Physical and magnetic properties of (Co, Ag) doped ZnO nanoparticles

Undoped and (Co, Ag) co-doped ZnO nanostructure powders are synthesized by chemical precipitation method without using any capping agent and annealed in air ambient at 500 A degrees C for 1 h. Here, the Ag concentration is fixed at 5 mol% and Co concentration is increased from 0 to 5 mol%. The X-ray diffraction studies reveal that undoped and doped ZnO powders consist of pure hexagonal structure and nano-sized crystallites. The novel Raman peak at 530 cm(-1) has corroborated with the Co doped ZnO nanoparticles. Moreover, the PL studies reveal that as the Co doping concentration increases and it enters into ZnO lattice as substitutional dopant, it leads to the increase of oxygen vacancies (Vo) and zinc interstitials (Zn-i). From the magnetization measurements, it is noticed that the co-doped ZnO nanostructures exhibit considerably robust ferromagnetism i.e. 4.29 emu g(-1) even at room temperature. These (Co, Ag) co-doped ZnO nanopowders can be used in the fabrication of spintronic and optoelectronic device applications.

Versatility of azide in serendipitous assembly of Copper(II) Magnetic Polyclusters

Engineering at the molecular level is one of the most exciting new developments for the generation of functional materials. However, the concept of designing polynuclear extended structures from bottom up is still not mature. Although progress has been made with secondary building units (SBUs) in metal organic frameworks (MOFs), the control seems to be just an illusion when it comes to bridging ligands such as the azide ion. When we say that the azido ligand is versatile in its bridging capabilities, what we mean is that it would be difficult to predict or control its bridging properties. However, this kind of serendipity is not always bad news. For example, scientists have shown that the azido ligand can mediate magnetic exchanges between paramagnetic metals in a predictable fashion (usually depending upon the bonding geometries). Therefore, it is a well-respected ligand in polynuclear assemblies. Serendipitous assemblies offer new magnetic structures that we may not otherwise even think about synthesizing. The azido ligand forms a variety of complexes with copper(II) using different blocking amines or pyridine based ligands. Its structural nature changes upon changing the substitution on amine, as well as the amount of blocking ligand. In principle, if we take any of these complexes and provide more coordination sites to the bridging azido ligands by removing a fraction of the blocking ligands, we can get new complexes with intricate structural networks and therefore different magnetic properties with the same components as used for the parent complex. In this Account, we mainly discuss the development of a number of new topological and magnetic exchange systems synthesized using this concept. Not all of these new complexes can be grouped according to their basic building structures or even by the ratio of the metal to blocking ligand. Therefore, we divided the discussion by the nuclearity of the basic building structures. Some of the complexes with the same nuclearities have very similar or even almost identical basic structures. However, the way these building units are joined together (by the azido bridges) to form the overall extended structures differ almost in every case. The complexes having the Cu-6 core are particularly interesting from a structural point of view. Although they have almost identical basic structures, some of them are extended in three dimensions, but two of them are extended in two dimensions by two different bridging networks. In the complexes having linear Cu-4 basic units, we find that using similar ligands does not always give the same bridging networks even within the basic building structures. These complexes have also enriched the field of molecular magnetism. One of the complexes with a Cu-3 building unit has provided us with the opportunity to study the competing behavior of two different kinds of magnetic exchange mechanism (ferromagnetic and antiferromagnetic) acting simultaneously between two metal ions. Through density functional theory calculations, we showed how they work independently and their additive nature to produce the overall effect. The exciting methodology for the generation of copper(II) polyclusters presented in this Account will provide the opportunity to explore analogous serendipitous assembly of diverse structures with interesting magnetic behavior using other transition metal ions having more than one unpaired electrons.

Spark plasma sintered HA-Fe3O4-based multifunctional magnetic Bbiocomposites

Although HA is highly biocompatible, one of the major disadvantages of HA include the lack of antibacterial property. In an earlier study, we demonstrated the potential role of magnetic field stimulation on bactericidal property in vitro. Following this, it was hypothesized that antibacterial property can be realized if bacteria are grown on magnetic biocomposites in vitro. In addressing this issue, this study demonstrates the development of HA-Fe3O4-based magnetic substrate with multifunctional properties. For this purpose, HA-xFe(3)O(4) (x: 10, 20 and 40wt%) powder compositions were sintered using uniquely designed spark plasma sintering conditions (three stage sintering with final holding temperature of 1050 degrees C for 5min). A saturation magnetization of 24emu/g is measured with HA-40%Fe3O4. Importantly, all the HA-Fe3O4 composites demonstrated bactericidal property by rupturing the membrane of Escherichia coli bacteria, while supporting cell growth of metabolically active human fetal osteoblast cells over 8d culture. A systematic decrease in bacterial viability with Fe3O4 addition is consistent with a commensurate increase in reactive oxygen species (ROS).

