Q.What are ferromagnetic substances?

A paramagnetic substance has unpaired electrons and is weakly attracted into a magnetic field; O₂ is the classic example, with two unpaired electrons in its π* orbitals.

Paramagnetism is the property of substances weakly attracted by an external magnetic field, arising because their atoms/molecules/ions contain one or more unpaired electrons, each behaving like a tiny magnetic dipole.

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Antiferromagnetism arises when neighbouring magnetic domains are locked in antiparallel alignment of equal strength, so their magnetic moments exactly cancel.

In a solid built of ions/atoms carrying unpaired electron spins, each small region (domain) has a net magnetic moment pointing in some direction. Materials are classed by how these domain moments arrange themselves:

• Ferromagnetic: all domain moments align parallel, in the same direction → gives a large net magnetisation (e.g. Fe₃O₄, CrO₂).
• Antiferromagnetic: domain moments align in equal numbers, in opposite (antiparallel) directions → the moments exactly cancel, giving zero net magnetisation (e.g. MnO, MnO₂).
• Ferrimagnetic: domain moments are also antiparallel, but of unequal magnitude, so they only partly cancel, leaving a small net moment (e.g. Fe₃O₄). …

Applying a magnetic field aligns all the magnetic domains of a ferromagnetic substance, creating a permanent magnet.

Ferromagnetic solids consist of small regions called domains, each acting like a tiny magnet, but randomly oriented in the unmagnetised material so their effects cancel out. When placed in an external magnetic field, all the domains get oriented in the direction of the applied field, and this alignment persists t …