Finite Element Formalism for Micromagnetism

The aim of this work is to present the details of the finite element approach we developed for solving the Landau-Lifschitz-Gilbert equations in order to be able to treat problems involving complex geometries. There are several possibilities to solve the complex Landau-Lifschitz-Gilbert equations numerically. Our method is based on a Galerkin-type finite element approach. We start with the dynamic Landau-Lifschitz-Gilbert equations, the associated boundary condition and the constraint on the magnetization norm. We derive the weak form required by the finite element method. This weak form is afterwards integrated on the domain of calculus. We compared the results obtained with our finite element approach with the ones obtained by a finite difference method. The results being in very good agreement, we can state that our approach is well adapted for 2D micromagnetic systems.Comment: Proceedings of conference EMF200

From agricultural practices to boundaries' objects in the collective actions design

International audienceFrom 2 case studies we analyse how the concept of farming practices could be used as to elaborate an boundaries' objects while drive a collective action involving a wide range of actors and farmers

Fast computation of magnetostatic fields by Non-uniform Fast Fourier Transforms

The bottleneck of micromagnetic simulations is the computation of the long-ranged magnetostatic fields. This can be tackled on regular N-node grids with Fast Fourier Transforms in time N logN, whereas the geometrically more versatile finite element methods (FEM) are bounded to N^4/3 in the best case. We report the implementation of a Non-uniform Fast Fourier Transform algorithm which brings a N logN convergence to FEM, with no loss of accuracy in the results

La recherche en partenariat : entre fiction et friction

Our paper deals with the issues and practices at stake in the interdisciplinary partnership research field. Taking as a starting point the observation of three on-going research projects confronting agriculture with environmental or sanitary issues, the authors analyse the effects produced, in terms of scientific results, by the relationships established among researchers and development partners. The hypothesis is that the partnership is based on a two-sided reality: fiction, on the one hand, goes with the assumption that while researchers and partners do consider each other as allies, they consistently avoid confrontation in order to let things run their course. Friction, on the other hand, may arise with disagreement and thus alter the course of events. As revealed by the results of the study, this two-sided reality is held in tension within each project. Their comparison brings out three key points required in the management of such projects: the degree of solidarity between the groups concerned, the kingpin role of mediators, and the manner in which the research is conducted to meet changes in the partnership.L'article explore les enjeux et les pratiques de recherches interdisciplinaires en partenariat. À partir d'une lecture du déroulement de trois projets de recherche, portant sur l'agriculture face à des enjeux sanitaires ou environnementaux, les auteurs analysent l'effet sur la production scientifique des relations établies avec des acteurs du développement. L'hypothèse est que ce partenariat s'inscrit dans une double réalité : l'une, "fictionnelle", qui postule que chercheurs et partenaires s'allient tout en évitant de se confronter vraiment, ce, afin de maintenir le cours des choses ; l'autre, "frictionnelle", qui surgit lorsque, dans une phase d'investissement plus poussé des acteurs, des désaccords apparaissent, ce qui réoriente le cours des événements. Les résultats révèlent la mise en tension de cette double réalité dans chacun des projets. Leur comparaison fait ressortir trois points-clés de la conduite de ces recherches : le degré de constitution et la force du "projet" propre des acteurs impliqués, le rôle pivot d'individus médiateurs et l'attention qu'il convient de porter aux reconfigurations éventuelles du partenariat qu'impliquent les évolutions mêmes du projet

Contacting individual Fe(110) dots in a single electron-beam lithography step

We report on a new approach, entirely based on electron-beam lithography technique, to contact electrically, in a four-probe scheme, single nanostructures obtained by self-assembly. In our procedure, nanostructures of interest are localised and contacted in the same fabrication step. This technique has been developed to study the field-induced reversal of an internal component of an asymmetric Bloch domain wall observed in elongated structures such as Fe(110) dots. We have focused on the control, using an external magnetic field, of the magnetisation orientation within N\'eel caps that terminate the domain wall at both interfaces. Preliminary magneto-transport measurements are discussed demonstrating that single Fe(110) dots have been contacted.Comment: 5 page