Publications

Recent Publications

The magnetic characterization of Fe doped TiO2 semiconducting oxide nanoparticles synthesized by sol-gel method

Abstract

In this work Fe doped TiO2 nanoparticles were synthesized at different Fe/Ti molar ratio from 1% to 5% by solgel technique. The post annealing of the samples was carried out at T=400, 600, and 800 degrees C. HRTEM of the samples revealed that the mean size of the nanoparticles increases from about 8 nm to about 100 nm as the annealing temperature increased. SQUID magnetometry of 1% and 5% Fe doped TiO2 has shown mixed ferromagnetic and paramagnetic phases within the crystal while ferromagnetic order with T-c about 350 K was only observed in 5% Fe: TiO2 sample annealed at T=800 degrees C. The oxygen vacancy mediated ferromagnetic (FM) interaction could be responsible for the observed FM.

X-ray photoemission spectroscopy investigation of Ce1-xEuxCrO3 nano-powders

Abstract

To reveal the surface elemental composition and chemical states of the Ce1-xEuxCrO3 nano-powders (x = 0.0, 0.3, 0.5, 0.7, 0.8, 1.0), X-ray photoelectron spectroscopy was carried out in two conditions of before and after surface cleaning. This surface characterization described the core level binding energies of cerium, europium and chromium with different oxidation states. These results verified the morphology of the particles' surface which can be a confirmation of the spin disorder in these core-shell structures. The effect of surface Ar sputtering on the oxidation states were studied. Copyright (C) 2016 John Wiley & Sons, Ltd.

Anomalous fermi liquid state in pyrochlore heavy electron superconductor Cd2Re2O7

Abstract

Cd2Re2O7 is a pyrochlore superconductor with a transition temperature T-c near 2 K. We report on the electronic background of Cd2Re2O7 at temperatures above and below T-c as determined from the far infrared optical properties. In the normal state at low temperatures and frequencies, Cd2Re2O7 behaves as a mass enhanced Fermi liquid. Comparing the coefficients of the quadratic frequency and temperature dependence of the optical- and dc-resistivities leads to the conclusion that Cd2Re2O7 is an anomalous Fermi liquid with contributions to the scattering from elastic processes. In the superconducting state the elastic scattering is found to be somewhat reduced. We also find evidence for a weak pseudogap-like feature which may be due to the hybridization of the localized and itinerant-electron states. The superconducting state magnetic penetration depth extracted from the imaginary part of the optical conductivity is a relatively large value of lambda(T = 0.5 K) approximate to 200 angstrom. (C) 2016 Elsevier B.V. All rights reserved.

Low-Temperature Electrical Resistivity of Bilayered LaSr2Mn2O7 Manganite

Abstract

Low-temperature transport and magneto-resistance properties were systemically studied for the bilayered polycrystalline LaSr2Mn2O7 manganite under an applied magnetic field from 0 to 9 T. The results obtained from the resistivity measurements between 70 and 130 K were fitted using the electron-electron (e-e) and electron-magnon (e-m) scattering models. The temperature dependence of resistivity showed an upturn behavior at low temperatures (similar to T < 45 K) under various applied magnetic fields. Best fits were obtained by using a variable-range hopping model. The magneto-resistance behavior observed at low temperatures supports the magnetic properties of the sample.

Magnetic structure, magnetoelastic coupling, and thermal properties of EuCrO3 nanopowders

Abstract

We carried out detailed studies of the magnetic structure, magnetoelastic coupling, and thermal properties of EuCrO3 nanopowders from room temperature to liquid helium temperature. Our neutron powder diffraction and x-ray powder diffraction measurements provide precise atomic positions of all atoms in the cell, especially for the light oxygen atoms. The low-temperature neutron powder diffraction data revealed extra Bragg peaks of magnetic origin, which can be attributed to a G(x) antiferromagnetic structure with an ordered moment of similar to 2.4 mu(B) consistent with the 3d(3) electronic configuration of the Cr3+ cations. Apart from previously reported antiferromagnetic and ferromagnetic transitions in EuCrO3 at low temperatures, we also observed an anomaly at about 100 K. This anomaly was observed in the temperature dependence of the sample's, lattice parameters, thermal expansion, Raman spectroscopy, permittivity, and conductance measurements. This anomaly is attributed to the magnetoelastic distortion in the EuCrO3 crystal.

Competing Jahn-Teller distortions and hydrostatic pressure effects in the quasi-one-dimensional quantum ferromagnet CuAs2O4

Abstract

CuAs2O4 is a S = 1/2 quasi-one-dimensional ribbon chain compound which orders ferromagnetically at 7.4 K under ambient conditions. CuAs2O4 features nearest-and next-nearest-neighbor spin-exchange interactions along the spin chains with a ratio alpha = J(nn)/(Jnnn) in close proximity to the quantum critical point at alpha = -4. We apply hydrostatic pressure up to similar to 11.5 GPa and examine the structural and magnetic properties using Raman spectroscopy, single-crystal synchrotron x-ray diffraction, and magnetic susceptibility measurements. External pressure severely reduces the axial Jahn-Teller elongations of the oxygen octahedra surrounding the Cu2+ cations and stabilizes the ferromagnetic ground state. At 9.2(2) GPa, we detect a structural phase transition leading to an increased twisting of the CuO2 ribbon chains and a large drop of the magnetic ordering temperature. Ab initio density functional theory calculations of the spin-exchange parameters, using the structural parameters as a function of pressure, support the experimental findings.

