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Sample records for modulu sr-0 jaderneho

  1. Influence of electron beam irradiation on the structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Nagaraja, B. S.; Rao, Ashok; Babu, P. D.; Sanjeev, Ganesh; Okram, G. S.

    2016-01-01

    We present systematic studies on the effect of electron beam irradiation on structural, electrical and thermal properties of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 manganites. The XRD patterns and Rietveld analysis show that the samples remain single phased even after they undergo electron beam irradiation. Both the series of the samples Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 show insulating trends in their temperature dependent electrical resistivity, ρ(T) behavior. The resistivity data for both the series of samples (pristine as well as irradiated) indicate that the small polaron hopping model is valid in high temperature region; on contrary, variable range hopping model governs the low temperature regime. Magnetic studies demonstrate that the Neel temperatures of pristine and irradiated samples of Gd0.5Sr0.5MnO3 and Dy0.5Sr0.5MnO3 do not change appreciably when they are subjected to irradiation. Thermo-electrical power is observed to increase with irradiation in Gd0.5Sr0.5MnO3 samples, whereas for Dy0.5Sr0.5MnO3 samples a decrease in thermo-electric power is seen when the samples are irradiated.

  2. Magnetoresistance of La0.5Sr0.5MnO3 nanoparticle compact

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Hong; Ji, Tian-Hao; Wang, Yi-Qian; Chen, Xin; Li, Run-Wei; Cai, Jian-Wang; Sun, Ji-Rong; Shen, Bao-Gen; Yan, Chun-Hua

    2000-05-01

    Magnetization, resistance, and current-voltage (I-V) measurements have been performed in La0.5Sr0.5MnO3 compact prepared by pressing sol-gel nanoparticles (46 nm) at 723 K with a high pressure (4 GPa). The pressed compound orders ferromagnetically at 340 K (TC) and has a substantial drop in the thermomagnetic curve below 158 K (TDP). After undergoing a metal-to-semiconductor transition at 140 K (TMS), the compound reenters into a strong semiconducting state below 60 K, demonstrating a charge localized behavior induced by the small grain rather than the magnetic disorder which is related with the frozen spin clusters below TDP. Instead of showing a feature near TMS, the magnetoresistance (MR) ratio increases almost linearly with decreasing temperature. The large low field MR corresponding to the sharp rise of magnetization is obtained at 5 K and, evidenced as the spin polarized intergrain tunneling (SPIT) effect by the nolinear I-V curve. Although La0.5Sr0.5MnO3 has a relatively high TC, the SPIT MR decays rapidly from 17.6% (5 K, 0.3 T) to 7.6% (150 K, 0.3 T), indicating that if trying to put the low field sensitivity of SPIT MR into application at room temperature, the selected compound having a higher TC seems to be a prerequisite.

  3. Study of coexisting phases in Bi doped La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Kambhala, Nagaiah; Chen, Miaoxiang; Li, Peng; Zhang, Xi-xiang; Rajesh, Desapogu; Bhagyashree, K. S.; Goveas, Lora Rita; Bhat, S. V.; Kumar, P. Anil; Mathieu, Roland; Angappane, S.

    2016-05-01

    We report the remarkable phase separation behavior in La0.67Sr0.33MnO3 doped with Bi3+ ion at La site. The temperature dependent resistivity and magnetization of La0.67-xBixSr0.33MnO3 (x>0) show the presence of phase separation of ferromagnetic metallic and charge ordered antiferromagnetic insulating phases. Markedly, the field dependant magnetization studies of La0.67-xBixSr0.33MnO3 (x=0.3) show the metamagnetic nature of ferromagnetic metallic state implying the competition of coexisting ferromagnetic metallic and charge ordered antiferromagnetic phases. The electron spin resonance and exchange bias studies of La0.67-xBixSr0.33MnO3 (x=0.4 and 0.5) substantiate the coexistence of ferromagnetic clusters in antiferromagnetic matrix.

  4. Ni-doped La0.5Sr0.5TiO3 nanofibers: Fabrication and intrinsic ferromagnetism

    NASA Astrophysics Data System (ADS)

    Ponhan, Wichaid; Amornkitbamrung, Vittaya; Maensiri, Santi

    2016-06-01

    We report room-temperature ferromagnetism in ∼104–133 nm nanofibers of La0.5Sr0.5Ti1‑ x Ni x O3 (0.02 ≤ x ≤ 0.05). As-spun nanofibers of La0.5Sr0.5Ti1‑ x Ni x O3 are fabricated by an electrospinning technique. Nanofibers of the as spun and calcined La0.5Sr0.5Ti1‑ x Ni x O3 samples are characterized using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), X-ray absorption near edge structure (XANES) determination, and vibrating sample magnetometry (VSM). The results of XRD analysis and TEM together with selected electron diffraction (SEAD) analysis indicate that La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers have a cubic perovskite structure with no secondary phase. The as-spun samples are paramagnetic, whereas the La0.5Sr0.5Ti1‑ x Ni x O3 samples are ferromagnetic having specific magnetizations of 0.098–0.484 emu/g at 10 kOe. The XPS spectra show that there are some oxygen vacancies in the nanofibers, which its may play an important role in inducing room-temperature ferromagnetism in La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers. XANES spectra show that most of the Ni ions in La0.5Sr0.5Ti1‑ x Ni x O3 nanofibers are in the Ni2+ state mixed with some Ni metal. The finding of room temperature ferromagnetism in this nanofibrous structure of the La0.5Sr0.5Ti1‑ x Ni x O3 system is of interest in research on diluted magnetic oxides.

  5. Strain dependent magnetocaloric effect in La0.67Sr0.33MnO3 thin-films

    NASA Astrophysics Data System (ADS)

    Kumar, V. Suresh; Chukka, Rami; Chen, Zuhuang; Yang, Ping; Chen, Lang

    2013-05-01

    The strain dependent magnetocaloric properties of La0.67Sr0.33MnO3 thin films deposited on three different substrates (001) LaAlO3 (LAO), (001) SrTiO3 (STO), and (001) La0.3Sr0.7Al0.65Ta0.35O9 (LSAT) have been investigated under low magnetic fields and around magnetic phase transition temperatures. Compared to bulk samples, we observe a remarkable decrease in the ferromagnetic transition temperature that is close to room temperature, closely matched isothermal magnetic entropy change and relative cooling power values in tensile strained La0.67Sr0.33MnO3 films. The epitaxial strain plays a significant role in tuning the peak position of isothermal magnetic entropy change towards room temperature with improved cooling capacity.

  6. Silica-Aerogel Composites Opacified with La(0.7)Sr(0.3)MnO3

    NASA Technical Reports Server (NTRS)

    Rhine, Wendell; Polli, Andrew; Deshpande, Kiranmayi

    2009-01-01

    As part of an effort to develop improved lightweight thermal-insulation tiles to withstand temperatures up to 1,000 C, silica aerogel/fused-quartz-fiber composite materials containing La0.7Sr0.3MnO3 particles as opacifiers have been investigated as potentially offering thermal conductivities lower than those of the otherwise equivalent silica-aerogel composite materials not containing La(0.7)Sr(0.3)MnO3 particles. The basic idea of incorporating opacifying particles into silica-aerogels composite to reduce infrared radiative contributions to thermal conductivities at high temperatures is not new: it has been reported in a number of previous NASA Tech Briefs articles. What is new here is the selection of La(0.7)Sr(0.3)MnO3 particles as candidate opacifiers that, in comparison with some prior opacifiers (carbon black and metal nanoparticles), are more thermally stable. The preparation of a composite material of the present type includes synthesis of the silica-aerogel component in a sol-gel process. The La(0.7)Sr(0.3)MnO3 particles, made previously in a separate process, are mixed into the sol, which is then cast onto fused-quartz-fiber batting. Then the aerogel-casting solution is poured into the mold, where it permeates the silica fiber felt. After the sol has gelled, the casting is aged and then subjected to supercritical drying to convert the gel to the final aerogel form. The separate process for making the La(0.7)Sr(0.3)MnO3 particles begins with the slow addition of corresponding proportions of La(CH3COOH)3, Mn(CH3COOH)3, and Sr(NO3)2 to a solution of H2O2 in H2O. The solution is then peptized by drop-wise addition of NH4OH to obtain a sol. Next, the sol is dried in an oven at a temperature of 120 C to obtain a glassy solid. The solid is calcined at 700 C to convert it to La(0.7)Sr(0.3)MnO3. Then La(0.7)Sr(0.3)MnO3 particles are made by ball-milling the calcined solid. The effectiveness of La(0.7)Sr(0.3)MnO3 particles as opacifiers and thermal

  7. Tunnelling anisotropic magnetoresistance at La0.67Sr0.33MnO3-graphene interfaces

    NASA Astrophysics Data System (ADS)

    Phillips, L. C.; Lombardo, A.; Ghidini, M.; Yan, W.; Kar-Narayan, S.; Hämäläinen, S. J.; Barbone, M.; Milana, S.; van Dijken, S.; Ferrari, A. C.; Mathur, N. D.

    2016-03-01

    Using ferromagnetic La0.67Sr0.33MnO3 electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ˜32-35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La0.67Sr0.33MnO3-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.

  8. Sol-Gel Synthesis of La(0.6)Sr(0.4)CoO(3-x) and Sm(0.5)Sr(0.5)CoO(3-x) Cathode Nanopowders for Solid Oxide Fuel Cells

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Wise, Brent

    2011-01-01

    Nanopowders of La(0.6)Sr(0.4)CoO(3-x) (LSC) and Sm(0.5)Sr(0.5)CoO(3-x) (SSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC) with La(Sr)Ga(Mg)O(3-x) (LSGM) as the electrolyte, were synthesized by low-temperature sol-gel method using metal nitrates and citric acid. Thermal decomposition of the citrate gels was followed by simultaneous DSC/TGA methods. Development of phases in the gels, on heat treatments at various temperatures, was monitored by x-ray diffraction. Solgel powders calcined at 550 to 1000 C consisted of a number of phases. Single perovskite phase La(0.6)Sr(0.4)CoO(3-x) or Sm(0.5)Sr(0.5)CoO(3-x) powders were obtained at 1200 and 1300 C, respectively. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The average particle size of the powders was approx.15 nm after 700 C calcinations and slowly increased to 70 to 100 nm after heat treatments at 1300 to 1400 C.

  9. Synthesis and luminescence characterization of Sr(0.5)Ca(0.5)TiO3:Sm(3+) phosphor.

    PubMed

    Vidyadharan, Viji; Remya, Mohan P; Gopi, Subhash; Thomas, Sunil; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange. PMID:26057096

  10. Improvement of La0.65Sr0.3MnO3-gamma-YSZ cathodes by infiltrating nanoSm0.6Sr0.4CoO3-gamma particles

    SciTech Connect

    Lu, Chun; Sholklapper, Tal; Chen, Xuan; Zhang, Xiaofeng; Jacobson, Craig P.; Visco, Steven J.; DeJonghe, Lutgard C.

    2004-05-01

    La0.65Sr0.3MnO3-delta-YSZ cathodes are infiltrated with Sm0.6Sr0.4CoO3-delta (SSC) at 800 C using a precipitation method. The effect of SSC infiltration has been characterized for symmetric cells and single cells at reduced temperatures. With SSC addition the cathode polarization resistance, determined from symmetric-cell measurements, significantly decreases: from approx. 19.8 to 8.5 Omega cdot cm2 at 600 C, and from 7.7 to 3.3 Omega cdot cm2 at 650 C. Consequently, the single-cell performance with 97 percentH2+3 percentH2O fuel is dramatically improved, which may be attributed to the superior electrocatalytic activity of SSC in the cathodes.

  11. Magnetocaloric effect in La 0.67Sr 0.33MnO 3 manganite above room temperature

    NASA Astrophysics Data System (ADS)

    Rostamnejadi, A.; Venkatesan, M.; Kameli, P.; Salamati, H.; Coey, J. M. D.

    2011-08-01

    The La0.67Sr0.33MnO3 composition prepared by sol-gel synthesis was studied by dc magnetization measurements. A large magnetocaloric effect was inferred over a wide range of temperature around the second-order paramagnetic-ferromagnetic transition. The change of magnetic entropy increases monotonically with increasing magnetic field and reaches the value of 5.15 J/kg K at 370 K for Δμ0H=5 T. The corresponding adiabatic temperature change is 3.3 K. The changes in magnetic entropy and the adiabatic temperature are also significant at moderate magnetic fields. The magnetic field induced change of the specific heat varies with temperature and has maximum variation near the paramagnetic-ferromagnetic transition. The obtained results show that La0.67Sr0.33MnO3 could be considered as a potential candidate for magnetic refrigeration applications above room temperature.

  12. Pressure-induced reemergence of superconductivity in topological insulator Sr0.065Bi2Se3

    NASA Astrophysics Data System (ADS)

    Zhou, Yonghui; Chen, Xuliang; Zhang, Ranran; Shao, Jifeng; Wang, Xuefei; An, Chao; Zhou, Ying; Park, Changyong; Tong, Wei; Pi, Li; Yang, Zhaorong; Zhang, Changjin; Zhang, Yuheng

    2016-04-01

    The recently discovered SrxBi2Se3 superconductor provides an alternative and ideal material base for investigating possible topological superconductivity. Here, we report that in Sr0.065Bi2Se3 , the ambient superconducting phase is gradually depressed upon the application of external pressure. At high pressure, a second superconducting phase emerges at above 6 GPa, with a maximum Tc value of ˜8.3 K. The joint investigations of the high-pressure synchrotron x-ray diffraction and electrical transport properties reveal that the reemergence of superconductivity in Sr0.065Bi2Se3 is closely related to the structural phase transition from an ambient rhombohedral phase to a high-pressure monoclinic phase around 6 GPa, and further to another high-pressure tetragonal phase above 25 GPa.

  13. Interrelation between Structure Magnetic Properties in La0.5Sr0.5CoO3

    SciTech Connect

    Biegalski, Michael D; Takamura, Y; Mehta, A; Gai, Zheng; Kalinin, Sergei; Ambaye, Hailemariam; Lauter, Valeria; He, Jun; Kim, Young Min; Borisevich, Albina Y; Siemons, Wolter; Christen, Hans M

    2014-01-01

    Differing anisotropic strain induced from the underlying substrates not only control the long-range structural symmetries in La0.5Sr0.5CoO3 but also impact the magnetic properties of these epitaxial thin films. The two dominant structural distortions: oxygen octahedral tilts and epitaxial strain, however, have complex and non-intuitive effects on the splitting of the t2g states and consequently on magnetization.

  14. Critical behavior and magnetic relaxation dynamics of Nd0.4Sr0.6MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kundu, S.; Nath, T. K.

    2013-07-01

    Detailed DC and AC magnetic properties of chemically synthesized Nd0.4Sr0.6MnO3 with different particle size (down to 27 nm) have been studied in details. We have found ferromagnetic state in the nanoparticles, whereas the bulk Nd0.4Sr0.6MnO3 is known to be an A-type antiferromagnet. A Griffiths-like phase has also been identified in the nanoparticles. Further, critical behaviour of the nanoparticles has been studied around the second-order ferromagnetic-paramagnetic transition region (|(T-T C)/T C| ⩽ 0.04) in terms of modified Arrott plot, Kouvel-Fisher plot and critical isotherm analysis. The estimated critical exponents (β, γ, δ) are quite different from those predicted according to three-dimensional mean-field, Heisenberg and Ising models. This signifies a quite unusual nature of the size-induced ferromagnetic state in Nd0.4Sr0.6MnO3. The nanoparticles are found to be interacting and do not behave like ideal superparamagnet. Interestingly, we find spin glass like slow relaxation of magnetization, aging and memory effect in the nanometric samples. These phenomena have been attributed to very broad distribution of relaxation time as well as to inter-particle interaction. Experimentally, we have found out that the dynamics of the nanoparticle systems can be best described by hierarchical model of spin glasses.

  15. Resistance switching mechanism of La0.8Sr0.2MnO3-δ thin films

    NASA Astrophysics Data System (ADS)

    Luo, X. D.; Gao, R. L.; Fu, C. L.; Cai, W.; Chen, G.; Deng, X. L.; Zhang, H. R.; Sun, J. R.

    2016-02-01

    Effects of oxygen vacancies on the electrical transport properties of oxygen stoichiometric La0.8Sr0.2MnO3 and oxygen-deficient La0.8Sr0.2MnO3-δ films have been investigated. The result presents that the oxygen-deficient films annealed in vacuum show obvious increase of resistance and lattice parameter. With the sweeping voltage or temperature increasing, the resistance exhibits obvious bipolar switching effect, no forming process was needed. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Mn-O-Mn conduction channel due to the accumulation of oxygen vacancies under high external electric field or temperatures and hence is believed to be responsible for the bipolar resistance switching effect and the enhanced resistivity compared with oxygen stoichiometric La0.8Sr0.2MnO3 film. These results may be important for practical applications in photoelectric or storage devices and point to a useful direction for other oxidizing materials.

  16. Sr0.95In0.05Li2Ti6O14: A high performance lithium host material

    NASA Astrophysics Data System (ADS)

    Qian, Shangshu; Yu, Haoxiang; Yan, Lei; Li, Peng; Lin, Xiaoting; Zhang, Yanyu; Long, Nengbing; Shui, Miao; Shu, Jie

    2016-08-01

    Via Sr-site substitution, a series of Sr0.95M0.05Li2Ti6O14 (Mz+ = Na+, Cu2+, In3+) are prepared as anode materials for lithium-ion batteries. It is found that the introduction of Na+, Cu2+ or In3+ into the crystal lattice can reduce the charge-transfer resistance and improve the lithium-ion diffusion coefficient of SrLi2Ti6O14. Especially for In3+-doping, it exhibits more obvious effect on these improvements. Furthermore, the substitution of Sr2+ by In3+ can also enhance the electronic conductivity via inducing a reduction of an equivalent number of Ti cations from Ti4+ to Ti3+. As a result, Sr0.95In0.05Li2Ti6O14 shows the best cycle and rate properties among all as-prepared samples. In addition, in-situ observation also proves that Sr0.95In0.05Li2Ti6O14 is a zero-strain lithium storage compound during charge/discharge process. As a result, it delivers a lithium storage capacity of 136.4 mAh g-1 at 200 mA g-1, 126.3 mAh g-1 at 400 mA g-1 and 121.0 mAh g-1 at 600 mA g-1. In contrast, SrLi2Ti6O14 only presents a charge capacity of 138.3 mAh g-1 at 200 mA g-1, 120.3 mAh g-1 at 400 mA g-1 and 111.3 mAh g-1 at 600 mA g-1. Therefore, In3+-doping is an effective method to enhance the electrochemical properties of SrLi2Ti6O14.

  17. Electron-phonon interactions in superconducting La1.84Sr0.16CuO4 films.

    PubMed

    Shim, Heejae; Chaudhari, P; Logvenov, Gennady; Bozovic, Ivan

    2008-12-12

    We have measured quasiparticle tunneling across a junction perpendicular to the superconducting copper oxide planes. The tunneling spectra show peaks in the density of states. There are 11 minima in the second derivative d2I/dV2, where I is the current and V the voltage, suggesting multiple boson-quasiparticle interactions. These minima match precisely with the published Raman scattering data, leading us to conclude that the relevant bosons in superconducting La1.84Sr0.16CuO4 films are phonons. PMID:19113657

  18. Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters

    NASA Astrophysics Data System (ADS)

    Suherman, P. M.; Jackson, T. J.; Tse, Y. Y.; Jones, I. P.; Chakalova, R. I.; Lancaster, M. J.; Porch, A.

    2006-05-01

    Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.

  19. Growth of Sr(0.61)Ba(0.39)Nb2O6 fibers - New results regarding orientation

    NASA Technical Reports Server (NTRS)

    Wilde, Jeffrey P.; Jundt, Dieter H.; Galambos, Ludwig; Hesselink, Lambertus

    1991-01-01

    The paper describes stable growth of Sr(0.61)Ba(0.39)Nb2O6 (SBN) single-crystal optical fibers (grown by the laser-heated pedestal growth method) along the 100-line and 110-line crystallographic axes. The orientation of SBN fibers was investigated using transmission holograms recorded by focusing two separate, but mutually coherent, optical wavefronts into one end of the fiber. Results showed that the crystal quality of 100-line and 110-line SBN fibers grown at a given pull velocity strongly depended on the fiber diameter; generally, the quality improves with decreasing diameter.

  20. Effect of injected spins with different polarized orientations on the vortex phase transition in La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhang, M. J.; Teng, M. L.; Hao, F. X.; Yin, Y. W.; Zeng, Z.; Li, X. G.

    2015-05-01

    The current-voltage (I-V) characteristics with spin injection were investigated for the epitaxial La0.7Sr0.3MnO3/La1.85Sr0.15CuO4 heterostructure rotated from H//c to H//ab in magnetic fields up to 14 T. It is found that all the I-V curves in various magnetic fields can be scaled with a three dimensional (3D) vortex glass model, and the spin injection can induce a better 3D scaling behavior, which is closely related to the decrease of the anisotropy parameter. A vortex phase diagram for the evolution of vortex glass transition field (Hg) and upper critical field (Hc2) indicates that both Hg and Hc2 are suppressed by spin injection, and this effect becomes more obvious in the case of H//ab, which probably originates from the different suppression on the superconducting pairing strength by different injected spins' orientations.

  1. Octonary resistance states in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 multiferroic tunnel junctions

    DOE PAGESBeta

    Yue -Wei Yin; Tao, Jing; Huang, Wei -Chuan; Liu, Yu -Kuai; Yang, Sheng -Wei; Dong, Si -Ning; Zhu, Yi -Mei; Li, Qi; Li, Xiao -Guang

    2015-10-06

    General drawbacks of current electronic/spintronic devices are high power consumption and low density storage. A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents four resistance states in a single device and therefore provides an alternative way to achieve high density memories. Here, an MFTJ device with eight nonvolatile resistance states by further integrating the design of noncollinear magnetization alignments between the ferromagnetic layers is demonstrated. Through the angle-resolved tunneling magnetoresistance investigations on La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 junctions, it is found that, besides collinear parallel/antiparallel magnetic configurations, the MFTJ shows at least two other stable noncollinear (45°more » and 90°) magnetic configurations. As a result, combining the tunneling electroresistance effect caused by the ferroelectricity reversal of the BaTiO3 barrier, an octonary memory device is obtained, representing potential applications in high density nonvolatile storage in the future.« less

  2. Combustion Synthesis of Sm0.5Sr0.5CoO3-x and La0.6Sr0.4CoO3-x Nanopowders for Solid Oxide Fuel Cell Cathodes

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Zhong, zhimin

    2005-01-01

    Nanopowders of Sm0.5Sr0.5CoO(3-x) (SSC) and La0.6Sr0.4CoO(3-x) (LSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells, were synthesized by a solution-combustion method using metal nitrates and glycine as fuel. Development of crystalline phases in the as-synthesized powders after heat treatments at various temperatures was monitored by x-ray diffraction. Perovskite phase in LSC formed more readily than in SSC. Single phase perovskites were obtained after heat treatment of the combustion synthesized LSC and SSC powders at 1000 and 1200 C, respectively. The as-synthesized powders had an average particle size of 12 nm as determined from x-ray line broadening analysis using the Scherrer equation. Average grain size of the powders increased with increase in calcination temperature. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy.

  3. Thermally assisted interlayer magnetic coupling through Ba0.05Sr0.95TiO3 barriers

    NASA Astrophysics Data System (ADS)

    Carreira, Santiago J.; Avilés Félix, Luis; Sirena, Martín; Alejandro, Gabriela; Steren, Laura B.

    2016-08-01

    We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component.

  4. Vortex pinning and dynamics in high performance Sr0.6K0.4Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Dong, Chiheng; Lin, He; Huang, He; Yao, Chao; Zhang, Xianping; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2016-04-01

    We have studied vortex pinning and dynamics in a Sr0.6K0.4Fe2As2 superconducting tape with critical current density Jc ˜ 0.1 MA/cm2 at 4.2 K and 10 T. It is found that grain boundary pinning is dominant in the vortex pinning mechanism. Furthermore, we observe large density of dislocations which can also serve as effective pinning centers. We find that the temperature dependence of critical current density is in agreement with the model of vortices pinned via spatial fluctuation of charge carrier mean free path. Magnetic relaxation measurement indicates that the magnetization depends on time in a logarithmic way. The relaxation rate in the low and intermediate temperature region is small, and it exhibits a weak temperature and field dependence. A crossover from elastic creep to plastic creep regime is observed. Finally, we conclude a vortex phase diagram for the high performance Sr0.6K0.4Fe2As2 superconducting tape.

  5. Superconductivity and abnormal pressure effect in Sr{}_{0.5}La{}_{0.5}FBiSe2 superconductor

    NASA Astrophysics Data System (ADS)

    Li, Lin; Xiang, Yongliang; Chen, Yihong; Jiao, Wenhe; Zhang, Chuhang; Zhang, Li; Dai, Jianhui; Li, Yuke

    2016-04-01

    Through the solid state reaction method, we synthesized a new BiSe2-based superconductor Sr{}0.5La{}0.5FBiSe2 with superconducting transition temperature T {}c ≈ \\quad 3.8 K. A strong diamagnetic signal below T c in susceptibility χ (T) is observed indicating the bulk nature of superconductivity. Different to most BiS2-based compounds where superconductivity develops from a semiconducting-like normal state, the present compound exhibits a metallic behavior down to T c . Under weak magnetic field or pressure, however, a remarkable crossover from metallic to insulating behaviors takes place around T min where the resistivity picks up a local minimum. With increasing pressure, T {}c decreases monotonously and T min shifts to high temperatures, while the absolute value of the normal state resistivity at low temperatures first decreases and then increases with pressure up to 2.5 GPa. These results imply that the electronic structure of Sr{}0.5La{}0.5FBiSe2 may be different to those in the other BiS2-based systems.

  6. 139La NMR investigation in underdoped La1.93Sr0.07CuO4

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Erb, A.; Büchner, B.; Grafe, H.-J.

    2012-05-01

    We report 139La and 63Cu nuclear magnetic and quadrupole resonance (NMR/NQR) studies in an underdoped La1.93Sr0.07CuO4 single crystal, focusing on the 139La NMR in the normal state. We demonstrate that the local structural distortions in the low-temperature orthorhombic structure cause the tilting of the direction of the electric field gradient (EFG) at the nuclei from the c axis, resulting in two NMR central transition spectra at both the 139La and 63Cu nuclei in an external field. Taking into account the tilt angle of the EFG, the temperature dependence of the 139La spectra allowed us to determine the 139La Knight shift and the structural order parameter. The angle and temperature dependence of the 139La spectrum is in perfect agreement with the macroscopic average structure and proves a displacive transition. The 139La nuclear spin-lattice relaxation rates, T1-1, suggest that La1.93Sr0.07CuO4 undergoes a gradual change to a temperature-independent paramagnetic regime in the high-temperature region. Both the spectra and T1-1 of the 139La as a function of temperature reveal a sharp anomaly around TS=387(1) K, implying a first-order-like structural transition, and a dramatic change below ˜70 K arising from collective glassy spin freezing.

  7. Enhanced refrigeration capacity and magnetic entropy change in La0.55Ce0.15Sr0.3MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Anwar, M. S.; Koo, Bon Heun

    2015-07-01

    The temperature dependent of the isothermal magnetic entropy change, Δ S M ( T), and the field dependence of the refrigeration capacity, RC, have been investigated in La0.7- x Ce x Sr0.30MnO3 ( x = 0.0 and 0.15). An enhanced RC and Δ S M ( T) were observed in La0.55Ce0.15Sr0.30MnO3. Under a magnetic field change of 2 T, the maximum improvement of 20% of Δ S M ( T) and 40% of RC, in comparison with La0.7Sr0.30MnO3, was observed. Moreover, Curie temperature of the La0.7Sr0.30MnO3 can tuned by adjusting the Ce concentration and makes this attractive for magnetic refrigeration at desired temperature. [Figure not available: see fulltext.

  8. Microstructure and dielectric tunable properties of Ba0.6Sr0.4TiO3-Mg2SiO4-MgO composite.

    PubMed

    He, Yanyan; Xu, Yebin; Liu, Ting; Zeng, Chunlian; Chen, Wanping

    2010-07-01

    Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composite ceramics were prepared by a solid-state reaction method and their dielectric tunable characteristics were investigated for the potential application as microwave tunable materials. The addition of Mg(2)SiO(4)-MgO into Ba(0.6)Sr(0.4)TiO(3) forms ferroelectric (Ba(0.6)Sr(0.4)TiO(3))-dielectric (Mg(2)SiO(4)-MgO) composites and shifts the Curie temperature to a lower temperature. The dielectric constant and loss tangent of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)- MgO composites have been decreased and the overall tunability is maintained at a sufficiently high level. The microwave dielectric properties of Ba(0.6)Sr(0.4)TiO(3)-Mg(2)Si(O4)-MgO composites were evaluated. Ba(0.6)Sr(0.4)TiO(3)-Mg(2)SiO(4)-MgO composites have tunability of 9.2 to 10.5% at 100 kHz under 2 kV/mm, indicating that it is a promising candidate material for tunable microwave applications requiring a low dielectric constant. PMID:20639146

  9. Vortex glass melting in single crystal La 1.825Sr 0.075CuO 4

    NASA Astrophysics Data System (ADS)

    Herbsommer, J. A.; Luzuriaga, J.; Cheong, S.-W.

    1996-02-01

    The vortex phase diagram in single crystalline La 1.85Sr 0.075CuO 4 has been studied using an AC-susceptibility technique. A peak in the out-of-phase ( χ“) component of the susceptibility indicates a transition from a pinned flux lattice (FLL) to an unpinned one. This peak is frequency dependent for all the values of the magnetic field measured (0.01 to 4 T), and this, as well as the general behavior found in the cuprates, has prompted us to interpret our data as evidence for a vortex-glass to liquid transition in the FLL. The activation energies obtained can be fitted to a theory developed by Vinokur et al. Measurements with the magnetic field at an angle with the Cu-O planes may also be understood qualitatively within this framework.

  10. Study of La0.9Sr0.1MnO3 manganite at different temperature

    NASA Astrophysics Data System (ADS)

    Patil, Swapnilkumar S.; Jha, Prafulla K.; Bhargava, Parag

    2015-05-01

    In this paper, the effect of sintering temperature on the structural properties of Sr doped lanthanum manganites is studied. The Sr doped manganites are synthesized using solid state reaction method. The structural properties of the sintered powders are examined by X-ray diffraction. The La0.9Sr0.1MnO3 powder samples exhibit a dominant peak along with increased peak intensity corresponding to the (104), (202), (204) reflections and some new peaks also appeared along (116),(036) and (0210) reflections compared to first sintering temperature (1250°C). This confirms a more polycrystalline nature of the powder at higher sintering temperature. The crystallite size varies between 45 nm to 50 nm. For relative study, the calculated average crystallite size and lattice parameters are noted in tabulated form.

  11. Magnetocaloric effect in epitaxial La0.56Sr0.44MnO3 alloy and digital heterostructures

    NASA Astrophysics Data System (ADS)

    Belyea, Dustin D.; Santos, Tiffany S.; Miller, Casey W.

    2012-04-01

    This work investigates the magnetocaloric effect of two epitaxial manganite heterostructures, one being a single layer La0.56Sr0.44MnO3 alloy with randomly distributed La and Sr cations, the other a digitally synthesized superlattice of LaMnO3 and SrMnO3 fabricated to be compositionally identical to the alloy. The magnetic entropy change and relative cooling power were larger for the alloy than the superlattice, though both are suppressed relative to bulk materials. These results indicate that disorder of the A-site cation species in the perovskite structure may play a crucial role in defining the magnetocaloric effect in complex oxide materials.

  12. Magnetic properties of (La0.56Ce0.14)Sr0.30MnO3 perovskite

    NASA Astrophysics Data System (ADS)

    Yahyaoui, Samia; Diep, H. T.

    2016-09-01

    We investigate in this paper magnetic properties of the perovskite compound (La0.56Ce0.14)Sr0.30MnO3. The method we use here is Monte Carlo simulation, in which we take into account different kinds of interactions between nearest and between next-nearest magnetic ions Mn3+ (S = 2), Mn4+ (S = 3 / 2) and Ce3+ (S = 1 / 2). Using a classical spin model, we have calculated the internal energy, the magnetization per ion type and their corresponding magnetic susceptibility, as well as the Edwards-Anderson order parameter for each ion kind. We also studied the applied-field effect on the system magnetization. Our results show a good agreement with experiments.

  13. Thermal gradient induced flexoelectric effects in bulk Ba0.67Sr0.33TiO3

    NASA Astrophysics Data System (ADS)

    Kim, Taeyang; Huang, Wenbin; Huang, Shujin; Jiang, Xiaoning

    2016-05-01

    Flexoelectric effect, denoting electric field gradient induced mechanical strain or mechanical strain gradient induced electric polarization, is a universal phenomenon in all dielectrics. Although research on the topic of flexoelectricity under stress fields and electric fields has advanced significantly, information regarding the phenomenon under thermal fields is rather limited. In this letter, the flexoelectricity field of Ba0.67Sr0.33TiO3 (BST) was investigated by generating temperature gradients along the lengths of samples with symmetric geometry. An electric field gradient induced by a thermal gradient was analyzed based on the temperature-dependent dielectric property of BST. The strain was then experimentally verified due to the electric field gradient. Experimental results suggest converse flexoelectric effect of BST samples with symmetric geometry in a thermal field. This result was not only consistent with the theoretical prediction, but it also followed the scaling effect of flexoelectricity.

  14. Large magnetocaloric effect in single crystal Pr0.63Sr0.37MnO3

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho

    2005-05-01

    This article reports the magnetocaloric effect in a single crystal Pr0.63Sr0.37MnO3, which undergoes a very sharp ferromagnetic-to-paramagnetic phase transition at ˜300K. A large magnetic entropy change of 8.52J/kgK and a large adiabatic temperature change of 5.65K for an applied field change of 50kOe were observed around 300K; this allows water to be used as a heat transfer fluid in the room-temperature magnetic refrigeration regime. The distribution of entropy change (ΔSM) was found to be very uniform and which is desirable for an Ericson-cycle magnetic refrigerator. The large magnetic entropy change induced by a relatively low magnetic field change is beneficial for household application.

