Defect engineering for nontrivial multiferroic orders in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>SrTi</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
Tao Xu, Takahiro Shimada, Masataka Mori, Gen Fujimoto, Jie Wang, Takayuki Kitamura
Abstract
Although nanoscale multiferroics with coupled ferroelectricity and magnetism are of great technological and fundamental importance, the ferroic orders are inevitably destroyed in atomic-scale dimensions due to the intrinsic size effect or depolarization field. Here, we propose a strategy for atomic-size multiferroics by engineering the otherwise detrimental point defects in nonmagnetic paraelectric $\mathrm{SrTi}{\mathrm{O}}_{3}$. Systematic exploration using first-principles and molecular dynamics simulations demonstrates that the Ti antisite $({\mathrm{Ti}}_{\mathrm{Sr}})$ defects in $\mathrm{SrTi}{\mathrm{O}}_{3}$ have a tendency toward clustering with compact closure, which contributes to complex electrical polarization due to the large off-centering displacements of ${\mathrm{Ti}}_{\mathrm{Sr}}$ defects and the resulting separation between negative and positive charges. The ${\mathrm{Ti}}_{\mathrm{Sr}}$ defects also give rise to highly localized magnetic moments attributed to their unpaired spin-polarized electrons. The defect clustering and the associated multiferroic properties thus lead to atomic-size multiferroics with unusual ferroic orders.