Piezomagnetism

the appearance of magnetization in a substance that is subjected to external pressure. Piezomagnetism can exist only in substances whose magnetic structure is antiferromagnetic; as a rule, therefore, piezomagnetism is not possible in paramagnetic and diamagnetic substances. Piezomagnetism is produced when the applied pressure changes the magnetic symmetry of an antiferromagnetic crystal in such a way that a weak ferromagnetism arises. Magnetization of the sample occurs as a result of the tilting of the antiferromagnetic sublattices or a change in their relative magnitudes of magnetization.

So far, piezomagnetism has been detected experimentally in only three antiferromagnetic crystals: MnF₂, CoF₂, and α-Fe₂O₃. In these crystals, the extent of magnetization J_i is proportional to the applied compressive stress σ_kl’ that is, J_i = ∧_iklσ_kl. Piezomagnetism is not strong; the maximum value of the coefficient ∧_ikl (in CoF₂) is 2 × 10^-3 gauss = cm²/kilogram force (~2 × 10^-12 tesla = m²/newton). There is also a thermodynamically converse effect, the linear magnetostriction of antiferromagnets. Here, the linear dimensions of crystals change in proportion to the intensity of the applied magnetic field.