Q.Explain the following with suitable examples:

• Ferromagnetism: strongly attracted; magnetic domains all align in the same direction and stay aligned, giving permanent magnetism. e.g. $Fe$, $Co$, $Ni$, $CrO_2$.
• Paramagnetism: weakly attracted due to unpaired electrons; magnetised in a field but lose it when the field is removed. e.g. $O_2$, $Cu^{2+}$, $Fe^{3+}$.
• Ferrimagnetism: domains align parallel and antiparallel in unequal numbers, leaving a small net moment. e.g. $Fe_3O_4$, ferrites $MgFe_2O_4$.
• Antiferromagnetism: domains align oppositely in equal numbers, cancelling to zero net moment. e.g. $MnO$. …

Step 1 – Ferromagnetism.

Substances very strongly attracted by a magnetic field. Their metal ions are grouped into small regions called domains; on magnetising, all domains orient in the field direction and this ordering persists after the field is removed — hence permanent magnets.

Examples: $Fe,\;Co,\;Ni,\;Gd,\;CrO_2$.

Step 2 – Paramagnetism.

Substances weakly attracted by a magnetic field because they contain unpaired electrons. They are magnetised only while in the field and lose magnetism once it is removed.

Examples: $O_2,\;Cu^{2+},\;Fe^{3+},\;Cr^{3+}$.

Step 3 – Ferrimagnetism.

The domain magnetic moments are aligned in parallel and antiparallel directions but in unequal numbers, so a net (small) magnetic moment remains.

Examples: $Fe_3O_4$ (magnetite) and ferrites $M^{2+}Fe_2O_4$ (e.g. $MgFe_2O_4$, $ZnFe_2O_4$).

Step 4 – Antiferromagnetism.

The domain moments are aligned in opposite directions in equal numbers, so they cancel exactly and the net magnetic moment is zero.

Examples: $MnO$.

Step 5 – 12-16 and 13-15 group compounds.

These are synthetic semiconductor compounds:

• 12-16 compounds: an element of group 12 with one of group 16, e.g. $ZnS,\;CdS,\;CdSe,\;HgTe$. …

Contrast the four magnetic behaviours by how the electron/domain magnetic moments are ordered: fully parallel (ferro), random unpaired (para), unequal antiparallel (ferri), equal antiparallel cancelling (antiferro). For 12-16 and 13-15, identify them as …

• Mixing up ferrimagnetism and antiferromagnetism — both have antiparallel moments, but ferri has unequal (net non-zero) and antiferro has equal (net zero).
• Giving $Fe_3O_4$ as ferromagnetic; it is the classic ferrimagnetic example. …