Iron brews rich physics
All the complexity of magnetism and superconductivity seems to appear even for a simple element like iron. The body-centred-cubic alpha phase is the well known ferromagnet (green), while if the high pressure and high-temperature gamma phase (blue) was stable at low temperatures it would form an antiferromagnet at 100 K and ambient pressure.
The hexagonal-close-packed epsilon phase (purple) is non-magnetic and becomes superconducting (yellow) at low temperatures. The origin of the superconductivity in the epsilon phase and the charge-pairing mechanism remains a mystery and a source of intense debate.