Anomalous magnetism of Pr in PrCoAsO

Detailed magnetization and magneto-transport measurements studies are carried out to unearth the anomalous magnetism of Pr in PrCoAsO compound. The studied PrCoAsO sample is single phase and crystallized in the tetragonal structure with space group P4/nmm in analogy of ZrCuSiAs type compounds. Detailed magnetization measurements showed that Co moments in PrCoAsO exhibit weakly itinerant ferromagnetic Co spins ordering at below 80 K with a small magnetic moments of similar to 0.12 mu B/f.u. High temperatures Curie-Weiss fit, resulted in effective paramagnetic moment mu(eff) (exp) of 5.91 mu(B)/f.u., which can be theoretically assigned to 3d Co (3.88 mu(B)) and 4f Pr (3.58 mu(B)). Further, a positive Curie-Weiss temperature (Theta) of 136 K is seen, indicating predominant ferromagnetic interactions in PrCoAsO. Detailed transport measurements showed that PrCoAsO exhibit metallic behavior and negative magneto-resistance below ferro-magnetically (FM) ordered state. Surprisingly, the situation of PrCoAsO is similar to non magnetic La containing LaCoAsO and strikingly different than that as reported for magnetic Nd, Sm and Gd i.e., (Nd/Sm/Gd)CoAsO. The magnetic behavior of PrCoAsO being closed to LaCoAsO and strikingly different to that of (Nd/Sm/Gd)CoAsO is unusual. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Magnetic and dielectric interactions in nano zinc ferrite powder: Prepared by self-sustainable propellant chemistry technique

The structural, magnetic and dielectric properties of nano zinc ferrite prepared by the propellant chemistry technique are studied. The PXRD measurement at room temperature reveal that the compound is in cubic spinel phase, belong to the space group Fd (3) over barm. The unit cell parameters have been estimated from Rietveld refinement. The calculated force constants from FTIR spectrum corresponding to octahedral and tetrahedral sites at 375 and 542 cm(-1) are 6.61 x 10(2) and 3.77 x 10(2) N m(-1) respectively; these values are slightly higher compared to the other ferrite systems. Magnetic hysteresis and EPR spectra show superparamagnetic property nearly to room temperature due to comparison values between magnetic anisotropy energy and the thermal energy. The calculated values of saturation magnetization, remenant magnetization, coercive field and magnetic moment supports for the existence of multi domain particles in the sample. The temperature dependent magnetic field shows the spin freezing state at 30 K and the blocking temperature at above room temperature. The frequency dependent dielectric interactions show the variation of dielectric constant, dielectric loss and impedance as similar to other ferrite systems. The AC conductivity in the prepared sample is due to the presence of electrons, holes and polarons. The synthesized material is suitable for nano-electronics and biomedical applications. (C) 2014 Elsevier B.V. All rights reserved.

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.

Synthesis and Characterization of CoFe2O4/Polyaniline Nanocomposites for Electromagnetic Interference Applications

The Cobalt ferrite (CoFe2O4) powders were synthesized by Co-precipitation method. The as prepared ferrite powders were incorporated into a polyaniline matrix at various volumetric ratios. The as prepared composites of ferrite and polyaniline powders were characterized using X-ray diffraction (XRD), transmission electron microscope (TEM). The particle size of CoFe2O4 is found to be 20 nm. The saturation magnetization (M-s) of all the composites was found to be decreasing with decrease of ferrite content, while coercivity (H-c) remained at the value corresponding to pure cobalt ferrite nanopowders. The complex permittivity (epsilon' and epsilon `') and permeability (mu' and mu `') of composite samples were measured in the range of 1 MHz to 1.1 GHz. The value of epsilon' and mu' found to be increased with ferrite volume concentration.

Reentrant Superspin Glass Phase in a La0.82Ca0.18MnO3 Ferromagnetic Insulator

We report results of the magnetization and ac susceptibility measurements down to very low fields on a single crystal of the perovskite manganite, La-0.82 Ca-0.18 MnO3. This composition falls in the intriguing ferromagnetic insulator region of the manganite phase diagram. In contrast to earlier beliefs, our investigations reveal that magnetically (and in every other sense), this is a single- phase system with a ferromagnetic ordering temperature of around 170 K. However, this ferromagnetic state is magnetically frustrated, and the system exhibits pronounced glassy dynamics below 90 K. Based on measured dynamical properties, we propose that this quasi-long-ranged ferromagnetic phase, and the associated superspin glass behavior, is the true magnetic state of the system, rather than being a macroscopic mixture of ferromagnetic and antiferromagnetic phases, as often suggested. Our results provide an understanding of the quantum phase transition from an antiferromagnetic insulator to a ferromagnetic metal via this ferromagnetic state as a function of x in La1-xCaxMnO3, in terms of the possible formation of magnetic polarons.

