Question

Ferrimagnetic is observed when the magnetic moments of the domains in the substance are?
A. Oppositely oriented and cancel each other’s magnetic moment
B. Aligned in parallel and anti-parallel directions in unequal numbers
C. Randomly oriented and their magnetic moments get cancelled
D. In same direction and get aligned in magnetic field

Answer 1

Hint – A ferrimagnetic material can be defined as that material in which the magnetic dipole of the atoms on different sublattices are opposed as in antiferromagnetism but in ferrimagnetic materials, opposing moments are not equal and so hence a spontaneous net magnetization remains as such.

Complete step-by-step answer:
Ferrimagnetism is considered to be a type of permanent magnetism that occurs in solid substances in which the magnetic fields associated with individual atoms spontaneously align themselves, some aligned in parallel, or in the same direction (as in the case of ferromagnetism), and others align themselves generally antiparallel, or paired off in opposite directions (as in the case of antiferromagnetism).
The magnetic behaviour of the single crystals of ferrimagnetic materials may therefore be accounted to the parallel alignment of the atoms individually.
But also remember that the spontaneous alignment that produces ferrimagnetism can be entirely disrupted above a temperature often known as the Curie point (q.v.), which is the characteristic of each ferrimagnetic material. But as soon as the temperature of the material is brought below the Curie point, ferrimagnetism revives.
So, option B that is “Aligned in parallel and antiparallel directions in unequal numbers” is correct.

Note – Ferrimagnetism generally occurs in magnetic oxides also known as ferrites. The natural magnetism which is exhibited by lodestones is that like of a ferrite, the mineral magnetite, which is a compound containing negative oxygen ions${O^{2 - }}$ and positive iron ions in two states which are iron(II) ions, $F{e^{2 + }}$, and iron(III) ions, $F{e^{3 + }}$ respectively. The oxygen ions are not magnetic, but both the iron ions are magnetic. The iron(III) ions are paired off in opposite directions so they do not produce any external magnetic field, but the iron(II) ions are all aligned in the same direction, accounting for the production of external magnetism.