Effect of low oxygen pressure on structural and magnetic properties of quenched SrFe12O19 thin films

Strontium hexaferrite thin films have been grown on glass substrates at room temperature in oxygen environment by pulsed laser deposition method. The effect of oxygen pressure (p(o2)) on the structural and magnetic properties has been investigated. The as-deposited films were found to be amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 850 A degrees C in air. The thickness of the film increased with p(o2). The film grown at p(o2) = 0.455 Pa had a clear hexagonal structure. The values of coercivity for the films were found to increase with p(o2).

Effect of zinc substitution on the nanocobalt ferrite powders for nanoelectronic devices

Zinc substituted cobalt ferrite powders {Co(1-x)ZnxFe2O4} (0.0 <= x <= 0.5) were prepared by the solution combustion method. The structural, morphological, magnetic and electrical properties of as synthesized samples were studied. Powder X-ray diffraction patterns reveals single phase, cubic spinel structure with space group No. Fd (3) over barm (227). As zinc concentration increases, the lattice constant increases and the crystallite size decreases. The minimum crystallite size of similar to 12 nm was observed for x = 0.5 composition. The synthesized ferrite compounds show ferrimagnetic behavior, with coercivity value of 10779 Oe (Hard ferrite) at 20 K and 1298 Oe (soft ferrite) at room temperature (RT). The maximum saturation magnetization recorded for the Co0.5Zn0.5Fe2O4 composition was 99.78 emu g(-1) and 63.83 emu g(-1) at 20 K and RT respectively. The dielectric parameters such as dielectric constant, loss tangent and AC conductivity were determined as a function of frequency at RT. The magnetic and dielectric properties of the samples illustrates that the materials were quite useful for the fabrication of nanoelectronic devices. (C) 2013 Elsevier B.V. All rights reserved.

Anomalous phase transitions in soft colloid-polymer binary mixtures

We have shown earlier [1] that these PGNPs resemble star polymers or spherical brushes in terms of their morphology in the melt. However, these particles show dynamics in melt which is quite different from other soft colloidal particles. Since most of the work on soft colloidal particles have been performed in solutions we have now explored the phase behavior of the PGNPs in good solvent using microscopic structural and dynamical measurements on binary mixtures of homopolymers and soft colloids consisting of polymer grafted nanoparticles. We observe anomalous structural and dynamical phase transitions of these binary mixtures, including appearance of spontaneous orientational alignment and logarithmic structural relaxations, as a function of added homopolymers of different molecular weights. Our experiments points to the possibility of exploiting the phase space in density and homopolymer size, of such hybrid systems, to create new materials with unique properties.

Magnetic Structure and Properties of the Rechargeable Battery Insertion Compound Na2FePO4F

The magnetic structure and properties of sodium iron fluorophosphate Na2FePO4F (space group Pbcn), a cathode material for rechargeable batteries, were studied using magnetometry and neutron powder diffraction. The material, which can be described as a quasi-layered structure with zigzag Fe-octahedral chains, develops a long-range antiferromagnetic order below similar to 3.4 K. The magnetic structure is rationalized as a super-exchange-driven ferromagnetic ordering of chains running along the a-axis, coupled antiferromagnetically by super-super-exchange via phosphate groups along the c-axis, with ordering along the b-axis likely due to the contribution of dipole dipole interactions.

Synthesis, Characterization, and Nuclear Magnetic Resonance Study of Chitosan-Coated Mn1-xZnxFe2O4 Nanocrystals

Ultra-fine crystallites of Mn1-xZnxFe2O4 series (0 <= x <= 1) were synthesized through wet chemical co- precipitation method followed by calcination at 200 degrees C for 4 hours. Formation of ferrites was confirmed by X-ray diffraction, TEM selected area diffraction (SAD) and Fourier Transform Infra-red Spectroscopy (FTIR). Nanocrystallites of different compositions in the series were coated with biocompatible chitosan in order to investigate their possible application as contrast agent for magnetic resonance imaging (MRI). Chitosan coating examined by FTIR, revealed a strong bonding of chitosan molecules to the surface of the ferrite nanocrystallites. Spin-spin, tau(2) relaxivities of nuclear spins of hydrogen protons of the solutions for different ferrites were measured from concentration dependence of relaxation time by nuclear magnetic resonance (NMR). All the compositions of Mn1-xZnxFe2O4 series possess higher values of tau(2) relaxivity thus making them suitable as contrast agents for tau(2) weighted imaging by MRI.

