Polarization curling and flux closures in multiferroic tunnel junctions

Abstract

Formation of domain walls in ferroelectrics is not energetically favourable in low-dimensional systems. Instead, vortex-type structures are formed that are driven by depolarization fields occurring in such systems. Consequently, polarization vortices have only been experimentally found in systems in which these fields are deliberately maximized, that is, in films between insulating layers. As such configurations are devoid of screening charges provided by metal electrodes, commonly used in electronic devices, it is wise to investigate if curling polarization structures are innate to ferroelectricity or induced by the absence of electrodes. Here we show that in unpoled Co/PbTiO3/(La,Sr)MnO3 ferroelectric tunnel junctions, the polarization in active PbTiO3 layers 9 unit cells thick forms Kittel-like domains, while at 6 unit cells there is a complex flux-closure curling behaviour resembling an incommensurate phase. Reducing the thickness to 3 unit cells, there is an almost complete loss of switchable polarization associated with an internal gradient.

Topological Defects with Distinct Dipole Configurations in PbTiO3/SrTiO3 Multilayer Films

“…In comparison with the recently increasing number of experimental reports on the preparation and characterization of magnetic skyrmions [3][4][5][6][7], there are only limited works in the literature on experimental characterizations of complex and nontrivial configurations of dipoles in ferroelectrics [8,21,30]. In the present study, we report on topological defects with distinct and novel configurations of electric dipoles in epitaxial multilayer films of PTO/STO.…”

“…In ferroelectrics, physical properties and structures of various DWs have been studied theoretically [14][15][16][17] and experimentally [18][19][20][21][22][23]. It was found that the DWs possess different properties from that of the domains, depending on details of the wall structure [24][25][26], and thus have been considered as functional elements in future electronics [27].…”

Multiferroic Phases and Transitions in Ferroelectric Lead Titanate Nanodots

“…Besides, the edge structure is the typical characteristics of perovskite oxides nanostructures395051, while ferroelectric nanodots with similar round corner morphology have also be fabricated experimentally38. It is also worth to mention that the vortex-type polarization has been observed directly in low-dimensional systems5253. Thus, the characteristics of the models are realistic and it is highly possible to realize low-dimensional multiferroics experimentally as proposed here.…”

Deterministic Switching of Ferroelectric Bubble Nanodomains

“…Topological structures (or defects) in ferroic materials, such as skyrmions, vortices, flux closures, incommensurate curl domains, and bubble domains, have recently attracted attention due to their emergent nature. They can display large current‐induced spin‐orbit torques, giant electromechanical response, enhanced or ballistic electron transport, chirality or colossal optical coefficients, to name just a few of their exciting properties.…”