Metamagnetism is a sudden (often, dramatic) increase in the

magnetization In classical electromagnetism, magnetization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material. Movement within this field is described by direction and is either Axial or Di ...

of a material with a small change in an externally applied

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. The metamagnetic behavior may have quite different physical causes for different types of metamagnets. Some examples of physical mechanisms leading to metamagnetic behavior are: # Itinerant metamagnetism -

Exchange splitting Exchange may refer to: Physics *Gas exchange is the movement of oxygen and carbon dioxide molecules from a region of higher concentration to a region of lower concentration. Places United States * Exchange, Indiana, an unincorporated community * ...

of the

Fermi surface In condensed matter physics, the Fermi surface is the surface in reciprocal space which separates occupied from unoccupied electron states at zero temperature. The shape of the Fermi surface is derived from the periodicity and symmetry of the cryst ...

in a

paramagnet Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

ic system of itinerant electrons causes an energetically favorable transition to bulk magnetization near the transition to a

ferromagnet Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials a ...

or other magnetically ordered state. # Antiferromagnetic transition - Field-induced spin flips in

antiferromagnet In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. ...

s 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 In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...

, a

continuous phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...

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.

References

{{magnetic states Magnetic ordering