  15. Strain modulated large magnetocaloric effect in Sm0.55Sr0.45MnO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Dasgupta, Papri; Poddar, A.; Sahoo, R. C.; Paladhi, D.; Nath, T. K.

    2015-01-01

    Epitaxial Sm0.55Sr0.45MnO3 thin films were deposited on LAO (001), LSAT (001), and STO (001) single crystalline substrates by pulsed laser deposition technique to investigate the correlation between the substrate induced film lattice strain and magnetocaloric effect (MCE). The film on LAO substrate (S_LAO), which is under compressive strain, undergoes ferromagnetic → paramagnetic transition at TC ˜ 165 K. The films on STO (S_STO) and LSAT (S_LSAT) substrates are under tensile strain and have TC ˜ 120 K and 130 K, respectively. At T < TC, the zero field cooled and field cooled magnetization curves of all the films show huge bifurcation. In case of S_STO and S_LSAT films, hysteresis is also observed between field cooled cooling and warming cycle in magnetization versus temperature measurement at low magnetic field similar to first order-like magnetic phase transition. No signature of first order magnetic phase transition has been observed in the case of S_LAO film. Most interestingly, both normal (i.e., negative ΔSM) and inverse (i.e., positive ΔSM) MCE around TC and above Tp, respectively, for S_STO and S_LSAT films have been observed with maximum value of MCE ˜ 10 J kg-1 K-1. The S_STO film also exhibits a large relative cooling power of 142 J/kg for a magnetic field change of 1 T. Our findings of substrate-induced strain modulated large MCE in epitaxial Sm0.55Sr0.45MnO3 films have been well explained through the substrate induced film lattice strain, and it may be useful for active magnetic refrigerant materials.

  16. Insight into the structure and functional application of the Sr0.95Ce0.05CoO3-δ cathode for solid oxide fuel cells.

    PubMed

    Yang, Wei; Zhang, Huairuo; Sun, Chunwen; Liu, Lilu; Alonso, J A; Fernández-Díaz, M T; Chen, Liquan

    2015-04-01

    A new perovskite cathode, Sr0.95Ce0.05CoO3-δ, performs well for oxygen-reduction reactions in solid oxide fuel cells (SOFCs). We gain insight into the crystal structure of Sr1-xCexCoO3-δ (x = 0.05, 0.1) and temperature-dependent structural evolution of Sr0.95Ce0.05CoO3-δ by X-ray diffraction, neutron powder diffraction, and scanning transmission electron microscopy experiments. Sr0.9Ce0.1CoO3-δ shows a perfectly cubic structure (a = a0), with a large oxygen deficiency in a single oxygen site; however, Sr0.95Ce0.05CoO3-δ exhibits a tetragonal perovskite superstructure with a double c axis, defined in the P4/mmm space group, that contains two crystallographically different cobalt positions, with distinct oxygen environments. The structural evolution of Sr0.95Ce0.05CoO3-δ at high temperatures was further studied by in situ temperature-dependent NPD experiments. At 1100 K, the oxygen atoms in Sr0.95Ce0.05CoO3-δ show large and highly anisotropic displacement factors, suggesting a significant ionic mobility. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ-electrolyte-supported (∼300 μm thickness) configuration yields peak power densities of 0.25 and 0.48 W cm(-2) at temperatures of 1023 and 1073 K, respectively, with pure H2 as the fuel and ambient air as the oxidant. The electrochemical impedance spectra evolution with time of the symmetric cathode fuel cell measured at 1073 K shows that the Sr0.95Ce0.05CoO3-δ cathode possesses superior ORR catalytic activity and long-term stability. Mixed ionic-electronic conduction properties of Sr0.95Ce0.05CoO3-δ account for its good performance as an oxygen-reduction catalyst. PMID:25756843

  17. The Role of Iron in the Enhancement of Negative Magnetoresistance in La0.8Sr0.2FexCo1-xO3-z

    SciTech Connect

    Nemeth, Z.; Homonnay, Z.; Vertes, A.; Hakl, J.; Vad, K.; Meszaros, S.; Lackner, B.; Kellner, K.; Gritzner, G.; Greneche, J.M.; Lindbaum, A.

    2005-04-26

    The role of iron in enhancing the magnetoresistance in the compounds La0.8Sr0.2FexCo1-xO3-z was investigated by studying the electronic and magnetic structure of La0.8Sr0.2FexCo1-xO3-z as a function of temperature. For this purpose 57Fe transmission Moessbauer spectroscopy, magnetoresistance, as well as AC and DC magnetization measurements were applied. The detailed study of the temperature dependence of 57Fe Moessbauer parameters gave possibility to explore correlations between the local electronic and magnetic state of iron and the magnetic susceptibility as well as magnetoresistance in La0.8Sr0.2FexCo1-xO3-z. On the basis of the obtained results an attempt was made to explain the exotic magnetic and MR properties of these perovskites.

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

    NASA Astrophysics Data System (ADS)

    Srivastava, Manoj K.; Singh, M. P.; Kaur, Amarjeet; Razavi, F. S.; Singh, H. K.

    2011-12-01

    Sm0.53Sr0.47MnO3 (SSMO) thin films (thicknesses ˜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 TC ˜ 96 and TIM ˜ 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 (θ) between the magnetic field (H) and plane of the film, shows colossal anisotropy. Magnetoresistance (MR) decreases drastically as θ increases from 0° (H//easy axis) to 90° (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.

  19. Strongly enhanced current densities in Sr0.6K0.4Fe2As2 + Sn superconducting tapes

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Xianping; Zhang, Haitao; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo

    2014-01-01

    Improving transport current has been the primary topic for practical application of superconducting wires and tapes. However, the porous nature of powder-in-tube (PIT) processed iron-based tapes is one of the important reasons for low critical current density (Jc) values. In this work, the superconducting core density of ex-situ Sr0.6K0.4Fe2As2 + Sn tapes, prepared from optimized precursors, was significantly improved by employing a simple hot pressing as an alternative route for final sintering. The resulting samples exhibited optimal critical temperature (Tc), sharp resistive transition, small resistivity and high Vickers hardness (Hv) value. Consequently, the transport Jc reached excellent values of 5.1 × 104 A/cm2 in 10 T and 4.3 × 104 A/cm2 in 14 T at 4.2 K, respectively. Our tapes also exhibited high upper critical field Hc2 and almost field-independent Jc. These results clearly demonstrate that PIT pnictide wire conductors are very promising for high-field magnet applications. PMID:24663054

  20. Magnetic investigation of silver sheathed Sr0.6K0.4Fe2As2 superconductor

    NASA Astrophysics Data System (ADS)

    Brunner, Boris; Reissner, Michael; Kováč, Pavol; Yao, Chao; Zhang, Xianping; Ma, Yanwei

    Magnetic investigation of a silver sheathed Sr0.6K0.4Fe2As2 tape prepared by ex-situ powder-in-tube technique (PIT) is reported. A transition temperature of 34.2 K was achieved. Dc magnetic measurements were performed in fields up to 14 T between 4.2 K and Tc. From hysteresis loops magnetic critical current densities Jc were determined. The tape exhibits excellent Jc performance. In low fields, the observed steep decline of Jc in increasing field is comparable to that measured in MgB2, although at a significantly lower absolute value. A kink-like crossover to a much flatter dependence at higher fields allows for a much better high field performance than that of MgB2. Such kink is also visible in the field dependence of the mean activation energies U, which were determined from magnetic relaxation measurements. The obtained U values are similar (< 40 meV at 4.2 K and 1 T) to those of Bi2212 tapes, but an order of magnitude smaller in comparison with good MgB2 wires.

  1. Structural and magnetic properties of Y0.33Sr0.67CoO2.79

    NASA Astrophysics Data System (ADS)

    Goossens, D. J.; Wilson, K. F.; James, M.; Studer, A. J.; Wang, X. L.

    2004-04-01

    The perovskite-based oxide Y0.33Sr0.67CoO2.79 has been magnetically and structurally characterized. The material shows a unit cell of 2×2×4 simple perovskite cubes with space group I4/mmm. This is a different structure to that observed in the much-studied (La,Sr)CoO3 oxides. Oxygen stoichiometry is established through thermogravimetric analysis and correlated with ac and dc magnetic measurements and magnetic neutron diffraction. Hysteresis with field and temperature is observed in the dc magnetization measurements, yet the absence of an imaginary component in the ac susceptibility suggests a time-independent cause for these effects such as the presence of independently ordering ferromagnetic regions due to compositional inhomogeneities within the (single-phase) sample. Rietveld magnetic refinements suggest that the Co moments are arranged antiferromagnetically below 320 K, with the ferromagnetic regions existing within the long-range ordered antiferromagnetic matrix. The staggered moments are (anti)parallel with the c axis and of magnitude 2μB, a moment most typical of intermediate spin Co3+. The material does not enter a spin glass or cluster glass phase, but appears to undergo a broad spin-state transition below 100 K.

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

    NASA Astrophysics Data System (ADS)

    Ehsani, M. H.; Kameli, P.; Ghazi, M. E.; Razavi, F. S.; Taheri, M.

    2013-12-01

    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 °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.

  3. Synthesis of Sr0.9K0.1FeO3-δ electrocatalysts by mechanical activation

    NASA Astrophysics Data System (ADS)

    Monteiro, J. F.; Waerenborgh, J. C.; Kovalevsky, A. V.; Yaremchenko, A. A.; Frade, J. R.

    2013-02-01

    Potassium-substituted SrFeO3-δ for possible application as oxygen evolution electrode in alkaline or molten salt media was prepared by mechanical activation and characterized by X-ray diffraction, dilatometric and thermogravimetric analysis, Mössbauer spectroscopy, and electrical conductivity measurements. Room temperature mechanical activation of a mixture of oxide precursors with subsequent thermal treatments at 700-900 °C results in the formation of Sr0.9K0.1FeO3-δ with tetragonal perovskite-like structure. Such allows to decrease the synthesis temperature, if compared to the conventional solid-state route, and to prevent possible volatilization of potassium. The results of Mössbauer spectroscopy studies indicate that the oxygen nonstoichiometry in the samples annealed in air at 900-1100 °C with subsequent rapid cooling vary in the range δ=0.30-0.32. The electrical conductivity in air exhibits a metal-like behaviour at temperatures above 400 °C and semiconductor behaviour in the low-temperature range, reaching 13-30 S/cm under prospective operation conditions for alkaline electrolyzers (≤90 °C).

  4. Critical behavior in single-crystalline La0.67Sr0.33CoO3

    NASA Astrophysics Data System (ADS)

    Khan, N.; Midya, A.; Mydeen, K.; Mandal, P.; Loidl, A.; Prabhakaran, D.

    2010-08-01

    The critical behavior of La0.67Sr0.33CoO3 single crystal has been investigated from the bulk magnetization measurements around the Curie temperature (TC) . The detailed analysis of the magnetization indicates the occurrence of a continuous ferromagnetic to paramagnetic phase transition at 223.0 K. The critical exponents β=0.361±0.007 , γ=1.31±0.001 , and δ=4.64±0.01 characterizing this second order phase transition, have been estimated using different techniques such as the Kouvel-Fisher plot, the Arrott-Noaks plot, and critical isotherm analysis. With these values of TC , β , and γ , one can scale the magnetization below and above TC following a single equation of state. The consistency in the values of the critical exponents obtained from different methods and the well-obeyed scaling behavior confirm that the calculated exponents are unambiguous and purely intrinsic to the system. These values of the exponents match well with those theoretically predicted for the three-dimensional Heisenberg model with nearest-neighbor interaction.

  5. Colossal elastoresistance, electroresistance and magnetoresistance in Pr0.5Sr0.5MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Guo, Xuexiang; Gao, J.

    2016-05-01

    Pr0.5Sr0.5MnO3 thin films on substrates of (001)-oriented LaAlO3 were epitaxially grown by pulsed laser deposition. It was found that a substrate-induced strain of ~1.3% brings a great resistivity change of ~98% at 25 K. We studied the dependence of resistivity on the applied electric current and magnetic field. In the greatly strained films of 60 nm thickness the electroresistance ER=[ρ(I1 μA)-ρ(I1000 μA)]/ρ(I1 μA) reaches ~70% at T=25 K, much higher than ER~7% in the strain-relaxed films of 400 nm thickness, implying the strain effect on ER. Also the magnetoresistance of the film falls with strain-relaxation. Therefore the electric properties of the film could be efficiently modified by strain, electric current and magnetic field. All of them may be explained by the effect on the percolative phase separation and competition in the half-doped manganite material. The manganite films located at phase boundary are expected to be an ideal compound for providing practical colossal effects of elastoresistance, electroresistance and magnetoresistance due to the multiphase coexistence.

  6. Dielectric dynamics of the polycrystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Pečnik, Tanja; Eršte, Andreja; Matavž, Aleksander; Bobnar, Vid; Ivanov, Maksim; Banys, Juras; Xiang, Feng; Wang, Hong; Malič, Barbara; Glinšek, Sebastjan

    2016-05-01

    Polycrystalline Ba0.5Sr0.5TiO3 films, with thicknesses between 90 and 600 nm, were prepared on alumina substrates at 900 °C by chemical solution deposition (CSD) and a dielectric spectroscopy investigation of the in-plane properties was performed. The 5-kHz permittivity ε‧ shows a non-monotonic thickness dependence, reaching 1230 at room temperature for the 310-nm-thick film, whose grain size is ∼75 nm. Its 15-GHz-value and losses are 1105 and 0.05, respectively. The temperature of the permittivity maximum T max at 5 kHz decreases with increasing thickness from 277 to 250 K for the 170- and 600-nm-thick films, respectively, which has been linked to the residual biaxial stress. A hysteresis is observed in the permittivity ε‧-electric field E DC characteristics in all the films up to ∼50 K above T max . Frequency dispersion in which permittivity decreases with increasing frequency is present below T max in films thicker than 90 nm. The high permittivity values of the thinnest films, which are among the highest reported in the (Ba,Sr)TiO3 films with grain sizes below 75 nm, are a direct proof of the optimized CSD processing conditions.

  7. Insulating phase at low temperature in ultrathin La0.8Sr0.2MnO3 films

    PubMed Central

    Feng, Yaqing; Jin, Kui-juan; Gu, Lin; He, Xu; Ge, Chen; Zhang, Qing-hua; He, Min; Guo, Qin-lin; Wan, Qian; He, Meng; Lu, Hui-bin; Yang, Guozhen

    2016-01-01

    Metal-insulator transition is observed in the La0.8Sr0.2MnO3 thin films with thickness larger than 5 unit cells. Insulating phase at lower temperature appeared in the ultrathin films with thickness ranging from 6 unit cells to 10 unit cells and it is found that the Mott variable range hopping conduction dominates in this insulating phase at low temperature with a decrease of localization length in thinner films. A deficiency of oxygen content and a resulting decrease of the Mn valence have been observed in the ultrathin films with thickness smaller than or equal to 10 unit cells by studying the aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy of the films. These results suggest that the existence of the oxygen vacancies in thinner films suppresses the double-exchange mechanism and contributes to the enhancement of disorder, leading to a decrease of the Curie temperature and the low temperature insulating phase in the ultrathin films. In addition, the suppression of the magnetic properties in thinner films indicates stronger disorder of magnetic moments, which is considered to be the reason for this decrease of the localization length. PMID:26928070

  8. Spectroellipsometric studies of sol-gel derived Sr0.6Ba0.4Nb2O6 films

    NASA Astrophysics Data System (ADS)

    Ho, Melanie M. T.; Tang, T. B.; Mak, C. L.; Pang, G. K. H.; Chan, K. Y.; Wong, K. H.

    2006-10-01

    Sr0.6Ba0.4Nb2O6 (SBN) films have been fabricated on (001)Si substrates by a sol-gel technique. The annealing process was carried out in air at various temperatures ranging from 200to700°C. Studies using x-ray diffractometry, high resolution transmission electron microscopy, and scanning electron microscopy showed that polycrystalline films, with a grain size of about 100nm, were obtained only for annealing temperatures ⩾600°C. The optical properties of these sol-gel derived SBN films were studied by spectroscopic ellipsometry (SE). In the analysis of the measured SE spectra, a triple-layer Lorentz model has been developed and used to deduce the optical properties of the SBN films. Our systematic SE measurements revealed that the refractive indices of the SBN films increase with the annealing temperature. This increase is more pronounced at around the crystallization temperature, i.e., between 500 and 600°C. The extinction coefficients of the films also exhibit a similar trend, showing a zero value for amorphous films and larger values for films annealed at above 600°C. Our results demonstrate that while crystallization helps to raise the refractive index of the film due to film densification, it also promotes scattering by grain boundary, resulting in a larger extinction coefficient.

  9. Colossal Piezoresistance in strained La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Viitaniemi, Maria; Kwak, In Hae; Biswas, Amlan

    2015-03-01

    Piezoresistance is the change in electrical resistance as a function of strain. A known mechanism leading to piezoresistance is thermodynamic phase separation. It has been shown that the compound (La1-yPry)1-xCaxMnO3 (LPCMO) exhibits colossal piezoresistance (CPR) at low temperatures due to electronic phase separation. For use in many applications, such as sensors, materials must exhibit CPR near room temperature. A possible candidate compound is La0.67Sr0.33MnO3 (LSMO) which has a Curie temperature of approximately 350 K. However, bulk LSMO single crystals do not show CPR since such samples are uniformly ferromagnetic and metallic with no phase separation. In this study, we examine the piezoresistance of ultrathin LSMO films grown on SrTiO3 (STO) substrates using a three-point beam bending method to control the compressive and tensile strain. It has been suggested that the lattice mismatch strain due to the substrate induces phase separation in these thin films. We have observed CPR in such strained LSMO thin films even at room temperature. NSF DMR-1410237.

  10. Reversible aging behavior of La0.8Sr0.2MnO3 electrodes at open circuit

    SciTech Connect

    Abernathy, H.; Finklea, H.; Mebane, D.; Chen, X.; Gerdes, K.; Salazar, M.

    2012-01-01

    La0.8Sr0.2MnO3 (LSM) electrodes on yttria-stabilized zirconia (YSZ) electrolytes were characterized at open circuit by impedance spectroscopy. An initial irreversible change in the polarization resistance is observed for cells aged with no prior current activation. After the initial break-in, the polarization resistance rises with time at 700 #1;C and decays at 800 #1;C, reversibly, over repeated temperature cycles. The initial irreversible break-in and subsequent reversible cycling behavior suggests multiple processes happening within the time and temperatures measured. The authors propose that these processes are (1) changes in the wetting behavior of the LSM on the YSZ and (2) the reversible segregation/desegregation of cations within LSM. Between 700 #1;C and 800 #1;C, there is a transition temperature at which the segregation behavior of cations to the cathode surface changes. These measurable changes in the impedance behavior of LSM indicate that cation segregation, while considered by some to be part of the cathode activation process, may be dictated by thermodynamic factors, and thus not strictly dependent on the passage of current through the cathode.

  11. Magnetism in La0.7Sr0.3Mn1-xCoxO3 (0 ≤ x ≤ 1)

    NASA Astrophysics Data System (ADS)

    Kumar, Ashutosh; Sharma, Himanshu; Tomy, C. V.; Thakur, Ajay D.

    2016-05-01

    We study the structural and magnetic properties of La0.7Sr0.3Mn1-xCoxO3 (0 ≤ x ≤ 1). Rietveld refinement of X-ray Diffraction (XRD) pattern suggests phase purity of the polycrystalline samples with R-3c space group. Interplay of Ferromagnetic (FM) and Antiferromagnetic (AFM) interaction upon Co substitution at Mn site in La0.7Sr0.3MnO3 is evident from magnetic measurements. There is an optimal cobalt substitution at which the coercive field is maximum.

  12. Strain-relaxation and critical thickness of epitaxial La1.85Sr0.15CuO4 films

    DOE PAGESBeta

    Meyer, Tricia L; Jiang, Lu; Park, Sungkyun; Egami, Takeshi; Lee, Ho Nyung

    2015-12-08

    We report the thickness-dependent strain-relaxation behavior and the associated impacts upon the superconductivity in epitaxial La1.85Sr0.15CuO4 films grown on different substrates, which provide a range of strain. We have found that the critical thickness for the onset of superconductivity in La1.85Sr0.15CuO4 films is associated with the finite thickness effect and epitaxial strain. In particular, thin films with tensile strain greater than ~0.25% revealed no superconductivity. We attribute this phenomenon to the inherent formation of oxygen vacancies that can be minimized via strain relaxation.

  13. Metamaterials: A New Ba0.6 Sr0.4 TiO3 -Silicon Hybrid Metamaterial Device in Terahertz Regime (Small 19/2016).

    PubMed

    Wu, Liang; Du, Ting; Xu, Ningning; Ding, Chunfeng; Li, Hui; Sheng, Quan; Liu, Ming; Yao, Jianquan; Wang, Zhiyong; Lou, Xiaojie; Zhang, Weili

    2016-05-01

    A giant terahertz modulation based on a Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial is reported by L. Wu, W. Zhang, and co-workers on page 2610. The proposed nanoscale Ba0.6 Sr0.4 TiO3 (BST) hybrid metamaterial, delivering a transmission contrast of up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate, is promising in developing high-performance real world photonic devices for terahertz technology. PMID:27167323

  14. Critical behavior near the ferromagnetic - paramagnetic phase transition in La0.7Sr0.3MnO3+d nanowires synthesized by hydrothermal method

    NASA Astrophysics Data System (ADS)

    Datta, Subarna; Ghosh, Barnali

    2015-06-01

    We report here the synthesis, characterization and magnetic properties of functional oxide nanowire (NW) of hole doped manganite La0.7Sr0.3MnO3+d (LSMO). The nanowires (NWs) are fabricated by hydrothermal method using autoclave at a temperature of 240°C. Due to size reduction of the NWs the volume of the unit cell decreases ~ 1% with respect to the bulk La0.7Sr0.3MnO3. The LSMO NWs have a ferromagnetic - paramagnetic transition temperature or Curie temperature (TC) at 311 K and it shows second order phase transition at TC as seen in bulk.

  15. Critical exponents and irreversibility lines of La0.9Sr0.1CoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Khan, N.; Midya, A.; Mandal, P.; Prabhakaran, D.

    2013-05-01

    We have studied the dynamic and static critical behavior of spin glass transition in insulating La0.9Sr0.1CoO3 single crystal by ac susceptibility and dc magnetization measurements in the vicinity of its freezing temperature (Tf). The dynamic scaling analysis of the frequency dependence of ac susceptibility data yields the characteristic time constant τ0=1.6(9)×10-12 s, the dynamic critical exponent zν=9.5(2), and a frequency dependence factor K =ΔTf/Tf(Δlogf)=0.017, indicating that the sample enters into a canonical spin-glass phase below Tf = 34.8(2) K. The scaling analysis of non-linear magnetization in the vicinity of Tf through the static scaling hypothesis yields critical exponents β = 0.89(1) and γ = 2.9(1), which match well with that observed for well known three-dimensional (3D) Heisenberg spin glasses. From the longitudinal component of zero-field-cooled and field-cooled magnetization measurement, we have constructed the H-T phase diagram which represents the field evolution of two characteristic temperatures: the upper one, Tw(H), indicates the onset of spin freezing in a uniform external field H, while the lower one, Ts(H), marks the onset of strong irreversibility of the frozen state. The low field Ts(H) follows the critical line suggested by d'Almeida-Thouless model for canonical spin glass, whereas the Tw(H) exhibits a re-entrant behavior with a maximum in the Tw(H) at a nonzero field above which it follows the Gabay-Toulouse (GT) critical line which is a characteristic of Heisenberg spin glass. The reentrant behavior of the GT line resembles that predicted theoretically for n-component vector spin glasses in the presence of a uniaxial anisotropy field.

  16. Reversible control of magnetism in La0.67Sr0.33MnO3 through chemically-induced oxygen migration

    NASA Astrophysics Data System (ADS)

    Grutter, A. J.; Gilbert, D. A.; Alaan, U. S.; Arenholz, E.; Maranville, B. B.; Borchers, J. A.; Suzuki, Y.; Liu, Kai; Kirby, B. J.

    2016-02-01

    We demonstrate reversible control of magnetization and anisotropy in La0.67Sr0.33MnO3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La0.67Sr0.33MnO3 leach oxygen from the film through a solid-state redox reaction to form porous Gd2O3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped La0.67Sr0.33MnO3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd2O3 layer and the magnetization of the La0.67Sr0.33MnO3 returns to the uncapped value. These findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.

  17. X-ray photoemission study of the infinite-layer cuprate superconductor Sr(0.9) La (0.1) CuO(2)

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Jung, C. U.; Kim, J. Y.; Kim, M. S.; Lee, S. Y.; Lee, S. I.

    2001-01-01

    The electron-doped infinite-layer superconductor Sr(0.9)La(0.1) CuO(2) is studied with x-ray photoemission spectroscopy (XPS). A nonaqueous chemical etchant is shown to effectively remove contaminants and to yield surfaces from which signals intrinsic to the superconductor dominate.

  18. Effect of sol-gel method on structural and electron magnetic resonance properties of Pr0.6Sr0.4MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Thaljaoui, R.; Boujelben, W.; Pękała, M.; Szydłowska, J.; Cheikhrouhou, A.

    2012-06-01

    Structural and electron magnetic resonance studies in a broad temperature range are reported for Pr0.6Sr0.4MnO3 manganite synthesized by sol-gel method. Temperature dependence of magnetic resonance spectra is analyzed in the paramagnetic state and compared to similar systems. Using the temperature variation of signal intensity the activation energy is calculated.

  19. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex. PMID:26032295

  20. Performance Enhancement of the Dielectric Properties of Sn-Doped Ba0.8Sr0.2TiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Brahem, R.; Farhat, N.; Graça, M. P. F.; Costa, L. C.

    2016-06-01

    The aim of this paper is to study performance enhancement of the dielectric properties of polycrystalline Ba_{0.8} Sr_{0.2} Ti_(1 - x) Snx O3, with 0 ≤ x ≤ 0.2 . The material was characterized by x-ray diffraction, scanning electron microscopy (SEM), micro-Raman spectroscopy and impedance spectroscopy technique. The results have been analyzed by studying the effects of substituting Sn4+ for Ti4+. The observed diffraction peaks have been indexed to a cubic structure with space group Pm3m. The calculated lattice parameters increase from 3.9834 Å to 4.0091 Å with increasing Sn concentration. The SEM micrographs show that with increasing Sn an increase of the grain size from x = 0 up to x = 0.15 was observed. The dielectric measurements confirm the relaxor behavior of all the concentrations of Ba_{0.8} Sr_{0.2} Ti_(1 - x) Sn}x O3 compounds. The Ba_{0.8} Sr_{0.2} Ti_{0.95} Sn_{0.05} O3 compound presents the most interesting properties, namely high dielectric constant value (ɛ^'(T_{{m}} ) = 5017 ) and a Curie temperature slightly above room temperature (T_{{c}} = 317 K) . An important dielectric constant value persists for a wide range of temperatures around room temperature. This is considered as an advantage of the Ba_{0.8} Sr_{0.2} Ti_{0.95} Sn_{0.05} O3 relaxor ferroelectrics.

  1. Surface characterization, in vitro and in vivo biocompatibility of Mg-0.3Sr-0.3Ca for temporary cardiovascular implant.

    PubMed

    Bornapour, M; Mahjoubi, H; Vali, H; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2016-10-01

    Magnesium-based alloys are attractive candidate materials for medical applications. Our earlier work showed that the ternary Mg-0.3Sr-0.3Ca alloy exhibits slower degradation rates than both binary Mg-Sr and Mg-Ca alloys. The ternary alloy immersed in simulated body fluid (SBF) forms a compact surface layer of corrosion products that we hypothesized to be a Sr-substituted hydroxyapatite (HA). The main objectives of the current work are to understand the bio-degradation mechanism of Mg-0.3Sr-0.3Ca, to identify the exact nature of its protective layer and to evaluate the in vitro and in vivo biocompatibility of the alloy for cardiovascular applications. To better simulate the physiological environment, the alloy was immersed in SBF which was daily refreshed. Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) confirmed the formation of a thin, Sr-substituted HA layer at the interface between the alloy and the corrosion products. In vitro biocompatibility evaluated via indirect cytotoxicity assays using HUVECs showed no toxicity effect and ions extracted from Mg-0.3Sr-0.3Ca in fact increased the viability of HUVECs after one week. In vivo tests were performed by implanting a tubular Mg-0.3Sr-0.3Ca stent along with a WE43 control stent into the right and left femoral artery of a dog. Post implantation and histological analyses showed no thrombosis in the artery with Mg-0.3Sr-0.3Ca stent after 5weeks of implantation while the artery implanted with WE43 stent was extensively occluded and thrombosed. Microscopic observation of the Mg-0.3Sr-0.3Ca implant-tissue interface confirmed the in situ formation of Sr-substituted HA on the surface during in vivo test. These results show that the interfacial layer protects the surface of the Mg-0.3Sr-0.3Ca alloy both in vitro and in vivo, and is the key factor in the bio-corrosion resistance of the alloy. PMID:27287101

  2. Electric polarization of Sr0.5Ba0.5MnO3: a multiferroic Mott insulator

    NASA Astrophysics Data System (ADS)

    Nourafkan, Reza

    2015-03-01

    Multiferroics, materials which display simultaneous magnetic and ferroelectric orders, are interesting both for their rich physics and for their promising practical applications. The search for multiferroic materials with strong-magnetoelectric coupling is challenging and requires an understanding of how the magnetic order, or more specifically the correlations, influence the electric polarization and vice versa. A calculations of the electric polarization in the paramagnetic (PM) insulating phase of multiferroics is essential to address this mutual influence. Ab inito calculations of the electric polarization are based on the modern theory of polarization, which is a single-electron theory. Thus, a correlation driven insulating state is beyond the scope of this approach. Here we show that combining correlated band structure calculations (DFT+DMFT) with a formula for the electric polarization of interacting insulators, expressed in terms of the full Green and vertex functions, allows for the first time to reliably calculate the polarization in the PM phase. We focus on the Mott insulator Sr0.5Ba0.5MnO3, in which both magnetic and ferroelectric instabilities are related to the Mn ions. We predict a ferroelectric polarization of ~= 16 . 5 μC / cm2 in the high temperature paramagnetic phase and recover the measured value of ~= 13 . 3 μC / cm2 in the low temperature antiferromagnetic phase. Our calculations reveal that the the driving force behind the ferroelectric distortion comes from the tendency of Mn eg states to establish a stronger covalency with the surrounding oxygens. This covalency is reduced by correlations, in particular by Hund coupling. On the other hand, the half-filled Mn t2 g orbitals give rise to the magnetic ordering which decreases the ionic displacement, hence its contribution to the polarization. For fixed ionic displacement, the magnetic order also slightly decreases the electronic contribution to the electric polarization by partially

  3. Study of magnetic transition and magnetic entropy changes of Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3 compounds

    NASA Astrophysics Data System (ADS)

    Nasri, Abir.; Hlil, E. K.; Lehlooh, A.-F.; Ellouze, M.; Elhalouani, F.

    2016-04-01

    In the present work, we analyze the magnetic transition and magnetic entropy change \\vertΔ SM\\vert of Pr0.6Sr0.4Mn1- x Fe x O3 samples. Using Arrott plots, we report that the phase transition for Pr0.6Sr0.4MnO3 sample is of second order, while the Pr0.6Sr0.4Mn0.9Fe0.1O3 sample exhibits a first-order magnetic phase transition. From the magnetization measurements at temperature close to the Curie temperature, the magnetic entropy change, \\vertΔ SM\\vert and the Relative Cooling Power (RCP) have been estimated. The maximum of magnetic entropy change \\vertΔ S_M^{max}\\vert reaches, under an applied magnetic field of 5T, 3.58 and 3.66J/kg K for Pr0.6Sr0.4MnO3 and Pr0.6Sr0.4Mn0.9Fe0.1O3, respectively. The RCP values have been estimated to 159.37 and 223.52J/kg. For both samples, the \\vertΔ SM\\vert values evaluated using the Maxwell theory were found in accordance with those calculated by the Landau theory.

  4. Synthesis and electrochemical performance of La0.7Sr0.3Co1-xFexO3 catalysts for zinc air secondary batteries

    NASA Astrophysics Data System (ADS)

    Ahn, Seyoung; Kim, Ketack; Kim, Hyunsoo; Nam, Sangyong; Eom, Seungwook

    2010-05-01

    We prepared La0.7Sr0.3Co1-xFexO3 (x=0.1-0.4) catalysts for a zinc air battery by using the citrate method under controlled pH. The prepared precursor powder was heat treated at the calcination temperature of 700 °C and examined for the optimum structure of the cathode. The structure and performance of the catalysts were examined by x-ray diffraction and a scanning electron microscope. The air electrode was prepared by blending the catalyst, Vulcan XC-72R (carbon black), and (polytetrafluoroethylene PTFE) suspension. The oxygen reduction reaction and the oxygen evolution reaction were examined by linear sweep voltammetry. The results showed that La0.7Sr0.3Co0.7Fe0.3O3 (LSCF0.7) is an excellent catalyst for the zinc air secondary battery.

