Itinerant Ferromagnetism in a Fermi Gas
Ferromagnetic phase transition in a gas of fermions in a periodic crystal (top, shown in blue) and in a gas without a crystalline structure (bottom). As the repulsive forces between the fermions are gradually increased, the fermions (red spheres) tend to point in the same direction. The red shadow shows the itinerant or delocalized nature of the fermions (or conduction electrons).