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Abstract
For rhombohedral multiferroelectrics, non-180° ferroelectric domain switching may induce ferroelastic and/or (anti-)ferromagnetic effect. So the determination and control of ferroelectric domain switching angles is crucial for nonvolatile information storage and exchange-coupled magnetoelectric devices. We try to study the intrinsic characters of polarization switching in BiFeO3 by introducing a special data processing method to determine the switching angle from 2D PFM (Piezoresponse Force Microscopy) images of randomly oriented samples. The response surface of BiFeO3 is first plotted using the piezoelectric tensor got from first principles calculations. Then from the normalized 2D PFM signals before and after switching, the switching angles of randomly oriented BiFeO3 grains can be determined through numerical calculations. In the polycrystalline BiFeO3 films, up to 34% of all switched area is that with original out-of-plane (OP) polarization parallel to the poling field. 71° polarization switching is more favorable, with the area percentages of 71°, 109° and 180° domain switching being about 42%, 29% and 29%, respectively. Our analysis further reveals that IP stress and charge migration have comparable effect on switching, and they are sensitive to the geometric arrangements. This work helps exploring a route to control polarization switching in BiFeO3, so as to realize desirable magnetoelectric coupling.
Highlights
For rhombohedral multiferroelectrics, non-180° ferroelectric domain switching may induce ferroelastic and/orferromagnetic effect
After analyzing various switching demonstrated in the polycrystalline sample, we found that, the 71° polarization switching is all in all more favorable than 109° and 180° switching, the possibility of any specific switching is determined by the energy related to the charge migration and IP stress
In our polycrystalline films, the percentage of 180° and 71° switching with original OP polarization (OPP) antiparallel to the poling field are similar (29% and 27%, respectively) after a 12 V polar scan, a further study with different poling voltages reveals that 71° switching with Pz′ > 0 happens more at lower voltages of 4 V and 6 V. (III) Investigations on epitaxial BFO films indicate that lateral constraints affect greatly and even decisively on the polarization switching behaviour[1,47], here we show that, the impact of IP stress is still comparable with charge migration in polycrystalline BFO films
Summary
Non-180° ferroelectric domain switching may induce ferroelastic and/or (anti-)ferromagnetic effect. We try to study the intrinsic characters of polarization switching in BiFeO3 by introducing a special data processing method to determine the switching angle from 2D PFM (Piezoresponse Force Microscopy) images of randomly oriented samples. For epitaxial BFO films of known orientation, the direction of polarization can be found out through the analysis of piezoresponse signals that are along out-of-plane (OP) and one in-plane (IP) directions, and the switching angles[8,24] could be obtained by comparing the polarizations before and after poling. Utilizing PFM characterization of epitaxial BFO films, Zavaliche et al studied the priorities of polarization switching with different angles under various poling voltages[24], and Baek et al investigated the relaxation route of switched domains[1]. A three-dimensional (3D) mapping method, in which piezoresponse signals from one OP and two IP directions were obtained through sample-rotating[29,39,40,41], was proposed and proved to be effective for some ferroelectric materials
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