N\'eel walls with prescribed winding number and how a nonlocal term can change the energy landscape

37 pages, 7 figuresInternational audienceWe study a nonlocal Allen-Cahn type problem for vector fields of unit length, arising from a model for domain walls (called N\'eel walls) in ferromagnetism. We show that the nonlocal term gives rise to new features in the energy landscape; in particular, we prove existence of energy minimisers with prescribed winding number that would be prohibited in a local model