Question

Why do ferrimagnetic substances possess small net magnetic moments in spite of the presence of a large number of unpaired electrons?

Answer 1

1. Ferrimagnetic substances have a small overall magnetic effect even though they have many unpaired electrons because the magnetic effects of their ions point in opposite directions, but these effects are not the same strength. Such substances group the atoms or ions into two sublattices with antiparallel spin alignment.
2. However, unlike in antiferromagnetic materials, where the opposing magnetic effects completely cancel each other out, in ferrimagnetic substances the cancellation is only partial because the two groups of magnetic effects are not equal in number or strength.
3. This results in a net magnetic moment that is much smaller than the total number of unpaired electrons would suggest. A common example of a ferrimagnetic substance is magnetite (Fe₃O₄), where the arrangement of Fe²⁺ and Fe³⁺ ions causes their magnetic effects to partially cancel each other out, resulting in a weak but clear magnetism in the material.