1,571 research outputs found
Interaction effects in assembly of magnetic nanoparticles
A specific absorption rate of a dilute assembly of various random clusters of
iron oxide nanoparticles in alternating magnetic field has been calculated
using Landau- Lifshitz stochastic equation. This approach simultaneously takes
into account both the presence of thermal fluctuations of the nanoparticle
magnetic moments, and magneto-dipole interaction between the nanoparticles of
the clusters. It is shown that for usual 3D clusters the intensity of magneto-
dipole interaction is determined mainly by the cluster packing density eta =
Np*V/Vcl, where Np is the average number of the particles in the cluster, V is
the nanoparticle volume, and Vcl is the cluster volume. The area of the low
frequency hysteresis loop and the assembly specific absorption rate have been
found to be considerably reduced when the packing density of the clusters
increases in the range of 0.005 < eta < 0.4. The dependence of the specific
absorption rate on the mean nanoparticle diameter is retained with increase of
eta, but becomes less pronounced. For fractal clusters of nanoparticles, which
arise in biological media, in addition to considerable reduction of the
absorption rate, the absorption maximum is shifted to smaller particle
diameters. It is found also that the specific absorption rate of fractal
clusters increases appreciably with increase of the thickness of nonmagnetic
shells at the nanoparticle surfaces.Comment: The paper is accepted for Nanoscale Res. Let
Map of metastable states for thin circular magnetic nano-cylinders
Nano-magnetic systems of artificially shaped ferromagnetic islands, recently
became a popular subject due to their current and potential applications in
spintronics, magneto-photonics and superconductivity. When the island size is
close to the exchange length of magnetic material (around 15 nm), its magnetic
structure becomes markedly different. It determines both static and dynamic
magnetic properties of elements, but strongly depends on their shape and size.
Here we map this dependence for circular cylindrical islands of a few exchange
lengths in size. We outline the region of metastability of "C"-type magnetic
states, proving that they are indeed genuine and not a result of pinning on
particle imperfections. A way to create the smallest particles with guaranteed
magnetic vortex state at zero field becomes evident. It is expected that the
map will help focus the efforts in planning of experiments and devices.Comment: 3 pages, 1 figur
Spherical quantum well
Standard power series are used to construct and analyze angular and radial
spheroidal functions, which are necessary for solving boundary value problems
for Helmholtz equation in a spheroid. With an advanced approach the low-lying
energy levels of a deep spheroidal quantum well are calculated as a function of
the spheroid semiaxes ratio a/b. The well-known results for cylindrical and
spherical wells are reproduced in the limits a/b >> 1, and a/b ~ 1,
respectively.Comment: 10 pages, 4 figure
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