  5. A-site-deficiency effect on critical behavior in the Pr0.6Sr0.4MnO3 compound.

    PubMed

    Elleuch, F; Bekri, M; Hussein, M; Triki, M; Dhahri, E; Hlil, E K; Bessais, L

    2015-10-28

    We present the effect of vacancy in Pr0.6Sr0.4MnO3via dc magnetisation measurements. Using various techniques such as modified Arrott plots, the Kouvel-Fisher method, and Widom scaling relationship the values of TC (ferromagnetic transition temperature), as well as the β, γ and δ (critical exponents) are estimated. Critical exponents for the stoichiometric sample and the strontium deficient sample match well with those predicted for the tricritical mean field model. The vacancy in Pr0.5□0.1Sr0.4MnO3 changes the universal class. The estimated critical exponents of the praseodymium deficient sample are close to those found out by the 3D-Ising model. PMID:26395805

  6. Structural properties and singular phase transitions of metallic Pr0.50Sr0.50CoO3 cobaltite.

    PubMed

    Padilla-Pantoja, Jessica; García-Muñoz, José Luis; Bozzo, Bernat; Jirák, Zdeněk; Herrero-Martín, Javier

    2014-12-01

    The Pr0.50Sr0.50CoO3 perovskite exhibits unique magnetostructural properties among the rest of the ferromagnetic/metallic Ln0.50Sr0.50CoO3 compounds. Existing reports are largely controversial. We have determined and described its structural evolution, which follows the Pm3̅m → R3̅c → Imma → I4/mcm transformations. The structural changes have been thoroughly described. The results are confronted with distinct nonconventional properties and spin-lattice coupling effects in another half-doped cobaltite based on praseodymium, Pr0.50Ca0.50CoO3. The Imma →  I4/mcm symmetry change is responsible for the unexpected second magnetic transition. PMID:25383644

  7. Increase of dielectric constant in PVDF by incorporating La1.8Sr0.2NiO4 into its matrix

    NASA Astrophysics Data System (ADS)

    Kumar, Rajnish; Goswami, Ashwin M.; Kar, Manoranjan

    2016-05-01

    To obtain the material with high dielectric constant and high dielectric strength for the technological applications, nanocomposite of Lanthanum Strontium Nickelete (La1.8Sr0.2NiO4) as nanofiller and polyvinylidene fluoride (PVDF) as polymer matrix has been prepared. The different nanofiler weight concentration varies from 2-8 weight percent. X-ray diffraction technique confirms the phase formation of nanocomposite. Differential scanning calorimeter (DSC) has been employed to study the percentage of crystallinity and Impedance measurement has been carried out to study the dielectric constant. DSC analysis shows decreasing trend of crystallinity whereas impedance analysis gives increasing dielectric constant with increasing La1.8Sr0.2NiO4 concentration in the nanocomposite. Also, these materials can be used as insulator in the transformer as the strength and dielectric behavior of present composite meets the technological requirements.

  8. Single crystalline La0.5Sr0.5MnO3 microcubes as cathode of solid oxide fuel cell

    SciTech Connect

    Mingjia Zhi; Guangwen Zhou; Zhanglian Hong; Jin Wang; Randall Gemmen; Kirk Gerdes; Ayyakkannu Manivannan; Dongling Mae; Nianqiang Wu

    2010-09-13

    The efficiency of solid oxide fuel cells (SOFCs) is heavily dependent on the electrocatalytic activity of the cathode toward the oxygen reduction reaction (ORR). In order to achieve better cathode performance, single crystalline La0.5Sr0.5MnO3 (LSM) microcubes with the {200} facets have been synthesized by the hydrothermal method. It is found that the LSM microcubes exhibit lower polarization resistance than the conventional polycrystalline La0.8Sr0.2MnO3 powder in air from 700 #2;C to 900 #2;C. The ORR activation energy of the LSM microcubes is lower than that of the conventional powder. The ORR kinetics for the microcubes is limited by the charge transfer step while that for the conventional powder is dominated by the oxygen adsorption and dissociation on the cathode surface.

  9. Epitaxial La0.5Sr0.5CoO3 thin films: Structure, magnetism, and transport

    NASA Astrophysics Data System (ADS)

    Torija, M. A.; Sharma, M.; Fitzsimmons, M. R.; Varela, M.; Leighton, C.

    2008-07-01

    La1-xSrxCoO3 has received considerable attention in bulk form. This is due to interest in the fundamental magnetic properties (spin-state transitions and magnetic phase separation) as well as potential applications in ferroelectric memory and solid-oxide fuel cells. The structure and properties in thin film form are not well understood, and the influence of dimensional confinement on effects such as magnetic phase separation is unknown. Here, we report a comprehensive investigation of structure, magnetism, and transport in strained epitaxial La0.5Sr0.5CoO3 (001) films deposited on SrTiO3 (001) substrates by reactive dc magnetron sputtering. The crystalline quality, phase purity, strain state, oxygen stoichiometry, morphology, and magnetic and electronic properties of the epilayers are all probed and are found to be particularly sensitive to the total sputtering gas pressure and the ratio of reactive to inert gas (PO2/PAr). The various structure-property relationships are discussed in detail, particularly with respect to the degree of oxygenation and oxygen-induced resputtering. The films are strained and tetragonally distorted due to the 1.9% lattice mismatch with SrTiO3. Significant strain relaxation occurs at thicknesses around 200 Å, resulting in a crossover from two-dimensional-like to three-dimensional growth. Polarized neutron reflectometry was combined with x-ray reflectometry to obtain chemical and magnetic depth profiles, which are compared with cross-sectional scanning transmission electron microscopy. The results indicate a thin (˜10 Å) layer at the film/substrate interface with significantly different structural properties to the bulk of the film, as well as a strongly graded magnetic and chemical profile at the film surface due to the significant roughness. The Curie temperature was found to decrease very slowly as the thickness is reduced down to ˜50 Å, at which point a rapid decrease occurs, almost coincident with a sharp decrease in saturation

  10. Synthesis crystal structure and ionic conductivity of Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10

    NASA Astrophysics Data System (ADS)

    Porob, Digamber G.; Guru Row, T. N.

    2004-12-01

    Two new compounds Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10 have been synthesized in the ternary system: MO-Bi 2O 3-V 2O 5 system ( M=M 2+). The crystal structure of Sr 0.5Bi 3V 2O 10 has been determined from single crystal X-ray diffraction data, space group P1¯ and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å 3. Ca 0.5Bi 3V 2O 10 is isostructural with Sr 0.5Bi 3V 2O 10, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å 3 and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi 2O 2) along c-axis formed by linkage of BiO 8 and BiO 6 polyhedra interconnected by MO 8 polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10 -5 and 3.63×10 -5 S cm -1 for Ca 0.5Bi 3V 2O 10 and Sr 0.5Bi 3V 2O 10, respectively at 725 °C.

  11. Dielectric resonance effect with negative permittivity in a La1.5Sr0.5NiO4+ δ ceramic

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Van Dang, Nguyen; Van Hong, Le; Phan, The-Long; Yu, Seong-Cho

    2014-11-01

    A polycrystalline sample of La1.5Sr0.5NiO4+ δ was prepared by using a solid-state reaction. X-ray diffraction proved the sample to be a single phase with a tetragonal structure (space group: I4/mmm). By using an iodometric titration method to determine the non-stoichiometric oxygen concentration ( δ) in La1.5Sr0.5NiO4+ δ , we found δ = -0.017, which corresponds to a doping level of n h = x + 2 δ = 0.466. Also, a strong increase of the magnetization in the M( T) curve at temperatures below the spin-ordering temperature ( T SO ~ 100 K) was observed. The M( H) curves show very small magnetic moments, which proves the weak ferromagnetic nature of La1.5Sr0.5NiO4+ δ . The dependences of the dielectric constant on the frequency and the temperature, ɛ( ω, T) = ɛ'( ω, T) + iɛ″( ω, T), was investigated in the frequency range of 1-13 MHz. At temperatures around room temperature, the maximum of the real part ( ɛ') was higher than 105. Particularly, an abnormal dependence of the permittivity on frequency was observed. Depending on temperature, a dielectric resonance was observed at about 500 kHz or 8 MHz. Interestingly, we observed the dielectric-resonance effect with a negative permittivity. Such a feature is very similar to that observed in left-handed materials. The fitting of the experimental data for the dielectric constant at frequencies around the resonance frequency to the equations associated with an equivalent RLC series circuit proves that La1.5Sr0.5NiO4+ δ belongs to the class of multiferroic materials.

  12. Performance Enhancement of the Dielectric Properties of Sn-Doped Ba0.8Sr0.2TiO3 Perovskite

    NASA Astrophysics Data System (ADS)

    Brahem, R.; Farhat, N.; Graça, M. P. F.; Costa, L. C.

    2016-06-01

    The aim of this paper is to study performance enhancement of the dielectric properties of polycrystalline {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3 , with 0 ≤ x ≤ 0.2 . The material was characterized by x-ray diffraction, scanning electron microscopy (SEM), micro-Raman spectroscopy and impedance spectroscopy technique. The results have been analyzed by studying the effects of substituting Sn4+ for Ti4+. The observed diffraction peaks have been indexed to a cubic structure with space group Pm3m. The calculated lattice parameters increase from 3.9834 Å to 4.0091 Å with increasing Sn concentration. The SEM micrographs show that with increasing Sn an increase of the grain size from x = 0 up to x = 0.15 was observed. The dielectric measurements confirm the relaxor behavior of all the concentrations of {Ba}_{0.8} {Sr}_{0.2} {Ti}_{(1 - x)} {Sn}x {O}3 compounds. The {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 compound presents the most interesting properties, namely high dielectric constant value (&epsilon^'(T_{m} ) = 5017 ) and a Curie temperature slightly above room temperature (T_{c} = 317 {K}) . An important dielectric constant value persists for a wide range of temperatures around room temperature. This is considered as an advantage of the {Ba}_{0.8} {Sr}_{0.2} {Ti}_{0.95} {Sn}_{0.05} {O}3 relaxor ferroelectrics.

  13. Tracing the origin of oxygen for La0.6Sr0.4MnO3 thin film growth by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Chen, J.; Döbeli, M.; Stender, D.; Lee, M. M.; Conder, K.; Schneider, C. W.; Wokaun, A.; Lippert, T.

    2016-02-01

    We report on the semi-quantitative analysis of pulsed laser induced plasma species as well as thin film compositions of La0.6Sr0.4MnO3 grown on SrTiO3 substrates under various background pressure regimes using an 18O isotope labelled La0.6Sr0.4MnO3 target. The importance of negative metal-oxygen or positive metal-oxygen ions to influence the final oxygen composition of the thin film is illustrated through the use of mass spectrometry, where the chemical reactions between the laser ablated target species with the oxygen background molecules are directly characterized. We find that the influence of metal-oxygen negative ions is not as important as the metal-oxygen positive ions to the final oxygen composition of the LSMO film, due to their low stability in high background partial pressures. Furthermore, we observe that the oxygen incorporated in La0.6Sr0.4MnO3 thin films coming from the target is ~44%, 29% and 1% at 2  ×  10-3 mbar, 1  ×  10-2 mbar and 2  ×  10-1 mbar, respectively. When growing films at 10-1 mbar on 18O2 exchanged substrates, almost all oxygen originates from the background and almost none from the substrate or target.

  14. Application of antiferromagnetic-Fermi-liquid theory to NMR experiments in La1.85Sr0.15CuO4

    NASA Astrophysics Data System (ADS)

    Monien, H.; Monthoux, P.; Pines, D.

    1991-01-01

    NMR experiments on La1.85Sr0.15CuO4 by Kitaoka et al. and Imai et al. are analyzed using the phenomenological antiferromagnetic (AF) Fermi liquid theory of Millis, Monien, and Pines, and the results are compared with those previously obtained for YBa2Cu3O7 and YBa2Cu3O6.63. A one-component model, with hyperfine couplings that are unchanged from those found previously for YBa2Cu3O7 and YBa2Cu3O6.63, and parameters obtained from experiment, provide a quantitative fit to the data. At all temperatures the antiferromagnetic correlations found in La1.85Sr0.15CuO4 are stronger than those found for the Y-Ba-Cu-O samples with the result that the characteristic energy for the antiferromagnetic paramagnons that describe the AF spin dynamics is quite low (Sr0.15CuO4, YBa2Cu3O7, and YBa2Cu3O6.63, and find that it displays a linear temperature dependence for all three materials. Our results support the proposal that the properties of a nearly antiferromagnetic Fermi liquid are genuinely novel, and suggest that both the spin and charge aspects of the normal-state properties of the cuprate oxide superconductors can be quantitatively explained in terms of quasiparticles coupled to antiferromagnetic paramagnons whose characteristic energy scale is

  15. More Cu, more problems: Decreased CO2 conversion ability by Cu-doped La0.75Sr0.25FeO3 perovskite oxides

    NASA Astrophysics Data System (ADS)

    Daza, Yolanda A.; Maiti, Debtanu; Hare, Bryan J.; Bhethanabotla, Venkat R.; Kuhn, John N.

    2016-06-01

    The effect of Cu doping on the conversion of CO2 to CO was investigated on H2-reduced La0.75Sr0.25FeO3 perovskite oxides. Six La0.75Sr0.25Fe1 -YCuYO3 perovskites, labeled Cu100*Y (with Y = 0, 0.10, 0.25, 0.50, 0.75, and 1) were synthesized and characterized through X-ray diffraction (XRD), temperature-programmed oxygen vacancy formation, and temperature-programmed reduction (TPR). The incorporation of Cu facilitates the formation of oxygen vacancies at lower temperatures but also increased the instability of the perovskite. DFT simulations suggested that the Cu10 sample is favored to produce oxygen vacancies compared to Cu0 and Cu25 samples, which was consistent with experimental oxygen vacancy formation results. For the Cu0, Cu10, and Cu25 samples, temperature-programmed CO2 conversion (TPO-CO2) after isothermal H2-reduction at 450 °C and post-reduction XRD were performed to evaluate the ability of the materials to convert CO2 at low temperatures and to identify the crystalline phases active in the reaction. The peak conversion of CO2 to CO was achieved 30 °C lower on the Cu10 sample versus the Cu0, but less CO was produced, due to a decreased re-oxidation activity of the Cu-doped samples. CO production was inhibited in the Cu25 sample, likely due to a combined effect of poor CO2 dissociative chemisorption energies on metallic Cu and increased thermodynamic stability of the oxygen vacant perovskites. Control experiments (Cu deposited onto La0.75Sr0.25FeO3) indicated the stability of the copper-containing perovskite oxides phases was the primary limiting factor preventing CO formation from CO2.

  16. Unexpected luminescence properties of Sr(0.25)Ba(0.75)Si2O2N2:Eu(2+)--a narrow blue emitting oxonitridosilicate with cation ordering.

    PubMed

    Seibald, Markus; Rosenthal, Tobias; Oeckler, Oliver; Fahrnbauer, Felix; Tücks, Andreas; Schmidt, Peter J; Schnick, Wolfgang

    2012-10-15

    Owing to a parity allowed 4f(6)((7)F)5d(1)→4f(7)((8)S(7/2)) transition, powders of the nominal composition Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) (2 mol% Eu(2+)) show surprising intense blue emission (λ(em)=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr(1-x)Ba(x)Si(2)O(2)N(2):Eu(2+), the described compound is a promising phosphor material for pc-LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X-ray diffraction methods was used to determine the crystal structure of Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+). HRTEM images reveal the intergrowth of nanodomains with SrSi(2)O(2)N(2) and BaSi(2)O(2)N(2)-type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi(2)O(2)N(2)-type domains was refined on single-crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON(3)-tetrahedra in pure BaSi(2)O(2)N(2), in Sr(0.25)Ba(0.75)Si(2)O(2)N(2):Eu(2+) corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties. PMID:22968845

  17. Sintering and Mixed Electronic-Ionic Conducting Properties of LA1.9SR0.1NIO4+δ Derived from a Polyaminocarboxylate Complex Precursor

    NASA Astrophysics Data System (ADS)

    Huang, Duan-Ping; Xu, Qing; Zhang, Feng; Chen, Wen; Liu, Han-Xing; Zhou, Jian

    2006-06-01

    La1.9Sr0.1NiO4+δ with a pure K2NiF4 phase was synthesized from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H5DTPA) as ligand, and the effect of sintering temperature on the microstructure and mixed electronic-ionic conducting properties of La1.9Sr0.1NiO4+δ ceramic was investigated in the range of 1400-1600 °C. Homogeneous and fine powder (100-200 nm) with a pure K2NiF4 phase was produced by calcining the complex precursor at 900 °C for 2 h in air. The increase of sintering temperature promoted the microstructural densification. Compared with a gradual increase of grain size with sintering temperature in the range of 1400-1500 °C, there is an exaggerated grain growth in the specimens sintered at 1550 °C and 1600 °C, respectively. Increasing sintering temperature from 1400 °C to 1500 °C resulted in an enhancement of electrical and ionic conducting properties. Further increase of the sintering temperature above 1500 °C declined the electrical and ionic conducting properties. The variation of the mixed conducting properties with sintering temperature was interpreted for the viewpoint of microstructural evolution. With respect to the mixed conducting properties, the preferred sintering temperature was ascertained to be 1500 °C for La1.9Sr0.1NiO4+δ. The specimen sintered at 1500 °C exhibits an electrical conductivity of 86 S/cm and an oxygen ionic conductivity of 3.8×10-2 S/cm at 800 °C.

  18. Significantly enhanced ferroelectricity and magnetic properties in (Sr0.5Ca0.5)TiO3-modified BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Liu, Xiao Qiang; Chen, Xiang Ming

    2015-05-01

    BiFeO3 multiferroic ceramics were modified by introducing (Sr0.5Ca0.5)TiO3 to form solid solutions. The single phase structure was easy to be obtained in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with Mr = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe3+ by Ti4+, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  19. Elastic Moduli of detwinned orthorhombic optimally doped LSCO (La2-0.16 Sr 0.16 CuO4)

    NASA Astrophysics Data System (ADS)

    Fanelli, Victor; Betts, Jonathan; Migliori, Albert; Suzuki, Yoko; Yan, Jiaqiang

    2010-03-01

    Accurate elastic modulus characterization of the superconducting phase transition (SC) in La2-0.16 Sr 0.16 CuO4 is difficult because the discontinuities in moduli are much smaller than fluctuations from twin boundary motion. Thus detwinning is required for a useful measurement and was achieved using mechanical stress along the tetragonal [110] direction (or equivalently, along the orthorhombic [100] direction) below the orthorhombic phase transition that is well below ambient temperature. Using resonant ultrasound spectroscopy (RUS) on the detwinned monocrystal, the discontinuities and moduli around the SC transition were measured.

  20. Effect of heterovalent substitution at Mn site on the magnetic and transport properties of La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Priolkar, K. R.; Rawat, R.

    Magnetic and transport properties of Ti substituted La0.67Sr0.33MnO3 are drastically affected with a change in preparation conditions. Low temperature infra-red absorption measurements reveal that this is perhaps due to inhomogeniety in substitution of Ti on Mn sites. It is found that, in the high temperature annealed samples, the substitution of Ti supresses the double exchange interaction due to the formation of Mn-O- Ti chains. While in the low temperature annealed case substitution of Ti causes formation of isolated ferromagnetic clusters linked to each other by a variable range hopping polaron.

  1. Interface ferromagnetism and orbital reconstruction in BiFeO3-La0.7Sr0.3MnO3 heterostructures

    SciTech Connect

    Yu, P; Lee, J.-S.; Okamoto, Satoshi; Rossell, M.D.; Huijben, M.; Yang, C.-H.; He, Q; Zhang, J.-X.; Yang, S.Y.; Lee, M.J.; Ramasse, Q.M.; Erni, R.; Chu, Y.-H.; Arena, D.A.; Kao, C.-C.; Martin, L.W.; Ramesh, R

    2010-01-01

    We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La0.7Sr0.3MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L2,3 edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.

  2. Sensitive electrochemical detection of glucose based on electrospun La(0.88)Sr(0.12)MnO3 naonofibers modified electrode.

    PubMed

    Xu, Duo; Luo, Liqiang; Ding, Yaping; Xu, Pengyu

    2015-11-15

    Electrochemical detection of glucose in alkaline solution was performed on La0.88Sr0.12MnO3 (LSMO) nanofibers modified carbon paste electrode. Perovskite-type oxide LSMO nanofibers were prepared by an electrospinning and calcination process. The morphologies, structures, and electrochemical behavior of the nanofibers were characterized by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectrum, and cyclic voltammetry. The modified electrode shows excellent electrocatalytic activity toward glucose. Under optimal conditions, the linear response was obtained in the range of 0.05-100 μM with high sensitivity and rapid response. PMID:26297817

  3. Preparation and Characterization of (Ba0.8Sr0.2)TiO3-Al2O3 Composite Oxide for Thin Film Capacitor

    NASA Astrophysics Data System (ADS)

    Jang, Joo-Hee; Kim, Tae-Yoo; Lee, Chang-Hyoung; Zhang, JingJing; Park, Eun-Mi; Park, Chan; Suh, Su-Jeong

    2011-07-01

    Barium strontium titanate-alumina composites were fabricated using a sol-gel and anodizing process for high performance thin film capacitors and the properties of the films were studied. The (Ba0.8Sr0.2)TiO3 (BST) films were formed by spin coating and subsequent annealing at 150-550 °C. The respective annealed films were anodized in a neutral borate solution. The capacitance density increased with increasing annealing temperature up to 450 °C but decreased at 550 °C. The capacitance density was approximately 28.46% higher with the BST coating than without the BST layer.

  4. Mechanical behavior of La0.8Sr0.2Ga0.8Mg0.2O3 perovskites

    SciTech Connect

    Pathak, Siddhartha; Steinmetz, David; Kuebler, Jakob; Payzant, E Andrew; Orlovskaya, Nina

    2009-01-01

    Mechanical properties such as Young's modulus, fracture toughness and slow crack growth have been measured for phase pure and highly dense (<5% porosity) La0.8Sr0.2Ga0.8Mg0.2O3 perovskites. The Young's modulus was measured to be ~175 GPa, while strength and fracture toughness both exhibited low values confirming the poor mechanical properties of the material. LSGM was also proved to be highly susceptible to slow crack growth in humid air at room temperature where in order to survive a one year period the static stresses in the material should be as low as 50 MPa for a 50% failure probability.

  5. Structural studies of zirconium doped Ba0.70Sr0.30TiO3 lead free ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Sharma, Sarita; Ram, Mast; Thakur, Shilpa; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Ba0.7Sr0.3(ZrxTi1-x)O3(BSZT, x=0,0.05,0.10,0.15,0.20) thin films were prepared by using sol gel method. Structural and microstructural properties were studied by using XRD, Raman Spectroscopy and atomic force microscopy (AFM) respectively. XRD and Raman Spectroscopy show the presence of tetragonal phase in multilayer BSZT thin film. The experimental results demonstrate that structural and microstructural properties of BSZT thin film were significantly dependent on variation of Zr content.

  6. Giant zero field cooled spontaneous exchange bias effect in phase separated La1.5Sr0.5CoMnO6

    NASA Astrophysics Data System (ADS)

    Krishna Murthy, J.; Venimadhav, A.

    2013-12-01

    We report a giant zero field cooled exchange bias (ZEB) effect (˜0.65 T) in La1.5Sr0.5CoMnO6 sample. Magnetic study has revealed a reentrant spin glass ˜90 K, phase separation to spin glass and ferromagnetic phases below 50 K and canted antiferromagnetic transition ˜10 K. A small conventional exchange bias (CEB) is established with the advent of spontaneous phase separation down to 10 K. Giant ZEB and enhanced CEB effects are found only below 10 K and are attributed to the large unidirectional anisotropy at the interface of isothermally field induced ferromagnetic phase and canted antiferromagnetic background.

  7. Strain induced enhanced ferromagnetic behavior in inhomogeneous low doped La0.95Sr0.05MnO3+δ

    NASA Astrophysics Data System (ADS)

    Das, S.; Amaral, J. S.; De, K.; Willinger, M.; Gonçalves, J. N.; Roy, A.; Dhak, P.; Giri, S.; Majumder, S.; Silva, C. J. R.; Gomes, M. J. M.; Mahapatra, P. K.; Amaral, V. S.

    2013-03-01

    We report an unusual high-temperature ferromagnetic transition in bulk single-phase nanocrystalline La0.95Sr0.05MnO3+δ, achieved through localized strain and inhomogeneous Sr-doping. Magnetization measurements show a well defined transition at 290 K and a broad one at ˜150 K. HRTEM imaging reveals the strain on the highly crystalline nanometer sized grains and Sr-doping gradients, while oxygen homogeneity at the grain interfaces is confirmed by EELS-spectra. The magnetic behavior, far from the expected bulk phase diagram, shows how local doping and strain can strongly tune the macroscopic properties of a bulk material.

  8. The effect of interface roughness on exchange bias in La0.7Sr0.3MnO3-BiFeO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Vafaee, Mehran; Finizio, Simone; Deniz, Hakan; Hesse, Dietrich; Zabel, Hartmut; Jakob, Gerhard; Kläui, Mathias

    2016-02-01

    We characterized the interfaces of heterostructures with different stack sequences of La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) and BFO/LSMO using TEM revealing sharp and rough interfaces, respectively. Magnetometry and magnetoresistance measurements do not show a detectable exchange bias coupling for the multistack with sharp interface. Instead, the heterostructures with rough and chemically intermixed interfaces exhibit a sizable exchange bias coupling. Furthermore, we find a temperature-dependent irreversible magnetization behavior and an exponential decay of coercive and exchange bias fields with temperature suggesting a possible spin-glass-like state at the interface of both stacks.

  9. Effect of biaxial strain on the electrical and magnetic properties of (001) La0.7Sr0.3MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Adamo, C.; Ke, X.; Wang, H. Q.; Xin, H. L.; Heeg, T.; Hawley, M. E.; Zander, W.; Schubert, J.; Schiffer, P.; Muller, D. A.; Maritato, L.; Schlom, D. G.

    2009-09-01

    We have studied the effect of biaxial strain on thin films of (001) La0.7Sr0.3MnO3. We deposited films by reactive molecular-beam epitaxy on different single crystalline substrates, varying the substrate-induced biaxial strain from -2.3% to +3.2%. Magnetization and electrical transport measurements reveal that the dependence of the Curie temperature on biaxial strain is in very good agreement with the theoretical predictions of Millis et al. [J. Appl. Phys. 83, 1588 (1998)].

  10. Synthesis and characteristic of nanocrystalline La0.7Sr0.3MnO3 manganites by solid state reaction route

    NASA Astrophysics Data System (ADS)

    Astik, Nidhi; Patil, Swapnilkumar; Bhargava, Parag; Jha, Prafulla K.

    2016-05-01

    Nanocrystalline stoichiometric La0.7Sr0.3MnO3 (x=0.3) manganites have been synthesized through solid-state reaction by ball milling mechanical method at two different sintering temperatures 1250°C and 1350°C. The synthesized samples were characterized using X-ray diffraction (XRD) and found to have rhombohedral crystal structure (R-3c). The calcined samples exhibited a pure single phase perovskite, had a crystallite size of about 47-51 nm. The morphology of the prepared nanocrystalline manganites were recorded by the field emission gun-scanning electron microscope (FEG-SEM) and EDAX.

  11. Investigation of conduction mechanism in Pr0.67Sr0.13Ag0.20MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Bhat, Masroor Ahamad; Gaur, N. K.

    2016-05-01

    We report the electronic conduction mechanism in Pr0.67Sr0.13Ag0.20MnO3 synthesized successfully by conventional solid state reaction method. The compound under investigation was subjected by X - Ray diffraction using Rietveld refinement which confirms the single phase nature of the sample. The resistivity behavior indicates the semiconducting behavior and reduction in resistivity on the application of magnetic fields. The electronic nature can further been evaluated by using variable range hopping (VRH) model and small polaron hopping model (SPH) showing that the double exchange interaction increases suppress the band gap and enhances carrier delocalization on the application of magnetic fields.

  12. Extreme sensitivity of magnetic properties on the synthesis routes in La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Ashutosh; Sharma, Himanshu; Tomy, C. V.; Thakur, Ajay D.

    2016-05-01

    La0.7Sr0.3MnO3 polycrystalline samples have been prepared using different synthesis routes. X-ray Diffraction (XRD) confirms that the samples are of single phase with R-3c space group. The surface morphology and particle size has been observed using Field Emission Scanning Electron Microscopy (FESEM). Magnetic measurement shows that the magnetization in the materials are affected by low crystallite size which destroys the spin ordering due to strain at grain boundaries and this also leads to reduction in magnetization as well as high coercivity in the material.

  13. Ethylene production by ODHE in catalytically modified Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) membrane reactors.

    PubMed

    Lobera, M Pilar; Escolástico, Sonia; Garcia-Fayos, Julio; Serra, José M

    2012-08-01

    Process intensification by the integration of membranes and high-temperature reactors offers several advantages with regard to conventional process schemes, that is, energy saving, safe operation, reduced plant/unit size, and higher process performance, for example, higher productivity, catalytic activity, selectivity, or stability. We present the study of oxidative dehydrogenation of ethane at 850 °C on a catalytic membrane reactor based on a mixed ionic-electronic conducting membrane. The surface of the membrane made of Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) has been activated by using different porous catalytic layers based on perovskites. The layer was deposited by screen printing, and the porosity and thickness was studied for the catalyst composition. The different catalyst formulations are based on partial substitution of A- and B-site atoms of doped strontium ferrite/cobaltites (A(0.6)Sr(0.4)Co(0.5)Fe(0.5)O(3-δ) and Ba(0.6)Sr(0.4)BO(3-δ)) and were synthesized by an ethylenediaminetetraacetic acid-citrate complexation route. The use of a disk-shaped membrane in the reactor enabled the direct contact of gaseous oxygen and hydrocarbons to be avoided, and thus, the ethylene content increased. High ethylene yields (up to ≈81 %) were obtained by using a catalytic coating based on Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ), which included macropores produced by the addition of graphite platelets into the screen-printing ink. The promising catalytic results obtained with this catalytically modified membrane reactor are attributed to the combination of 1) the high activity, as a result of the high temperature and oxygen species diffusing through the membrane; 2) the control of oxygen dosing and the low concentration of molecules in the gas phase; and 3) suitable fluid dynamics, which enables appropriate feed contact with the membrane and the rapid removal of products. PMID:22791570

  14. Nickel-Doped La0.8Sr0.2Mn(1-x)Ni(x)O3 Nanoparticles Containing Abundant Oxygen Vacancies as an Optimized Bifunctional Catalyst for Oxygen Cathode in Rechargeable Lithium-Air Batteries.

    PubMed

    Wang, Zhaodong; You, Ya; Yuan, Jing; Yin, Ya-Xia; Li, Yu-Tao; Xin, Sen; Zhang, Dawei

    2016-03-01

    In this work, Ni-doped manganite perovskite oxides (La0.8Sr0.2Mn(1-x)Ni(x)O3, x = 0.2 and 0.4) and undoped La0.8Sr0.2MnO3 were synthesized via a general and facile sol-gel route and used as bifunctional catalysts for oxygen cathode in rechargeable lithium-air batteries. The structural and compositional characterization results showed that the obtained La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) contained more oxygen vacancies than did the undoped La0.8Sr0.2MnO3 as well as a certain amount of Ni(3+) (eg = 1) on their surface. The Ni-doped La0.8Sr0.2Mn(1-x)Ni(x)O3 (x = 0.2 and 0.4) was provided with higher bifunctional catalytic activities than that of the undoped La0.8Sr0.2MnO3. In particular, the La0.8Sr0.2Mn0.6Ni0.4O3 had a lower total over potential between the oxygen evolution reaction and the oxygen reduction reaction than that of the La0.8Sr0.2MnO3, and the value is even comparable to that of the commercial Pt/C yet is provided with a much reduced cost. In the lithium-air battery, oxygen cathodes containing the La0.8Sr0.2Mn0.6Ni0.4O3 catalyst delivered the optimized electrochemical performance in terms of specific capacity and cycle life, and a reasonable reaction mechanism was given to explain the improved performance. PMID:26900959

  15. Substrate-related structural, electrical, magnetic and optical properties of La0.7Sr0.3MnO3 films

    NASA Astrophysics Data System (ADS)

    Liu, G. Z.; Yang, Y. Y.; Qiu, J.; Chen, X. X.; Jiang, Y. C.; Yao, J. L.; Zhao, M.; Zhao, R.; Gao, J.

    2016-02-01

    La0.7Sr0.3MnO3 (LSMO) film exhibits certain unique properties which make it an ideal material for heterostructure-based multifunctional devices. In this paper, La0.7Sr0.3MnO3 thin films were grown epitaxially on SrTiO3, LaAlO3(LAO) and (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7(LSAT) substrates, and their structural, electrical, magnetic and optical properties were examined and compared, aiming at revealing and explaining the effects of substrate on fundamental physical properties of LSMO films. Results show that (i) the effects of substrate materials on the electrical conductivity and paramagnetic-ferromagnetic transition temperature of the LSMO films could be ignored, and (ii) the LSMO film on LAO substrate has much higher coercive field and slower photoinduced relaxation process than other samples. This unusual behavior observed in the LSMO film on the LAO substrate could be related to the nature of the LAO substrate itself, on which the LSMO film showed different easy magnetization direction, and the film also exhibited relatively poor crystalline quality due to the twin domain structure of LAO crystal. Our results may help to understand the substrate-related electrical, magnetic and optical properties for perovskite manganite films.

  16. Electrical Characteristics and Preparation of (Ba0.5Sr0.5)TiO3 Films by Spray Pyrolysis and Rapid Thermal Annealing

    NASA Astrophysics Data System (ADS)

    Koo, Horng-Show; Chen, Mi; Ku, Hong-Kou; Kawai, Tomoji

    2007-04-01

    Functional films of (Ba0.5Sr0.5)TiO3 on Pt (1000 Å)/Ti (100 Å)/SiO2 (2000 Å)/Si substrates are prepared by spray pyrolysis and subsequently rapid thermal annealing. Barium nitrate, strontium nitrate and titanium isopropoxide are used as starting materials with ethylene glycol as solvent. For (Ba0.5Sr0.5)TiO3 functional thin film, thermal characteristics of the precursor powder scratched from as-sprayed films show a remarkable peak around 300-400 °C and 57.7% weight loss up to 1000 °C. The as-sprayed precursor film with coffee-like color and amorphous-like phase is transformed into the resultant film with white, crystalline perovskite phase and characteristic peaks (110) and (100). The resultant films show correspondent increases of dielectric constant, leakage current and dissipation factor with increasing annealing temperatures. The dielectric constant is 264 and tangent loss is 0.21 in the resultant films annealed at 750 °C for 5 min while leakage current density is 1.5× 10-6 A/cm2 in the film annealed at 550 °C for 5 min.

  17. Effects of fluorine doping on thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Zhen; Zhou, YuCheng; Wang, Chunlei; Li, Jichao; Zhu, Yuanhu; Li, Maokui; Mei, Liangmo

    2015-02-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6 ceramics, doped with different contents of fluorine at the oxygen sites, were investigated in the temperature range of 323 to 1073 K. The electrical resistivity is reduced significantly after fluorine doping. However, the magnitudes of electrical resistivity, Seebeck coefficient (S), and slope of S at high temperatures (dS/dT) vary non-monotonically with increasing doping contents, indicating that doped fluorine ions not only act as electron donors, but also influence band structure. The lattice thermal conductivity decreases when fluorine ions are slightly doped, and increases with increasing fluorine content because of the increasing average grain size. The thermoelectric performance is enhanced by slight fluorine doping due to the increase of the power factor and the reduction of thermal conductivity. The thermoelectric figure of merit reaches maximum value (0.21 at 1073 K) in the Sr0.61Ba0.39Nb2O5.95F0.05 sample.

