Lattice defect-formulated ferromagnetism and UV photo-response in pure and Nd, Sm substituted ZnO thin films.

The induction of charge and spin in diluted magnetic semiconductor ZnO is explored for spintronic devices and its wide direct band gap (3.37 eV) and large exciton binding energy (60 meV) exhibit potential in UV photodetectors. We reported the ferromagnetic and optical properties of pure ZnO, Zn0.97Nd0.03O and Zn0.97Sm0.03O thin films. These thin films were synthesized by a metallo-organic decomposition method and annealed at 500 °C for 7 h. Rietveld refinement of the XRD data results in a wurtzite ZnO structure with Nd, Sm doping. The dopants and nanoparticle size are responsible for wurtzite structural deformation, inducing lattice strain effect, which may influence the band gap energy and high-TC ferromagnetism of ZnO. The average size of ZnO nanoparticles with Nd, Sm doping is 10 nm, confirmed with atomic force microscopy. The Raman spectra confirm the wurtzite structure of ZnO with crystalline quality and lattice defect formation with dopant Nd, Sm ions. A near-band-edge emission due to band gap energy is evaluated with photoluminescence spectra, which also involved multiple visible emissions due to oxygen vacancies. The oxygen vacancies-mediated magnetic interactions impart room temperature ferromagnetism in pure ZnO which is enhanced with Nd, Sm doping. The electron paramagnetic resonance spectra revealed the effects of defects and unpaired electrons responsible for observed room temperature ferromagnetism. The zero field cooling and field cooling magnetic measurements include antiferromagnetic interactions without any spin-glass formation. The observed ferromagnetism also correlates with first principle calculations reported for Nd, Sm-doped ZnO and suggests long-range ferromagnetic ordering attributed to defect carriers. The Nd, Sm doping into ZnO thin films significantly enhances absorption in the UV region and suggests its usability for UV detectors. Under UV irradiation (λ = 325 nm), the value of photocurrent in Nd, Sm:ZnO thin films is highly enhanced for possible use in UV sensors.

Development of electrochemical biosensor based on CNT-Fe3O4 nanocomposite to determine formaldehyde adulteration in orange juice.

An electrochemical biosensor was developed to determine formaldehyde (HCHO) adulteration commonly found in food. The current responses of various electrodes based on multiwalled carbon nanotubes (CNTs) and synthesized nanocomposite (CNT-Fe3O4) were measured using cyclic voltammetry. The nanocomposite based biosensor shows comparatively high sensitivity (527 µA mg/L-1 cm-2), low detection limit (0.05 mg/L) in linear detection range 0.05-0.5 mg/L for formaldehyde detection using formaldehyde dehydrogenase (FDH) enzyme. In real sample analysis, the low obtained RSD values (less than 1.79) and good recovery rates (more than 90%) signify an efficient and precise sensor for the selective quantification of formaldehyde in orange juice. The developed biosensor has future implications for determining formaldehyde adulteration in citrus fruit juices and other liquid foods in agri-food chain to further resolve global food safety concerns, control unethical business practices of adulteration and reduce the widespread food borne illness outbreaks.

Graphene quantum dots-based nano-biointerface platform for food toxin detection.

Due to the similar electrochemical properties to graphene oxide (GO), graphene quantum dots (GQDs) are considered as a highly potential candidate for designing an electrochemical biosensor. In this report, GQDs were synthesized having an average diameter of 7 nm and utilized for the fabrication of an electrochemical immunosensor for the detection of food toxin, aflatoxin B1 (AFB1). An electrophoretic deposition technique was utilized to deposit the chemically synthesized GQDs onto indium tin oxide (ITO)-coated glass substrate. Further, the monoclonal antibodies of AFB1 were covalently immobilized onto deposited electrode GQDs/ITO using EDC-NHS as a crosslinker. The structural and morphological studies of GQDs and conjugated anti-AFB1 with GQDs have been investigated using UV-visible spectroscopy, photoluminescence spectroscopy, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy techniques, etc. The electrochemical impedance spectroscopy and cyclic voltammetry measurements were carried out for electrical characterization and biosensing studies. This simple monodisperse GQDs-based platform yields heterogeneous electron transfer (97.63 × 10-5 cm s-1), the time constant (0.005 s) resulting in improved biosensing performance. The electrochemical immunosensor shows high sensitivity 213.88 Ω (ng mL-1)-1 cm-2. The limit of detection for standard samples and contaminated maize samples was found to be 0.03 ng mL-1 and 0.05 ng g-1, respectively, which is lower than the maximum acceptable limit according to the European Union. This result indicates its potential application for aflatoxin B1 detection in food contents. Graphical abstract ᅟ.

