Secondary ferroics

Dominance of the other terms gives rise to similar expressions for other secondary ferroics. 

Secondary ferroics. SrXi03 (which is an incipient ferroelectric) and NaNb03 (which is an antiferroelectric) may be considered to be ferrobielectric. Xhe dielectric anisotropy in antiferroelectric domains can give rise to high values of induced polarization that are orientationally different in different domains. Xhus, they give rise to domain rearrangement under applied fields. Quartz is a classic example of... 

When the switching of a crystal can be performed only by application of two kinds of external fields (like electric field and mechanical strain, magnetic field and mechanical strain, magnetic and electric fields or two fields of the same types), these materials are called the secondary ferroics (e.g. NH4CI, C0F2, CraOs, SiOa etc.). So, the terms primary and secondary are related to the number of external fields, necessary to switch the domains in a substance. The higher order ferroics are also existent. 

Besides above four types of ferroics, a large number of multiferroics with other structures is known. The information can be found in Refs. [2, 13, 14]. In the next section we discuss an important (both for fundamental science and applications) question about magnetoelectic coupling in the secondary ferroics with coexistence of magnetization and electric polarization (ferromagnetoelectrics in Table 1.1). 

It follows from Eq. (1.19) that ME effect can be large mainly in ferroelectric and/or in ferromagnetic materials and especially in secondary ferroics, namely in ferromagnetoelectrics with coexistence of spontaneous magnetization and electric polarization. 

The materials with ME effect consist of about 50 % composites and 25 % single phase systems, which are the secondary ferroics. The other 25 % include solid solutions, laminar structures consisting of several layers with thickness about one millimeter as well as nanostructures in the form of thin films, nanorods etc. 

The book consists of five chapters. The first chapter has introductory character. It contains the general definitions and classification of primary and secondary ferroics with the listing of different ferroic materials. For the sake of generaUty,... 

A hexagonal representation of proper and improper primary ferroics as proposed by Newnham Cross (1981) is given in Fig. 6.54. The order parameter for proper ferroics appears on the diagonals of the hexagon, while the sides of the hexagon represent improper ferroics. They indicate the cross-coupled origin of ferroic phenomena. An improper primary ferroic in this classification is distinguished from a true secondary... 

It has already been indicated in the Sect. 1.1 that the primary, secondary and higher-order ferroics are defined by the number of external fields necessary to switch the ferroic from one orientational state to another. In particular, the primary ferroics can be switched under the application of one kind of physical fields (magnetic, electric, elastic). Besides three mentioned types of primary ferroics, there are six more types of secondary ones, where the difference between orientational (domain) states thermodynamic potential (free energy) Ag is proportional either to square or to the product of external fields as it is shown in the Table 1.1. 

The majority of secondary and higher-order ferroics belong to four crystallographic compounds ... 

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