  18. Effect of oxygen vacancies on the magnetic structure of the La0.6Sr0.4FeO3-δ perovskite: A neutron diffraction study

    NASA Astrophysics Data System (ADS)

    Chu, Z.; Yelon, W. B.; Yang, J. B.; James, W. J.; Anderson, H. A.; Xie, Y.; Malik, S. K.

    2002-05-01

    Magnetic interactions in perovskite compounds of the type La1-xSrxMO3-δ (M=3d transition such as Mn and Fe) are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La0.6Sr0.4FeO3-δ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N2, air and mixtures of CO/CO2. All La0.6Sr0.4FeO3-δ compounds maintain the rhombohedral structure (space group R3¯c). The air- or oxygen-annealed samples have almost no oxygen vacancies while those made in the reducing atmosphere show 7%-11% oxygen vacancies. The rhombohedral distortion decreases in the reduced samples. All the samples exhibit antiferromagnetic ordering at room temperature, although a small ferromagnetic moment may also be present. The samples with little or no oxygen vacancies show a room temperature magnetic moment of ˜1.4μB at the Fe site while those having >7% oxygen vacancies show a moment of ˜4.0μB. Magnetization measurements reveal a much higher magnetic ordering temperature in samples with oxygen vacancies

  19. Dual Extraction of Photogenerated Electrons and Holes from a Ferroelectric Sr0.5Ba0.5Nb2O6 Semiconductor.

    PubMed

    Fan, Dayong; Zhu, Jian; Wang, Xiuli; Wang, Shengyang; Liu, Yong; Chen, Ruotian; Feng, Zhaochi; Fan, Fengtao; Li, Can

    2016-06-01

    The separation of photogenerated charges is a critical factor in photocatalysis. Recently, anomalous photovoltaic (APV) field effects (Voc ∼ 10(3) V/cm) in ferroelectrics, with their strong driving force for charge separation, have attracted much attention in photocatalysis and photoelectrocatalysis. However, it is still unknown whether photogenerated electrons and holes can be simultaneously extracted by the strong driving force toward the surface of ferroelectrics and can become available for surface reactions. This issue becomes critically important in photocatalysis because the surface reaction utilizes both the electrons and holes that reach the surface. In this work, a model lateral symmetric structure, metal/Sr0.5Ba0.5Nb2O6/metal (metal = Ag or Pt), as an electrode was fabricated. The dual extractions of photogenerated electrons and holes on the two opposite metal electrodes were achieved, as revealed by photovoltaic and ferroelectrical hysteresis measurements and photoassisted Kelvin probe force microscopy (KPFM). It was found that the high Schottky barriers of the two opposite Sr0.5Ba0.5Nb2O6-Pt electrodes are key factors that alter the two space charge regions (SCRs) by a poling effect. The resulting built-in electrical fields with parallel directions near both electrodes significantly enhance the charge separation ability. Our model unravels the driving force of charge separation in ferroelectric semiconductors, thus demonstrating the potential for highly efficient charge separation in photocatalysis. PMID:27183145

  20. Internal electrical and strain fields influence on the electrical tunability of epitaxial Ba0.7Sr0.3TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Bagdzevicius, S.; Mackeviciute, R.; Ivanov, M.; Fraygola, B.; Sandu, C. S.; Setter, N.; Banys, J.

    2016-03-01

    Perpetual demand for higher transfer speed and ever increasing miniaturization of radio and microwave telecommunication devices demands new materials with high electrical tunability. We have investigated built in electrical and strain fields' influence on the electrical tunability in Ba0.7Sr0.3TiO3 thin film hetero-system grown by pulsed laser deposition technique. We observed the built in electrical field by local piezo-force microscopy (as deflected hysteresis loops) and macroscopic impedance analysis (as asymmetric tunability curves), with the calculated 88 kV/cm built in field at room temperature. Negative -1.4% misfit strain (due to clamping by the substrate) enhanced ferroelectric phase transition temperature in Ba0.7Sr0.3TiO3 thin film by more than 300 K. Built in fields do not deteriorate functional film properties—dielectric permittivity and tunability are comparable to the best to date values observed in Ba1-xSrxTiO3 thin films.

  1. Epitaxial Ferroelectric Ba(0.5)Sr(0.5)TiO3 Thin Films for Room-Temperature High-Frequency Tunable Element Applications

    NASA Technical Reports Server (NTRS)

    Chen, C. L.; Feng, H. H.; Zhang, Z.; Brazdeikis, A.; Miranda, F. A.; VanKeuls, F. W.; Romanofsky, R. R.; Huang, Z. J.; Liou, Y.; Chu, W. K.; Chu, C. W.

    1999-01-01

    Perovskite Ba(0.5)SR(0.5)TiO3 thin films have been synthesized on (001) LaAl03 substrates by pulsed laser ablation. Extensive X-ray diffraction, rocking curve, and pole-figure studies suggest that the films are c-axis oriented and exhibit good in-plane relationship of <100>(sub BSTO)//<100>(sub LAO). Rutherford Backscattering Spectrometry studies indicate that the epitaxial films have excellent crystalline quality with an ion beam minimum yield chi(sub min) Of only 2.6 %. The dielectric property measurements by the interdigital technique at 1 MHz show room temperature values of the relative dielectric constant, epsilon(sub r), and loss tangent, tan(sub delta), of 1430 and 0.007 with no bias, and 960 and 0.001 with 35 V bias, respectively. The obtained data suggest that the as-grown Ba(0.5)SR(0.5)TiO3 films can be used for development of room-temperature high-frequency tunable elements.

  2. Disorder induced superconductor-insulator transition in epitaxial La1.85Sr0.15CuO4 thin films

    NASA Astrophysics Data System (ADS)

    Jang, Han-Byul; Yang, Chan-Ho

    La2-xSrxCuO4is a well-known superconducting system showing various electronic properties as a function of Sr content. Especially, epitaxial thin layers of the compound show enormous increase of superconducting critical temperature (Tc) by a compressive strain. It has been reported that Tc can be controlled by misfit strain, thickness, and oxygen annealing. In this study, we report structural and transport properties of high quality epitaxial La1.85Sr0.15CuO4thin films. According to x-ray diffraction study, c-axis lattice parameter shows no significant change for various film thicknesses and the in-plane lattice parameters of the films are coherently matched with that of substrate. Electronic transport measurements show a clear superconductor-to-insulator transition (SIT), accompanying variation of Tc depending on film thickness. These results are analyzed by using the McMillan equation to find the relation between the Tc and a disorder correlating with film thickness. We have found the disorder exhibits an explicit power-law behavior with respect to film thickness in our La1.85Sr0.15CuO4 thin films.

  3. Ferroelectric and magnetic properties of multiferroic BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated with Si (100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, J. T.; Nori, S.; Kumar, D.; Lee, Bongmook; Misra, V.; Narayan, J.

    2015-05-01

    We report on the electrical, ferroelectric, and magnetic properties of BiFeO3 (BFO)-La0.7Sr0.3MnO3 heterostructures deposited epitaxially onto Si(100) substrates. Temperature dependent (200-350 K) current-voltage (I-V), switching spectroscopy piezo-response force microscopy (SSPFM), and temperature dependent (5-300 K) anisotropic magnetization measurements have been performed. The BFO (100-nm thick)-based device structures were fabricated with a 250 nm thick La0.7Sr0.3MnO3 bottom electrode and 200 μm circular top Pt electrodes. I-V measurements performed at various temperatures indicated that the devices retained their as-deposited characteristics and exhibited non-leaky behavior up to at least 50 cycles. The temperature-dependent measurements showed clear diode-like behavior and resistive (hysteretic) switching behaviour. Characteristic butterfly loops (of several cycles) were observed in the PFM amplitude signals of the BFO film. In addition, the phase signal indicated a clear (180°) switching behavior at the switching voltage of 4-5 V, providing unambiguous evidence for the occurrence of ferroelectricity in BFO films integrated on Si (100). The temperature- and angle-dependent zero field cooled isothermal (5 K) magnetization measurements were consistent with the presence of uniaxial magnetic anisotropy. This work makes an important step for the fabrication of CMOS-compatible BFO devices for memory applications.

  4. Evidence of spin glass like ordering and electronic phase arrest in Pr3+ doped Sm0.5Sr0.5MnO3 bulk manganites

    NASA Astrophysics Data System (ADS)

    Giri, S. K.; Panda, J.; Nath, T. K.

    2012-06-01

    The effect of doping of rare earth Pr3+ ion replacing Sm3+ in Sm0.5Sr0.5MnO3 is investigated in details. Measurements of linear and non linear ac magnetic susceptibility, resistivity, magnetoresistance on chemically synthesized (Sm0.5-xPrx)Sr0.5MnO3 shows various interesting features with doping level x=0.15. Here we observe the frequency independent FM-PM transition at higher temperature followed by a frequency dependent re-entered magnetic transition at lower temperature through complex ac susceptibility measurements. We have ascribed our observation to the formation of finite size ferromagnetic clusters which are formed as a consequence of intrinsic phase separation and undergo Spin glass-like freezing below certain temperature in this manganite. The magnetoresistance of the samples also show strong irreversibility with respect to sweeping of the field between highest positive and negative values. All these experimental results have been attributed to phase separation effect and kinetic arrest of electronically phase separated system.

  5. Impact of Ni doping on La0.7Sr0.3NixMn1-xO3 perovskite manganite materials

    NASA Astrophysics Data System (ADS)

    Thamilmaran, P.; Arunachalam, M.; Sankarrajan, S.; Sakthipandi, K.

    2015-12-01

    On-line ultrasonic measurements on La0.7Sr0.3Mn1-xNixO3 perovskite manganite material (x=0.01, 0.02 and 0.03) were performed on the samples synthesised by solid state reaction technique. The XRD studies on the samples confirm the crystalline nature with single phase rhombohedral structure having R3C space group. The average size of the particles determined using SEM images are 0.587, 0.412 and 0.356 μm for x=0.01, 0.02 and 0.03 respectively. The temperature dependent ultrasonic velocities and attenuation measurements on the samples were used to reveal the ferromagnetic to paramagnetic phase transition temperature (Curie temperature) 374, 358 and 342 K for the values of x=0.01, 0.02 and 0.03 respectively. In addition, ultrasonic measurements confirm that the increase in Ni doping concentration in La0.7Sr0.3Mn1-xNixO3 perovskites leads to a decrease in Curie temperature. The change in Mn3+/Mn4+ ratio with the phase transition temperature was explained on the basis of variation in amplitude of observed anomaly in ultrasonic measurements. The replacement of Mn4+ ion by Ni2+ ion leads to a change in the structural parameters and in the concentration of Mn3+ and Mn4+ ions.

  6. Phase transformation, dielectric and magnetic properties of Nb doped Bi0.8Sr0.2FeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Reetu, Agarwal, Ashish; Sanghi, Sujata; Ashima, Ahlawat, Neetu; Monica

    2012-06-01

    Bi0.8Sr0.2Fe1-xNbxO3 (x = 0.0, 0.05, and 0.10) multiferroics were prepared by solid state reaction method. X-ray diffraction and Rietveld analysis show that crystal structure is rhombohedral for x = 0.0, 0.05 samples and triclinic for x = 0.10 sample. These samples showed dispersion in dielectric constant (έ) and dielectric loss (tan δ) values at lower frequencies. For x = 0.05 sample, both έ and tan δ are lower than for Bi0.8Sr0.2FeO3 sample indicating its high resistivity. For x = 0.10 sample, the value of έ is enhanced which may be due to formation of stronger dipoles in triclinic structure. Temperature dependence of frequency exponent "s" of power law suggests that correlated barrier hopping (CBH) model is applicable at lower temperatures and quantum mechanical tunneling model is appropriate at higher temperatures for describing the conduction mechanism in x = 0.0 and x = 0.05 samples; while in x = 0.10 sample, CBH model is appropriate in studied temperature range. Significant enhancement observed in magnetization for x = 0.10 sample is due to the structural phase transition from rhombohedral to triclinic caused by Nb substitution. For this sample, values of remnant magnetization (Mr) and coercive field (Hc) are 0.155 emu/g and 2.695 kOe, respectively.

  7. Magnetic transition behavior of perovskite manganites Nd0.5Sr0.3Ca0.2MnO3 polycrystalline

    NASA Astrophysics Data System (ADS)

    Ru, Xing; Su-Lei, Wan; Wen-Qing, Wang; Lin, Zheng; Xiang, Jin; Min, Zhou; Yi, Lu; Jian-Jun, Zhao

    2016-04-01

    A polycrystalline sample Nd0.5Sr0.3Ca0.2MnO3 is prepared by the conventional solid state reaction method. The structure and magnetic properties are investigated with x-ray diffraction (XRD) patterns, a superconducting quantum interference device (SQUID), and electron spin resonance (ESR). The sample is in single phase with the space group Pbnm symmetry. With the decrease of temperature, Nd0.5Sr0.3Ca0.2MnO3 undergoes three magnetic transitions: ferromagnetic transition at T C ≈ 210 K, charge-ordering at T CO ≈ 175 K, and antiferromagnetic transition at T N = 155 K. In addition, the activation energy E a ≈ 52.78 meV can be extracted by curve fitting. Project supported by the National Natural Science Foundation of China (Grant Nos. 11164019, 51562032, and 61565013), the Inner Mongolia Natural Science Foundation, China (Grant Nos. 2015MS0109, NJZZ11166, and NJZY12202), and the Science and Technology in Baotou Production-Study-Research Cooperation Projects, China (Grant No. 2014X1014-01).

  8. A New Ba0.6 Sr0.4 TiO3 -Silicon Hybrid Metamaterial Device in Terahertz Regime.

    PubMed

    Wu, Liang; Du, Ting; Xu, Ningning; Ding, Chunfeng; Li, Hui; Sheng, Quan; Liu, Ming; Yao, Jianquan; Wang, Zhiyong; Lou, Xiaojie; Zhang, Weili

    2016-05-01

    Metamaterials, offering unprecedented functionalities to manipulate electromagnetic waves, have become a research hotspot in recent years. Through the incorporation of active media, the exotic electromagnetic behavior of metamaterials can be dramatically empowered by dynamic control. Many ferroelectric materials such as BaSrTiO3 (abbreviated as BST), exhibiting strong response to external electric field, hold great promise in both microwave and terahertz tunable devices. A new active Ba0.6 Sr0.4 TiO3 -silicon hybrid metamaterial device, namely, a SRR (square split-ring resonator)-BaSrTiO3 thin film-silicon three-layer structure is fabricated and intensively studied. The active Ba0.6 Sr0.4 TiO3 thin film hybrid metamaterial, with nanoscale thickness, delivers a transmission contrast up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate. This work has significantly increased the low modulation rate of ferroelectric based devices in terahertz range, a major problem in this field remaining unresolved for many years. The proposed BST metamaterial is promising in developing high-performance real world photonic devices for terahertz technology. PMID:27007192

  9. Electrical transport and magnetic behaviors of La0.67Sr0.33Mn1-xBxO3 (B = Cr, Ru)

    NASA Astrophysics Data System (ADS)

    Acharya, Deepshikha; Bhargav, Abhinav; Tank, Tejas M.; Sanyal, Sankar P.

    2016-05-01

    Polycrystalline samples of La0.67Sr0.33Mn1-xCrxO3 (with x=0, 0.05 and 0.1) and La0.67Sr0.33Mn1-xRuxO3 (with x = 0.05 and 0.1) were synthesized using the conventional solid state reaction route and found single phase in nature. Electrical resistivity measurements as a function of temperature in range 5 K-400 K and as a function of magnetic field up to 5 Tesla were performed using d.c. four-probe method. Magnetization data were acquired as a function of temperature in a range 10 K-400 K with an applied magnetic field of 500 Oe. When Mn is partially substituted by Cr and Ru the system displays dramatic changes in the electrical transport behavior and shows double-peaked feature in resistivity curve. Both Cr and Ru substitutions effectively reduce insulator-metal transition (TP) and paramagnetic-ferromagnetic transition (TC) temperatures implying that there might exist FM interaction between Mn+3 and Cr+3 as well Mn+3 and Ru+4. The largest low-temperature magnetoresistance (MR%) is attributed to grain boundary effects and difference in size disorder for Cr and Ru substituted compounds.

  10. Influence of Cu substitution for Mn on the structure, magnetic, magnetocaloric and magnetoresistance properties of La 0.7Sr 0.3MnO 3 perovskites

    NASA Astrophysics Data System (ADS)

    Chau, Nguyen; Niem, Pham Quang; Nhat, Hoang Nam; Luong, Nguyen Hoang; Tho, Nguyen Duc

    2003-04-01

    Structural, magnetic, magnetocaloric and magnetoresistance (MR) studies on La 0.7Sr 0.3Mn 0.95Cu 0.05O 3 (No. 1) and La 0.7Sr 0.3Mn 0.9Cu 0.1O 3 (No. 2) perovskites are reported. The crystal structure of the samples is rhombohedral with a change of the lattice constants depending on the Cu content. FC and ZFC thermomagnetic measurements for both compositions at low field indicate that a spin-glass-like state (or cluster glass) occurs at low temperatures and a very sharp change of magnetization around the phase-transition point. The Curie temperature, TC, does almost not depend on the content of Cu substitution. A maximum magnetic-entropy change, Δ Sma x, of 1.96 and 2.07 J/kg K at 13.5 kOe and 350 K is observed for sample No. 1 and No. 2, respectively. Therefore, they can be considered as active magnetic refrigerant materials for room-temperature applications. Electrical-resistance measurements show that both samples are metallic conductor for T< TC and semiconductor for T> TC; moreover, the MR is maximal around TC.

  11. Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La0.6Sr0.4MnO3Nanoparticles

    PubMed Central

    2009-01-01

    The intrinsically core/shell structured La0.6Sr0.4MnO3nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of −41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than −10 dB is obtained in the 5.5–11.3 GHz range for absorber thicknesses of 1.5–2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La0.6Sr0.4MnO3nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials. PMID:20596374

  12. Preparation of Ba0.09Sr0.91TiO3/YBa2Cu3O7-x bilayers and investigation of their dielectric properties

    NASA Astrophysics Data System (ADS)

    Jia, Jiqiang; Zhao, Gaoyang; Shi, Xiaoxue; Lei, Li

    2016-08-01

    YBa2Cu3O7-x (YBCO) films of 110 nm thickness were prepared on LaAlO3 (LAO) substrates via the sol-gel method. Subsequently, about 400 nm thick Ba0.09Sr0.91TiO3 (BST) films were epitaxially grown on the YBCO and LNO films surface; the BST films exhibited a strong c-axis orientation. The dielectric adjustability and relative dielectric constant was investigated in the range of 300-83 K. Results indicate that the tunability of the Ba0.09Sr0.91TiO3/YBa2Cu3O7-x (BST/YBCO) displayed an increase relative to c-axis-oriented BST on LaNiO3 (LNO). The tunability was further enhanced as the operating temperature decreased, yet the loss tangent (tanδ) decreased. The tunability and the tanδ at 100 kHz and 83 K were 58% and 0.029, respectively.

  13. Multiferroic properties of Pb0.90Sr0.10TiO3-CoFe2O4 nanostructured bilayered thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Kotnala, R. K.; Negi, N. S.

    2015-05-01

    Pb0.90Sr0.10TiO3-CoFe2O4(PST10-CFO) nanostructured bilayered thin film were grown on Si (100) substrate by using metallo-organic decomposition chemical route and spin coating technique. Results show that PST (pervoskite structure) and CFO (spinel) phase coexist in the bilayered thin films, annealed at 650°C for 2hr and no obvious impurity phase can be detected. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), atomic force microscope (AFM) respectively. Excellent ferroelectric behavior at different voltage was observed, with two platinum electrodes only at surface of the bilayer thin film. A room temperature ferromagnetic behavior was observed in the bilayered Pb0.90Sr0.10TiO3-CoFe2O4 nanostructured thin film. The saturation magnetization and variation in coercivity value of the bilayer thin film is lower than that of the pure CFO film in the presence of non ferromagnetic PST layer which is the attributed that the significant coupling between the two phases.

  14. Spark Plasma Sintering Temperature Effect on Structural, Dielectric and Ferroelectric Properties of Ba0.9Sr0.1TiO3 Nanocrystalline Ceramics

    NASA Astrophysics Data System (ADS)

    Mudinepalli, Venkata Ramana; Lin, Wen-Chin; Song, S.-H.; Murty, B. S.

    2015-11-01

    A combination of mechanical alloying and spark plasma sintering (SPS) was used to process Ba0.9Sr0.1TiO3 (abbreviated as BST) with a high-density and homogeneous microstructure, at a temperature 300°C to 400°C lower than that used in conventional sintering. The SPS technique was employed to prepare dense Ba0.9Sr0.1TiO3 nano-ceramics at different temperatures ranging from 800°C to 1000°C within a very short time. The SPS samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, electrical, ferroelectric and piezoelectric property measurements. The dielectric constant both at room temperature and Curie temperature increased with increasing SPS temperature. The coercive field increased continuously with rising SPS temperature, but the spontaneous polarization increased gradually up to 900°C and then decreased considerably with further increases in SPS temperature. In addition, the prepared nano-ceramic exhibited excellent piezoelectric properties.

  15. Fluctuations of the order parameter in R 0.55Sr0.45MnO3 manganites near the metal-insulator phase transition

    NASA Astrophysics Data System (ADS)

    Bukhanko, F. N.; Bukhanko, A. F.

    2013-06-01

    The magnetic phase transformations induced by changes of the composition, external magnetic field strength, and temperature in manganites with a nearly half-filled conduction band in the vicinity of the metal-insulator phase transition have been investigated experimentally. It has been found that the substitution of rare-earth ions (Sm) for Nd ions with a larger ionic radius in R 0.55Sr0.45MnO3 manganites leads to a linear decrease in the Curie temperature T C from 270 to 130 K and a transformation of the second-order ferromagnetic (FM) phase transition into a first-order phase transition. The results of measurements of the alternating-current (ac) magnetic susceptibility in the (Nd1 - y Sm y )0.55Sr0.45MnO3 system indicate the existence of a Griffiths-like phase in samples with a samarium concentration y > 0.5 in the temperature range T C < T < T* (where T* ˜ 220 K). For samples with y > 0.5, the magnetization isotherms at temperatures above T C exhibit specific features in the form of reversible metamagnetic phase transitions associated with strong fluctuations of the short-range ferromagnetic order in the system of Mn spins in the high-temperature Griffiths phase consisting of ferromagnetic clusters. According to the results of measurements of the ac magnetic susceptibility in the (Sm1 - y Gd y )0.55Sr0.45MnO3 system for a gadolinium concentration y = 0.5, there is an antiferromagnetic (AFM) phase with an unusually low critical temperature of the spin ordering T N ≊ 48.5 K. An increase in the external static magnetic field at 4.2 K leads to an irreversible induction of the ferromagnetic phase, which is stable in the temperature range 4.2-60 K. In the temperature range 60 K < T < 150 K, there exists a high-temperature Griffiths-like phase consisting of clusters (correlations) with a local charge/orbital ordering. The metastable antiferromagnetic structure is retained in samples with gadolinium concentrations y = 0.6 and 0.7, but it is destroyed with a further

  16. Interfacial Ion Intermixing Effect on Four-Resistance States in La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 Multiferroic Tunnel Junctions.

    PubMed

    Huang, Weichuan; Lin, Yue; Yin, Yuewei; Feng, Lei; Zhang, Dalong; Zhao, Wenbo; Li, Qi; Li, Xiaoguang

    2016-04-27

    A multiferroic tunnel junction (MFTJ), employing a ferroelectric barrier layer sandwiched between two ferromagnetic layers, presents at least four resistance states in a single memory cell and therefore opens an avenue for the development of the next generation of high-density nonvolatile memory devices. Here, using the all-perovskite-oxide La0.7Sr0.3MnO3/BaTiO3/La0.7Sr0.3MnO3 as a model MFTJ system, we demonstrate asymmetrical Mn-Ti sublattice intermixing at the La0.7Sr0.3MnO3/BaTiO3 interfaces by direct local measurements of the structure and valence, which reveals the relationship between ferroelectric polarization directions and four-resistance states, and the low temperature anomalous tunneling behavior in the MFTJ. These findings emphasize the crucial role of the interfaces in MFTJs and are quite important for understanding the electric transport of MFTJs as well as designing high-density multistates storage devices. PMID:27055530

  17. The ionic conductivity, thermal expansion behavior, and chemical compatibility of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ as SOFC cathode material

    NASA Astrophysics Data System (ADS)

    Fan, Baoan; Yan, Jiabao; Yan, Xiaochao

    2011-10-01

    In this paper, the ionic conductivities of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ were measured by electron-blocked alternating current impedance analysis technique. The results show that the oxygen ion conductivity of La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ is nearly five times higher than that of La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ, which makes La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ cathode more conductive than YSZ electrolyte. Consequently, the electrochemical reaction region is extended from the interface between the cathode and the electrolyte to the whole surface of the cathode grains, with a result of the cathode polarization overpotential being decreased and the cell electrical performance being improved. Besides, the XRD results show that both La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ begin to react with 8YSZ([Y 2O 3] 0.08·[ZrO 2] 0.92) at 850 °C, but La 0.54Sr 0.44Co 0.2Fe 0.8O 3-δ with a faster reaction rate. The thermal expansion experiments manifest that the two LSCFs have approximate thermal expansion coefficients, being about 14 × 10 -6-15 × 10 -6 K -1 from 500 °C to 700 °C, which is moderately higher than that of 8YSZ.

  18. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries

    PubMed Central

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-01-01

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g –1, one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  19. Hierarchical mesoporous perovskite La0.5Sr0.5CoO2.91 nanowires with ultrahigh capacity for Li-air batteries.

    PubMed

    Zhao, Yunlong; Xu, Lin; Mai, Liqiang; Han, Chunhua; An, Qinyou; Xu, Xu; Liu, Xue; Zhang, Qingjie

    2012-11-27

    Lithium-air batteries have captured worldwide attention due to their highest energy density among the chemical batteries. To provide continuous oxygen channels, here, we synthesized hierarchical mesoporous perovskite La(0.5)Sr(0.5)CoO(2.91) (LSCO) nanowires. We tested the intrinsic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity in both aqueous electrolytes and nonaqueous electrolytes via rotating disk electrode (RDE) measurements and demonstrated that the hierarchical mesoporous LSCO nanowires are high-performance catalysts for the ORR with low peak-up potential and high limiting diffusion current. Furthermore, we fabricated Li-air batteries on the basis of hierarchical mesoporous LSCO nanowires and nonaqueous electrolytes, which exhibited ultrahigh capacity, ca. over 11,000 mAh⋅g(-1), one order of magnitude higher than that of LSCO nanoparticles. Besides, the possible reaction mechanism is proposed to explain the catalytic activity of the LSCO mesoporous nanowire. PMID:23150570

  20. Anomalous field-induced magnetoresistance behavior in Pr0.5Sr0.5MnO3 at low temperatures

    NASA Astrophysics Data System (ADS)

    Kumar, Dhirendra; Shahee, Aga; Rawat, Rajeev; Lalla, N. P.

    2012-06-01

    Low-temperature (LT) XRD and magnetoresistance (MR) have been studied in the single phase polycrystalline Pr0.5Sr0.5MnO3 with space-group I4/mcm. The resistance-vs-temperature (R-T) variation at zero-field show a broad paramagnetic to ferromagnetic metallic (FMM) transition at Tc ˜ 240K and it further undergoes FMM to antiferromagnetic insulating (AFMI) transition at TN ˜ 90K with a broad hysteresis indicates a disorder broadened first order phase transition (FOPT). The zero-field cooled (ZFC) MR at 5K shows an open loop with virgin curve lying outside the envelope curve. This anomalous behavior vanishes with increasing temperature. This has been attributed to field-induced transformation of AFMI to FMM phase, which remains arrested down to zero magnetic field at 5K.

  1. Epitaxial growth and properties of La0.7Sr0.3MnO3 thin films with micrometer wide atomic terraces

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Zhao, Yuelei; Tang, Chi; Su, Tang; Song, Qi; Shi, Jing; Han, Wei

    2015-07-01

    La0.7Sr0.3MnO3 (LSMO) films with extraordinarily wide atomic terraces are epitaxially grown on SrTiO3 (100) substrates by pulsed laser deposition. Atomic force microscopy measurements on the LSMO films show that the atomic step is ˜4 Å and the atomic terrace width is more than 2 μm. For a 20 monolayers (MLs) LSMO film, the magnetization is determined to be 255 ± 15 emu/cm3 at room temperature, corresponding to 1.70 ± 0.11 μB per Mn atom. As the thickness of LSMO increases from 8 MLs to 20 MLs, the critical thickness for the temperature dependent insulator-to-metal behavior transition is shown to be 9 MLs. Furthermore, post-annealing in oxygen environment improves the electron transport and magnetic properties of the LSMO films.

  2. Silica-coated La0.75Sr0.25MnO3 nanoparticles for magnetically driven DNA isolation.

    PubMed

    Trachtová, Stěpánka; Kaman, Ondřej; Spanová, Alena; Veverka, Pavel; Pollert, Emil; Rittich, Bohuslav

    2011-11-01

    Magnetic La(0.75)Sr(0.25)MnO(3) nanoparticles possessing an approximately 20-nm-thick silica shell (LSMO(0.25)@SiO(2) ) were characterised and tested for the isolation of PCR-ready bacterial DNA. The results presented here show that the nanoparticles do not interfere in PCR. DNA was apparently reversibly adsorbed on their silica shell from the aqueous phase system (16% PEG 6000-2 M NaCl). The method proposed was used for DNA isolation from complex food samples (dairy products and probiotic food supplements). The isolated DNA was compatible with PCR. The main advantages of the nanoparticles tested for routine use were their high colloidal stability allowing a more precise dosage and therefore high reproducibility of DNA isolation. PMID:21919199

  3. Real-time observation of pulse reshaping using Sr0.61Ba0.39Nb2O6 single crystal fiber in a microwave cavity

    NASA Astrophysics Data System (ADS)

    Huang, Chuanyong; Guo, Ruyan; Bhalla, Amar S.

    2005-03-01

    Ferroelectric single crystal fiber Sr0.61Ba0.39Nb2O6 (SBN) is evaluated for optical pulse engineering in terms of wavelength shifting and pulse compression/expansion through nonlinear optical (Pockels) effect at microwave frequencies. The microwave-photonic interaction was investigated experimentally in a TE103 microwave cavity at 10GHz. It is shown that the frequency component of an optical pulse can be controlled effectively using the SBN single crystal in a microwave cavity without the need of contact electrodes or any interruption to the optical system. The technique may be utilized in several aspects of optical communications such as channel definition and security encoding of the signal, and shows potential for a range of optoelectronic applications.

  4. Magnetoelectric coupling at the interface of BiFeO3/La0.7Sr0.3MnO3 multilayers

    SciTech Connect

    Calderon, M. J.; Liang, Shuhua; Yu, Rong; Salafranca, Juan; Scalapino, D. J.; Dong, Shuai; Yunoki, Seiji; Brey, L.; Moreo, Adriana; Dagotto, Elbio R

    2011-01-01

    Electric-field controlled exchange bias in a heterostructure composed of the ferromagnetic manganite La0.7Sr0.3MO3 and the ferroelectric antiferromagnetic BiFeO3 has recently been demonstrated experimentally. By means of a model Hamiltonian, we provide a possible explanation for the origin of this magnetoelectric coupling. We find, in agreement with experimental results, a net ferromagnetic moment at the BiFeO3 interface. The induced ferromagnetic moment is the result of the competition between the eg-electron double exchange and the t2g-spin antiferromagnetic superexchange that dominates in bulk BiFeO3. The balance of these simultaneous ferromagnetic and antiferromagnetic tendencies is strongly affected by the interfacial electronic charge density, which, in turn, can be controlled by the BiFeO3 ferroelectric polarization.

  5. Thermal hysteresis in the luminescence of Cr3+ ions in Sr0.6Ba0.4 (NbO3)2

    NASA Astrophysics Data System (ADS)

    Ramirez, M. O.; Jaque, D.; Montes, M.; García Solé, J.; Bausá, L. E.; Ivleva, L.

    2004-04-01

    The temperature dependence of the emission spectrum of Cr3+ ions in Sr0.6Ba0.4 (NbO3)2 has been systematically investigated around the ferroelectric phase transition of this crystal (≈370 K). In spite of the strong thermal quenching of the luminescence occurring at these temperatures, the emission spectrum is still clearly detectable and shows dramatic changes in both line shape and intensity when passing through the phase transition temperature. A redshift of about 6 nm occurs when the crystal is driven from the polar to the nonpolar phase. In addition, this shift displays a thermal hysteresis, then providing the possibility of realizing a bistable spectral system based on this material.

  6. Turning antiferromagnetic Sm0.34Sr0.66MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach

    NASA Astrophysics Data System (ADS)

    Suwardi, Ady; Prasad, Bhagwati; Lee, Shinbuhm; Choi, Eun-Mi; Lu, Ping; Zhang, Wenrui; Li, Leigang; Blamire, Mark; Jia, Quanxi; Wang, Haiyan; Yao, Kui; MacManus-Driscoll, Judith L.

    2016-04-01

    Ferromagnetic insulating thin films of Sm0.34Sr0.66MnO3 (SSMO) on (001) SrTiO3 substrates with a TC of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High TC ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ~40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low TC.

  7. Effects of swift heavy ion irradiation on dielectric relaxation and conduction mechanism in Ba0.90Sr0.10TiO3

    NASA Astrophysics Data System (ADS)

    Mohan, C. R. K.; Dey, Ranajit; Patel, Shiv P.; Pandey, R. K.; Sharma, M. P.; Bajpai, P. K.

    2016-04-01

    The effects of 100 MeV O8+ ion beam irradiation on the structural and dielectric behavior of Ba0.90Sr0.10TiO3 ceramics have been analyzed. Ion irradiation does not change the crystalline structure, however the tetragonal distortion increases. The low frequency dielectric dispersion especially at high temperatures increases significantly after ion irradiation. The dielectric relaxation phenomenon has been probed through complex impedance and electric modulus approaches. The observed dielectric relaxation has distributed relaxation times and is a thermally activated process. Ion irradiation enhances the cationic disordering. The contributions of grains and grains boundaries towards impedance have been separated. It is inferred that the grain boundaries become more resistive due to ion irradiation and is associated to oxygen vacancies annihilation. Ion irradiation also decreases the bulk ferroelectric polarization demonstrating that the surface or near surface modifications may tune the bulk properties in polar dielectrics.

