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. Accordingly, physicists and engineers usually define magnetization as the quanti ...
of a material with a small change in an externally applied
magnetic field
A magnetic field (sometimes called B-field) is a physical 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 ...
. 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 of the
Fermi surface
In condensed matter physics, the Fermi surface is the surface in reciprocal space which separates occupied electron states from unoccupied electron states at zero temperature. The shape of the Fermi surface is derived from the periodicity and sym ...
in a
paramagnetic 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) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromag ...
or other magnetically ordered state.
# 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
In physics, chemistry, and other related fields like biology, 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 Sta ...
, 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.
References
{{magnetic states
Magnetic ordering