Separation of domain walls with nonlocal interaction and their renormalised energy by $Γ$-convergence in thin ferromagnetic films.

Radu Ignat, Roger Moser

Research output: Contribution to journalArticlepeer-review

Abstract

We analyse two variants of a nonconvex variational model from micromagnetics with a nonlocal energy functional, depending on a small parameter ϵ>0. The model gives rise to transition layers, called Néel walls, and we study their behaviour in the limit ϵ→0. The analysis has some similarity to the theory of Ginzburg-Landau vortices. In particular, it gives rise to a renormalised energy that determines the interaction (attraction or repulsion) between Néel walls to leading order. But while Ginzburg-Landau vortices show attraction for degrees of the same sign and repulsion for degrees of opposite signs, the pattern is reversed in this model. In a previous paper, we determined the renormalised energy for one of the models studied here under the assumption that the Néel walls stay separated from each other. In this paper, we present a deeper analysis that in particular removes this assumption. The theory gives rise to an effective variational problem for the positions of the walls, encapsulated in a Γ-convergence result. In the second part of the paper, we turn our attention to another, more physical model, including an anisotropy term. We show that it permits a similar theory, but the anisotropy changes the renormalised energy in unexpected ways and requires different methods to find it.

Original languageEnglish
Pages (from-to)395-475
Number of pages81
JournalJournal of Differential Equations
Volume339
Early online date6 Sept 2022
DOIs
Publication statusPublished - 5 Dec 2022

Keywords

  • Compactness
  • Domain walls
  • Renormalised energy
  • Repulsive/attractive interaction
  • Γ-convergence

ASJC Scopus subject areas

  • Analysis
  • Applied Mathematics

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