Physical Properties Of Multiferroic Materialsfabricated By Doping Perovskite ABO₃

In addition to the experimental research,the first-principles density-functional theory is another favorable analysis method for the research of multiferroic materials,especially the analysis of the electronic structure.In this paper,the impact of doped-Co on the electronic structure and magnetic properties of oxygen-deficient ferroelectric BaTiO₃?BTO?has been investigated based on the first-principles density-functional theory.Co ion can not exhibit net magnetic moment for the Co-doped BTO without considering oxygen vacancy?Ov?.Most importantly,for the Co-doped BTO with Ov,Co-Ov complex is the most stable when the Ov is located at the nearest apical site,and Co ion prefers a high spin state.Besides,the two Co-Ov complexes are found to energetically favor a linear arrangement along c-direction.The room-temperature magnetic ordering and insulating behavior can be realized in Co-doped ferroelectric BTO while taking into account of Ov.These findings not only explain experimental observation of ferromagnetism in the Co-doped BTO,but also suggest the exotic multiferroic behaviors in these oxygen-deficient BTO with Co dopant.On the other hand,we also demonstrate the magnetocaloric effect of Ba-doped EuTiO₃(Eu_1-xBa_xTiO₃)within the framework of the transverse-field Ising model and the site-dilution model based on the Heisenberg model.By introducing an appropriate coupling term,we have investigated the intrinsic coupling between the magnetic and electrical subsystems.Our results show that the Eu_1-xBa_xTiO₃ exhibits the large magnetocaloric effect in low concentration doping structure,which is in good agreement with the experimental results.This work suggests that Eu_1-xBa_xTiO₃ with the low doping concentration could be the excellent potential material for magnetic refrigeration.