  8. Energy-dependent crossover from anisotropic to isotropic magnetic dispersion in lightly-doped La1.96Sr0.04CuO4

    SciTech Connect

    Matsuda, Masaaki; Granroth, Garrett E; Fujita, M.; Yamada, K.; Tranquada, John M.

    2013-01-01

    Inelastic neutron scattering experiments have been performed on lightly-doped La$_{1.96}$Sr$_{0.04}$CuO$_{4}$, which shows diagonal incommensurate spin correlations at low temperatures. We previously reported that this crystal, with a single orthorhombic domain, exhibits the ``hourglass" dispersion at low energies [Phys. Rev. Lett. 101, 197001 (2008)]. In this paper, we investigate in detail the energy evolution of the magnetic excitations up to 65 meV. It is found that the anisotropic excitations at low energies, dispersing only along the spin modulation direction, crossover to an isotropic, conical dispersion that resembles spin waves in the parent compound La$_2$CuO$_{4}$. The change from two-fold to full symmetry on crossing the waist of the hourglass reproduces behavior first identified in studies of underdoped YBa$_2$Cu$_3$O$_{6+x}$. We discuss the significance of these results.

  9. Turning antiferromagnetic Sm(0.34)Sr(0.66)MnO3 into a 140 K ferromagnet using a nanocomposite strain tuning approach.

    PubMed

    Suwardi, Ady; Prasad, Bhagwati; Lee, Shinbuhm; Choi, Eun-Mi; Lu, Ping; Zhang, Wenrui; Li, Leigang; Blamire, Mark; Jia, Quanxi; Wang, Haiyan; Yao, Kui; MacManus-Driscoll, Judith L

    2016-04-21

    Ferromagnetic insulating thin films of Sm(0.34)Sr(0.66)MnO3 (SSMO) on (001) SrTiO3 substrates with a T(C) of 140 K were formed in self-assembled epitaxial nanocomposite thin films. High T(C) ferromagnetism was enabled through vertical epitaxy of the SSMO matrix with embedded, stiff, ∼40 nm Sm2O3 nanopillars giving a c/a ratio close to 1 in the SSMO. In contrast, bulk and single phase SSMO films of the same composition have much stronger tetragonal distortion, the bulk having c/a >1 and the films having c/a <1, both of which give rise to antiferromagnetic coupling. The work demonstrates a unique and simple route to creating ferromagnetic insulators for spintronics applications where currently available ferromagnetic insulators are either hard to grow and/or have very low T(C). PMID:27020599

  10. Perpendicular Exchange-Biased Magnetotransport at the Vertical Heterointerfaces in La(0.7)Sr(0.3)MnO3:NiO Nanocomposites.

    PubMed

    Zhang, Wenrui; Li, Leigang; Lu, Ping; Fan, Meng; Su, Qing; Khatkhatay, Fauzia; Chen, Aiping; Jia, Quanxi; Zhang, Xinghang; MacManus-Driscoll, Judith L; Wang, Haiyan

    2015-10-01

    Heterointerfaces in manganite-based heterostructures in either layered or vertical geometry control their magnetotransport properties. Instead of using spin-polarized tunneling across the interface, a unique approach based on the magnetic exchange coupling along the vertical interface to control the magnetotransport properties has been demonstrated. By coupling ferromagnetic La0.7Sr0.3MnO3 and antiferromagnetic NiO in an epitaxial vertically aligned nanocomposite (VAN) architecture, a dynamic and reversible switch of the resistivity between two distinct exchange biased states has been achieved. This study explores the use of vertical interfacial exchange coupling to tailor magnetotransport properties, and demonstrates their viability for spintronic applications. PMID:26394548

  11. Debye’s temperature and heat capacity for Sr0.15Ba0.85Bi2Nb2O9 relaxor ferroelectric ceramic

    NASA Astrophysics Data System (ADS)

    Peláiz-Barranco, A.; González-Abreu, Y.; Saint-Grégoire, P.; Guerra, J. D. S.; Calderón-Piñar, F.

    2016-02-01

    A lead-free relaxor ferroelectric, Sr0.15Ba0.85Bi2Nb2O9, was synthesized via solid-state reaction and the temperature-dependence of the heat capacity was measured in a wide temperature range. The dielectric permittivity was also measured between 500Hz and 5MHz in the same temperature range. No anomaly has been detected in the heat capacity curve for the whole temperature range covered in the present experiments, while broad peaks have been observed in the dielectric permittivity with high frequency dispersion. A typical relaxor behavior has been observed from the dielectric analysis. The Debye’s temperature has showed a minimum value near the freezing temperature. The results are discussed considering the spin-glass model and the high frequency dispersion, which has been observed for the studied relaxor system.

  12. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    DOE PAGESBeta

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. Moreover, the Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. But, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  13. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1-yCryO3 thin films.

    PubMed

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1-yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm(2). The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides. PMID:27001006

  14. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1‑yCryO3 thin films

    NASA Astrophysics Data System (ADS)

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-03-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1‑yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm2. The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides.

  15. Ordered La0.7Sr0.3MnO3 nanohole arrays fabricated on a nanoporous alumina template by pulsed laser ablation

    NASA Astrophysics Data System (ADS)

    Kumaresavanji, M.; Gomes, I. T.; Apolinario, A.; Rolo, A. G.; Almeida, B. G.; Lopes, A. M. L.; Araujo, J. P.

    2016-03-01

    Highly ordered nanohole arrays of {{La}}0.7{{Sr}}0.3{{MnO}}3 manganite have been synthesized using pulsed laser deposition on nanoporous alumina template. Their structure and phase formation were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD). The magnetic measurements were performed with respect to temperature and field and exhibit a ferromagnetic to paramagnetic transition at 284 K. In addition, the temperature dependence of electrical resistance was measured at different magnetic fields and an insulating phase throughout all the temperatures was observed. The low temperature ferromagnetic insulating state is discussed by the presence of a canted ferromagnetic state induced by the nanoholes. The present work shows the feasibility of combining both the nanoporous alumina template and pulsed laser ablation for the fabrication of perovskite manganite nanohole arrays which can also be extended to fabricate other multicomponent oxide nanohole materials.

  16. Anisotropy of the Electron-Doped Infinite-Layer Superconductor Sr0.9La0.1CuO2

    NASA Astrophysics Data System (ADS)

    Kim, Heon-Jung; Park, Min-Seok; Jung, C. U.; Lee, Sung-Ik; Kim, Mun-Seog

    Anisotropy of a c-axis aligned Sr0.9La0.1CuO2 infinite-layer superconductor was studied by measuring the magnetization in different temperature (M(T)) and angle (M(θ)). The M(θ) and the critical temperature as a function of the angle (Tc2(θ)) deduced from M(T) was well described by the anisotropic Ginzburg-Landua theory with a moderate anisotropy value γ≈9. This low value, which is comparable to that of YBa2Cu3O7-δ implied strong interlayer coupling between CuO2 planes. In this compound, the strong interlayer coupling was thought to solely result from the crystal structure without charge reservoir blocks.

  17. Possible surface antiferromagnetism and no evidence for intergranular tunneling magnetoresistance in La0.5Sr0.5CoO3-δ cobaltites

    NASA Astrophysics Data System (ADS)

    Troyanchuk, I. O.; Bushinsky, M. V.; Lobanovsky, L. S.

    2013-12-01

    The magnetization and magnetoresistance (MR) of La0.5Sr0.5CoO3-δ have been studied as function of surface/volume ratio and oxygen deficit. All the samples have positive and negative components of MR at low temperature. The small positive component is predominated in low field regime below and well above the coercive field. The positive MR under magnetic moment reorientation is in contradiction with scenario of negative intergranular tunneling magnetoresistance being the hallmark of half-metallic polycrystalline oxides. The oxygen deficit leads to a gradual stabilization of antiferromagnetic phase in bulk and concomitant enhancement of the MR. The decrease in value of magnetization and enhancement of the negative MR component in compacted at high pressure/room temperature powder with a large surface/volume ratio can be ascribed to antiferromagnetism at the surface.

  18. Pb0.3Sr0.7TiO3 thin films for high-frequency phase shifter applications

    NASA Astrophysics Data System (ADS)

    Jain, M.; Karan, N. K.; Katiyar, R. S.; Bhalla, A. S.; Miranda, F. A.; Keuls, F. W. Van

    2004-07-01

    Pb0.3Sr0.7TiO3(PST30) thin films were synthesized on platinized silicon (Pt /Si) and lanthanum aluminate (LAO) substrates using chemical solution deposition technique. The films on LAO substrate were highly (100) oriented, whereas the films on Pt /Si substrate were polycrystalline. The low dielectric loss in the PST30/LAO films makes them attractive for fabricating tunable dielectric devices. An eight-element coupled microstrip phase shifter was fabricated on PST30/LAO film and tested in the frequency range ˜15-17GHz. The maximum figure of merit (κ =phase shift per dB loss) of ˜56°/dB was obtained for PST30 film, which was better than commonly observed value in pure barium strontium titanate films. This makes PST30 a potential candidate material for further investigations for microwave applications.

  19. Orientation effect on microwave dielectric properties of Si-integrated Ba0.6Sr0.4TiO3 thin films for frequency agile devices

    NASA Astrophysics Data System (ADS)

    Kim, Hyun-Suk; Hyun, Tae-Seon; Kim, Ho-Gi; Kim, Il-Doo; Yun, Tae-Soon; Lee, Jong-Chul

    2006-07-01

    The effect of texture with (100) and (110) preferred orientations on dielectric properties of Ba0.6Sr0.4TiO3 (BST) thin films grown on SrO (9nm) and CeO2 (70nm ) buffered Si substrates, respectively, was investigated. The coplanar waveguide (CPW) phase shifter using (100) oriented BST films on SrO buffered Si exhibited a much-enhanced figure of merit of 24.7°/dB, as compared to that (10.2°/dB) of a CPW phase shifter using (110) oriented BST films on CeO2 buffered Si at 12GHz. This work demonstrates that the microwave properties of the Si-integrated BST thin films are highly correlated with crystal orientation.

  20. Crystal structure of La 0.4Sr 0.6CoO 2.71 investigated by TEM and XRD

    NASA Astrophysics Data System (ADS)

    Gspan, C.; Grogger, W.; Bitschnau, B.; Bucher, E.; Sitte, W.; Hofer, F.

    2008-11-01

    The structure of the oxygen-deficient perovskite La 0.4Sr 0.6CoO 3-δ ( δ=0.29) was investigated by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). Domains between 50 and 250 nm in size were observed in the electron microscope. Weak superstructure reflections were found with both X-ray and electron diffraction. Investigations of these superstructure reflections by selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED) showed that the domains in a crystal are orientated in a 90° relationship. High-resolution transmission electron microscopy (HRTEM) images from the domain boundary also revealed a 90° orientation dependency. Using the symmetry of CBED patterns, the point group 4/ mmm was determined. By comparing reflections from the SAED pattern with possible reflections, the space group I4/ mmm (No. 139) could be isolated and finally the crystal structure was refined by Rietveld refinement.

  1. Effect of Nb doping at Mn site on thermal expansion of Pr0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Rao, Ashok; Poornesh, P.; Wu, K. K.; Kuo, Y. K.; Agarwal, S. K.

    2013-10-01

    In this study we present results on effect of Nb doping on thermal expansion of Pr0.7Sr0.3MnO3. Thermal expansion measurements were done using three terminal capacitance method. The pure sample shows a jump at the insulator-metal (I-M) transition temperature, and with Nb doping, a fourfold decrease in the jump is found. Since thermal expansion is a bulk property, this suggests that the dopants are not in the form of local clusters; rather they are distributed uniformly throughout the sample. Temperature variation of Gruniesen ratio α/CP shows that for temperatures below I-M transition, the ratio is weakly dependent on temperature. Pressure dependence on the transition temperature, dTP/dP and jump in compressibility, Δβ, of these samples has been estimated using well-known Ehrenfest equations. The present results are in fairly good agreement with those reported in the literature.

  2. Effect of Quenching on Magnetoresistance Properties in the Pr 0.5Sr 0.5MnO 3 Perovskite Manganite

    NASA Astrophysics Data System (ADS)

    Boujelben, W.; Ellouze, M.; Cheikh-Rouhou, A.; Pierre, J.; Joubert, J. C.

    2002-05-01

    We report on the magnetization, resistivity and magnetoresistance (MR) measurements on polycrystalline Pr0.5Sr0.5MnO3. Quenching samples from 1400°C to room temperature in water (sample I) or in air (sample II) leads to different behaviors. Powder X-ray diffraction patterns for samples I and II could be indexed, respectively, in rhombohedral perovskite structure with R3c space group and in the orthorhombic one with Imma space group. Magnetization measurements show that both samples exhibit a paramagnetic-ferromagnetic transition at 280 K (sample I) and 265 K (sample II). At low temperature, sampleI presents a ferromagnetic spin-canted state, while sample II behaves as an antiferromagnet below 160 K. Resistivity and magnetoresistance studies show a net difference as a function of the quenching conditions.

  3. Domain wall transformations and hopping in La(0.7)Sr(0.3)MnO(3) nanostructures imaged with high resolution x-ray magnetic microscopy.

    PubMed

    Finizio, S; Foerster, M; Krüger, B; Vaz, C A F; Miyawaki, T; Mawass, M A; Peña, L; Méchin, L; Hühn, S; Moshnyaga, V; Büttner, F; Bisig, A; Le Guyader, L; El Moussaoui, S; Valencia, S; Kronast, F; Eisebitt, S; Kläui, M

    2014-11-12

    We investigate the effect of electric current pulse injection on domain walls in La(0.7)Sr(0.3)MnO(3) (LSMO) half-ring nanostructures by high resolution x-ray magnetic microscopy at room temperature. Due to the easily accessible Curie temperature of LSMO, we can employ reasonable current densities to induce the Joule heating necessary to observe effects such as hopping of the domain walls between different pinning sites and nucleation/annihilation events. Such effects are the dominant features close to the Curie temperature, while spin torque is found to play a small role close to room temperature. We are also able to observe thermally activated domain wall transformations and we find that, for the analyzed geometries, the vortex domain wall configuration is energetically favored, in agreement with micromagnetic simulations. PMID:25336527

  4. Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown by PLD

    NASA Astrophysics Data System (ADS)

    James, K. K.; Satish, B.; Jayaraj, M. K.

    2014-01-01

    Ferroelectric thin films of Ba0.7Sr0.3TiO3 (BST) were deposited on Si/SiO2/TiO2/Pt (PtSi) substrate by pulsed laser deposition (PLD). Crystalline films with perovskite structure were obtained without post-deposition annealing. Phase purity of the deposited films was confirmed by x-ray diffraction. The lowest value of FWHM obtained for the film deposited at oxygen pressure 5.4×10-4 mbar and substrate temperature 600°C, indicates the high crystallinity of the film. The room temperature dielectric constant at 100 kHz was 85. Butterfly loop, which is the characteristic of ferroelectric materials, was obtained in the regime of -4 to +4V. The leakage current density was nearly 9×10-13 Acm-2.

  5. Memory effects and magnetic relaxation in single-crystalline La0.9Sr0.1CoO3

    NASA Astrophysics Data System (ADS)

    Khan, N.; Mandal, P.; Prabhakaran, D.

    2014-07-01

    We report a detailed investigation of magnetic relaxation and memory effects in La0.9Sr0.1CoO3 single crystal from dc magnetization measurements. The analysis of magnetic relaxation at different temperatures and magnetic fields below the freezing temperature Tf reveals the characteristics of the spin-glass phase. Below Tf, striking memory effects have been clearly observed in different experimental protocols. The memory effect in the zero-field-cooled magnetization further establishes that the glassy magnetic state arises from the cooperative spin-spin interaction but not due to the independent relaxation of metastable phase clusters. The asymmetric response with respect to negative and positive temperature changes favors the hierarchical model of memory effects rather than the droplet model discussed in other works for different insulating and metallic Heisenberg spin glasses.

  6. Size dependence in magnetic memory, relaxation and interaction of La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Ghosh, Nilotpal; Datta, Subarna; Ghosh, Barnali

    2015-05-01

    We report the study of memory effect, relaxation and interaction of La0.67Sr0.33MnO3 (LSMO) particles of two different sizes, bulk (~60-150 μm) and nano (~80 nm) synthesized by using polymeric precursor route. Magnetic relaxation measurement has been carried out and the analysis shows the existence of two relaxation times in both the cases. Our dynamic light scattering (DLS) studies indicate the presence of two different size distributions in LSMO nano particle sample. This is attributed to the fact that particles of two different sizes can relax separately. It has been observed that both the samples show signature of magnetic memory effect. Because, the effect of disordered surface layer is more in LSMO nano than LSMO bulk particles, LSMO nano particles are found to favor demagnetized state where as LSMO bulk prefer magnetized state.

  7. Structure, magnetic and magnetoresistance properties of Pr0.67Sr0.33MnO3 manganite oxide prepared by ball milling method

    NASA Astrophysics Data System (ADS)

    Chérif, W.; Ellouze, M.; Lehlooh, A.-F.; Elhalouani, F.; Mahmood, S. H.

    2012-07-01

    A sample of Pr0.67Sr0.33MnO3 nanoparticles was synthesized by the ball milling method. X-ray diffraction pattern of the sample showed orthorhombic system with Pnma space group. The average crystallite size of 110 nm was obtained by both Scanning Electron Microscopy and X-ray diffraction. Magnetic measurements showed para-to-ferromagnetic transition with a Curie temperature of TC=269 K. Electrical investigations showed that all our samples exhibit a semi-conducting behavior above TC and a metallic-like one at lower temperatures. The sample exhibited a large magnetoresistance of 30% at room temperature in an applied magnetic field of 2 T. The transport and the magnetic properties were interpreted in terms of the existence of magnetic polarons in the sample.

  8. Electrospun La0.8Sr0.2MnO3 nanofibers for a high-temperature electrochemical carbon monoxide sensor

    NASA Astrophysics Data System (ADS)

    Zhi, Mingjia; Koneru, Anveeksh; Yang, Feng; Manivannan, Ayyakkannu; Li, Jing; Wu, Nianqiang

    2012-08-01

    Lanthanum strontium manganite (La0.8Sr0.2MnO3, LSM) nanofibers have been synthesized by the electrospinning method. The electrospun nanofibers are intact without morphological and structural changes after annealing at 1050 °C. The LSM nanofibers are employed as the sensing electrode of an electrochemical sensor with yttria-stabilized zirconia (YSZ) electrolyte for carbon monoxide detection at high temperatures over 500 °C. The electrospun nanofibers form a porous network electrode, which provides a continuous pathway for charge transport. In addition, the nanofibers possess a higher specific surface area than conventional micron-sized powders. As a result, the nanofiber electrode exhibits a higher electromotive force and better electro-catalytic activity toward CO oxidation. Therefore, the sensor with the nanofiber electrode shows a higher sensitivity, lower limit of detection and faster response to CO than a sensor with a powder electrode.

  9. Magnetic field penetration depth of La(1.85)Sr(0.15)CuO4 measured by muon spin relaxation

    NASA Technical Reports Server (NTRS)

    Kossler, W. J.; Kempton, J. R.; Yu, X. H.; Schone, H. E.; Uemura, Y. J.

    1987-01-01

    Muon-spin-relaxation measurements have been performed on a high-Tc superconductor La(1.85)Sr(0.15)CuO4. In an external transverse magnetic field of 500 G, a magnetic field penetration depth of 2000 A at T = 10 K has been determined from the muon-spin-relaxation rate which increased with decreasing temperature below Tc. From this depth and the Pauli susceptibility, the superconducting carrier density is estimated at 3 x 10 to the 21st per cu cm. The zero-field relaxation rates above and below Tc were equal, which suggests that the superconducting state in this sample is not associated with detectable static magnetic ordering.

  10. Influence of heat treatment on the magnetic and magnetocaloric properties in Nd0.6Sr0.4MnO3 compound

    NASA Astrophysics Data System (ADS)

    Ahmed, A. M.; Mohamed, H. F.; Diab, A. K.; Mohamed, Sara A.; García-Granda, S.; Martínez-Blanco, D.

    2016-07-01

    In the present investigation, the effect of annealing temperature on the structural, electrical transport and the magnetocaloric effect of Nd0.6Sr0.4MnO3 manganites have been studied. Rietveld refinement of XRD data reveals that all samples are single phase with a space group (Pnma). Heat treatment enhances the grain size and decreases the porosity. All samples suffer Curie transition from ferromagnetic to paramagnetic. Magnetocaloric parameters have been determined by the analysis of isothermal M (H) curves around Curie temperature (ΔH = 2 T) for samples. Heat treatment enhances magnetic entropy, which reaches a maximum at Tan = 900 °C. In addition, the rate cooling power records highest value at Tan = 700 °C.

  11. Electrical conduction mechanism and improved multiferroic properties of NFO/ (Pb0.50Sr0.50) TiO3 bilayer nanostructure composite thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Ram, Mast; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Multiferroic 2-2 type layered NFO/ (Pb0.50Sr0.50) TiO3 composite thin film on Pt/TiO2/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (Ps ˜ 8.69, Pr ˜ 3.19 µC/cm2 and Ec ˜ 419kV/cm) and magnetic properties (Ms), (Mr) and (Hc) is (104emu/cc, 0.8emu/cc and 25Oe.) were observed at room temperature. Our observation provides an effective way to manipulate the conduction behavior to understand the leakage current density of multiferroic composites film at the interface. Poole-Frankel tunneling conduction mechanism dominates the leakage current of films in the relatively high electric filed.

  12. Electronic conduction mechanism for NFO/(Pb0.80Sr0.20) TiO3 bi-layered nanostructure multiferroic composite thin film

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    Multiferroic 2-2 type bi-layered NFO/(Pb0.80Sr0.20) TiO3 composite thin film on Pt/TiO2/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (Ps ~ 17.25, Pr ~ 8.02 µC/cm2 and Ec ~ 404kV/cm) and magnetic properties (Ms ~ 117emu/cc, Mr ~ 0.83emu/cc and Hc ~ 20Oe) were observed at room temperature. The leakage current densities in NFO/PST composites film have been studied. Poole-Frankel bulk limited conduction mechanism dominates of film at relatively high electric filed.

  13. Enhanced ferromagnetic and metal insulator transition in Sm0.55Sr0.45MnO3 thin films: Role of oxygen vacancy induced quenched disorder

    NASA Astrophysics Data System (ADS)

    Srivastava, M. K.; Siwach, P. K.; Kaur, A.; Singh, H. K.

    2010-11-01

    Effect of quenched disorder (QD) caused by oxygen vacancy (OV) and substrate induced inhomogeneous compressive strain, on the magnetic and transport properties of oriented polycrystalline Sm0.55Sr0.45MnO3 thin films is investigated. QD is related intimately to the ordering/disordering of the OVs and controls the paramagnetic-ferromagnetic/insulator-metal transition. OV ordered films show enhanced TC/TIM˜165 K, which is depressed by oxygen annealing. OV disordering realized by quenching reduces TC/TIM. The first order IM transition observed in SSMO single crystals is transformed into nonhysteretic and continuous one in the OV ordered films. QD appears to be diluted by OV disorder/annihilation and results in stronger carrier localization.

  14. Evolution of photoinduced effects in phase-separated Sm0.5Sr0.5Mn1−yCryO3 thin films

    PubMed Central

    Chai, Xiaojie; Xing, Hui; Jin, Kexin

    2016-01-01

    Systematic study on electrical transport properties has been performed in Sm0.5Sr0.5Mn1−yCryO3 thin films illuminated by the light. An evolution of persistent and transient photoinduced effects induced by the impurity doping and temperature has been observed, which is closely related to the number of ferromagnetic clusters. The maximum persistent photoinduced effect is observed at y = 0.08 and the corresponding value is about 61.7% at the power density of 13.7 mW/mm2. The underlying mechanism can be understood by the coexistence and competition of the multiphases in phase-separated manganites induced by Cr-doping. These results would pave the way for practical applications in innovative photoelectric devices of all-oxides. PMID:27001006

  15. Strain Effects in La0.7Sr0.3MnO3 Films by X-ray Absorption Spectroscopy

    SciTech Connect

    Ramos, A.Y.; Neto, N.M. Souza; Giacomelli, C.; Tolentino, H.C.N.; Ranno, L.; Favre-Nicolin, E.

    2003-01-24

    We report on Mn K-edge X-ray absorption study, in plane and out of plane, of La0.7Sr0.3MnO3 films, epitaxially grown on a tensile substrate SrTiO3 by laser ablation. From Extended X-ray Absorption Fine Structure in the film plane we observe a small increase of Mn-Mn distances with respect to relaxed film. In addition, a small distortion of the MnO6 octahedron is evidenced from Extended and Near Edge Absorption measurements. The respective amplitudes found for these two effects are on the same order, so that no modification of the Mn-O-Mn angle is evidenced.

  16. Strong perpendicular exchange bias in epitaxial La0.7Sr0.3MnO3:LaFeO3 nanocomposite thin films

    NASA Astrophysics Data System (ADS)

    Fan, Meng; Zhang, Wenrui; Jian, Jie; Huang, Jijie; Wang, Haiyan

    2016-07-01

    Strong exchange bias (EB) in perpendicular direction has been demonstrated in vertically aligned nanocomposite (VAN) (La0.7Sr0.3MnO3)1-x : (LaFeO3)x (LSMO:LFO, x = 0.33, 0.5, 0.67) thin films deposited by pulsed laser deposition. Under a moderate magnetic field cooling, an EB field as high as ˜800 Oe is achieved in the VAN film with x = 0.33, suggesting a great potential for its applications in high density memory devices. Such enhanced EB effects in perpendicular direction can be attributed to the high quality epitaxial co-growth of vertically aligned ferromagnetic LSMO and antiferromagnetic LFO phases, and the vertical interface coupling associated with a disordered spin-glass state. The VAN design paves a powerful way for integrating perpendicular EB effect within thin films and provides a new dimension for advanced spintronic devices.

  17. Planar-type spin valves based on low-molecular-weight organic materials with La0.67Sr0.33MnO3 electrodes

    NASA Astrophysics Data System (ADS)

    Ikegami, Tomonori; Kawayama, Iwao; Tonouchi, Masayoshi; Nakao, Satoru; Yamashita, Yoshiro; Tada, Hirokazu

    2008-04-01

    The spin injection and transport properties of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) were investigated utilizing planar-type spin-valve devices with half-metallic La0.67Sr0.33MnO3 electrodes. The devices showed clear spin-valve characteristics with a magnetoresistance (MR) ratio of up to 29% at 5K. The MR ratio was found to depend on the gap spacing of the electrodes, the applied bias voltage, temperature, and the crystallinity of the films. It was also affected by gas adsorption onto the films, indicating that the spins were scattered by carriers and/or radical ions in the films generated through charge transfer from gas molecules.

  18. Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures

    NASA Astrophysics Data System (ADS)

    Zheng, Dongxing; Jin, Chao; Li, Peng; Wang, Liyan; Feng, Liefeng; Mi, Wenbo; Bai, Haili

    2016-04-01

    The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z2 ‑ r2 and low energy x2 ‑ y2 orbitals, which makes electrons occupy the localized x2 ‑ y2 orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices.

  19. Large magnetic entropy change above 300 K in a La 0.7Ca 0.2Sr 0.1MnO 3 single crystal

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Peng, Hua-Xin; Yu, Seong-Cho; Hwi Hur, Nam

    2005-04-01

    A detailed study of the magneto-caloric effect in a single crystal of La0.7Ca0.2Sr0.1MnO3 has been made. The magnetic entropy change (Δ SM) reaches a maximum value of ∼7.45 J/kg K at ∼308 K for a 50 kOe field change, which is ideal for room-temperature magnetic refrigeration applications. Due to the absence of grains in the manganite single crystal, the Δ SM distribution of this sample is much more uniform than that of gadolinium and polycrystalline manganites, which is desirable for an Ericson-cycle magnetic refrigerator. The single crystal has the large magnetic entropy change induced by low magnetic field change, which is beneficial for the household application of active magnetic refrigerant (AMR) materials. These results indicate that the present single crystal is an excellent candidate as a working material for room-temperature AMR.

  20. Large magnetocaloric effect in La0.845Sr0.155Mn1-xMxO3 (M = Mn, Cu, Co) perovskites

    NASA Astrophysics Data System (ADS)

    Phan, Manh-Huong; Phan, The-Long; Yu, Seong-Cho; Tho, Nguyen Duc; Chau, Nguyen

    2004-06-01

    We present the results of an investigation on the magnetocaloric effect in the perovskites of La0.845Sr0.155Mn1-xMxO3 (M = Mn, Cu, Co). It is found that there was a large magnetic entropy change, i.e. a large magneto-caloric effect, in all these samples. Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu-doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology. The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic-paramagnetic transition temperature (TC) - which is experimentally verified by electron paramagnetic resonance study.

  1. Induced Ti magnetization at La0.7Sr0.3MnO3 and BaTiO3 interfaces

    NASA Astrophysics Data System (ADS)

    Liu, Yaohua; Tornos, J.; te Velthuis, S. G. E.; Freeland, J. W.; Zhou, H.; Steadman, P.; Bencok, P.; Leon, C.; Santamaria, J.

    2016-04-01

    In artificial multiferroics hybrids consisting of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and ferroelectric BaTiO3 epitaxial layers, net Ti moments are found from polarized resonant soft x-ray reflectivity and absorption. The Ti dichroic reflectivity follows the Mn signal during the magnetization reversal, indicating exchange coupling between the Ti and Mn ions. However, the Ti dichroic reflectivity shows stronger temperature dependence than the Mn dichroic signal. Besides a reduced ferromagnetic exchange coupling in the interfacial LSMO layer, this may also be attributed to a weak Ti-Mn exchange coupling that is insufficient to overcome the thermal energy at elevated temperatures.

  2. Microwave dielectric and optical properties of amorphous and crystalline Ba0.5Sr0.5TiO3 thin films

    NASA Astrophysics Data System (ADS)

    Goud, J. Pundareekam; Joseph, Andrews; Ramakanth, S.; Naidu, Kuna Lakshun; Raju, K. C. James

    2016-05-01

    The thin films of composition Ba0.5Sr0.5TiO3 (BST5) were deposited by Pulsed Laser Deposition technique on amorphous fused silica substrates at room temperature (RT) and at 700°C. The film deposited at RT is amorphous while the other crystallized in cubic structure. The refractive index (n) and optical band gap (Eg) extracted from transmission spectra in the 190 -2500 nm range. Microwave dielectric properties were investigated using the Split Post Dielectric Resonators (SPDR) technique at spot frequencies of 10GHz and 20GHz. The experimental results show that thin films deposited at high temperature (700°C) shows very high dielectric constant for both 10GHz and 20 GHz. These high dielectric constant films can be used in a wide range of applications such as capacitors, non-volatile high speed random access memories, and electro-optic devices.

  3. Orbital Reconstruction Enhanced Exchange Bias in La0.6Sr0.4MnO3/Orthorhombic YMnO3 Heterostructures

    PubMed Central

    Zheng, Dongxing; Jin, Chao; Li, Peng; Wang, Liyan; Feng, Liefeng; Mi, Wenbo; Bai, Haili

    2016-01-01

    The exchange bias in ferromagnetic/multiferroic heterostructures is usually considered to originate from interfacial coupling. In this work, an orbital reconstruction enhanced exchange bias was discovered. As La0.6Sr0.4MnO3 (LSMO) grown on YMnO3 (YMO) suffers a tensile strain (a > c), the doubly degenerate eg orbital splits into high energy 3z2 − r2 and low energy x2 − y2 orbitals, which makes electrons occupy the localized x2 − y2 orbital and leads to the formation of antiferromagnetic phase in LSMO. The orbital reconstruction induced antiferromagnetic phase enhances the exchange bias in the LSMO/YMO heterostructures, lightening an effective way for electric-field modulated magnetic moments in multiferroic magnetoelectric devices. PMID:27090614

  4. Electromagnetic transport properties and magnetoresistance of La 0.7Ca 0.2Sr 0.1MnO 3-Ag composites prepared by electroless process

    NASA Astrophysics Data System (ADS)

    Xiong, C. S.; Cui, Y. F.; Xiong, Y. H.; Pi, H. L.; Bao, X. C.; Huang, Q. P.; Zeng, Y.; Wei, F. F.; Zheng, C. F.; Zhu, J.

    2008-09-01

    A series of bulk polycrystalline La 0.7Ca 0.2Sr 0.1MnO 3 (LCSMO)-Ag composites were prepared by electroless plating process and several kinds of physical properties have been studied systemically. According to the results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electromagnetic transport properties, we can see that Ag-added segregated at the surfaces or interfaces of LCSMO grains. The metal-insulator transition temperature ( TP) and Curie temperature ( Tc) were almost unchanged but ρ decreased with increasing plating time. We also observed Ag-added can significantly enhance the magnetoresistance (MR) near TP under a low applied field (3000 Oe) and the room temperature MR reached to 35% under 20 kOe, which is encouraging for practical applications. We can suggest that improved grain boundary effect by Ag-added is responsible for the enhancement.

  5. Dielectric and enhanced pyroelectric properties of (Pb0.325Sr0.675)TiO3 ceramics under direct current bias field

    NASA Astrophysics Data System (ADS)

    Lei, Xiuyun; Dong, Xianlin; Mao, Chaoliang; Chen, Ying; Cao, Fei; Wang, Genshui

    2012-12-01

    (Pb0.325Sr0.675)TiO3 (PST) ceramics were prepared by a traditional solid-state reaction technique. The dielectric and enhanced pyroelectric properties of PST ceramics were investigated under a DC bias field. The dielectric permittivity and dielectric loss of PST ceramics at Curie temperature were 2.97 × 10-4 and 0.006 without DC bias field, respectively. With a DC electric field of 0-500 V/mm, the maximum pyroelectric coefficient and the largest figure of merit (Fd) of PST ceramics were obtained, about 60 × 10-8 C cm-2 K-1 and 26 × 10-5 Pa-1/2, respectively. PST ceramics with such superior electric field enhanced pyroelectric properties have the potential for uncooled focal plane array detectors application.

