Science.gov

Sample records for mn al bi

  1. High-pressure synthesis of BiFeO3-BiAlO3 and BiFeO3-MnTiO3 solid solution

    NASA Astrophysics Data System (ADS)

    Shimura, Gen; Kusaba, Keiji; Miyawaki, Tetsuya; Niwa, Ken; Asano, Hidefumi; Hasegawa, Masashi

    2013-06-01

    There have been so many investigations for high-pressure synthesis of perovskite-type oxides in the material science field. Multiferroic material is particularly attracted in the field of electronic device materials. BiFeO3 (ferroelectric antiferromagnet) is known as the only Bi-contained perovskite which can be synthesized at ambient pressure. We investigated solid solution systems of BiFeO3-BiAlO3 and BiFeO3-MnTiO3 under high pressure and high temperature to synthesize a new multiferroic compound in the present study. Chemical reagents of simple oxides were mixed with a mortar as a starting material. The mixture was rapped with a gold foil, and it encased in a cubic pressure-medium with a graphite furnace. High pressure experiments were carried out using two DIA-type high pressure apparatuses installed in Nagoya University. X-ray powder diffraction patterns of all recovered specimens were collected using Cu-K α radiation and magnetic susceptibilities for some of the recovered specimens were measured using a vibrating sample magnetometer. In the system of BiFeO3-BiAlO3, the BiFeO3-type solid solution was only obtained in the both Fe- and Al-rich composition. While in the system of BiFeO3-MnTiO3, no solid solutions were observed.

  2. Origin of interface magnetism in BiMnO3/SrTiO3 and LaAlO3/SrTiO3 heterostructures.

    PubMed

    Salluzzo, M; Gariglio, S; Stornaiuolo, D; Sessi, V; Rusponi, S; Piamonteze, C; De Luca, G M; Minola, M; Marré, D; Gadaleta, A; Brune, H; Nolting, F; Brookes, N B; Ghiringhelli, G

    2013-08-23

    Possible ferromagnetism induced in otherwise nonmagnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3. By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated with magnetic Ti3+ ions at the interface itself for LaAlO3/SrTiO3 and to Mn3+ ions in the overlayer for BiMnO3/SrTiO3. In LaAlO3/SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon.

  3. Leakage current limiting mechanisms and ferroelectric properties of BiAlO3/La0.67Sr0.33MnO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Yanan; Luo, Bingcheng; Chen, Changle; Xing, Hui; Wang, Jianyuan; Jin, Kexin

    2017-03-01

    The BiAlO3/La0.67Sr0.33MnO3 heterostructure was deposited on LaAlO3 (111) substrate by pulse laser deposition technology. X-ray diffraction measurement indicates that BiAlO3 thin films belong to tetragonal phase. Two different leakage current mechanisms, i.e., Space Charge Limited Current and Schottky emission models are observed in J-E characteristics of BiAlO3/La0.67Sr0.33MnO3 heterostructure in different temperature regions, respectively. The ferroelectric hysteresis loops measured by positive-up negative-down method show intrinsic remnant polarization (2Pr = 2.4 μC/cm2) at the applied electric field of 750 kV/cm, with the 80 nm thickness of BiAlO3 thin films at room temperature. The domain imagines and local piezoelectric hysteresis loops obtained by Piezoresponse Force Microscopy technique further reveal the intrinsic ferroelectricity of. BiAlO3 thin films at room temperature.

  4. Development of MnBi permanent magnet: neutron diffraction of MnBi powder

    SciTech Connect

    Cui, Jun; Choi, Jung-Pyung; Li, Guosheng; Polikarpov, Evgueni; Darsell, Jens T.; Kramer, Matthew J.; Zarkevich, Nikolai; Wang, L. L.; Johnson, D. D.; Marinescu, Melania; Huang, Qingzhen; Wu, Hui; Vuong, Nguyen V.; Liu, J.Ping

    2014-03-05

    MnBi attracts great attention in recent years for its great potential as permanent magnet materials. MnBi phase is difficult to obtain because of the rather drastic peritectic reaction between Mn and Bi. In this paper, we report our effort on synthesizing high purity MnBi compound using conventional powder metallurgical approaches. Neutron diffraction was carried out to investigate the crystal and nuclear structure of the obtained power. The result shows that the purity of the obtained powder is about 91wt.% at 300K, and the magnetic moment of the Mn atom in MnBi lattice is 4.424 and 4.013 μB at 50 K and 300 K respectively.

  5. Magnetism of MnBi-Based Nanomaterials

    SciTech Connect

    Kharel, P; Shah, VR; Skomski, R; Shield, JE; Sellmyer, DJ

    2013-07-01

    Nanostructured MnBi ribbons doped with impurity elements including B, C, Fe, Hf, Sm and Tb were prepared using the arc melting and melt-spinning techniques. The melt-spun ribbons were annealed in vacuum furnace at 350 degrees C to obtain the intended hexagonal structure. The external impurity doping made a significant change in the magnetic properties of the nanostructured MnBi ribbons including a decrease in saturation magnetization (M-s) and anisotropy energy (K) and an increase in coercivity H-c. However, Hf and C co-doping showed the opposite effect with a small increase in both M-s and K. Interestingly, the anisotropy energy of the boron doped sample increased by about 15% irrespective of the small decrease in magnetization. A significant increase in H-c of MnBi ribbons was found due to Hf, Tb and Sm doping. H-c as high as 13 kOe was achieved in Hf-doped sample after the sample was aligned in a magnetic field. A thermal hysteresis was observed at the structural phase transition of MnBi, which shifts by about 5 K towards higher temperatures due to impurity doping. The observed magnetic properties of the impurity doped MnBi ribbons are explained as the consequences of the disorder and the competing ferromagnetic and antiferromagnetic interactions.

  6. The microstructure of MnBi/Bi eutectic alloys

    NASA Technical Reports Server (NTRS)

    Ravishankar, P. S.; Wilcox, W. R.; Larson, D. J.

    1980-01-01

    Directionally solidified eutectic alloys of the system MnBi/Bi have been investigated with reference to the dependence of the fiber spacing on the growth rate and the interfacial temperature gradient. It is found that the fiber spacing varies as the inverse square root of the growth rate and does not depend on the temperature gradient in contrast to the claims that all faceted/non-faceted eutectics should show a temperature gradient influence.

  7. Magnetic properties of single-phase MnBi grown from MnBi{sub 49} melt

    SciTech Connect

    Xiao, X. F.; Si, P. Z. Feng, H.; Yu, S. J.; Ge, H. L.; Ye, Q. L.; Liu, J. J.

    2014-05-07

    The single-phase NiAs-type MnBi, embedded in Bi matrix, was grown from homogeneous MnBi{sub 49} melt at low temperatures to prevent the formation of Mn{sub 1.08}Bi. An abrupt magnetization change was observed at ∼240 K. The origin of this change was ascribed to the movement of the Mn atoms between the regular sites and the interstitial sites in the MnBi lattices. The splitting of the x-ray photoelectron lines of MnBi indicates the presence of two binding states of Mn atoms, one of which was ascribed to interstitial Mn atoms. A large coercivity up to 1.79 T at 400 K was observed in the as-grown bulk isotropic MnBi alloys.

  8. Absence of ferroelectricity in BiMnO3 ceramics

    NASA Astrophysics Data System (ADS)

    Goian, V.; Kamba, S.; Savinov, M.; Nuzhnyy, D.; Borodavka, F.; Vaněk, P.; Belik, A. A.

    2012-10-01

    We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at TC1 = 475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above TC1. Step-like dielectric anomaly observed at TC1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic but only antipolar ferromagnet.

  9. Synthesis and characterization of Mn-Bi alloy

    SciTech Connect

    Mishra, Ashutosh; Patil, Harsha; Jain, G.; Mishra, N.

    2012-06-05

    High purity MnBi low temperature phase has been prepared and analyzed using X-ray diffraction, Lorentz-Polarization Factor and Fourier transforms infrared measurement. After synthesis of samples structural characterization has done on samples by X-ray diffraction, which shows that after making the bulk sample is in no single phase MnBi has been prepared by sintering Mn and Bi powders. By Lorentz-Polarization Factor is affecting the relative intensity of diffraction lines on a powder form. And by FTIR which shows absorption peaks of MnBi alloys.

  10. Magnetic properties of MnBi based alloys: First-principles calculations for MnBi-Co and MnBi-Co-Fe cases

    SciTech Connect

    Hong, YK; Park, J; Mryasov, ON; Kim, SG; Kim, S; Lee, J; Abo, GS; Choi, CJ; Lee, J

    2013-05-01

    First-principles calculations of fundamental magnetic properties were performed for ordered MnBi, MnBi-Co, and MnBi-Co-Fe alloys to evaluate maximum energy product (BH)(max). Full potential linear-augmented plane wave (FLAPW) and linear-muffin-tin-orbital (LMTO) calculations using density functional theory (DFT) within the local spin density approximation (LSDA) were used and found to give a reasonable description of saturation magnetization (M-s), effective anisotropy constant (K-eff), and Curie temperature (T-c) for NiAs-structured MnBi crystal. We found that upon addition of Co, the M-s and K-eff increased, while T-c reduced. The magnetic anisotropy changed from weak anisotropy easy plane for MnBi to the strong easy axis anisotropy for MnBi-Co and MnBi-Co-Fe. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

  11. Magnetic interactions in BiFe₀.₅Mn₀.₅O₃ films and BiFeO₃/BiMnO₃ superlattices.

    PubMed

    Xu, Qingyu; Sheng, Yan; Khalid, M; Cao, Yanqiang; Wang, Yutian; Qiu, Xiangbiao; Zhang, Wen; He, Maocheng; Wang, Shuangbao; Zhou, Shengqiang; Li, Qi; Wu, Di; Zhai, Ya; Liu, Wenqing; Wang, Peng; Xu, Y B; Du, Jun

    2015-03-13

    The clear understanding of exchange interactions between magnetic ions in substituted BiFeO3 is the prerequisite for the comprehensive studies on magnetic properties. BiFe0.5Mn0.5O3 films and BiFeO3/BiMnO3 superlattices have been fabricated by pulsed laser deposition on (001) SrTiO3 substrates. Using piezoresponse force microscopy (PFM), the ferroelectricity at room temperature has been inferred from the observation of PFM hysteresis loops and electrical writing of ferroelectric domains for both samples. Spin glass behavior has been observed in both samples by temperature dependent magnetization curves and decay of thermo-remnant magnetization with time. The magnetic ordering has been studied by X-ray magnetic circular dichroism measurements, and Fe-O-Mn interaction has been confirmed to be antiferromagnetic (AF). The observed spin glass in BiFe0.5Mn0.5O3 films has been attributed to cluster spin glass due to Mn-rich ferromagnetic (FM) clusters in AF matrix, while spin glass in BiFeO3/BiMnO3 superlattices is due to competition between AF Fe-O-Fe, AF Fe-O-Mn and FM Mn-O-Mn interactions in the well ordered square lattice with two Fe ions in BiFeO3 layer and two Mn ions in BiMnO3 layer at interfaces.

  12. Spatial profile of thermoelectric effects during Peltier pulsing in Bi and Bi/MnBi eutectic

    NASA Technical Reports Server (NTRS)

    Silberstein, R. P.; Larson, D. J., Jr.

    1987-01-01

    The spatial profile of the thermal transients that occur during and following the current pulsing associated with Peltier Interface Demarcation during directional solidification is studied. Results for pure Bi are presented in detail and compared with corresponding results for the Bi/MnBi eutectic. Significant thermal transients occur throughout the sample that can be accounted for by the Peltier effect, the Thomson effect, and Joule heating. These effects are separated and their behavior is studied as a function of time, current density, and position with respect to the solid/liquid interface.

  13. Thermal Stability of MnBi Magnetic Materials

    SciTech Connect

    Cui, Jun; Choi, Jung-Pyung; Li, Guosheng; Polikarpov, Evgueni; Darsell, Jens T.; Overman, Nicole R.; Olszta, Matthew J.; Schreiber, Daniel K.; Bowden, Mark E.; Droubay, Timothy C.; Kramer, Matthew J.; Zarkevich, Nikolai; Wang, L. L.; Johnson, Duane D.; Marinescu, Melania; Takeuchi, Ichiro; Huang, Qingzhen; Wu, Hui; Reeve, Hayden; Vuong, Nguyen V.; Liu, J.Ping

    2014-01-01

    MnBi attracts great attention in recent years for its great potential as permanent magnet materials. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase for exchange coupling nanocomposite magnet. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn is easy to react with oxygen. MnO formation is irreversible and causes degradation to the magnetic properties. In this paper, we report our effort on developing MnBi permanent magnet. High purity MnBi (>90%) can be routinely produced in large quantity. The obtained powder exhibit 74 emu/g saturation magnetization at room temperature with 9 T applied field. After alignment, the powder exhibits 11.6 MGOe, and the sintered bulk magnet exhibit 7.8 MGOe at room temperature. Thermal stability study shows that the MnBi is stable up to 473 K in air.

  14. Influence of freezing rate changes of MnBi-Bi eutectic microstructure. [effects of space processing

    NASA Technical Reports Server (NTRS)

    Wilcox, W. R.; Doddi, K.; Nair, M.; Larson, D. J.

    1983-01-01

    In an attempt to explain the influence of space processing on the microstructure of MnBi-Bi, eutectic mixtures were directionally solidified with a sudden change of translation rate. The MnBi fiber spacing was able to adapt to the changing freezing rate as predicted by heat transfer computations. Thus the microstructure adapts more rapidly than the freezing rate could be changed in the present experiments.

  15. BiFeO{sub 3}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} heterostructures deposited on spark plasma sintered LaAlO{sub 3} substrates

    SciTech Connect

    Pravarthana, D.; Lacotte, M.; David, A.; Prellier, W.; Trassin, M.; Haw Chu, Jiun; Ramesh, R.; Salvador, P. A.

    2014-02-24

    Multiferroic BiFeO{sub 3} (BFO)/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} heterostructured thin films were grown by pulsed laser deposition on polished spark plasma sintered LaAlO{sub 3} (LAO) polycrystalline substrates. Both polycrystalline LAO substrates and BFO films were locally characterized using electron backscattering diffraction, which confirmed the high-quality local epitaxial growth on each substrate grain. Piezoforce microscopy was used to image and switch the piezo-domains, and the results are consistent with the relative orientation of the ferroelectric variants with the surface normal. This high-throughput synthesis process opens the routes towards wide survey of electronic properties as a function of crystalline orientation in complex oxide thin film synthesis.

  16. Magnetic field effects on reactive sintering of MnBi

    NASA Astrophysics Data System (ADS)

    Abematsu, Ken-ichi; Mitsui, Yoshifuru; Taira, Atsushi; Miyazaki, Daiki; Takaki, Akio; Umetsu, Rie Y.; Takahashi, Kohki; Koyama, Keiichi

    2016-08-01

    Annealing temperature of reactive sintering of MnBi was optimized. The highest fraction of MnBi phase was obtained to be 93wt.% at annealing temperature of 280°C. Magnetic field effects on solid- and liquid-state sintering of MnBi were described. The reacted fraction of MnBi was enhanced by the application of magnetic field of 15 T for solid- state sintering. In contract, reacted fraction was not influenced by magnetic field for liquid-state sintering. Both of in- field solid- and liquid-state sintered samples realized the highly crystal orientation of MnBi phase along the applied magnetic field direction. The Lotgering factor of the MnBi phase was obtained to be 1.0 for both in-field sintered samples, which was an "almost complete" uniaxial orientation. Due to the crystal orientation, anisotropic magnetic properties exhibited. The anisotropy field of the bulk sample was evaluated to be 4 T at room temperature, which also suggested the uniaxial orientation of the sample.

  17. Unexpected Magnetic Domain Behavior in LTP-MnBi

    SciTech Connect

    Nguyen, PK; Jin, S; Berkowitz, AE

    2013-07-01

    Low-temperature-phase MnBi (LTP-MnBi) has attracted much interest as a potential rare-earth-free permanent magnet material because of its high uniaxial magnetocrystalline anisotropy at room temperature, K approximate to 10(7) ergs/cc, and the unusual increase of anisotropy with increasing temperature, with an accompanying increasing coercive force (H-C) with temperature. However, due to the complex Mn-Bi phase diagram, bulk samples of LTP-MnBi with the optimum saturation moment, similar to 75-76 emu/g have been achieved only with zone-refined single crystals. We have prepared polycrystalline samples of LTP-MnBi by induction melting and annealing at 300 degrees C. The moment in 70 kOe is 73.5 emu/g, but H-C is only 50 Oe. This is quite surprising-the high saturation moment indicates the dominating presence of LTP-MnBi. Therefore, an H-C c of some significant fraction of 2K/M-S approximate to 30 kOe would seem reasonable in this polycrystalline sample. By examining "Bitter" patterns, we show that the sample is composed of similar to 50 - 100 mu m crystallites. The randomly oriented crystallites exhibit the variety of magnetic domain structures and orientations expected from the hexagonal-structured MnBi with its strong uniaxial anisotropy. Clearly, the reversal of magnetization in the sample proceeds by the low-field nucleation of reversed magnetization in each crystallite, rather than by a wall-pinning mechanism. When the annealed sample was milled into fine particles, H-C increased by several orders of magnitude, as expected.

  18. Influence of gravity on the microstructure of the MnBi/Bi eutectic

    NASA Technical Reports Server (NTRS)

    Rydzewski, J. H.; Wilcox, W. R.

    1991-01-01

    Directional solidification of MnBiBi eutectic in space produced MnBi fibers that were significantly finer and closer together than when solidification was carried out on earth under otherwise identical conditions. Use of a strong magnetic field during solidification on earth gave about the same results as solidification in space, indicating that convection is the cause of the difference in microstructure. However, 15 years of theoretical and experimental research have failed to reveal the mechanism for this phenomenon. It has been found that temperature gradient has no effect; the concentration field in front of the freezing interface is not altered sufficiently by buoyancy-driven convection to explain it, even if the MnBi fibers project out in front of the Bi matrix; and the Soret effect is not sufficiently large. On the other hand, vigorous forced convection caused a change in microstructure in agreement with theory.

