Defect-induced hedgehog polarization states in multiferroics

Quasi-1D ferroic structures are nanoscale functional units that possess unique properties and hold great promise for the development of new device paradigms. In recent years, extensive efforts have been made towards fabricating and manipulating spin skyrmions or polarization vortices in ferromagnetics/ferroelectrics. Yet, another type of quasi-1D ferroelectric state known as polarization hedgehog, in which all the polarization vectors diverge from the center of the structure, remains unexplored. Here, we show the possiblity to stablize hedgehog polarization states by utilizing the interaction between ferroelectric polarization and deliberately introduced charged defects in the ferroelectric matrix. Atomic-scale scanning transmission electron microscopy imaging reveals that exotic polarization rotation patterns at the hedgehog polarization states can cause local changes in lattice symmetries leading to mixed-phase structures resembling the morphotropic phase boundary with high piezoelectricity. Engineering defects thus may provide a new route for developing ferroelectic/multiferroic-based nanodevices.