First-principles Study Of D⁰Magnetism In Li-doped SnO₂

In recent years, non-magnetic ions doped semiconductors have attracted aconsiderable attention due to their d0magnetism. It was found that the magnetictransition mental (TM) dopants often segregate to form ferromagnetic clusters,precipitates or secondary phases in TM-doped semiconductors. However,non-magnetic ions dopants can effectively eliminate these extrinsic magneticbehaviors in doped semiconductors. The semiconductor based on oxide can achieven-type doping and is a new class of ferromagnetic semiconductors with high Curietemperature. Recently, d0magnetism has been observed in some semiconductingoxides by doping with nonmagnetic elements. As an important wide-band-gapsemiconductor, d0magnetism of non-magnetic ions doped SnO2has been investigatedextensively. Recently, d0magnetism have been reported in non-magnetic Li dopedSnO2. It has been reported that the saturation magnetic moments increase with theincreasing of Li concentration, and for9%Li-doped compounds, the momentsincrease with an increase in annealing temperature. However, there has not been atheoretical calculation report to provide atomic understanding for the mechanismabout d0magnetism in Li doped SnO2. In this thesis, first-principles calculations areused to investigate the effect of Li substitution, Li interstitial and oxygen vacancy onelectronic structure and magnetic properties of Li doped SnO2to understand d0magnetism. The main results are as follows:1. The calculations demonstrate that oxygen vacancy and Li at the interstitialsite can not introduce magnetism in SnO2. However, Li doped at the Sn site inducesmagnetism in SnO2with oxygen vacancy and the induced magnetic momentincreases with the increasing of Li concentration. As can be seen, the momentinduced by doping mainly comes from the2p orbitals of oxygen around substitutional Li. For Li doping system with oxygen vacancies, the formation energyof Li at the interstitial site increase, while that of Li doped at the Sn site obviouslydecrease, which indicate that the doping atoms should substitute for the host Snatoms in Li doped SnO2with oxygen vacancies.2. For9%Li-doped system, formation energy of Li doped at the Sn site andinduced magnetic moment by Li doping increase with the decreasing of oxygenvacancy concentration. Similarly the moment induced by doping mainly comes fromthe2p orbitals of oxygen around substitutional Li.In conclusion, the calculated results for Li-doped system coincide withexperimental results and the observed d0magnetism in Li doped SnO2should beattributed to Li doped at the Sn site.