  19. The influences of convection on directional solidification of eutectic Bi/MnBi

    NASA Technical Reports Server (NTRS)

    Larson, David J., Jr.

    1988-01-01

    Eutectic alloys of Bi-Mn were directionally solidified using the Bridgman-Stockbarger technique to determine the influences of gravitationally-driven thermo-solutal convection on the Bi-MnBi rod eutectic. Experiments were conducted that varied the level of convection by varying the growth parameters and growth orientation, by microgravity damping, by applied magnetic field damping, and by imposing forced convection. Peltier interface demarcation and in situ thermocouple measurements were used to monitor interface velocity and thermal gradient and to evaluate interface planarity.

  20. Interlayer electronic transport in CaMnBi2 antiferromagnet

    NASA Astrophysics Data System (ADS)

    Wang, Aifeng; Graf, D.; Wu, Lijun; Wang, Kefeng; Bozin, E.; Zhu, Yimei; Petrovic, C.

    2016-09-01

    We report interlayer electronic transport in CaMnBi2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. The small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi2, which features an anisotropic Dirac cone, our results suggest that magnetic-field-induced changes in interlayer conduction are also present in layered bismuth-based materials with a zero-energy line in momentum space created by the staggered alkaline earth atoms.

  1. Interlayer electronic transport in CaMnBi2 antiferromagnet

    DOE PAGES

    Wang, Aifeng; Graf, D.; Wu, Lijun; ...

    2016-09-12

    Here, we report interlayer electronic transport in CaMnBi2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. Furthermore, the small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi2 , which features an anisotropic Dirac cone, our results suggest that magnetic-field-induced changes in interlayer conduction are also present in layered bismuth-based materials with a zero-energy line in momentum space created by the staggered alkaline earth atoms.

  2. XRD, LPF and FTIR investigation of Mn-Bi alloy

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Patil, Harsha; Jain, Garima

    2014-09-01

    High purity MnBi low temperature phase has been prepared and analyzed using X- ray diffraction, Lorentz-Polarization Factor and Fourier transforms infrared measurement. After synthesis of samples structural characterization has done on samples by X-ray diffraction, which shows that after making the bulk sample is in no single phase MnBi has been prepared by sintering Mn and Bi powder. The X-ray diffraction measurements were carried out using Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube and the wavelength of x-ray was 0.154nm (Cu K-alpha).and x-rays were detected using a fast counting detector based on Silicon strip technology (Bruker LynxEye detector). By Lorentz- Polarization Factor is affecting the relative intensity of diffraction lines on a powder form. The infrared absorption spectra of the alloys and intermetallic compound were measured at room temperature, in the wave number range 4000 to 400 cm-1 by a computerized spectrometer type Jasco FTIR-300 (JAPAN) using the KBr pellet technique. And by FTIR which shows absorption peaks of MnBi alloys.

  3. Phase diagram for Bi1-xCaxMnO3 (x < 0.4)

    NASA Astrophysics Data System (ADS)

    Qin, Yuhai; Tyson, Trevor; Cheong, Sang-Wook; Xu, Xiao-Nong

    2008-03-01

    The multiferroic BiMnO3 system, in which ferroelectronic and ferromagnetic orders can coexist, has attracted much research work in the past years for its potential technological applications. For the more general system Bi1-xCaxMnO3, the phase diagram for the Ca rich region (x > 0.4) has been established[1]. In order to understand the multiferroic behavior near the x=0 system, the hole-doped region (0Bi1-xCaxMnO3, by performing detailed structural (XRD and XAFS), magnetization (ZFC/FC) and electrical measurements on Bi1-xCaxMnO3 (0al, Phys. Rev. B: Condensed Matter and Materials Physics 63, 134412/1 (2001).

  4. Magnetic field effect on the liquidus boundary of Bi-Mn binary system

    NASA Astrophysics Data System (ADS)

    Mitsui, Yoshifuru; Koyama, Keiichi; Oikawa, Katsunari; Watanabe, Kazuo

    2014-10-01

    The magnetic field effect (MFE) on liquidus boundary of Bi-Mn binary system was investigated by differential thermal analysis (DTA) and the computer coupling of phase diagram method (CALPHAD). The liquidus boundary for Bi-18at.%Mn and Bi-24at.%Mn rose clearly by the application of the magnetic fields. The MFE for liquidus boundary temperature Tliq changed from ΔTliq∝B2 to ΔTliq∝B because of the large increase of the peritectic temperature from BiMn and BiMn1.08 by the application of magnetic field.

  5. Structural Investigations of MnO-Bi2O3 and MnO-Bi2O3-As2O3 Glass Systems by IR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ardelean, I.; Todor, Ioana; Păşcuţă, P.; Ioncu, V.

    Glasses from xMnO . (100-x)Bi2O3 and xMnO . (100-x)[Bi2O3 . As2O3] systems, with 0<= x<= 50 mol% were obtained in the same conditions and characterized by IR spectroscopy. The influence of a gradual increase of MnO content on the glass structure and the effect of changing the glass matrix compositions, were projected. The presence and the dependence of the bismuthate structural units BiO3 and BiO6 on the MnO content was analyzed.

  6. Magnetic properties and thermal stability of MnBi/NdFeB hybrid bonded magnets

    NASA Astrophysics Data System (ADS)

    Cao, S.; Yue, M.; Yang, Y. X.; Zhang, D. T.; Liu, W. Q.; Zhang, J. X.; Guo, Z. H.; Li, W.

    2011-04-01

    Magnetic properties and thermal stability were investigated for the MnBi/NdFeB (MnBi = 0, 20, 40, 60, 80, and 100 wt.%) bonded hybrid magnets prepared by spark plasma sintering (SPS) technique. Effect of MnBi content on the magnetic properties of the hybrid magnets was studied. With increasing MnBi content, the coercivity of the MnBi/NdFeB hybrid magnets increases rapidly, while the remanence and maximum energy product drops simultaneously. Thermal stability measurement on MnBi magnet, NdFeB magnet, and the hybrid magnet with 20 wt.% MnBi indicates that both the NdFeB magnet and the MnBi/NdFeB hybrid magnet have a negative temperature coefficient of coercivity, while the MnBi magnet has a positive one. The (BH)max of the MnBi/NdFeB magnet (MnBi = 20 wt.%) is 5.71 MGOe at 423 K, which is much higher than 3.67 MGOe of the NdFeB magnet, indicating a remarkable improvement of thermal stability.

  7. Photoelectrochemical Performance Observed in Mn-Doped BiFeO3 Heterostructured Thin Films

    PubMed Central

    Xu, Hao-Min; Wang, Huanchun; Shi, Ji; Lin, Yuanhua; Nan, Cewen

    2016-01-01

    Pure BiFeO3 and heterostructured BiFeO3/BiFe0.95Mn0.05O3 (5% Mn-doped BiFeO3) thin films have been prepared by a chemical deposition method. The band structures and photosensitive properties of these films have been investigated elaborately. Pure BiFeO3 films showed stable and strong response to photo illumination (open circuit potential kept −0.18 V, short circuit photocurrent density was −0.023 mA·cm−2). By Mn doping, the energy band positions shifted, resulting in a smaller band gap of BiFe0.95Mn0.05O3 layer and an internal field being built in the BiFeO3/BiFe0.95Mn0.05O3 interface. BiFeO3/BiFe0.95Mn0.05O3 and BiFe0.95Mn0.05O3 thin films demonstrated poor photo activity compared with pure BiFeO3 films, which can be explained by the fact that Mn doping brought in a large amount of defects in the BiFe0.95Mn0.05O3 layers, causing higher carrier combination and correspondingly suppressing the photo response, and this negative influence was more considerable than the positive effects provided by the band modulation. PMID:28335343

  8. Micromagnetism of MnBi:FeCo thin films

    NASA Astrophysics Data System (ADS)

    Rana, T. H.; Manchanda, P.; Balamurugan, B.; Kashyap, A.; Gao, T. R.; Takeuchi, I.; Cun, J.; Biswas, S.; Sabirianov, R. F.; Sellmyer, D. J.; Skomski, R.

    2016-02-01

    MnBi:FeCo hard-soft bilayers are investigated using micromagnetic simulations with open boundary conditions and two-dimensional (2D) periodic boundary conditions (PBC). Open and PBC yield similar coercivities of about 1.01 T, in agreement with experiment, but the hysteresis-loop shape is very different in the two theoretical approaches. The difference is ascribed to edge effects, which occur in open boundary conditions but not in PBC and experiment. Near the nucleation field, a curling or vortex mode develops in dots with circular cross sections. The curling mode, which is caused by magnetostatic self-interaction, does not negatively affect the high coercivity of 1.01 T. The magnetostatic self-interaction contributes to the favorable second-quadrant behavior of the MnBi:FeCo thin films.

  9. Bi-substitution-induced magnetic moment distribution in spinel Bi(x)Co(2-x)MnO(4) multiferroic.

    PubMed

    Rajeevan, N E; Kumar, Ravi; Shukla, D K; Thakur, P; Brookes, N B; Chae, K H; Choi, W K; Gautam, S; Arora, S K; Shvets, I V; Pradyumnan, P P

    2009-10-07

    We report the near-edge x-ray absorption spectroscopy (NEXAFS) at the Co/Mn L(3,2) edge and oxygen K edge of the well-characterized Bi-substituted Co(2)MnO(4) multiferroic samples. The evolution of peak features in NEXAFS spectra of the Co/Mn L(3,2) edge and O K edge show the Bi-induced redistribution of magnetic cations (Co/Mn). The variation in valence states of Co and Mn in all the substituted compositions is consistent with the observed ferrimagnetic behaviour of the samples. Magnetization data show the decrease in molecular field complementing the ferrimagnetism. The role of Bi in the enhancement of magnetic interactions as well as the appearance of ferroelectricity in Bi(x)Co(2-x)MnO(4) (0≤x≤0.3) is discussed.

  10. Magnetotransport measurements on Mn-doped Bi2Se3 Thin Films

    NASA Astrophysics Data System (ADS)

    Babakiray, Sercan; Johnson, Trent; Borisov, Pavel; Lederman, David

    2014-03-01

    The intrinsic n type conductivity of bulk topological insulator Bi2Se3 was compensated with Mn dopant to increase the resistivity. In addition, the magnetic character of Mn ions causes a gap opening of the corresponding Dirac cone surface states. We investigated the effect of the Mn on crystal structure as well as the transport and magnetic properties of Bi2-xMnxSe3 thin films grown by molecular beam epitaxy on Al2O3 (0001) substrates. Characteristic features in the form of the Kondo effect and weak anti-localization were observed at different Mn concentrations up to temperatures of 50 K accompanied by enhanced resistance and reduced carrier mobility. The phase coherence length of the two-dimensional sheet conductance decreased with increasing Mn-concentration, however the protected surface states were still present up to x =0.063. This work was supported by a Research Challenge Grant from West Virginia Higher Education Policy Commission (HEPC.dsr.12.29). Some of the work was performed using the West Virginia University Shared Research Facilities.

  11. Magnetic field effects on liquid-phase reactive sintering of MnBi

    NASA Astrophysics Data System (ADS)

    Mitsui, Yoshifuru; Abematsu, Ken-ichi; Umetsu, Rie Y.; Takahashi, Kohki; Koyama, Keiichi

    2016-02-01

    Magnetic fields effects on liquid-phase reaction sintering on MnBi were investigated. The liquid-phase reaction was so fast even in a zero field that the fraction of in-field sintered ferromagnetic MnBi phase was independent of the external magnetic field. However, the ferromagnetic MnBi crystals in the in-field sintered sample were oriented along the external magnetic field direction. The Lotgering factor of the in-field sintered sample was 0.99. This result indicated that almost completely anisotropic MnBi phase could be obtained by in-field liquid phase reactive sintering.

  12. In situ investigation of spinodal decomposition in hypermonotectic Al Bi and Al Bi Zn alloys

    NASA Astrophysics Data System (ADS)

    Schaffer, P. L.; Mathiesen, R. H.; Arnberg, L.; Di Sabatino, M.; Snigirev, A.

    2008-05-01

    Spinodal decomposition of hypermonotectic Al-6 wt.%Bi, Al-8 wt.%Bi and Al-6 wt.%Bi-8 wt.%Zn alloys has been investigated using synchrotron radiography. In the case of the 6 and 8 wt.%Bi binary alloys undercoolings of 70 and 110 K, respectively, were required to initiate the L→L1+L2 reaction, which appeared to occur very close to the monotectic reaction temperature. The nucleated L2 droplets were set in collective size-dependent motion by forces coupled to external fields (gravity and imposed temperature gradient) as well as forces arising due to internal fluctuations of the system. With experimental conditions similar to those realized during strip casting of the same materials, it was found that the size-dependant droplet velocity field combined with Stokes drag at the L1-L2 interfaces as well as attractive and repulsive diffusion-coupling between adjacent L2 droplets, yield complex meso- to microscale hydrodynamics. The hydrodynamics are the dominating mechanisms for L2 droplet coagulation, and are accordingly decisive for the final size distribution and geometrical dispersion of the soft Bi-rich component in the cast material. A different decomposition mode was observed in the Al-6 wt.%Bi-8 wt.%Zn ternary alloy, with the L2 droplets undergoing an immiscible-miscible-immiscible transition. In contrast to what was found for the binaries, L2 domains formed at relatively small undercoolings, and very little droplet motion was observed, as all L2 domains nucleated and remained on the crucible walls until they encroached on the monotectic front. At small distances from the monotectic front a Zn-rich solute boundary layer preceding the α-Al, caused the L2 domains to dissolve as Bi-Zn-Al regains complete miscibility upon reaching a critical Zn-concentration. In the shallow mush region behind the monotectic reaction, a high Zn solid solubility and a relatively fast diffusion of Zn in α-Al combine to cause a rapid diminishing Zn concentration in the mush liquid

  13. Directional solidification of Bi-Mn alloys using an applied magnetic field

    NASA Technical Reports Server (NTRS)

    Decarlo, J. L.; Pirich, R. G.

    1987-01-01

    Off-eutectic compositions of Bi-Mn were directionally solidified in applied transverse magnetic fields up to 3 kG, to determine the effects on thermal and solutal convection. Plane front directional solidification of eutectic and near-eutectic Bi-Mn results in a two-phase rodlike morphology consisting of ferromagnetic MnBi rods in a Bi solid solution matrix. Compositions of either side of the eutectic were studied in growth orientations vertically up and down. Temperature gradient was monitored during growth by means of an in-situ thermocouple. For Bi-rich compositions, the magnetic field appeared to increase mixing as determined from thermal, morphological, chemical, and magnetic analyses. For Mn-rich compositions, morphological and chemical analyses suggest some reduction in mixing due to application of the magnetic force. The capability for carrying out directional solidification of Bi-Mn in high longitudinal magnetic fields was established.

  14. Response of MnBi-Bi eutectic to freezing rate changes

    NASA Technical Reports Server (NTRS)

    Nair, M.; Fu, T.-W.; Wilcox, W. R.; Doddi, K.; Ravishankar, P. S.; Larson, D.

    1982-01-01

    Reference is made to a study by Fu and Wilcox (1981), which treated theoretically the influence on freezing rate of sudden changes in translation rate in the Bridgman-Stockbarger technique. This treatment is extended here to a linear ramped translation rate and an oscillatory freezing rate. It is found that oscillations above a few hertz are highly damped in small-diameter apparatus. An experimental test is carried out of the theoretical predictions for a sudden change of translation rate. The MnBi-Bi eutectic is solidified with current-induced interface demarcation. The experimental results accord reasonably well with theory if the silica ampoule wall is assumed to either (1) contribute only a resistance to heat exchange between the sample and the furnace wall or (2) transmit heat effectively in the axial direction by radiation. In an attempt to explain the fact that a finer microstructure is obtained in space, MnBi-Bi microstructure is determined when the freezing rate is increased or decreased rapidly. Preliminary results suggest that fiber branching does not occur as readily as fiber termination.

  15. Structural and ferromagnetic properties of an orthorhombic phase of MnBi stabilized with Rh additions

    SciTech Connect

    Taufour, Valentin; Thimmaiah, Srinivasa; March, Stephen; Saunders, Scott; Sun, Kewei; Lamichhane, Tej Nath; Kramer, Matthew J.; Bud’ko, Sergey L.; Canfield, Paul C.

    2015-07-28

    The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT MnBi). The properties of the HT MnBi, which is stable between 613 and 719 K, have not been studied in detail because of its transformation to the stable low-temperature MnBi (LT MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn1.0625–xRhxBi [x=0.02(1)] adopts a new superstructure of the NiAs/Ni2In structure family. It is ferromagnetic below a Curie temperature of 416 K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT MnBi. The saturation magnetization is approximately 3μB/f.u. at low temperatures. Thus, while this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.

  16. Structural and ferromagnetic properties of an orthorhombic phase of MnBi stabilized with Rh additions

    DOE PAGES

    Taufour, Valentin; Thimmaiah, Srinivasa; March, Stephen; ...

