| Property | Diamagnetic | Paramagnetic | Ferromagnetic |
|---|---|---|---|
| Susceptibility χ | Small, negative (χ < 0) | Small, positive (0 < χ << 1) | Very large, positive (χ >> 1, up to 10^{5}) |
| Relative permeability μᵣ | Slightly < 1 (e.g., 0.99999) | Slightly > 1 (e.g., 1.00001) | Much >> 1 (up to 10^{5}) |
| Behaviour in external field | Weakly repelled; moves from strong to weak field region | Weakly attracted; moves from weak to strong region | Strongly attracted; used to concentrate flux |
| Examples | Cu, Bi, , Ag, Au, diamond, | Al, , Na, Mg, Pt, Mn | Fe, Co, Ni, Gd (gadolinium) |
| Temperature dependence | Nearly independent of T | χ = C/T (Curie's law); decreases with rising T | Strongly T-dependent; loses ferromagnetism above Curie temp |
| Curie Temperature | Not applicable | Not applicable | Fe: 770°C; Co: 1115°C; Ni: 358°C |
| Magnetization direction | Opposite to applied field | Along applied field (weak) | Strongly along applied field; persists after removal |
| Domains | No magnetic domains | No magnetic domains | Has magnetic domains; alignment of domains = magnetization |
| Retentivity | None | None | Exists (residual B after H removed) |
| Coercivity | None | None | Exists (reverse H needed to demagnetize) |
| NEET frequency | Medium | Medium | High (hysteresis, applications) |
Key NEET trap: Don't confuse permeability (μ) with susceptibility (χ). Relation: μᵣ = 1 + χ. For diamagnets: χ < 0 → μᵣ < 1. For ferromagnets: χ >> 1 → μᵣ >> 1.