Xinke Wang

Non-volatile, reversible switching of the magnetic moment in Mn-doped ZnO films

We report on the observation of a non-volatile, reversible switching of the magnetic moment in Mn-doped ZnO thin films. The system is a typical oxide memristor based on an oxygen-deficient semiconductor oxide. In the present study, the oxide semiconductor is ferromagnetic at room temperature. We found that the bistable switching of the resistive state was accompanied by a bistable switching of the magnetic moment at room temperature. Our results support the hypothesis that ferromagnetism in Mn-doped ZnO is mediated by oxygen-vacancies.

Non-volatile, electric control of magnetism in Mn-substituted ZnO

We show that the magnetic properties of a dilute semiconductor oxide can be altered in a reversible and non-volatile manner by the application of an electric field. The selected ferromagnetic oxide was manganese-substituted zinc oxide. Bipolar resistive memory switching was induced in the film sandwiched between two metallic electrodes. The bistable switching of the resistive state was accompanied by a bistable switching of the magnetic moment. The scalability of the system was investigated by fabricating devices with lateral size down to 400 nm.

Magnetism as a probe of the origin of memristive switching in p-type antiferromagnetic NiO

We induced bipolar resistive switching in p-type nickel oxide. By probing the magnetic properties of the films, we proved that bipolar resistive switching in this antiferromagnetic oxide was due to the formation and rupture of oxygen-vacancy filaments, rather than electrochemical growth and dissolution of nickel-ion filaments. In the low resistive state, oxygen-mediated super-exchange interaction was suppressed along the conductive paths. This led to a reduction of the saturation moment but not the appearance of a ferromagnetic phase, excluding the formation of nickel filaments.

Removal of organic pollutants from red water by magnetic-activated coke

AbstractA magnetic adsorbent, magnetic-activated coke (MAC), is incorporated with Fe3O4 particles for removal of organic materials from 2,4,6-trinitrotoluene red water. The MAC is characterized by N2 adsorption, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectroscopy. Adsorption of organic pollutants is evaluated systematically by varying the adsorbent dosage, exposure time, temperature, pH, and dilution ratios of 2,4,6-trinitrotoluene red water. The equilibrium adsorption data can be better fitted with the Freundlich isotherm than Langmuir isotherm except at 343 K. The adsorption kinetics follows a pseudo-second-order model and thermodynamic analysis indicates an endothermic and spontaneous adsorption process. The settling rate after adsorption suggests that the response of MAC under an external magnetic field is very fast.

Chemical states and ferromagnetism in heavily Mn-substituted zinc oxide thin films

A concentration of Manganese as high as 8% was successfully diluted into Zinc Oxide epitaxial films deposited by pulsed laser deposition. The films showed strong ferromagnetism with a large coercivity. Low temperature X-ray absorption spectroscopy measurements indicated that all the Manganese ions substitute for Zinc sites of the wurtzite lattice in the valency of +2. Photoluminescence measurements excluded the presence of Zinc vacancies, as well as Zn interstitials. All the magnetic moments measured were to ascribe to the formation of bound magnetic polarons, with no other contribution due to Manganese-secondary phases or Zinc vacancy-mediated double exchange interaction.

Novel polyaluminum ferric chloride composite coagulant from Bayer red mud for wastewater treatment

AbstractA novel composite inorganic polyaluminum ferric chloride (PAFC) coagulant was prepared from Bayer red mud and was usable for wastewater treatment. The reaction parameters affecting the PAFC coagulant performance such as the type of alkali used as the polymerization adjuster, pH, reaction temperature, and reaction time were examined in this study. The structure and morphology of the product were characterized by infrared spectra (FTIR), X-ray diffraction, and scanning electron microscopy. The optimized conditions for preparation were decided as using Ca(AlO2)2 and NaOH together as the polymerization adjuster to reach a pH value of 2.47 with the mixture being kept at 80°C for 6 h. Furthermore, the coagulation performance of the PAFC coagulant was tested in real wastewater samples of pretreated oily sewage and printing and dyeing wastewater. The prepared PAFC coagulant outperformed commercially available PAC coagulant.

Novel multiple coagulant from Bayer red mud for oily sewage treatment

AbstractMultiple coagulants for the treatment of wastewater were prepared. To obtain the optimum synthetic conditions of coagulants, response surface methodology was used to establish the relationship between parameters and the treatment efficiency. In addition, parameters affecting the coagulation–flocculation process, such as the dosage of attapulgite (ATP), the dosage of poly-dimethyl-diallyl-ammonium chloride (PDMDAAC), and the reaction temperature, were investigated. The optimized parameters to prepare multiple coagulant were determined as the dosage of ATP and PDMDAAC being 4 and 2%, respectively, and the reaction temperature being 60°C. The coagulation performance for oily sewage showed that the optimum dosage of coagulant for the maximum treatment was 100 mg/L and the sedimentation time was 30 min at 60°C. In the coagulation–flocculation process, the COD of the oily water decreased from 534 to 246 mg/L and its turbidity decreased from 124 to 2.0 NTU.

Multiple-mode excitation in spin-transfer nanocontacts with dynamic polarizer

We report our study on the emission response of a magnetic nanocontact with dynamic polarizer in perpendicular magnetic field. In this configuration three modes are accessible, two of which correspond to the precessional motion of a vortex in one of the two ferromagnetic layers with the other working as a static polarizer. At high currents a third mode can be observed that is ascribed to the simultaneous precession of two vortices, one in each layer, with the other layer working as a dynamic polarizer.

Growth and characterization of nonpolar, heavily Mn-substituted ZnO films

Eight percent of Mn was successfully diluted into nonpolar ZnO films deposited by pulsed laser deposition on single crystal (100) SrTiO3 substrates. X-ray diffraction patterns and energy-dispersive X-ray spectroscopy confirmed high crystallinity of the films and excluded unintentional magnetic doping. A unique surface domain structure was observed by scanning electron microscope and atomic force microscope, which might play a vital role to strain release induced by lattice mismatch between nonpolar (11–20) ZnO film and (100) SrTiO3 substrate. In addition, the films showed strong ferromagnetism with a large coercivity HC ∼ 180 Oe at room temperature. The large magnetic moment is ascribed to carrier-mediated exchange interaction between the Mn ions, where the majority of the carriers are oxygen vacancies.