Dielectric relaxation and anti-ferromagnetic coupling of BiEu03 and BiGd03

BiEuO3 (BE) and BiGdO3 (BG) are synthesized by the solid-state reaction technique. Rietveld refinement of the X-ray diffraction data shows that the samples are crystallized in cubic phase at room temperature having Fm3m symmetry with the lattice parameters of 5.4925(2) and 5.4712(2) A for BE and BG, respectively. Raman spectra of the samples are investigated to obtain the phonon modes of the samples. The dielectric properties of the samples are investigated in the frequency range from 42 Hz to 1.1 MHz and in the temperature range from 303 K to 673 K. An analysis of the real and imaginary parts of impedance is performed assuming a distribution of relaxation times as confirmed by the Cole-Cole plots. The frequency-dependent maxima in the loss tangent are found to obey an Arrhenius law with activation energy similar to 1 eV for both the samples. The frequency-dependent electrical data are also analyzed in the framework of conductivity formalism. Magnetization of the samples are measured under the field cooled (EC) and zero field cooled (ZFC) modes in the temperature range from 5 K to 300 K applying a magnetic Field of 500 Oe. The FC and ZFC susceptibilities show that BE is a Van Vleck paramagnetic material with antiferromagnetic coupling at low temperature whereas BG is an anti-ferromagnetic system. The results are substantiated by the M-11 loops of the materials taken at 5 K in the ZFC mode. (C) 2014 Elsevier B.V. All rights reserved

Structural and thermodynamic properties of Fe1.12Te with multiple phase transitions

The parent compound of iron chalcogenide superconductors, Fe1+yTe, with a range of excess Fe concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature synchrotron X-ray powder diffraction, magnetization, and specific heat measurements. Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples possessing excess Fe content in the range of 0.11 <= y <= 0.13. On cooling, an antiferromagnetic transition, T-N approximate to 57K is observed. A closer examination of powder diffraction data suggests that the transition at TN is not purely magnetic, but accompanied by the commencement of a structural phase transition from tetragonal to orthorhombic symmetry. This is followed by a second prominent first-order structural transition at T-S with T-S < T-N, where an onset of monoclinic distortion is observed. The results point to a strong magneto-structural coupling in this material. (C) 2014 AIP Publishing LLC.

Dynamics of a driven magneto-martensitic ribbon

We investigate the dynamics of a sinusoidally driven ferromagnetic martensitic ribbon by adopting a recently introduced model that involves strain and magnetization as order parameters. Retaining only the dominant mode of excitation we reduce the coupled set of partial differential equations for strain and magnetization to a set of coupled ordinary nonlinear equations for the strain and magnetization amplitudes. The equation for the strain amplitude takes the form of parametrically driven oscillator. Finite strain amplitude can only be induced beyond a critical value of the strength of the magnetic field. Chaotic response is seen for a range of values of all the physically interesting parameters. The nature of the bifurcations depends on the choice of temperature relative to the ordering of the Curie and the martensite transformation temperatures. We have studied the nature of response as a function of the strength and frequency of the magnetic field, and magneto-elastic coupling. In general, the bifurcation diagrams with respect to these parameters do not follow any standard route. The rich dynamics exhibited by the model is further illustrated by the presence of mixed mode oscillations seen for low frequencies. The geometric structure of the mixed mode oscillations in the phase space has an unusual deep crater structure with an outer and inner cone on which the orbits circulate. We suggest that these features should be seen in experiments on driven magneto-martensitic ribbons. (C) 2014 Elsevier B. V. All rights reserved.

Epitaxial Co metal thin film grown by pulsed laser deposition using oxide target

We report here the growth of epitaxial Co metal thin film on c-plane sapphire by pulsed laser deposition (RD) using Co:ZnO target utilizing the composition inhomogeneity of the corresponding plasma. Two distinct plasma composition regions have been observed using heavily alloyed Co0.6Zn0.4O target. The central and intense region of the plasma grows Co:ZnO film; the extreme tail grows only Co metal with no trace of either ZnO or Co oxide In between the two extremes, mixed phases (Co +Co-oxides +Co:ZnO) were observed. The Co metal thin film grown in this way shows room temperature ferromagnetism with large in plane magnetization similar to 1288 emu cm(-3) and a coerciviLy of similar to 230 Oe with applied field parallel to the film-substrate interface. Carrier density of the film is similar to 10(22) cm(-3). The film is epiLaxial single phase Co metal which is confirmed by both X-ray diffraction and transmission electron microscopy characierizaLions. Planar Hall Effect (PHE) and Magneto Optic Kerr Effect (MOKE) measurements confirm that the film possesses similar attributes of Co metal. The result shows that the epiLaxial Co metal thin film can be grown from its oxides in the PLD. (C) 2014 Elsevier B.V. All rights reserved.

