Q.(i) What type of magnetic substances are used to make permanent magnets?

Permanent magnets are made from ferromagnetic materials because their magnetic domains remain aligned permanently; ferrimagnetic materials have unequal antiparallel alignment giving a weaker net moment.

(i) In a ferromagnetic substance, the metal ions are grouped into small regions called domains, each acting like a tiny magnet. Normally the domains are randomly oriented so there is no net magnetism, but on applying a magnetic field, all domains align in the field direction, producing a strong net magnetisation. Crucially, in certain ferromagnetic materials this alignment persists even after the external field is removed (high retentivity/coercivity) — such substances are used to make permanent magnets (e.g., alloys like alnico, or materials like CrO2 used in magnetic tapes).

(ii) Schematic alignment of magnetic moments:

• Ferromagnetic: all the magnetic moments are aligned in the same direction and are of the same magnitude, giving a large net magnetic moment. Represented schematically as: ↑ ↑ ↑ ↑ ↑ ↑ (all arrows same length, same direction) …