Investigation On The Structure And Properties Of In₂O₃-based Diluted Magnetic Semiconductor

Since Dietl et al, theoretically predicted the room temperature ferromagnetism in Mn doped ZnO and GaN semiconductors, diluted magnetic semiconductors (DMSs), which simultaneously exploit the charge and spin properties of electrons, have drawed much attention because of the potential applications in spintronics. The studies of transition metal (TM) doped semicondutor oxide, like, TiO2, ZnO, SnO2 and In2O3 have been carried on extensively. The next multi-function devices required material with good optical, electrical and magnetic properties, so look for a material who can control the carrier concentration, high mobility, high magnetic moment and the high transparency is crucial. In2O3 is a promising candidate to meet the above properties as a DMSs host.Ni-In2O3 nanoparticles and thin films were both prepared though simple sol-gel method. The solubility of Ni ions into In2O3 lattice was firstly clarified. Furthermore, the regulation of structure and properties variation with the doping contents was discussed either in Ni-In2O3 nanoparticles, or in Ni-In2O3 thin films. At last, we studid the influence of annealed temperature on the structure, magnetic and optical performance in Ni-In2O3 thin films..In(NO3)3·4.5H2O, Ni(NO3)2·6H2O, acetyl acetone and ethylene glycol monomethyl ether were introduced as a precursor raw materials for sol. The sol was dried at 110℃, and then annealed at different temperatures to fabricate powder samples, or preparation thin films under the same heat treatment through dip-coating method.The XRD results of (In1-xNix)2O3-δnanopowders show that no trace of secondary phases can be detected within the XRD detection limit when the Ni content up to 10%, implying the maximum solubility of Ni in In2O3 host lattice is about 10%. Above the solubility limit, secondary phases start to appear in the XRD patterns. Because of the limited sensitivity of XRD, we employed the XPS to further demonstrate the nonexistence of second phases by investigating the chemical states of In, O, and Ni ions in (In0.9Ni0.1)2O3-δsample annealed at 500℃. The results strongly suggest that Ni ions were successfully incorporated into In2O3 host lattice as Ni2+ without forming any detectable impurity phases. Meanwhile, a large number of oxygen vacancies were introduced through the O1s photoelectron spectra of the samples.Within the solubility of Ni ions, the doping can promote the incorporation of particles growing up. (In1-xNix)2O3-δ(x=0.05,0.1) simples exhibit well ferromagnetic behavior. The saturation magnetization increased with the Ni content increasing because the magnetic exchange interaction enhanced with the average distance between magnetic ions decreases with Ni content increasing. While increasing annealing temperature, the particle size and saturation magnetization tends to decrease. The maximum saturation magnetization (Ms) is up to 0.44emu/g (0.11μB/Ni) in (In0.9Ni0.1)2O3-δnanopowders at 500℃). The obtained Ms value for Ni-doped In2O3 nanoparticles is smaller than that,0.7μB/Ni at 300K, for Ni-doped In2O3 films by PLD method, whereas for Ni-doped In2O3 bulks, the maximum magnetic moment was only 0.06μB/Ni at 300K. The different result from films, nanoparticles and bulks is probably due to the amount of the defects which are responsible for the shallow donors. The cation defects and oxygen vacancies play an important role in the change of carrier concentration in this system.Based on the above analysis of the mechanism of this systems, we regarded thin films may have superior magnetic properties. Consequently, we prepared (In1-xNix)2O3-δthin films under the same conditions, expecting it to have better magnetic properties, furthermore the structure and properties were also investigated. (In1-xNix)2O3-δthin films of the XRD patterns showed the same law with nanoparticles. The calculated lattice constant linearly decreases with Ni content increasing while no significant changes in lattice constant when x≥0.1, indicating the solubility of Ni ions in In2O3 thin films is 10%. With Ni content increasing within the solubility, the growth ability of particles increased, Ni ions'exchange interaction enhanced and the lattice distortion increased, so the film particles'size, saturation magnetization were increasing, and the transmittance was gradually decreased. The research on (In0.9Ni0.1)2O3-δfilm samples with different annealed temperatures (400℃,450℃,500℃,550℃) show that the grain size and saturation magnetization increased firstly and then decreased with the increase of annealed temperatures. The maximum Ms is up to 356emu/g (11.8μB/Ni) at 500℃. Because the samples have the same amount of Ni incorporation, magnetic enhancement means that a higher carrier concentration which made a lot light scattering and then the minimum visible light transmittance.