    2015-07-28

    The article addresses the possibility of alloy elements in MnBi which may modify the thermodynamic stability of the NiAs-type structure without significantly degrading the magnetic properties. The addition of small amounts of Rh and Mn provides an improvement in the thermal stability with some degradation of the magnetic properties. The small amounts of Rh and Mn additions in MnBi stabilize an orthorhombic phase whose structural and magnetic properties are closely related to the ones of the previously reported high-temperature phase of MnBi (HT MnBi). The properties of the HT MnBi, which is stable between 613 and 719 K, have notmore » been studied in detail because of its transformation to the stable low-temperature MnBi (LT MnBi), making measurements near and below its Curie temperature difficult. The Rh-stabilized MnBi with chemical formula Mn1.0625–xRhxBi [x=0.02(1)] adopts a new superstructure of the NiAs/Ni2In structure family. It is ferromagnetic below a Curie temperature of 416 K. The critical exponents of the ferromagnetic transition are not of the mean-field type but are closer to those associated with the Ising model in three dimensions. The magnetic anisotropy is uniaxial; the anisotropy energy is rather large, and it does not increase when raising the temperature, contrary to what happens in LT MnBi. The saturation magnetization is approximately 3μB/f.u. at low temperatures. Thus, while this exact composition may not be application ready, it does show that alloying is a viable route to modifying the stability of this class of rare-earth-free magnet alloys.« less

  17. Interlayer electronic transport in CaMnBi>2mn> antiferromagnet

    SciTech Connect

    Wang, Aifeng; Graf, D.; Wu, Lijun; Wang, Kefeng; Bozin, E.; Zhu, Yimei; Petrovic, C.

    2016-09-12

    Here, we report interlayer electronic transport in CaMnBi2 single crystals. Quantum oscillations and angular magnetoresistance suggest coherent electronic conduction and valley polarized conduction of Dirac states. Furthermore, the small cyclotron mass, high mobility of carriers, and nontrivial Berry's phase are consistent with the presence of Dirac fermions on the side wall of the warped cylindrical Fermi surface. Similarly to SrMnBi2 , which features an anisotropic Dirac cone, our results suggest that magnetic-field-induced changes in interlayer conduction are also present in layered bismuth-based materials with a zero-energy line in momentum space created by the staggered alkaline earth atoms.

  18. Light-controlled resistive switching memory of multiferroic BiMnO3 nanowire arrays.

    PubMed

    Sun, Bai; Li, Chang Ming

    2015-03-14

    A multiferroic BiMnO3 nanowire array was prepared using a hydrothermal process and its resistive switching memory behaviors were further investigated. The prominent ferroelectricity can be well controlled by white-light illumination, thus offering an excellent light-controlled resistive switching memory device using a Ag/BiMnO3/Ti structure at room temperature.

  19. On the synthesis and microstructure analysis of high performance MnBi

    NASA Astrophysics Data System (ADS)

    Chen, Yu-Chun; Sawatzki, Simon; Ener, Semih; Sepehri-Amin, Hossein; Leineweber, Andreas; Gregori, Giuliano; Qu, Fei; Muralidhar, Shreyas; Ohkubo, Tadakatsu; Hono, Kazuhiro; Gutfleisch, Oliver; Kronmüller, Helmut; Schütz, Gisela; Goering, Eberhard

    2016-12-01

    Highly anisotropic MnBi powder with over 90 wt% low-temperature phase can be prepared using conventional arc-melting and 2 hour-low energy ball milling (BM) followed by magnetic separation. After proper alignment, the purified Mn55Bi45(Mn45Bi55) powder show remarkable magnetic properties: mass remanence of 71(65) Am2/kg and coercivity of 1.23(1.18) T at 300 K. The nominal maximum energy product of 120 kJ/m3 is achieved in the purified 2h-BM Mn55Bi45 powder, close to theoretical value of 140.8 kJ/m3. The Mn55Bi45(Mn45Bi55) bulk magnets show the highest volume remanence of 0.68(0.57) T at 300 K, while they were consolidated at 573(523) K by a pressure of 200 MPa for 5 minutes using hot-compaction method. In addition to the observed grain size, the coercivity of the hot-compacted samples at 300 K was found to be strongly related to the amount of metallic Mn and Bi residue at the grain-boundary. Our study proves that the magnetic properties of the Mn45Bi55 bulk magnets are stable up to 500 K, and the nominal (BH)max values are still above 40 kJ/m3 at 500 K showing the potential ability for high-temperature applications.

  20. Exchange coupling in MnBi/Fe-Co thin film bilayers

    NASA Astrophysics Data System (ADS)

    Fang, Lei; Gao, Tieren; Fackler, Sean; Maruyama, Shingo; Takeuchi, Ichiro; Cui, Jun; Krammer, M. J.; Johnson, Duane; Arenholz, Elke; Borchers, Julie; Kirby, Brian; Ratcliff, William; Skomski, Ralph; Lofland, Samuel

    2014-03-01

    To achieve enhanced energy products of MnBi for rare-earth free permanent magnet applications, we studied the exchange coupled soft/hard bilayers based on MnBi films. By using DC magnetron sputtering, we fabricated pure MnBi films with magnetization of 500 emu/cc and coercivity of 1.6 T. A (BH)max of 6.2 MGOe is obtained for pure MnBi films. A large enhancement in (BH)max due to exchange coupling in MnBi/Fe-Co bilayers is observed with Fe-Co thicknesses between 2 and 5 nm. The highest (BH)max obtained is 14.0 MGOe at room temperature with a single phase magnetization curve for a MnBi (20 nm)/Co (2 nm) bilayer. TEM and XPS studies indicate there is no oxidation between soft/hard interface. The XMCD results show that the soft moments of Fe/Co at a thickness of 2 nm are perpendicular to the MnBi plane, indicating nearly perfect hard-soft coupling. Moreover, a micromagnetic calculation on perpendicularly-coupled MnBi/Fe-Co bilayers suggests a critical coupling thickness of 4 nm of the soft layer. We will also discuss results from polarized neutron reflectometry measurements performed on the bilayers. This work is funded by ARPA-E.

  1. Mechanical and electrical properties of low temperature phase MnBi

    NASA Astrophysics Data System (ADS)

    Jiang, Xiujuan; Roosendaal, Timothy; Lu, Xiaochuan; Palasyuk, Olena; Dennis, Kevin W.; Dahl, Michael; Choi, Jung-Pyung; Polikarpov, Evgueni; Marinescu, Melania; Cui, Jun

    2016-01-01

    Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi magnets for motor applications. Physical properties other than magnetic ones could significantly affect motor design. Here, we report results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their temperature dependence. A MnBi ingot was prepared using an arc melting technique and subsequently underwent grinding, sieving, heat treatment, and cryomilling. The resultant powders with a particle size of ˜5 μm were magnetically aligned, cold pressed, and sintered at a predefined temperature. Micro-hardness testing was performed on a part of original ingot and we found that the hardness of MnBi was 109 ± 15 HV. The sintered magnets were subjected to compressive testing at different temperatures and it was observed that a sintered MnBi magnet fractured when the compressive stress exceeded 193 MPa at room temperature. Impedance spectra were obtained using electrochemical impedance spectroscopy at various temperatures and we found that the electrical resistance of MnBi at room temperature was about 6.85 μΩ m.

  2. Mechanical and Electrical Properties of Low Temperature Phase MnBi

    SciTech Connect

    Jiang, Xiujuan; Roosendaal, Timothy J.; Lu, Xiaochuan; Palasyuk, Olena; Dennis, Kevin W.; Dahl, Michael E.; Choi, Jung-Pyung; Polikarpov, Evgueni; Marinescu, Melania; Cui, Jun

    2016-01-21

    The low temperature phase (LTP) MnBi is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and its large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have started to consider MnBi magnet for motor applications. In addition to the magnetic properties, there are other physical properties that could significantly affect a motor design. Here, we report the results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their dependence on temperature. We found at room temperature the sintered MnBi magnet fractures when the compression stress exceeds 193 MPa; and its room temperature electric resistance is about 6.85 μΩ-m.

  3. Ferromagnetism below 10K in Mn-doped BiTe

    NASA Astrophysics Data System (ADS)

    Bos, J. W. G.; Lee, M.; Morosan, E.; Zandbergen, H. W.; Lee, W. L.; Ong, N. P.; Cava, R. J.

    2006-11-01

    Ferromagnetism is observed below 10K in [Bi0.75Te0.125Mn0.125]Te . This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi antisite occupancy in the Bi2Te3 blocks. These TeBi antisite defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the solubility is limited to x=0.067 , while the latter has xmax=0.125 . The magnetism in [Bi1-xMnx]Te changes little with x , while that for [Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x>0.067 . Magnetic hysteresis and the anomalous Hall effect are observed for the ferromagnetic samples.

  4. Effect of ball milling and heat treatment process on MnBi powders magnetic properties

    SciTech Connect

    Xie, Wei; Polikarpov, Evgueni; Choi, Jung-Pyung; Bowden, Mark E.; Sun, Kewei; Cui, Jun

    2016-09-01

    The metallic compound MnBi has high intrinsic coercivity with large positive temperature coefficient. The coercivity of MnBi exceeds 12 kOe and 26 kOe at 300 K and 523 K, respectively. Hence MnBi is a good candidate for the hard phase in exchange coupled nanocomposite magnets. In order to maximize the loading of the soft phase, the size of the MnBi particle has to be close to 500 nm, the size of single magnetic domain. Low energy milling is the common method to reduce MnBi particle size. However, only 3-7 mu m size particle can be achieved without significant decomposition. Here, we report our effort on preparing submicron MnBi powders using traditional powder metallurgy methods. Mn55Bi45 magnetic powders were prepared using arc melting method, followed by a series of thermal-mechanical treatment to improve purity, and finished with low energy ball milling at cryogenic temperature to achieve submicron particle size. The Mn55Bi45 powders were decomposed during ball milling process and recovered during 24 h 290 degrees C annealing process. With increasing ball-milling time, the saturation magnetization of MnBi decreases, while the coercivity increases. Annealing after ball milling recovers some of the magnetization, indicating the decomposition occurred during the ball-milling process can be reversed. The coercivity of Mn55Bi45 powders are also improved as a result of the heat treatment at 290 degrees C for 24 h. The world record magnetization 71.2 emu/g measured applying a field of 23 kOe has been achieved via low energy ball mill at room temperature

  5. Interplay of Dirac electrons and magnetism in CaMnBi2 and SrMnBi2.

    PubMed

    Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-Long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming

    2016-12-16

    Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin-Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices.

  6. Interplay of Dirac electrons and magnetism in CaMnBi2 and SrMnBi2

    NASA Astrophysics Data System (ADS)

    Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-Long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming

    2016-12-01

    Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin-Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices.

  7. Interplay of Dirac electrons and magnetism in CaMnBi2 and SrMnBi2

    PubMed Central

    Zhang, Anmin; Liu, Changle; Yi, Changjiang; Zhao, Guihua; Xia, Tian-long; Ji, Jianting; Shi, Youguo; Yu, Rong; Wang, Xiaoqun; Chen, Changfeng; Zhang, Qingming

    2016-01-01

    Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. Here we report on a two-magnon Raman scattering study of AMnBi2 (A=Ca, Sr), a prototypical magnetic Dirac system comprising alternating Dirac carrier and magnetic layers. We present the first accurate determination of the exchange energies in these compounds and, by comparison with the reference compound BaMn2Bi2, we show that the Dirac carrier layers in AMnBi2 significantly enhance the exchange coupling between the magnetic layers, which in turn drives a charge-gap opening along the Dirac locus. Our findings break new grounds in unveiling the fundamental physics of magnetic Dirac materials, which offer a novel platform for probing a distinct type of spin–Fermion interaction. The results also hold great promise for applications in magnetic Dirac devices. PMID:27982036

  8. Enhanced photovoltaic properties in bilayer BiFeO3/Bi-Mn-O thin films

    NASA Astrophysics Data System (ADS)

    Chakrabartty, Joyprokash; Nechache, Riad; Harnagea, Catalin; Li, Shun; Rosei, Federico

    2016-05-01

    We report an external solar power conversion efficiency of ˜1.43% in BiFeO3(BFO)/BiMnO3(BMO) bilayer thin films. Both films are epitaxially grown on (111) oriented niobium doped SrTiO3 (NSTO) single crystal substrates by pulsed laser deposition. By illuminating the BFO/BMO films under 1 Sun (AM 1.5 G), we found a remarkably high fill factor of ˜0.72, much higher than values reported for devices based on BFO or BMO alone. In addition, we demonstrate that the photocurrent density and photovoltage are tunable by changing the polarization direction in the BFO/BMO bilayer, as confirmed by the macroscopic polarization-voltage (P-V) hysteresis loop. This effect is described in terms of a more favorable energy band alignment of the electrode/bilayer/NSTO heterostructure junction, which controls photocarrier separation.

  9. High-spin configuration of Mn in Bi2Se3 three-dimensional topological insulator

    NASA Astrophysics Data System (ADS)

    Wolos, Agnieszka; Drabinska, Aneta; Borysiuk, Jolanta; Sobczak, Kamil; Kaminska, Maria; Hruban, Andrzej; Strzelecka, Stanislawa G.; Materna, Andrzej; Piersa, Miroslaw; Romaniec, Magdalena; Diduszko, Ryszard

    2016-12-01

    Electron paramagnetic resonance was used to investigate Mn impurity in Bi2Se3 topological insulator grown by the vertical Bridgman method. Mn in high-spin S=5/2, Mn2+, configuration was detected regardless of the conductivity type of the host material. This means that Mn2+(d5) energy level is located within the valence band, and Mn1+(d6) energy level is outside the energy gap of Bi2Se3. The electron paramagnetic resonance spectrum of Mn2+ in Bi2Se3 is characterized by the isotropic g-factor |g|=1.91 and large axial parameter D=-4.20 GHz h. This corresponds to the zero-field splitting of the Kramers doublets equal to 8.4 GHz h and 16.8 GHz h, respectively, which is comparable to the Zeeman splitting for the X-band. Mn in Bi2Se3 acts as an acceptor, effectively reducing native-high electron concentration, compensating selenium vacancies, and resulting in p-type conductivity. However, Mn-doping simultaneously favors formation of native donor defects, most probably selenium vacancies. For high Mn-doping it may lead to the resultant n-type conductivity related with strong non-stoichiometry and degradation of the crystal structure - switching from Bi2Se3 to BiSe phase.

  10. Strong anisotropy of Dirac cones in SrMnBi2 and CaMnBi2 revealed by angle-resolved photoemission spectroscopy.

    PubMed

    Feng, Ya; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Xie, Zhuojin; Yi, Hemian; Liang, Aiji; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Dai, Xi; Fang, Zhong; Zhou, X J

    2014-06-20

    The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net.

  11. Strong Anisotropy of Dirac Cones in SrMnBi2 and CaMnBi2 Revealed by Angle-Resolved Photoemission Spectroscopy

    PubMed Central

    Feng, Ya; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Xie, Zhuojin; Yi, Hemian; Liang, Aiji; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Dai, Xi; Fang, Zhong; Zhou, X. J.

    2014-01-01

    The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net. PMID:24947490

  12. Magnetic and thermoelectric properties of three different atomic ratio of Bi/Mn in BiMn2O5: DFT approach

    NASA Astrophysics Data System (ADS)

    Khan, Wilayat; Reshak, A. H.; Rafezi Ahmad, Khairel; Alahmed, Z. A.

    2014-11-01

    Electronic structure and magnetic properties of the three different samples of BiMn2O5, are calculated using the density functional theory (DFT). These samples have different Bi/Mn concentration. For simplicity, we suggest to call them as A, B and C. The calculated band structures show half metallicity for all samples, and possess 100% spin polarization at the Fermi level. The spin up/down density of states are calculated using Engel-Vosko generalized gradient approximation (EV-GGA). We have discussed the effect of Mn magnetic moment (μB) on the electronic and magnetic properties of the entire samples. The temperature dependent thermoelectric properties like electrical and thermal conductivity, Seebeck coefficient and power factor are also calculated, employing the Boltzmann transport theory under the BoltzTraP code. Our results indicated that these properties are strongly dependent on Bi/Mn concentration.

  13. Multiferroic, magnetoelectric and optical properties of Mn doped BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Chauhan, Sunil; Kumar, Manoj; Chhoker, Sandeep; Katyal, S. C.; Singh, Hemant; Jewariya, Mukesh; Yadav, K. L.

    2012-03-01

    Mn doped BiFeO3 (5, 10 and 15 mol%) nanoparticles were synthesized using sol-gel technique. The influence of Mn doping on structural, dielectric, magnetic, magnetoelectric and optical properties of BiFeO3 was studied. Rietveld refinement of XRD patterns showed rhombohedral to orthorhombic phase transition for 15 mol% Mn doped BiFeO3 sample. Magnetic measurements revealed the enhancement of ferromagnetic property with increasing Mn doping in BiFeO3. The characteristic dielectric anomaly, expected in the vicinity of antiferromagnetic transition temperature TN (Neel temperature) was found in all Mn doped BiFeO3 samples. The magnetoelectric coupling was evidenced by the change in capacitance with the change in the applied magnetic field. On increasing Mn concentration from 5 to 15 mol% in BiFeO3, a change in magnetocapacitance from 1.46% to 2.6% showed the improvement of multiferroic properties. In order to explore the optical properties of Mn doped BiFeO3 nanoparticles, their photoluminescent properties were also investigated.

  14. Large linear magnetoresistance in a new Dirac material BaMnBi2

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Yan; Yu, Qiao-He; Xia, Tian-Long

    2016-10-01

    Dirac semimetal is a class of materials that host Dirac fermions as emergent quasi-particles. Dirac cone-type band structure can bring interesting properties such as quantum linear magnetoresistance and large mobility in the materials. In this paper, we report the synthesis of high quality single crystals of BaMnBi2 and investigate the transport properties of the samples. BaMnBi2 is a metal with an antiferromagnetic transition at T N = 288 K. The temperature dependence of magnetization displays different behavior from CaMnBi2 and SrMnBi2, which suggests the possible different magnetic structure of BaMnBi2. The Hall data reveals electron-type carriers and a mobility μ(5 K) = 1500 cm2/V·s. Angle-dependent magnetoresistance reveals the quasi-two-dimensional (2D) Fermi surface in BaMnBi2. A crossover from semiclassical MR ˜ H 2 dependence in low field to MR ˜ H dependence in high field, which is attributed to the quantum limit of Dirac fermions, has been observed in magnetoresistance. Our results indicate the existence of Dirac fermions in BaMnBi2. Project supported by the National Natural Science Foundation of China (Grant No. 11574391), the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant No. 14XNLQ07).

