Magnetic 3d-ions doped into wide-gap oxides show signatures of room temperature ferromagnetism, although their concentration is two orders of magnitude smaller than that in conventional magnets. The prototype of these exceptional materials is Co-doped ZnO, for which an explanation of the room temperature ferromagnetism is still elusive. Here we demonstrate that magnetism originates from Co oxygen-vacancy pairs with a partially filled level close to the ZnO conduction band minimum. The magnetic interaction between these pairs is sufficiently long-ranged to cause percolation at moderate concentrations. However, magnetically correlated clusters large enough to show hysteresis at room temperature already form below the percolation threshold and explain the current experimental findings. Our work demonstrates that the magnetism in ZnO:Co is entirely governed by intrinsic defects and a phase diagram is presented. This suggests a recipe for tailoring the magnetic properties of spintronics materials by controlling their intrinsic defects.

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Impurity-Ion pair induced high-temperature ferromagnetism in Co-doped ZnO

Zinc (Zn) doped hematite (α-Fe2O3) nanoparticles with varying concentrations (pure, 2%, 4% and 6%) were synthesized via sol-gel method. The influence of divalent Zn ions on structural, optical and dielectric behavior of hematite were studied. X-ray diffraction (XRD) pattern of synthesized samples were indexed to rhombohedral R3c space group of hematite with 14–21 nm crystallite size. The lattice parameter (a and c) values increase upto Zn 4% and decrease afterwards. The surface morphology of prepared nanoparticles were explored using transmission electron microscopy (TEM). The band gap measured from Tauc’s plot, using UV-Vis spectroscopy, showed reduction in its values upto Zn 4% and the reverse trend was obtained in higher concentrations. The dielectric properties of pure and Zn doped hematite were investigated at room temperature and followed the same trends as that of XRD parameters and band gap. Photocatalytic properties of nanoparticles were performed for hazardous Rose bengal dye and showed effective degradation in the presence of UV light. Hence, Zn2+ doped hematite can be considered as an efficient material for the potential applications in the domain of photocatalysis and also higher value of dielectric constant at room temperature makes them applicable in high energy storage devices.

https://www.mdpi.com/2073-4352/10/4/273/pdf

Zn Doped α-Fe2O3: An Efficient Material for UV Driven Photocatalysis and Electrical Conductivity

High quality silver (Ag) decorated CeO2 nanoparticles were prepared by a facile one-step chemical method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), High resolution transmission electron microscopy (HR-TEM), fourier transform infrared spectrometer (FT-IR), electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), UV-Visible absorption (UV-Vis), photoluminescence (PL) and thermogravimetric analysis. The decoration of Ag on CeO2 surface was confirmed by XRD, EPR and HR-TEM analysis. Harmful textile pollutant Rose Bengal dye was degraded under sunlight using the novel Ag decorated CeO2 catalyst. It was found that great enhancement of the degradation efficiency for Ag/CeO2 compared to pure CeO2, it can be ascribed mainly due to decrease in its band gap and charge carrier recombination rate. The Ag/CeO2 sample exhibited an efficient photocatalytic characteristic for degrading RB under visible light irradiation with a high degradation rate of 96% after 3 h. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the decoration of Ag on the CeO2 surface.

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Silver decorated CeO2 nanoparticles for rapid photocatalytic degradation of textile rose bengal dye.

Electronic structure and photocatalytic activity of samarium doped cerium oxide nanoparticles for hazardous rose bengal dye degradation

Nano-magnetic ferrites with composition Mg1−xZnxFe2O4 (x = 0.3, 0.4, 0.5, 0.6, and 0.7) have been prepared by coprecipitation method. X-ray diffraction (XRD) studies showed that the lattice parameter was found to increase from 8.402 to 8.424 A with Zn2+ ion content from 0.3 to 0.7. Fourier transform infrared (FTIR) spectra revealed two prominent peaks corresponding to tetrahedral and octahedral at around 560 and 430 cm−1 respectively that confirmed the spinel phase of the samples. Transmission electron microscopy (TEM) images showed that the particle size was noted to increase from 18 to 24 nm with an increase in Zn content from x = 0.3 to 0.7. The magnetic properties were studied by vibrating sample magnetometer (VSM) and electron paramagnetic resonance (EPR) which ascertained the superparamagnetic behavior of the samples and contribution of superexchange interactions. The maximum magnetization was found to vary from 23.80 to 32.78 emu/g that increased till x = 0.5 and decreased thereafter. Further, X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical composition and substantiate their oxidation states.

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Zn 2+ substituted superparamagnetic MgFe 2 O 4 spinel-ferrites: Investigations on structural and spin-interactions

UV-irradiated photocatalytic performance of yttrium doped ceria for hazardous Rose Bengal dye

X-ray Analysis of MgO Nanoparticles by Modified Scherer’s Williamson-Hall and Size-Strain Method

In present work, we have reported the room temperature ferromagnetism in lanthanum (La)-doped magnesium oxide (MgO) nanoparticles. It has been found that the magnetic character increases with dilute concentration of La up to 4% and decreases afterwards. The conception of ferromagnetic ordering in such systems is understood on the basis of oxygen intrinsic defects in the host matrix which was elucidated through X-ray photoelectron spectroscopy (XPS) measurements. XPS studies infer that Mg 2p edge is not altered with the incorporation of La ions in the host lattice. However, effective variation in the intensity of O1s edge confirms the presence of defects in the material. EPR (electron paramagnetic resonance) signal peak to peak line width increases with increase in La content and supports the defects present in the material which in turn is related with the change in particle size and saturation magnetisation. These results demonstrate the key role played by defects in stabilising the room temperature ferromagnetic ordering in MgO nanoparticles.

Neha Rani

Papers

Electronic structure and photocatalytic activity of samarium doped cerium oxide nanoparticles for hazardous rose bengal dye degradation

UV-irradiated photocatalytic performance of yttrium doped ceria for hazardous Rose Bengal dye

X-ray Analysis of MgO Nanoparticles by Modified Scherer’s Williamson-Hall and Size-Strain Method

Role of Oxygen Vacancies for Mediating Ferromagnetic Ordering in La-Doped MgO Nanoparticles

MgO nanostructures at different annealing temperatures for d0 ferromagnetism