High temperature carrier controlled ferromagnetism in alkali doped ZnO nanorods

Recent efforts in developing spintronic and magneto-optoelectric material for applications have relied on the use of magnetic semiconductors doped with transition metals and have met with limited success. Using a fresh synthesis approach using alkali ions we demonstrate that alkali doped zinc oxide can provide high temperature magnetic semiconductors. We report studies on nanocrystalline powder and pellets of p-type ZnO:Li and ZnO:Na that exhibit ferromagnetism up to 554 K. The ferromagnetic behavior was confirmed from magnetic hysteresis, ferromagnetic resonance, magnetic force microscopy, and explained by a model where substitutional Li+/Na+ in cation site induce local magnetic moments on oxygen atoms. Optimum dopant concentrations enable ferromagnetic exchange interaction leading to high Curie temperature

Direct Evidence for Multiferroic Magnetoelectric Coupling in 0.9BiFeO(3)-0.1BaTiO(3)

Magnetic, dielectric and calorimetric studies on 0.9BiFeO(3)-0.1BaTiO(3) indicate strong magnetoelectric coupling. XRD studies reveal a very remarkable change in the rhombohedral distortion angle and a significant shift in the atomic positions at the magnetic T-c due to an isostructural phase transition. The calculated polarization using Rietveld refined atomic positions scales linearly with magnetization. Our results provide the first unambiguous, atomic level evidence for magnetoelectric coupling of intrinsic multiferroic origin in a BiFeO3-based system

Ultrafast adsorption of organic dyes by activated-carbon@Fe3O4 nanoscale composites: An effective solution for water purification

Superparamagnetic (SPM) Fe3O4 nanoparticles (NPs) decorated activated charcoal (AC) skeletal (AC@Fe3O4) type nanoscale composites (NCs) have been prepared by a scalable and facile approach involving impregnation of AC with stable dispersion of SPM Fe3O4 NPs followed by controlled vacuum drying. These NCs exhibit coupled magnetic character and porosity which can be easily optimized by controlling weight ratio of two phases. The electron microscopy images show the presence of clustered Fe3O4 particles present all over the surface of porous AC particles and prevalence of meso-pores, which provides the channels for ingress and immobilization of sorbent moieties. The magnetometry and nitrogen adsorption measurements reveal that magnetic character increases whereas porosity decreases with the increase in Fe3O4 NP loading. These NCs have been demonstrated for purification of water containing methylene blue (MB) dye as an impurity. The porosity of these composites allow rapid adsorption (<1 min) of MB with good removal efficiency (> 99%) and their magnetic behaviour helps in instantaneous separation of MB adsorbed NC particles by the application of external magnetic field. The sorbent can be reused several times after proper regeneration with retention of more than 95% of the original adsorption capacity

Resistivity dependent dielectric and magnetic properties of Pb(Fe0.012Ti0.988)O3 nanoparticles

High resistivity in nanostructured Pb(Fe0.012Ti0.988)O3 system prepared by using polyvinyl alcohol (PVA) in chemical route is observed. The PVA acts as a surfactant to limit the particle size. The Fe substitution for Ti controls the chemical stoichiometry and reduces the lattice distortion, i.e., c/a ratio, and hence the transition temperature reduces with Fe content. The phase structure, morphology, particle size, dc resistivity, and dielectric and magnetic properties of Pb(Fe0.012Ti0.988)O3 nanoparticles have been characterized by x-ray diffraction, transmission/scanning electron microscopy, source meter, LCR meter, and vibrating sample magnetometer. The results indicate that the nanosize particles have high resistivity, which improves the dielectric constant at high-frequency region and increases magnetization of the specimens. The observed variable-range-hopping conduction mechanism indicates that Fe doping leads to the occurrence of local defect states in the PbTiO3 lattice. The dispersionless dielectric properties with low loss are observed up to 15 MHz. The dielectric properties are improved than those obtained by the conventional process. The initial permeability values do not exhibit much variation up to ferromagnetic transition temperature after which it falls sharply. The large value of saturation magnetization is observed at room temperature

Enhanced visible fluorescence in highly transparent Al-doped ZnO film by surface plasmon coupling of Ag nanoparticles

ZnO:Al (AZO) film has been deposited on quartz substrate by Pulsed laser deposition and showed monophasic hexagonal structure of c-axis oriented nanorods upto 80 nm in height. AZO film was optimally conjugated with Ag nanoparticles (Ag NPs) in a hybrid nanostructure to achieve significant enhancement in the visible fluorescence emission. Augmented near field and extinction spectra of shape tailored Ag NPs and their dimers are simulated through FDTD method, and a direct association with fluorescence enhancement is established. Such plasmon-enhanced visible emission from a transparent conducting oxide could be very important for solar cell applications

Double Perovskite Sr2FeMoO6: A Potential Candidate for Room Temperature Magnetoresistance Device Applications

The family of double perovskites first received attention in the 1960s, but the discovery of low field magnetoresistnace (LFMR) and half metallicity of the Sr2FeMoO6 (SFMO) compound was made by Kobayashi et al. in 1998. A fully spin polarized half-metal SFMO (Tc > 400) with excellent magnetoresistance response relatively at small applied fields and high temperatures makes SFMO an ideal candidate for room temperature spintronics applications. Primarily, most of the research work on double perovskites SFMO has been focused on bulk ceramic samples and aimed to understand their structural, magnetic, and magnetotransport properties, along with correlation among them. A material such as SFMO that exhibits a large decrease in resistivity and magnetically order well above room temperature is necessary for the advancement of spintronic devices. If the bulk properties observed could be reproduced in thin films, industrially produced SFMO-based spintronic devices could become a reality. Therefore, the purpose of this chapter is to present the detailed background and descriptions of the double perovskite Sr2FeMoO6 (SFMO) thin films and heterostructures with main emphasis to improve or achieve room temperature magnetoresistance properties especially for room temperature magnetoresistive device applications

Giant magnetoelectric coupling interaction in BaTiO3/BiFeO3/BaTiO3 trilayer multiferroic heterostructures

Multiferroic trilayer thin films of BaTiO3/BiFeO3/BaTiO3 were prepared by RF-magnetron sputtering technique at different thicknesses of BiFeO3 layer. A pure phase polycrystalline growth of thin films was confirmed from X-ray diffraction results. The film showed maximum remnant electric polarization (2P(r)) of 13.5 mu C/cm(2) and saturation magnetization (M-s) of 61 emu/cc at room temperature. Thermally activated charge transport dominated via oxygen vacancies as calculated by their activation energy, which was consistent with current-voltage characteristics. Magnetic field induced large change in resistance and capacitance of grain, and grain boundary was modeled by combined impedance and modulus spectroscopy in the presence of varied magnetic fields. Presence of large intrinsic magnetoelectric coupling was established by a maximum 20% increase in grain capacitance (C-g) with applied magnetic field (2 kG) on trilayer having 20 nm BiFeO3 layer. Substantially higher magnetoelectric coupling in thinner films has been observed due to bonding between Fe and Ti atoms at interface via oxygen atoms. Room temperature magnetoelectric coupling was confirmed by dynamic magnetoelectric coupling, and maximum longitudinal magnetoelectric coupling of 515 mV/cm-Oe was observed at 20 nm thickness of BiFeO3. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications for obtaining higher voltage at lower applied magnetic field