  15. In-situ Observation and Differential Thermal Analysis of MnBi in High Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Miyazaki, Daiki; Mitsui, Yoshifuru; Abematsu, Ken-ichi; Takahashi, Kohki; Watanabe, Kazuo; Uda, Satoshi; Koyama, Keiichi

    For investigating in-field process of melting and solidification visually and quantitatively, in-situ observation system with differential thermal analysis (DTA) utilized in high temperature and in high magnetic field was developed. Decomposition processes of the bulk sample of ferromagnetic MnBi were directly observed with collecting DTA data under high magnetic field of 10 T for the 290-770 K temperature range. When the temperature was over decomposition point (ferromagnetic MnBi → paramagnetic Mn1.08Bi + liquid), liquid phase appeared on the sample surface. Furthermore, when the temperature was over peritectic temperature (∼ 700 K: paramagnetic Mn1.08BiMn + liquid), the sample surface was broken and a large quantity of the liquid phase appeared from the sample. The in-situ observation also suggested that the decomposition temperature increased from 620 K for a zero field to 638 K for a magnetic field of 10 T.

  16. Experimental and density functional study of Mn doped Bi2Te3 topological insulator

    NASA Astrophysics Data System (ADS)

    Ghasemi, A.; Kepaptsoglou, D.; Figueroa, A. I.; Naydenov, G. A.; Hasnip, P. J.; Probert, M. I. J.; Ramasse, Q.; van der Laan, G.; Hesjedal, T.; Lazarov, V. K.

    2016-12-01

    We present a nanoscale structural and density functional study of the Mn doped 3D topological insulator Bi2Te3. X-ray absorption near edge structure shows that Mn has valency of nominally 2+. Extended x-ray absorption fine structure spectroscopy in combination with electron energy loss spectroscopy (EELS) shows that Mn is a substitutional dopant of Bi and Te and also resides in the van der Waals gap between the quintuple layers of Bi2Te3. Combination of aberration-corrected scanning transmission electron microscopy and EELS shows that Mn substitution of Te occurs in film regions with increased Mn concentration. First-principles calculations show that the Mn dopants favor octahedral sites and are ferromagnetically coupled.

  17. Electrical Transport Properties of Mn doped Bi2Se3 Thin Films

    NASA Astrophysics Data System (ADS)

    Babakiray, Sercan; Johnson, Trent; Borisov, Pavel; Lederman, David

    2015-03-01

    Magnetic impurity doping in topological insulators manifest itself with a gap opening in the Dirac cone as a result of breaking the time reversal symmetry. Moreover, the magnetic impurities affect the structural and quantum transport properties of topological insulators by increasing the disorder and by changing the bulk charge carrier type, charge carrier density and Hall mobility. Here, we investigated the effect of Mn doping on the structural and electrical transport properties of Bi2-xMnxSe3 thin films which are 12 quintuple layers thick and grown on Al2O3 (0001) single crystal substrates via molecular beam epitaxy (MBE). Hikami-Larkin-Nagaoka (HLN) formalism was used to study the weak antilocalization (WAL). Increasing Mn doping concentration was found to increase the bulk charge carrier density and to decrease the Hall mobility. A decrease was also observed in the phase coherence length related to WAL as a function of Mn content x. Values of another WAL parameter, the pre-factor alpha, showed that the top and bottom surfaces were coupled through the bulk conducting channels. The temperature dependence of phase coherence length indicated the electrical transport was dominated by 2D electron-electron scattering for the undoped, and by bulk weak localization effects for the Mn doped samples, respectively.

  18. High-Performance MnBi Alloy Prepared Using Profiled Heat Treatment

    SciTech Connect

    Nguyen, Van V.; Poudyal, Narayan; Liu, Xubo; Liu, J. Ping; Sun, Kewei; Kramer, Matthew J.; Cui, Jun

    2014-12-01

    The profiled heat treatment (PHT) method has been used to synthesize MnBi alloys with high-purity low-temperature phase (LTP). In the PHT method, the arc-melted MnBi alloy was remelted then slowly cooled by a pseudo-equilibrium solidification process to promote the formation of LTP phase. The PHT-treated MnBi alloys had an LTP phase up to 94 wt.% and a magnetization of 73 emu/g under a field of 9 T. Scanning electron microscopy showed that there exist some micrometer-sized Mn-rich inclusions in the LTP matrix of the PHT MnBi alloy. The PHT MnBi alloys were crushed into powders with an average size of ~3 μm by low-energy ball milling. These MnBi powders were aligned in an 18 kOe field and warm compacted into a bulk magnet at 300 °C for 30 min. The magnet had a density of 8.2 g/cm3 and magnetic properties of Ms = 6.7 kG, Mr = 5.3 kGs, i Hc = 5 kOe, and (BH)max = 6.1 MGOe

  19. Covalent bonds in AlMnSi icosahedral quasicrystalline approximant

    PubMed

    Kirihara; Nakata; Takata; Kubota; Nishibori; Kimura; Sakata

    2000-10-16

    Electron density distributions were obtained using the maximum entropy method with synchrotron radiation powder data. In the metallic Al12Re, metallic bonding was observed for the icosahedral Al12 cluster with central Re atom. In the nonmetallic alpha-AlMnSi 1/1 approximant, covalent bonds were found in the electron density distribution of the Mackay icosahedral cluster without central atom. Rather than the Hume-Rothery mechanism, the covalency of Al (Si) icosahedron and that between Al (Si) and Mn atoms is considered to be the origin of the pseudogap and nonmetallic behavior of alpha-AlMnSi.

  20. Preparation and Magnetic Properties of MnBi/Co Nanocomposite Magnets

    NASA Astrophysics Data System (ADS)

    Nguyen, Truong Xuan; Vuong, Oanh Kim Thi; Nguyen, Hieu Trung; Nguyen, Vuong Van

    2017-02-01

    The method of synthesis and the magnetic properties of MnBi/Co nanocomposite magnets prepared with a combination of the magnetically hard MnBi alloy and semi-hard Co nanowires (CoNWs) have been investigated. The MnBi alloys were produced by arc-melting and temperature-gradient-driven annealing techniques. The CoNWs with high spontaneous magnetization M s (125 emu/g) and large aspect ratio α (5 ÷ 10) were synthesized by the solvothermal method. The nanocomposite MnBi/Co powder mixtures were cold ball-milled, aligned in an 18-kOe-field and warm-compacted into bulk magnets at 300°C under a uniaxial pressure of 2000 psi for 10 min. The magnetization and coercivity of the nanocomposite magnets were improved due to the intrinsic high magnetization and shape anisotropy of the CoNWs. The energy product, (BH)max, of the MnBi/Co nanocomposite magnets with 15 wt.% CoNWs reached its highest value of 4.8 MGOe. The simulation of magnetic properties of MnBi/Co magnets is also discussed in detail.

  1. Chemical vapor transport and characterization of MnBi2Se4

    NASA Astrophysics Data System (ADS)

    Nowka, Christian; Gellesch, Markus; Enrique Hamann Borrero, Jorge; Partzsch, Sven; Wuttke, Christoph; Steckel, Frank; Hess, Christian; Wolter, Anja U. B.; Teresa Corredor Bohorquez, Laura; Büchner, Bernd; Hampel, Silke

    2017-02-01

    Layered metal chalcogenides such as MnBi2Se4 are interesting candidates for a wide field of applications such as for thermo- and photoelectrics. High-quality single crystals are necessary in order to investigate their properties which can be prepared by chemical vapor transport (CVT). The CVT of MnBi2Se4 has not been investigated until this point and is subject of the presented paper. We obtained needle-like MnBi2Se4 single crystals with a length up to 15 mm. The magnetic characterization has shown an antiferromagnetic transition around 14 K. Additionally, electrical transport described MnBi2Se4 as a narrow band-gap semiconductor (EGap=0.15 eV). Thermodynamic data for MnBi2Se4 at room temperature were determined to H ° = - 305 KJ ·mol-1 , S=321 J K-1·mol-1 and Cp = 167.568 + 25.979 ·10-3 · TJ ·K-1 ·mol-1 , respectively. Our results on CVT-grown single crystals confirm reported data from literature and complete the data set for MnBi2Se4.

  2. Magnetic self-assembly for the synthesis of magnetically exchange coupled MnBi/Fe–Co composites

    SciTech Connect

    Xu, Xia; Hong, Yang-Ki; Park, Jihoon; Lee, Woncheol; Lane, Alan M.; Cui, Jun

    2015-11-15

    Exchange coupled hard/soft MnBi/Fe–Co core/shell structured composites were synthesized using a magnetic self-assembly process. MnBi particles were prepared by arc-melting, and Fe–Co nanoparticles were synthesized by an oleic acid assisted chemical reduction method. Grinding a mixture of micron-sized MnBi and Fe–Co nanoparticles in hexane resulted in MnBi/Fe–Co core/shell structured composites. The MnBi/Fe–Co (95/5 wt%) composites showed smooth magnetic hysteresis loops, enhanced remanent magnetization, and positive values in the ΔM curve, indicating exchange coupling between MnBi and Fe–Co particles. - Graphical abstract: Both MnBi and Fe–Co particles were dispersed in hexane for grinding. Because of the oleic acid used during the Fe–Co nanoparticle synthesis, they could be well dispersed in hexane. During the grinding, the size of MnBi particles was decreased, hexane was evaporated, and the Fe–Co nanoparticles were concentrated in the solvent and magnetically attracted by MnBi particles, forming a core/shell structure. - Highlights: • Exchange coupled MnBi/Fe–Co composites are synthesized through magnetic selfassembly. • Magnetic exchange coupling is demonstrated by smooth magnetic hysteresis loops, enhanced remanent magnetization, and dominant positive peak in the ΔM curve. • The experimental results in magnetic properties are close to the theoretical calculation results.

  3. High Curie temperature Bi(1.85)Mn(0.15)Te3 nanoplates.

    PubMed

    Cheng, Lina; Chen, Zhi-Gang; Ma, Song; Zhang, Zhi-dong; Wang, Yong; Xu, Hong-Yi; Yang, Lei; Han, Guang; Jack, Kevin; Lu, Gaoqing Max; Zou, Jin

    2012-11-21

    Bi(1.85)Mn(0.15)Te(3) hexagonal nanoplates with a width of ~200 nm and a thickness of ~20 nm were synthesized using a solvothermal method. According to the structural characterization and compositional analysis, the Mn(2+) and Mn(3+) ions were found to substitute Bi(3+) ions in the lattice. High-level Mn doping induces significant lattice distortion and decreases the crystal lattice by 1.07% in the a axis and 3.18% in the c axis. A high ferromagnetic state with a Curie temperature of ~45 K is observed in these nanoplates due to Mn(2+) and Mn(3+) ion doping, which is a significant progress in the field of electronics and spintronics.

  4. τ-MnAl with high coercivity and saturation magnetization

    SciTech Connect

    Wei, J. Z.; Song, Z. G.; Yang, Y. B.; Liu, S. Q.; Du, H. L.; Han, J. Z.; Zhou, D.; Wang, C. S.; Yang, Y. C.; Franz, A.; Többens, D.; Yang, J. B.

    2014-12-15

    In this paper, high purity τ-Mn{sub 54}Al{sub 46} and Mn{sub 54−x}Al{sub 46}C{sub x}alloys were successfully prepared using conventional arc-melting, melt-spinning, and heat treatment process. The magnetic and the structural properties were examined using x-ray diffraction (XRD), powder neutron diffraction and magnetic measurements. A room temperature saturation magnetization of 650.5 kAm{sup -1}, coercivity of 0.5 T, and a maximum energy product of (BH){sub max} = 24.7 kJm{sup -3} were achieved for the pure Mn{sub 54}Al{sub 46} powders without carbon doping. The carbon substituted Mn{sub 54−x}Al{sub 46}C{sub x}, however, reveals a lower Curie temperature but similar saturation magnetization as compared to the carbon-free sample. The electronic structure of MnAl shows that the Mn atom possesses a magnetic moment of 2.454 μ{sub B} which results from strong hybridization between Mn-Al and Mn-Mn. We also investigated the volume and c/a ratio dependence of the magnetic moments of Mn and Al. The results indicate that an increase in the intra-atomic exchange splitting due to the cell volume expansion, leads to a large magnetic moment for the Mn atom. The Mn magnetic moment can reach a value of 2.9 μ{sub B} at a volume expansion rate of ΔV/V ≈ 20%.

  5. Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in BaMnBi2

    DOE PAGES

    Li, Lijun; Wang, Kefeng; Graf, D.; ...

    2016-03-28

    Here, we report two-dimensional quantum transport and Dirac fermions in BaMnBi2 single crystals. BaMnBi2 is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotron mass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.

  6. Thermodynamic Modeling of the Al-Cr-Mn Ternary System

    NASA Astrophysics Data System (ADS)

    Cui, Senlin; Jung, In-Ho

    2017-03-01

    The phase diagram information available in the literature on the Al-Cr-Mn system was comprehensively evaluated and optimized for the first time to obtain a set of Gibbs energies of all the solid and liquid phases in the Al-Cr-Mn system. The Modified Quasi-chemical Model (MQM) was utilized to describe the Gibbs energy of the liquid phase of the Al-Cr-Mn system. The Compound Energy Formalism (CEF) was used to model the solid solution phases. A revision of the Al-Mn system was simultaneously conducted to consider the γ_H (Al8Mn5) phase. The liquid Cr-Mn phase was also remodeled using the Modified Quasi-chemical Model (MQM) to obtain a consistent description of the ternary Al-Cr-Mn liquid phase. Accurate description of the phase diagram of the entire Al-Cr-Mn system was obtained from the thermodynamic models with optimized parameters in the present study, and the model parameters can be used to predict the thermodynamic properties of the ternary system.

  7. Theoretical study on the role of dynamics on the unusual magnetic properties in MnBi

    PubMed Central

    Shanavas, K. V.; Parker, David; Singh, David J.

    2014-01-01

    We study the electronic structure and lattice dynamics in the ferromagnet MnBi using first-principles calculations and a tight-binding model. The band structure around the Fermi level is dominated by Bi-p states which are the primary contributors to the magnetic anisotropy energy in the low temperature structure. A tight-binding model consisting of Mn-d and Bi-p states is developed and the parameters are determined from first-principles calculations. Phonon dispersions and elastic moduli exhibit several interesting features. The results imply that the magnetic interaction with the crystal lattice in MnBi is considerably more complex than previously thought and in particular that there is a rich interplay between phonons and magnetism involving both magnetoelastic and magnetostrictive coupling. PMID:25428000

  8. Theoretical study on the role of dynamics on the unusual magnetic properties in MnBi

    SciTech Connect

    Shanavas, K. V.; Parker, David; Singh, David J.

    2014-11-27

    Here we study the electronic structure and lattice dynamics in the ferromagnet MnBi using first-principles calculations and a tight-binding model. The band structure around the Fermi level is dominated by Bi-p states which are the primary contributors to the magnetic anisotropy energy in the low temperature structure. A tight-binding model consisting of Mn-d and Bi-p states is developed and the parameters are determined from first-principles calculations. Phonon dispersions and elastic moduli exhibit several interesting features. In conclusion, the results imply that the magnetic interaction with the crystal lattice in MnBi is considerably more complex than previously thought and in particular that there is a rich interplay between phonons and magnetism involving both magnetoelastic and magnetostrictive coupling.

  9. Theoretical study on the role of dynamics on the unusual magnetic properties in MnBi

    DOE PAGES

    Shanavas, K. V.; Parker, David; Singh, David J.

    2014-11-27

    Here we study the electronic structure and lattice dynamics in the ferromagnet MnBi using first-principles calculations and a tight-binding model. The band structure around the Fermi level is dominated by Bi-p states which are the primary contributors to the magnetic anisotropy energy in the low temperature structure. A tight-binding model consisting of Mn-d and Bi-p states is developed and the parameters are determined from first-principles calculations. Phonon dispersions and elastic moduli exhibit several interesting features. In conclusion, the results imply that the magnetic interaction with the crystal lattice in MnBi is considerably more complex than previously thought and in particularmore » that there is a rich interplay between phonons and magnetism involving both magnetoelastic and magnetostrictive coupling.« less

  10. Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

    SciTech Connect

    Wang, M.; Wadley, P.; Campion, R. P.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Charlton, T. R.; Kinane, C. J.; Langridge, S.

    2015-08-07

    We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields.

  11. Magnetotransport study of Dirac fermions in YbMnBi>2mn> antiferromagnet

    SciTech Connect

    Wang, Aifeng; Zaliznyak, I.; Ren, Weijun; Wu, Lijun; Graf, D.; Garlea, V. O.; Warren, J. B.; Bozin, E.; Zhu, Yimei; Petrovic, C.

    2016-10-15

    We report quantum transport and Dirac fermions in YbMnBi2 single crystals. YbMnBi2 is a layered material with anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, and small cyclotron mass indicate the presence of Dirac fermions. Lastly, angular-dependent magnetoresistance indicates a possible quasi-two-dimensional Fermi surface, whereas the deviation from the nontrivial Berry phase expected for Dirac states suggests the contribution of parabolic bands at the Fermi level or spin-orbit coupling.

