Metamagnetism

Metamagnetism is a magnetic phenomenon in which an applied magnetic field induces a rapid increase in magnetization in certain materials, typically transforming a low-magnetization state—often antiferromagnetic or paramagnetic—into a high-magnetization, ferromagnet‑like state. In many antiferromagnets, the field along an easy axis can trigger a spin-flop transition, where spins reorient to a canted configuration and, at a higher field, align more closely with the field, producing a steep rise in magnetization. In other cases the material undergoes a first-order metamagnetic transition between antiferromagnetic and ferromagnetic orders, evidenced by a discontinuity in the magnetization at a critical field Hc and often accompanied by hysteresis.

Some itinerant-electron systems exhibit metamagnetism without local moments; a high density of states at the Fermi level can satisfy the Stoner criterion under applied field, driving a transition to a polarized state. The critical field Hc and the nature of the transition are sensitive to temperature, pressure, and composition, and a metamagnetic quantum critical point can occur at zero temperature under tuning.

Experimentally, metamagnetism is identified by M(H) curves with a sharp jump or S-shaped onset, changes in neutron scattering patterns, and notable magnetocaloric effects. Materials studied include certain rare-earth and transition-metal intermetallics, FeRh, and other itinerant magnets.

Metamagnetism provides insight into exchange interactions and electronic structure, and has been explored for potential applications in magnetic refrigeration and spintronic devices.