The effect of quasiparticle self-energy on Cd2Re2O7 superconductor

Abstract

The magnitude and the temperature dependence of the superconducting order parameter Delta(T) of single crystals of Cd2Re2O7 (T-c = 1.02 K) was measured using point-contact spectroscopy. To fit the conductance spectra and to extract the order parameter at different temperatures we generalized the Blonder-Tinkham-Klapwijk theory by including the self-energy of the quasiparticles into the Bogoliubov equations. This modification enabled excellent fits of the conductance spectra. Delta(T) increases steeply below the superconducting transition temperature of 1.02 K and levels off below similar to 0.8 K at a value of 0.22(1) meV, approximate to 40\% larger than the BCS value. Our results indicate the presence of a strong electron-phonon interaction and an enhanced quasiparticle damping and may be related to a possible phase transition within the superconducting region at similar to 0.8 K.

Exchange bias effect and glassy-like behavior of EuCrO3 and CeCrO3 nano-powders

Abstract

The magnetic properties of nano-sized EuCrO3 and CeCrO3 powders, synthesized by a solution combustion method, were investigated using DC/AC magnetization measurements. An exchange bias effect, magnetization irreversibility and AC susceptibility dispersion in these samples provided evidence for the presence of the spin disorder magnetic phase. The exchange bias phenomenon, which is assigned to the exchange coupling between the glassy-like shell and canted antiferromagnetic core, showed the opposite sign in EuCrO3 and CeCrO3 at low temperatures, suggesting different exchange interactions at the interfaces in these compounds. We also observed a sign reversal of exchange bias in CeCrO3 at different temperatures. (C) 2015 AIP Publishing LLC.

Mechanism of sign crossover of the anisotropic magneto-resistance in La0.7-xPrxCa0.3MnO3 thin films

Abstract

Magneto-resistive anisotropy (AMR) has been studied in 45 nm thick La0.7-xPrxCa0.3MnO3 (LPCMO) manganite films (with Pr doping x between 0 and 0.40) deposited on LaAlO3 (LAO) and SrTiO3 (STO) substrates. The AMR in compressively strained films undergoes a sign change from positive to negative at low temperatures, whereas its sign does not change in films subjected to tensile strain. Temperature dependence of magnetization in a magnetic field applied parallel and perpendicular to the (100)-plane of the films shows that at low temperatures strain-induced rotation of the easy-axis magnetization determines the sign of the AMR. At higher temperatures near the T-MI the sign of the AMR is the same in both LPCMO/LAO and LPCMO/STO films, suggesting the dominating influence of percolative transport in the plane of these films at these temperatures. (C) 2015 AIP Publishing LLC.

Placing a crown on Dy-III - a dual property Ln(III) crown ether complex displaying optical properties and SMM behaviour

Abstract

Two mononuclear Dy-III crown ether complexes {[}Dy(15C5)(H2O)(4)](ClO4)(3)center dot(15C5)center dot H2O (1) and {[}Dy(12C4)(H2O)(5)](ClO4)(3)center dot H2O (2) have been prepared and characterized. X-ray diffraction studies show that both compounds crystallize as half sandwich type structures with muffin and pseudo-capped square antiprismatic geometries respectively. Despite the comparable local environments of the Dy-III ions they display remarkably different dynamic magnetic properties with only 1 displaying SMM properties in zero field. The solid state emission spectra for both 1 and 2 display sharp bands associated with f-f transitions. From the fine structure of the F-4(9/2) -> H-6(15/2) band, the Stark splitting of the H-6(15/2) ground state permitted the energy difference between the ground and first excited state to be determined. For 1 this value (Delta E = 58.0 +/- 3.0 cm(-1) ) is in excellent agreement with ab initio calculations and the experimentally observed SMM behaviour. For 2, the photoluminescence data and theoretical calculations support a less well isolated ground state (Delta E = 30 +/- 3.0 cm(-1)) in which a rapid relaxation process affords no SMM behaviour in zero-field.

