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Ferrimagnetism

Precipitation reactions are used to produce iron(III) oxide (Fe2O3 called hematite) and mixed iron(II)/iron(III) oxide (Fe3O4 called magnetite). The particles in the slurry of hematite are not attracted to a magnet, but the particles in the slurry of magnetite are.

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Keywords

precipitation, solubility, magnetic properties, ferrimagnetic, hematite, magnetite, magnetism, transition elements, bonding, metals, d block

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One hundred milliliters of 0.1 molar iron(III) ammonium sulfate are added to fifty milliliters of 0.1 molar iron(II) ammonium sulfate. Addition of aqueous ammonia to the iron(III) solution gives brown iron(III) oxide, called hematite. Addition of ammonia to the iron(II)/iron(III) mixture gives black Fe3O4, called magnetite.

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Later the two substances are tested for magnetism. When the brown hematite is placed near a magnet, no interaction is observed. However, magnetite particles are strongly attracted, because the substance is ferrimagnetic.

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