Electronic structure, Born effective charges and spontaneous polarization in magnetoelectric gallium ferrite

Abstract

We present a theoretical study of the structure-property correlation in gallium ferrite, based on first-principles calculations followed by a subsequent comparison with experiments. The local spin density approximation (LSDA + U ) of the density functional theory has been used to calculate the ground state structure, electronic band structure, density of states and Born effective charges. The calculations reveal that the ground state structure is orthorhombic Pc2 1 n having A-type antiferromagnetic spin configuration, with lattice parameters matching well with those obtained experimentally. Plots of the partial density of states of constituent ions exhibit noticeable hybridization of Fe 3d, Ga 4s, Ga 4p and O 2p states. However, the calculated charge density and electron localization function show a largely ionic character of the Ga/Fe-O bonds which is also supported by a lack of any significant anomaly in the calculated Born effective charges with respect to the corresponding nominal ionic charges. The calculations show a spontaneous polarization of ∼59 μC cm −2 along the b-axis which is largely due to asymmetrically placed Ga1, Fe1, O1, O2 and O6 ions.

Room Temperature Nanoscale Ferroelectricity in MagnetoelectricGaFeO3Epitaxial Thin Films

“…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.…”

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

“…[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.…”

Structure and Properties of Magnetoelectric Gallium Ferrite: A Brief Review

“…Revival [3] of research on multiferroics and magnetoelectrics in early 2000s, triggered by advancement in the synthesis, characterization and computational techniques also led to a renewed interest in research on a variety of materials including GFO. Temperature dependent structural studies made by Arima et al [5] and by Mukherjee et al [12] using a combination of techniques (XRD, Neutron and synchrotron diffraction techniques and Raman spectroscopy) show that GFO retains its orthorhombic Pc2 1 n symmetry over 4-700 K. These studies also attribute the observed ferrimagnetism to the cation site disorder in an otherwise antiferromagnetic structure [5,12], further supported by recent theoretical calculations [13,14]. Magnetism in GFO has a strong relation with the composition [4][5][6] and processing conditions [4,5] of the samples.…”

“…Consequently the ionic positions in the unit cell are also affected resulting in variations in cation-cation and catio-oxygen bond lengths and bond angles whose understanding is crucial from the perspective of the understanding of polarization in GFO. Crystal structure of GFO has also been studied theoretically by Roy et al [13] who calculated the lattice parameters of GFO using density functional theory implemented under different approximation schemes such as local spin density approximation (LSDA + U) and generalized gradient approximation (GGA + U) with inclusion of on-site Coulomb repulsion parameter, U. The calculated ground state lattice parameters in the relaxed state were: a = 8.6717 Å, b = 9.3027 Å and c = 5.0403 Å for LSDA + U and a = 8.7712 Å, b = 9.4094 Å and c = 5.0981 Å for GGA + U, respectively, which correspond well to the experimental XRD and neutron diffraction data as discussed earlier [13].…”

“…Crystal structure of GFO has also been studied theoretically by Roy et al [13] who calculated the lattice parameters of GFO using density functional theory implemented under different approximation schemes such as local spin density approximation (LSDA + U) and generalized gradient approximation (GGA + U) with inclusion of on-site Coulomb repulsion parameter, U. The calculated ground state lattice parameters in the relaxed state were: a = 8.6717 Å, b = 9.3027 Å and c = 5.0403 Å for LSDA + U and a = 8.7712 Å, b = 9.4094 Å and c = 5.0981 Å for GGA + U, respectively, which correspond well to the experimental XRD and neutron diffraction data as discussed earlier [13]. Subsequent calculations of bond lengths using the relaxed ionic positions is also in excellent agreement with the experimental data [5,12,13].…”