Synergistic effect of static magnetic field and HA-Fe3O4 magnetic composites on viability of S. aureus and E. coli bacteria

In addressing the issue of prosthetic infection, this work demonstrated the synergistic effect of the application of static magnetic field (SMF) and ferrimagnetic substrate properties on the bactericidal property in vitro. This aspect was studied using hydroxyapatite (HA)-xFe(3)O(4) (x=10, 20, and 40 wt.%) substrates, which have different saturation magnetization properties. During bacteria culture experiments, 100 mT SMF was applied to growth medium (with HA-xFe(3)O(4) substrate) in vitro for 30, 120, and 240 min. A combination of MTT assay, membrane rupture assays, live/dead assay, and fluorescence microscopic analysis showed that the bactericidal effect of SMF increases with the exposure duration as well as increasing Fe3O4 content in biomaterial substrates. Importantly, the synergistic bactericidal effect was found to be independent of bacterial cell type, as similar qualitative trend is measured with both gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus) strains. The reduction in E. coli viability was 83% higher on HA-40 Wt % Fe3O4 composite after 4 h exposure to SMF as compared to nonexposed control. Interestingly, any statistically significant difference in ROS was not observed in bacterial growth medium after magnetic field exposure, indicating the absence of ROS enhancement due to magnetic field. Overall, this study illustrates significant role being played by magnetic substrate compositions towards bactericidal property than by magnetic field exposure alone. (c) 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 102B: 524-532, 2014.

Effect of pH on structural and magnetic properties of nanocrystalline Y3Fe5O12 by aqueous co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesised at different pH using co-precipitation method. The effect of pH on the phase formation of YIG is characterised using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 13, 19 and 28 nm for pH=10, 11 and 12 respectively. It is found that as the pH of the solution increase the particle size is also increases. It is also clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 600, 700, 800 and 900 degrees C for 5 h using conventional sintering method. The phase formation is completed at 800 degrees C/5 h which is correlated with TG/DTA. The average grain size of the samples is found to be similar to 161 nm. The high values of M-s=23 emu g(-1) and H-c=22 Oe were recorded for the sample sintered at 900 degrees C.

Size Control and Magnetic Property Trends in Cobalt Ferrite Nanoparticles Synthesized Using an Aqueous Chemical Route

Cobalt ferrite (CoFe2O4) is an engineering material which is used for applications such as magnetic cores, magnetic switches, hyperthermia based tumor treatment, and as contrast agents for magnetic resonance imaging. Utility of ferrites nanoparticles hinges on its size, dispersibility in solutions, and synthetic control over its coercivity. In this work, we establish correlations between room temperature co-precipitation conditions, and these crucial materials parameters. Furthermore, post-synthesis annealing conditions are correlated with morphology, changes in crystal structure and magnetic properties. We disclose the synthesis and process conditions helpful in obtaining easily sinterable CoFe2O4 nanoparticles with coercive magnetic flux density (H-c) in the range 5.5-31.9 kA/m and M-s in the range 47.9-84.9 A.m(2)Kg(-1). At a grain size of similar to 54 +/- 2 nm (corresponding to 1073 K sintering temperature), multi-domain behavior sets in, which is indicated by a decrease in H-c. In addition, we observe an increase in lattice constant with respect to grain size, which is the inverse of what is expected of in ferrites. Our results suggest that oxygen deficiency plays a crucial role in explaining this inverse trend. We expect the method disclosed here to be a viable and scalable alternative to thermal decomposition based CoFe2O4 synthesis. The magnetic trends reported will aid in the optimization of functional CoFe2O4 nanoparticles

Phase transformation, improved ferroelectric and magnetic properties of (1-x) BiFeO3-xPb(Zr0.52Ti0.48)O-3 solid solutions

The authors prepared (1 - x) BiFeO3 - (x)Pb(Zr0.52Ti0.48)O-3 for x <= 0.30 by sol-gel method and investigated the material's structures, magnetic and electrical properties. Detailed Rietveld analysis of X-ray diffraction data revealed that the system retains distorted rhombohedral R3c structure for x <= 0.10 but transforms to monoclinic (Cc) structure for x > 0.10. Disappearance of some Raman modes corresponding to A1 modes and the decrease in the intensities of the remaining A1 modes with increasing x in the Raman spectra, which is a clear indication of structural modification and symmetry changes brought about by PZT doping. Enhanced magnetization with PZT doping content may be attributed to the gradual change and destruction in the spin cycloid structure of BiFeO3. The leakage current density at 3.5 kV/cm was reduced by approximately three orders of magnitude by doping PZT (x = 0.30), compared with BFO ceramics. (C) 2014 AIP Publishing LLC.

