Epitaxial Coherence at Interfaces as Origin of High Magnetoelectric Coupling in Multiferroic BaTiO₃–BiFeO₃ Superlattices

Abstract

Multiferroic superlattices consisting of 15 double layers BaTiO3–BiFeO3 show a very high magnetoelectric voltage coefficient αME of up to 49 V cm−1 Oe−1 at 300 K, measured at 1 kHz with zero direct current (DC) bias magnetic field. However, the microscopic origins of such high αME values, and the temperature and DC magnetic field dependencies of αME are not understood up to now. Therefore, in this study two superlattices grown at high/low oxygen partial pressures having high/low αME values, respectively, are compared. While at high growth pressure the strain contrast in high‐resolution transmission electron microscopy images is limited to few layers at the substrate interface, the low‐pressure sample shows much more pronounced microstrain. This is additionally visualized in Fourier transformed images, and the out‐of‐plane lattice parameter of the single BaTiO3 layer is increased near the interface. In addition to a low density of oxygen vacancies, it seems to be important to avoid micromechanical clamping of the 2D single‐phase nanolayers of the multiferroic BaTiO3–BiFeO3 superlattices to achieve high magnetoelectric coupling.

Enhanced Magnetoelectric Coupling in BaTiO3-BiFeO3 Multilayers—An Interface Effect

“…This field dependency was observed for all BTO-BFO multilayer samples since [8][9][10][11][12][13]. By variation of the p O 2 pressure during growth we found an increase of oxygen octahedral tilt [8] and micro-strain [9] with lowered p O 2 that correlated with a decrease of the respective α ME values. Note, however, that the pulse numbers were kept constant for these experiments, yielding increasingly larger double layer thickness (d dl ) values with decreasing p O 2 .…”

“…While the BFO single layers and composite films show a maximum and subsequent decrease in α ME when H bias is increased from 0 T to 6 T, similar to the behavior of bulk samples [7], multilayers show a saturating behavior [6]. This field dependency was observed for all BTO-BFO multilayer samples since [8][9][10][11][12][13]. By variation of the p O 2 pressure during growth we found an increase of oxygen octahedral tilt [8] and micro-strain [9] with lowered p O 2 that correlated with a decrease of the respective α ME values.…”

Interface induced out-of-plane magnetic anisotropy in magnetoelectric BiFeO3-BaTiO3 superlattices

“…When more layers are added, the subsequent interfaces show perfect atomic arrangement with sharp atomic interfaces. 27 Therefore, we can infer that these highquality interfaces contribute to the formation of the out-ofplane magnetic anisotropy.…”

“…27 These interfaces contain a number of imperfections including oxygen defects, which according to Yang et al, 26 weaken the out-of-plane magnetic anisotropy. When more layers are added, the subsequent interfaces show perfect atomic arrangement with sharp atomic interfaces.…”

Effect of insertion of low leakage polar layer on leakage current and multiferroic properties of BiFeO3/BaTiO3 multilayer structure

“…Among multiferroic oxides, Bismuth ferrite (BiFeO 3 ) is the only multiferroic material at room temperature with high Curie (T C ~ 1103 K) and Neel (T N ~ 643 K) temperature possessing both ferroelectric and ferromagnetic properties, making it suitable for high temperature applications [1][2][3][4][5]. It may be seen from the recent research that the properties may be enhanced by material engineering including doping with other metal ions or making multilayered structures [11][12][13][14][15][16][17]. Barium titanate (BaTiO 3 ) is a promising perovskite material, well established for its versatile ferroelectric, non-linear optic, piezoelectric and dielectric properties [6][7][8][9][10].…”