Antiferromagnetic Substance

a substance in which an antiferromagnetic ordering of magnetic moments of the atoms or ions has been established. A substance usually becomes antiferromagnetic below a fixed temperature T_N (where N refers to the Néel point) and remains antiferromagnetic down to T = 0°K. Among the antiferromagnetic elements are solid oxygen (α-modification at T < 24°K), chromium (T_N = 310° K), and a number of rare earth metals. The latter usually exhibit complex antiferromagnetic structures in the temperature region between T_N and T₁, (0°K< T₁ < T_N). At lower temperatures they become ferromagnetic. Data on the best known rare earth antiferromagnetic substances are shown in Table 1.

Close to 1,000 chemical compounds are known that become antiferromagnetic at certain temperatures. A number of the simplest antiferromagnetic substances and their temperatures T_N are given in Table 2. Most antiferromagnetic substances have T_N values substantially below room temperatures. For all hydrated salts, T_N does not exceed 10°K; for example, T_N = 4.31°K for CuCl₂ . 2H₂O.