Perovskites ferromagnetic

In general, double exchange can operate in compounds that have a cation in two valence states. Many crystalline stractures potentially fulfil these requirements, including the ion pairs already noted and Co VCo ). However, pairs of 

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Table 7.2 Ferromagnetic perovskites and perovskite-related phases...

A.B., Young, D.P., Aral, M., and Takayama-Muromachi, E. (2006) Specific-heat evidence of strong electron correlations and thermoelectric properties of the ferromagnetic perovskite SrCoOs a. Phys. Rev. B, 7 172406. 

Zener, C. 1951. Interaction between the (/-shells in the transition metals. II. Ferromagnetic compounds of manganese with perovskite structure. Physical Review 82 403-405. 

Ferromagnetic interactions in nonmetallic perovskites. J. Phys. Chem. Solids 26, 1969 (1965). 

By analogy with ferromagnetism, ferroelectricity is the property by which a crystal has a permanent electric dipole moment which can be reversed by the application of an electric field. The perovskite BaTiOs, in which the BaO layers are compressed and the Ti02 layers stretched (see Fig. 13.1), is a ferroelectric... 

Fig. 13.3. The phase diagram of Ao.33A o.67Mn03 (A = divalent cation, A = rare earth) as a function of temperature and the global instability index of the idealized perovskite structure. The points show the observed transition temperatures in various compounds. FMM = ferromagnetic metal, PMI = paramagnetic insulator, FMI = ferromagnetic insulator (from Rao et al. 1998).

The highly symmetrical perovskite structure is very common for MM X3 type compounds. Some of the many hundreds of such compounds are listed in Table 5.6. Because of their important ferroelectric, ferromagnetic, and superconducting properties, many compounds have been synthesized varying the ratios of metals to optimize desired properties. New compounds are reported frequently. We will discuss structures related to perovskite in Sections 5.3.5, 5.3.6, 5.3.7, 5.4.11, 5.4.12, and 5.4.13. 

Table 5.7. Ferromagnetic compounds with the ordered perovskite structure.

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