Magneto-structural study of the multiferroic BiFeo(3)-SrTiO3

The structural and magnetic study of the pseudo-binary multiferroic (1 x)BiFeO3 (x)SrTiO3 has been investigated as a function of composition and temperature. In contrary to the previous studies, detailed examination revealed that the reported anomaly in the magnetization at x-0.30 does not occur at the composition induced rhombohedral-cubic phase boundary, but within the rhombohedral phase itself. The rhombohedral to cubic transition occurs at x > 0.4. Evidence of magneto-elastic coupling near the Neel temperature and nucleation-growth mode of the rhombohedral-cubic transformation, with both the phases coexisting over a range of temperature was found. (C) 2014 Elsevier B.V. All rights reserved.

Effect of Zn substitution on the structural and magnetic properties of Ni-Co ferrites

A series of ferrite samples with the compositional formula, Ni0.5Co0.5-xZnxFe2O4 (0 <= x <= 0.5), was prepared using the citrate based sol gel method for the better understanding of zinc doping on the structural and magnetic properties. The Rietveld-refined X-ray diffraction data revealed that the samples are having cubic structure with the Fd-3m space group. The lattice parameter increased linearly with increasing Zn content. The surface morphology and stoichiometric ratio of the compositional elements were analyzed by scanning electron microscopy equipped with energy dispersive spectroscopy (EDS). EDS showed that the elemental ratios were stoichiometric. An examination of the magnetic properties revealed an increase in saturation magnetization with increasing Zn concentration up to x=0.3 and a decrease thereafter. These results could be explained using Neel's collinear two-sub-lattice model and three-sub-lattice non-collinear model suggested by Yafet and Kittel. The magnetic cubic anisotropy constant determined by the law of approach to saturation decreased with increasing Zn content. The underlying mechanism behind observed behavior was discussed qualitatively. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

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.

Studies on a frustrated Heisenberg spin chain with alternating ferromagnetic and antiferromagnetic exchanges

We study Heisenberg spin-1/2 and spin-1 chains with alternating ferromagnetic (J(1)(F)) and antiferromagnetic (J(1)(A)) nearest-neighbor interactions and a ferromagnetic next-nearest-neighbor interaction (J(2)(F)). In this model frustration is present due to the non-zero J(2)(F). The model with site spin s behaves like a Haldane spin chain, with site spin 2s in the limit of vanishing J(2)(F) and large J(1)(F)/J(1)(A). We show that the exact ground state of the model can be found along a line in the parameter space. For fixed J(1)(F), the phase diagram in the space of J(1)(A)-J(2)(F) is determined using numerical techniques complemented by analytical calculations. A number of quantities, including the structure factor, energy gap, entanglement entropy and zero temperature magnetization, are studied to understand the complete phase diagram. An interesting and potentially important feature of this model is that it can exhibit a macroscopic magnetization jump in the presence of a magnetic field; we study this using an effective Hamiltonian.

Correlating defect induced ferromagnetism and gas sensing properties of undoped tin oxide sensors

A correlation between gas sensing properties and defect induced Room Temperature Ferromagnetism (RTFM) is demonstrated in non-stoichiometric SnO2 prepared by solution combustion method. The presence of oxygen vacancies (V-O), confirmed by RTFM is identified as the primary factor for enhanced gas sensing effect. The as-prepared SnO2 shows high saturation magnetization of similar to 0.018 emu/g as compared to similar to 0.002 and similar to 0.0005 emu/g in annealed samples and SnO2 prepared by precipitation respectively. The SnO2 prepared by precipitation which is an equilibrium method of synthesis shows lesser defects compared to the combustion product and hence exhibits lesser sensitivity in spite of smaller crystallite size. The study utilizes RTFM as a potential tool to characterize metal oxide gas sensors and recognizes the significance of oxygen vacancies in sensing mechanism over the microstructure. (C) 2014 AIP Publishing LLC.

Role of Cu2+ ions substitution in magnetic and conductivity behavior of nano-CoFe2O4

Cobalt copper ferrite nanopowders with composition Co1-xCu5Fe2O4 (0.0 <= x <= 0.5) was synthesized by solution combustion method. The powder X-ray diffraction studies reveal the formation of single ferrite phase with particle size of similar to 11-35 nm. Due to increase in electron density with in a material, X-ray density increase with increase of Cu2+ ions concentration. As Cu2+ ions concentration increases, saturation magnetization decreases from 38.5 to 26.7 emu g(-1). Further, the squareness ratio was found to be similar to 0.31-0.46 which was well below the typical value 1, which indicates the existence of single domain isolated ferrimagnetic samples. The dielectric and electrical modulus was studied over a frequency range of 1 Hz to 1 MHz at room temperature using the complex impedance spectroscopy technique. Impedance plots showed only one semi-circle which corresponds to the contributions of grain boundaries. The lower values of dielectric loss at higher frequency region may be quite useful for high frequency applications such as microwave devices. (C) 2014 Elsevier B.V. All rights reserved.