  12. Combined effects of Bi deficiency and Mn substitution on the structural transformation and functionality of BiFeO3 films

    NASA Astrophysics Data System (ADS)

    Chen, Jingyi; Wang, Yao; Deng, Yuan

    2014-11-01

    Mn-doped BiFeO3 films with Mn contents of 5 and 10 mol. % were prepared via a chemical route. A carefully controlled amount of Bi deficiency was introduced to further tune the lattice structure and the functionality of multiferroic BiFeO3. The crystal structure of Bi1-δFe1-xMnxO3 films was investigated by X-ray diffraction and Raman spectra; a rhombohedral-to-orthorhombic phase transition was revealed. The observed double hysteresis loops and two capacitance maxima from polarization vs electric field and capacitance-voltage measurements indicate an antiferroelectric-like behavior. Additionally, the coexistence of ferroelectric (FE) and antiferroelectric (AFE) phases in Bi1-δFe1-xMnxO3 films was revealed from the domain structures obtained by piezoelectric force microscopy. The effects of Mn substitution in conjunction with Bi deficiency on the FE-AFE phase transition and electrical behavior of BiFeO3 films are discussed in detail. Meanwhile, magnetic and photoluminescence measurements on the films illustrate that Mn substitution gives rise to the net magnetic moment and the defects induced by both Bi deficiency and Mn substitution influence the electronic structure of BiFeO3 films. This study thus shows a simple and effective way to control the functionalities of BiFeO3 films.

  13. Triclinic crystal structure distortion of multiferroic BiMn7O12.

    PubMed

    Sławiński, Wojciech A; Okamoto, Hiroshi; Fjellvåg, Helmer

    2017-04-01

    The quadruple perovskite BiMn7O12 obtained via high-pressure synthesis was investigated by high-resolution synchrotron X-ray powder diffraction over a temperature range of 10 to 295 K. Careful Rietveld analysis reveals triclinic lattice distortion of BiMn7O12 at 295 K, which increases upon cooling to 10 K. Also hkl-dependent anisotropic Bragg reflection shape was introduced to give a precise description of the diffracted intensities. Importantly BiMn7O12 crystal structure was described in the non-centrosymmetric I1 triclinic space group. We also demonstrate the use of irreducible representations analysis (ISODISTORT program) for crystal structure distortion from Im to I1 space group. The irreducible representation which describes crystal structure distortion points towards possible ferroelectricity. Finally anisotropic thermal lattice expansion was observed.

  14. The magnetic and multiferroic properties in BiMnO3

    NASA Astrophysics Data System (ADS)

    Zhai, Liang-Jun; Wang, Huai-Yu

    2017-03-01

    In this paper, the magnetic and multiferroic properties in the multiferroic material BiMnO3 are studied. A Heisenberg type Hamiltonian for BiMnO3 is proposed, in which the nearest and farther neighbors are considered. Thermodynamic quantities such as magnetization and magnetic susceptibility for different magnetic orderings under high pressure or magnetic field are calculated, and the simulation results fit the experimental results. Farther neighboring exchanges can result in the coexistence of the ferromagnetic ordering and certain antiferromagnetic ordering with no centrosymmetry. Our study demonstrates that the BiMnO3 should be the type-II multiferroic, and the ferromagnetic and ferroelectric orderings could coexist. The magnetic field control of ferroelectric polarization is also studied. The ferroelectric polarization is always suppressed by the external magnetic field.

  15. Processing of magnetically anisotropic MnBi particles by surfactant assisted ball milling

    NASA Astrophysics Data System (ADS)

    Kanari, K.; Sarafidis, C.; Gjoka, M.; Niarchos, D.; Kalogirou, O.

    2017-03-01

    MnBi particles are obtained from bulk MnBi using mechanochemical processing. The structure and magnetic properties of the MnBi particles are investigated by means of X-ray diffraction analysis, scanning electron microscopy and magnetometry. Surfactant assisted high energy ball milling results to the samples' degradation even after one hour of milling. In the case of surfactant assisted low energy ball milling the increase of ball milling duration decreases the average particle size while the particles seem to be more separated. The saturation magnetization (Ms) was found to decrease for large milling times beginning from 61 Am2/kg, while the coercivity (μ0Hc) increases with the increase of ball milling duration up to 35 min where it reaches 1.62 T and thereafter it decreases.

  16. Ferromagnetism and the electronic band structure in (Ga,Mn)(Bi,As) epitaxial layers

    SciTech Connect

    Yastrubchak, O.; Sadowski, J.; Domagala, J. Z.; Andrearczyk, T.; Wosinski, T.

    2014-08-18

    Impact of Bi incorporation into (Ga,Mn)As layers on their electronic- and band-structures as well as their magnetic and structural properties has been studied. Homogenous (Ga,Mn)(Bi,As) layers of high structural perfection have been grown by the low-temperature molecular-beam epitaxy technique. Post-growth annealing treatment of the layers results in an improvement of their structural and magnetic properties and an increase in the hole concentration in the layers. The modulation photoreflectance spectroscopy results are consistent with the valence-band model of hole-mediated ferromagnetism in the layers. This material combines the properties of (Ga,Mn)As and Ga(Bi,As) ternary compounds and offers the possibility of tuning its electrical and magnetic properties by controlling the alloy composition.

  17. Thermoelectric and morphological effects of peltier pulsing on directional solidification of eutectic Bi-Mn

    NASA Astrophysics Data System (ADS)

    Silberstein, R. P.; Larson, D. J.; Dressler, B.

    1984-12-01

    We have carried out extensive in situ thermal measurements during Peltier Interface Demarcation (PID) during directional solidification of eutectic Bi/MnBi. We have observed that significant thermal transients occur throughout the sample as a result of the Peltier pulsing. We have separated the contributions of the Peltier, Thomson, and Joule heats, and studied them as a function of pulse intensity and polarity. The Joule and the combined Peltier and Thomson thermal contributions were determined as a function of time during and after the current pulses, close to the solid/liquid interface. Variations of the Bi/MnBi particle morphology clearly reveal the interface shape, changes in interface velocity, meltback, and temporary loss of cooperative growth, as a result of the pulsing.

  18. Thermoelectric and morphological effects of Peltier pulsing on directional solidification of eutectic Bi-Mn

    NASA Technical Reports Server (NTRS)

    Silberstein, R. P.; Larson, D. J., Jr.; Dressler, B.

    1984-01-01

    Extensive in situ thermal measurements using Peltier Interface Demarcation (PID) during directional solidification of eutectic Bi/MnBi were carried out. Observations indicate that significant thermal transients occur throughout the sample as a result of the Peltier pulsing. The contributions of the Peltier, Thomson, and Joule heats were separated and studied as a function of pulse intensity and polarity. The Joule and the combined Peltier and Thomson thermal contributions were determined as a function of time during and after the current pulses, close to the solid/liquid interface. Variations of the Bi/MnBi particle morphology clearly reveal the interface shape, changes in interface velocity, meltback, and temporary loss of cooperative growth, as a result of the pulsing.

  19. Magnetotransport study of Dirac fermions in YbMnBi2 antiferromagnet

    NASA Astrophysics Data System (ADS)

    Wang, Aifeng; Zaliznyak, I.; Ren, Weijun; Wu, Lijun; Graf, D.; Garlea, V. O.; Warren, J. B.; Bozin, E.; Zhu, Yimei; Petrovic, C.

    2016-10-01

    We report quantum transport and Dirac fermions in YbMnBi2 single crystals. YbMnBi2 is a layered material with anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, and small cyclotron mass indicate the presence of Dirac fermions. Angular-dependent magnetoresistance indicates a possible quasi-two-dimensional Fermi surface, whereas the deviation from the nontrivial Berry phase expected for Dirac states suggests the contribution of parabolic bands at the Fermi level or spin-orbit coupling.

  20. Magnetotransport study of Dirac fermions in YbMnBi2 antiferromagnet

    DOE PAGES

    Wang, Aifeng; Zaliznyak, I.; Ren, Weijun; ...

    2016-10-15

    We report quantum transport and Dirac fermions in YbMnBi2 single crystals. YbMnBi2 is a layered material with anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, and small cyclotron mass indicate the presence of Dirac fermions. Lastly, angular-dependent magnetoresistance indicates a possible quasi-two-dimensional Fermi surface, whereas the deviation from the nontrivial Berry phase expected for Dirac states suggests the contribution of parabolic bands at the Fermi level or spin-orbit coupling.

  1. Swift heavy ion induced nano-dimensional phase separation in liquid immiscible binary Mn-Bi

    NASA Astrophysics Data System (ADS)

    Srivastava, S. K.; Khan, S. A.; Sudheer Babu, P.; Avasthi, D. K.

    2014-08-01

    Pulsed laser deposited 60 nm thin film of homogeneous Mn0.82Bi0.18 composite has been irradiated by 100 MeV Au ions at fluence 1 × 1013 ions/cm2, and investigated by field emission scanning electron microscopy, X-ray diffraction, magnetic hysteresis, X-ray photoelectron spectroscopy, and nanoindentation measurements. Dispersed nanostructures of soft Bi-rich phase of about 20 nm diameter emerged in a hard Mn-rich matrix on irradiation. Such structures, as synthesized by the present novel swift heavy ion irradiation approach, are usable as self-lubricating thin films.

  2. Bi deficiency-tuned functionality in multiferroic Bi1-δFe0.95Mn0.05O3 films

    PubMed Central

    Chen, Jingyi; Wang, Yao; Wang, Hui; Zhang, Shuangmei; Deng, Yuan

    2016-01-01

    Structural evolution and ferroelectric (FE)-to-antiferroelectric (AFE) transition behaviors were observed in Bi1-δFe0.95Mn0.05O3 (100)-textured films with a carefully controlled Bi deficiency concentration δ. Raman spectra revealed an orthorhombic structural transition induced by Mn substitution. The polarization-electric field hysteresis loops and capacitance-voltage loops of Bi1-δFe0.95Mn0.05O3 films clearly demonstrated antiferroelectric behavior with increasing δ. The responses of the domain structure of the Bi1-δFe0.95Mn0.05O3 film under positive and negative applied voltages directly suggested the coexistence of FE and AFE phases. The existence of (100) superstructure reflections and antiparallel displacements of the Bi atoms along the [100] direction observed by transmission electron microscopy unambiguously reveal the AFE phase. The chemical substitution-induced orthorhombic structural transition in BiFe0.95Mn0.05O3 film implies that as the δ concentration increases, the changes in Bi-O bonding and the stereochemical activity of Bi 6s lone pair affect both the ferroelectric distortion and the antiferrodistortive rotation and therefore drive the Bi1-δFe0.95Mn0.05O3 crystal lattice to form a PbZrO3-type orthorhombic phase with an AFE order. A continuing increase in Bi deficiency creates defect dipole complexes which produce an internal field leading to a preferred direction of the ferroelectric domain. The Bi deficiency in multiferroic BiFeO3 provides a new route by which to tune functionality. PMID:26775621

  3. Bi deficiency-tuned functionality in multiferroic Bi1-δFe0.95Mn0.05O3 films

    NASA Astrophysics Data System (ADS)

    Chen, Jingyi; Wang, Yao; Wang, Hui; Zhang, Shuangmei; Deng, Yuan

    2016-01-01

    Structural evolution and ferroelectric (FE)-to-antiferroelectric (AFE) transition behaviors were observed in Bi1-δFe0.95Mn0.05O3 (100)-textured films with a carefully controlled Bi deficiency concentration δ. Raman spectra revealed an orthorhombic structural transition induced by Mn substitution. The polarization-electric field hysteresis loops and capacitance-voltage loops of Bi1-δFe0.95Mn0.05O3 films clearly demonstrated antiferroelectric behavior with increasing δ. The responses of the domain structure of the Bi1-δFe0.95Mn0.05O3 film under positive and negative applied voltages directly suggested the coexistence of FE and AFE phases. The existence of (100) superstructure reflections and antiparallel displacements of the Bi atoms along the [100] direction observed by transmission electron microscopy unambiguously reveal the AFE phase. The chemical substitution-induced orthorhombic structural transition in BiFe0.95Mn0.05O3 film implies that as the δ concentration increases, the changes in Bi-O bonding and the stereochemical activity of Bi 6s lone pair affect both the ferroelectric distortion and the antiferrodistortive rotation and therefore drive the Bi1-δFe0.95Mn0.05O3 crystal lattice to form a PbZrO3-type orthorhombic phase with an AFE order. A continuing increase in Bi deficiency creates defect dipole complexes which produce an internal field leading to a preferred direction of the ferroelectric domain. The Bi deficiency in multiferroic BiFeO3 provides a new route by which to tune functionality.

  4. Bi deficiency-tuned functionality in multiferroic Bi1-δFe0.95Mn0.05O3 films.

    PubMed

    Chen, Jingyi; Wang, Yao; Wang, Hui; Zhang, Shuangmei; Deng, Yuan

    2016-01-18

    Structural evolution and ferroelectric (FE)-to-antiferroelectric (AFE) transition behaviors were observed in Bi1-δFe0.95Mn0.05O3 (100)-textured films with a carefully controlled Bi deficiency concentration δ. Raman spectra revealed an orthorhombic structural transition induced by Mn substitution. The polarization-electric field hysteresis loops and capacitance-voltage loops of Bi1-δFe0.95Mn0.05O3 films clearly demonstrated antiferroelectric behavior with increasing δ. The responses of the domain structure of the Bi1-δFe0.95Mn0.05O3 film under positive and negative applied voltages directly suggested the coexistence of FE and AFE phases. The existence of (100) superstructure reflections and antiparallel displacements of the Bi atoms along the [100] direction observed by transmission electron microscopy unambiguously reveal the AFE phase. The chemical substitution-induced orthorhombic structural transition in BiFe0.95Mn0.05O3 film implies that as the δ concentration increases, the changes in Bi-O bonding and the stereochemical activity of Bi 6s lone pair affect both the ferroelectric distortion and the antiferrodistortive rotation and therefore drive the Bi1-δFe0.95Mn0.05O3 crystal lattice to form a PbZrO3-type orthorhombic phase with an AFE order. A continuing increase in Bi deficiency creates defect dipole complexes which produce an internal field leading to a preferred direction of the ferroelectric domain. The Bi deficiency in multiferroic BiFeO3 provides a new route by which to tune functionality.

  5. Kinetic parameters and structural variations in Cu-Al-Mn and Cu-Al-Mn-Mg shape memory alloys

    NASA Astrophysics Data System (ADS)

    Canbay, Canan Aksu

    2017-02-01

    In this work polycrystalline Cu-Al-Mn and Cu-Al-Mn-Mg SMAs were fabricated by arc melting. The thermal analysis was made to determine the characteristic transformation temperatures of the samples and kinetic parameters. Also the effect of Mg on transformation temperatures and kinetic parameters detected. The structural analysis was made to designate the diffraction planes of martensite phase at room temperature and this was supported by optical measurement observations.

  6. High Pressure XANES studies on Mn dopeHigh Pressure XANES studies on Mn doped Bi2 Te3

    NASA Astrophysics Data System (ADS)

    Light, Brian; Kumar, Ravhi; Baker, Jason; Dharmalingam, Prabhakaran; Park, Changyong; Unlv Team; Hpcat; Carnegie Institute Of Washington Collaboration

    Bi2Te3, Bi2Se3, and Sb2Te3 are narrow band-gap semiconductors have been extensively studied along with their alloys due to their promising technological applications as thermoelectric materials. More recently pressure induced superconductivity and structural transition have been observed in these materials around 7 GPa [1, 2]. Here we have performed high pressure x-ray near edge spectroscopy (XANES) measurements at Bi L-III edge on Mn (0.1) doped Bi2Te3 samples to understand the variation of the Bi valence across the pressure induced superconductivity regime. We have inferred notable changes in the Bi valence at high pressure conditions. The results will be discussed in detail. Work at the University of Nevada Las Vegas (ALC) is funded by U.S. Department of Energy Award DE-SC0001928. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by DOE-BES, DOE-NNSA, NSF, and the W.M. Keck Foundation. APS is supported by DOE-BES, under Contract No. DE-AC02-06CH1135.

  7. Phase diagram for Bi1-xCaxMnO3 (x < 0.5)

    NASA Astrophysics Data System (ADS)

    Qin, Yuhai; Tyson, Trevor; Cheong, Sang-Wook; Xu, Xiaonong

    2007-03-01

    The multiferroic BiMnO3 system, in which ferroelectronic and ferromagnetic orders can coexist, has attracted much research work in the past years for its potential technological applications. For the more general system Bi1-xCaxMnO3, the phase diagram for the Ca rich region (x > 0.4) has been established [1]. In order to understand the multiferroic behavior near the x=0 system, the hole-doped region (0Bi1-xCaxMnO3, by performing detailed structural (XRD and XAFS), magnetization (ZFC/FC) and electrical measurements on Bi1-xCaxMnO3 (0

  8. The effect of Mn content on magnetism and half-metallicity of off-stoichiometric Co2MnAl

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Zhou, Ting; Chen, Xiaorui; Yuan, Hongkuan; Chen, Hong

    2015-08-01

    Using the first-principles calculations within density functional theory (DFT), we investigate the influence of Mn content on magnetism and half-metallicity of off-stoichiometric Co2MnAl. From our calculation, the Mn-poor structure most likely results from antisite disorders where Mn atoms are partially substituted by Co (CoMn antisite) or Al (AlMn antisite) due to their lower formation energy than the structure missing Mn atom. Besides, the half-metallicity is immune to AlMn antisite, while the impurity Co atom in CoMn antisite is responsible for the dramatic decrease in spin polarization. Besides, in the Mn-rich structure where excess impurity Mn occupy the Co sites, impurity Mn atom exhibits antiparallel coupling with other magnetic atoms, resulting in ferrimagnetism. With increasing of Mn content, the spin polarization of Mn-rich structure increases from 75% to 100%. When Mn content rises up to α = 1.875, the corresponding compound Co1.125 Mn1.875 Al owns the perfect spin polarization and stable half-metallicity due to the reason that its Fermi level is situated nearly in the middle of the spin down gap. Hence, a large tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJs) could be obtained by using Mn-rich Co2MnAl electrode. Furthermore, when Mn content reaches up to α = 2, the compound converts to inverse Heusler compound Mn2CoAl with an unique band structure that the conduction and valence band edges of the spin up electrons touch at the Fermi level, it is therefore classified to be spin gapless semiconductors.

  9. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    SciTech Connect

    Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; Parker, David S.; McGuire, Michael A.; Sales, Brian C.; Lumsden, Mark D.; Williams, T. J.; Taylor, A. E.

