The combination of both can lead to spin glass behavior. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. If the energy is expressed as the sum of all pairs, i, j, over an interaction term J(i,j), times the spin of atom i times the spin of atom j, J < 0 is a ferromagnetic interaction and J > 0 is an antiferromagnetic interaction. Above the Neel temperature, the material is typically paramagnetic. Generally, antiferromagnetic order may exist at sufficiently low temperatures, vanishing at and above a certain temperature, the Neel temperature. In 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 pointing in opposite directions. An anti-ferromagnetic interaction acts to anti-align neighboring spins.
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