DC magnetization studies of nano- and micro-particles of bilayered manganite LaSr2Mn2O7

Abstract

Systematic studies of the magnetic properties of LaSr2Mn2O7 as a function of crystalline grain size provide information on how the crystalline grain size affects the magnetic and charge ordering in this compound. The half-doped bilayered manganite LaSr2Mn2O7 (x = 0.5) in its bulk form has the CE-type anti-ferromagnetic (CE-AFM) charge ordering phase transition. In this work, we prepare LaSr2Mn2O7 ceramic samples using the Pechini sol-gel method in order to produce different grain sizes, and the effects of different crystalline grain sizes between 200 and 1000 nm on the magnetic properties of the compound, obtained by a SQUID magnetometer, are investigated. The DC magnetization (DCM) measurements for all samples indicate that the crystalline grain size has no considerable effect on the charge ordering transition temperature, T-CO (just a few degrees shift to lower temperatures as the grain sizes become bigger). The width of the peak observed in these measurements (transition to the charge ordering phase) becomes broader, and susceptibility measurement at the zero field cooling (ZFC) and filed cooling (FC) increases as the grain size becomes systematically smaller. The results obtained from the magnetic hysteresis curves confirm the ground state phase of the system is anti-ferromagnetic and the Arrott plots obtained manifest existence of the first and second order magnetic phase transition in all samples. In addition, in the sample with a grain size of 200 nm, enhancement of the magnetic properties, which is accompanied with the formation of FM phase on the surface of grain or particle, is observed. (C) 2013 Elsevier B.V. All rights reserved.

Characterization of the spin-1/2 linear-chain ferromagnet CuAs2O4

Abstract

The magnetic and lattice properties of the S = 1/2 quantum-spin-chain ferromagnet CuAs2O4, mineral name trippkeite, were investigated. The crystal structure of CuAs2O4 is characterized by the presence of corrugated CuO2 ribbon chains. Measurements of the magnetic susceptibility, heat capacity, electron paramagnetic resonance, and Raman spectroscopy were performed. Our experiments conclusively show that a ferromagnetic transition occurs at similar to 7.4 K. Ab initio DFT calculations reveal dominant ferromagnetic nearest-neighbor and weaker antiferromagnetic next-nearest-neighbor spin exchange interactions along the ribbon chains. The ratio of J(nn)/J(nnn) is near -4, placing CuAs2O4 in close proximity to a quantum critical point in the J(nn)-J(nnn) phase diagram. TMRG simulations used to analyze the magnetic susceptibility confirm this ratio. Single-crystal magnetization measurements indicate that a magnetic anisotropy forces the Cu2+ spins to lie in an easy plane perpendicular to the c axis. An analysis of the field-and temperature-dependent magnetization by modified Arrott plots reveals a 3d-XY critical behavior. Lattice perturbations induced by quasihydrostatic pressure and temperature were mapped via magnetization and Raman spectroscopy.

Structural and Physical Properties of BiVO3

Abstract

Conference on Electronic, Photonic, Plasmonic, Phononic and Magnetic Properties of Nanomaterials, London, CANADA, AUG 12-16, 2013}}, Abstract = {{We report the phase stabilization and properties of BiVO3 (BVO) thin films, grown on (001) SrTiO3 and LaAlO3, using the pulsed laser deposition technique. Bi and V are in 3+ oxidation states as measured by using x-ray photoelectrons spectroscopy. BVO exhibits a Curie-Weiss paramagnetic behaviour and about -26 K Weiss temperature. This demonstrates the presence of a strong correlation effect due to the spin fluctuation. Additionally, these films exhibit a semiconducting behaviour owing to the thermally activated conduction process. A plausible explanation of the observed properties is presented by comparing with the closely related LaVO3 and other orthovanadates.

An investigation on magnetic interacting La0.6Sr0.4MnO3 nanoparticles

Abstract

Nanoparticles of La0.6Sr0.4MnO3 (LSMO) with an equivalent average particle size of similar to 20nm were synthesized by nitrate-complex auto-ignition method. The structural and magnetic properties were investigated systematically. The X-Ray diffraction study coupled with the Rietveld refinement of XRD data showed that sample crystallize in a rhombohedral structure with space group of R-3C. The stretching and bending modes in Fourier transform infrared (FTIR) spectroscopy is observed which indicates the formation of the perovskite structure of LSMO. The nature of DC magnetization versus field M(H) plot for sample resembles qualitatively with ferromagnetic (FM) systems. The AC-susceptibility data obtained at different frequencies confirmed the presence of a frequency dependent freezing temperature around room temperature. Based on the interparticle interaction strength and phenomenological models (Neel-Brown, Vogel-Fulcher and Critical slowing down) the magnetic dynamic behavior of nanoparticles was characterized. By fitting the experimental data with mentioned models the possibility existence of superparamagnetic/spin glass states were considered. The obtained values from fitting performance showed that there is a strong interaction between magnetic nanoparticles of LSMO.

Tunable magnetic and magnetocaloric properties of La0.6Sr0.4MnO3 nanoparticles

Abstract

Nanoparticles of La0.6Sr0.4MnO3 with different particle sizes are synthesized by the nitrate-complex auto-ignition method. The structural and magnetic properties of the samples are investigated by X-Ray diffraction (XRD), Fourier transform infra-red (FT-IR) spectroscopy, transmission electron microscopy (TEM), and DC magnetization measurements. The XRD study coupled with the Rietveld refinement shows that all samples crystallize in a rhombohedral structure with the space group of R-3 C. The FT-IR spectroscopy and TEM images indicate formation of the perovskite structure with the average sizes of 20, 40, and 100 nm for the samples sintered at 700, 800, and 1100 degrees C, respectively. The DC magnetization measurements confirm tuning of the magnetic properties due to the particle size effects, e. g., reduction in the ferromagnetic moment and increase in the surface spin disorder by decreasing the particle size. The magnetocaloric effect (MCE) study based on isothermal magnetization vs. filed measurements in all samples reveals a relatively large MCE around the Curie temperature of the samples. The peak around the Curie temperature gradually broadens with reduction of the particle size. The data obtained show that although variations in the magnetic entropy and adiabatic temperature decrease by lowering the particle size, variation in the relative cooling power values are the same for all samples. These results make this material a proper candidate in the magnetic refrigerator application above room temperature at moderate fields. (C) 2013 AIP Publishing LLC.

