CHEMICAL VAPOR DEPOSITION OF THIN FILM MATERIALS FOR ...

2.2 Spinel ferrite: Nickel Ferrite and Lithium Ferrite
2.2.1 Physical Properties and Potential Applications
Nickel ferrite (NiFe2O4) and lithium ferrite (LiFe5O8) belong to the family of
ferrimagnetic ferrites, which possess both high permeability and resistivity.[73] In terms of
crystal structure, NiFe2O4 and LiFe5O8 are both spinel structure. In a spinel (AB2O4) structure,
the unit cell consists of eight formula units and the 8 A 2+ and 16 B 3+ cations are distributed in the
interstices of the 32 close packed oxygen anions (Fig.15). If all of the 8 A 2+ occupy tetrahedral
sites and all of the 16 B 3+ occupy octahedral sites then the structure is called normal spinel; If all
of the 8 A 2+ and 8 B 3+ occupy octahedral sites and 8 B 3+ occupy tetrahedral sites, the structure is
called inverse spinel.
Fig. 15. Representation of a spinel structure. Adapted from ref. [73].
Usually, NiFe2O4 and LiFe5O8 both exist in inverse spinel structure at room temperature
and their formulas can be written as Fe 3+ [Ni 2+ Fe 3+ ]O4 and Fe 3+ [Li + 0.5Fe 3+ 1.5]O4 respectively.
According to the Néel model, the ferrimagnetism of these ferrite materials comes from a
mechanism of superexchange, in which different magnetic cation occupied sublattices are
antialigned with each other in the presence of an external magnetic field and thus imbalance in
the number of antialigned sublattices results in net magnetism.
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