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).

Itinerant Ferromagnetism
G.B. Jo, Y.R. Lee, J.H. Choi, C.A. Christensen, T.H. Kim, J.H. Thywissen, D.E. Pritchard, and W. Ketterle:
_Itinerant ferromagnetism in a Fermi gas of ultracold atoms._Science 325 , 1521-1524 (2009).
Preprint Paper
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