Antiferromagnetism

Antiferromagnetism is a characteristic property of some materials such as manganese, chromium, hematite, oxides MnO2, FeO, CoO, etc. (called antiferromagnetic materials); in these materials, contrary to what happens for ferromagnetic materials (in which the configuration of minimum energy occurs for parallel spins), the interaction between the atoms is such as to create a configuration of minimum energy when the spins are antiparallel. In other words, materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions.

Due to defects in the atomic structure, the antiparallel configuration is never perfectly respected, and therefore a small residual magnetic moment is generated; this phenomenon is called parasitic ferromagnetism.

Substances that exhibit the phenomenon of antiferromagnetism, therefore, do not have magnetic properties since, although there is a very high degree of polarization, the two opposite polarizations neutralize each other. However, above a certain value of temperature, called Neel temperature, the alignment of the dipoles suddenly disappears and the substances in question have paramagnetic properties.