Multiferroic materials

If we can combine ferroelectrically polarizable guest molecules with PCPMs, then we can obtain new types of multiferroic materials, where ferroelectricity and ferromagnetism coexist. Such multifunctional materials have recently aroused increasing interest from the viewpoint of the development of new materials with very large magnetoelectric effects. [Mn3(HCOO)6] EtOH is considered to be the first ferroelectric PCP.182 Because the desolvated compound [Mn3(HCOO)6] shows a very small and almost temperature-independent dielectric constant, irrespective of the direction of the electric field,183 the observed ferroelectric property is considered to come mainly from the guest EtOH molecules. 

Ferroelectrics may And application in magnetoelectric devices, either in combination with magnetic materials or intrinsically as a multiferroic material. The latter represents a rare class of materials that are both ferroelectric and ferromagnetic, and often also ferroelastic, in the same phase [113]. This means that, simultaneously, they can undergo spontaneous polarization, magnetization, and deformation that can be reoriented by the respective application of an electric or magnetic fleld, or by... 

Key Materials and Technologies for Efficient Direct Thermal-to-Electrical Conversion Symposium on Advanced Dielectrics, Piezoelectric, Ferroelectric, and Multiferroic Materials Materials for Solid State Lighting... 

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. 

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... 

Strictly speaking, multiferroic materials should have ME effects that the two or more ferro properties can couple with each other. The magnetic AMFF compounds are good candidates for multiferroics. Computational studies on [Gua][Cu/Cr(HCOO)3] proved this point because the ferromagnetic component is believed to be coupled to the spontaneous polarization and they are mutually reversible however, this is waiting for experimental confirmation. Finally, Ln AMFFs might be expected to be good candidates for such materials. 

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]. 

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