Ferrites

OutlinesCrystal structure of ferrites• Normal spinel structure• Inverse spinel structureMagnetisation in a ferrite

moleculeApplication of ferrites

Crystal structure of ferritesFerrites are compounds of iron

oxides with oxides of other metals

General chemical formula - MOFe2O3 or MFe2O4

Metal ions in tetrahedral and octahedral sites

Normal spinel structureeight divalent metal ions(M2+)

occupy tetrahedral or A-sites and 16 trivalent metal ions(Fe3+) occupy octahedral or B-sites

usual notation for this structure is M2+[Fe2

3+]O4

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Octahedral (B-sites)

Tetrahedral (A-sites)

Inverse spinel structureeight divalent metal ions(M2+)

occupy octahedral or B-sites and 16 trivalent metal ions(Fe3+) occupy tetrahedral or A-sites

usual notation for this structure is Fe3+[Fe3+M2+]O4

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Octahedral (B-sites)

Tetrahedral (A-sites)

MagnetisationThe saturation magnetisation

may be calculated from the number of unpaired spins of the ions

Unbalanced magnetic spins in iron

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Ground state spin direction in iron ferrite with inverse spinel structure

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Ground state spin direction in M2+Fe2O4

ferrite with inverse spinel structure

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Example:

ApplicationSoft magnetic ferrites are used in

the production of cores for inductor coils used in telecommunications

Used in microwave applications such as isolator

Increase the sensitivity and selectivity of the receiver used in radio

production of ultrasonic waves

Continued…Storing information devices such

as magnetic tapes or discsHard magnetic ferrites are used

in manufacturing permanent magnets

ferrox cube are used in switching circuits, matrix storage and in shift registers of components

e.g. Magnesium-magnese ferrite

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