  6. Magnetoelectric properties of (Pb0.60Sr0.40)TiO3-CFO composite thin film synthesized by metallo-organic decomposition

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Kotnala, R. K.; Negi, N. S.

    2015-06-01

    (Pb0.60Sr0.40) TiO3-CFO composite thin films were grown on Pt/TiO2/Si substrate by novel metallo-Organic process using spin coating technique. The structural, surface morphology and micro structural properties were confirmed by X-Ray diffraction (XRD), Raman spectroscopy, atomic force microscope (AFM) and TEM respectively. The lattice constant of the composite thin film crystallized in the pervoskite and spinel phase was 3.9531 and 8.571 Å. Excellent ferroelectric behavior at 10V was observed, a room temperature magnetic hysteresis shows good results. The saturation magnetization value of the bilayer thin film is lower than that of the pure CFO film which is may be attributed to presence of non ferromagnetic PST layer A high initial behavior of dynamic ME response coefficient for the film was observed. The ME effect of the film strongly depends on the magnetic bias.

  7. Magnetic and structural investigations on La0.6Sr0.4MnO3 nanostructured manganite: Evidence of a ferrimagnetic shell

    NASA Astrophysics Data System (ADS)

    Andrade, V. M.; Caraballo-Vivas, R. J.; Costas-Soares, T.; Pedro, S. S.; Rocco, D. L.; Reis, M. S.; Campos, A. P. C.; Coelho, A. A.

    2014-11-01

    This paper presents the structural and magnetic properties of La0.6Sr0.4MnO3 nanoparticles with sizes from 21 to 106 nm, which have been prepared using the sol-gel method. The reduction of the nanoparticles' size tends to broaden the paramagnetic to ferromagnetic transition, as well as to promote magnetic hysteresis and a remarkable change on the magnetic saturation. In order to better understand the magnetic behavior of those nanoparticles, a simple model based on a ferromagnetic core and a ferrimagnetic shell was considered, where the magnetization was described in terms of the standard mean-field Brillouin function. This model matches the experimental data, leading to conclusion the nanoparticles with size <40 nm are single magnetic domain. In addition, the output fitting parameters give information on the Landé factor of the core and shell.

  8. Nanoscale Mapping of the Magnetic Properties of (111)-Oriented La(0.67)Sr(0.33)MnO3.

    PubMed

    O'Shea, Kerry J; MacLaren, Donald A; McGrouther, Damien; Schwarzbach, Danny; Jungbauer, Markus; Hühn, Sebastian; Moshnyaga, Vasily; Stamps, Robert L

    2015-09-01

    Spatially resolved analysis of magnetic properties on the nanoscale remains challenging, yet strain and defects on this length-scale can profoundly affect a material's bulk performance. We present a detailed investigation of the magnetic properties of La0.67Sr0.33MnO3 thin films in both free-standing and nanowire form and assess the role of strain and local defects in modifying the films' magnetic properties. Lorentz transmission electron microscopy is used to measure the magnetocrystalline anisotropy and to map the Curie temperature and saturation magnetization with nanometric spatial resolution. Atomic-scale defects are identified as pinning sites for magnetic domain wall propagation. Measurement of domain wall widths and crystalline strain are used to identify a strong magnetoelastic contribution to the magnetic anisotropy. Together, these results provide unique insight into the relationship between the nanostructure and magnetic functionality of a ferromagnetic complex oxide film. PMID:26252745

  9. Strain Relaxation in Thin Films of La1.85Sr0.15CuO4 Grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Zaytseva, I.; Cieplak, M. Z.; Abal'Oshev, A.; Berkowski, M.; Domukhovski, V.; Paszkowicz, W.; Shalimov, A.

    2007-01-01

    X-ray diffraction, resistivity, and susceptibility measurements are used to examine the effects of film thickness d (from 17 to 250 nm) on the structural and superconducting properties of La1.85Sr0.15CuO4 films grown by pulsed laser deposition on SrLaAlO4 substrates. For each d the film sgrow with a variable strain, ranging from a large compressive strain in the thinnest films to a negligible or tensile strain in thick films. Our results indicate that the tensile strain is not caused by the off-stoichiometric layer at the substrate-film interface. Instead, it may be caused by the extreme oxygen deficiency in some of the films.

  10. Enhanced Shrinkage of Lanthanum Strontium Manganite (La0.90Sr0.10MnO3+δ) Resulting from Thermal and Oxygen Partial Pressure Cycling

    SciTech Connect

    McCarthy, Ben; Pederson, Larry R.; Anderson, Harlan U.; Zhou, Xiao Dong; Singh, Prabhakar; Coffey, Greg W.; Thomsen, Ed C.

    2007-10-01

    Exposure of La0.9Sr0.1MnO3+δ to repeated oxygen partial pressure cycles (air/10 ppm O2) resulted in enhanced densification rates, similar to behavior shown previously due to thermal cycling. Shrinkage rates in the temperature range 700 to 1000oC were orders of magnitude higher than Makipirtti-Meng model estimations based on stepwise isothermal dilatometry results at high temperature. A maximum in enhanced shrinkage due to oxygen partial pressure cycling occurred at 900oC. Shrinkage was greatest when LSM-10 bars that were first equilibrated in air were exposed to gas flows of lower oxygen fugacity than in the reverse direction. The former creates transient cation and oxygen vacancies well above the equilibrium concentration, resulting in enhanced mobility. These vacancies annihilate as Schottky equilibria is re-established, whereas the latter condition does not lead to excess vacancy concentrations.

  11. Quench behavior of Sr0.6K0.4Fe2As2/Ag tapes with AC and DC transport currents at different temperature

    NASA Astrophysics Data System (ADS)

    Liu, Qi; Zhang, Guomin; Yang, Hua; Li, Zhenming; Liu, Wei; Jing, Liwei; Yu, Hui; Liu, Guole

    2016-09-01

    In applications, superconducting wires may carry AC or DC transport current. Thus, it is important to understand the behavior of normal zone propagation in conductors and magnets under different current conditions in order to develop an effective quench protection system. In this paper, quench behavior of Ag sheathed Sr0.6K0.4Fe2As2 (Sr-122 in the family of iron-based superconductor) tapes with AC and DC transport current is reported. The measurements are performed as a function of different temperature (20 K-30 K), varying transport current and operating frequency (50 Hz-250 Hz). The focus of the research is the minimum quench energy (MQE), the normal zone propagation velocity (NZPV) and the comparison of the related results with AC and DC transport current.

  12. Eu2+ concentration effects in KCa0.8Sr0.2I3:Eu2+: A novel high-performance scintillator

    NASA Astrophysics Data System (ADS)

    Wu, Yuntao; Zhuravleva, Mariya; Lindsey, Adam C.; Koschan, Merry; Melcher, Charles L.

    2016-06-01

    We report here the effect of Eu2+ concentration in KCa0.8Sr0.2I3:Eu2+ single crystal scintillators. KCa0.8Sr0.2I3:Eu2+ single crystals doped with 0.5, 1, 3, 5, and 7 mol% Eu2+ were grown by the Bridgman method. The effects of varying Eu2+concentration and crystal volume on the scintillation properties, including light yield, energy resolution, nonproportionality, scintillation decay time and afterglow level, were systematically investigated. For 5 mm×5 mm×5 mm samples, the best light yield of 86,000±4000 photons/MeV was achieved with a content of 5 mol% Eu2+; its energy resolution of 2.5% at 662 keV was comparable to that of LaBr3:Ce3+ and SrI2:Eu2+. With larger samples of about 2.2 cm3, the best performances achieved were for 3 mol% Eu2+ concentration, i.e. a light yield of 76,000±4000 photons/MeV and an energy resolution of 3% at 662 keV. A direct correlation between nonproportionality and Eu2+ concentration was found. A continuous lengthening of scintillation decay time and x-ray induced afterglow level with increasing Eu2+ concentration was observed. The self-absorption effect was evaluated by using the Stokes shift and the temperature dependence of the photoluminescence decay (PL) of the Eu2+ centers. The sample with the highest dopant concentration had more severe temperature quenching of the Eu2+5d-4f emission than the sample with the lowest dopant concentration, which could be ascribed to the thermally activated concentration quenching.

  13. Suppression of superconductivity in La1.85Sr0.15Cu1-yNiyO4: The relevance of local lattice distortions

    NASA Astrophysics Data System (ADS)

    Haskel, D.; Stern, E. A.; Polinger, V.; Dogan, F.

    2001-02-01

    The effect of Ni substitution upon the local structure of La1.85Sr0.15Cu1-yNiyO4 is commonly neglected when addressing the Ni-induced destruction of the superconducting state at y≈0.03 and a metal-insulator transition at y≈0.05. It is also sometimes assumed that direct substitution of a dopant into the CuO2 planes has a detrimental effect on superconductivity due to in-plane lattice distortions around the dopants. We present here results from angular-dependent x-ray absorption fine structure (XAFS) measurements at the Ni, La and Sr K-edges of oriented powders of La1.85Sr0.15Cu1-yNiyO4 with y=0.01, 0.03, 0.06. A special magnetic alignment geometry allowed us to measure pure ĉ and ab̂ oriented XAFS at the Ni K-edge in identical fluorescence geometries. Both the near-edge absorption spectra (XANES) and the XAFS unequivocally show that the NiO6 octahedra are largely contracted along the c-axis, by ≈ 0.16 Å. Surprisingly, the Ni-O planar bonds and the Ni-O-Cu/Ni planar buckling angle are nearly identical to their Cu counterparts. The NiO6 octahedral contraction drives the macroscopic ĉ-axis contraction observed with Ni-doping. The local ĉ-axis strongly fluctuates, due to the different NiO6 and CuO6 octahedral configurations and the much stronger bonding of a La+3 ion than a Sr+2 ion to the O(2) apical oxygens. We discuss the relevance of these findings to the mechanisms of Tc suppresion and hole-localization by Ni dopants.

  14. Performance assessment of Bi0.3Sr0.7Co0.3Fe0.7O3-δ-LSCF composite as cathode for intermediate-temperature solid oxide fuel cells with La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte

    NASA Astrophysics Data System (ADS)

    Khaerudini, Deni S.; Guan, Guoqing; Zhang, Peng; Hao, Xiaogang; Wang, Zhongde; Xue, Chunfeng; Kasai, Yutaka; Abudula, Abuliti

    2015-12-01

    Perovskite-type Bi0.3Sr0.7Co0.3Fe0.7O3-δ (BiSCF3737) oxide with perfectly cubic structure based on the Pm-3m space group has been developed and investigated as cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). BiSCF3737 is incorporated into (La0.6Sr0.4)0.9Co0.2Fe0.8O3±δ (LSCF) to form a composite cathode called LSCF-BiSCF. X-ray diffraction (XRD) results demonstrate that BiSCF3737 has an extremely desirable chemical compatibility with LSCF as well as with La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. The cells with LSGM electrolyte (0.5 mm thickness) and symmetrical electrodes are fabricated for electrocatalaytic activity test. Compared with the pure constituent (LSCF or BiSCF3737), the composite with optimum composition, i.e., LSCF50-BiSCF50, exhibits better electrochemical activity for oxygen reduction. The LSGM electrolyte-supported (∼300 μm thickness) cell with LSCF50-BiSCF50 composite cathode exhibits higher power densities of 0.617 and 0.802 W cm-2 at 650 and 700 °C, respectively, with humidified H2 (∼3% H2O) as the fuel and ambient air as the oxidant. Over 78 h stability test at 600 °C indicates that a little performance decrease occurs but no interfacial damage happens, suggesting that LSCF50-BiSCF50 is a potential material for IT-SOFCs.

  15. Magnetic anisotropy of epitaxially (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films on SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Ahn, Yoonho; Seo, Jeongdae; Son, Jong Yeog

    2016-06-01

    We investigated magnetic properties of epitaxial Sr0.8Ho0.2CoO3-δ thin films grown on single crystal SrTiO3 substrates deposited by pulsed laser deposition method. On the single crystal (100) and (111) SrTiO3 substrates, the (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films were obtained, respectively. The (100)- and (111)-oriented Sr0.8Ho0.2CoO3-δ thin films exhibited rough surface with grains and smooth surface with a step and terrace structure, respectively. This result suggests they grow in an island and layer-by-layer growth mode, respectively. The (111)-oriented Sr0.8Ho0.2CoO3-δ thin film exhibited ferromagnetic hysteresis with remnant magnetization of 0.15 μB / Co . In contrast, superparamagnetic hysteresis was observed in the (100)-oriented Sr0.8Ho0.2CoO3-δ thin film.

  16. Structure refinement of Ba0.5Sr0.5Co0.8Fe0.2O3-d as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFC)

    NASA Astrophysics Data System (ADS)

    Zakaria, Nurhamidah; Osman, Rozana A. M.; Idris, Mohd Sobri

    2016-07-01

    Ba0.5Sr0.5Co0.8Fe0.2O3-δ was successfully prepared using modified solid-state synthesis routes. The lowest temperature to obtained single phase of Ba0.5Sr0.5Co0.8Fe0.2O3-δ is about 900°C for 15 hours. Longer period of time are required compared to only 5 hours at 950°C as established in literatures. The X-ray Diffraction (XRD) data confirmed that Ba0.5Sr0.5Co0.8Fe0.2O3-δ is formed a cubic perovskite with the space group of Pm-3m. The lattice parameters of Ba0.5Sr0.5Co0.8Fe0.2O3-δ are a = 3.990 (1) Å and unit cell volume is V = 63.5 (1) Å3. The Rietveld refinement of XRD data revealed that the crystal structure of Ba0.5Sr0.5Co0.8Fe0.2O3-δ slightly changes as a function of temperature.

  17. Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

    NASA Astrophysics Data System (ADS)

    Srivastava, Manoj K.; Singh, Sandeep; Siwach, P. K.; Kaur, Amarjeet; Awana, V. P. S.; Maurya, K. K.; Singh, H. K.

    2013-05-01

    Highly oriented polycrystalline Sm0.55Sr0.45MnO3 thin films (thickness ˜100 nm) deposited on LaAlO3 (LAO, (001)), SrTiO3 (STO, (001)) and (La0.18Sr0.82) (Al0.59Ta0.41)O3 (LSAT, (001)) single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The out of plane lattice parameter (OPLP) of the film on LAO is slightly larger than that of the corresponding bulk. In contrast, the OPLP of the films on STO and LSAT are slightly smaller than the corresponding bulk value. This suggests that the film on LAO is under compressive strain while LSAT and STO are under tensile strain. The films on LAO and LSAT show simultaneous paramagnetic-ferromagnetic (PM-FM) and insulator-metal transition (IMT) temperature at TC/TIM ˜ 165 K and 130 K, respectively. The PM-FM and IM transition occur at TC ˜ 120 K and TIM ˜ 105 K, respectively in the film on STO substrate. At T < TC, the zero field cooled-field cooled (ZFC-FC) magnetization of all the films shows strong bifurcation. This suggests the presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic-charge order (AFM-CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. The films on LAO and STO show peak CMR around TC/TIM, while the film on LSAT shows MR > 99 % over a very wide temperature range of ˜40 K centred on TC/TIM. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM-CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.

  18. Electrochemical properties of the Sm 0.5Sr 0.5CoO 3-La 0.8Sr 0.2Ga 0.8Mg 0.15Co 0.05O 3 (LSGMC5)/LSGMC5 interface modified by an LSGMC5 interlayer synthesized using the citrate method

    NASA Astrophysics Data System (ADS)

    Wang, Shizhong; Zhong, Hao; Zou, Yuman

    A La 0.8Sr 0.2Ga 0.8Mg 0.15Co 0.05O 3 (LSGMC5) interlayer synthesized using the citrate method was added between an Sm 0.5Sr 0.5CoO 3 (SSC)-LSGMC5 electrode and an LSGMC5 electrolyte pellet synthesized using a solid-state reaction, and we found that the electrode activity was improved dramatically. The SEM images of the samples demonstrated that the contact between the electrode and the interlayer was much better than the contact between the electrode and electrolyte without the interlayer. The addition of the interlayer resulted in an increased three-phase boundary length and electrode/electrolyte two-phase interfacial area. An SSC-LSGMC5 electrode sintered at 1123 K deposited onto an interlayer sintered at 1673 K exhibited the highest performance among the samples studied. The electrode resistance was about 0.08 Ω cm 2 at near equilibrium conditions, and the cathodic overpotential at a current density of 1 A cm -2 was only about 70 mV at 973 K in oxygen. The introduction of the interlayer did not change the oxygen reaction mechanism, and the significant increase in electrode performance was due to the increase in the number of active sites for oxygen reduction.

  19. A modified liquid-phase-assisted sintering mechanism for La0.8Sr0.2Cr1-xFexO3-δ-A high density, redox-stable perovskite interconnect for solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Wei, Tao; Liu, Xiaojuan; Yuan, Chun; Gao, Qingyu; Xin, Xianshuang; Wang, Shaorong

    2014-03-01

    Fe-doped lanthanum strontium chromites, i.e., La0.8Sr0.2Cr1-xFexO3-δ (x = 0.1, 0.2, 0.3, 0.4, and 0.5), are synthesised and evaluated as potential interconnect materials for SOFCs. A modified liquid-phase-assisted sintering mechanism is employed to improve the sintering abilities of La0.8Sr0.2Cr1-xFexO3-δ powders. A distinct transient liquid phase forms during the sintering process, which spreads into a uniform layer and covers the grain boundaries, thereby enhancing densification. Additionally, it is determined that the amount of liquid phase formed during liquid-phase-assisted sintering significantly affects the densification of doped lanthanum chromites. Relative densities of 94.6% and 96.6% are successfully obtained for La0.8Sr0.2Cr0.6Fe0.4O3-δ and La0.8Sr0.2Cr0.5Fe0.5O3-δ, respectively. Furthermore, these compounds are also redox-stable after being heated to 900 °C in flowing H2 for 6 h. The electrical conductivity increases with Fe-doping levels, and the conductivity of La0.8Sr0.2Cr0.5Fe0.5O3-δ is measured to be 21.88 S cm-1 in air and 6.45 S cm-1 in 5% H2/Ar at 800 °C. Therefore, dense La0.8Sr0.2Cr0.5Fe0.5O3-δ is a promising interconnect alternative for solid oxide fuel cells.

  20. Band gap formation in La0.7Sr0.3MnO3 (LSMO) thin films measured by reflectivity/absorption and ultrafast spectroscopy

    NASA Astrophysics Data System (ADS)

    Cabrera, Guerau; Trappen, Robbyn; Chu, Ying-Hao; Holcomb, Mikel

    Thin film La0.7Sr0.3MnO3 (LSMO) is a prime candidate for highly spin-polarized magnetic-tunnel-junction memories. Due to its magnetic properties, it is also a good candidate for applications utilizing electrical control of magnetism when grown adjacent to a ferroelectric layer such as Pb(Zr/Ti)O3 (PZT). Recently, Wu and others have seen the emergence of a band gap (about 1eV) in LSMO thin films, when grown adjacent to PZT. Currently, it is understood that LSMO is a half-metal, with a pseudo-gap due to a low desity of states (DOS) near the Fermi level. The transition from pseudo-gap to band gap is not yet fully understood. It is therefore our aim to investigate the formation of this band gap through optical reflectivity/absorption and ultrafast carrier dynamics for a variety of thicknesses ranging from a few nanometers to thicker films (about 100 nm).

  1. Microporous La0.8Sr0.2MnO3 perovskite nanorods as efficient electrocatalysts for lithium-air battery

    NASA Astrophysics Data System (ADS)

    Lu, Fanliang; Wang, Yarong; Jin, Chao; Li, Fan; Yang, Ruizhi; Chen, Fanglin

    2015-10-01

    Efficient electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the most critical factor to influence the performance of lithium-air batteries. We present La0.8Sr0.2MnO3 (LSM) perovskite nanorods as high active electrocatalyst fabricated via a soft template method for lithium-air batteries. The as-prepared LSM nanorods are microporous with numerous defects and large surface area (20.6 m2 g-1), beneficial to the ORR and OER in the discharge and charge processes, respectively. Lithium-air batteries based on the microporous LSM nanorods electrocatalysts show enhanced electrochemical performances, including high first discharge specific capacity (6890 mAh g-1(electrode) at 200 mA g-1), low overpotential, good rate capability (up to 400 mA g-1), and cycle stability (only 1.1% voltage loss after 30 circles of specific capacity limit of 1000 mAh g-1 tested at 200 mA g-1). The improved performance might be due to the synergistic effect of the unique microporous and one-dimensional structure and numerous defects of the prepared LSM catalyst.

  2. Thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics in different oxygen-reduction conditions

    NASA Astrophysics Data System (ADS)

    Li, Yi; Liu, Jian; Wang, Chun-Lei; Su, Wen-Bin; Zhu, Yuan-Hu; Li, Ji-Chao; Mei, Liang-Mo

    2015-04-01

    The thermoelectric properties of Sr0.61Ba0.39Nb2O6-δ ceramics, reduced in different conditions, are investigated in the temperature range from 323 K to 1073 K. The electrical transport behaviors of the samples are dominated by the thermal-activated polaron hopping in the low temperature range, the Fermi glass behavior in the middle temperature range, and the Anderson localized behavior in the high temperature range. The thermal conductivity presents a plateau at high-temperatures, indicating a glass-like thermal conduction behavior. Both the thermoelectric power factor and the thermal conductivity increase with the increase of the degree of oxygen-reduction. Taking these two factors into account, the oxygen-reduction can still contribute to promoting the thermoelectric figure of merit. The highest ZT value is obtained to be ˜0.19 at 1073 K in the heaviest oxygen reduced sample. Project supported by the National Basic Research Program of China (Grant No. 2013CB632506) and the National Natural Science Foundation of China (Grant Nos. 51202132 and 51002087).

  3. Effects of oxygen content on the structural and transport properties in epitaxial Nd0.7Sr0.3MnO thin films

    NASA Astrophysics Data System (ADS)

    Meng, Ying; He, Wenlan; Li, Aixia; Li, Guang; Jin, Shaowei

    2012-07-01

    Epitaxial Nd0.7Sr0.3MnO3-x (NSMO) thin films, 120 nm thickness, were grown coherently on the (0 0 1) (LaAlO3)0.3 (Sr2AlTaO6)0.7 (LSAT) substrates by using pulsed-laser deposition (PLD). Effects of oxygen contents controlled by post-annealing in vacuum on the structural and transport properties of the NSMO films were carefully studied by x-ray reciprocal space maps (RSMs) and resistivity measurements. It is clearly shown that both the out-of-plane lattice parameters of the films and the transition temperatures Tp (peak resistance) can simultaneously change as the oxygen contents, the in-plane lattice coherency is maintained consistently with that of the LSAT substrate at the same time. The larger altered transport properties are chiefly ascribed to the increase of Mn3+ ions and the distortion of MnO6 octahedra in films. The oxygen compositions are deduced from the out-of-plane lattice parameters of coherency epitaxy NSMO films. The Kröger-Vink notation was used for explaining the correlation of oxygen vacancy and transport properties.

  4. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures

    PubMed Central

    Renshaw Wang, X.; Sun, L.; Huang, Z.; Lü, W. M.; Motapothula, M.; Annadi, A.; Liu, Z. Q.; Zeng, S. W.; Venkatesan, T.; Ariando

    2015-01-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

  5. Influence of epitaxial growth on phase competition in Pr 0.5Sr 0.5MnO 3 films

    NASA Astrophysics Data System (ADS)

    Chen, Liping; Chen, Yuansha; Ma, Yubin; Lian, Guijun; Zhang, Yan; Xiong, Guangcheng

    2012-03-01

    A series of Pr0.5Sr0.5MnO3 (PSMO) films with various thickness were epitaxially grown on substrates of (0 0 1)-oriented (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT), LaAlO3 (LAO) and SrTiO3 (STO), and (0 1 1)-oriented STO using pulse laser deposition. Influence of epitaxial growth on phase competition was investigated. A ferromagnetic metal to antiferromagnetic insulator (FMM-AFI) transition upon cooling is present in both largely compressed situations deposited on LAO (0 0 1) and tensile cases deposited on STO (0 0 1) but absent in little strained films grown on LSAT (0 0 1), indicating that the antiferromagnetic insulating state is favored by strains. On the other hand, the 400 nm films deposited on (0 1 1)-oriented STO as well as LAO substrates show FMM-AFI transition. These results reveal that both the orientation of epitaxial growth and substrate-induced strain affect the FMM-AFI transition.

  6. Al3+ doping effects and high-field phase diagram of La0.5Sr0.5Mn1-x Al x O3

    NASA Astrophysics Data System (ADS)

    Shang, C.; Xia, Z. C.; Wei, M.; Jin, Z.; Chen, B. R.; Shi, L. R.; Ouyang, Z. W.; Huang, S.; Xiao, G. L.

    2016-01-01

    Magnetization measurements of La0.5Sr0.5Mn1-x Al x O3 (0  ⩽  x  ⩽  0.25) under pulsed high magnetic fields up to 50 T have been carried out, in which the Al3+ ions doping and magnetic field effects on the charge-ordering/antiferromagnetic to ferromagnetic phase transitions have been discussed. A triple-phase diagram with the critical field, doping level and temperature has been determined, in which the antiferromagntic and ferromagnetic phase boundaries were clearly defined. The change from long-range charge-ordered/antiferromagnetic phases to the robust short-range ones upon the Al3+-doping was observed. According to the experimental results, we assume that Al3+ ion doping at the Mn sites dilutes the Mn3+-O-Mn4+ network, weakens the double-exchange interaction and further suppresses the FM phase (metallic conduction), which leads to the critical magnetic fields destroying the antiferromagnetic order increase with the increase of the doping level.

  7. Enhanced colloidal stability of polymer coated La0.7Sr0.3MnO3 nanoparticles in physiological media for hyperthermia application.

    PubMed

    Thorat, N D; Otari, S V; Patil, R M; Khot, V M; Prasad, A I; Ningthoujam, R S; Pawar, S H

    2013-11-01

    Surface of La(0.7)Sr(0.3)MnO3 (LSMO) magnetic nanoparticles (MNPs) is functionalized with polymer (dextran) and their colloidal stability in various mediums is carried out. The influence of the surface functionalization of LSMO MNPs on their colloidal stability in physiological media is studied and correlated with their hyperthermia properties. Many studies have concerned the colloidal stability of MNPs coated with polymer, but their long-term stability when such complexes are exposed to physiological media is still not well understood. After zeta potential study, it is found that the dextran coating on MNPs improves the colloidal stability in water as well as in physiological media like PBS. The specific absorption rates (SAR) of these MNPs are found to be in 50-85 W/g in different concentrations of glucose and NaCl; and there values are suitable for hyperthermia treatment of cancer cells under AC magnetic field. After incorporation of MNPs up to 0.2-1mg/mL in 2 × 10(5)cells/mL (L929), the apoptosis and necrosis studies are carried out by acridine orange and ethidium bromide (AO and EB) staining and followed by visualization of microstructures under a fluorescence microscope. It is found that there are no morphological changes (i.e. no signs of cell rounding, bubble formation on the membrane and nuclear fragmentation) suggesting biocompatibility of dextran coated LSMO nanoparticles up to these concentrations. PMID:23838191

  8. Broad-band dielectric spectroscopy and ferroelectric soft-mode response in the Ba(0.6)Sr(0.4)TiO(3) solid solution.

    PubMed

    Ostapchuk, T; Petzelt, J; Hlinka, J; Bovtun, V; Kužel, P; Ponomareva, I; Lisenkov, S; Bellaiche, L; Tkach, A; Vilarinho, P

    2009-11-25

    Ceramic Ba(0.6)Sr(0.4)TiO(3) (BST-0.6) samples were studied in the broad spectral range of 10(6)-10(14) Hz by using several dielectric techniques in between 20 and 800 K. The dominant dielectric dispersion mechanism in the paraelectric phase was shown to be of strongly anharmonic soft-phonon origin. The whole soft-mode response in the vicinity of the ferroelectric transition was shown to consist of two coupled overdamped THz excitations, which show classical features of a coupled soft and central mode, known from many ferroelectric crystals with a dynamics near the displacive and order-disorder crossover. Similar behaviour has been recently revealed and theoretically simulated in pure BaTiO(3) (see Ponomareva et al 2008 Phys. Rev. B 77 012102 and Hlinka et al 2008 Phys. Rev. Lett. 101 167402). Also for the BST system, this feature was confirmed by the theory based on molecular dynamics simulations with an effective first-principles Hamiltonian. In all the ferroelectric phases, additional relaxation dispersion appeared in the GHz range, assigned to ferroelectric domain-wall dynamics. The microwave losses were analysed from the point of view of applications. The paraelectric losses above 1 GHz are comparable with those in single crystals and appear to be of intrinsic multi-phonon origin. The ceramic BST system is therefore well suited for applications in the whole microwave range. PMID:21832494

  9. Influence of Ga doping on rare earth moment ordering and ferromagnetic transition in Nd0.7Sr0.3Co1-xGaxO3

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Maheswar Repaka, D. V.; Aparnadevi, M.; Tripathi, T. S.; Mahendiran, R.

    2013-05-01

    We report the impact of dilution of Co sublattice by non-magnetic Ga3+ ion on the magnetic, electrical, and magnetoresistive properties in Nd0.7Sr0.3Co1-xGaxO3 for x = 0-0.12. Field-cooled magnetization of the parent compound (x = 0) shows an anomalous maximum at T* = 54.6 K much below the onset of ferromagnetic transition (TC = 160 K) of the Co sublattice, which is attributed to the polarization of Nd-4f moments antiparallel to the Co-3d sublattice. Both TC and T* shift to low temperature with increasing x and the Nd-4f spin reverses from antiparallel to parallel with increasing strength of the magnetic field. While the value of high field magnetization is not seriously affected by Ga doping, coercive field at 10 K increases dramatically with increasing x. Ga substitution transforms ferromagnetic metallic state into ferromagnetic insulating state for x ≥ 0.03 and decreases the magnitude of magnetoresistance from 6% for x = 0% to 0.5% for x = 0.12.

  10. Investigations of atomic structure and bonding at domain boundaries in bulk La0.5Eu0.2Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Sun, B. Z.; He, L. L.; Luo, F.; Yan, C. H.

    2005-08-01

    The article [1] featured on the cover of this issue investigates the formation of the orthorhombic phase and 120° large-angle orientation domains in bulk La0.7Sr0.3MnO3 compound doped with Eu. The cover picture is a transmission electron microscopy image of the domain boundaries of this phase. Insets show the composite [012] zone electron diffraction pattern (bottom right) and diffraction patterns from the single domains. The 120° rotational symmetry originates from the three-fold axis of the high-temperature pseudo-cubic phase.The first author is a Ph. D. candidate in the Institute of Metal Research of the Chinese Academy of Sciences, working on microstructural characterization on the atomic scale for colossal magnetoresistance materials.This issue does also contain an important Rapid Research Letter contribution by Cai and Sandhage [2] on the shape-preserving reactive conversion of biosilica shell surfaces of diatoms, a topic at the interface of materials and biological sciences.

  11. Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals

    NASA Astrophysics Data System (ADS)

    Felner, I.; Tsindlekht, M. I.; Drachuck, G.; Keren, A.

    2013-02-01

    Optimally doped La1.85Sr0.15CuO4 single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (HC2) and the surface critical field (HC3) were measured. The H-T phase diagram is presented. Close to TC = 35 K, for the c-crystal, {\\boldsymbol{\\gamma}}^{c}={H}_{{C3}}^{c}/{H}_{{C2}}^{c}=1.8 0(2), whereas for the a-crystal the {\\boldsymbol{\\gamma}}^{a}={H}_{{C3}}^{a}/{H}_{{C2}}^{a}=4.0(2) obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the ‘paramagnetic Meissner effect’ (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γa and the PME are connected to each other.

  12. Anisotropy of the upper critical fields and the paramagnetic Meissner effect in La1.85Sr0.15CuO4 single crystals.

    PubMed

    Felner, I; Tsindlekht, M I; Drachuck, G; Keren, A

    2013-02-13

    Optimally doped La(1.85)Sr(0.15)CuO(4) single crystals have been investigated by dc and ac magnetic measurements. These crystals have rectangular needle-like shapes with the long needle axis parallel to the crystallographic c axis (c-crystal) or parallel to the basal planes (a-crystal). In both crystals, the temperature dependence of the upper critical fields (H(C2)) and the surface critical field (H(C3)) were measured. The H-T phase diagram is presented. Close to T(C) = 35 K, for the c-crystal, γ(C) = H(C3)(c)/H(C2)(c) = 1.80(2), whereas for the a-crystal the γ(a) = H(C3)(a)/H(C2)(a) = 4.0(2) obtained is much higher than 1.69, predicted by the ideal mathematical model. At low applied dc fields, positive field-cooled branches known as the 'paramagnetic Meissner effect' (PME) are observed; their magnitude is inversely proportional to H. The anisotropic PME is observed in both a- and c-crystals, only when the applied field is along the basal planes. It is speculated that the high γ(a) and the PME are connected to each other. PMID:23315336

  13. Surface stoichiometry of La0.7Sr0.3MnO3 during in vacuo preparation; A synchrotron photoemission study

    NASA Astrophysics Data System (ADS)

    Monsen, Å. F.; Song, F.; Li, Z. S.; Boschker, J. E.; Tybell, T.; Wahlström, E.; Wells, J. W.

    2012-09-01

    We present a study of the surface stoichiometry and contamination of La0.7Sr0.3MnO3 thin films following exposure to air and subsequent in vacuo preparation. Samples were studied using both soft X-ray synchrotron photoemission (hν = 150 to 350 eV) and traditional Mg-Kα XPS (hν = 1253.6 eV) whilst annealing incrementally to ≈ 510°C in low pressures of O2. In all cases, a Mn depleted and Sr rich surface oxide layer is observed, it is of reduced crystalline quality and is charge depleted. This surface layer is weakly affected by subsequent annealing, and is partially reversed by annealing in higher O2 pressure. Surface carbon contamination is incrementally removed by annealing at increased temperatures, and at 270 °C, it is reduced to ≈ 0.4% of the topmost unit cell. The modification of the surface stoichiometry and electronic properties is consistent with the reported loss of magnetic properties in thin LSMO films.

  14. Magnetic and Mössbauer studies on oxygen deficient perovskite, La0.6Sr0.4FeO3-δ

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Yelon, W. B.; James, W. J.; Zhou, X. D.; Xie, Y. X.; Anderson, H. U.; Chu, Z.