    2016-05-09

    Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientation that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.

  10. Extended magnetic exchange interactions in the high-temperature ferromagnet MnBi

    DOE PAGES

    Christianson, Andrew D.; Hahn, Steven E.; Fishman, Randy Scott; ...

    2016-05-09

    Here, the high-temperature ferromagnet MnBi continues to receive attention as a candidate to replace rare-earth-containing permanent magnets in applications above room temperature. This is due to a high Curie temperature, large magnetic moments, and a coercivity that increases with temperature. The synthesis of MnBi also allows for crystals that are free of interstitial Mn, enabling more direct access to the key interactions underlying the physical properties of binary Mn-based ferromagnets. In this work, we use inelastic neutron scattering to measure the spin waves of MnBi in order to characterize the magnetic exchange at low temperature. Consistent with the spin reorientationmore » that occurs below 140~K, we do not observe a spin gap in this system above our experimental resolution. A Heisenberg model was fit to the spin wave data in order to characterize the long-range nature of the exchange. It was found that interactions up to sixth nearest neighbor are required to fully parameterize the spin waves. Surprisingly, the nearest-neighbor term is antiferromagnetic, and the realization of a ferromagnetic ground state relies on the more numerous ferromagnetic terms beyond nearest neighbor, suggesting that the ferromagnetic ground state arises as a consequence of the long-ranged interactions in the system.« less

  11. Carbonate phobic (Zn,Mn)-Al hydrotalcite-like compounds

    NASA Astrophysics Data System (ADS)

    Sampieri, Alvaro; Fetter, Geolar; Pfeiffer, Heriberto; Bosch, Pedro

    2007-05-01

    The synthesis method of three series of nitrated (Zn,Mn)-Al hydrotalcites in the presence of microwave irradiation is presented. MnO 4- anions were partially incorporated between the layers of those compounds and a staged intercalation occurred. In the presence of CO 2, nitrated and permanganate intercalated hydrotalcites were tested in CO 32- retention. Carbonate phobic character was observed and it may be correlated to the poor basicity of hydrotalcites, thus, to the electronegativity of M 2+ cations.

  12. Structure and magnetic properties of the MnBi low temperature phase

    NASA Astrophysics Data System (ADS)

    Yang, J. B.; Yelon, W. B.; James, W. J.; Cai, Q.; Roy, S.; Ali, N.

    2002-05-01

    High purity MnBi low temperature phase has been prepared and analyzed using magnetic measurements and neutron diffraction. The low-temperature phase of the MnBi alloy has a coercivity μ0iHc of 2.0 T at 400 K, and exhibits a positive temperature coefficient from 0 to at least 400 K. The neutron data refinement indicated that the Mn atom changes its spin direction from c axis above room temperature to nearly perpendicular to the c axis at 50 K. A canted magnetic structure has been observed below 200 K. The anisotropy field increases with increasing temperature which gives rise to a high coercivity at the higher temperatures. The anisotropic bonded magnets have maximum energy products (BH)max of 7.7 and 4.6 MGOe at room temperature and 400 K, respectively.

  13. Effect of Ti doping on high pressure behavior of BiMn{sub 2}O{sub 5}

    SciTech Connect

    Pandey, K. K. Poswal, H. K. Sharma, Surinder M.; Kumar, Ravi

    2014-04-24

    Our high pressure x-ray diffraction studies on BiMn{sub 1.5}Ti{sub 0.5}O{sub 5} show iso-structural phase transition above 12 GPa similar to the one observed in undoped BiMn{sub 2}O{sub 5}; however anisotropic compressional behavior is found to be more enhanced in the doped case. Unlike undoped system, an anomalous lattice expansion along c axis has been observed in BiMn{sub 1.5}Ti{sub 0.5}O{sub 5} above 12 GPa; whereas the b lattice parameter has been found to be more compressible as compared to BiMn{sub 2}O{sub 5}. As doping with Ti reduces the magnetic interactions among Mn ions, the observed changes are suggestive of having adverse magnetic implications in the observed iso-structural phase transition.

  14. Role of O defects at the BiMnO3/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Jilili, J.; Cossu, F.; Schwingenschlögl, U.

    2016-08-01

    We use first principles calculations to study ideal and O deficient BiMnO3/SrTiO3 superlattices. The ideal superlattice is characterized by parallel alignment of the Mn and Ti magnetic moments at the n-interface, while an antiparallel alignment has been reported experimentally. O defects at the n-interface are found to favor the MnO2 and BiO layers over the TiO2 layer. The band gap of the superlattice is strongly reduced when the MnO2 layer is O deficient and {d}3{z2-{r}2} states are observed at the Fermi energy when the BiO layer is O deficient. Only in the latter case the Mn and Ti magnetic moments at the n-interface align antiparallel. Therefore, O defects in the BiO layer turn out to be essential for reproducing the experimental interface magnetism and for understanding its mechanism.

  15. Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl

    SciTech Connect

    Chaturvedi, A; Yaqub, R; Baker, I

    2014-01-22

    MnAl is a promising rare-earth free permanent magnet for technological use. We have examined the effects of consolidation by back-pressure, assisted equal channel angular extrusion processing on mechanically-milled, gas-atomized Mn-46% at. Al powder. X-ray diffraction showed both that the extruded rod consisted mostly of metastable tau phase, with some of the equilibrium gamma(2) and beta phases, and that it largely retained the as-milled nanostructure. Magnetic measurements show a coercivity of <= 4.4 kOe and a magnetization at 10 kOe of <= 40 emu/g. In addition, extrusions exhibit greater than 95% of the theoretical density. This study opens a new window in the area of bulk MnAl magnets with improved magnetic properties for technological use.

  16. CaMn2Al10: Itinerant Mn magnetism on the verge of magnetic order

    DOE PAGES

    Steinke, L.; Simonson, J. W.; Yin, W. -G.; ...

    2015-07-24

    We report the discovery of CaMn2Al10, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83μB/Mn, significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈ 9% of Rln2. These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility χ is anisotropic below 20 K, with a maximum ratio of χ[010]/χ[001] ≈ 3.5. A strong power-lawmore » divergence χ(T) ~ T–1.2 below 20 K implies incipient ferromagnetic order, an Arrott plot analysis of the magnetization suggests a vanishing low Curie temperature TC ~ 0. Our experiments indicate that CaMn2Al10 is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.« less

  17. CaMn2Al10 : Itinerant Mn magnetism on the verge of magnetic order

    NASA Astrophysics Data System (ADS)

    Steinke, L.; Simonson, J. W.; Yin, W.-G.; Smith, G. J.; Kistner-Morris, J. J.; Zellman, S.; Puri, A.; Aronson, M. C.

    2015-07-01

    We report the discovery of CaMn2Al10 , a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83 μB/Mn , significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈9 % of R ln 2 . These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility χ is anisotropic below 20 K, with a maximum ratio of χ[010 ]/χ[001 ]≈3.5 . A strong power-law divergence χ (T ) ˜T-1.2 below 20 K implies incipient ferromagnetic order with a low Curie temperature TC<2 K . Our experiments indicate that CaMn2Al10 is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.

  18. Isovalent Bi3+ substitution induced structural and magnetic transitions in LaMnO3

    NASA Astrophysics Data System (ADS)

    Joseph, D. Paul; Lin, J. W.; Kumar, N. Pavan; Chen, W. C.; Lin, J. G.

    2016-11-01

    Rare earth perovskite manganites have attracted renewed attention due to scientific aspect and prospective device applications. This work explores the structural and magnetic properties of La(1-x)BixMnO3 (x=0-0.5) with isovalent Bi3+ ions substituted at the La3+site synthesized through solid state reaction method. Doping of 'Bi3+' in LaMnO3 induces transition from orthorhombic to cubic phase for x≥ 0.3. Decrease in the magnetic transition temperature in ZFC-FC data is correlated to the distortion induced by 'Bi3+' doping. Spin glass like feature is witnessed in orthorhombic phase and it diminished appreciably for x≥0.3 in the cubic symmetry. At 10 K, coercivity decreases in orthorhombic phase, whereas it increases marginally in cubic phase. Thus, isovalent Bi3+ doping in LaMnO3 is found to induce structural change from orthorhombic to cubic which is also reflected in the magnetic properties as a change over from hard to soft magnetic phase. In addition, a phenomenological model is applied for fitting the field cooled magnetization data. The results of fitting and the related magneto-caloric effect are also discussed in this paper.

  19. Electrodynamic response of the type-II Weyl semimetal YbMnBi>2mn>

    SciTech Connect

    Chinotti, M.; Pal, A.; Ren, W. J.; Petrovic, C.; Degiorgi, L.

    2016-12-01

    Weyl fermions play a major role in quantum field theory but have been quite elusive as fundamental particles. These quasi-two-dimensional bismuth layers based materials were recently designed and provide an arena for studying the interplay between anisotropic Dirac fermions, magnetism, and structural changes, allowing the formation of Weyl fermions in condensed matter. We perform an optical investigation of YbMnBi 2 , a representative type-II Weyl semimetal, and contrast its excitation spectrum with the optical response of the more conventional semimetal EuMnBi 2 . This comparative study allows us to disentangle the optical fingerprints of type-II Weyl fermions, but also challenges the present theoretical understanding of their electrodynamic response.

  20. Reconnaissance geology of the Bi'r Al Badriyah quadrangle, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Overstreet, William C.; Whitlow, J.W.; Kahr, V.P.; Ankary, A.O.

    1972-01-01

    The Bi'r al Badriyah quadrangle covers an area of 2843 sq km in the extreme eastern part of the Precambrian Shield in central Saudi Arabia. The Precambrian rocks in the southeastern part of the area are unconformably overlain by limestone of Permian age, which occupies only a small part of the quadrangle. Three great sequences of Precambrian rocks are recognized and called, from oldest to youngest, the Halaban Group, the Bi'r Khountina Group, and the Murdama Group. From evidence within the quadrangle itself the three groups are seen to be separated by erosional unconformities, and the Halaban and Bi'r Khountina Groups are intruded by granitic and gabbroic plutonic rocks and a wide variety of dikes. Exposures north of the quadrangle show that the Murdama Group is also intruded by granitic rocks. The Halaban Group, consists of three formations called, from oldest to youngest, the Umm Mushraha Formation, the Jebal al Egfool Formation, and the Wadi al Jifr Formation. These rocks are variably metamorphosed, but characteristically they are at the epidote-albite amphibolite facies of regional metamorphism, are polymetamorphic, and rest unconformably on ancient granite gneiss. The Umm Mushraha Formation consists of amphibolite, schistose andesite, and greenstone associated with minor meta-agglomerate, meta-graywacke, and marble. The Jebal al Egfool Formation consists of sheared and metamorphosed volcanic rocks of intermediate composition, and the Wadi al Jifr Formation is made up of metamorphosed felsic volcanic rocks. Rocks of the Bi'r Khountina Group are rather similar to the Halaban Group in original composition, but they are separated from the Halaban by an angular unconformity and have distinctive formations of conglomerate (the Idsas Formation), marble (the Fawara Formation), and graywacke (the Abu Sawarir Formation) at the base. Most of the Bi'r Khountina Group consists of andesitic volcanic rocks in the Badriyah Formation. Mostly, the Bi'r Khountina Group is

  1. A structural and calorimetric study of the transformations in sputtered Al-Mn and Al-Mn-Si films

    SciTech Connect

    Chen, L.C.; Spaepen, F. ); Robertson, J.L.; Moss, S.C. ); Hiraga, K. )

    1990-09-01

    Scanning and isothermal calorimetry, together with x-ray diffraction and high resolution transmission electron microscopy (TEM), have been used to characterize Al-Mn and Al-Mn-Si films sputtered onto substrates at 60 {degree}C, 45 {degree}C, and {minus}100 {degree}C. In the case of Al{sub 0.83}Mn{sub 0.17}, the monotonically decreasing isothermal calorimetric signal, characteristic of a grain growth process, has proved decisive in identifying the as-sputtered amorphous'' state as microquasicrystalline, with an average grain size of {similar to}20 A in agreement with an estimate of correlation range from the x-ray pattern. The TEM at 400 keV reveals well-defined atomic or lattice images in annealed films but only barely resolved grains (ordered clusters) in the as-sputtered films. The relation between the metallic glass and the microquasicrystalline state in these alloys is discussed.

  2. AlMn Transition Edge Sensors for Advanced ACTPol

    NASA Astrophysics Data System (ADS)

    Li, Dale; Austermann, Jason E.; Beall, James A.; Becker, Daniel T.; Duff, Shannon M.; Gallardo, Patricio A.; Henderson, Shawn W.; Hilton, Gene C.; Ho, Shuay-Pwu; Hubmayr, Johannes; Koopman, Brian J.; McMahon, Jeffrey J.; Nati, Federico; Niemack, Michael D.; Pappas, Christine G.; Salatino, Maria; Schmitt, Benjamin L.; Simon, Sara M.; Staggs, Suzanne T.; Van Lanen, Jeff; Ward, Jonathan T.; Wollack, Edward J.

    2016-07-01

    Advanced ACTPol (AdvACT) will use an array of multichroic polarization-sensitive AlMn transition edge sensor (TES) bolometers read out through time-division multiplexing. Aluminum doped with a low concentration of manganese can be deposited to a bulk film thickness for a more reliable superconducting critical temperature uniformity compared to thin bilayers. To build the TES, the AlMn alloy is deposited, over Nb wiring, to a specific thickness to set the TES normal resistance. The doping concentration of manganese coarsely defines the TES critical temperature, while a fine tuning is achieved by heating the deposited film to a specific temperature. The TES island is connected to the thermal bath via four silicon-nitride membranes, where their geometry defines the thermal conductance to the temperature of the bath. Lastly, the TES heat capacity is increased by addition of PdAu electrically connected to the AlMn film. Designs and performance characteristics of these AlMn TESs are presented for use in AdvACT.

  3. Magnetic BiMn-α phase synthesis prediction: First-principles calculation, thermodynamic modeling and nonequilibrium chemical partitioning

    SciTech Connect

    Zhou, S. H.; Liu, C.; Yao, Y. X.; Du, Y.; Zhang, L. J.; Wang, C. -Z.; Ho, K. -M.; Kramer, M. J.

    2016-04-29

    BiMn-α is promising permanent magnet. Due to its peritectic formation feature, there is a synthetic challenge to produce single BiMn-α phase. The objective of this study is to assess driving force for crystalline phase pathways under far-from-equilibrium conditions. First-principles calculations with Hubbard U correction are performed to provide a robust description of the thermodynamic behavior. The energetics associated with various degrees of the chemical partitioning are quantified to predict temperature, magnetic field, and time dependence of the phase selection. By assessing the phase transformation under the influence of the chemical partitioning, temperatures, and cooling rate from our calculations, we suggest that it is possible to synthesize the magnetic BiMn-α compound in a congruent manner by rapid solidification. The external magnetic field enhances the stability of the BiMn-α phase. In conclusion, the compositions of the initial compounds from these highly driven liquids can be far from equilibrium.

  4. Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

    SciTech Connect

    Choi, Yongseong; Jiang, Xiujuan; Bi, Wenli; Lapa, Pavel; Chouhan, Rajiv K.; Paudyal, D.; Varga, Tamas; Popov, Dmitry; Cui, Jun; Jiang, J. S.

    2016-11-28

    Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong uniaxial magnetic anisotropy above its ~ 90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) measurements at the Mn K and Bi L2,3 edges show induced magnetism in Bi, which is strongly coupled to the magnetism of Mn. Temperature- and pressure-dependent XMCD results reveal that hydrostatic pressure mimics the effect of temperature, driving a transition from uniaxial to in-plane anisotropy. The pressure and temperature transitions are shown to be connected to an anisotropic lattice contraction in NiAs-type structures. Temperature and pressure, hence, induce coupled structural and magnetic responses, highlighting the importance of both anisotropic lattice change and Mn-Bi hybridization in leading to the magnetic anisotropy change across the SRT. Lastly, the dependence of magnetic anisotropy on the anisotropic lattice change is confirmed by density functional theory.

  5. Electrodynamic response of the type-II Weyl semimetal YbMnBi2

    DOE PAGES

    Chinotti, M.; Pal, A.; Ren, W. J.; ...

    2016-12-01

    Weyl fermions play a major role in quantum field theory but have been quite elusive as fundamental particles. These quasi-two-dimensional bismuth layers based materials were recently designed and provide an arena for studying the interplay between anisotropic Dirac fermions, magnetism, and structural changes, allowing the formation of Weyl fermions in condensed matter. We perform an optical investigation of YbMnBi 2 , a representative type-II Weyl semimetal, and contrast its excitation spectrum with the optical response of the more conventional semimetal EuMnBi 2 . This comparative study allows us to disentangle the optical fingerprints of type-II Weyl fermions, but also challengesmore » the present theoretical understanding of their electrodynamic response.« less

  6. Gravitationally induced convection during directional solidification of off-eutectic Mn-Bi alloys

    NASA Technical Reports Server (NTRS)

    Pirich, R. G.

    1982-01-01

    The effects of thermal and solute gradient, gravity induced convection during vertical directional solidification, on longitudinal macrosegregation of Bi and Mn rich off-eutectic starting compositions, has been studied as a function of composition, growth velocity and gravity vector orientation. Since the morphology of these alloys is characterized by an aligned, rodlike permanent magnet composite when grown cooperatively, the magnetic properties were used to measure composition segregation and the transition from dendritic to composite growth. Severe macrosegregation was observed in all cases studied and the degree of convection inferred by modeling the observed composition segregation using a stagnant film approach. Morphological stability was found to follow a constitutional supercooling-type law for both Bi and Mn rich compositions.

  7. Electrodynamic response of the type-II Weyl semimetal YbMnBi2

    NASA Astrophysics Data System (ADS)

    Chinotti, M.; Pal, A.; Ren, W. J.; Petrovic, C.; Degiorgi, L.

