antiferromagnetic substance[¦an·tē‚fer·ō‚mag′ned·ik ′səb·stəns]
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 TN (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 (TN = 310° K), and a number of rare earth metals. The latter usually exhibit complex antiferromagnetic structures in the temperature region between TN and T1, (0°K< T1 < TN). 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 TN are given in Table 2. Most antiferromagnetic substances have TN values substantially below room temperatures. For all hydrated salts, TN does not exceed 10°K; for example, TN = 4.31°K for CuCl2 . 2H2O.
A. S. BOROVIK-ROMANOV