    2002-05-01

    Samples of La0.6Sr0.4Fe3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N2, O2, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO2 reduced samples. The heat treatment in the reducing atmosphere creates oxygen vacancies and increases unit cell volume. However, the Fe-O bond length remains nearly constant, resulting in distortion/rotation of the oxygen octahedra which increases the Fe-O-Fe bond angle as much as 12 degrees. This dramatically affects the Fe-O-Fe superexchange coupling and plays a key role in the increase of the Nèel temperatures.

  15. Magnetocaloric effect of monovalent K doped manganites Pr0.6Sr0.4-xKxMnO3 (x=0 to 0.2)

    NASA Astrophysics Data System (ADS)

    Thaljaoui, R.; Boujelben, W.; Pękała, M.; Pękała, K.; Fagnard, J.-F.; Vanderbemden, P.; Donten, M.; Cheikhrouhou, A.

    2014-02-01

    Magnetic and magnetocaloric properties are reported for polycrystalline monovalent potassium doped manganites Pr0.6Sr0.4-xKxMnO3 (x=0, 0.05, 0.1, 0.15 and 0.2) crystallized in orthorhombic structure with Pnma space group. The increasing K content shifts the paramagnetic to ferromagnetic transition temperature from 310 K for x=0 to 269 K for x=0.2. The magnetic entropy change under magnetic field variation of 2 T is found to be 1.95, 3.09, 2.89, 3.05 and 3.2 J/kgK for x varying from 0 to 0.2, respectively. The highest relative cooling power of 102 J/kg is observed for the undoped sample. The sensitivity of magnetic entropy change to magnetic field is estimated by a local N(T) exponent exhibiting the characteristic temperature variation. Phenomenological universal curves of entropy change and Arrott plots confirm the second order phase transition.

  16. Influences of spark plasma sintering temperature on the microstructures and thermoelectric properties of (Sr0.95Gd0.05)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Liang-Liang; Qin, Xiao-Ying; Liu, Yong-Fei; Liu, Quan-Zhen

    2015-06-01

    (Sr0.95Gd0.05)TiO3 (SGTO) ceramics are successfully prepared via spark plasma sintering (SPS) respectively at 1548, 1648, and 1748 K by using submicron-sized SGTO powders synthesized from a sol-gel method. The densities, microstructures, and thermoelectric properties of the SGTO ceramics are studied. Though the Seebeck coefficient shows no obvious difference in the case that SPS temperatures range from 1548 K to 1648 K, the electrical conductivity and the thermal conductivity increase remarkably due to the increase in grain size and density. The sample has a density higher than 98% theoretical density as the sintering temperature increases up to 1648 K and shows average grain sizes increasing from ˜ 0.7 μm to 7 μm until 1748 K. As a result, the maximum of the dimensionless figure of merit of ˜ 0.24 is achieved at ˜ 1000 K for the samples sintered at 1648 K and 1748 K, which was ˜ 71% larger than that (0.14 at ˜ 1000 K) for the sample sintered at 1548 K due to the enhancement of the power factor. Project supported by the National Natural Science Foundation of China (Grant Nos. 11174292, 51101150, and 11374306).

  17. Thermodynamic conditions during growth determine the magnetic anisotropy in epitaxial thin-films of La0.7Sr0.3MnO3

    NASA Astrophysics Data System (ADS)

    Vila-Fungueiriño, J. M.; Tinh Bui, Cong; Rivas-Murias, B.; Winkler, E.; Milano, J.; Santiso, J.; Rivadulla, F.

    2016-08-01

    The suitability of a particular material for use in magnetic devices is determined by the process of magnetization reversal/relaxation, which in turn depends on the magnetic anisotropy. Therefore, designing new ways to control magnetic anisotropy in technologically important materials is highly desirable. Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic ferromagnet La0.7Sr0.3MnO3 (LSMO) is determined by the proximity to thermodynamic equilibrium conditions during growth. We performed a series of x-ray diffraction and ferromagnetic resonance (FMR) experiments in two different sets of samples: the first corresponds to LSMO thin-films deposited under tensile strain on (0 0 1) SrTiO3 by pulsed laser deposition (PLD; far from thermodynamic equilibrium); the second were deposited by a slow chemical solution deposition (CSD) method, under quasi-equilibrium conditions. Thin films prepared by PLD show fourfold in-plane magnetic anisotropy, with an overimposed uniaxial term. However, the uniaxial anisotropy is completely suppressed in the CSD films. This change is due to a different rotation pattern of MnO6 octahedra to accommodate epitaxial strain, which depends not only on the amplitude of tensile stress imposed by the STO substrate, but also on the growth conditions. Our results demonstrate that the nature and magnitude of the magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during thin-film deposition.

  18. Alignment of energy levels at the Alq3/La0.7Sr0.3MnO3 interface for organic spintronic devices

    NASA Astrophysics Data System (ADS)

    Zhan, Y. Q.; Bergenti, I.; Hueso, L. E.; Dediu, V.; de Jong, M. P.; Li, Z. S.

    2007-07-01

    The electronic structure of the interface between tris(8-hydroxyquinolino)-aluminum (Alq3) and La0.7Sr0.3MnO3 (LSMO) manganite was investigated by means of photoelectron spectroscopy. As demonstrated recently, this interface is characterized by efficient spin injection in organic spintronic devices. We detected a strong interface dipole of about 0.9eV that shifts down the whole energy diagram of the Alq3 with respect to the vacuum level. This modifies the height of the barrier for the injection into highest occupied molecular orbital level to 1.7eV , indicating more difficult hole injection at this interface than expected for the undistorted energy level diagram. We believe that the interface dipole is due to the intrinsic dipole moment of the Alq3 layer. The presented data lead to significant progress in understanding the electronic structure of LSMO/Alq3 interface and represent a step toward the description of spin transport in organic spin valves.

  19. Twinned domain induced magnonic modes in La0.7Sr0.3MnO3/SrTiO3(001) thin films

    NASA Astrophysics Data System (ADS)

    Wahlström, Erik; Macia, Ferran; Boschker, Jos E.; Monsen, Åsmund; Norblad, Per; Mathieu, Roland; Kent, Andrew D.; Tybell, Thomas

    2015-03-01

    By defining a periodic magnetic structure it iss possible to excite magnonic modes other than standard uniform magnetodynamic modes. However, a traditional top-down approach to define structures at length scales <100 nm is often challenging. Here we present a bottom up approach to such magnonic lattices. In order to achieve this we rely on epitaxial thin films of a prototypical perovskite, La0.7Sr0.3MnO3, on top of SrTiO3(001), with an intended structural twinned domain geometry, acting as a periodic perturbation for the magnonic lattice. Variable temperature ferromagnetic resonance spectroscopy (FMR) gives evidence for additional magnonic modes. We will show that the origin of these modes can be related to a spatial modulation of the Curie temperature induced by the twin domain formation. This yields a temperature dependent magnetic variation in the saturation magnetization that forms the magnonic structure. We will discuss how film thickness and structural domain periodicity affects the excited modes. In particular the temperature dependence of the magnetic structure will be discussed and used in a model description of the system that accounts for the major features of FMR spectra.

  20. Selective electrochemical decomposition of outgrowths and nanopatterning in La0.7Sr0.3MnO3 perovskite thin films

    PubMed Central

    Cavallini, Massimiliano; Graziosi, Patrizio; Calbucci, Marco; Gentili, Denis; Cecchini, Raimondo; Barbalinardo, Marianna; Bergenti, Ilaria; Riminucci, Alberto; Dediu, Valentin

    2014-01-01

    The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La0.7Sr0.3MnO3 perovskite as a representative material but in principle it can be extended to many other conductive systems. PMID:25491921

  1. Hot pressing to enhance the transport Jc of Sr0.6K0.4Fe2As2 superconducting tapes

    PubMed Central

    Lin, He; Yao, Chao; Zhang, Xianping; Dong, Chiheng; Zhang, Haitao; Wang, Dongliang; Zhang, Qianjun; Ma, Yanwei; Awaji, Satoshi; Watanabe, Kazuo; Tian, Huanfang; Li, Jianqi

    2014-01-01

    High-performance Sr0.6K0.4Fe2As2 (Sr-122) tapes have been successfully fabricated using hot pressing (HP) process. The effect of HP temperatures (850–925°C) on the c-axis texture, resistivity, Vickers micro-hardness, microstructure and critical current properties has been systematically studied. Taking advantage of high degree of c-axis texture, well grain connectivity and large concentration of strong-pinning defects, we are able to obtain an excellent Jc of 1.2 × 105 A/cm2 at 4.2 K and 10 T for Sr-122 tapes. More importantly, the field dependence of Jc turns out to be very weak, such that in 14 T the Jc still remains ~ 1.0 × 105 A/cm2. These Jc values are the highest ever reported so far for iron-pnictide wires and tapes, achieving the level desired for practical applications. Our results clearly strengthen the position of iron-pnictide conductors as a competitor to the conventional and MgB2 superconductors for high field applications. PMID:25374068

  2. Protein and polymer immobilized La0.7Sr0.3MnO3 nanoparticles for possible biomedical applications

    NASA Astrophysics Data System (ADS)

    Bhayani, K. R.; Kale, S. N.; Arora, Sumit; Rajagopal, Rajashree; Mamgain, H.; Kaul-Ghanekar, R.; Kundaliya, Darshan C.; Kulkarni, S. D.; Pasricha, Renu; Dhole, S. D.; Ogale, S. B.; Paknikar, K. M.

    2007-08-01

    La0.7Sr0.3MnO3 (LSMO) is a mixed-valent room temperature ferromagnet with properties that are attractive for their applicability in biomedicine. We report, for the first time, immobilization of commonly used biocompatible molecules on LSMO nanoparticles, namely bovine serum albumin and dextran. The former was conjugated to LSMO using 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (CDI) as a coupling agent while the latter was used without any coupler. These bioconjugated nanoparticles exhibit several properties that suggest their applicability in the field of biomedicine, namely (a) no changes in the Curie temperature at ~360 K after conjugation with biomolecules, (b) rapid attainment of the desired temperature (48 °C) at low concentration (e.g. fluidized dextran-coated system at 80 µg ml-1) upon exposure to 20 MHz radio-frequency, (c) extremely low cytotoxicity in skin carcinoma, human fibrosarcoma and neuroblastoma cell lines and (d) high stability of the LSMO system with negligible leaching of ionic manganese into the delivery medium, indicating their safety in possible human applications.

  3. Potentiometric NO2 Sensors Based on Thin Stabilized Zirconia Electrolytes and Asymmetric (La0.8Sr0.2)0.95MnO3 Electrodes

    PubMed Central

    Zou, Jie; Zheng, Yangong; Li, Junliang; Zhan, Zhongliang; Jian, Jiawen

    2015-01-01

    Here we report on a new architecture for potentiometric NO2 sensors that features thin 8YSZ electrolytes sandwiched between two porous (La0.8Sr0.2)0.95MnO3 (LSM95) layers—one thick and the other thin—fabricated by the tape casting and co-firing techniques. Measurements of their sensing characteristics show that reducing the porosity of the supporting LSM95 reference electrodes can increase the response voltages. In the meanwhile, thin LSM95 layers perform better than Pt as the sensing electrode since the former can provide higher response voltages and better linear relationship between the sensitivities and the NO2 concentrations over 40–1000 ppm. The best linear coefficient can be as high as 0.99 with a sensitivity value of 52 mV/decade as obtained at 500 °C. Analysis of the sensing mechanism suggests that the gas phase reactions within the porous LSM95 layers are critically important in determining the response voltages. PMID:26205270

  4. Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films.

    PubMed

    Niu, Wei; Gao, Ming; Wang, Xuefeng; Song, Fengqi; Du, Jun; Wang, Xinran; Xu, Yongbing; Zhang, Rong

    2016-01-01

    Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T(1/2) dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory. PMID:27181882

  5. Downscaling at submicrometer scale of the gap width of interdigitated Ba0.5Sr0.5TiO3 capacitors.

    PubMed

    Khalfallaoui, Abderrazek; Burgnies, Ludovic; Blary, Karine; Velu, Gabriel; Lippens, Didier; Carru, Jean-Claude

    2015-02-01

    The goal of this work was to study the influence of shrinking the gap width between the fingers of interdigitated tunable capacitors (IDCs). Voltage control of the capacitance was achieved with a 500-nm-thick Ba0.5Sr0.5TiO3 film which is in paraelectric state at room temperature. Eight devices with finger spacing ranging from 3 μm down to 0.25 μm were fabricated by the sol-gel deposition technique, electron beam patterning, and gold evaporation. The equivalent capacitance, quality factor, and tunability of the devices were measured subsequently by vector network analysis from 40 MHz to 40 GHz and for a dc bias voltage varying from -30 V to +30 V. This experimental study mainly shows that a decrease of the gap below 1 μm 1) introduces a frequency dependence of the capacitance caused by resonance effects with the finger inductance; 2) degrades the quality factor above 20 GHz, and 3) optimizes the tunability of the devices by enhancing the local electric field values. As a consequence, some trade-offs are pointed out related to the goal of ultra-thin ferroelectric film which can be voltage controlled by means of finger-shaped electrodes with deep submicrometer spacing. PMID:25643075

  6. Avalanches and hysteresis at the structural transition in stripe-ordered La1.48Nd0.4Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Baity, P. G.; Saraswat, Garima; Popović, Dragana; Sasagawa, T.

    The coupling or intertwining of lattice, spin and charge orders and their effects on superconductivity are of great current interest in the physics of cuprates. The rare-earth-doped cuprate La1.48Nd0.4Sr0.12CuO4 (LNSCO), for example, exhibits a first-order structural phase transition (SPT) from the low-temperature orthorhombic (LTO) to the low-temperature tetragonal (LTT) phase, with the onset of the static charge stripe order roughly coinciding with the SPT. We present out-of-plane magnetoresistance measurements around the LTO-LTT transition in LNSCO single crystals with H ∥ c up to 12 T and H ∥ ab up to 9 T. Hysteresis is observed for both field orientations, but for H ∥ c we also find evidence for the existence of metastable states and collective dynamics in the form of avalanches and return point memory. Such behavior indicates that, in LNSCO, the LTO-LTT structural transition can be driven with H. A detailed analysis of the avalanche statistics is used to determine their size and field dependence, and to extract information about the domain structure and dynamics of domain walls. Our results shed light on the interplay of lattice, spin and charge degrees of freedom in stripe-ordered La-based cuprates. Supported by NSF DMR-1307075 and NHMFL via NSF DMR-1157490 and the State of Florida.

  7. Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4

    DOE PAGESBeta

    Jacobsen, H.; Zaliznyak, I. A.; Savici, A. T.; Winn, B. L.; Chang, S.; Hücker, M.; Gu, G. D.; Tranquada, J. M.

    2015-11-20

    Tmore » he relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4 a superconductor with a transition temperature of c = 20 K. At << c, we find incommensurate spin fluctuations with a quasielastic energy spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below ~ 10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Moreover, we observed a weak elastic (3 ⁻30) superlattice peak that implies a reduced lattice symmetry. he presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2-xSrxCuO4. he coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.« less

  8. Magnetic properties of BaTiO3/La0.7Sr0.3MnO3 thin films integrated on Si(100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Fan, Wu; Prater, J. T.; Narayan, J.

    2014-12-01

    Two-phase multiferroic heterostructures composed of room-temperature ferroelectric BaTiO3 (BTO) and ferromagnetic La0.7Sr0.3MnO3 (LSMO) epitaxial thin films were grown on technologically important substrate Si (100). Bilayers of BTO/LSMO thin films display ferromagnetic Curie transition temperatures of ˜350 K, close to the bulk value, which are independent of BTO films thickness in the range of 25-100 nm. Discontinuous magnetization jumps associated with BTO structural transitions were suppressed in M(T) curves, probably due to substrate clamping effect. Interestingly, at cryogenic temperatures, the BTO/LSMO structure with BTO layer thickness of 100 nm shows almost 2-fold higher magnetic coercive field, 3-fold reduction in saturation magnetization, and improved squareness compared to the sample without BTO. We believe that the strong in-plane spin pinning of the ferromagnetic layer induced by BTO layer at BTO/LSMO interface could cause such changes in magnetic properties. This work forms a significant step forward in the integration of two-phase multiferroic heterostructures for CMOS applications.

  9. Microstructures of La 1.85Sr 0.15CuO 4 doped with Ni at high doping level

    NASA Astrophysics Data System (ADS)

    Wu, X. S.; Jiang, S. S.; Pan, F. M.; Lin, J.; Xu, N.; Mao Zhiqiang; Xu Gaoji; Zhang Yuheng

    1996-02-01

    Ceramic superconductors of La 1.85Sr 0.15Cu 1- yNi yO 4 with 0.00 ≤ y ≤ 0.50 were synthesized. There is no impurity phase detected in the entire Ni doped region. The structure of these Ni-doped samples was characterized by X-ray diffraction studies. The atomic structural parameters were obtained by Rietveld refinements for the Ni-doped samples with y ≤ 0.50. Some meaningful bond distances were determined according to the refined results. According to the variations of some bond distances with y, the whole doping range could be divided into two regions: low doping level (LDL) and high doping level (HDL). The bond length between the two apical oxygen atoms in the CuO 6 octahedra for the Ni-doped samples increased with increasing content of Ni in the LDL, and decreased in the HDL. The average bond distance of LaO was not changed in the whole doping region. The metal-insulator transition was also observed in this Ni-doped system.

  10. Evidence of weak localization in quantum interference effects observed in epitaxial La0.7Sr0.3MnO3 ultrathin films

    PubMed Central

    Niu, Wei; Gao, Ming; Wang, Xuefeng; Song, Fengqi; Du, Jun; Wang, Xinran; Xu, Yongbing; Zhang, Rong

    2016-01-01

    Quantum interference effects (QIEs) dominate the appearance of low-temperature resistivity minimum in colossal magnetoresistance manganites. The T1/2 dependent resistivity under high magnetic field has been evidenced as electron-electron (e-e) interaction. However, the evidence of the other source of QIEs, weak localization (WL), still remains insufficient in manganites. Here we report on the direct experimental evidence of WL in QIEs observed in the single-crystal La0.7Sr0.3MnO3 (LSMO) ultrathin films deposited by laser molecular beam epitaxy. The sharp cusps around zero magnetic field in magnetoresistance measurements is unambiguously observed, which corresponds to the WL effect. This convincingly leads to the solid conclusion that the resistivity minima at low temperatures in single-crystal manganites are attributed to both the e-e interaction and the WL effect. Moreover, the temperature-dependent phase-coherence length corroborates the WL effect of LSMO ultrathin films is within a two-dimensional localization theory. PMID:27181882

  11. Microstructures and electrical properties of La 0.8Sr 0.2MnO 3 films synthesized by sol-gel method

    NASA Astrophysics Data System (ADS)

    Zhu, Xinde; Li, Shengli; Yang, Xiaojie; Qiu, Jie

    2007-11-01

    La 0.8Sr 0.2MnO 3 (LSMO) thin films were fabricated on alumina substrates by an improved sol-gel dip-coating process. It was found that multiple dip-coating process could not be performed until the pre-firing temperature reached 600 °C. Different amounts of LSMO powders were added to precursor solution with an aim to avoid cracks in LSMO thin films during calcining caused by the shrinkage mismatch between the film and the substrate. The structure and surface morphology of the films prepared from precursors with and without LSMO powders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the addition of 56.4 wt.% LSMO powders into the sol-gel precursor solution significantly modified the microstructure of films. A single LSMO perovskite phase was obtained on alumina substrate after calcining at 800 °C for 4 h by the improved sol-gel method. The sheet resistance of the films prepared with different processing parameters was measured by four-point dc method. Results indicated that the sheet resistance of films decreased with increasing the number of coating applications and the amount of LSMO powders.

  12. Ultrafast Dynamics of the Symmetry Breaking in Charge-ordered La1.75Sr0.25NiO4 Single Crystals

    NASA Astrophysics Data System (ADS)

    Coslovich, Giacomo; Kemper, Alexander F.; Behl, Sascha; Huber, Bernhard; Bechtel, Hans A.; Sasagawa, Takao; Martin, Michael C.; Kaindl, Robert A.

    We report equilibrium and ultrafast optical pump-THz probe spectroscopy of the stripe-phase rare-earth nickelate compound La1.75Sr0.25NiO4, unveiling the ultrafast dynamics of the crystal symmetry breaking and of local electronic arrangements. At low temperatures the folding of finite momenta vibrations due to symmetry breaking lead to the appearance of new IR-active resonances, particularly around the phonon bending mode frequency (~11 THz). Ultrafast experiments in the multi-THz spectral range show sharp THz reflectivity modulations associated with the phonon zone-folding dynamics, while the background conductivity is reminiscent of the opening of the mid-IR pseudogap. We combine experimental data with DFT calculations of the phonon dispersion to reveal the distinct dynamics of the LO and TO phonon modes at finite momenta. This work provides new insight in the role of polar electron-phonon coupling and symmetry breaking in charge-ordered systems. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

  13. Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays

    NASA Astrophysics Data System (ADS)

    Kumaresavanji, M.; Sousa, C. T.; Pires, A.; Pereira, A. M.; Lopes, A. M. L.; Araujo, J. P.

    2014-08-01

    High aspect ratio La0.7Sr0.3MnO3 nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, -△SM = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of -△SM = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △SM value, the NTs present an expanded temperature dependence of -△SM curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

  14. Electric-field-induced strain effects on the magnetization of a Pr0.67Sr0.33MnO3 film

    DOE PAGESBeta

    Zhang, B.; Sun, C. -J.; Lu, W.; Venkatesan, T.; Han, M. -G.; Zhu, Y.; Chen, J.; Chow, G. M.

    2015-05-26

    The electric-field control of magnetic properties of Pr0.67Sr0.33MnO3 (PSMO) film on piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) substrate was investigated. The piezoelectric response of the PMNT substrate to the electric field produced strain that was coupled to the PSMO film. The in-plane compressive (tensile) strain increased (decreased) the magnetization. The change of magnetic moment was associated with the Mn ions. First principle simulations showed that the strain-induced electronic redistribution of the two eg orbitals (3dz2 and 3dx2-y2) of Mn ions was responsible for the change of magnetic moment. This work demonstrates that the magnetoelectric effect in manganite/piezoelectric hetero-structures originates from the change inmore » eg orbital occupancy of Mn ions induced by strain rather than the interfacial effect.« less

  15. Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4

    SciTech Connect

    Jacobsen, H; Zaliznyak, Igor; Savici, Andrei T; Winn, Barry L; Chang, S; Hucker, M.; Gu, Genda; Tranquada, John M.

    2015-01-01

    The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4, a superconductor with a transition temperature of Tc=20 K. At T Tc, we find incommensurate spin fluctuations with a nearly energy-independent spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below 10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent O sites within the CuO2 planes. Furthermore, we observed a weak elastic (33 0) superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2 xSrxCuO4. The coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.

  16. Neutron scattering study of spin ordering and stripe pinning in superconducting La1.93Sr0.07CuO4

    DOE PAGESBeta

    Jacobsen, H; Zaliznyak, Igor; Savici, Andrei T; Winn, Barry L; Chang, S; Hucker, M.; Gu, Genda; Tranquada, John M.

    2015-01-01

    The relationships among charge order, spin fluctuations, and superconductivity in underdoped cuprates remain controversial. We use neutron scattering techniques to study these phenomena in La1.93Sr0.07CuO4, a superconductor with a transition temperature of Tc=20 K. At T Tc, we find incommensurate spin fluctuations with a nearly energy-independent spectrum and no sign of a gap within the energy range from 0.2 to 15 meV. A weak elastic magnetic component grows below 10 K, consistent with results from local probes. Regarding the atomic lattice, we have discovered unexpectedly strong fluctuations of the CuO6 octahedra about Cu-O bonds, which are associated with inequivalent Omore » sites within the CuO2 planes. Furthermore, we observed a weak elastic (33 0) superlattice peak that implies a reduced lattice symmetry. The presence of inequivalent O sites rationalizes various pieces of evidence for charge stripe order in underdoped La2 xSrxCuO4. The coexistence of superconductivity with quasi-static spin-stripe order suggests the presence of intertwined orders; however, the rotation of the stripe orientation away from the Cu-O bonds might be connected with evidence for a finite gap at the nodal points of the superconducting gap function.« less

  17. Combinatorial studies in Ba0.45Sr0.55TiO3 thin films for microwave components by radio frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Reinholz, Aaron; Pokhodnya, Konstantin

    2014-03-01

    The optimization of dielectric properties of ferroelectric thin films for microwave applications can be limited due to the time and resources consumption of the corresponding device fabrication and testing for each doping level. We report the use of a combinatorial technique to achieve the optimal doping level of Ba0.45Sr0.55TiO3 (BST) thin film with three dopants, Mg, Nb and lanthanide (Ln) metal. The process uses two R.F. magnetron sputtering BST sources doped with few at. % of MgII/NbV in charge compensating concentration and LnIV, respectively. The guns were shifted and tilted each by 30° in opposite directions to realize the dopants gradient across a static wafer. The film is reactively co-sputtered on the static 4'' platinized Al2O3 wafer. The film crystallinity and phase purity were analyzed and correlated to its dielectric properties measured on 2432 MIM capacitors that are of lithographically fabricated using Pt top electrode. After electrical testing, the wafer was diced into 22 16x16 mm2 samples, and the elemental analysis of each piece was performed. The correlation between the composition and dielectric properties was established and the optimal dopant concentrations for obtaining maximum tunability of 75% and minimum loss of 0.02 were determined.

  18. Pulse and quasi-static remagnetization peculiarities and relaxation properties of Nd0.5Sr0.5MnO3 single crystal

    NASA Astrophysics Data System (ADS)

    Dovgii, V. T.; Linnik, A. I.; Kamenev, V. I.; Tarenkov, V. Yu.; Sidorov, S. L.; Todris, B. M.; Mikhailov, V. I.; Davideiko, N. V.; Linnik, T. A.; Popov, Ju. F.; Balbashov, A. M.

    2016-06-01

    Hysteresis features of magnetization and resistance of Nd0.5Sr0.5MnO3 single crystal in quasi-static (up to 9 T) and pulse (up to 14 T) magnetic fields are studied. The relaxation processes of magnetization and resistance after the action of a magnetic field of 9 T are also studied. It is shown that relaxation curves are approximated by two exponents with different time constants. These two constants relate to relaxation of the metastable ferromagnetic phase towards two different crystal structures (Imma and p21/m). Mechanism of phase transitions: antiferromagnetic insulator↔ferromagnetic metal (AFM/I↔FM/M) and existence of a high-conductive state of a sample after removal of magnetizing field in the temperature range below 150 K is proposed. The mechanism is connected with structural transition induced by magnetic field (due to magnetostriction) and slow relaxation of the FM-phase (larger volume) to the equilibrium AFM-phase (smaller volume) after field removal. It is shown that during pulse magnetization at the temperature 18 K time required for the AFM/I→FM/M phase transition is by six-seven orders of magnitude less than for realization of the FM/M→AFM/I phase transition.

  19. Temperature evolution of the luminescence decay of Sr0.33Ba0.67Nb2O6 : Pr3+.

    PubMed

    Mahlik, S; Lazarowska, A; Speghini, A; Bettinelli, M; Grinberg, M

    2014-04-23

    This article presents a spectroscopic investigation of Sr(0.33)Ba(0.67)(NbO2)3, doped with 1 mol% of Pr(3+). Photoluminescence and luminescence kinetics were measured at different temperatures at ambient (ferroelectric phase) and 76 kbar pressures (paraelectric phase). The photoluminescence spectrum is dominated by (1)D2 → (3)H4 transition of Pr(3+) in both phases. At ambient pressure when the system is excited with UV radiation, the intensity of dominant (1)D2 → (3)H4 emission evidently increases in the 200-293 K temperature range. This effect is attributed to enhancement of the excitation of the (1)D2 state through the praseodymium trapped exciton state, which at higher temperatures does not populate the higher lying (3)P0 state. Additionally, under UV radiation the material exhibits afterglow luminescence activated by temperature that can also have an impact on the increase of the (1)D2 emission. We propose that the afterglow luminescence is related to the existence of electron traps. At a pressure of 76 kbar the depth of the electron traps decreases in comparison to the ones observed at ambient pressure. However, the phase transition does not change the number of electron traps. PMID:24695003

  20. Parallel charge sheets of electron liquid and gas in La0.5Sr0.5TiO3/SrTiO3 heterostructures.

    PubMed

    Renshaw Wang, X; Sun, L; Huang, Z; Lü, W M; Motapothula, M; Annadi, A; Liu, Z Q; Zeng, S W; Venkatesan, T; Ariando

    2015-01-01

    We show here a new phenomenon in La0.5Sr0.5TiO3/SrTiO3 (LSTO/STO) heterostructures; that is a coexistence of three-dimensional electron liquid (3DEL) and 2D electron gas (2DEG), separated by an intervening insulating LSTO layer. The two types of carriers were revealed through multi-channel analysis of the evolution of nonlinear Hall effect as a function of film thickness, temperature and back gate voltage. We demonstrate that the 3D electron originates from La doping in LSTO film and the 2D electron at the surface of STO is due to the polar field in the intervening insulating layer. As the film thickness is reduced below a critical thickness of 6 unit cells (uc), an abrupt metal-to-insulator transition (MIT) occurs without an intermediate semiconducting state. The properties of the LSTO layer grown on different substrates suggest that the insulating phase of the intervening layer is a result of interface strain induced by the lattice mismatch between the film and substrate. Further, by fitting the magnetoresistance (MR) curves, the 6 unit cell thick LSTO is shown to exhibit spin-orbital coupling. These observations point to new functionalities, in addition to magnetism and superconductivity in STO-based systems, which could be exploited in a multifunctional context. PMID:26669575

  1. Size-induced Griffiths phase-like in ferromagnetic metallic La0.67Sr0.33MnO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Baaziz, H.; Tozri, A.; Dhahri, E.; Hlil, E. K.

    2016-04-01

    The La0.67Sr0.33MnO3 (LSMO) compound was prepared by the citrate-gel method and annealed at different temperatures (600 °C (L6), 800 °C (L8), 1000 °C (L10) and 1200 °C (L12)). X-ray diffraction (XRD), transmission electron microscopy (TEM) and magnetic measurements were used to investigate the particle size effects on the physical properties. All samples were found to be single phase crystallizing in rhombohedral symmetry with R 3 bar c space group. It was also found that the reduction of grain size intensively affects the magnetic properties of these compounds. The variation in the magnetic properties as a function of the particle size may be explained in terms of core-shell model. For the L6, L8 and L10 samples, the weaker effective magnetic moments and the deviation of the inverse susceptibility from the Curie-Weiss law were observed, indicating the possible existence of a Griffiths-like cluster phase. However, the latter was found to disappear for L12. The reduction of Griffiths phase may be related to the weaker FM interactions which were weakened by the size reduction, possibly due to the surface spin disorders. Otherwise, the competition between paramagnetic and ferromagnetic phases may strongly affect the magnetic properties that may result in the disappearance of the Griffiths phase.

  2. Ultra high energy density nanocomposite capacitors with fast discharge using Ba0.2Sr0.8TiO3 nanowires.

    PubMed

    Tang, Haixiong; Sodano, Henry A

    2013-04-10

    Nanocomposites combining a high breakdown strength polymer and high dielectric permittivity ceramic filler have shown great potential for pulsed power applications. However, while current nanocomposites improve the dielectric permittivity of the capacitor, the gains come at the expense of the breakdown strength, which limits the ultimate performance of the capacitor. Here, we develop a new synthesis method for the growth of barium strontium titanate nanowires and demonstrate their use in ultra high energy density nanocomposites. This new synthesis process provides a facile approach to the growth of high aspect ratio nanowires with high yield and control over the stoichiometry of the solid solution. The nanowires are grown in the cubic phase with a Ba0.2Sr0.8TiO3 composition and have not been demonstrated prior to this report. The poly(vinylidene fluoride) nanocomposites resulting from this approach have high breakdown strength and high dielectric permittivity which results from the use of high aspect ratio fillers rather than equiaxial particles. The nanocomposites are shown to have an ultra high energy density of 14.86 J/cc at 450 MV/m and provide microsecond discharge time quicker than commercial biaxial oriented polypropylene capacitors. The energy density of our nanocomposites exceeds those reported in the literature for ceramic/polymer composites and is 1138% greater than the reported commercial capacitor with energy density of 1.2 J/cc at 640 MV/m for the current state of the art biaxial oriented polypropylene. PMID:23464509

  3. Conduction mechanism in Eu0.5Sr0.5Mn0.9Cr0.1O3 perovskite

    NASA Astrophysics Data System (ADS)

    Modi, Anchit; Bhat, Masroor Ahmad; Pandey, Devendra K.; Gaur, N. K.

    2016-05-01

    A systematic study of polycrystalline sample with composition Eu0.5Sr0.5Mn0.9Cr0.1O3 has been undertaken and synthesized by conventional solid state reaction techniques. The room temperature XRD study reveals the single phase formation of the reported compound with orthorhombic structure having Pbnm space group. The temperature dependent resistivity study indicates the highly resistive nature of the compound especially in the low temperature region exhibits a semiconductor behavior and favored the variable range hopping conduction model. The obtained experimental data in the temperature range of our study can be described by the equation ρ(T) = ρ0exp[(T*/T)1/4]. The fitting results are used for the calculation of the temperature scale T* ˜ 9.05×106 K and finally the density of state at Fermi level N(EF) is calculated to be ˜ 61.63 × 1018 eV-1 cm-3.

  4. Selective electrochemical decomposition of outgrowths and nanopatterning in La 0.7 Sr 0.3 MnO3 perovskite thin films.

    PubMed

    Cavallini, Massimiliano; Graziosi, Patrizio; Calbucci, Marco; Gentili, Denis; Cecchini, Raimondo; Barbalinardo, Marianna; Bergenti, Ilaria; Riminucci, Alberto; Dediu, Valentin

    2014-01-01

    The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La 0.7 Sr 0.3 MnO3 perovskite as a representative material but in principle it can be extended to many other conductive systems. PMID:25491921

  5. Selective electrochemical decomposition of outgrowths and nanopatterning in La0.7Sr0.3MnO3 perovskite thin films

    NASA Astrophysics Data System (ADS)

    Cavallini, Massimiliano; Graziosi, Patrizio; Calbucci, Marco; Gentili, Denis; Cecchini, Raimondo; Barbalinardo, Marianna; Bergenti, Ilaria; Riminucci, Alberto; Dediu, Valentin

    2014-12-01

    The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La0.7Sr0.3MnO3 perovskite as a representative material but in principle it can be extended to many other conductive systems.