Influence of Sm-doping on the structural, magnetic, and electrical properties of La0.8-xSmxSr0.2MnO3 (0 < x < 0.45) manganites

Abstract

Structural, magnetic, and electrical properties of the La0.8-xSmxSr0.2MnO3 (0 <= x <= 0.45) manganites prepared by a solid-state reaction technique was studied systematically. It was found that with increase in the Sm content, the crystal structure transformed from rhombohedral (x < 0.3 samples) to orthorhombic (x > 0.3 samples). The ac magnetic susceptibility measurements show that all samples undergo a transition from paramagnetic (PM) to ferromagnetic (FM) phase at the Curie temperature, TC, which decreases from 296 K down to 165 K with increase in the Sm doping level from x = 0 to x = 0.45. In addition, the glassy state exists in the x = 0.15-0.45 samples, which is stronger in higher doped compounds (x = 0.30 and x = 0.45). This behavior indicates that the substitution of Sm weakens the double exchange (DE) process. The field dependence of magnetization for the samples shows a soft FM nature with a small hysteresis loop and a low coercive field, Hc, for the doped samples. The irreversibility in the magnetization for increasing and decreasing the applied field is due to the glassy behavior observed in highly doped samples. The temperature dependence of resistivity, rho(T), measurement indicates that by increasing the Sm doping level, the metal-insulator transition temperature decreases, and the heavily doped samples become insulators. The metallic region of the rho(T) curve for the x = 0-0.10 samples was fitted with the model of electron-electron and electron-magnon scattering, while the insulating region was fitted with the small polaron hopping (SPH) at T > theta(D)/2 (theta(D), Debye temperature) and the variable range hopping (VRH) models at T < theta(D)/2. (C) 2013 Elsevier B.V. All rights

Anomalous Magnetic Properties of the Bilayered LaSr2Mn2-zCozO7 (z=0-0.15) Manganite

Abstract

The Co-doped bilayered LaSr2Mn2O7 manganite at low Co concentrations (0-0.15) was synthesized by the sol-gel process. The X-ray diffraction (XRD) technique confirms phase formation for all the samples under investigation. The results of ac magnetic susceptibility measurements indicate the effect of Co doping on the magnetic ordering phases. The indications of charge ordering (CO) transitions were observed in all the prepared compounds. The CO magnetic phase transition temperature was observed systematically shift to lower temperatures as the Co concentration increases. There was an anomalous oscillating magnetic behavior in all samples with a few peaks before the CO temperature in the paramagnetic (PM) region so that with an increasing Co doping, the number of peaks and amplitude were decreased. Also, the ac susceptibility measurements were performed in the presence of an applied dc magnetic field to further study of this oscillating behavior.

A Study of Structural and Physical Properties of Heavily Co-doped LaSr2Mn2O7 Bi-layered Manganite

Abstract

In this paper, we report the influence of cobalt doping on the structure and magnetic properties of bilayered-perovskite LaSr2Mn2-xCoxO7 (x = 0.25, 0.3). Parent and doped samples were synthesized through the sol-gel method under optimized conditions. X-ray diffraction studies coupled with the Rietveld refinement of xrd data, show that both doped and parent samples crystallize in a Sr3Ti2O7-type layered perovskite structure. Temperature dependent magnetic behavior of the parent sample exhibits an antiferromagnetic and a charge-ordering state around 220 K. Magnetic field dependence of magnetization M(H) for doped samples at 20 K show well-defined M-H loops confirming the formation of intrinsic ferromagnetic ordering due to the Co doping. Additionally, we studied the ac-magnetic susceptibility and magnetization relaxation process in our samples. Dynamic scaling analysis hints an existence of glassy magnetic states in doped samples. Electrical and magnetic properties of our samples further demonstrate that Co doping suppresses charge ordering in bilayered LaSr2Mn2O7.

Effect of Nd doping on the magnetic properties of charge-ordered Bi0.6-x Nd (x) Ca0.4MnO3 (0.0a parts per thousand currency signxa parts per thousand currency sign0.6) perovskite manganites

Abstract

We have studied structure, magnetic and transport properties of polycrystalline Bi0.6-x Nd (x) Ca0.4MnO3 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6). Substitution of Nd at Bi sites induces a strong interplay between the magnetic and charge ordering. The charge-ordering temperature (T (CO)) decreases with increasing x. Further, the antiferromagnetic ordering temperature (T (N)) increases sharply at both extremes and remains nearly constant for x=0.2-0.4. At T < T (N) a transition to a metamagnetic glass-like state is also seen. Nd doping also leads to enhancement in the magnetic moment and a concomitant decrease in resistivity up to x=0.3 and then an increase in resistivity up to x=0.5. Furthermore, Nd doping promotes an antiferromagnetic to ferromagnetic type fluctuation in the materials at room temperature, as evidenced by the change in the value of the paramagnetic Curie temperature. We find that the local lattice distortion induced by the size mismatch between the A-site cations and the 6s(2) character of Bi3+ lone pair electrons explains the observed peculiarity in magnetic and transport properties of Nd-doped Bi0.6Ca0.4MnO3.

