Origin of ferroelectricity in the multiferroic barium fluoridesBaMF4: A first principles study

Abstract

We present a first-principles study of the series of multiferroic barium fluorides with the composition BaMF 4 , where M is Mn, Fe, Co, or Ni. We discuss trends in the structural, electronic, and magnetic properties, and we show that the ferroelectricity in these systems results from the freezing in of a single unstable polar phonon mode. In contrast to the case of the standard perovskite ferroelectrics, this structural distortion is not accompanied by charge transfer between cations and anions. Thus, the ferroelectric instability in the multiferroic barium fluorides arises solely due to size effects and the special geometrical constraints of the underlying crystal structure.

Multiferroic BaCoF4 in Thin Film Form: Ferroelectricity, Magnetic Ordering, and Strain

“…However, the theoretical analysis of Ederer and Spaldin has suggested that FE switching in the Mn and Fe compounds may require electric fields larger than those applied in the experiments. 5 Note that a similar crystal structure and geometrical (or topological) ferroelectricity have recently been studied in the orthorhombic oxide polymorph LaTaO 4 , 17 and therefore our results can be relevant to this broader class of materials.…”

“…3 The best known example is the BaMF 4 compound, where M=Mn, Fe, Co, or Ni. Recent theoretical studies 4,5 focused on their magnetoelectric and multiferroic properties. To the best of our knowledge, however, only studies of bulk form BaMF 4 have been reported in the scientific literature.…”

“…16 Distorted MF 6 octahedra share corners in the ac-plane, forming puckered sheets which are separated by Ba ions along the b-axis (Figure 1a). 5 Their long range ferroelectric (FE) order theoretically originates from MF 6 octahedra rotations about the a-axis and polar displacements of Ba cations along the c-axis. 5 The combination of these two effects results in geometric proper ferroelectricity.…”

Intrinsic magneto-dielectric effect in the diluted magnetic ferroelectric fluoride BaMg1−Mn F4 (0≤x≤0.07)

“…In the centrosymmetry structure, M-F-M bond distance is too small to accommodate two M-F bonds. In order to accommodate two M-F bonds the M-F-M segment bends outward leading to the collective distortions of fluorine octahedra rotations and Ba cation displacements [10,11]. The distortion of cations and anions leads to the charge separation (centers of cations and anions does not coincide to form dipoles) resulting in a spontaneous polarization.…”

Multiferroic Materials: Physics and Properties

“…Therefore, BaMnF 4 has been classified as a geometric ferroelectric along with hexagonal manganites and ferrites. 45 …”