    2016-12-01

    Weyl fermions play a major role in quantum field theory but have been quite elusive as fundamental particles. Materials based on quasi-two-dimensional bismuth layers were recently designed and provide an arena for studying the interplay between anisotropic Dirac fermions, magnetism, and structural changes, allowing the formation of Weyl fermions in condensed matter. Here, we perform an optical investigation of YbMnBi2, a representative type-II Weyl semimetal, and contrast its excitation spectrum with the optical response of the more conventional semimetal EuMnBi2. Our comparative study allows us to disentangle the optical fingerprints of type-II Weyl fermions, but also challenges the present theoretical understanding of their electrodynamic response.

  8. The role of spin fluctuations in the anomalous anisotropy of MnBi

    NASA Astrophysics Data System (ADS)

    Barker, Joseph; Mryasov, Oleg

    2016-12-01

    MnBi is unusual for having a magnetic anisotropy energy which increases with temperature. Recent theoretical works have studied how the lattice effects the anisotropy. However, the role of spin fluctuations has been hitherto overlooked, even though this is the primary mechanism for the temperature dependence of anisotropy in magnetic materials. We have created a model of MnBi including all anisotropy terms which are indicated from experiments and theory. Parameterizing based on experimental measurements we used the Callen-Callen theory to calculate the temperature dependence of the magnetic anisotropy due to spin fluctuations. An excellent agreement is found with experiments, across the entire temperature range. Our results indicate the driving force to be the competition between in-plane single ion and out of plane two-ion anisotropies.

  9. Preparation and Magnetic Properties of MnBi-based Hard/Soft Composite Magnets

    SciTech Connect

    Ma, Yilong; Liu, Xubo; Gandha, Kinjal; Vuong, Nguyen V.; Yang, Y. B.; Yang, Jinbo; Poudyal, Narayan; Cui, Jun; Liu, J.Ping

    2014-05-07

    Bulk anisotropic composite magnets based on MnBi/Co(Fe) exhibiting the different morphology of the soft magnetic phase were prepared by powder metallurgy processing. First, single-phase MnBi bulk magnets were produced using a maximum energy product [(BH)m] of 6.3 MGOe at room temperature. The nanoscale soft phase with the different morphology was then added to form a composite magnet. It was observed that addition of magnetic soft-phase nanoparticles and nanoflakes causes a dramatic coercivity reduction. However, the addition of soft magnetic phase nanowires enhanced the composite magnetization without sacrificing the coercivity. Nevertheless, a kink was still observed on the demagnetization curves and the coercivity decreased when the soft-phase content was larger than 10 wt. %, which was caused by the agglomeration of the soft phase nanowires that also led to a decreased degree of texture.

  10. Swift thermal steering of domain walls in ferromagnetic MnBi stripes

    PubMed Central

    Sukhov, Alexander; Chotorlishvili, Levan; Ernst, Arthur; Zubizarreta, Xabier; Ostanin, Sergey; Mertig, Ingrid; Gross, Eberhard K. U.; Berakdar, Jamal

    2016-01-01

    We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory. PMID:27076097

  11. Swift thermal steering of domain walls in ferromagnetic MnBi stripes

    NASA Astrophysics Data System (ADS)

    Sukhov, Alexander; Chotorlishvili, Levan; Ernst, Arthur; Zubizarreta, Xabier; Ostanin, Sergey; Mertig, Ingrid; Gross, Eberhard K. U.; Berakdar, Jamal

    2016-04-01

    We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory.

  12. Swift thermal steering of domain walls in ferromagnetic MnBi stripes.

    PubMed

    Sukhov, Alexander; Chotorlishvili, Levan; Ernst, Arthur; Zubizarreta, Xabier; Ostanin, Sergey; Mertig, Ingrid; Gross, Eberhard K U; Berakdar, Jamal

    2016-04-14

    We predict a fast domain wall (DW) motion induced by a thermal gradient across a nanoscopic ferromagnetic stripe of MnBi. The driving mechanism is an exchange torque fueled by magnon accumulation at the DWs. Depending on the thickness of the sample, both hot-to-cold and cold-to-hot DW motion directions are possible. The finding unveils an energy efficient way to manipulate DWs as an essential element in magnetic information processing such as racetrack memory.

  13. Thermally activated processes and superparamagnetism in Bi12MnO20 nanoparticles: A comparative study

    NASA Astrophysics Data System (ADS)

    de Oliveira, L. A. S.; Pentón-Madrigal, A.; Guimarães, A. P.; Sinnecker, J. P.

    2016-03-01

    Manganese sillenite (Bi12MnO20) nanoparticles having average particle size between 22 and 43 nm were synthesized by a low temperature soft chemical route under refluxing conditions. A careful structural and microstructural characterization by means of high resolution X-ray diffraction experiments and transmission electron microscopy is presented. The as-cast powder displayed an isotropic superparamagnetic (SPM) behavior with a blocked state for temperatures below TB ∼ 13.0 K. We used three different measurement techniques to extract and compare the Bi12MnO20 blocking temperatures. First, we extracted TB with the modified Bean-Livingstone model from the coercive field temperature dependence obtained from hysteresis curves measured as a function of temperature. Then, the blocking temperature distribution function, f(TB), was obtained by deriving the zero field-cooled/field-cooled curves difference. For each applied field, the maximum of the distribution function gave us the mean blocking temperature value. Finally, the maximum of the magnetic susceptibility imaginary part as a function of frequency was used, combined with the Néel-Brown equation, to extract the blocking temperature. All measurement techniques yield an equivalent dependence of TB with H of the Bi12MnO20 superparamagnetic nanoparticles.

  14. Magnetic, electronic, and optical properties of double perovskite Bi2FeMnO6

    NASA Astrophysics Data System (ADS)

    Ahmed, Towfiq; Chen, Aiping; Yarotski, Dmitry A.; Trugman, Stuart A.; Jia, Quanxi; Zhu, Jian-Xin

    2017-03-01

    Double perovskite Bi2FeMnO6 is a potential candidate for the single-phase multiferroic system. In this work, we study the magnetic, electronic, and optical properties in BFMO by performing the density functional theory calculations and experimental measurements of magnetic moment. We also demonstrate the strain dependence of magnetization. More importantly, our calculations of electronic and optical properties reveal that the onsite local correlation on Mn and Fe sites is critical to the gap opening in BFMO, which is a prerequisite condition for the ferroelectric ordering. Finally, we calculate the x-ray magnetic circular dichroism spectra of Fe and Mn ions (L2 and L3 edges) in BFMO.

  15. Investigation of Low Temperature Non-Linear Magnetization Behavior in Al and Ga - Substituted La0.4Bi0.6Mno3 Manganites

    NASA Astrophysics Data System (ADS)

    Dayal, Vijaylakshmi; v, Punith Kumar; Hadimani, Ravi; Jiles, David; David C Jiles Team; Vijaylakshmi Dayal Collaboration

    Low temperature magnetization measurements have been carried out for the samples containing Al and Ga at B-site in La0.4Bi0.6MnO3 manganites. The magnetization (M) vs. T(K) data shows strong ferromagnetic behavior with highest magnetization of 6.45 emu/g for La0.4Bi0.6Mn0.95Al0.05O3 and 5.40 emu/g for La0.4Bi0.6Mn0.90Al0.1O3 samples respectively for an applied magnetic field of H =100 Oe at T =20 K. Similarly at T =20 K for La0.4Bi0.6Mn0.95Ga0.05O3 the highest magnetization (MS) was found to be 5.44 emu/g and for La0.4Bi0.6Mn0.90Ga0.1O3 the MS is 5.05 emu/g. The decrease in magnetization with both Al and Ga substitution produces magnetic dilution with increasing concentrations. Both Al and Ga substituted samples exhibit non-linear behavior in their magnetization (MNL) curves around 40 -120 K due to the frustrations arising from mismatch in their magnetic spin arrangements. The quantity non linear susceptibility, χNL = - MNL/H, diverges as the temperature approaches the frustrated region Tf from above (i.e.TC) . Further from dχNL/dT vs. T(K) plots and critical analysis with unusual critical exponent's γ and β gives an experimental evidence for the observed non linearity and magnetic frustration.

  16. Development of Fe-Mn-Al-X-C alloys

    NASA Technical Reports Server (NTRS)

    Schuon, S. R.

    1982-01-01

    Development of a low cost Cr-free, iron-base alloy for aerospace applications involves both element substitution and enhancement of microstructural strengthening. When Mn is substituted for Ni and Al or Si is substituted for Cr, large changes occur in the mechanical and thermal stability of austenite in FeMnAlC alloys. The in situ strength of MC or M2C (M = Ti, V, Hf, Ta, or Mo) in FeMnAlC alloys was determined. The high temperature tensile strength depends more on the distribution of carbides than the carbide composition. Precipitation of a high volume percent-ordered phase was achieved in Fe2OMnlONi6Al6Ti (lC) alloys. As case, these alloys have a homogeneous austenitic structure. After solutioning at 1100 C for 5 hr followed by aging at 600 C for 16 hr, gamma prime or a perovskite carbide is precipitated. Overaging occurs at 900 C where eta is precipitated.

  17. Electron-hole asymmetry, Dirac fermions, and quantum magnetoresistance in BaMnBi2

    SciTech Connect

    Li, Lijun; Wang, Kefeng; Graf, D.; Wang, Limin; Wang, Aifeng; Petrovic, C.

    2016-03-28

    Here, we report two-dimensional quantum transport and Dirac fermions in BaMnBi2 single crystals. BaMnBi2 is a layered bad metal with highly anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, small cyclotron mass, and the first-principles band structure calculations indicate the presence of Dirac fermions in Bi square nets. Quantum oscillations in the Hall channel suggest the presence of both electron and hole pockets, whereas Dirac and parabolic states coexist at the Fermi level.

  18. First principles study of structure and properties of La- and Mn-modified BiFeO3

    NASA Astrophysics Data System (ADS)

    Antonov, V.; Georgieva, I.; Trendafilova, N.; Kovacheva, D.; Krezhov, K.

    2012-07-01

    First principles calculations have been performed to study the effects of the La3+ and Mn3+ substitutions in the multiferroic BiFeO3. The real compositions Bi1-xLaxFeO3 and BiFe1-xMnxO3 with x = 0.0, 0.1, 0.2, 0.3 were modeled by substitution of one, two and three Bi3+ or Fe3+ by La3+ or Mn3+ in the orthorhombic BiFeO3 structure, respectively. Density functional theory within the generalized gradient approximation with Hubbard correction of Dudarev (GGA + U) and plane wave pseudo-potential approach has been used to track the changes that occur in the structural parameters, electronic structure, magnetic, optical and polarization properties of the modified BiFeO3. The substitution of one Bi3+ with La3+ increases the band gap energy whereas the augmentation of La3+ substitutes decreases it. The substitutions of Fe3+ with Mn3+ do not change the band gap energy. The calculations predicted larger polarization of the modified BiFeO3, antiferromagnetism for Bi1-xLaxFeO3 and small ferrimagnetism for BiFe1-xMnxO3. Better multiferroic properties are expected for BiFe1-xMnxO3 materials (x = 0.1, 0.2) due to the increasing polarization and ferrimagnetic behavior. The optical properties were estimated by the calculated imaginary and real parts of the dielectric function. The increase of La3+ and Mn3+ substitutes lead to lower absorption intensity at energy range 2-7 eV.

  19. Spark plasma sintering of Mn-Al-C hard magnets.

    PubMed

    Pasko, A; LoBue, M; Fazakas, E; Varga, L K; Mazaleyrat, F

    2014-02-12

    Structural and magnetic characterization of isotropic Mn-Al-C bulk samples obtained by spark plasma sintering (SPS) is reported. This technique, to the best of our knowledge, has not been used for preparation of Mn-Al-based permanent magnets previously. Transformation from the parent -phase to the ferromagnetic τ-phase occurred on heating in the process of sintering. The phase constitution of the melt-spun precursors and consolidated samples was determined by x-ray diffraction. Magnetic hysteresis loops were recorded using a vibrating sample magnetometer. The compositional dependence of the coercivity, magnetization and density of the sintered materials is analysed. To combine good magnetic properties with proper densification, further optimization of the production parameters is necessary.

  20. Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

    SciTech Connect

    Choi, Yongseong; Jiang, Xiujuan; Bi, Wenli; Lapa, Pavel; Chouhan, Rajiv K.; Paudyal, D.; Varga, Tamas; Popov, Dmitry; Cui, Jun; Haskel, Daniel; Jiang, J. S.

    2016-11-01

    Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong magnetic anisotropy above its 90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) shows induced magnetism in Bi 5d band, which is strongly coupled to the magnetism of Mn. A clear increase in Bi orbital-to-spin moment ratio is observed above the SRT. Hydrostatic pressure mimics the e*ect of temperature on the SRT, and the pressure effect also leads to anisotropic lattice contraction, which is known to be induced by cooling. These results reveal that temperature and pressure can similarly induce the coupled structural and magnetic responses, suggesting the importance of the anisotropic lattice change and Mn-Bi hybridization to the magnetic anisotropy change across the SRT.

  1. First principles investigation of electronic and magnetic structures of centrosymmetric BiMnO3 using an improved approach

    NASA Astrophysics Data System (ADS)

    Zhu, X. H.; Chen, X. R.; Liu, B. G.

    2016-10-01

    Recent temperature-dependent x-ray diffraction and Raman spectroscopy experiment proved that single-crystalline BiMnO3 assumes a centrosymmetric monoclinic structure (C2/c space group). Here we investigate magnetic structure and electronic structure of this centrosymmetric BiMnO3 phase by using the modified Becke-Johnson (mBJ) exchange functional within the density functional theory (DFT). Our mBJ calculated semiconductor gap, magnetic moment, and other aspects of the electronic structure, in contrast with previous DFT results, are in good agreement with recent experimental values. This satisfactory description of the electronic structure and magnetism of the BiMnO3 is because mBJ reasonably captures the kinetic property and correlation of electrons. Our calculated results with mBJ approach are both useful to study such Bi-based perovskite oxide materials for spintronics applications.

  2. Towards a Superplastic Forming of Fe-Mn-Al Alloys

    SciTech Connect

    Guanabara, Paulo Jr.; Bueno, Levi de O.; Ferreira Batalha, Gilmar

    2011-01-17

    The aim is to study the characteristics of superplasticity, mostly on non qualified materials, such as austenitic steel of the Fe-Mn-Al alloy, which has some of the specific material parameters closely related to microstructural mechanisms. These parameters are used as indicators of material superplastic potentiality. The material was submitted to hot tensile testing, within a temperature range from 600 deg. C to 1000 deg. C and strain-rates varying from 10{sup -6} to 1 s{sup -1}. The strain rate sensitivity parameter (m) and observed maximum elongation until rupture ({epsilon}{sub r}) could be determined and also obtained from the hot tensile test. The experiments stated a possibility of superplastic behaviour in a Fe-Mn-Al alloy within a temperature range from 700 deg. C to 900 deg. C with grain size around 3 {mu}m (ASTM grain size 12) and average strain rate sensitivity of m {approx} 0.54, as well as a maximum elongation at rupture around 600%. The results are based on a more enhanced research from the authors; however, this paper has focused just on the hot tensile test, as further creep tests results are not available herein. There are rare examples of superplasticity study of an austenitic steel Fe-Mn-Al alloy, thus this work showed some possibility of exploring the potential use of such materials in this regime at temperatures {>=}700 deg. C.

  3. AlMn Transition Edge Sensors for Advanced ACTPol

    NASA Technical Reports Server (NTRS)

    Li, Dale; Austermann, Jason E.; Beall, James A.; Tucker, Daniel T.; Duff, Shannon M.; Gallardo, Patricio A.; Henderson, Shawn W.; Hilton, Gene C.; Ho, Shuay-Pwu; Hubmayr, Johannes; Koopman, Brian J.; McMahon, Jeffrey J.; Nati, Federico; Niemack, Michael D.; Pappas, Christine G.; Salatino, Maria; Schmitt, Benjamin L.; Simon, Sara M.; Staggs, Suzanne T.; Van Lanen, Jeff; Ward, Jonathan T.; Wollack, Edward J.

    2016-01-01

    Advanced ACTPol (Adv ACT) will use an array of multichroic polarization sensitive AIMn transition edge sensor (TES) bolometers read out through time-division multiplexing. Aluminum doped with a low concentration of manganese can be deposited to a bulk film thickness for a more reliable superconducting critical temperature uniformity compared to thin bilayers. To build the TES, the AlMn alloy is deposited, over Nb wiring, to a specific thickness to set the TES normal resistance. The doping concentration of manganese coarsely defines the TES critical temperature, while a fine tuning is achieved by heating the deposited film to a specific temperature. The TES island is connected to the thermal bath via four silicon-nitride membranes, where their geometry defines the thermal conductance to the temperature of the bath. Lastly, the TES heat capacity is increased by addition of PdAu electrically connected to the AlMn film. Designs and performance characteristics of these AlMn TESs are presented for use in AdvACT.

  4. Neutron diffraction study of Bi doped cubic spinel Co{sub 2}MnO{sub 4}

    SciTech Connect

    Rajeevan, N. E.; Kaushik, S. D.; Kumar, Ravi

    2015-06-24

    Polycrystalline Bi doped spinel Bi{sub x}Co{sub 2-x}MnO{sub 4} compounds were prepared by solid state reaction route. Room temperature neutron diffraction study reveals that all the compounds are formed in cubic phase and there is no change in the crystal structure due to Bi doping and the compound has cubic structure with Fd-3m space group. Cell parameter found to increase with respect to Bi doping and ferrimagnetic nature is established through magnetization. Low temperature neutron diffraction is carried out and emphasis the ferrimagnetic ordering in the samples of Bi{sub x}Co{sub 2-x}MnO{sub 4} series.