Structural, electrical, and magnetic properties of Pb2-xLaxCrO5 (0 <= x<= 0.15)

Abstract

We report structural, electrical, and magnetic properties of a parent and La-doped polycrystalline Pb2-xLaxCrO5. The X-ray study suggests that La-doping alters the lattice parameters of Pb2CrO5 and the solubility limit of La is 7.5\%. Temperature dependent resistivity data exhibit that both doped and parent materials are semiconducting in nature. Furthermore, La-doping induces electrical conduction and significantly reduces the electrical bandgap of Pb2CrO5. A lowest bandgap of 1.16 eV is observed in the samples containing 7.5\% of La. Magnetic measurements reveal that Pb2CrO5 is characterized by a weak Curie-Weiss type paramagnetic behavior with the effective magnetic moment of 0.17 mu(B). Also, La-doping has induced a ferromagnetic behavior with a Curie temperature of 293 K. Observed physical properties are explained based on the possible oxygen vacancy and multiple oxidation states of Cr induced by La-doping. (C) 2012 Elsevier B.V. All rights reserved.

Multifunctional nanoparticles for rapid bacterial capture, detection, and decontamination

Abstract

Fluorescent magnetic nanoparticles (FMNPs) with a core-shell structure are synthesized through a one-pot chemical method followed by the bioconjugation of gentamycin (Gm). The average diameter of the FMNPs is estimated to be 65 +/- 8 nm. The results of transmission electron microscopy (TEM), X-ray absorption near edge structure spectroscopy (XANES), and fluorospectrometry indicate that the FMNPs consist of a Fe3O4 core and a fluorescent silica (SiO2) shell. The FMNPs show typical superparamagnetic properties with a blocking temperature (T-B) of 120 K. We demonstrate that gentamicin (Gm)-bioconjugated FMNPs can capture gram-negative bacteria, i.e. E. coli, (1 x 10(7) CFU mL(-1) from 10 mL of solution) within 20 min. TEM micrographs clearly show that the Gm-FMNPs disrupt the cell wall of E. coli prior to the lysis of E. coli as the interaction time (t) increases; whereas FMNPs without Gm are inert towards E. coli. In addition, the Gm-FMNPs are able to detect diluted E. coli cells at a concentration as low as 1 x 10(3) CFU mL(-1), which is revealed by a slight red-shift in fluorescent emissions from 517 nm to 528 nm along with a dramatic decrease in intensity. The Gm-conjugated FMNPs can be a multifunctional platform for simultaneous rapid capture, sensitive detection, and decontamination of bacteria.

Far-IR excitations in Cd2Re2O7 in the normal and superconducting states

Abstract

Cd2Re2O7 is a pyrochlore superconductor with a transition temperature T-c near 1 K. We report on the far-infrared optical properties of Cd2Re2O7 at temperatures above and below T-c with a particular emphasis on changes in the spectrum below T-c. Seventeen phonon modes are observed in the normal state optical conductivity spectrum of Cd2Re2O7 at low temperatures in good agreement with a factor group analysis. In the superconducting state, a softening (similar to 1 cm(-1)) of the phonon modes at 35 and 61 cm(-1) occurs and thermal reflectance spectra show the development of two additional strong absorption features, near 9.6 and 19.3 cm(-1). The dominant presence of lattice vibrational modes in the optical spectrum suggests that electron-phonon interaction plays an important role in the normal and superconducting state properties of Cd(2)R(e)2O(7).

Effect of Cu doping and oxygen-annealing on the magnetic properties of Nd0.5Sr0.5Mn1-xCuxO3-delta (x=0.0, 0.01, 0.03, 0.05 and 0.10)

Abstract

The polycrystalline samples with nominal compositions Nd0.5Sr0.5Mn1-xCuxO3 (x = 0.0, 0.01, 0.03, 0.05 and 0.10) have been synthesized with the aim to study the change in the structural, magnetic and electrical properties due to substitution of Cu for Mn and oxygen-annealing. The temperature dependence magnetization measurement shows a charge ordering transition (T-CO) at 240 K in Nd0.5Sr0.5MnO3 sample. The Neel temperature (T-N) increases with increasing the Cu doping content but changes induced by even 0.1 Cu doping are quite small. As compared to the air sintered samples, higher values of TN are observed for the oxygen annealed samples. Furthermore, oxygen annealing enhances the magnetization of the samples. It is also found that T-C increases and T-N decreases with increase in the applied magnetic-field. The value of resistivity decreases with the increasing Cu content from x = 0.0 to x = 0.03 and afterwards it increases with increasing value of x up to 0.10 for both air and oxygen sintered samples. It is also found that oxygen annealed samples exhibit higher resistivity than the air sintered samples. In the present paper the results are discussed according to the change of magnetic exchange interaction caused by Cu-doping. It is also found that the amount of Mn4+ appears to be the main variable which influences the physical properties. (C) 2012 Elsevier B.V. All rights reserved.

