Magnetoelectric Ordering of BiFeO3 from the Perspective of Crystal Chemistry

Abstract

In this paper we examine the role of crystal chemistry factors in creating conditions for formation of magnetoelectric ordering in BiFeO 3 . It is generally accepted that the main reason of the ferroelectric distortion in BiFeO 3 is concerned with a stereochemical activity of the Bi lone pair. However, the lone pair is stereochemically active in the paraelectric orthorhombic ß-phase as well. We demonstrate that a crucial role in emerging of phase transitions of the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order types belongs to the change of the degree of the lone pair stereochemical activity -its consecutive increase with the temperature decrease. Using the structural data, we calculated the sign and strength of magnetic couplings in BiFeO 3 in the range from 945º down to 25º С and found the couplings, which undergo the antiferromagneticferromagnetic transition with the temperature decrease and give rise to the antiferromagnetic ordering and its delay in regard to temperature, as compared to the ferroelectric ordering. We discuss the reasons of emerging of the spatially modulated spin structure and its suppression by doping with La 3+ .

Antiferromagnetic spin-frustrated layers of corner-sharing Cu4 tetrahedra on the kagome lattice in volcanic minerals Cu5O2(VO4)2(CuCl), NaCu5O2(SeO3)2Cl3, and K2Cu5Cl8(OH)4·2H2O

“…Structural phase transitions accompanied with magnetic transitions can occur as within the frames of the same space group as with symmetry changes, for example, replacement of a noncentrosymmetrical space group by a symmetrical one and vice versa. In our opinion, the Na-and K-ilinskite minerals are characterized with a versatility of magnetic transitions not less rich than BiFeO 3 : in the latter case, as we showed in [74,75], the lone pair of electrons of the trivalent bismuth has an important role.…”

Covalency driven modulation of paramagnetism and development of lone pair ferroelectricity in multiferroic Pb3TeMn3P2O14

“…A large value of △E 1 and smaller value of △E 2 attribute higher stereochemical activity of the lone pair 5 . Here, to estimate △E 2 , we considered the minimal distance…”

Interplay between breathing and polar instabilities in transition metal perovskites with active A-sites

“…Higher localization corresponds to higher asymmetry, which results in division of O-coordination around the A-site into two coordination spheres, as discussed in Ref. [27]. In order to estimate the degree of localization of the lone pair in a quantitative manner, we computed the spread of effective Pb or Bi 6s Wannier function, obtained in a massive downfolding calculation by integrating out everything else other than A-site s. By construction, this takes into account the hybridization between A 6s, A 6p, and O 2p.…”