Perovskites multiferroic

Ferroic is a generic term for crystals that have an internal structure that can be switched from one stable orientation to another that is equally stable, by the application of a suitable driving force along an appropriate direction. Multiferroics are 

The perovskite BiFeOj is a ferroelectric phase above a temperature of approximately 1100 K due to the Bi + lone pair of electrons, which gives rise to polarisation along 111 . This phase becomes a G-type antiferromagnetic phase with 640 K. 

Multiferroic behaviour is not confined to simple perovskite structures. Thin films of the more complex layered ferroelectric perovskite-derived Aurivillius phase 

BigTi gFCj 52 110 68 18 multiferroic behaviour and undergo ferroelectric 

Tilley, Understanding Solids, 2nd edition, John Wiley Sons, Ltd, Chichester (2013), Chapter 12. 

---

In the layered Ruddlesden-Popper and Dion-Jacobson phases, improper ferroelectricity can also arise in a form termed hybrid improper ferroelectricity. Here, the ferroelectricity arises when two non-polar rotations of BO octahedra combine to produce a polar stmcture. The same effect may well also occur in the Aurivillius phases although this has not yet been proven. The creation of improper ferroelectric polarisation due to magnetic interactions in multiferroic perovskites is described in Section 7.10. 

Sergienko, I.A. and Dagotto, E. (2006) Role of the Dzyaloshinskii-Moriya interaction in multiferroic perovskites. Phys. Rev. B, 73, 094434. 

Xy is the intrinsic surface stress tensor that determines the excess pressure exerted on the solid under the curved surface [137]. We used the isotropic approximation (X . = (x8y, where x is the scalar coefficient. Due to the lack of experimental measurements of the x value for EuTiOs, we select an experimentally reasonable value based on the data for surface tension coefficients measured in ferroelectric ABO3 perovskites. The values reported for other ABOs-type perovskites vary in the range 3-30 N/m 36.6 N/m for PbTiOs [142] (or even 50N/m [143]), 2.6-10 N/m for PbTiOs and BaTiOs nanowires [144], and 9.4 N/m for Pb(Zr,Ti)03 [145]. Here we use averaged (x value 10 N/m, which is close to that extracted recently from Pb(Zr,Ti)03 sponges tetragonality temperature dependence. For comparison, we characterize the effect of (x = 30 N/m (higher end of the reported values) on the multiferroic phase transition. 

For some applications, such as in multiferroic materials based devices, it is the crystal symmetry of the multiferroic what matters. In these materials the presence or not of a centre of symmetry is crucial for the observation of ferroelectricity. With this regard, there are cases, as in some AMnOs perovskites (A=Y or Dy), in which the synthetic route determines whether an orthorhombic compound with a centre of symmetry (i.e. non ferroelectric) or a hexagonal phase without the centre (i.e. ferroelectric) is formed (Carp et al., 2003 Dho et al., 2004). Consequently, preparative conditions have to be carefully selected in order to obtain crystal phases with the adequate structure. The use of more than one synthesis method is thus worth trying in all cases. 

B. Bersuker, Pseudo Jahn-Teller origin of perovskite multiferroics, magnetic-ferroelectric crossover, and magnetoelectric effects. The d -d problem, Phys. Rev. Lett., 108, 137202 (2012). 

Multiferroics materials that have, at least, two of the three ferroic orders ferroelectricity -ferromagnetism and ferroelasticity. For example, perovskites - BlFeOs, Bii La FeOa, Bii Nd . FeOa, Aurivillius - Bi7Ti3Fe302i... 

Multiferroic materials exhibits both ferroelectric and magnetic in nature and have much attracted research interest due to their potential application in multistate data storage and electric field controlled spintronics. Among all the studies related to the materials, transition metal oxides with perovskite structure are noteworthy [22,26]. 

Multiferroic materials with double-perovskite structure aA BB O ) are solid solutions of two perovskites ABO and [a B O3). In [aa BB oj, A and A represent alkaline rare earth cations (La, Y, and Ce), while B and B are transition metal cations (Ni and Co). If A and A represent the same chemical element, the double perovskite has the general formula (AjBB O ) and the crystal structure of A B B Og -type perovskite, as shown in Figure 2. Alkali-earth and lanthanide (smaller ion) ions are alone usually occupied in the A site [27,28]. If the A ion is too small, the common expected distortions are cation displacement with BOg and octahedral ones [29]. 

Ishiwata S, Tokunaga Y, Taguchi Y, Tokura Y. High-pressure hydrothermal crystal growth and multiferroic properties of a perovskite YMnOs- Journal of American Chemical Society 2011 133 13818-13820. 

Liu F, Li J, li Q, Wang Y, Zhao X, Hu Y, Wang C, Liu X. High pressure synthesis, structure, and multiferroic properties of two perovskite compoimds Y2FeMnOg and Y2CrMnOe. Dalton Transaction 2014 43 1691-1698. 

---