First principles study of the electric polarization and of its switching in the multiferroic GaFeO₃system

Abstract

The electric polarization in the multiferroic GaFeO(3) system is determined from its electronic structure using first principles methods and the modern theory of polarization. By carefully following the electric polarization on a path connecting the polar and centrosymmetric structures, it is found to be -25 μC cm(-2), which is ten times larger than a previous estimation given in the literature a few years ago and two times smaller than the value obtained in a recent similar study. The switching of this electric polarization through a centrosymmetric structure is discussed in terms of the total energy barrier. It is exhibited that such a switching is particularly difficult to achieve in relation to the tetrahedral environment of half of the Ga atoms. The switching via domain wall motion is also discussed.

Phase stability of multiferroic GaFeO3 up to 1368 K from in situ neutron diffraction

“…The estimated polarization value is found to be in a fairly good agreement with the one reported using first principle calculations. 26 The charge density can shed light on bonding in GaFeO 3 , especially the partial covalency character of the cation-anion bonds, which can be further correlated with the functional properties of GaFeO 3. Our findings suggest that although most of the charges are symmetrically distributed along the radius of the atomic circles, indicating the largely ionic nature of bonding, a small amount of covalency is shown by minor asymmetry of the charges around the oxygen anions connected to the Fe 1 , Fe 2 , Ga 1 , and Ga 2 ions (see SM 29 ).…”

“…[5][6][7][8] GaFeO 3 is also a prominent candidate of multiferroic materials due to its large magnetoelectric effect, magneto-optic, and piezoelectric properties. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] GaFeO 3 has been investigated by using various techniques, which show interesting properties of this material such as magnetization-induced second harmonic generation, 13 optical and dc magnetoelectric effect, 12,14 as well as ultrafast electric and magnetic response induced by irradiation of a femtosecond laser pulse, 15 Faraday rotation, 16 an unusual large orbital magnetic moment. 17 These properties make this compound very attractive for potential applications.…”

Room Temperature Nanoscale Ferroelectricity in MagnetoelectricGaFeO3Epitaxial Thin Films

“…While an early report 19 attributed asymmetrically placed Ga1 ions within the unit cell responsible for observed piezoelectric response of GFO, recent first-principles calculations 20 showed that within the inherently distorted structure of GFO, large ionic displacements with respect to the centrosymmetric positions result in a large spontaneous polarization in the ground state 20 and even hint towards possible ferroelectric switching. 21 Thus, inability to observe saturated ferroelectric hysteresis loops (if any) in GFO bulk and single crystal samples is likely to emanate from the measurement difficulties, possibly due to substantial electrical leakage above 200 K. [22][23][24] On the other hand, epitaxial thin films of pure and doped GFO, grown on a variety of single crystalline substrates show a large reduction in the leakage current 24,25 and are more likely to demonstrate ferroelectric behavior if probed locally.…”

“…Initially, we identified orthorhombic Pnna as the possible centrosymmetric structure of GFO which transforms to noncentrosymmetric Pc2 1 n (Pna2 1 , according to international table of crystallography) structure, using the calculation approaches reported earlier 20,21 . for GFO using GGA+U and is in agreement with literature.…”

“…for GFO using GGA+U and is in agreement with literature. 21 However, the magnitude of the energy barrier is quite large in comparison to common perovskite ferroelectric oxides such as PbTiO 3 and PbZrO 3 30 . The abnormally large change in the energy upon ferroelectric phase transition cannot be explained by the large structural distortion alone and lack of any structural phase transition makes it even more puzzling.…”