Magnetization, phonon, and X-ray edge absorption in barium-doped BiFeO3 ceramics

Abstract

Magnetization hysteresis loops, dc and ac magnetic susceptibilities, and Raman vibrations have been characterized in (Bi 1-x Ba x )FeO 3-d ceramics for x = 0.0, 0.05, 0.10, and 0.15 as functions of temperature. Ferromagnetic hysteresis loops were observed in Ba-doped compounds with increasing magnetization as Ba substitution increases. High-resolution synchrotron Fe K-and L 2,3 -edge X-ray absorptions reveal an Fe 3? valence and a modification of the Fe-O-Fe bond structure by the A-site Ba substitution. The oxygen K-edge X-ray absorption suggests that the hybridization of the O 2p and Fe 3d orbitals was reduced by the Ba 2? substitution. Field-cooled and zero-field-cooled magnetic susceptibilities reveal a spin-glass behavior, which was enhanced with increasing Ba substitution. Raman vibrations of the Bi-and Fe-sensitive E(2) and A 1 (1) modes reveal frequency softening and step-like anomalies in full-width-at-half-maximum in the vicinity of *150-250 K, which were attributed to spin-phonon interaction while magnetic ordering transitions take place.

Electronic structure of BiFeO3 in the presence of strong electronic correlations

“…However, the most common values for BiFeO 3 crystals and films are in the range between 5 and 7 eV, which is consistent with U = 6.0 eV used in the GGA+DMFT study of insulator-metal transition of compressed BiFeO 3 [13]. However, in spite of these theoretical efforts, neither the changes of the Mott insulating state of paramagnetic BiFeO 3 with increasing U nor the electronic spectrum [22,24] hidden in the ferromagnetic ordered state of bulk [20] and thick BiFeO 3 films [11] were addressed so far. In this work, we shed light onto this problem within LDA+DMFT approximation [33], showing that the emergent strongly correlated electronic state is caused by large transfer of spectral weight with concomitant formation of orbital-selective localized moments in BiFeO 3 .…”

“…4. Comparison between the total 3d LDA+DMFT DOS for the Fe 3+ and Fe 2+ oxidation states with experimental hard x-ray photoelectron spectroscopy (HAXPES) of bulk (square) [14] and BiFeO 3 thick films (circle) [22] as well as with O K-edge x-ray absorption (XAS) spectra (diamond) [24], showing good qualitative theoryexperiment agreement at energies between −3.0 ω 5.0 eV is visible. In particular, the low-energy line shape in HAXPES and the double-bump feature in XAS are accurately resolved in the LDA+DMFT spectrum for U = 7.0 eV.…”

“…Since the oxidation state of BiFeO 3 systems remains uncertain [19,23,53], for a detailed analysis of dynamical MO electronic interactions we compare our LDA+DMFT results in Fig. 4 with experimental hard x-ray photoelectron spectroscopy (HAXPES) of bulk [14] and BiFeO 3 thick films [22] as well as with O K-edge x-ray absorption spectra (XAS) [24]. In view of the fact that only the five 3d bands have been included in the LDA+DMFT treatment, we focus on the energy window (which, however, is rather wide) −3.…”

“…Due to the large orbital radius of the Bi-6s 2 lone pairs, the crystal structure of Bi perovskites is usually distorted to low symmetries, producing spontaneous ferroelectric polarization along certain crystallographic directions [6]. Among the Bi perovskites, BiFeO 3 is the most systematically studied system both from theory [7][8][9][10][11][12][13][14] and experimental [3,4,[15][16][17][18][19][20][21][22][23][24] perspectives.…”

“…Likewise, here we present a self-consistent study of electronic structure calculations using the LDA+DMFT approach for BiFeO 3 parent compound. The calculated density-of-states (DOS) is compared with experimental photoemission (PES) [14,22] and inverse photoemission spectroscopy (IPES) [24] data. We show how this can provide a consistent explanation for the more relevant electron correlation fingerprints in the occupied and unoccupied states as well as to optical-absorption spectra of BiFeO 3 singlecrystal [21] within the same theoretical framework.…”