Question

(i) Write the type of magnetism observed when the magnetic moments are aligned in parallel and antiparallel directions in unequal numbers?
(ii) Which stoichiometric defect decreases the density of the crystal?

Answer 1

Magnetism refers to the force exerted by the magnets when they either attract or repel each other. Magnetism is mainly caused by the migration of electric charges. Each substance is made up of atoms and each atom comprises electrons that carry the electric charges.

Complete answer
(i) Ferromagnetism is actually the basic mechanism in which certain materials acquire the ability to form permanent magnets, or they are attracted to magnets. The process of ferromagnetism mainly arises owing to the interaction between the neighbouring atomic dipoles as well as the alignment of permanent dipoles in atoms which result from the unpaired electrons in outer shells. The magnetic moments in ferromagnet have the capability to align parallel to each other under the impact of a magnetic field.
Therefore, Ferrimagnetism is observed when the magnetic moments are aligned in parallel and anti–parallel directions in unequal numbers.

(ii) When some lattice sites are left vacant during the crystal formation, the defect is known as vacancy defect. An atom is usually missing from the regular atomic site in case of vacancy defects. Schottky defect is a vacancy defect that leads to the lowering of the density of the crystal. In this type of defect, an equal number of cation as well as anion is found to be missing from the interstitial site which lowers the density.
Hence, vacancy defects such as Schottky defects decrease the density of the crystal.

Note:
Never get confused between Schottky defect and Frenkel defect. In case of Schottky defect, the size difference between cation as well as anion is small and both cations and anions leave the crystal. On the other hand, Frenkel defect comprises ionic crystals in which anion is larger compared to cation and here only smaller sized cation leaves the lattice structure.