Study On The D⁰ Ferromagnetism In In₂O₃-based Nanoparticles

The discovery of d⁰ ferromagnetism opens a new way for further exploring the mechanism of ferromagnetism.Studies on how to obtain and explain the d⁰ferromagnetism in pristine and nonmagnetic elements doped oxides have been conducted in recent years.In₂O₃ is widely used in industry due to its excellent optical,electrical and gas-sensitive properties.But,till now,reports on d⁰ ferromagnetism in In₂O₃ are limited,and questions on how to explain the mechanism of the ferromagnetism in In₂O₃ clearly and control it precisely are still controversial.In our work,pristine and nonmagnetic element?Li,Mg and Sn?doped In₂O₃ nanoparticles were prepared by sol-gel method.The corresponding lattice structure,valence states,optical and magnetic properties of the samples are analyzed systematically,and the mechanism of d⁰ ferromagnetism in In₂O₃ are studied.Following works are carried out:Firstly,pristine In₂O₃ nanoparticles with the air annealing temperature ranging from 500 to 900°C were prepared,and the effects of annealing temperature on ferromagnetism in In₂O₃ samples were studied.Results show that the content of oxygen vacancies is higher in the samples with the lower or excessively high annealing temperature than that in the sample annealing at 700°C.Combining the enhanced ferromagnetism in the Ar-annealed samples,we think that d⁰ferromagnetism in our samples is directly related with the singly charged oxygen vacancies at the surface of In₂O₃ nanoparticles.Secondly,in order to study the effects of acceptor doping on d⁰ ferromagnetism in In₂O₃,two series of the Li-doped and Mg-doped In₂O₃ nanoparticles with different doping concentration were prepared.Results show that proper nonmagnetic elements in low valance doping can effectively enhance the d⁰ ferromagnetism.As the doping concentration increases,the saturation magnetization firstly increases and then decreases.The density functional theory calculations show that alkali metal element doping can reduce the formation energy of indium vacancies effectively and indium vacancies bring in a local magnetic moment.We think that the ferromagnetism in alkali metal element doped In₂O₃ may result from the p-p hybridization between the O atoms located around the indium vacancies and the substituted cations,and the ferromagnetic coupling between the net moments depends on the effective concentration of holes.Thirdly,in order to study the co-doping effects of the donor and acceptor,a series of Sn and Mg co-doped In₂O₃ nanoparticles((In_0.88Sn_?0.12-x?Mg_x)₂O₃)were prepared by varying the ratio of two doping elements?x=0.02,0.04,0.06,0.08,0.10?.Results show that the saturation magnetization firstly goes down and then goes up,as the ratio of Sn with respect to Mg decreases from 5:1 to 1:5.And the weakest saturation magnetization is obtained in the sample with equal doping concentration of Sn and Mg.We think that as the doping concentration of Sn decreases from 10 to 6at.%,the main defects are oxygen vacancies and Sn-related donor defects,and the ferromagnetism mainly originates from oxygen vacancies,which is mediated by the density of donor defects.As the doping concentration of Mg increases from 6 to 10at.%,the main defects are indium vacancies related defect complexes,and the ferromagnetism is mainly induced by the indium vacancies,in which the ferromagnetic coupling between the net moments depends on the effective concentration of holes.