Correlated polarization switching in the proximity of a 180° domain wall Vasudeva Rao Aravind, 1,2 A. N. Morozovska, 3 Saswata Bhattacharyya, 1 D. Lee (이동화, 4 S. Jesse, 5 I. Grinberg, 6 Y. L. Li, 7 S. Choudhury, 1 P. Wu, 1 K. Seal, 5 A. M. Rappe, 6 S. V. Svechnikov, 3 E. A. Eliseev, 8 S. R. Phillpot, 4 L. Q. Chen, 1 Venkatraman Gopalan, 1, * and S. V. Kalinin 5,† 1 Materials Research Institute and Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, USA 2 Physics Department, Clarion University of Pennsylvania, Clarion, Pennsylvania 16214, USA 3 V. Lashkarev Institute of Semiconductor Physics, National Academy of Science of Ukraine, 41, pr. Nauki, 03028 Kiev, Ukraine 4 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, USA 5 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 6 Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, 19104 USA 7 Pacific Northwest National Laboratory, Richland, Washington 99352, USA 8 Institute for Problems of Materials Science, National Academy of Science of Ukraine, 3, Krjijanovskogo, 03142 Kiev, Ukraine Received 6 April 2010; revised manuscript received 5 June 2010; published 27 July 2010 Domain-wall dynamics in ferroic materials underpins functionality of data storage and information technol- ogy devices. Using localized electric field of a scanning probe microscopy tip, we experimentally demonstrate a surprisingly rich range of polarization reversal behaviors in the vicinity of the initially flat 180° ferroelectric domain wall. The nucleation bias is found to increase by an order of magnitude from a two-dimensional 2D nucleus at the wall to three-dimensional nucleus in the bulk. The wall is thus significantly ferroelectrically softer than the bulk. The wall profoundly affects switching on length scales on the order of micrometers. The mechanism of correlated switching is analyzed using analytical theory and phase-field modeling. The long- range effect is ascribed to wall bending under the influence of a tip with bias that is well below the bulk nucleation level at large distances from the wall. These studies provide an experimental link between the macroscopic and mesoscopic physics of domain walls in ferroelectrics and atomistic models of 2D nucleation. DOI: 10.1103/PhysRevB.82.024111 PACS numbers: 77.80.Dj, 68.37.-d, 77.80.Fm, 77.84.Ek I. INTRODUCTION Dynamics of interfaces and their interaction with micro- structure and defects is the key element determining func- tionality of ferroelectric and ferromagnetic materials, 1 elec- trochemical systems, 2–4 and phase transformations. 5 Interface dynamics controls the switching speed, critical bias, and retention in ferroic 6 and phase change memories, energy storage density in batteries and capacitors, and micro- structure and properties of materials. 7 This recognition of the role of interface behavior in materials science and energy and information technologies has stimulated an intensive ef- fort on understanding the relationship between electronic, atomic, and mesoscopic structures and dynamic behavior of the interface. Domain-walls separating regions with opposite ferroelec- tric polarization are the prototypical example of interfaces in ferroic materials and have been extensively studied over the last 60 years. 8 The narrow width of the 180° wall necessi- tates the formation of the two-dimensional 2D nuclei as a rate-limiting step in wall motion and results in strong lattice and defect pinning. 9 Notably, similar motion mechanisms op- erate at phase transformation and solid-state reaction fronts and other high-energy interfaces. On the mesoscopic scale, wall-defect interactions give rise to a rich spectrum of dy- namic behaviors 1,10 reflected in the complex self-affine wall geometries observed down to 10– 30 nm length scales. 11,12 The synergy between electron and scanning probe mi- croscopies has allowed comprehensive understanding of the static domain-wall structures at atomic and mesoscopic scales. 13–15 Switching of ferroelectric domains generated in the two limits of extremely large fields applied far away from the domain wall i.e., bulk switching through nucleation or smaller fields applied at the domain wall i.e., field-induced domain-wall motion have been investigated in previous work and are likewise now well understood. 1 In the interme- diate region, a number of observations, 16–18 including the correlated nucleation at the moving domain-wall front, 19,20 suggest that the walls can strongly affect the properties of adjacent material due to long-range electrostatic and elastic fields. Nevertheless, fundamental questions, such as whether the nucleation energy of a 2D nucleus 21 on the wall can be measured directly, and especially the effect of the wall on the nucleation in the vicinity of the wall 22 have never been an- swered experimentally. Here, we report on experimental studies of the nucleation behavior of ferroelectric domains using the spatially local- ized electric field of a biased scanning probe microscopy SPM tip. This allows us to directly measure the intrinsic critical voltage for the formation of 2D nucleus at the wall 23,24 as well as to reveal the influence of the wall on the nucleation in the bulk. Surprisingly, we find that nuclei formed in the bulk interact with the domain wall even at extremely large micron-scale range, significantly lowering the barriers for domain nucleation. These finding have obvi- ous implications for dynamics of polycrystalline ferroelec- trics, and similar mechanisms can be operational in other systems with high-energy interfaces, including electrochemi- cal systems and solid-solid transformations. PHYSICAL REVIEW B 82, 024111 2010 1098-0121/2010/822/02411111 ©2010 The American Physical Society 024111-1