Magnetism in Solids: Five Types, Five Examples

The magnetic behaviour of a solid depends entirely on whether it has unpaired electrons and how those electrons are spatially organised.

Diamagnetic substances have no unpaired electrons. All electron spins cancel in pairs, leaving no net magnetic moment. These solids are weakly repelled from magnetic fields. Examples: NaCl, $C_{6}H_{6}$, $H_{2}O$, noble gas solids.

Paramagnetic substances have unpaired electrons, but they are randomly oriented with no domain structure. A field weakly aligns some of them, causing weak attraction. Examples: $O_{2}$, $Cu^{2+}$, $Fe^{3+}$ ions. Paramagnetism follows Curie's law (χ ∝ 1/T).

Ferromagnetic substances (Fe, Co, Ni) have unpaired electrons that spontaneously align in large domains. The result is strong, permanent magnetism. Above the Curie temperature, thermal energy destroys domain order, converting the material to paramagnetic.

Antiferromagnetic materials (MnO, Mn$O_{2}$) have adjacent magnetic moments in exactly antiparallel arrangement with equal magnitudes — they cancel, giving zero net magnetism despite unpaired electrons.

Ferrimagnetic materials ($Fe_{3}O_{4}$, ferrites) are like antiferromagnetics except the antiparallel moments are unequal in magnitude, giving a net non-zero magnetic moment. $Fe_{3}O_{4}$ contains $Fe^{2+}$ (4 unpaired $e^{-}$) and $Fe^{3+}$ (5 unpaired $e^{-}$) in different sublattices — unequal cancellation → natural permanent magnet.