Magnetic and charge ordering properties of Bi0.6-xEuxCa0.4MnO3 (0.0 <= x <= 0.6)

Abstract

We have studied structure, magnetic and transport properties of polycrystalline Bi0.6-xEuxCa0.4MnO3 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) perovskite manganites. Magnetic measurements show that the charge-ordering temperature (T-CO) decreases with increasing x up to x=0.4 and then slightly increases with further increasing x up to x=0.6. Further, the antiferromagnetic (AFM) ordering temperature (T-N) decreases with increasing x. At T

Energy loss of protons in SrTiO3 studied by medium energy ion scattering

Abstract

The energy loss of medium energy protons (55-170 keV/amu) was studied for a thin SrTiO3 film on Si. The thickness of the film and the structure of the SrTiO3/Si interface was determined by the combination of X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS) and medium energy ion scattering (MEIS). These film parameters, together with energy losses extracted from MEIS spectra, were used to calculate stopping cross sections of SrTiO3 by an iterative procedure. In comparison with Andersen and Ziegler values, the data are systematically lower over the whole energy range. (C) 2012 Elsevier By. All rights reserved.

Effect of A-site cation size on magnetic and charge-ordering properties of Ln(0.5)Sr(0.5)Mn(0.9)Cu(0.1)O(3) (Ln = La, Pr, Nd, or Ho

Abstract

The structural, magnetic, and electrical properties of Ln(0.5)Sr(0.5)Mn(0.9)Cu(0.1)O(3) (Ln = La, Pr, Nd, or Ho) perovskite manganites have been investigated to explore the influence of A-site cation radius (< r(A)>) and the A-site cation size-disorder (sigma(2)) on the various interdependent phenomena such as ferromagnetism (FM), phase separation (PS), and charge ordering (CO). The temperature dependence magnetization (M-T) curve of La-based sample shows four distinct points at similar to 269 K, 255 K, 200 K, and 148 K corresponding to strong FM, cluster glass (CG), weak FM, and charged ordered antiferromagnetic (COAFM) transitions, respectively. Our investigation shows that Neel temperatures (T-N) increases, whereas Curie (T-c) and irreversibility temperatures (T-irr) decrease with decreasing < r(A)>, i.e., with increasing sigma(2). Furthermore, the value of the magnetization decreases and resistivity increases with decreasing < r(A)>. All samples exhibit insulating behavior in the temperature range 77-300 K and above 110K the electronic conduction mechanism has been described within the framework of the variable range hopping (VRH) model. (c) 2012 Elsevier B.V. All rights reserved.

Magnetic and charge ordering properties of Bi0.6-x(RE)(x)Ca0.4MnO3 (0.0 <= x <= 0.6) perovskite manganites

Abstract

In this work, we studied structural, magnetic, and charge ordering properties of polycrystalline Bi0.6-x (RE)(x) Ca0.4MnO3 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) samples, synthesized via solid state reaction route and by taking RE = La, Pr, and Nd, separately. The temperature dependence magnetization measurement reveals that the x = 0.0 compound (BCMO) exhibits a charge ordered (CO) and antiferromagnetic (AFM) phase with the charge ordering temperature (T-CO) similar to 289 K and the antiferromagnetic ordering temperature (T-N) similar to 136 K. Only a small fraction of La-dopant in BCMO is sufficient to destroy the CO completely, whereas a large concentration of La (viz., x = 0.2 to x = 0.6) promotes ultimately a paramagnetic to ferromagnetic (PM-FM) transition, and the PM-FM transition temperature (T-C) decreases progressively from 241 K to 203 K as x increases from 0.2 to 0.5. In contrast, systematic substitution of Pr or Nd at Bi site induces an intriguing interplay between the charge ordering and antiferromagnetism. Our results demonstrate that the value of T-CO decreases with increasing value of ``x{''} and the value of T-N increases sharply at both the extremes; however, it remains nearly constant from x 0.2 to 0.4. In our samples, a glassy magnetic states are also observed at far below the T-N. (C) 2012 American Institute of Physics.

