582 research outputs found
Dynamic binding of driven interfaces in coupled ultrathin ferromagnetic layers
We demonstrate experimentally dynamic interface binding in a system
consisting of two coupled ferromagnetic layers. While domain walls in each
layer have different velocity-field responses, for two broad ranges of the
driving field, H, walls in the two layers are bound and move at a common
velocity. The bound states have their own velocity-field response and arise
when the isolated wall velocities in each layer are close, a condition which
always occurs as H->0. Several features of the bound states are reproduced
using a one dimensional model, illustrating their general nature.Comment: 5 pages, 4 figures, to be published in Physical Review Letter
Highly asymmetric magnetic domain wall propagation due to coupling to a periodic pinning potential
Magneto-optical microscopy and magnetometry have been used to study
19 magnetization reversal in an ultrathin magnetically soft [Pt/Co]2 ferromagnetic film
20 coupled to an array of magnetically harder [Co/Pt]4 nanodots via a predominantly
21 dipolar interaction across a 3 nm Pt spacer. This interaction generates a spatially
22 periodic pinning potential for domain walls propagating through the continuous
23 magnetic film. When reversing the applied field with respect to the static nanodot
24 array magnetization orientation, strong asymmetries in the wall velocity and switching
25 fields are observed. Asymmetric switching fields mean that the hysteresis of the film is
26 characterized by a large bias field of dipolar origin which is linked to the wall velocity
27 asymmetry. This latter asymmetry, though large at low fields, vanishes at high fields
28 where the domains become round and compact. A field-polarity-controlled transition
29 from dendritic to compact faceted domain structures is also seen at low field and a
30 model is proposed to interpret the transition
Exchange bias in GeMn nanocolumns: the role of surface oxidation
We report on the exchange biasing of self-assembled ferromagnetic GeMn
nanocolumns by GeMn-oxide caps. The x-ray absorption spectroscopy analysis of
this surface oxide shows a multiplet fine structure that is typical of the Mn2+
valence state in MnO. A magnetization hysteresis shift |HE|~100 Oe and a
coercivity enhancement of about 70 Oe have been obtained upon cooling (300-5 K)
in a magnetic field as low as 0.25 T. This exchange bias is attributed to the
interface coupling between the ferromagnetic nanocolumns and the
antiferromagnetic MnO-like caps. The effect enhancement is achieved by
depositing a MnO layer on the GeMn nanocolumns.Comment: 7 pages, 5 figure
Model of bound interface dynamics for coupled magnetic domain walls
A domain wall in a ferromagnetic system will move under the action of an
external magnetic field. Ultrathin Co layers sandwiched between Pt have been
shown to be a suitable experimental realization of a weakly disordered 2D
medium in which to study the dynamics of 1D interfaces (magnetic domain walls).
The behavior of these systems is encapsulated in the velocity-field response
v(H) of the domain walls. In a recent paper [P.J. Metaxas et al., Phys. Rev.
Lett. 104, 237206 (2010)] we studied the effect of ferromagnetic coupling
between two such ultrathin layers, each exhibiting different v(H)
characteristics. The main result was the existence of bound states over
finite-width field ranges, wherein walls in the two layers moved together at
the same speed. Here, we discuss in detail the theory of domain wall dynamics
in coupled systems. In particular, we show that a bound creep state is expected
for vanishing H and we give the analytical, parameter free expression for its
velocity which agrees well with experimental results.Comment: 9 page
Quantitative analysis of shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy
Shadow X-ray Magnetic Circular Dichroism Photo-Emission Electron Microscopy
(XMCD-PEEM) is a recent technique, in which the photon intensity in the shadow
of an object lying on a surface, may be used to gather information about the
three-dimensional magnetization texture inside the object. Our purpose here is
to lay the basis of a quantitative analysis of this technique. We first discuss
the principle and implementation of a method to simulate the contrast expected
from an arbitrary micromagnetic state. Text book examples and successful
comparison with experiments are then given. Instrumental settings are finally
discussed, having an impact on the contrast and spatial resolution : photon
energy, microscope extraction voltage and plane of focus, microscope background
level, electric-field related distortion of three-dimensional objects, Fresnel
diffraction or photon scattering
Magnetic Anisotropy of a Single Cobalt Nanoparticle
Using a new microSQUID set-up, we investigate magnetic anisotropy in a single
1000-atoms cobalt cluster. This system opens new fields in the characterization
and the understanding of the origin of magnetic anisotropy in such
nanoparticles. For this purpose, we report three-dimensional switching field
measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix.
