Single spin-torque vortex oscillator using combined bottom-up approach and e-beam lithography

A combined bottom-up assembly of electrodeposited nanowires and electron beam lithography technique has been developed to investigate the spin transfer torque and microwave emission on specially designed nanowires containing a single Co/Cu/Co pseudo spin valve. Microwave signals have been obtained even at zero magnetic field. Interestingly, high frequency vs. magnetic field tunability was demonstrated, in the range 0.4 - 2 MHz/Oe, depending on the orientation of the applied magnetic field relative to the magnetic layers of the pseudo spin valve. The frequency values and the emitted signal frequency as a function of the external magnetic field are in good quantitative agreement with the analytical vortex model as well as with micromagnetic simulations.Comment: 9 pages, 4 figure

Influence Of Current Leads On Critical Current For Spin Precession In Magnetic Multilayers

In magnetic multilayers, a dc current induces a spin precession above a certain critical current. Drive torques responsible for this can be calculated from the spin accumulation $\bar{\Delta\mu}$. Existing calculations of $\bar{\Delta\mu}$ assume a uniform cross section of conductors. But most multilayer samples are pillars with current leads flaring out immediately to a much wider cross-section area than that of the pillar itself. We write spin-diffusion equations of a form valid for variable cross section, and solve the case of flat electrodes with radial current distribution perpendicular to the axis of the pillar. Because of the increased volume available for conduction-electron spin relaxation in such leads, $\bar{\Delta\mu}$ is reduced in the pillar by at least a factor of 2 below its value for uniform cross section, for given current density in the pillar. Also, $\bar{\Delta\mu}$ and the critical current density for spin precession become nearly independent of the thickness of the pinned magnetic layer, and more dependent on the thickness of the spacer, in better agreement with measurements by Albert et al. (2002).Comment: To appear in J. Magn. Magn. Mate

Intrinsic switching field distribution of arrays of Ni80Fe20 nanowires probed by in situ\mathit{in\, situ} magnetic force microscopy

The progress of magnetization reversal of weakly packed ferromagnetic Ni80Fe20 nanowire arrays of different diameters (40, 50, 70 and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighbouring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays.Comment: 4 pages, 5 figures. To appear in Journal of Superconductivity and Novel Magnetis

Magnetic force microscopy investigation of arrays of nickel nanowires and nanotubes

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements.Comment: 7 pages, 5 figure

Current-voltage characteristics of quasi-one-dimensional superconductors: An S-curve in the constant voltage regime

Applying a constant voltage to superconducting nanowires we find that its IV-characteristic exhibits an unusual S-behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j_{c2} at which the pure superconducting state becomes unstable and j_{c1}<j_{c2} at which the phase slip state is realized in the system.Comment: 4 pages, 5 figures, replaced with minor change

Influence de facteurs environnementaux influençant la teneur en urée dans le lait de vache en Wallonie et estimation des rejets azotés

Study on environmental factors influencing the urea content of cow's milk in Wallonia and estimation of nitrogen rejection. In Wallonia (South of Belgium), the urea content of milk produced on farms is assessed by the "Comité du lait". A total of 8,295,337 pieces of data recording the urea content in milk tanks was collected on Walloon farms in 2000 and during the period 2002-2011. These data were analyzed using a linear model. The fixed effects of the agricultural area or vulnerable zone, the month, the year and the interactions between these parameters were included in the model. The levels of fat and protein content in the milk were used as covariates. The average urea content in milk was found to be 255 mg·l-1. Four percent of the observations recorded a urea content of over 350 mg·l-1 and 14% recorded a urea content of over 400 mg·l-1. The models explained 38% and 35% of the variation in milk urea for the agricultural area and the vulnerable area variables, respectively. Within these models, the variables of month, region, year and the month-year interaction were the components that provided the most information. Milk urea content was higher in the summer period – April to October – than during the winter period – November to March – (287 vs 210 mg·l-1). This observation can be explained by the change in the cows' diet. During the summer, most of the cows grazed; ingestion of grass can lead to a nitrogen surplus in the diet. In the so-called "Limoneuse" and "Sablo-limoneuse" agricultural areas, recorded urea content was lower than in "Ardenne" and "Haute-Ardenne" (223 and 220 mg vs 278 and 284 mg·l-1, respectively). This difference can be explained by a greater use of grass in the diet in Ardenne and Haute-Ardenne. In vulnerable areas, urea content was lower (236 vs 273 mg·l-1). Annual nitrogen production calculated using different prediction equations ranged from 82 to 119 kg N per cow depending on the agricultural area

