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Au/Co/SmCo/Au films with different SmCo and Co thickness were grown on silicon (100) substrates by electron-beam evaporation. The morphology of these films has been analyzed by transmission electron microscopy. The magnetic properties of the bilayers were investigated by magneto-optical Kerr effect. Hysteresis loops show a SmCo/Co single-phase behavior indicating a strong exchange coupling between the soft and hard phases. Also, we have shown that the magnetization reversal dynamics is dominated by domain wall motion.

An easy method based on the chemical charge neutrality and low temperature magnetic measurements is proposed to estimate the cationic distribution of Co x Fe 3-x O 4 (0 3+ cations located in the octahedral B sites has been quantified and found to be increased with x (about 30% for x = 1.5). The results have been compared to the literature and found to be accurate with advance techniques as Neutron powder diffraction and in-field Mossbauer spectroscopy. The validity of our method is discussed: when the grain size is less than 6 nm and when the nanoparticles are in a core-shell structure the method cannot be applied. Furthermore, the dependence of the magnetocrystalline anisotropy on the cobalt content x is related to the evolution of the Co 3+ cations. Our method offers the possibility to calculate the cationic distribution of spinel ferrite systems ones they have the suitable physico-chemical properties.

In this paper, we report on self-assembled Co nanoparticles deposited in and on porous silicon (PS) matrix by using UHV evaporation. Four samples were prepared by varying the Co deposited thickness (t = 3, 5, 7 and 10 nm). All samples have been investigated by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Physical Properties Measurement System (PPMS). The increase of t has induced an increase of the nanoparticle diameter from 3 nm to about 150 nm. Referring to the magnetic characterizations, this increase has been followed by a single to multi-domain transition. Therefore, this has been evidenced by a switching from superparamagnetism to purely ferromagnetism accompanied by a change in the magnetic reversal dynamics. Thus, by performing micromagnetic calculation, we have shown that a transition from the uniform rotation to vortex state occurs at a critical diameter of about 55 nm.

International audience; In this work, we present a correlation between High Resolution Transmission Electron Microscopy (HRTEM) and in-field Mössbauer spectrometry to point out exchange coupling behavior, surface effects and chemical disorder in CoxFe3-xO4 cobalt ferrite nanoparticles. The samples were synthesized by a solvothermal chemical route. The hysteresis loops, recorded by using Vibrating Sample Magnetometer (VSM), suggest a jump-like behavior nearby zero applied magnetic fields. The HRTEM micrographs illustrate the presence of faceted nanoparticles for x

Cobalt ferrites nanoparticles Co x Fe 3-x O 4 (1≤ x B ) range from 294 to 240 K. Kneller's law fitting of the coercive field dependence on the temperature exhibits a non-neglected interparticle interaction and a wide size distribution according to the difference found between T B and the Kneller transition temperature T BK .

In this study, SmCo-based films with different thicknesses were grown on a Kapton substrate by ultra-high vacuum (UHV) evaporation process. Two effects on magnetic properties of SmCo films have been investigated: the effect of the variation of the magnetic layer thickness and the effect of the substrate temperature. The morphology and the structure were explored by atomic force microscopy and X-ray diffraction. It has been shown that the film morphology and its crystallographic orientation changed significantly with increasing thickness. Magnetic measurements reveal a strong correlation between magnetic and structural properties. The highest magnetic squareness ratio M r/ M s (0.8) and a maximum coercive field at room temperature, of about 2 kOe, are obtained when the SmCo layer thickness is 15 nm.

International audience; In this work, we report on magnetic nanoparticles of CoxFe3-XO4 (x 0) gives spinel structure of space group Fd-3m for all samples. Magnetization curves, recorded by a Vibrating Sample Magnetometer (VSM), are the sign of two exchange-coupled magnetic phases (x > 0). This was in disagreement with XRD and SAED analyses which showed only one structural phase. Large (similar to 250 nm and less) rectangular and small spheroidal nanoparticles have been found by Transmission Electron Microscopy (TEM). The increase of cobalt content favors the formation of monodisperse nanoparticles. Following a subsequent heat treatment, a fraction of the as prepared samples (depending on x) has been transformed into hematite phase with a disappearance of the exchange-coupling behavior. In situ Micro-Raman analyses were necessary to investigate on the growing of the nanoparticles and the ferrite-hematite transformation. We have also deduced, that the synthesized phase with the cobalt ferrite one (till x < 1) was the magnetite Fe3O4. Then, we have pointed out the effect of performing local spectroscopy and the effect of having mixed ferrites on the structural and the physical properties. (C) 2016 Elsevier B.V. All rights reserved.

The aim of this work is to study the dielectric properties of thin films of tungsten trioxide. WO3 is an interesting material in the field of gas sensors. Here, we investigate the dependence of the electrical conductivity with temperature as well as the effect of the pressure on the thermal activation energy. For this purpose, we have used Impedance Spectroscopy (IS) to study the dielectric properties of RF sputtered WO3 thin films. Particularly, we have emphasized the effect of oxygen pressure on the surface conductivity.