Magnetoelectric Couplings at Fe/BiFeO₃(001) Heterointerfaces Studied by First-Principles Calculations

Ferromagnet(FM)/ferroelectric(FE) interfaces have emerged as structures with strong magnetoelectric(ME) couplings. Particularly, by replacing the FE with a multiferroic material(MF) which possesses antiferromagnetic order coupled to the electric polarization, large ME couplings can be expected due to the additional magnetic coupling at the interface. BiFeO₃(BFO) which has a strong MF property is a promising material for FM/MF interfaces.

In this study, we examine ME couplings at bcc Fe/BFO(001) heterointerfaces whose lattice mismatch is 2.1% by using first-principles calculations based on density functional theory. We construct four types of interface systems where all atomic positions are optimized. After structural optimizations, we specify the energetically most stable stacking positions of bcc Fe on BFO. Moreover, it is found that the stability of two different termination plane, BiO and FeO₂, in BFO(001) depends on the Bi- or O-rich condition of crystal growth. Calculating magnetic anisotropy energy, we find that each interface system shows strong anisotropy due to interface effect. Furthermore, changes in anisotropy can be seen before and after reversal of electric polarization of BFO. Then, we determine the magnitude of ME coupling of these systems by evaluating ME tensors.