First Principles Study On Mn Doping To Improve The Properties Of BiFeO₃

As people's demands on science and technology are getting higher and higher,multiferroic materials have widely attracted attention from researchers in the field of new multifunctional devices.BiFeO3,as one of the few single-phase multiferroic materials at room temperature,has excellent ferroelectric and antiferromagnetic properties,making it broadly applied in the fields of data storage,microwave devices,spintronics,etc.However,the film is prone to induce defects during its preparation and thus only has weak ferromagnetism,which makes it greatly limited in practical applications.Through continuous researches and explorations,researchers discovered that doping was an effective method to improve the multiferroic properties of BiFeO3 thin films,and Mn is one of the representatives.Experimental results show that Mn doping can not only significantly reduce the oxygen vacancy of the film,but also improve the magnetoelectric properties.However,because of the formation of miscellaneous phases in the films,it is difficult to analyze many microscopic mechanisms of the properties of Mn-doped BiFeO3,which restricts the regulation of the performance of BFO film.In view of problems above,we use the first-principle calculation software VASP to calculate the stabilization relationship and magnetielectric properties of the Mn-doped BiFeO3 system of the rhombohedral(R3c),orthorhombic(Pbnm),and tetragonal(P4mm)phases which usually appear in the experiment.The oxygen vacancies and substrates that affect the performance of BFO film are also theoretically analyzed.The results of thermodynamic calculations show that Mn doping tends to induce the formation of orthorhombic phase in the system.The ferromagnetic performance analysis shows that the magnetic property of the doping system are improved significantly with the increase of Mn doping concentration,which is mainly due to the increase of the magnetic moment of Bi Fe1-x Mnx O3 and the decrease of VO concentration.At the same time,Mn doping will also induce the Fermi level of the system to gradually move to the conduction band,which will reduce the Schottky barrier between BFO film and the metal electrode in the experiment.Moreover,the ferroelectric performance analysis shows that the spontaneous polarization of the rhombohedral phase is higher than that of the orthorhombic phase but lower than that of the tetragonal phase,and Mn doping has a weak adverse effect on the ferroelectricity to every phase.Thus,in order to ensure the high ferroelectricity of BFO film,the formation of tetragonal phase is promoted by suppressing the orthorhombic phase as much as possible in the experiment.Furthermore,Oxygen vacancies have a negative effect on the magnetic properties of the doped system,but don't affect its ferroelectric properties.And the impurity band introduced can well explain the phenomenon of high leakage current caused by oxygen vacancy.Finally,the epitaxial stress doesn't change the magnetic moment,but induces the movement of Fermi level to the valence band,and also has a weak effect on the spontaneous polarization of BFO film.