71 research outputs found
Numerical calculation of magnetic form factors of complex shape nano-particles coupled with micromagnetic simulations
We investigate the calculation of the magnetic form factors of nano-objects
with complex geometrical shapes and non homogeneous magnetization
distributions. We describe a numerical procedure which allows to calculate the
3D magnetic form factor of nano-objects from realistic magnetization
distributions obtained by micromagnetic calculations. This is illustrated in
the canonical cases of spheres, rods and platelets. This work is a first step
towards a 3D vectorial reconstruction of the magnetization at the nanometric
scale using neutron scattering techniques.Comment: 7 pages, 5 figures. To appear in Physics Procedi
Exchange bias in Co/CoO core-shell nanowires: Role of the antiferromagnetic superparamagnetic fluctuations
The magnetic properties of Co (=15 nm, =130nm) nanowires are reported.
In oxidized wires, we measure large exchange bias fields of the order of 0.1 T
below T ~ 100 K. The onset of the exchange bias, between the ferromagnetic core
and the anti-ferromagnetic CoO shell, is accompanied by a coercivity drop of
0.2 T which leads to a minimum in coercivity at K. Magnetization
relaxation measurements show a temperature dependence of the magnetic viscosity
S which is consistent with a volume distribution of the CoO grains at the
surface. We propose that the superparamagnetic fluctuations of the
anti-ferromagnetic CoO shell play a key role in the flipping of the nanowire
magnetization and explain the coercivity drop. This is supported by
micromagnetic simulations. This behavior is specific to the geometry of a 1D
system which possesses a large shape anisotropy and was not previously observed
in 0D (spheres) or 2D (thin films) systems which have a high degree of symmetry
and low coercivities. This study underlines the importance of the AFM
super-paramagnetic fluctuations in the exchange bias mechanism.Comment: 10 pages, 10 figures, submitted to Phys. Rev.
Selected immobilization of individual nanoparticles by spot-exposure electron-beam-induced deposition
High temperature structural and magnetic properties of cobalt nanowires
We present in this paper the structural and magnetic properties of high
aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in
situ X ray diffraction (XRD) and SQUID characterizations. We show that the
anisotropic shapes, the structural and texture properties are preserved up to
500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the
magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant
and Ms the saturation magnetization. Hc decreases linearly when the temperature
is increased due to the loss of the Co magnetocrystalline anisotropy
contribution. At 500K, 50% of the room temperature coercivity is preserved
corresponding to the shape anisotropy contribution only. We show that the
coercivity drop is reversible in the range 300 - 500 K in good agreement with
the absence of particle alteration. Above 525 K, the magnetic properties are
irreversibly altered either by sintering or by oxidation.Comment: 8 pages, 7 figures, submitted to Journal of Solid State Chemistr
Dipolar interactions in magnetic nanowires aggregates
We investigate the role of dipolar interactions on the magnetic properties of
nanowires aggregates. Micromagnetic simulations show that dipolar interactions
between wires are not detrimental to the high coercivity properties of magnetic
nanowires composites even in very dense aggregates. This is confirmed by
experimental magnetization measurements and Henkel plots which show that the
dipolar interactions are small. Indeed, we show that misalignment of the
nanowires in aggregates leads to a coercivity reduction of only 30%. Direct
dipolar interactions between nanowires, even as close as 2 nm, have small
effects (maximum coercivity reduction of ~15%) and are very sensitive to the
detailed geometrical arrangement of wires. These results strenghten the
potential of magnetic composite materials based on elongated single domain
particles for the fabrication of permanent magnetic materials.Comment: 7 pages, 8 figures, submitted to Journal of Applied Physic
The azido ligand: a useful tool in designing chain compounds exhibiting alternating ferro- and antiferro-magnetic interactions
