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Parois et vortex en micromagnétisme

Tristan Rivière — 2002

Journées équations aux dérivées partielles

Nous présenterons l’énergie libre modélisant les états (polarisations) des matériaux ferromagnétiques. Le problème variationnel associé contient de nombreux régimes asymptotiques dans lesquels «on voit» se former des défauts du type vortex, du type paroi (Bloch et Neel Walls) ou du type mixte paroi-vortex (Cross-Tie Walls). Le but de cet exposé est de présenter les travaux qui s’efforcent de donner une justification mathématique à la création de ces singularités. Nous décrirons l’insuffisance des...

Asymptotic analysis for the Ginzburg-Landau equations

Tristan Rivière — 1999

Bollettino dell'Unione Matematica Italiana

Questo lavoro costituisce un survey sui problemi di limite asintotico per le soluzioni delle equazioni di Ginzburg-Landau in dimensione due. Vengono presentati essenzialmente i risultati di [BBH] e [BR] sulla formazione ed il comportamento asintotico dei vortici in un dominio bidimensionale nel caso fortemente repulsivo (large K limit).

Lines vortices in the U(1) - Higgs model

Tristan Riviere — 2010

ESAIM: Control, Optimisation and Calculus of Variations

For a given U(1)-bundle over = λ 2 {}, where the are distinct points of λ 2 , we minimise the U(1)-Higgs action and we make an asymptotic analysis of the minimizers when the coupling constant tends to infinity. We prove that the curvature (= magnetic field) converges to a limiting curvature that we give explicitely and which is singular along line vortices which connect the . This work is the three dimensional equivalent of previous works in dimension two (see [3] and [4]). The results presented here...

Connecting topological Hopf singularities

Robert HardtTristan Rivière — 2003

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

Smooth maps between riemannian manifolds are often not strongly dense in Sobolev classes of finite energy maps, and an energy drop in a limiting sequence of smooth maps often is accompanied by the production (or bubbling) of an associated rectifiable current. For finite 2-energy maps from the 3 ball to the 2 sphere, this phenomenon has been well-studied in works of Bethuel-Brezis-Coron and Giaquinta-Modica-Soucek where a finite mass 1 dimensional rectifiable current occurs whose boundary is the...

Singular Bundles with Bounded L 2 -Curvatures

Thiemo KesselTristan Rivière — 2008

Bollettino dell'Unione Matematica Italiana

We consider calculus of variations of the Yang-Mills functional in dimensions larger than the critical dimension 4. We explain how this naturally leads to a class of - a priori not well-defined - singular bundles including possibly "almost everywhere singular bundles". In order to overcome this difficulty, we suggest a suitable new framework, namely the notion of singular bundles with bounded L 2 -curvatures.

Complex Ginzburg-Landau equations in high dimensions and codimension two area minimizing currents

Fanghua LinTristan Rivière — 1999

Journal of the European Mathematical Society

There is an obvious topological obstruction for a finite energy unimodular harmonic extension of a S 1 -valued function defined on the boundary of a bounded regular domain of R n . When such extensions do not exist, we use the Ginzburg-Landau relaxation procedure. We prove that, up to a subsequence, a sequence of Ginzburg-Landau minimizers, as the coupling parameter tends to infinity, converges to a unimodular harmonic map away from a codimension-2 minimal current minimizing the area within the homology...

Néel and Cross-Tie wall energies for planar micromagnetic configurations

François AlougesTristan RivièreSylvia Serfaty — 2002

ESAIM: Control, Optimisation and Calculus of Variations

We study a two-dimensional model for micromagnetics, which consists in an energy functional over S 2 -valued vector fields. Bounded-energy configurations tend to be planar, except in small regions which can be described as vortices (Bloch lines in physics). As the characteristic “exchange-length” tends to 0, they converge to planar divergence-free unit norm vector fields which jump along line singularities. We derive lower bounds for the energy, which are explicit functions of the jumps of the limit....

Néel and Cross-Tie Wall Energies for Planar Micromagnetic Configurations

François AlougesTristan RivièreSylvia Serfaty — 2010

ESAIM: Control, Optimisation and Calculus of Variations


We study a two-dimensional model for micromagnetics, which consists in an energy functional over -valued vector fields. Bounded-energy configurations tend to be planar, except in small regions which can be described as vortices (Bloch lines in physics). As the characteristic “exchange-length” tends to 0, they converge to planar divergence-free unit norm vector fields which jump along line singularities. We derive lower bounds for the energy, which are explicit functions of the...

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