magnetic-materilas-2017-posters-abstracts

allied

academies

Mater Sci Nanotechnol 2017

Volume 1 Issue 3

Magnetic Materials 2017

Page 93

October 09-10, 2017 London, UK

International Conference on

Magnetic structures and excitations of 3D

nanoparticles

Jean-Claude S Levy

Paris Diderot University, France

agnetic nanoparticles are produced for memory

applications as well as for biomedical applications

since they can be driven or stirred by external magnetic

fields. Networks of nanoparticles evidenced interesting

spectra of excitations opening the way to materials with a

low index such as metamaterials. The magnetic structures

and excitations of 3D nanoparticles are rather badly known

because of the occurrence of long ranged coupling such as

dipolar interaction which competes with local interactions

such as an exchange. The goal of this paper is to introduce a

systematic view of these magnetic structures and excitations

for different materials and samples. The characteristic

parameter is the ratio between dipolar interaction and

exchange. This effective ratio evolves with both materials

and sample size. The results of Langevin numerical analysis

of both structures and excitations of a 64*64*64 cube show a

set of transitions from a uniform domain structure to a final

multidomain structure where singularity lines design a full

3D network as shown in the figure, a snapshot of an actual

movie. Among the steps: a single vortex (or antivortex) line,

the occurrence of a 2D network of vortex lines. As expected

in such small samples super-paramagnetism occurs and there

is a rather slow dancing collective motion of these singularity

lines. These rather localized collective motions generalize

the gyrotropic vortex motion of a 2D nanoparticle. The low-

frequency excitations are directly obtained from Langevin

simulations while higher energy excitations are derived from

the dynamical matrix approximation, evidencing gaps in the

spectrum. The low energy spectrum shows a critical behavior

of the super-paramagnetism blocking time. These behaviors

would be modulated by the addition of extra interactions

such as anisotropy and Dzyaloshinskii-Moriya interaction for

instance with the introduction of skyrmions

Materials Science and Nanotechnology