  6. Thermoelectric and electrical properties of Ba0.5Sr0.5Co x Ru x Fe(12-2 x)O19 ferrite*

    NASA Astrophysics Data System (ADS)

    Singh, Charanjeet; Jaroszewski, Maciej; Bindra Narang, Sukhleen; Ravinder, D.

    2016-04-01

    Thermoelectric and electrical characteristics investigation of M-type hexagonal ferrite, Ba0.5Sr0.5CoxRuxFe(12-2x)O19 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2), have been carried out from 303 K to 473 K. The static current density-electric field characteristics have been measured at room temperature. The Seebeck coefficient indicates n-type behavior at lower substitution and p-type conduction at higher substitution. The different electrical parameters are affected by change in grain size with substitution of Co2+ and Ru4+ ions. The existence of polarons is confirmed from increase in conductivity with frequency. The static conduction due to applied electric field is discussed qualitatively in terms of space charge limited current, ionic hopping, Poole-Frenkel and Schottky-Richardson mechanisms. The large current density has been observed at higher substitution. Contribution to the Topical Issue "Materials for Dielectric Applications", edited by Maciej Jaroszewski and Sabu Thomas.

  7. Dielectric properties of low-temperature sintered Ba0.6Sr0.4TiO3 derived from citrate method

    NASA Astrophysics Data System (ADS)

    Zhang, X. F.; Xu, Q.; Huang, Y. H.; Huang, D. P.; Kim, B. H.

    2011-03-01

    Superfine and uniform Ba0.6Sr0.4TiO3 powder with average particle size of 56 nm was derived from citrate method at calcining temperature of 550 °C. The desired morphological feature of the powder was found to be effective in reducing sintering temperature of the ceramic specimens. Sintering at 1260 °C produced ceramic specimen with a fine-grained (about 0.5 μn) microstructure and reasonable densification around 95% of the theoretical density. The dielectric properties of the ceramic specimen were investigated in terms of dielectric thermal spectrum, polarization versus electric-field relation and dielectric nonlinearity under bias electric-field. The ceramic specimen exhibited a dielectric constant (epsilonr) of 3530 and a dielectric loss (tan δ) of 0.47% at 10 kHz and zero bias field together with a tunability of 39.3% at 10 kHz and 20 kV/cm. Moreover, the dielectric nonlinearity was detected to be sensitive to the field history. This sensitivity was tentatively explained with respect to the existence of polar nano-regions (PNRs) superimposed on macroscopically paraelectric background of the ceramic matrix.

  8. Influence of Calcining Temperature on CuO-Modified (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 Ceramics

    NASA Astrophysics Data System (ADS)

    Yang, Cheng-Fu; Wu, Long; Wu, Tien-Shou

    1992-07-01

    The sintering of (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (abbreviated as BSTZ) with different amounts of CuO, which is used as the liquid phase promoter for lowering the temperature required to densify BSTZ, is studied using two types of calcined powders. For 1050°C calcination, the calcined powder contains BaTiO3, SrTiO3 and some raw materials such as ZrO2 and BaCO3. With sintering, some residual raw materials form unknown phases or low-dielectric-constant compounds with CuO, causing the liquid phase effect of CuO to disappear. For 1170°C calcination, the calcined powder completely forms ABO3 phases containing (Ba, Sr)TiO3 and BaZrO3. The sintering temperature for densification of ceramics is lowered, and the firing characteristics critically depend on the amount of CuO added and the sintering temperature.

  9. Magnetic field dependence of high- Tc interface superconductivity in La1.55Sr0.45CuO4/La2CuO4 heterostructures

    DOE PAGESBeta

    Gasparov, V. A.; Drigo, L.; Audouard, A.; He, Xi; Božović, I.

    2016-07-11

    Heterostructures made of a layer of a cuprate insulator La2CuO4 on the top of a layer of a nonsuperconducting cuprate metal La1.55Sr0.45CuO4 show high-Tc interface superconductivity confined within a single CuO2 plane. Given this extreme quasi-two-dimensional quantum confinement, it is of interest to find out how interface superconductivity behaves when exposed to an external magnetic field. With this motivation, we have performed contactless tunnel-diode-oscillator-based measurements in pulsed magnetic fields up to 56 T as well as measurements of the complex mutual inductance between a spiral coil and the film in static fields up to 3 T. Remarkably, we observe thatmore » interface superconductivity survives up to very high perpendicular fields, in excess of 40 T. Additionally, the critical magnetic field Hm(T) reveals an upward divergence with decreasing temperature, in line with vortex melting as in bulk superconducting cuprates.« less

  10. Thickness dependent structural, magnetic and magneto-transport properties of epitaxial Nd0.50Sr0.50MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Pawan; Singh, Hari Krishna

    2016-05-01

    We report the thickness-dependent structural, magnetic and magneto-transport properties in epitaxial Nd0.50Sr0.50MnO3 thin films (10 to 300nm) prepared by DC magnetron sputtering technique on single crystalline (001) oriented substrate LaAlO3. X-ray diffraction pattern reveals the epitaxial growth of all the films and the out-of-plane lattice parameter of films were found to increase with thickness. As thickness of the film increases the paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature (TC), charge ordered transition temperature (TCO) and magnetic moment were found to increase with a strong bifurcation in ZFC-FC magnetization. The asymmetry in the coercivity seen in field dependent magnetization loops (M-H loops) suggests the presence of exchange bias (EB) effect. While temperature dependent resistivity of films show the semiconducting nature for thickness 10-200nm in temperature range from 5-300K, the film of thickness 300nm shows the insulator to metal transition with transition temperature (TIM) at 175K. Temperature dependent low field magnetoresistance (LFMR) measured at 4kOe found to decrease with thickness and for high field magnetoresistance (HFMR) at 40kOe and 60kOe also show similar dependence and a crossover at intermediate temperature range in the magnitude of MR between 10nm and 200nm films at constant field. Colossal increase in magnetoresistance observed for 10nm film at low temperature.

  11. Contact resistance to SrRuO3 and La0.67Sr0.33MnO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Abuwasib, Mohammad; Lee, Hyungwoo; Gruverman, Alexei; Eom, Chang-Beom; Singisetti, Uttam

    2015-12-01

    Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and LSMO films after exposure to plasma treatment. Severe contact resistance degradation was observed for Ti contacts as compared to Pt after reactive ion etching on LSMO films. The effect of oxygen (O2) plasma on LSMO was observed to be most severe with non-ohmic behavior with Ti contacts, which can affect the functionality of FTJ devices. Finally, the thermal stability of contacts was investigated, Pt contacts to SRO show low resistance ohmic behavior even after annealing at 900 °C, making it a suitable contact for FTJ devices.

  12. Gate control of ferromagnetic insulating phase in lightly-doped La0.875Sr0.125MnO3-δ film

    NASA Astrophysics Data System (ADS)

    Kuang, H.; Wang, J.; Hu, F. X.; Zhao, Y. Y.; Liu, Y.; Wu, R. R.; Sun, J. R.; Shen, B. G.

    2016-02-01

    The electric field effect on the lightly doped La0.875Sr0.125MnO3-δ (LSMO) thin film in electric double-layer transistors was investigated by measuring transport properties of the film under various gate voltages. It was found that the positive gate bias leads to an increase of the charge-orbital ordering (COO) transition temperature and a decrease of the Curie temperature TC, indicating the suppression of ferromagnetic metal (FMM) phases and preference of COO/ferromagnetic insulator (FMI) with the hole depletion by gate bias. Such different electric field effects can be ascribed to the weakening of the ferromagnetic interaction and enhancement of Jahn-Teller (JT) distortion caused by the transformation of JT inactive Mn4+-ions to JT active Mn3+-ions. Moreover, a step-like increase in the high temperature region of the ρ-T curve, which is related to the transition of cooperative JT distortion, was found to develop with increasing the positive bias, indicating that the cooperative JT distorted phase is stabilized by the depletion of holes in LSMO film. These results demonstrate that the modulation of holes via electric field strongly affects the balance between energy gains of different interactions and thus produce different effects on the competing FMI, FMM, and cooperative JT distorted phases in LSMO film.

  13. Ac magnetotransport in La 0.7Sr 0.3Mn 0.95Fe 0.05O 3 at low dc magnetic fields

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Mahendiran, R.

    2011-12-01

    We report the ac electrical response of La 0.7Sr 0.3Mn 1- xFe xO 3(x=0.05) as a function of temperature, magnetic field (H) and frequency of radio frequency ( rf) current ( f=0.1-20 MHz). The ac impedance (Z) was measured while rf current directly passes through the sample as well as in a coil surrounding the sample. It is found that with increasing frequency of the rf current, Z(T) shows an abrupt increase accompanied by a peak at the ferromagnetic Curie temperature. The peak decreases in magnitude and shifts down with increasing value of H. We find a magnetoimpedance of ΔZ/Z=-21% for ΔH=500 Oe at f=1 MHz around room temperature when the rf current flows directly through the sample and ΔZ/Z=-65.9% when the rf current flows through a coil surrounding the sample. It is suggested that the magnetoimpedance observed is a consequence of suppression of transverse permeability which enhances skin depth for current flow. Our results indicate that the magnetic field control of high frequency impedance of manganites is more useful than direct current magnetoresistance for low-field applications.

  14. Electrochemical stability of Sm(0.5)Sr(0.5)CoO(3-δ)-infiltrated YSZ for solid oxide fuel cells/electrolysis cells.

    PubMed

    Fan, Hui; Han, Minfang

    2015-01-01

    Composite SSC (Sm(0.5)Sr(0.5)CoO(3-δ))-YSZ (yttria stabilized zirconia) oxygen electrodes were prepared by an infiltration process. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) of the composite electrodes showed the formation of SSC perovskite and a well-connected network of SSC particles in the porous YSZ backbone, respectively. The electrochemical performance of the cell was investigated under both fuel cell and steam electrolysis modes using polarization curves and electrochemical impedance spectroscopy (EIS). The cell experienced a large degradation rate at 700 °C with a constant voltage of 0.7 V for over 100 h under power generation operation. The subsequent post-cell SEM micrograph revealed that agglomeration of the infiltrated SSC particles was possibly the cause for the performance deterioration. Furthermore, the long-term stability of the cell was examined at 700 °C with a constant voltage of 1.3 V under steam electrolysis mode. SEM associated with energy dispersive X-ray spectroscopy (EDS) was employed to characterize the post-test cell after the long-term electrolysis operation and it indicated that besides the agglomeration of SSC particles, the delamination of the SSC-YSZ oxygen electrode from the YSZ electrolyte, as well as segregation of cobalt-enriched particles (particularly cobalt oxides) at the interface, was probably responsible for the cell degradation under the steam electrolysis mode. PMID:26212177

  15. Positive exchange-bias and giant vertical hysteretic shift in La0.3Sr0.7FeO3/SrRuO3 bilayers

    PubMed Central

    Rana, Rakesh; Pandey, Parul; Singh, R. P.; Rana, D. S.

    2014-01-01

    The exchange-bias effects in the mosaic epitaxial bilayers of the itinerant ferromagnet (FM) SrRuO3 and the antiferromagnetic (AFM) charge-ordered La0.3Sr0.7FeO3 were investigated. An uncharacteristic low-field positive exchange bias, a cooling-field driven reversal of positive to negative exchange-bias and a layer thickness optimised unusual vertical magnetization shift were all novel facets of exchange bias realized for the first time in magnetic oxides. The successive magnetic training induces a transition from positive to negative exchange bias regime with changes in domain configurations. These observations are well corroborated by the hysteretic loop asymmetries which display the modifications in the AFM spin correlations. These exotic features emphasize the key role of i) mosaic disorder induced subtle interplay of competing AFM-superexchange and FM double exchange at the exchange biased interface and, ii) training induced irrecoverable alterations in the AFM spin structure. PMID:24569516

  16. Understanding the origin of photoluminescence in disordered Ca 0.60Sr 0.40WO 4: An experimental and first-principles study

    NASA Astrophysics Data System (ADS)

    Longo, V. M.; Orhan, E.; Cavalcante, L. S.; Porto, S. L.; Espinosa, J. W. M.; Varela, J. A.; Longo, E.

    2007-04-01

    Visible photoluminescence (PL) was observed for the first time at room temperature in structurally disordered calcium strontium tungstate powder, Ca 0.60Sr 0.40WO 4 (CSW), obtained by the polymeric precursor method. The PL behavior of CSW powders has been analyzed as a function of the disorder rate, based on experimental and theoretical studies. Quantum mechanical theory based on density functional theory at the B3LYP level has been employed to study the electronic structure of two periodic models representing both crystalline and disordered powders. Their electronic structures have been analyzed in terms of density of states, band dispersion and charge densities. The calculations indicate a break in symmetry when passing from crystalline to disordered models, creating localized electronic levels above the valence band. Moreover, a negative charge transfer process takes place from the [WO 3] cluster to the [WO 4] cluster. The polarization induced by the break in symmetry and the existence of localized levels favors the creation of trapped holes and electrons, originating the PL phenomenon.

  17. Interfacial dislocations in (111) oriented (Ba0.7Sr0.3)TiO3 films on SrTiO3 single crystal

    DOE PAGESBeta

    Shen, Xuan; Yamada, Tomoaki; Lin, Ruoqian; Kamo, Takafumi; Funakubo, Hiroshi; Wu, Di; Xin, Huolin L.; Su, Dong

    2015-10-08

    In this study, we have investigated the interfacial structure of epitaxial (Ba,Sr)TiO3 films grown on (111)-oriented SrTiO3 single-crystal substrates using transmission electron microscopy (TEM) techniques. Compared with the (100) epitaxial perovskite films, we observe dominant dislocation half-loop with Burgers vectors of a<110> comprised of a misfit dislocation along <112>, and threading dislocations along <110> or <100>. The misfit dislocation with Burgers vector of a <110> can dissociate into two ½ a <110> partial dislocations and one stacking fault. We found the dislocation reactions occur not only between misfit dislocations, but also between threading dislocations. Via three-dimensional electron tomography, we retrievedmore » the configurations of the threading dislocation reactions. The reactions between threading dislocations lead to a more efficient strain relaxation than do the misfit dislocations alone in the near-interface region of the (111)-oriented (Ba0.7Sr0.3)TiO3 films.« less

  18. Apparent Oxygen Uphill Diffusion in La0.8Sr0.2MnO3 Thin Films upon Cathodic Polarization

    PubMed Central

    Huber, Tobias M.; Navickas, Edvinas; Friedbacher, Gernot; Hutter, Herbert

    2015-01-01

    Abstract The impact of cathodic bias on oxygen transport in La0.8Sr0.2MnO3 (LSM) thin films was investigated. Columnar‐grown LSM thin films with different microstructures were deposited by pulsed laser deposition. 18O tracer experiments were performed on thin film microelectrodes with an applied cathodic bias of −300 or −450 mV, and the microelectrodes were subsequently analyzed by time‐of‐flight secondary ion mass spectrometry. The 18O concentration in the cathodically polarized LSM microelectrodes was strongly increased relative to that in the thermally annealed film (without bias). Most remarkable, however, was the appearance of a pronounced 18O fraction maximum in the center of the films. This strongly depended on the applied bias and on the microstructure of the LSM thin layers. The unusual shape of the 18O depth profiles was caused by a combination of Wagner–Hebb‐type stoichiometry polarization of the LSM bulk, fast grain boundary transport and voltage‐induced modification of the oxygen incorporation kinetics, PMID:27525207

  19. Electron microscopic studies of the antiferroelectric phase in Sr 0.60Ca 0.40TiO 3 ceramic

    NASA Astrophysics Data System (ADS)

    Anwar, Shahid; Lalla, N. P.

    2008-05-01

    The structural variants and their coexistence across the antiferroelectric phase transition in Sr 0.60Ca 0.40TiO 3 ceramic has been studied through transmission electron microscopy (TEM) at room temperature and ˜100 °C. A clear evidence of the presence of superlattice reflections, corresponding to the cell doubling along the c-axis of Pbnm (or b-axis along Pnma), occurring during paraelectric to antiferroelectric transition, has been obtained through selected area electron diffraction, convergent beam electron diffraction and lattice-resolution imaging. Coexistence of the Pbnm and Pbcm phases at room temperature has been observed and attributed to the strain/disorder-induced broadening of the first-order antiferroelectric phase transition. Drastic changes in the domain structure during Pbnm to Pbcm transformation have been observed. This clearly indicates that the antiferrodistortive transition responsible for the occurrence of the antiferroelectric phase is of completely different origin and it is not just an additional follow-up of the already-existing ordering due to a-a-c+ tilt schemes in the Pbnm domain. Thermal cycling studies on microstructural changes indicate some kind of memory mechanism, which retains the memory of the original a-a-c+ tilt schemes in the Pbnm phase. This has been attributed to the symmetry conforming short-range order (SC-SRO) of the point defects.

  20. Novel microstructural strategies to enhance the electrochemical performance of La0.8Sr0.2MnO3-δ cathodes.

    PubMed

    Dos Santos-Gómez, L; Losilla, E R; Martín, F; Ramos-Barrado, J R; Marrero-López, D

    2015-04-01

    Novel strategies based on spray-pyrolysis deposition are proposed to increase the triple-phase boundary (TPB) of La0.8Sr0.2MnO3-δ (LSM) cathodes in contact with yttria-stabilized zirconia (YSZ) electrolyte: (i) nanocrystalline LSM films deposited on as-prepared YSZ surface; (ii) the addition of poly(methyl methacrylate) microspheres as pore formers to further increase the porosity of the film cathodes; and (iii) the deposition of LSM by spray pyrolysis on backbones of Zr0.84Y0.16O1.92 (YSZ), Ce0.9Gd0.1O1.95 (CGO), and Bi1.5Y0.5O3-δ (BYO) previously fixed onto the YSZ. This last method is an alternative to the classical infiltration process with several advantages for large-scale manufacturing of planar solid oxide fuel cells (SOFCs), including easier industrial implementation, shorter preparation time, and low cost. The morphology and electrochemical performance of the electrodes are investigated by scanning electron microscopy and impedance spectroscopy. Very low values of area specific resistance are obtained, ranging from 1.4 Ω·cm(2) for LSM films deposited on as-prepared YSZ surface to 0.06 Ω-cm(2) for LSM deposited onto BYO backbone at a measured temperature of 650 °C. These electrodes exhibit high performance even after annealing at 950 °C, making them potentially suitable for applications in SOFCs at intermediate temperatures. PMID:25793738

  1. Determination of magnetic parameters in La0.7Sr0.3MnO3/SrTiO3 thin films using EMCD

    NASA Astrophysics Data System (ADS)

    Li, Gen; Song, Dongsheng; Li, Zhi Peng; Zhu, Jing

    2016-06-01

    It is well known that the magnetic state of the La0.7Sr0.3MnO3 (LSMO) thin-film heterostructure is strongly correlated with the lattice, spin, orbital, and charge states, since these influence the electric and magnetic transport properties even on the unit-cell level. Therefore, understanding the material's magnetic properties on the nanoscale is important for the development of novel applications. The recently developed electron magnetic-circular dichroism (EMCD) technique allows the determination of atomic site-specific magnetic information via the use of transmitted electrons; however, its sensitivity is not high enough to quantitatively acquire magnetic information in many weak magnetism systems. Here, we utilized a dynamical diffraction-effect assisted EMCD technique to quantitatively determine the spin and orbital magnetic moment of LSMO/SrTiO3 thin films on the nanometer scale using a transmission electron microscope. Further, data processing was optimized to enhance the intensity of the EMCD signals for manganese, which have very weak magnetism at room temperature. High signal-to-noise ratio and accurate quantitative magnetic measurement are eventually achieved. Finally, the spin magnetic moments (0.73 ± 0.26 μB) are derived, and we also limited the ratio of the orbital to spin magnetic moment within an interval of (-0.03, 0.01). Our results not only present the nanoscale magnetic parameters of LSMO/SrTiO3, but also demonstrate how the measurement limit of the spin (or orbital) magnetic moment can be achieved, which is via the developed dynamical diffraction effect assisted EMCD technique.

  2. Structure, magnetic and electrical transport properties of the perovskites La0.67-xEuxSr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Dhahri, Neila; Dhahri, Abdessalem; Dhahri, Jemai; Hlil, El-kebir; Dhahri, Essebti

    2013-01-01

    In this paper we report the structural, magnetic and electrical properties of a series of nanocrystalline La0.67-xEuxSr0.33MnO3 (0≤x≤0.3) materials which were prepared by the solid-state reaction method in air. The X-ray powder diffraction has shown that all our synthesized samples are a single phase and have crystallized in the hexagonal symmetry with R3barC space group. The scanning electron microscopy has shown smooth and densified structures, clean and pure images. Electric and magnetic measurements show that all our samples had exhibited a ferromagnetic to paramagnetic transition and a metallic to semiconductor one when temperature increases. The substitution of La3+ by Eu3+ leads to a continuously simultaneous decrease of the Curie temperature TC (from 350 K for x=0.0-258 K for x=0.3) and the metal-semi-conductor transition temperature Tp (from 310 K for x=0.0-224 K for x=0.3). The electrical resistivity data were analyzed using different theoretical models and it has been concluded that at low temperatures (ferromagnetic metallic region) the resistivity may originate from grain/domain boundary, electron-electron scattering and two-magnon scattering effects. While in the paramagnetic insulating regime, the variation of resistivity with temperature may be explained by adiabatic small polaron Hopping mechanism and variable-range hopping mechanisms. The values of activation energies were found decreasing, while the density of states at the Fermi-level, N (EF) was increasing with decreasing . A suitable explanation for the observed behavior is given.

  3. Investigations on the spin-glass state in Dy0.5Sr0.5MnO3 single crystals through structural, magnetic and thermal properties

    NASA Astrophysics Data System (ADS)

    Harikrishnan, S.; Naveen Kumar, C. M.; Bhat, H. L.; Elizabeth, Suja; Rößler, U. K.; Dörr, K.; Rößler, S.; Wirth, S.

    2008-07-01

    Single crystals of Dy0.5Sr0.5MnO3 are grown using the optical floating zone technique, and their structural, magnetic, transport and thermal properties have been investigated. Magnetization measurements under field-cooled and zero-field-cooled conditions display irreversibility below 35 K. The magnetization does not saturate up to fields of 5 T in the temperature range 5-350 K. AC susceptibility shows a cusp around 32 K that shifts to higher temperature with increasing frequency. This frequency dependence of the peak temperature follows a critical slowing down with exponent zν = 3.6. Electrical resistivity shows insulating behavior, and the application of magnetic fields up to 10 T does not change this qualitative behavior. However, a marked negative magnetoresistance is observed in the paramagnetic phase reaching 80% at 70 K and 10 T. The observed resistivity behavior does not obey an activated type of conduction. These features are characteristic of spin-glass behavior in this half-doped insulating manganite. It is argued that the spin-glass-like state originates from the A-site disorder, which in turn results from the random distribution of cations with different ionic radii. Specific-heat measurements reveal a sizable linear contribution at low temperature that may be associated with the glassy magnetic ordering and a Schottky-like anomaly in a wide temperature range between 8 and 40 K. The distribution of Schottky levels is explained by the inhomogeneity of the molecular field in the spin-glass state that leads to variable splitting of the Kramers ground-state doublets in Dy3+.

  4. Preparation Process and Dielectric Properties of Ba(0.5)Sr(0.5)TiO3-P(VDF-CTFE) Nanocomposites

    NASA Technical Reports Server (NTRS)

    Zhang, Lin; Wu, Peixuang; Li, Yongtang; Cheng, Z. -Y.; Brewer, Jeffrey C.

    2014-01-01

    Ceramic-polymer 0-3 nanocomposites, in which nanosized Ba(0.5)Sr(0.5)TiO3 (BST) powders were used as ceramic filler and P(VDF-CTFE) 88/12 mol% [poly(vinylidene fluoridechlorotrifluoroethylene)] copolymer was used as matrix, were studied over a concentration range from 0 to 50 vol.% of BST powders. It is found that the solution cast composites are porous and a hot-press process can eliminate the porosity, which results in a dense composite film. Two different configurations used in the hot-press process are studied. Although there is no clear difference in the uniformity and microstructure of the composites prepared using these two configurations, the composite prepared using one configuration exhibit a higher dielectric constant with a lower loss. For the composite with 40 vol. BST, a dielectric constant of 70 with a loss of 0.07 at 1 kHz is obtained at room temperature. The composites exhibit a lower dielectric loss than the polymer matrix at high frequency. However, at low frequency, the composites exhibit a higher loss than the polymer matrix due to a low frequency relaxation process that appears in the composites. It is believed that this relaxation process is related to the interfacial layer formed between BST particle and the polymer matrix. The temperature dependence of the dielectric property of the composites was studied. It is found that the dielectric constant of these composites is almost independent of the temperature over a temperature range from 20 to 120 C. Key words: A. Polymer-matrix composites (PMCs); B. Electrical Properties; E. Casting; E. Heat treatment; Dielectric properties.

  5. Electrostatic versus Electrochemical Doping and Control of Ferromagnetism in Ion-Gel-Gated Ultrathin La0.5Sr0.5CoO3-δ.

    PubMed

    Walter, Jeff; Wang, Helin; Luo, Bing; Frisbie, C Daniel; Leighton, Chris

    2016-08-23

    Recently, electrolyte gating techniques employing ionic liquids/gels in electric double layer transistors have proven remarkably effective in tuning charge carrier density in a variety of materials. The ability to control surface carrier densities at levels above 10(14) cm(-2) has led to widespread use in the study of superconductivity, insulator-metal transitions, etc. In many cases, controversy remains over the doping mechanism, however (i.e., electrostatic vs electrochemical (e.g., redox-based)), and the technique has been less applied to magnetic materials. Here, we discuss ion gel gating of nanoscale 8-unit-cell-thick hole-doped La0.5Sr0.5CoO3-δ (LSCO) films, probing in detail the critical bias windows and doping mechanisms. The LSCO films, which are under compressive stress on LaAlO3(001) substrates, are metallic and ferromagnetic (Curie temperature, TC ∼ 170 K), with strong anomalous Hall effect and perpendicular magnetic anisotropy. Transport measurements reveal that negative gate biases lead to reversible hole accumulation (i.e., predominantly electrostatic operation) up to some threshold, whereas positive bias immediately induces irreversibility. Experiments in inert/O2 atmospheres directly implicate oxygen vacancies in this irreversibility, supported by atomic force microscopy and X-ray photoelectron spectroscopy. The results are thus of general importance, suggesting that hole- and electron-doped oxides may respond very differently to electrolyte gating. Reversible voltage control of electronic/magnetic properties is then demonstrated under hole accumulation, including resistivity, magnetoresistance, and TC. The sizable anomalous Hall coefficient and perpendicular anisotropy in LSCO provide a particularly powerful probe of magnetism, enabling direct extraction of the voltage-dependent order parameter and TC shift. The latter amounts to ∼7%, with potential for much stronger modulation at lower Sr doping. PMID:27479878

  6. Structural and magnetic properties of La0.7Sr0.1AgxMnO3-δ perovskite manganites

    NASA Astrophysics Data System (ADS)

    Hou, Xue; Ji, Deng-Hui; Qi, Wei-Hua; Tang, Gui-De; Li, Zhuang-Zhi

    2015-05-01

    Ag-doped manganite powder samples, La0.7Sr0.1AgxMnO3-δ (x = 0.00, 0.025, 0.05, 0.075, and 0.10) were synthesized using the sol-gel method. X-ray diffraction patterns indicated that the samples had two phases with the perovskite being the dominant phase and Mn3O4 being the second phase. X-ray energy dispersive spectra indicated that the ratio of Ag to La was very close to that of the nominal composition in the samples. The specific saturation magnetizations at 300 K increased from 32.0 A·m2/kg when x = 0.00 to 46.8 A·m2/kg when x = 0.10. The Curie temperature, TC, of the samples increased from 310 K when x = 0.00 to 328 K when x = 0.10. Because the atomic concentration ratios of La, Sr, and Mn in the five samples were all the same and only the Ag concentration changed, the variations of the specific saturation magnetizations at 300 K and the Curie temperatures suggested that the Ag cations have been doped into the A sites of the perovskite phase in the samples. Project supported by the National Natural Science Foundation of China (Grant No. NSF-11174069), the Natural Science Foundation of Hebei Province, China (Grant No. E2011205083), the Key Item Science Foundation of Hebei Province, China (Grant No. 10965125D), the Key Item Science Foundation of the Education Department of Hebei Province, China (Grant No. ZD2010129), and the Young Scholar Science Foundation of the Education Department of Hebei Province, China (Grant No. QN20131008).

  7. Two-dimensional incommensurately modulated structure of (Sr0.13Ca0. 87)2CoSi2O7 crystals.

    PubMed

    Bagautdinov, B; Hagiya, K; Kusaka, K; Ohmasa, M; Iishi, K

    2000-10-01

    The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations. PMID:11006557

  8. Effect of praseodymium doping on the structural, magnetic and magnetocaloric properties of Sm0.55Sr0.45MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Mleiki, A.; Othmani, S.; Cheikhrouhou-Koubaa, W.; Koubaa, M.; Cheikhrouhou, A.; Hlil, E. K.

    2015-12-01

    The effect of praseodymium doping on the microstructure, magnetic and magnetocaloric effects in Sm0.55-xPrxSr0.45MnO3 (x=0.0 and x=0.1) has been investigated. Our compounds have been elaborated using the conventional solid-state reaction at high temperature. X-Ray diffraction study reveals that our samples crystallize in the distorted orthorhombic system with Pbnm space group. Magnetization measurements M (T) at H=0.05 T were performed and show a paramagnetic (PM) to ferromagnetic (FM) transition with decreasing temperature. Praseodymium doping leads to an increase of the Curie temperature TC from 95 K (x=0.0) to 132 K (x=0.1). Moreover, we observe a small anomaly in the M (T) behavior around 30 K. It has been shown that x=0.1 sample exhibit first order FM-PM phase transition under low magnetic field accompanied by a thermal hysteresis in the field cooled cooling and warming protocols. However, the phase transition from PM to FM is modified from first order to second order above a critical field HC. A metamagnetic behavior has been observed in the M (H) curves around 110 K for x=0.0 and 160 K for x=0.1. The maximum of the magnetic entropy change (- ΔSMmax) was calculated using the isothermal magnetization curves M (H) under magnetic field change of 5 T and is found to be 6.56 J kg-1 K-1 for x=0.0 and 7.14 J kg-1 K-1 for x=0.1. The relative cooling power (RCP) is found to be 222.6 J/Kg and 258.8 J/Kg for x=0.0 and x=0.1, respectively. This suggests that these compounds may be suitable candidates for magnetic refrigeration.

  9. Chromium deposition and poisoning of La(0.8)Sr(0.2)MnO3 oxygen electrodes of solid oxide electrolysis cells.

    PubMed

    Chen, Kongfa; Hyodo, Junji; Dodd, Aaron; Ai, Na; Ishihara, Tatsumi; Jian, Li; Jiang, San Ping

    2015-01-01

    The effect of the presence of an Fe-Cr alloy metallic interconnect on the performance and stability of La(0.8)Sr(0.2)MnO3 (LSM) oxygen electrodes is studied for the first time under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The presence of the Fe-Cr interconnect accelerates the degradation and delamination processes of the LSM oxygen electrodes. The disintegration of LSM particles and the formation of nanoparticles at the electrode/electrolyte interface are much faster as compared to that in the absence of the interconnect. Cr deposition occurs in the bulk of the LSM oxygen electrode with a high intensity on the YSZ electrolyte surface and on the LSM electrode inner surface close to the electrode/electrolyte interface. SIMS, GI-XRD, EDS and XPS analyses clearly identify the deposition and formation of chromium oxides and strontium chromate on both the electrolyte surface and electrode inner surface. The anodic polarization promotes the surface segregation of SrO and depresses the generation of manganese species such as Mn(2+). This is evidently supported by the observation of the deposition of SrCrO4, rather than (Cr,Mn)3O4 spinels as in the case under the operating conditions of solid oxide fuel cells. The present results demonstrate that the Cr deposition is essentially a chemical process, initiated by the nucleation and grain growth reaction between the gaseous Cr species and segregated SrO on LSM oxygen electrodes under SOEC operating conditions. PMID:26206416

  10. Improved electrochemical stability at the surface of La(0.8)Sr(0.2)CoO3 achieved by surface chemical modification.

    PubMed

    Tsvetkov, Nikolai; Lu, Qiyang; Yildiz, Bilge

    2015-01-01

    The degradation of the surface chemistry on perovskite (ABO3) oxides is a critical issue for their performance in energy conversion systems such as solid oxide fuel/electrolysis cells and in splitting of H2O and CO2 to produce fuels. This degradation is typically in the form of segregation and phase separation of dopant cations from the A-site, driven by elastic and electrostatic energy minimization and kinetic demixing. In this study, deposition of Ti at the surface was found to hinder the dopant segregation and the corresponding electrochemical degradation on a promising SOFC cathode material, La(0.8)Sr(0.2)CoO3 (LSC). The surface of the LSC films was modified by Ti (denoted as LSC-T) deposited from a TiCl4 solution. The LSC and LSC-T thin films were investigated by electrochemical impedance spectroscopy, nano-probe Auger electron spectroscopy, and X-ray photoelectron spectroscopy (XPS), upon annealing at 420-530 °C in air up to about 90 hours. The oxygen exchange coefficient, k(q), on LSC-T cathodes was found to be up to 8 times higher than that on LSC cathodes at 530 °C and retained its stability. Sr-rich insulating particles formed at the surface of the annealed LSC and LSC-T films, but with significantly less coverage of such particles on the LSC-T. From this result, it appears that modification of the LSC surface with Ti reduces the segregation of the blocking Sr-rich particles at the surface, and a larger area on LSC surface (with a higher Sr doping level in the lattice) is available for the oxygen reduction reaction. The stabilization of the LSC surface through Ti-deposition can open a new route for designing surface modifications on perovskite oxide electrodes for high temperature electro- and thermo-chemical applications. PMID:26227310