Study Of Structural, Magnetic And Electric Properties Of Bi0.6-xNdxCa0.4MnO3 (0.0 <= x <= 0.6) Perovskite Manganites

Abstract

In the present paper, we have studied structure, magnetic and transport properties of polycrystalline Bi0.6-xNdxCa0.4MnO3 (x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) samples synthesized via solid state reaction route. The magnetic measurements reveal that the charge ordering temperature (T-CO) decreases with increasing x. Further, the antiferromagnetic (AFM) ordering temperature (T-N) increases sharply at both extremes and remains nearly constant for x= 0.2 - 0.4. At T

Impact of substrate on magnetic phase coexistence in bicritical Sm0.53Sr0.47MnO3 thin films

Abstract

Sm0.53Sr0.47MnO3 thin films were deposited on single crystal LaAlO3 (LAO/(001)) and SrTiO3 (STO/(001)) substrates by DC magnetron sputtering. The theta-2 theta and omega-2 theta scans show that these films have very good crystallinity and the films on LAO and STO are under compressive and tensile strain, respectively. The films on LAO and STO substrates show ferromagnetic (insulator-metal) transition at T-C similar to 126 K (at T-IM similar to 128 K) and 120 K (T-IM similar to 117 K), respectively. The magnetic state at T < T-C is akin to cluster glass, which is formed by the presence of charge ordered-antiferromagnetic clusters in the ferromagnetic matrix. Huge drop in the resistivity at T-IM and the associated hysteresis with respect to cooling and warming cycles reveal the bicritical and the first order nature of phase transition, which is also confirmed by the Banerjee criterion. The differences and similarities in the functional properties of films are explained in terms of substrate modified magnetic phase coexistence. (C) 2011 Elsevier Ltd. All rights reserved.

Low field anisotropic colossal magnetoresistance in Sm0.53Sr0.47MnO3 thin films

Abstract

Sm0.53Sr0.47MnO3 (SSMO) thin films (thicknesses similar to 200 nm) were deposited by on-axis dc magnetron sputtering on the single crystal LSAT (001) substrates. These films are oriented along the out of plane c-direction. The ferromagnetic and insulator-metal transition occurs at T-C similar to 96 and T-IM similar to 91 K, respectively. The magnetization easy axis is observed to lie in the plane of the film while the magnetic hard axis is found to be along the normal to this. The magnetotransport of the SSMO films, which was measured as a function of angle (theta) between the magnetic field (H) and plane of the film, shows colossal anisotropy. Magnetoresistance (MR) decreases drastically as theta increases from 0 degrees (H//easy axis) to 90 degrees (H//hard axis). The out-of-plane anisotropic MR is as high as 88\% at H = 3.6 kOe and 78 K. The colossal anisotropy has been explained in terms of the magnetic anisotropies at play and the magnetic domain motion in applied magnetic field. (C) 2011 American Institute of Physics.

Optical, Structural, and Magnetic Properties of ZnO:Co Nanoparticles Prepared by a Thermal Treatment of Ball Milled Precursors

Abstract

In this study, ZnO nanoparticles with different cobalt concentration were prepared by a simple and rapid method. This method is based on a short time solid state milling and calcinations of zinc acetate, cobalt acetate, and citric acid powders. The samples were characterized using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Fourier Transform Infrared (FTIR), photoluminescence, and UV-vis. spectroscopy. It was shown that a very low substitution of Co (less than 1\% of molecular weight) has little effect on the lattice parameters of ZnO and significantly decreases the band gap (E (g) ) value of the synthesized ZnO:Co nanoparticles. Calculation based on the XRD data shows that the average crystallite sizes of ZnO particles are nearly 18 nm. Photoluminescence spectroscopy shows that many defects such as interstitial zinc, zinc vacancy, and exciton recombination are responsible for the observed optical properties. Magnetization measurements which were performed by using a superconducting quantum interference device (SQUID) magnetometer determine the paramagnetic behavior for all samples due to the absence of oxygen vacancy.

Effect of PbZr0.52Ti0.48O3 thin layer on structure, electronic and magnetic properties of La0.65Sr0.35MnO3 and La0.65Ca0.30MnO3 thin-films

Abstract

Epitaxial thin film heterostructures of high dielectric PbZr1-xTixO3 (PZT) and La(1-x)A(x)MnO(3) (A-divalent alkaline earth metals such as Sr (LSMO) and Ca (LCMO)) were grown on SrTiO3 substrates and their structure, temperature dependence of electrical resistivity, and magnetization were investigated as a function of the thickness of the LSMO(LCMO) layer. The microstructures of the samples were analyzed by TEM. By applying an electric field across the PZT layer, we applied a ferrodistortive pressure on the manganite layer and studied the correlations between lattice distortion and electric transport and magnetic properties of the CMR materials. (C) 2011 American Institute of Physics.

One-pot synthesis and characterization of rhodamine derivative-loaded magnetic core-shell nanoparticles

