Magnetic domain wall induced ferroelectricity in double perovskites

摘要

Recently, a magnetically induced ferroelectricity occurring at magnetic domain wall of double perovskite Lu_2CoMnO_6 has been reported experimentally. However, there exists a conflict whether the electric polarization is along b or c direction. Here, by first-principles calculations, we show that the magnetic domain wall (with ↑↑↓↓ spin configuration) can lead to the ferroelectric displacements of R~(3+), Ni~(2+), Mn~(4+), and O~(2-) ions in double perovskites R_2NiMnO_6 (R = rare earth ion) via exchange striction. The resulted electric polarization is along b direction with the P2_1 symmetry. We further reveal the origin of the ferroelectric displacements as that: (1) on a structural point of view, such displacements make the two out-of-plane Ni-O-Mn bond angles as well as Ni-Mn distance unequal, and (2) on an energy point of view, such displacements weaken the out-of-plane Ni-Mn super-exchange interaction obviously. Finally, our calculations show that such a kind of ferroelectric order is general in ferromagnetic double perovskites.