Impact of intrinsic defects on ferroelectric polarization in YFeO₃

Multiferroic materials have experienced a vast interest due to their inherent coupling between electric and magnetic degrees of freedom offering a high potential for memory applications. Because of fundamental limitations, only a small set of materials demonstrate both ferromagnetic and ferroelectric properties at room temperatures. Defect and strain engineering opens a promising route to discover novel multiferroic materials by inducing ferroelectricity in paraelectric materials having magnetic ions. Although bulk YFeO₃ (YFO) has a centrosymmetric crystal structure, our recent experimental investigations indicated that epitaxial YFO thin films can become ferroelectric. We attribute the ferroelectric behavior to the presence of point defects that introduce a dipole moment polarizing the surrounding regions. In this work, we investigate a variety of intrinsic defects in YFO by means of DFT calculations and the Berry phase approach. Our calculations demonstrate that yttrium antisite defects Y_Fe can break the inversion symmetry causing a switchable polarization up to ~7 μC/cm². In addition, we predict that rare-earth antisite defects will also induce the formation of ferroelectric regions in other RFeO₃ orthoferrites (R=Lu, Yb etc).