Abstract

A new method to produce elaborate nanostructure with magnetic and fluorescent properties in one entity is reported in this article. Magnetite (Fe3O4) coated with fluorescent silica (SiO2) shell was produced through the one-pot reaction, in which one reactor was utilized to realize the synthesis of superparamagnetic core of Fe3O4, the formation of SiO2 coating through the condensation and polymerization of tetraethylorthosilicate (TEOS), and the encapsulation of tetramethyl rhodamine isothiocyanate-dextran (TRITC-dextran) within silica shell. Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) were carried out to investigate the core-shell structure. The magnetic core of the core-shell nanoparticles is 60 +/- A 10 nm in diameter. The thickness of the fluorescent SiO2 shell is estimated at 15 +/- A 5 nm. In addition, the fluorescent signal of the SiO2 shell has been detected by the laser confocal scanning microscopy (LCSM) with emission wavelength (lambda(em)) at 566 nm. In addition, the magnetic properties of TRITC-dextran loaded silica-coating iron oxide nanoparticles (Fe3O4@SiO2 NPs) were studied. The hysteresis loop of the core-shell NPs measured at room temperature shows that the saturation magnetization (M (s)) is not reached even at the field of 70 kOe (7T). Meanwhile, the very low coercivity (H (c)) and remanent magnetization (M (r)) are 0.375 kOe and 6.6 emu/g, respectively, at room temperature. It indicates that the core-shell particles have the superparamagnetic properties. The measured blocking temperature (T (B)) of the TRITC-dextran loaded Fe3O4@SiO2 NPs is about 122.5 K. It is expected that the multifunctional core-shell nanoparticles can be used in bio-imaging.

Effect of vanadium deficiency on properties of polycrystalline LaVO3

Abstract

We report the influence of V deficiency on structure, transport, and magnetic properties of polycrystalline LaVO3. Up to 10\% V-deficient samples were synthesized using standard solid state chemistry route. Structural and spectroscopic studies show that it intricately modifies lattice parameters and oxidation states of V. Further temperature dependent resistivity data reveal that V deficiency induces an enhancement in the resistivity and activation energy. The paramagnetic moment of these samples depends on net V composition while all samples exhibit a paramagnetic-to-antiferromagnetic transition at about 140 K. These distinct properties are understood owing to the presence of multiple oxidations states of V, predominantly V3+ and V4+, in nonstoichiometric LaVO3. (C) 2011 American Institute of Physics.

Magnetic and Structural Properties of Ni/NiO Nanoparticles Prepared Using Nickel Acetate and Polyvinyl Acetate Precursor

Abstract

Ni/NiO nanoparticles were synthesized using a mixture of nickel acetate and polyvinyl acetate as precursors, followed by heating between 350-450 A degrees C. The prepared samples were investigated using XRD, TEM and SQUID magnetometry. Depending on the heating temperature, the average sizes of Ni and NiO crystallites were found to be in the ranges of 25-37 nm and 10-26 nm, respectively. The analysis of XRD patterns shows that the volume percentage of Ni can be easily controlled by the heating temperature. Magnetization measurements show that the samples consist of ferromagnetic moments which are blocked at low temperatures and a disordered NiO component which causes spin-glass like behavior.

A search for defect related ferromagnetism in SrTiO3

Abstract

Room temperature ferromagnetic hysteresis is observed in commercial SrTiO3 substrates purchased from a variety of suppliers. It is shown that the ferromagnetic signal comes from the unpolished surfaces. Surface impurity phases cannot be detected using either x-ray diffraction or energy dispersive x-ray spectra on the unpolished surfaces. However, a possible correlation between surface disorder (x-ray diffraction peak linewidth) and ferromagnetism is observed. Ar ion bombardment (10-90 keV) can be used to produce surface layer disorder but is not found to induce ferromagnetism. Annealing of the substrates at temperatures ranging from 600 to 1100 degrees C is found to alter the hysteresis curves differently depending on whether the annealing is performed in air or in vacuum. Identical annealing behavior is observed if the substrates are artificially spiked with iron. This suggests that the ferromagnetic hysteresis of as purchased SrTiO3 could be due to Fe contamination of the unpolished surfaces. In addition, it is shown that no ferromagnetism is observed in samples that contain 10(19)-10(21) cm(-3) of oxygen vacancies if all the faces are polished. (C) 2010 American Institute of Physics.

Persistent supercurrents in ring-shaped Bi2Sr2CaCu2Ox single crystal

Abstract

A superconducting ring could be used to simulate the supercurrent conduction, and its interaction with magnetic vortices in a superconducting solenoid, allowing one to investigate the nature of the vortex structure and its pinning in the presence of the persistent supercurrent. The dissipation of the persistent supercurrent has been studied in a ring-shaped high purity single crystal of Bi2Sr2CaCu2Ox in order to obtain the information about the exponent mu, a parameter in the scaling relation between the effective energy barrier against vortex motion U-eff and the persistent current density J. The measurements of the persistent supercurrent decay show a transition from a strongly nonlogarithmic to a logarithmic decay regime with an increasing temperature. In response to a small increase in the concentration of oxygen vacancies mu decreases in the logarithmic decay regime but remains almost constant in the nonlogarithmic one. (C) 2010 American Institute of Physics.

Evidence for random networks of diodes in thin films of LaVO3 on SrTiO3 substrates

Abstract

Highly conducting interfaces of transition metal oxide heterolayers could provide a promising access to transition metal oxide based electronic devices similar to those based on semiconductor heterostructures. Recently, metallic conductivity has been reported at the LaAlO3/SrTiO3 heterointerface. Here we report the observation of diodelike behavior and the formation of a random diode network in thin films of LaVO3 deposited on as-polished SrTiO3 substrates. Depending on films annealing conditions we observed linear or nonlinear I-V characteristic below 50 K.