First-principles Study Of The Physical Properties Of Multiferroic Thin Films

Multiferroic materials develops quickly and has widely attention by theresearchers. BiFeO3is one of multiferroic materials, has both ferroelectricity andantiferromagnetic at room temperature. By raising the effect of magnetoelectriccoupling of materials, can apply to new multistate memory."Magnetic read electricwrite" can improve the speed of information reading and writing. Combined withsemiconductor silicone material, the magnetoelectric film preparation expected torealize miniaturization, integration and multifunctionalization. So study of thephysical properties of BiFeO3multiferroic materials, such as electronic, magneticand the magnetoelectric coupling, has important significance.This article based on first principles and density functional theory, using theMaterial Studio and VASP software, study of the electronic and magnetic of massiveBiFeO3, CoFe2O4and BiFeO3/CoFe2O4composite film in detail. Calculation usingthe generalized gradient approximation (GGA) method handle exchange associationenergy, and using projection plane wave (PAW) pseudo-potential method to deal withthe energy of atomic core. Used proper cut-off energy and k point, optimization ofmassive BiFeO3, CoFe2O4and BiFeO3/CoFe2O4composite thin model. Get (1) themassive BiFeO3lattice constant a=b=5.56, c=13.64,α=120°, β=γ=90°.(2)CoFe2O4lattice constant a=b=c=8.36, α=β=γ=90°, consistent with theexperimental values and others calculated values. And then calculate the band andstates density of the three models.(1) Massive BiFeO3has energy gap of0.95eV,total density of states at spin up the same as at spin down. Confirm the massiveBiFeO3antiferromagnetic characteristics. A state density regions where below theFermi level10eV, come from states density of Bi atomic. Between the Fermi level tobelow8eV, the state density of Bi Fe atoms have overlapping with the state densityof O atom, show they bonding.(2) CoFe2O4have the energy gap of0.57eV at spin up,and don’t have energy gap at spin down, reflect the characteristics of the half metal.The States Density of Co and Fe atoms are asymmetry between spin up and spindown, near the Fermi level below7eV with a peak. The total density of states where below the Fermi level6eV main come from O atoms. Around the Fermi level below6eV, the state density of Co and Fe atom overlap with O atom significantly.(3) Thestate density of Co, Fe atoms and O atoms change since the polarization directionchange.Agree with the changes of the total magnetic moment.