Cobalt ferrite is a semi-hard
ferrite with the chemical formula of CoFe
2O
4 (CoO·Fe
2O
3). The substance can be considered as between soft and hard magnetic material and is usually classified as a semi-hard material.
Uses
It is mainly used for its magnetostrictive applications like sensors and actuators thanks to its high saturation
magnetostriction
Magnetostriction is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field changes the magnetostrictive ...
(~200 ppm). CoFe
2O
4 has also the benefits to be
rare-earth
The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set of ...
free, which makes it a good substitute for
Terfenol-D. Moreover, its magnetostrictive properties can be tuned by inducing a magnetic uniaxial anisotropy. This can be done by magnetic annealing, magnetic field assisted compaction, or reaction under uniaxial pressure. This last solution has the advantage to be ultra fast (20 min) thanks to the use of
spark plasma sintering. The induced magnetic anisotropy in cobalt ferrite is also beneficial to enhance the
magnetoelectric effect in composite.
Cobalt ferrite can be also used as electrocatalyst for oxygen evolution reaction and as material for fabricating electrodes for electrochemical capacitors (also named supercapacitors) for energy storage. These uses take advantage of the redox reactions occurring at the surface of the ferrite. Cobalt ferrite prepared with controlled morphology and size to enhance the surface area, and thus the number of active sites, has been published.
One disadvantage of the cobalt ferrite for some applications is their low electrical conductivity. Nanostructures of cobalt ferrite with different shape can be synthesized on conducting substrates, such as reduced graphene oxide, to alleviate this disadvantage.
See also
*
Ferrite
References
Ceramic materials
Ferromagnetic materials
Ferrites
Cobalt(II) compounds
Iron(III) compounds
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