Static field limit of excitation probabilities in laser-atom interactions

We consider the interaction of atomic hydrogen, in its ground state, with an electromagnetic pulse whose duration is fixed in terms of the number of optical cycles. We study the probability of excitation of the atom in the static field limit i.e. for field frequencies going to zero. Despite the fact that the well-known Born–Fock adiabatic theorem is valid only for a system whose energy spectrum is discrete, we show that it is still possible to use this theorem to derive, in the low frequency limit, an analytical formula which gives the probability of transition to any excited state of the atom as a function of the field intensity, the carrier envelope phase and the number of optical cycles within the pulse. The results for the probability of excitation to lowlying excited states, obtained with this formula, agree with those we get by solving the timedependent Schrödinger equation. The domain of validity is discussed in detail

Le développement territorial durable : le cas d'une expérience dans le Nordeste du Brésil.

Cette communication traite d'une expérience de recherche-action de développement territorial durable au niveau du territoire du Alto Sertão du Oiaui et du Pernambuco dans le Nordeste du Brésil

Qualité microbiologique des fromages artisanaux fabriqués au lait cru en Région wallonne

Microbiological quality of craft raw milk cheeses produced in Wallonia. The main objective of this study was to evaluatethe bacteriological quality of raw milk cheeses produced in the southern part of Belgium (Wallonia) and to compare withsamples coming from other European countries. Results from bacteriological analyses of 153 cheese samples have beencompared with regard to food microbial standards (92/46 EC Directive). It can be concluded from this work that 69% of thesamples may be considered as acceptable, while 31% showed coliforms and Staplylococcus aureus counts exceeding thestandard values. As far as pathogens were concerned, 0.7% and 7.2% of the samples have were found unsatifactory with thecriteria related to Salmonella and Listeria monocytogenes, respectively. Enterobacteriaceae contamination has also beenevaluated and demonstrated an average log count of about 3.78 cfu/g. Cheeses produced from ewe milk showed anoutstanding microbiological quality since all samples turned out to be acceptable regarding the S. aureus counts and devoidof Salmonella and L. monocytogenes contamination. Although no seasonal effect on the bacteriological quality could beobserved, the microbial quality decreased after the production stage, i.e. mainly during the storage and the distribution.Cheese made by small producers seems to be better than those originating from industrial enterprises. By comparing theseresults with those obtained on cheese samples produced in some other European countries, it appears that the mean qualitylevel of Walloon raw milk cheeses is quite satifactory

Magnetic force microscopy study of the switching field distribution of low density arrays of single domain magnetic nanowires

In the present work, we report on the in situ magnetic force microscopy (MFM) study of the magnetization reversal in two-dimensional arrays of ferromagnetic Ni80Fe20 and Co55Fe45 nanowires(NW) with different diameters (40, 50, 70 and 100 nm) deposited inside low porosity (P<1%) nanoporous polycarbonate membranes. In such arrays, the nanowires are sufficiently isolated from each other so that long range dipolar interactions can be neglected. The MFM experiments performed for different magnetization states at the same spot of the samples are analysed to determine the switching field distribution (SFD). The magnetization curves obtained from the MFM images are relatively square shaped. The SFD widths are narrower compared to those obtained for high density arrays. The weak broadening of the curves may be ascribed to the NW intrinsic SFD. The influence of diameter and composition of the ferromagnetic NW is also investigated.Comment: 6 pages, 4 figures, To appear in Journal of Applied Physic