Manipulation On The Local Structures And Magnetic Properties Of Co/Sn Noncompensated P–n Codoped In₂O₃ Based Dilute Magnetic Oxides

In this paper,the Co/Sn co-doped In₂O₃ diluted magnetic semiconductor（DMSs）films ware deposited on SiO₂/Si（100）and white glass substrates by RF-magnetron sputtering technique.The local structure,spin-dependent magnetic and transport properties of In₂O₃ based DMS films were investigated systemically by X-ray diffraction（XRD）,Transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）,X-ray absorption fine structure（XAFS）,Hall effects,resistivity-temperature curves（r-T）,the magnetoresistance（MR）,superconducting quantum interference device（SQUID）and UV,the main results are following:1、Different doping concentrations of(In_0.98-xCo_xSn_0.02)₂O₃ films were deposited.The detailed structural analyses suggest that all the films have a cubic bixbyite structure of In₂O₃,the doped Co exist in the films as a valence state of +2,combined with large amount of oxygen vacancies.The XAFS results show that the doped Co ions substitute for In³⁺ sites of In₂O₃ lattice.When the concentration increased to 0.05,Co metal clusters appeared in the films,and the metal clusters increased with the increasing of Co concentration.The transport properties measurements show that all the films show a negative MR component at different temperatures.The Hall measurements indicated that the resistivity increases and the carrier concentration nc decreases with Co doping concentration.The electronic conducting mechanism is dominated by Mott variable range hopping（VRH）behavior at low temperature and Hard band gap hopping behavior at high temperature,suggesting that the carriers are strongly localized.The UV transmission spectra measurement show the transmittance intensity of films and the band gap decreases with the increases of Co concentration,resulting in an obvious red shift in the absorption edge position.Magnetic characterizations show that all the films show intrinsic room-temperature（RT）ferromagnetism and Ms increases then decreases with Co doping.The carrier concentration shows different changing tendency compared with the room temperature ferromagnetism induced by the mediated carriers is ruled out.However,the room temperature ferromagnetism can be ascribed to oxygen-induced bound magnetic polarizations.For films with high Co doping concentration,the isolated magnetic ions Co at substitutional sites increase.Superexchange between Co ions that are near neighbours through oxygen ions is antiferromagnetic interaction,which lead to the Ms weakened.2、Different doping concentrations of(In_0.95-xCo_0.05Sn_x)₂O₃ films were deposited.The detailed structure shows that the co-doped In₂O₃ films have a cubic bixbyite structure.The doped Co and Sn ions substitute for In³⁺ sites of In₂O₃ lattice with the valence state of +2 and +4 in the films,respectively.When the Sn concentration increased to 0.02,Co metal clusters appeared in the films,and the metal clusters vanished with the increasing of Sn concentration.The strong Coulomb interaction between Sn4+ and Co2+ can not only reduce the formation energies of CoIn but also suppress Co clusters.The transport properties measurements show that all the films show semiconducting behavior.The Hall measurements indicated that all films possess n-type conductivity and the carrier concentration nc increases and the resistivity decreases gradually as a function of Sn concentration.The electronic conducting mechanism is dominated by Mott variable range hopping（VRH）behavior at low temperature and Hard band gap hopping behavior at high temperature,suggesting that the carriers are strongly localized.The UV transmission spectra measurement show that the transmittance intensity of films and the band gap increases with the increases of Sn concentration,resulting in an obvious blue shift in the absorption edge position.Magnetic characterizations show that all the films are intrinsic RT ferromagnetism and the Ms increases with Sn doping.The room temperature ferromagnetism induced by the mediated carriers and Co clusters is ruled out due to strongly localized of the carriers and superparamagnetic Co.The interaction between the doped Co ions have a strong connection with oxygen vacancies,which induces the formation of bound magnetic polarons.All the results indicate that the room-temperature intrinsic ferromagnetism is ascribed to the bound magnetic polarons model.The concentration of Co In and BMP increases with the increases of Sn doping,then the Ms increases.