Extensive calculations based on density functional theory have been carried out to understand the origin of magnetism in undoped ZnO thin films as found in recent experiments. The observed magnetism is confirmed to be due to Zn, instead of O, vacancy. The main source of the magnetic moment, however, arises from the unpaired 2p electrons at O sites surrounding the Zn vacancy with each nearest-neighbor O atom carrying a magnetic moment ranging from 0.490 to 0.740 B. Moreover, the study of vacancy-vacancy interactions indicates that in the ground state, the magnetic moments induced by Zn vacancies prefer to ferromagnetically couple with the antiferromagnetic state lying 44 meV higher in energy. Since this is larger than the thermal energy at room temperature, the ferromagnetic state can be stable against thermal fluctuations. Calculations and discussions are also extended to ZnO nanowires that have larger surface to volume ratio. Here, the Zn vacancies are found to lead to the ferromagnetic state too. The present theoretical study not only demonstrates that ZnO samples can be magnetic even without transition-metal doping but also suggests that introducing Zn vacancy is a natural and an effective way to fabricate magnetic ZnO nanostructures. In addition, vacancy mediated magnetic ZnO nanostructures may have certain advantages over transition-metal doped systems in biomedical applications.

https://absimage.aps.org/image/MAR08/MWS_MAR08-2007-004197.pdf

Zinc Vacancy induced magnetism in ZnO thin films and nanowires

We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Photothermal CO2 reduction technology has attracted tremendous interest as a solution for the greenhouse effect and energy crisis, and thereby it plays a critical role in solving environmental problems and generating economic benefits. In2 O3- x has emerged as a potential photothermal catalyst for CO2 conversion into CO via the light-driven reverse water gas shift reaction. However, it is still a challenge to modulate the structural and electronic characteristics of In2 O3 to enhance photothermocatalytic activity synergistically. In this work, a novel route to activate inert In(OH)3 into 2D black In2 O3- x nanosheets via photoinduced defect engineering is proposed. Theoretical calculations and experimental results verify the existence of bifunctional oxygen vacancies in the 2D black In2 O3- x nanosheets host, which enhances light harvesting and chemical adsorption of CO2 molecules dramatically, achieving 103.21 mmol gcat -1 h-1 with near-unity selectivity for CO generation and meanwhile excellent stability. This study reveals an exciting phenomenon that light is an ideal external stimulus on the layered In2 O3 system, and its electronic structure can be adjusted efficiently through photoinduced defect engineering; it can be anticipated that this synthesis strategy can be extended to wider application fields.

Photoinduced Defect Engineering: Enhanced Photothermal Catalytic Performance of 2D Black In 2 O 3− x Nanosheets with Bifunctional Oxygen Vacancies

Using first principles calculations based on the density functional theory and generalized gradient approximation we show that the ground state of Mn doped ZnO $(10\\overline{1}0)$ thin film changes from antiferromagnetic to ferromagnetic when codoped with N. The ferromagnetic coupling between Mn spins arises due to the overlap between N $2p$ and Mn $3d$ electrons in the spin up band, rendering the system half-metallic character.

http://absimage.aps.org/image/MAR05/MWS_MAR05-2004-000489.pdf

Carrier-mediated Ferromagnetism in N Co-doped (Zn, Mn)O (10 0) Thin Film

This work reports the study concerning the structure and magnetic properties of undoped CeO2 and Fe-doped CeO2 (Ce1 xFexO2, 0.01 � x � 0.07) nanospheres with diameters of 100�200 nm prepared by hydrothermal method using polyvinylpyrrolidone (PVP) as surfactant. The prepared samples were studied by using X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray absorption near-edge structure (XANES), and vibrating sample magnetometry (VSM). The XRD results showed that Fe-doped CeO2 was single-phased with a cubic structure, and with Fe 3+ successfully substituting in Ce 4+ sites. Raman spectra showed a redshift of F2g mode that caused by the Fe doping. The samples of both undoped CeO2 and Fe-doped CeO2 exhibited room temperature ferromagnetism, and the saturated magnetization (Ms) increased with increasing Fe content until x = 0.05, and then the samples displayed ferromagnetic loops as well as paramagnetic behavior. The roles of Ce 3+ and Fe 3+ spin electrons are discussed for the ferromagnetism in the Fe-doped CeO2.

/pdf/structure-and-magnetic-properties-of-monodisperse-fe3-doped-2yf3q3dvnp.pdf

Structure and Magnetic Properties of Monodisperse Fe3+-doped CeO2 Nanospheres

Structural, optical, and magnetic properties of Fe doped In2O3 powders

Nickel (Ni) doped SnO2 powder samples were prepared using solid-state reaction with dopant concentrations in the range of 3 at.% to 15 at.%. The influence of Ni doping on structural, optical, and magnetic properties of the powder samples has been investigated. All the Ni doped powder samples exhibited tetragonal structure of SnO2. A decrease in optical band gap was observed with increase of Ni doping levels. The vibrating sample magnetometer measurements revealed that the Ni doped SnO2 powder samples were ferromagnetic at room temperature.

https://downloads.hindawi.com/journals/acmp/2014/284237.pdf

Structural and Magnetic Properties of Ni Doped

Room temperature ferromagnetism in Cd1−xCrxTe diluted magnetic semiconductor crystals

Structural, optical and magnetic properties of (In1−xNix)2O3 (0≤x≤0.09) powders synthesized by solid state reaction

Nanocrystalline Cadmium Telluride (CdTe) thin films were deposited onto glass substrates using electron beam evaporation technique. The effect of substrate temperature on the structural, morphological and optical properties of CdTe thin films has been investigated. All the CdTe films exhibited zinc blende structure with (111) preferential orientation. The crystallite size of the films increased from 35 nm to 116 nm with the increase of substrate temperature and the band gap of the films decreased from 2.87 eV to 2.05 eV with the increase of the crystallite size.

/pdf/effect-of-substrate-temperature-on-structural-and-optical-12agnhtx54.pdf

M. Kuppan

Papers

Structural, optical, and magnetic properties of Fe doped In2O3 powders

Structural and Magnetic Properties of Ni Doped

Room temperature ferromagnetism in Cd1−xCrxTe diluted magnetic semiconductor crystals

Structural, optical and magnetic properties of (In1−xNix)2O3 (0≤x≤0.09) powders synthesized by solid state reaction

Effect of Substrate Temperature on Structural and Optical Properties of Nanocrystalline CdTe Thin Films Deposited by Electron Beam Evaporation