Tuning the polarization and magnetism in BiCoO ₃ by strain and oxygen vacancy effect: A first-principle study

The tensile strain and oxygen vacancy effects on the electronic and magnetic properties of multiferroic material BiCoO ₃ have been studied by density functional theory U calculations. It is found that the oxygen vacancy at the top of the pyramid structure along the 〈001〉 direction (denoted as O1) can be stabilized at 1 and 2 charge states, which significantly changes the local magnetic moment of Co ions and possibly provides net magnetic moments to the BiCoO ₃ system. While the tensile strain degrades the polarization of BiCoO ₃ about 20 C/cm ², the formation of oxygen vacancies becomes easier as the strain increases up to 5%. It indicates that the polarization and magnetic property of BiCoO ₃ could be tuned by the strain and oxygen vacancies, though the polarization of BiCoO ₃ is slightly degraded by the oxygen vacancies. Meanwhile, the change of electronic structure and magnetic property introduced by oxygen vacancy is illustrated according to the crystal field theory.