Electrochemical genosensor based on template assisted synthesized polyaniline nanotubes for chronic myelogenous leukemia detection.

This work reports a facile approach to synthesize polyaniline nanotubes (PANI-NT) by using manganese oxide as sacrificial templates. This template assisted polyaniline nanotubes (t-PANI-NT) were utilized as electrode material after deposition onto the indium tin oxide (ITO) coated glass substrates by using the electrophoretic technique. The structural, morphological and electrochemical characterizations of the t-PANI-NT show relatively better results compared to chemically synthesized PANI-NT (c-PANI-NT). Moreover, the t-PANI-NT/ITO electrode exhibits improved electron transfer coefficient (α = 0.63) and charge transfer rate constant (ks = 0.05912 s-1) in comparison to c-PANI-NT/ITO electrode (α = 0.56 and ks = 0.06548 s-1). The obtained t-PANI-NT/ITO electrodes have been further immobilized with biotinylated DNA sequence, specific to chronic myelogenous leukemia (CML) by using avidin-biotin as a cross-linking agent. Electrochemical impedance spectroscopy studies revealed that the genosensor displays linearity in wide range of target DNA concentration (10-6 to 10-16 M) with an outstanding differentiation ability and low detection limit of 10-16 M. The experimental results of this highly sensitive and specific genosensor with clinical samples of CML positive patients and control negative patients indicate its potential for clinical diagnostics.

Synthesis and characterization of pectin-6-aminohexanoic acid-magnetite nanoparticles for drug delivery.

In this study, we have synthesized magnetic nanocomposites of magnetite nanoparticles coated with 6-aminohexanoic acid and pectin (MAP). The size of the aqueous dispersion of the nanocomposites was 147nm with a Polydispersity index (PDI) of 0.32, and the nanocomposites were stable in NaCl up to a concentration of 0.45% (w/v) after which they aggregated. The dispersion of the nanocomposites was stable in Dulbecco's Modified Eagle's medium (DMEM) in the presence of 5 and 10% fetal bovine serum (FBS). Curcumin was used as a model drug to evaluate the potential of the nanocomposites for drug delivery applications. The release behavior of curcumin from the nanocomposites showed a biphasic pattern with initial burst release followed by a slow release, and the size of the aqueous dispersion of curcumin loaded nanocomposites was 159nm with a PDI of 0.34.

Multifunctional gold coated iron oxide core-shell nanoparticles stabilized using thiolated sodium alginate for biomedical applications.

In this paper we report synthesis of aqueous based gold coated iron oxide nanoparticles to integrate the localized surface plasma resonance (SPR) properties of gold and magnetic properties of iron oxide in a single system. Iron oxide-gold core shell nanoparticles were stabilized by attachment of thiolated sodium alginate to the surface of nanoparticles. Transmission electron microscope (TEM) micrograph presents an average elementary particle size of 8.1±2.1nm. High resolution TEM (HR-TEM) and X-ray photon spectroscopy further confirms the presence of gold shell around iron oxide core. Gold coating is responsible for reducing saturation magnetization (Ms) value from ~41emu/g to ~24emu/g - in thiolated sodium alginate stabilized gold coated iron oxide core-shell nanoparticles. The drug (curcumin) loading efficiency for the prepared nanocomposites was estimated to be around 7.2wt% (72µgdrug/mg nanoparticles) with encapsulation efficiency of 72.8%. Gold-coated iron oxide core-shell nanoparticles could be of immense importance in the field of targeted drug delivery along with capability to be used as contrast agent for MRI & CT.

Cation distribution: a key to ascertain the magnetic interactions in a cobalt substituted Mg-Mn nanoferrite matrix.

