Effect of hydrogenation vs. re-heating on intrinsic magnetization of Co doped In2O3

Influence of Co doping for In in In₂O₃ matrix has been investigated to study the effect on magnetic vs. electronic properties. Rietveld refinement of X-ray diffraction patterns confirmed formation of single phase cubic bixbyite structure without any parasitic phase. Photoelectron spectroscopy and refinement results further revealed that dopant Co²⁺ ions are well incorporated at the In³⁺ sites in In₂O₃ lattice and also ruled out formation of cluster in the doped samples. Magnetization measurements infer that pure In₂O₃ is diamagnetic and turns to weak ferromagnetic upon Co doping. Hydrogenation further induces a huge ferromagnetism at 300 K that vanishes upon re-heating. Experimental findings confirm the induced ferromagnetism to be intrinsic, and the magnetic moments to be associated with the point defects (oxygen vacancies V_o) or bound magnetic polarons around the dopant ions.     

High temperature ferromagnetism of the vacuum-annealed (In1−xFex)2O3 powders

(In_1−xFe_x)₂O₃ (x = 0.02, 0.05, 0.2) powders were prepared by a solid state reaction method and a vacuum annealing process. A systematic study was done on the structural and magnetic properties of (In_1−xFe_x)₂O₃ powders as a function of Fe concentration and annealing temperature. The X-ray diffraction and high-resolution transmission electron microscopy results confirmed that there were not any Fe or Fe oxide secondary phases in vacuum-annealed (In_1−xFe_x)₂O₃ samples and the Fe element was incorporated into the indium oxide lattice by substituting the position of indium atoms. The X-ray photoelectron spectroscopy revealed that both Fe²⁺ and Fe³⁺ ions existed in the samples. Magnetic measurements indicated that all samples were ferromagnetic with the magnetic moment of 0.49-1.73 μ_B/Fe and the Curie temperature around 783 K. The appearance of ferromagnetism was attributed to the ferromagnetic coupling of Fe²⁺ and Fe³⁺ ions via an electron trapped in a bridging oxygen vacancy.     

Synthesis and characterization of room-temperature ferromagnetism in Fe- and Ni-co-doped In2O3

Observation of room-temperature ferromagnetism in Fe- and Ni-co-doped In₂O₃ samples (In_0.9Fe_0.1−xNi_x)₂O₃ (0?x?0.1) prepared by citric acid sol-gel auto-igniting method is reported. All of the samples with intermediate x values are ferromagnetic at room-temperature. The highest saturation magnetization (0.453 μ_B/Fe+Ni ions) moment is reached in the sample with x=0.04. The highest solubility of Fe and Ni ions in the In₂O₃ lattice is around 10 and 4 at%, respectively. The 10 at% Fe-doped sample is found to be weakly ferromagnetic, while the 10 at% Ni-doped sample is paramagnetic. Extensive structure including Extended X-ray absorption fine structure (EXAFS), magnetic and magneto-transport including Hall effects studies on the samples indicate the observed ferromagnetism is intrinsic rather than from the secondary impurity phases.     

Electronic structure analysis of Mn- and Fe-codoped In2O3 by photoemission yield measurements

The valence band electronic structures of Mn- and/or Fe-doped In₂O₃, i.e., In₂O₃:Mn, In₂O₃:Fe, and In₂O₃:(Mn, Fe), are investigated by photoemission yield measurements. Significant changes are observed in the threshold energy of photoemission, depending on the doped magnetic ions, which indicates that an additional occupied band appears above the top of the valence band of In₂O₃ owing to doping with Mn and/or Fe ions. It is confirmed that the order of the threshold energies of photoemission, E_PET, is E_PET(In₂O₃:Mn)<E_PET(In₂O₃:(Mn, Fe))<E_PET(In₂O₃:Fe)<E_PET(In₂O₃). To gain a better understanding of these results, first-principles molecular orbital calculations are also carried out, which successfully explain the observed changes in the photoemission threshold energies.     

Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy,Ti3+-V O defect complexes(or clusters) have been identified in annealed crystals at a high vacuum.We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism.In addition,excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.     

Effect of annealing atmosphere on magnetism for Fe-doped BaTiO3 ceramic

Ba(Ti_0.3Fe_0.7)O₃ ceramic was prepared by solid-state reaction and post-annealed in vacuum and oxygen, respectively. The as-prepared and annealed samples are all single-phase, crystallizing in a 6H-BaTiO₃-type hexagonal perovskite structure. Room-temperature ferromagnetism is exhibited in all ceramics. For the as-prepared sample, the super-exchange interactions of Fe³⁺ in different occupational sites (pentahedral and octahedral sites) are expected to produce the ferromagnetism observed. After annealing in vacuum, the magnetization is reduced while the exchange mechanism remains unchanged. On the contrary, O₂ annealing can effectively enhance the magnetization due to the presence of Fe⁴⁺, an unusual valence for iron. The simultaneous presence of Fe³⁺ and Fe⁴⁺ allows new exchange mechanism responsible for the ferromagnetic interaction. The exchange couplings of Fe ions with mixed valences (Fe³⁺ and Fe⁴⁺) determine the magnetic behavior.     

Effect of W co-doping on the optical,magnetic and electrical properties of Fe-doped BaSnO3

The effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO₃ has been studied. Polycrystalline BaSnO₃, BaSn_0.96Fe_0.04O₃ and BaSn_0.95Fe_0.04W_0.01O₃ samples were prepared using solid state reaction. In the analysis of powder X-ray diffraction patterns, the samples were found to be free of secondary phases. Diffuse reflectance spectra evidenced the substitution of Fe and W for Sn in the host BaSnO₃. Micro-Raman spectra confirmed the existence of oxygen vacancies in the samples. Upon W-1% co-doping, the ferromagnetic character of Fe-4% doped BaSnO₃ is suppressed drastically and its Curie temperature is reduced to 310 K from 462 K. The existence of F-centers and ferromagnetic interactions at room temperature is evidenced by the electron paramagnetic resonance and ferromagnetic resonance signals observed in the electron spin resonance spectra of the undoped and Fe-4% doped, (Fe-4% and W-1%) co-doped BaSnO₃ samples respectively. Suppression of ferromagnetism upon W co-doping is due to the fact that each W⁶⁺ ion donates two electrons to the host lattice and it reduces the number of oxygen vacancies that are essential for ferromagnetism to exist in the Fe-doped BaSnO₃ samples.     

Control of ferromagnetism in Fe-doped In2O3 by carbothermal annealing

Fe-doped In₂O₃ powders were prepared using the sol–gel method. Solubility of Fe ions in the In₂O₃ host compound reached up to 50%. Lattice constant decreased linearly as Fe doping concentration increased, indicating that Fe ions were incorporated into the host lattice and occupied the In sites. Ferromagnetism could be obtained from the samples with carbothermal annealing. The dependence of ferromagnetism on the carbon dosage was observed. The greater the carbon dosage, the higher the concentration of oxygen vacancies (V_o) created, and the more robust the ferromagnetism.     

Synthesis of monodisperse In2O3 nanoparticles and their d0 ferromagnetism

Monodisperse indium oxide (In₂O₃) nanoparticles (NPs) with the average diameter of 11 nm were prepared by a solvothermal method. The In₂O₃ NPs were characterized by X-ray diffraction, Raman and transmission electron microscopy. The intrinsic nature of ferromagnetism in In₂O₃ NPs has been established with the experimental observation of magnetic hysteresis loop. Photoluminescence and UV–visible studies were employed to evidence the presence of oxygen vacancies and revealed that the oxygen vacancies contribute to the ferromagnetism. The origin of ferromagnetism in In₂O₃ NPs may be due to exchange interactions among localized electron spin moments resulting from oxygen vacancies.     