Intense Acoustic Burst Ultrasound Modulated Optical Tomography for Elasticity Mapping of Soft Biological Tissue Mimicking Phantom: A Laser Speckle Contrast Analysis Study

This report addresses the assessment of variation in elastic property of soft biological tissues non-invasively using laser speckle contrast measurement. The experimental as well as the numerical (Monte-Carlo simulation) studies are carried out. In this an intense acoustic burst of ultrasound (an acoustic pulse with high power within standard safety limits), instead of continuous wave, is employed to induce large modulation of the tissue materials in the ultrasound insonified region of interest (ROI) and it results to enhance the strength of the ultrasound modulated optical signal in ultrasound modulated optical tomography (UMOT) system. The intensity fluctuation of speckle patterns formed by interference of light scattered (while traversing through tissue medium) is characterized by the motion of scattering sites. The displacement of scattering particles is inversely related to the elastic property of the tissue. We study the feasibility of laser speckle contrast analysis (LSCA) technique to reconstruct a map of the elastic property of a soft tissue-mimicking phantom. We employ source synchronized parallel speckle detection scheme to (experimentally) measure the speckle contrast from the light traversing through ultrasound (US) insonified tissue-mimicking phantom. The measured relative image contrast (the ratio of the difference of the maximum and the minimum values to the maximum value) for intense acoustic burst is 86.44 % in comparison to 67.28 % for continuous wave excitation of ultrasound. We also present 1-D and 2-D image of speckle contrast which is the representative of elastic property distribution.

Rapid, microwave-assisted synthesis of Gd2O3 and Eu:Gd2O3 nanocrystals: characterization, magnetic, optical and biological studies

Ultra-small crystals of undoped and Eu-doped gadolinium oxide (Gd2O3) were synthesised by a simple, rapid microwave-assisted route, using benzyl alcohol as the reaction solvent. XRD, XPS and TEM analysis reveal that the as-prepared powder material consists of nearly monodisperse Gd2O3 nanocrystals with an average diameter of 5.2 nm. The nanocrystals show good magnetic behaviour and exhibit a larger reduction in relaxation time of water protons than the standard Gd-DTPA complex currently used in MRI imaging. Cytotoxicity studies (both concentration- and time-dependent) of the Gd2O3 nanocrystals show no adverse effect on cell viability, evidencing their high biological compatibility. Finally, Eu:Gd2O3 nanocrystals were prepared by a similar route and the red luminescence of Eu3+ activator ions was used to study the cell permeability of the nanocrystals. Red fluorescence from Eu3+ ions observed by fluorescence microscopy shows that the nanocrystals (Gd2O3 and Eu:Gd2O3) can permeate not only the cell membrane but can also enter the cell nucleus, rendering them candidate materials not only for MRI imaging but also for drug delivery when tagged or functionalized with specific drug molecules.

Graphene Oxide-MnFe2O4 Magnetic Nanohybrids for Efficient Removal of Lead and Arsenic from Water

We show that the hybrids of single-layer graphene oxide with manganese ferrite magnetic nanoparticles have the best adsorption properties for efficient removal of Pb(II), As(III), and As(V) from contaminated water. The nanohybrids prepared by coprecipitation technique were characterized using atomic force and scanning electron microscopies, Fourier transformed infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and surface area measurements. Magnetic character of the nanohybrids was ascertained by a vibrating sample magnetometer. Batch experiments were carried out to quantify the adsorption kinetics and adsorption capacities of the nanohybrids and compared with the bare nanoparticles of MnFe2O4. The adsorption data from our experiments fit the Langmuir isotherm, yielding the maximum adsorption capacity higher than the reported values so far. Temperature-dependent adsorption studies have been done to estimate the free energy and enthalpy of adsorption. Reusability, ease of magnetic separation, high removal efficiency, high surface area, and fast kinetics make these nanohybrids very attractive candidates for low-cost adsorbents for the effective coremoval of heavy metals from contaminated water.