Ferromagnetism
A strong magnetic phenomenon in which atomic magnetic moments spontaneously align parallel into localized magnetic domains, producing permanent magnetization.
Governing formula
μ_r ≫ 1 (μ_r ~ 1,000–100,000)
SI unit
Dimensionless
In depth
Driven by quantum mechanical exchange interactions. Above the Curie temperature T_C, thermal agitation destroys domain alignment and ferromagnetic materials become paramagnetic.
Examples in the real world
Iron, nickel, cobalt, and neodymium permanent magnets strongly attracting metallic objects.