Ferromagnetism in carbon-doped In2O3 thin films

Carbon-doped In₂O₃ thin films exhibiting ferromagnetism at room temperature were prepared on Si (100) substrates by the rf-magnetron co-sputtering technique. The effects of carbon concentration as well as oxygen atmosphere on the ferromagnetic property of the thin films were investigated. The saturated magnetizations of thin films varied from 1.23 to 4.86 emu/cm³ with different carbon concentrations. The ferromagnetic signal was found stronger in samples with higher oxygen vacancy concentrations. In addition, deposition temperature and different types of substrates also affect the ferromagnetic properties of carbon-doped In₂O₃ thin films. This may be related to the oxygen vacancies in the thin film system. The experiment suggests that oxygen vacancies play an important role in introducing ferromagnetism in thin films.     

Magnetism due to oxygen vacancies and/or defects in undoped semiconducting and insulating oxide thin films

Room temperature ferromagnetism was observed in HfO₂, TiO₂, and In₂O₃ films grown on yttrium-stabilized zirconia, LaAlO₃, and MgO substrates, respectively. While the magnetic moment is rather modest in the case of In₂O₃ films, it is very large in the other two cases. Thin film form, which might create necessary defects and/or oxygen vacancies, must be the main reason for undoped semiconducting and insulating oxides to become ferromagnetic. From the results, a serious question arises if a transition-metal doping indeed plays any essential role in producing ferromagnetism (FM) in non-magnetic oxides.     

Coexistence of paramagnetism and ferromagnetism in Fe-TiO2 nanoparticle

Magnetic properties of pure and Fe doped rutile TiO₂ and TiO_2-ε are investigated using the first principle density functional theory. The results show that the considered systems are ferromagnetic. Furthermore, the origin of ferromagnetism is discussed and it is found that the double exchange and super-exchange are the main interactions in these compounds. Based on the calculations, the magnitude of the magnetic moment depends on the concentration of impurities and oxygen vacancies and the largest magnetic moment corresponds to the Fe_xTi_1-xO_2-ε. Moreover, using a model based on the bound magnetic polarons, the coexistence of ferromagnetic and paramagnetic phases can occur in Fe_xTi_1-xO₂ containing different impurity ions such as Fe⁺² and Fe⁺³ with different Curie temperatures. The finding may presents the potential application of the considered system as diluted magnetic semiconductor.     

Intrinsic magnetic properties of In2O3 and transition metal-doped-In2O3

This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In₂O₃. Undoped nanocrystalline In₂O₃ is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In₂O₃ samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit.     

Fabrication and photoluminescence characteristics of In2O3 nanohillocks

Uniformly distributed polycrystalline indium nanohillocks are synthesized on silicon substrates with Au catalyst by using the radio frequency magnetic sputtering technique. The results show that the Au catalyst plays a key role in the formation of indium nanohillocks. After thermally oxidizing the indium nanohillocks at 500 ℃ in air for 5 h, the indium nanohillocks totally transform into In₂O₃ nanohillocks. The energy-dispersive X-ray spectroscopy result indicates that many oxygen vacancies and oxygen-indium vacancy pairs exist in the In₂O₃ nanohillocks. Photoluminescence spectra under an Ne laser excitation at 280 nm show broad emissions at 420 nm and 470 nm with a shoulder at 450 nm related to oxygen vacancies and oxygen-indium vacancies at room temperature.     

Preparation, structure and ferromagnetic properties of the nanocrystalline Ti1-xMnxO2 thin films grown by radio frequency magnetron co-sputtering

This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.     

The investigation of room temperature ferromagnetism in (1 0 0) oriented BaNb2O6 PLD films on LaAlO3 (1 0 0) substrate

(1 0 0) oriented BaNb₂O₆ films have been successfully grown on LaAlO₃ (1 0 0) substrate at 750 °C or 450 °C in vacuum by pulsed laser deposition. The deposited BaNb₂O₆ PLD films exhibit room-temperature ferromagnetism. Ab initio calculations demonstrate that stoichiometric BaNb₂O₆ and that with barium vacancy are nonmagnetic, while oxygen and niobium vacancy can induce magnetism due to the spin-polarization of Nb s electrons and O p electrons respectively. Moreover, ferromagnetic coupling is energetically more favorable when two Nb/O vacancies are located third-nearest-neighbored. The observed room temperature ferromagnetism in BaNb₂O₆ films should be mainly induced by oxygen vacancies introduced during vacuum deposition, with certain contribution by Nb vacancies.     

