6.8 Ferrimagnetic Materials

These are materials which again, like antiferromagnetic materials, show antiparallel alignment of moments at particular atomic sites i.e. magnetic moment of one crystal sub-lattice is anti-parallel to the other. But since most of these materials consist of cations of two or more types, sub-lattices contain two different types of ions with different magnetic moment for two types of atoms and as a result, net magnetization is not equal to zero. The examples of such materials are various kinds of cubic spinel ferrites such as NiFe₂O₄, CoFe₂O₄, Fe₃O₄ (or FeO.Fe₂O₃), CuFe₂O₄ etc. Other examples are hexagonal ferrites likes BaFe₁₂O₁₉, garnets such as Y₃Fe₅O₁₂, represented by a general formula R₃Fe₅O₁₂ where R, in addition to yttrium can be one of lanthanide atoms such as lanthanum, cerium, samarium etc.

A schematic representation of this inequality in the neighbouring magnetic moment can be like this:

These materials also follow a temperature dependence of magnetization and susceptibility near Curie transition (actually Néel transition) in a similar manner as shown by the ferromagnetic materials.  These materials, like ferromagnetic materials, show significantly large magnetization below the magnetic transition temperature and hence, often the temperature dependent behavior is clubbed with that of ferromagnetic materials.