Ferroics

Ferroïques (Fr). Ferroika (Ge). Ferroici (It). Material ferroico (Sp).

Definition

A term introduced by Aizu (1970) to describe materials that show switchable properties under an external stimulus. In particular the difference in free energy densities between two switched states of the material can be written in the form:

where P, M and ε are the electric polarization, magnetization and strain, respectively; and E, H and σ are the applied electric field, magnetic field and uniaxial stress. The first three terms in the series are known as primary ferroics, whilst the others are secondary ferroics. In order, these terms give rise to the following ferroics:

• Ferroelectrics
• Ferromagnets
• Ferroelastics
• Ferrobielectrics
• Ferrobimagnets
• Ferrobielastics
• Ferromagnetoelectrics
• Ferroelastoelectrics (or piezoelectrics)
• Ferromagnetoelastics
• Ferrotrielectrics……

Today, the secondary ferroics with mixed fields are known as multiferroics, a term that tends to be used principally for ferromagnetoelectrics, the interest here being in the ability of these materials to change magnetisation under an applied electric field or to change electric polarisation under an applied magnetic field. A good review of the subject is given by Wadhawan (1982).

References

• Aizu, K. (1970). Phys. Rev. B, 2, 754–772. Possible species of ferromagnetic, ferroelectric, and ferroelastic crystals
• Wadhawan, V. K. (1982). Phase Trans. 3, 3–103. Ferroelasticity and related properties of crystals