Coexistence of paramagnetism and ferromagnetism in Fe-TiO2 nanoparticle

Magnetic properties of pure and Fe doped rutile TiO₂ and TiO_2-ε are investigated using the first principle density functional theory. The results show that the considered systems are ferromagnetic. Furthermore, the origin of ferromagnetism is discussed and it is found that the double exchange and super-exchange are the main interactions in these compounds. Based on the calculations, the magnitude of the magnetic moment depends on the concentration of impurities and oxygen vacancies and the largest magnetic moment corresponds to the Fe_xTi_1?xO_2?ε. Moreover, using a model based on the bound magnetic polarons, the coexistence of ferromagnetic and paramagnetic phases can occur in Fe_xTi_1?xO₂ containing different impurity ions such as Fe⁺² and Fe⁺³ with different Curie temperatures. The finding may presents the potential application of the considered system as diluted magnetic semiconductor.     

Structural and Magnetic Properties of Fe-Doped Anatase TiO2 Films Annealed in Vacuum

Structural and magnetic properties of Fe-doped anatase TiO2 films fabricated by sol-gel spin coating are investigated. X-ray diffraction measurements reveal that Fe^3＋ ions are incorporated into the TiO2 lattice. No ferromagnetism-related secondary phases and magnetic nanopaxticles are observed in the films. The presence of electron paramagnetic resonance signals at 9- 2.0 supports oxygen vacancies and/or defects generated in the films after annealing in vacuum. Magnetic measurements indicate that Fe-doped anatase TiO2 films are ferromagnetic at room temperature. These observations suggest that oxygen vacancies and/or defects axe energetically favorable for the long range Fe^3＋-Fe^3＋ ferromagnetic coupling in Fe-doped anatase TiO2 films.     

Co-doped In2O3 thin films: Room temperature ferromagnets

Laser-ablated Co-doped In₂O₃ thin films were fabricated under various growth conditions on R-cut Al₂O₃ and MgO substrates. All Co:In₂O₃ films are well-crystallized, single phase, and room temperature ferromagnetic. Co atoms were well substituted for In atoms, and their distribution is greatly uniform over the whole thickness of the films. Films grown at 550 °C showed the largest magnetic moment of about 0.5 μ_B/Co, while films grown at higher temperatures have magnetic moments of one order smaller. The observed ferromagnetism above room temperature in Co:In₂O₃ thin films has confirmed that doping few percent of magnetic elements such as Co into In₂O₃ could result in a promising magnetic material.     

Ferromagnetism induced by oxygen-vacancy complex in (Mn,in) codoped ZnO

Mn doped Zinc oxide (ZnO) thin films were prepared by metal organic chemical vapor deposition (MOCVD) technique. Structural characterizations by X-ray diffraction technique (XRD) and photoluminescence (PL) indicate the crystal quality of ZnO films. PL and Raman show a large fraction of oxygen vacancies (V_O²⁺) are generated by vacuum annealed the film. The enhancement of ferromagnetism in post-annealed (Mn, In) codoped ZnO could result from V_O²⁺ incorporation. The effect of V_O²⁺ on the magnetic properties of (Mn, In) codoped ZnO has been studied by first-principles calculations. It is found that only In donor cannot induce ferromagnetism (FM) in Mn-doped ZnO. Besides, the presence of V_O²⁺ makes the Mn empty 3d-t_2g minority state broadened, and a t_2g-V_O²⁺ hybrid level at the conduction band minimum forms. The presence of V_O²⁺ can lead to strong ferromagnetic coupling with the nearest neighboring Mn cation by BMP model based on defects reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Mn 3d electrons trapped in oxygen vacancies.