Question

Account for the magnetic behaviour of the following spinels: ZnFe₂O₄ is antiferromagnetic, MgFe₂O₄ is ferromagnetic and its magnetic momentum increases with increase in temperature, MnFe₂O₄ is ferromagnetic and its magnetic momentum is independent of temperature.

Answer 1

MgFe2O4 is a mixed spinel and because of the higher concentration of Fe3+ in the octahedral sites than in the tetrahedral sites, it exhibits a small net magnetic moment and is ferromagnetic material.

In ZnFe2O4, all the magnetic Fe3+ sites are on octahedral sites and are separated by a plane of O2- ions. the superexchange interaction involving the two Fe3+ ions resembles that of antiferromagnetic material

MnFe2O4 is an example of partly normal and partly inverse spinel structure, where the Mn3+ and Fe3+ share in certain proportions the A and B sites