| In this paper,the effect of adsorption oxygen and doping on Ti O2 vacancy induced magnetism is studied by first principles calculation.The purpose of this paper is to resolve the controversy about the magnetic source in current experiments and theoretical calculations,and to provide theoretical basis for the research and development of the devices.The rutile Ti O2(110)surface is chosen as the research object.The effect of adsorption oxygen on magnetism induced by vacancy in rutile Ti O2(110)surface was discussed.The different valence states of vacancy and the concentration of absorbed oxygen have been studied.The vacancy types can be divided into 6 types according to different valence states and coordination bonds.According to the charge state,the vacancy is divided into the vacancy with charge state of 0,+1and+2(V0,V+,V2+),respectively.The O2 is adsorbed on the surface with different charge state vacancies,and the number of adsorbed O2 is one.The results showed that oxygen molecules could not be adsorbed spontaneously on the surface without defects.When the surface containing two coordination bond oxygen vacancy,oxygen vacancy with charge+1 is the reason for the magnetic moment on the defect surface,and O2adsorption generates the magnetic moment on the surface containing oxygen vacancy with charge+2 in r-Ti O2(110)surface.Surface containing two coordination bond oxygen vacancy has higher oxygen adsorption capacity than surface containing three coordination bond oxygen vacancy.The study was extended to the surface of rutile Ti O2(001),which is widely used in optics,to study the synergistic effect of adsorbed oxygen and vacancy.There is one category oxygen vacancy in rutile Ti O2(001)surface.Thus,it can be investigated how O2 adsorption under different O2 coverage exerts an impact on the magnetism of the rutile Ti O2(001)surface.The surfaces for O2 adsorption included the defect-free surface and the O-deficient surfaces with the charge states of 0,+1 and+2.Nonmagnetic defect-free surface is difficult to absorb the O2molecule.Stabilities of oxygen vacancies with various valences at the top layer rely on their charge states,and the magnetic of the defective surface is connected with V+instead of V0and V2+.At low O2 coverage,the endothermic adsorptions of O2 molecule may case a nonzero local magnetic moment in the neutral reduced surface while its exothermic adsorption cannot.For the+1 or+2O-deficient surface,the O2 molecule is exothermically adsorbed on the surface and obtains some electrons to form a superoxide anion,which leads to the existence of magnetism.At high O2 coverage,the chemisorption of new O2molecule on the neutral O2-preadsorbed substrate are connected to the adsorption sites and O-O bond oriented.Endothermic adsorption of new O2 molecule induces the magnetic moment on nonmagnetic O2-preadsorbed substrate,while the substrate with the charge state of+1 or+2 prevents more O2 molecule adsorptions.On the basis of the above,we have considered the effect of Mn element doping on the magnetic coupling of oxygen-deficient anatase Ti O2,and discussed various magnetic coupling conditions in the model.The anatase Ti O2 with(1+(2(8)has an intrinsic magnetic moment,while anatase Ti O2 containing(12+(2(8) has no intrinsic magnetic moment.The doping of Mn atoms can increase the local magnetic moment of anatase Ti O2 with(1+(2(8),and the intervention of Mn can induce the local magnetic moment in anatase Ti O2 with(12+(2(8).In addition,the different valence states of the vacancies and the distance between the doped atoms will affect the magnetic coupling of anatase Ti O2.In our report,the generation of magnetic moment in materials can not only consider the influence of intrinsic defects,but also pay attention to the influence of external conditions on materials in the preparation process.According to the results of this paper,we think that the magnetic properties of materials are the result of the synergism between the defects of materials and the external oxygen molecules. |
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