Ferromagnetism
Definition and meaning of Ferromagnetism in chemistry.
Ferromagnetism is a form of magnetism in which unpaired electron spins on neighboring atoms align spontaneously and parallel to one another, producing strong, persistent magnetization that remains even after an external magnetic field is removed.
In more detail
The alignment arises from the quantum mechanical exchange interaction, which lowers the energy of the system when adjacent unpaired d-electron spins point the same way rather than opposing each other. Within a solid, this alignment occurs locally in regions called magnetic domains; applying an external field grows and reorients these domains so their moments add up, giving a large net magnetization. Above a characteristic Curie temperature, thermal agitation overwhelms the exchange interaction, domains randomize, and the material becomes merely paramagnetic. Because magnetization can persist after the field is removed, ferromagnets show hysteresis and can serve as permanent magnets.
Key facts
| Field | Physical Chemistry |
|---|---|
| Common example | Fe (iron) |
| Curie temperature of iron | 770 °C (1043 K) |
| Other ferromagnetic elements | Co, Ni, Gd |
Iron metal (Fe) is ferromagnetic below its Curie temperature of 770°C; when exposed to a magnetic field, its domains align and it can retain magnetization afterward, as in a permanent bar magnet.
Frequently asked questions
What causes ferromagnetism at the atomic level?
The exchange interaction, a quantum mechanical effect between neighboring atoms' unpaired electrons, favors parallel spin alignment. Combined with the crystal structure, this produces spontaneous magnetization within small regions called domains.
What happens to a ferromagnet above its Curie temperature?
Thermal energy overcomes the exchange interaction, the magnetic domains randomize, and the material becomes paramagnetic, losing its spontaneous magnetization.