The effect of Co2+ substitution into nanocrystalline Mg-Mn ferrite synthesized by a solution combustion technique has been studied. The cation distribution has been inferred from X-ray diffraction, the magnetization technique, and Mössbauer spectroscopy. The X-ray analysis and cation distribution data have been used to investigate the detailed structural parameters such as hopping lengths, ionic radii of tetrahedral and octahedral sites, oxygen positional parameter, site bond as well as edge lengths, bond lengths, and bond angles. The variation in the theoretically predicted bond angles suggested the strengthening of the A-B super-exchange interactions, and the same has been supported by M-H and M-T, as well as by Mössbauer studies. The ZFC-FC study revealed that anisotropy increases with the incorporation of cobalt ions. The values of magneton number, theoretical lattice parameter, and Curie temperature that have been calculated by using the cation distribution are found to match well with the experimentally obtained values.

Surfactant-assisted synthesis of polythiophene/Ni0.5Zn0.5Fe2-xCexO4 ferrite composites: study of structural, dielectric and magnetic properties for EMI-shielding applications.

This work reports the exploitation of nanocrystalline Ni0.5Zn0.5Fe2-xCexO4 ferrite for potential application by designing quasi-spherical shaped polythiophene (PTH) composites via in situ emulsion polymerization. The structural, electronic, dielectric, magnetic, and electromagnetic interference (EMI) shielding properties of PTH/Ni0.5Zn0.5Fe2-xCexO4 composites were investigated. Our results suggest that these properties could be optimized by modulating the concentration of x (composition) in the polymer matrix. Higher values of ε' and ε'' were obtained on composite formation, and could be due to the heterogeneity developed in the material. An enhancement in the value of saturation magnetization (123 emu g-1 for x = 0.04) and Curie temperature was obtained with Ce concentration, which is useful for high density recording purposes. A low value of saturation magnetization was obtained for the PTH/Ni0.5Zn0.5Fe2-xCexO4 composite (36 emu g-1 for x = 0.04). This could be attributed to the non-magnetic nature of the polymer. A total shielding effectiveness (SET = SEA + SER) up to 34 dB (≈99.9% attenuation) was recorded for PTH/Ni0.5Zn0.5Fe2-xCexO4 composites (x = 0.04) in a frequency range of 8.2-12.4 GHz (X-band), which surpasses the shielding criteria of SET > 30 dB for commercial purposes. Such a material with high SE identifies its potential for making electromagnetic shields. The effect of Ce substitution on the microstructure, dielectric, impedance and magnetic properties of PTH/Ni0.5Zn0.5Fe2-xCexO4 ferrite composites was also investigated. X-ray diffraction analysis confirmed cubic spinel phase formation, and the broad reflection peaks indicated the formation of smaller sized particles. The smaller energy band gap (2.53 eV) of the composite indicated that this material could be used for photocatalysis in the visible region. Dielectric and impedance measurements were carried out in a frequency range of 8.2-12.4 GHz. Dielectric properties were improved considerably by the substitution of Ce3+ ions in PTH/Ni0.5Zn0.5Fe2-xCexO4 composites. Impedance spectroscopy was used to study the effect of grain and grain boundaries on the electrical properties of PTH/Ni0.5Zn0.5Fe2-xCexO4 composites. Cole-Cole plots showed the formation of single semi-circles for all samples in the measured frequency range. This showed that the composite material was composed of good conducting grains and poorly conducting grain boundaries.

Realizing ferromagnetic ordering in SnO2 and ZnO nanostructures with Fe, Co, Ce ions.

We report the defects/vacancies that attribute to room temperature ferromagnetism in SnO2 in contrast to ZnO [Phys. Chem. Chem. Phys., 2016, 18, 5647], which has observed ferromagnetic ordering below room temperature, since both the systems involve similar dopant Fe, Co, and Ce ions. The Fe, Co, Ce doped SnO2 nanostructures were synthesized by a sol-gel process. The Rietveld refinement of the X-ray diffraction data detects a rutile SnO2 structure, with structural defects due to the deformation of the unit cell with doping. The pure, Fe and Co doped SnO2 have nanoparticle formation that is induced to nanorods with Ce co-doping. However, ZnO retained a nanorod-type shape with Fe and Co ions and changed to nanoparticles with Ce co-doping. The rutile SnO2 structure and defect formation with Fe, Co, and Ce ions is also confirmed with Raman vibrational modes. The observed lattice defects due to oxygen vacancies are shown by the photoluminescence study. The weak room temperature ferromagnetism is observed with Fe and Co ions in SnO2, which is enhanced with Ce ions. The zero field (ZFC) and field cooling magnetic measurements indicate an improvement in magnetization with a cusp in the ZFC curve at low temperature, observed due to an antiferromagnetic transition. It also induced variations in the magnetic coercive field due to the phenomenon of superparamagnetism, spin glasses, and magnetic clustered growth. This can be further confirmed with ac magnetic susceptibility measurements that show magnetic transitions as well as frequency dispersive and dependent behaviors of χ'(T)/χ''(T). However, the Fe, Co, Ce doped ZnO exhibit paramagnetic behavior at room temperature due to favorable antiferromagnetic interactions and have a ferromagnetic transition at low temperature with little ferromagnetic cluster growth.

