Biomedical Engineering Reference
In-Depth Information
of 8 nm, with an appropriately adjusted anisotropy field (6000 Oe), would
meet both thermal stability and signal/noise requirements. Media with an
average grain size of 8 nm should not be extraordinarily hard to generate,
but the model imposes another, very demanding, requirement on the grain
size; namely that the grains should be monodisperse. As current
technologies reach their limit, nanoscale materials seem to have the greatest
potential for further developments in high-density magnetic data storage.
2.2 Magnetic nanocomposites
Imagine being able to record 100movies on a disk the size of a CD. This is
the potential of holographic data storage based on developments in
nanotechnology. Nanoscale structures are an intermediate form of matter,
which fills the gap between atoms/molecules and bulk materials. These types
of structures frequently exhibit unusual physical and chemical properties
which differ from those observed in bulk three-dimensional materials. One
way forward in the field of high-density data storage systems is to utilize
magnetic nanoparticles embedded in various matrices.
Magnetic nanocomposites are generally composed of ferromagnetic
particles [28, 29] of nanometer grained size distributed either in a non-
magnetic or magnetic matrix. The size and distribution of the particles play
an important role in determining the properties of these materials.
Generally, the electrical and magnetic behavior of nanostructured systems
is governed by both the intrinsic properties of the nanostructures and their
interactions with the matrix. Thus, the magnetic behavior of the system can
be controlled by the size, shape, chemical composition and structure of the
nanoparticles, and/or by the nature of the matrix in which they are
embedded. However, the preparation of stable magnetic nanoscale materials
that contain uniformly distributed nanoparticles (in a specified range of sizes
of nanoparticles with a narrow size distribution) using conventional
techniques is rather difficult. The fabrication and future utilization of
such types of nanosized systems requires the use of novel technological
processes.
The critical temperature of magnetic particles is an important property,
and it is difficult to calculate the magnetization of nanomaterials without
knowledge of the critical temperature. A variational cumulant expansion
(VCE) [100-102] method has been developed for the calculation of the
critical point of magnetic films. The methodology is, in principle, capable of
dealing with a crystal of any lattice structure and of any geometric shape.
The critical point T
c
for thin films of cubic lattices has been investigated with
simple cubic (sc), body-centered-cubic (bcc) and face-centered-cubic (fcc)
structures as a function of the number of monolayers L grown along various
directions such as
<
110
>
,
<
111
>
and
<
100
>
. It has been found that T
c
is