A one-pot reaction of NiII 1, CoII 2, FeII 3 and MnII 4 with 2,2A-bipyridine (bipy) and azide in water leads to [M(bipy)(N3)2]n chains where the metal ion is alternatively bridged by double end-on (EO) and end-to-end (EE) azido bridges; theoretical analysis of the variable-temperature magnetic susceptibility data of 1 and 4 reveals the occurrence of intrachain alternating ferro- (through EO) and antiferro-magnetic (through EE) interactions.Julve Olcina, Miguel, [email protected] ; Lloret Pastor, Francisco, [email protected] ; Clemente Juan, Juan Modesto, [email protected]
Chemical tuning of Coulomb blockade at room-temperature in ultra-small platinum nanoparticle self-assemblies
This work describes self-assemblies of ultra-small platinum nanoparticles, the electrical properties of which can be adjusted through slight modifications of the assemblies' constituents. Elaborating such systems, stable in air for months, is a first step towards nanoelectronic systems, where the charging energy of the nanoparticles is tuned by the nature of the ligands
Substitution modelling in life cycle assessment of municipal solid waste management
Life cycle assessment (LCA) is gaining importance worldwide in guiding waste management policies. The capacity of co-products such as recycled materials and recovered energy to avoid primary production of equivalent products largely determines the environmental performance of waste treatment technologies. Estimating the reductions in resource use, emissions, and impacts enabled by this substitution of primary production is often the most influential and controversial factor in quantifying the overall environmental performance of a waste management strategy. This study aims to critically evaluate the modelling of substitution in LCAs of recovered material from municipal solid waste management systems (MSWMS) by answering two questions. First, to what extent is substitution modelling transparently documented in the literature? Second, are the substitution ratios justified to represent physically realistic replacement of one product by another? To address these questions, we performed a systematic analysis of 51 LCA studies on MSWMS published in the peer-reviewed literature. We found that 22% of the substitution ratios are only implicitly expressed. A significant proportion of substitution ratios is not justified (65%), while for the remaining 35%, justifications do not represent physically realistic substitutions. We call for more rigor and transparency, and we propose guidance for the documentation of substitution ratios, with the aim of reaching more credible and robust analyses. For the justification of a substitution ratio to be considered physically realistic, information should notably be provided concerning loss of quality, the function performed by substitutable materials, and the sector of use
Chemical ordering in bimetallic FeCo nanoparticles: From a direct chemical synthesis to application as efficient high-frequency magnetic material
Single-crystalline FeCo nanoparticles with tunable size and shape were prepared by co-decomposing two metal-amide precursors under mild conditions. The nature of the ligands introduced in this organometallic synthesis drastically affects the reactivity of the precursors and, thus, the chemical distribution within the nanoparticles. The presence of the B2 short-range order was evidenced in FeCo nanoparticles prepared in the presence of HDAHCl ligands, combining 57Fe Mössbauer, zero-field 59Co ferromagnetic nuclear resonance (FNR), and X-ray diffraction studies. This is the first time that the B2 structure is directly formed during synthesis without the need of any annealing step. The as-prepared nanoparticles exhibit magnetic properties comparable with the ones for the bulk (Ms = 226 Am2·kgÂż1). Composite magnetic materials prepared from these FeCo nanoparticles led to a successful proof-of-concept of the integration on inductor-based filters (27% enhancement of the inductance value at 100 MHz).This work was performed in the frame of TOURS 2015, and the project was supported by the French âProgramme de lâĂ©conomie numĂ©rique des Investissements dâAvenirâ. We gratefully acknowledge the International Associated Laboratory (LIA)-M2OZART for financial support. Some of the HR-STEM and EELS studies were conducted at the Laboratorio de Microscopias Avanzadas, Instituto de Nanociencia de Aragon, Universidad de Zaragoza, Spain. R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through project MAT2016-79776-P (AEF/FEDER. UE). In IPCMS Strasbourg, the work was supported by the CNRS LIA âNANOFUNCâ and the LABEX NIE (no. ANR-11-LABX-0058_NIE)
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