We are able to separate the different magnetic anisotropy contributions and
evidence the dominating role of the cluster surface.Comment: 4 pages, 8 figure
Magnetisation switching in a ferromagnetic Heisenberg nanoparticle with uniaxial anisotropy: A Monte Carlo investigation
We investigate the thermal activated magnetisation reversal in a single
ferromagnetic nanoparticle with uniaxial anisotropy using Monte Carlo
simulations. The aim of this work is to reproduce the reversal magnetisation by
uniform rotation at very low temperature in the high energy barrier hypothesis,
that is to realize the N\'eel-Brown model. For this purpose we have considered
a simple cubic nanoparticle where each site is occupied by a classical
Heisenberg spin. The Hamiltonian is the sum of an exchange interaction term, a
single-ion anisotropy term and a Zeeman interaction term. Our numerical data of
the thermal variation of the switching field are compared to an approximated
expression and previous experimental results on Co nanoparticles
Recent developments for beam intensity increase operation
International audienceThe aim of the beam intensity increase operation (THI project) is to multiply the present intensities for lightest ions by a factor of fifteen in order to reach maximum power of six kilowatts [1]. The main objective is the production of large amounts of rare isotopes, either with SISSI (device intended for producing radioactive beams), or with SPIRAL (production and acceleration of radioactive ion beams). As part of this THI project, new developments have been required such as spiral scanners, for beanl profile measurements, and safety system to protect equipments against beam losses. Other developments are being carried on to improve the high intensity beam operation
Influencia del deterioro incipiente producido por el hongo de pudrición parda Serpula lacrymans, sobre las propiedades mecánicas de compresión normal y paralela a la fibra en madera de Pinus radiata D. Don
Several buildings and structures of wood are attacked by rot fungi, leading in some cases, slight weight losses that result in reductions in the strength properties of the material.
In this work was evaluated the influence of early rot decay in wood, in mechanical properties of normal and parallel compression.
For this, were inoculated samples of Pinus radiata D. Don with brown rot fungi Serpula Lacrymans. These samples were tested in three differents periods of fungal exposure.
The results identified a significant decrease in percentage of the properties under study.Diversas edificaciones y estructuras construidas en madera son atacadas por hongos de pudrición, provocando en algunos casos, leves pérdidas de peso que se traducen en disminución en las propiedades resistentes del material.
En este trabajo se evaluó la influencia de estados incipientes de pudrición en madera, en las propiedades mecánicas de compresión paralela y compresión normal.
Para esto, se inocularon probetas de Pinus radiata D. Don. con el hongo de pudrición parda Serpula lacrymans, las cuales fueron posteriormente ensayadas mecánicamente en tres diferentes períodos de exposición fúngica.
Los resultados obtenidos determinaron una importante disminución porcentual de las propiedades bajo estudio
Spatially periodic domain wall pinning potentials: Asymmetric pinning and dipolar biasing
Domain wall propagation has been measured in continuous, weakly disordered,
quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially
periodic domain wall pinning potentials. The potentials are generated
non-destructively using the stray magnetic field of ordered arrays of
magnetically hard [Co/Pt] nanoplatelets which are patterned above and are
physically separated from the continuous magnetic layer. The effect of the
periodic pinning potentials on thermally activated domain wall creep dynamics
is shown to be equivalent, at first approximation, to that of a uniform,
effective retardation field, , which acts against the applied field,
. We show that depends not only on the array geometry but also on
the relative orientation of and the magnetization of the nanoplatelets. A
result of the latter dependence is that wall-mediated hysteresis loops obtained
for a set nanoplatelet magnetization exhibit many properties that are normally
associated with ferromagnet/antiferromagnet exchange bias systems. These
include a switchable bias, coercivity enhancement and domain wall roughness
that is dependent on the applied field polarity.Comment: 12 pages, 9 figure
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