Antiferromagnetism

In materials that exhibit antiferromagnetism, the spins of magnetic electrons align in a regular pattern with neighboring spins pointing in opposite directions. This is the opposite of ferromagnetism. Generally, antiferromagnetic materials exhibit antiferromagnetism at a low temperature, and become disordered above a certain temperature; the transition temperature is called the Neel temperature. Above the Neel temperature, the material is typically paramagnetic.

The antiferromagnetic behaviour at low temperature usually results in diamagnetic properties, but can sometimes display ferrimagnetic behaviour, which in many physically observable properties is more similar to ferromagnetic intereactions.

The magnetic susceptibility of an antiferromagnetic material will appear to go through a maximum as the temperature is lowered; in contrast, that of a paramagnet will continually increase with decreasing temperature.

Antiferromagnetic materials have a negative coupling between adjacent moments and low frustration.

Antiferromagnetic materials are relatively uncommon. An example is the heavy-fermion superconductor URu₂Si₂. There are also numerous examples among high nuclearity metal clusters.

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