Defects-assisted ferromagnetism due to bound magnetic polarons in Ce into Fe, Co:ZnO nanoparticles and first-principle calculations.

Zn0.94TM0.03Ce0.03O [Zn0.94Fe0.03Ce0.03O (ZFCeO) and Zn0.94Co0.03Ce0.03O (ZCCeO)] nanoparticles were synthesized by a sol-gel process. Elemental analysis of these nanoparticles detects the weight percentage of Zn, Co, Fe, Ce and O in each sample. The Rietveld refinement of the X-ray diffraction pattern obtains the occupancy of dopant atoms, Wurtzite ZnO structure, crystallinity and lattice deformation with doping. The Ce doping into ZFO and ZCO form nanoparticles than nanorods was observed in pure ZnO, ZFO and ZCO samples that described due to chemical and ionic behavior of Ce, Fe, Co and Zn ions. The Raman active modes have peak broadening, intensity changes and peak shifts with metal doping that induces lattice defects. Photoluminescence spectra show blue-shifts at near-band edges and defects that influence broad visible emission with Ce doping. An enhancement in ferromagnetism in the magnetic hysteresis at 5 K is measured. The zero-field cooling and field cooling at H = 500 Oe and T = 300-5 K could confirm antiferromagnetic interactions mediated by defect carriers. The bound magnetic polaron at defect sites is responsible for the observed ferromagnetism. The ac magnetic susceptibility measurements determine the antiferromagnetic to ferromagnetic transition with some magnetic clustered growth in the samples and reveal a frequency independent peak that shows the Neel temperature. Weak room temperature ferromagnetism and optical quenching in ZFCeO are described by valance states of Fe and Ce ions, respectively. Using first-principle calculations, we studied the occupancy of Ce (replacing Zn atoms) in the Wurtzite structure.

Fe3C-filled carbon nanotubes: permanent cylindrical nanomagnets possessing exotic magnetic properties.

The present study aims to deduce the confinement effect on the magnetic properties of iron carbide (Fe3C) nanorods filled inside carbon nanotubes (CNTs), and to document any structural phase transitions that can be induced by compressive/tensile stress generated within the nanorod. Enhancement in the magnetic properties of the nanorods is attributed to tensile stress as well as to compression, present in the radial direction and along the nanotube axis, respectively. Finally, the growth of permanent cylindrical nanomagnets has been optimized by applying a field gradient. Besides presenting the growth model of in situ filling, we have also proposed the mechanism of magnetization of the nanotubes. Magnetization along the tube axis has been probed by confirming the pole formation. Fe3C has been selected because of its ease of formation, low TC and incompressibility.

Strong Magnetoelectric Coupling of Pb1-xSrx(Fe0.012Ti0.988)O3 Nanoparticles.

Pb1-xSrx(Fe012Ti0.988)O3 (PSFT) nanoparticles were prepared by a chemical synthesis using polyvinyl alcohol as surfactant. X-ray diffraction pattern has been used to analyze the phase structure and average particles size. Transmission electron microscopy is used to confirm the nano size of the PSFT particles. The magnetoelectric (ME) coupling is observed at room temperature by measuring the ME coefficient (αE) as the function of applied dc magnetizing field under the influence of ac magnetic field of 2 Oe and frequency 800 Hz. The maximal value of αE is observed in PSFT3. The ME coupling is also studied by observing the variation of polarization hysteresis measured in the presence of zero and 0.2 T of external magnetic field.

Interfacial Charge Induced Magnetoelectric Coupling at BiFeO3/BaTiO3 Bilayer Interface.

