Vortex switching in ferroelectric nanodots and its feasibility by a homogeneous electric field: Effects of substrate, dislocations and local clamping force

Taking into account the effects of asymmetric mechanical fields (e.g., caused by substrate, dislocations and local clamping force), we conduct phase-field simulations to investigate the evolution of vortex domain structure in ferroelectric nanodots. For nanodots under different mechanical constraints, their characteristics of the domain evolution, e.g., the hysteresis loop, the domain patterns and the evolution paths, have been revealed and compared comprehensively. Our calculations show that substrate, dislocations and local clamping force significantly affect the domain evolution of the nanodots, leading to distinct behaviors from those of the free-standing ones. For such systems, as the asymmetric mechanical field breaks the symmetry of vortex domain nucleation and growth, the evolution of the vortex domain structure is dominated by a specific region of dipoles, which we name "dominant dipoles". As a result, the nanodots exhibit distinct evolution paths, and the coercive field of vortex switching by a curled electric field is reduced compared with the free-standing ones. More importantly, for such systems, it is possible to realize single-vortex switching by a homogeneous electric field through controlling the flowing direction of the dominant dipoles. Our study provides useful information on the practical control of the vortex domain structure in ferroelectric nanostructures by conventional electrostatic fields. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.