A material’s ability to retain strong magnetism after an external field is removed is a property of:
**Hysteresis loop** plots B versus H for ferromagnetic material, retentivity (remanence) is residual B at H=0 after saturation, coercivity is reverse H needed to reduce B to zero. Hard ferromagnets have high retentivity and coercivity, retaining strong magnetism after external field removed, suitable for permanent magnets. Ferromagnetic materials, especially hard ones, retain strong magnetism after the external field is removed due to the persistence of aligned domains, making them suitable for permanent magnets. This distinguishes them from soft ferromagnetic or other materials. Substituting
Ref: NCERT > Physics Book > Magnetism and Matter > Hysteresis, Retentivity, Coercivity and Permanent Magnets
