Metamagnetism

1. Itinerant metamagnetism - Exchange splitting of the Fermi surface in a paramagnetic system of itinerant electrons causes an energetically favorable transition to bulk magnetization near the transition to a ferromagnet or other magnetically ordered state.
2. Antiferromagnetic transition - Field-induced spin flips in antiferromagnets cascade at a critical energy determined by the applied magnetic field.

Depending on the material and experimental conditions, metamagnetism may be associated with a first-order phase transition, a continuous phase transition at a critical point (classical or quantum), or crossovers beyond a critical point that do not involve a phase transition at all. These wildly different physical explanations sometimes lead to confusion as to what the term "metamagnetic" is referring in specific cases.