Bilayer thin films of BiFeO3-BaTiO3 at different thicknesses of BiFeO3 were prepared by RF-magnetron sputtering technique. A pure phase polycrystalline growth of thin films was confirmed from XRD results. Significantly improved ferroelectric polarization (2Pr ∼ 30 µC/cm(2)) and magnetic moment (Ms ∼ 33 emu/cc) were observed at room temperature. Effect of ferroelectric polarization on current conduction across the interface has been explored. Accumulation and depletion of charges at the bilayer interface were analyzed by current-voltage measurements which were further confirmed from hysteretic dynamic resistance and capacitance voltage profiles. Magnetoelectric coupling due to induced charges at grain boundaries of bilayer interface was further investigated by room temperature magnetocapacitance analysis. A room temperature magnetocapacitance was found to originate from induced charge at the bilayer interface which can be manipulated by varying the thickness of BFO to obtain higher ME coupling coefficient. Dynamic magnetoelectric coupling was investigated, and maximum longitudinal magnetoelectric coupling was observed to be 61 mV/cm·Oe at 50 nm thickness of BiFeO3. The observed magnetoelectric properties are potentially useful for novel room temperature magnetoelectric and spintronic device applications.

Temperature tuned defect induced magnetism in reduced graphene oxide.

The existence of ferromagnetism in the wonder material graphene has opened up the path for many future spintronics and memory applications. But simultaneously it is very important to understand the variation of these properties with temperature in regards to the device applications. Here we observed defect induced ferromagnetism in chemically reduced graphene and the effect of temperature on it. Several theoretical studies have proved that the main cause of ferromagnetism in graphene is due to various defects. The observed results established that these defects can be mended by treating the samples at elevated temperatures but sacrificing the ferromagnetism simultaneously. Hence, temperature plays a crucial role in controlling the magnetism as well as the defects in graphene. In this study we revealed that at 600 °C the self-repair mechanism helps the defects to mend but resulting in the decrement of magnetization and providing a good quality graphene with less defects.

Defect induced photoluminescence and ferromagnetic properties of bio-compatible SWCNT/Ni hybrid bundles.

Designing of bio-compatible nanomagnets with multiple functionalities receives immense scientific attention due to their potential applications in bio-labeling, medical diagnosis and treatment. Here we report the synthesis of Nickel (Ni) incorporated single-walled carbon nanotube (SWCNT) hybrid and bio-compatible bundles having interesting magnetic and photoluminescence (PL) properties. The SWCNT exhibits a high-crystallinity and it has an average diameter of ∼1.7 nm. Ni particles of 10-20 nm were incorporated within the SWCNT bundles. These hybrid bundles exhibit PL and it is attributed to the presence of delocalized π electrons and their recombination at the defective sites of SWCNT. Magnetic characterization revealed that the SWCNT/Ni hybrid bundle possesses a high (50 Oe) coercivity compared to bulk Ni and a long range ferromagnetic ordering at room temperature. MTT-assay has been conducted to study the cytotoxicity of these hybrid nanostructures.

Direct evidence for multiferroic magnetoelectric coupling in 0.9BiFeO3-0.1BaTiO3.

Magnetic, dielectric and calorimetric studies on 0.9BiFeO3-0.1BaTiO3 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 Tc 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.

Magnetic properties of iron nanoparticles prepared by exploding wire technique.

Nanoparticles of iron were prepared in distilled water using very thin iron wires and sheets, by the electro-exploding wire technique. Transmission electron microscopy reveals the size of the nanoparticles to be in the range 10 to 50 nm. However, particles of different sizes can be segregated by using ultrahigh centrifuge. X-ray diffraction studies confirm the presence of the cubic phase of iron. These iron nanoparticles were found to exhibit fluorescence in the visible region in contrast to the normal bulk material. The room temperature hysteresis measurements upto a field of 1.0 tesla were performed on a suspension of iron particles in the solution as well as in the powders obtained by filtration. The hysteresis loops indicate that the particles are superparamagnetic in nature. The saturation magnetizations was approximately 60 emu/gm. As these iron particles are very sensitive to oxygen a coating of non-magnetic iron oxide tends to form around the particles giving it a core-shell structure. The core particle size is estimated theoretically from the magnetization measurements. Suspensions of iron nanoparticles in water have been proposed to be used as an effective decontaminant for ground water.