.2. The magnetic
bits which record data in thin film magnetic media are
comprised of many grains.
In order to achieve high recording densities with bits having well defined shapes and boundaries it
is necessary to decrease the size of the grains such that they
remain significantly smaller than the bit size. If the grains
become too small, however, one reaches the superparamagnetic
limit in which the magnetic moment of the individual bits
becomes thermally unstable. Self-assembled arrays of nanoparticles
can, in principle, reduce transition jitter by having
uniformly sized magnetic grains separated by a well-defined
center-to-center grain distance. Jitter is the noise in the magnetic
signal from the media that arises from the poorly defined
boundary of the magnetic bit formed by randomly shaped and
randomly sized magnetic grains.
Thus the ideal magnetic media
would be formed of nanoparticles which are of uniform, small
size and packed into arrays with the highest possible density.
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