Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks

Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic resonance spectra of individual micron-size disks with identical diameter, 1 $m$m, but different layer structures. For a disk composed of a single 43.3 nm thick permalloy (Py) layer, the lowest energy mode in the perpendicular configuration is the uniform precession. The higher energy modes are standing spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30) nm multilayer structure, it has been interpreted that the lowest energy mode becomes a precession localized at the Cu/Py interfaces. When the multilayer is changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is coupled to the precession of the thin layer

Bistability of vortex core dynamics in a single perpendicularly magnetized nano-disk

Microwave spectroscopy of individual vortex-state magnetic nano-disks in a perpendicular bias magnetic field, $H$, is performed using a magnetic resonance force microscope (MRFM). It reveals the splitting induced by $H$ on the gyrotropic frequency of the vortex core rotation related to the existence of the two stable polarities of the core. This splitting enables spectroscopic detection of the core polarity. The bistability extends up to a large negative (antiparallel to the core) value of the bias magnetic field $H_r$, at which the core polarity is reversed. The difference between the frequencies of the two stable rotational modes corresponding to each core polarity is proportional to $H$ and to the ratio of the disk thickness to its radius. Simple analytic theory in combination with micromagnetic simulations give quantitative description of the observed bistable dynamics.Comment: 4 pages, 3 figures, 1 table, 16 references. Submitted to Physical Review Letters on December 19th, 200

Méthode de calcul multi-échelle pour la prédiction de l'apparition des contraintes résiduelles dans le procédé d'empilement par soudage et consolidation en continu

Le procédé d'empilement par soudage et consolidation en continu est un procédé prometteur utilisé dans l'industrie aéronautique pour fabriquer des pièces de grande taille. Dans les conditions standard d'élaboration, les pièces réalisées par ce type de procédé sont le siège d'importantes contraintes résiduelles. Le manque de connaissances sur l'origine et le développement des contraintes résiduelles est un frein important à la validation industrielle de ce procédé. On propose dans cette étude de développer une méthode de calcul multi-échelle permettant d'évaluer la formation des contraintes résiduelles au cours du procédé. Cette méthode, basée sur l'utilisation de la méthode des « éléments naturels » et de la méthode de Karhunen-Loeve, prend en compte l'évolution des propriétés thermomécaniques du matériau au cours du procédé, qui est facteur prépondérant dans la formation des contraintes résiduelles

Meso-macro optical experimental analysis of woven composite reinforcements in plane shear during their forming

National audienc

Estimation of marine source-term following Fukushima Dai-ichi accident

International audienceCs 134 Cs 131 I Environmental half time a b s t r a c t Contamination of the marine environment following the accident in the Fukushima Dai-ichi nuclear power plant represented the most important artificial radioactive release flux into the sea ever known. The radioactive marine pollution came from atmospheric fallout onto the ocean, direct release of contaminated water from the plant and transport of radioactive pollution from leaching through contaminated soil. In the immediate vicinity of the plant (less than 500 m), the seawater concentrations reached 68 000 Bq.L À1 for 134 Cs and 137 Cs, and exceeded 100 000 Bq.L À1 for 131 I in early April. Due to the accidental context of the releases, it is difficult to estimate the total amount of radionuclides introduced into seawater from data obtained in the plant. An evaluation is proposed here, based on measurements performed in seawater for monitoring purposes. Quantities of 137 Cs in seawater in a 50-km area around the plant were calculated from interpolation of seawater measurements. The environmental halftime of seawater in this area is deduced from the time-evolution of these quantities. This halftime appeared constant at about 7 days for 137 Cs. These data allowed estimation of the amount of principal marine inputs and their evolution in time: a total of 27 PBq (12 PBqe41 PBq) of 137 Cs was estimated up to July 18. Even though this main release may be followed by residual inputs from the plant, river runoff and leakage from deposited sediments, it represents the principal source-term that must be accounted for future studies of the consequences of the accident on marine systems. The 137 Cs from Fukushima will remain detectable for several years throughout the North Pacific, and 137 Cs/ 134 Cs ratio will be a tracer for future studies

Dynamic diagenetic modelling and the impact of biota.

International audienc