  5. Bi-directional-bi-dimensionality alignment of self-supporting Mn3O4 nanorod and nanotube arrays with different bacteriostasis and magnetism

    NASA Astrophysics Data System (ADS)

    Chen, Qun; Wei, Chengzhen; Gao, Feng; Pang, Huan; Lu, Qingyi

    2013-11-01

    Self-supported Mn3O4 patterns of aligned nanorods and nanotubes were synthesized through a bi-directional-bi-dimensionality growth model by using sodium gluconate and urea as additives under mild hydrothermal conditions without the use of any substrates. In one direction, Mn3O4 grows to form one-dimensional nanorods or nanotubes, while in the other direction Mn3O4 grows into two-dimensional nanoplates to support the nanorods or nanotubes to align into arrays. These two kinds of new nanostructures, a nanotube pattern and a nanorod pattern, show similar and good bacteriostasis for Gram positive bacteria, but for Gram negative bacteria the nanotube pattern shows much better bacterial restraint than the nanorod pattern. Magnetic studies show that the nanorod arrays display similar magnetic properties to the commercial Mn3O4, while the nanotube arrays show different ferromagnetic behaviors with enhanced remnant magnetization and saturation magnetization (Ms) at low temperature.Self-supported Mn3O4 patterns of aligned nanorods and nanotubes were synthesized through a bi-directional-bi-dimensionality growth model by using sodium gluconate and urea as additives under mild hydrothermal conditions without the use of any substrates. In one direction, Mn3O4 grows to form one-dimensional nanorods or nanotubes, while in the other direction Mn3O4 grows into two-dimensional nanoplates to support the nanorods or nanotubes to align into arrays. These two kinds of new nanostructures, a nanotube pattern and a nanorod pattern, show similar and good bacteriostasis for Gram positive bacteria, but for Gram negative bacteria the nanotube pattern shows much better bacterial restraint than the nanorod pattern. Magnetic studies show that the nanorod arrays display similar magnetic properties to the commercial Mn3O4, while the nanotube arrays show different ferromagnetic behaviors with enhanced remnant magnetization and saturation magnetization (Ms) at low temperature. Electronic supplementary

  6. Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

    SciTech Connect

    McGuire, Michael A.; Cao, Huibo; Chakoumakos, Bryan C.; Sales, Brian C.

    2014-11-18

    Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature TSR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropy of the atomic displacement parameters for Bi with increasing temperature above TSR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.

  7. Symmetry-lowering lattice distortion at the spin reorientation in MnBi single crystals

    DOE PAGES

    McGuire, Michael A.; Cao, Huibo; Chakoumakos, Bryan C.; ...

    2014-11-18

    Here we report structural and physical properties determined by measurements on large single crystals of the anisotropic ferromagnet MnBi. The findings support the importance of magnetoelastic effects in this material. X-ray diffraction reveals a structural phase transition at the spin reorientation temperature TSR = 90 K. The distortion is driven by magneto-elastic coupling, and upon cooling transforms the structure from hexagonal to orthorhombic. Heat capacity measurements show a thermal anomaly at the crystallographic transition, which is suppressed rapidly by applied magnetic fields. Effects on the transport and anisotropic magnetic properties of the single crystals are also presented. Increasing anisotropy ofmore » the atomic displacement parameters for Bi with increasing temperature above TSR is revealed by neutron diffraction measurements. It is likely that this is directly related to the anisotropic thermal expansion in MnBi, which plays a key role in the spin reorientation and magnetocrystalline anisotropy. Finally, the identification of the true ground state crystal structure reported here may be important for future experimental and theoretical studies of this permanent magnet material, which have to date been performed and interpreted using only the high temperature structure.« less

  8. Atomic decoration of a random-cluster model for icosahedral-phase AlMnSi

    SciTech Connect

    Robertson, J.L.; Moss, S.C. )

    1991-01-21

    Preliminary results on the atomic decoration of a random-cluster model for icosahedral-phase alloys are presented. The calculated neutron and x-ray intensities compare quite favorably with experimental intensity data on {ital i}-AlMnSi. The origin of the peak at {ital Q}=1.62 A{sup {minus}1}, associated with the prepeak found in amorphous'' AlMnSi, as well as the ubiquitous diffuse'' scattering, seen experimentally under the groups of strong peaks in all icosahedral-phase alloys, are revealed selectively in the calculated partial intensities for Al-Al, Al-Mn, and Mn-Mn correlations.

  9. Synthesis, characterization and electrochemical performance of Al-substituted Li₂MnO₃

    DOE PAGES

    Dhital, Chetan; Huq, Ashfia; Paranthaman, Mariappan Parans; ...

    2015-08-08

    Li2MnO3 is known to be electrochemically inactive due to Mn in tetravalent oxidation state. Several compositions such as Li2MnO3 , Li1.5Al0.17MnO3, Li1.0Al0.33MnO3 and Li0.5Al0.5MnO3 were synthesized by a sol–gel Pechini method. All the samples were characterized with x-ray diffraction, Raman, x-ray photoelectron spectroscopy, scanning electron microscopy, Tap density and BET analyzer. X-ray diffraction patterns indicated the presence of monoclinic phase for pristine Li2MnO3and mixed monoclinic/spinel phases (Li2 - xMn1 - yAlx + yO3 + z) for Al-substituted Li2MnO3compounds. The Al substitution seems to occur both at Li and Mn sites, which could explain the presence of spinel phase. X-ray photoelectronmore » spectroscopy for Mn 2p orbital reveals a significant decrease in binding energy for Li1.0Al0.33MnO3 and Li0.5Al0.5MnO3 compounds. Cyclic voltammetry, charge/discharge cycles and electrochemical impedance spectroscopy were also performed. A discharge capacity of 24 mAh g-1 for Li2MnO3, 68 mAh g-1 for Li1.5Al0.17MnO3, 58 mAh g-1 for Li1.0Al0.33MnO3 and 74 mAh g-1 for Li0.5Al0.5MnO3 were obtained. As a result, aluminum substitutions increased the formation of spinel phase which is responsible for cycling.« less

  10. Robust antiferromagnetism preventing superconductivity in pressurized (Ba 0.61 K 0.39)Mn2Bi2.

    PubMed

    Gu, Dachun; Dai, Xia; Le, Congcong; Sun, Liling; Wu, Qi; Saparov, Bayrammurad; Guo, Jing; Gao, Peiwen; Zhang, Shan; Zhou, Yazhou; Zhang, Chao; Jin, Shifeng; Xiong, Lun; Li, Rui; Li, Yanchun; Li, Xiaodong; Liu, Jing; Sefat, Athena S; Hu, Jiangping; Zhao, Zhongxian

    2014-12-05

    BaMn2Bi2 possesses an iso-structure of iron pnictide superconductors and similar antiferromagnetic (AFM) ground state to that of cuprates, therefore, it receives much more attention on its properties and is expected to be the parent compound of a new family of superconductors. When doped with potassium (K), BaMn2Bi2 undergoes a transition from an AFM insulator to an AFM metal. Consequently, it is of great interest to suppress the AFM order in the K-doped BaMn2Bi2 with the aim of exploring the potential superconductivity. Here, we report that external pressure up to 35.6 GPa cannot suppress the AFM order in the K-doped BaMn2Bi2 to develop superconductivity in the temperature range of 300 K-1.5 K, but induces a tetragonal (T) to an orthorhombic (OR) phase transition at ~20 GPa. Theoretical calculations for the T and OR phases, on basis of our high-pressure XRD data, indicate that the AFM order is robust in the pressurized Ba0.61K0.39Mn2Bi2. Both of our experimental and theoretical results suggest that the robust AFM order essentially prevents the emergence of superconductivity.

  11. Robust antiferromagnetism preventing superconductivity in pressurized (Ba0.61K0.39)Mn2Bi2

    DOE PAGES

    Gu, Dachun; Dai, Xia; Le, Congcong; ...

    2014-12-05

    BaMn2Bi2 possesses an iso-structure of iron pnictide superconductors and similar antiferromagnetic (AFM) ground state to that of cuprates, therefore, it receives much more attention on its properties and is expected to be the parent compound of a new family of superconductors. When doped with potassium (K), BaMn2Bi2 undergoes a transition from an AFM insulator to an AFM metal. Consequently, it is of great interest to suppress the AFM order in the K-doped BaMn2Bi2 with the aim of exploring the potential superconductivity. Here, we report that external pressure up to 35.6 GPa cannot suppress the AFM order in the K-doped BaMn2Bi2more » to develop superconductivity in the temperature range of 300 K–1.5 K, but induces a tetragonal (T) to an orthorhombic (OR) phase transition at ~20 GPa. Theoretical calculations for the T and OR phases, on basis of our high-pressure XRD data, indicate that the AFM order is robust in the pressurized Ba0.61K0.39Mn2Bi2. Utlimately, both of our experimental and theoretical results suggest that the robust AFM order essentially prevents the emergence of superconductivity.« less

  12. Preparation and property of magnetic photocatalyst BiOCl/Mn x Zn1- x Fe2O4

    NASA Astrophysics Data System (ADS)

    Feng, Shan; Xu, Longjun; Liu, Chenglun; Du, Haigang; Xie, Taiping; Zhu, Qianqian

    2017-02-01

    The magnetic photocatalyst BiOCl/Mn x Zn1- x Fe2O4 was prepared by impregnation-calcination method. The structure and properties of the prepared photocatalyst were characterized by FTIR, XRD, SEM, TEM, UV-vis DRS, and VSM. Mn x Zn1- x Fe2O4 inhibited the growth along (001) crystal face and promoted (110) crystal surface exposure of BiOCl. The as-prepared magnetic composite appeared flower-like microspheres assembled with nanosheets. The average crystallite size and the nanosheet thickness range of BiOCl/Mn x Zn1- x Fe2O4 were 57.6 and 75.7-112.2 nm, respectively. The band gap energy ( E g) of BiOCl/Mn x Zn1- x Fe2O4 was 2.48 eV, which was lower than that of BiOCl. The saturation magnetization ( Ms), coercive force ( Hc), and remanent magnetization ( Mr) of BiOCl/Mn x Zn1- x Fe2O4 were respectively 4.64 emu g-1, 50.12 G and 0.09 emu g-1, indicating a good resistance to demagnetization and paramagnetism. The optimum synthesis condition of BiOCl/Mn x Zn1- x Fe2O4 was obtained by orthogonal experiments, and the degradation ratio of RhB with the photocatalyst was 99.6% at 30 min. After four cycles, the degradation ratio of RhB with the recovered photocatalyst was still above 83%.

  13. BiMnFe(2)O(6) a Polysynthetically Twinned hcp MO Structure

    SciTech Connect

    T Yang; A Abakumov; J Hadermann; G Van Tendeloo; I Nowik; P Stephens; J Hemberger; A Tsirlin; K Ramanujachary; et al.

    2011-12-31

    The most efficient use of spatial volume and the lowest potential energies in the metal oxide structures are based on cubic close packing (ccp) or hexagonal close packing (hcp) of anions with cations occupying the interstices. A promising way to tune the composition of close packed oxides and design new compounds is related to fragmenting the parent structure into modules by periodically spaced planar interfaces, such as twin planes at the unit cell scale. The unique crystal chemistry properties of cations with a lone electron pair, such as Bi{sup 3+} or Pb{sup 2+}, when located at interfaces, enables them to act as 'chemical scissors', to help relieve configurational strain. With this approach, we synthesized a new oxide, BiMnFe{sub 2}O{sub 6}, where fragments of the hypothetical hcp oxygen-based MO structure (the NiAs structure type), for the first time, serve as the building modules in a complex transition metal oxide. Mn{sup 3+} and Fe{sup 3+} ions are randomly distributed in two crystallographically independent sites (M1 and M2). The structure consists of quasi two-dimensional blocks of the 2H hexagonal close packed MO structure cut along the (114) crystal plane of the hcp lattice and stacked along the c axis. The blocks are related by a mirror operation that allows BiMnFe{sub 2}O{sub 6} to be considered as a polysynthetically twinned 2H hcp MO structure. The transition to an AFM state with an incommensurate spin configuration at {approx}212 K is established by {sup 57}Fe Moessbauer spectroscopy, magnetic susceptibility, specific heat and low temperature powder neutron diffraction.

  14. BiMnFe2O6 a Polysynthetically Twinned hcp MO Structure

    SciTech Connect

    T Yang; A Abakumov; J Hadermann; G Van Tendeloo; I Nowik; P Stephens; J Hemberger; M Croft; A Ignatov; et al.

    2011-12-31

    The most efficient use of spatial volume and the lowest potential energies in the metal oxide structures are based on cubic close packing (ccp) or hexagonal close packing (hcp) of anions with cations occupying the interstices. A promising way to tune the composition of close packed oxides and design new compounds is related to fragmenting the parent structure into modules by periodically spaced planar interfaces, such as twin planes at the unit cell scale. The unique crystal chemistry properties of cations with a lone electron pair, such as Bi{sup 3+} or Pb{sup 2+}, when located at interfaces, enables them to act as 'chemical scissors', to help relieve configurational strain. With this approach, we synthesized a new oxide, BiMnFe{sub 2}O{sub 6}, where fragments of the hypothetical hcp oxygen-based MO structure (the NiAs structure type), for the first time, serve as the building modules in a complex transition metal oxide. Mn{sup 3+} and Fe{sup 3+} ions are randomly distributed in two crystallographically independent sites (M1 and M2). The structure consists of quasi two-dimensional blocks of the 2H hexagonal close packed MO structure cut along the (114) crystal plane of the hcp lattice and stacked along the c axis. The blocks are related by a mirror operation that allows BiMnFe{sub 2}O{sub 6} to be considered as a polysynthetically twinned 2H hcp MO structure. The transition to an AFM state with an incommensurate spin configuration at {approx}212 K is established by {sup 57}Fe Moessbauer spectroscopy, magnetic susceptibility, specific heat and low temperature powder neutron diffraction.

  15. Simulation Study of Al-1Mn/Al-10Si Circular Clad Ingots Prepared by Direct Chill Casting

    NASA Astrophysics Data System (ADS)

    Wu, Li; Kang, Huijun; Chen, Zongning; Fu, Ying; Wang, Tongmin

    2016-02-01

    A modified direct chill casting process based on Novelis FusionTM Technology co-casting process was used recently to prepare Al-1Mn/Al-10Si circular clad ingots. In the current study, a comprehensive simulation model was developed to investigate the direct chill casting process for preparing the Al-1Mn/Al-10Si circular clad ingots, and a parametric study and experimental research of the direct chill casting process was conducted to explore potential success and failure casting conditions. The simulation results revealed the bonding mechanism of the Al-1Mn/Al-10Si interface in the direct chill casting process and identified the effect of certain parameters on casting performance. The results indicated that the effect of casting speed and Al-1Mn casting temperature on the variations of the minimum solid fraction of Al-1Mn at the interface is stronger than that of cooling water flow rate in inner mold, while Al-10Si casting temperature is the weakest of the four casting parameters. The corresponding experimental results verified that Al-1Mn/Al-10Si circular clad ingot with acceptable metallurgical bonding can be successfully prepared by direct chill casting process under the proper casting parameters. The thickness of diffusion zone is about 40 μm, and the fractured position in tensile test was located in the Al-1Mn alloy side which indicated the strength of the interfacial region is higher than that of Al-1Mn alloy.

  16. Magnetic Transitions in the Spin-5/2 Frustrated Magnet BiMn2PO6 and Strong Lattice Softening in BiMn2PO6 and BiZn2PO6 Below 200 K

    SciTech Connect

    Nath, R; Ranjith, K M; Roy, B; Johnston, D C; Furukawa, Y; Tsirlin, A A

    2014-07-01

    The crystallographic, magnetic, and thermal properties of polycrystalline BiMn2PO6 and its nonmagnetic analog BiZn2PO6 are investigated by x-ray diffraction, magnetization M, magnetic susceptibility χ, heat capacity Cp, and P31 nuclear magnetic resonance (NMR) measurements versus applied magnetic field H and temperature T as well as by density-functional band theory and molecular-field calculations. Both compounds show a strong monotonic lattice softening on cooling, where the Debye temperature decreases by a factor of two from ΘD~650 K at T=300 K to ΘD~300 K at T=2 K. The χ(T) data for BiMn2PO6 above 150 K follow a Curie-Weiss law with a Curie constant consistent with a Mn+2 spin S=5/2 with g factor g=2 and an antiferromagnetic (AFM) Weiss temperature θCW≃-78 K. The χ data indicate long-range AFM ordering below TN≃30 K, confirmed by a sharp λ-shaped peak in Cp(T) at 28.8 K. The magnetic entropy at 100 K extracted from the Cp(T) data is consistent with spin S=5/2 for the Mn+2 cations. The band-theory calculations indicate that BiMn2PO6 is an AFM compound with dominant interactions J1/kB≃6.7 K and J3/kB≃5.6 K along the legs and rungs of a Mn two-leg spin-ladder, respectively. However, sizable and partially frustrating interladder couplings lead to an anisotropic three-dimensional magnetic behavior with long-range AFM ordering at TN≃30 K observed in the χ, Cp, and NMR measurements. A second magnetic transition at ≈10 K is observed from the χ and NMR measurements but is not evident in the Cp data. The Cp data at low T suggest a significant contribution from AFM spin waves moving in three dimensions and the absence of a spin-wave gap. A detailed analysis of the NMR spectra indicates commensurate magnetic order between 10 and 30 K, while below 10 K additional features appear that may arise from an incommensurate modulation and/or spin canting. The commensurate order is consistent with microscopic density functional calculations that yield a

  17. Growth and characterization of (In,Ga,Mn)As and (In,Al,Mn)As epilayers and heterostructures

    NASA Astrophysics Data System (ADS)

    Maksimov, O.; Sheu, B. L.; Schiffer, P.; Samarth, N.

    2004-03-01

    Lattice-matched III-Mn-V semiconductors on InP (001) substrates provide an attractive route toward the design of more magnetically concentrated ferromagnetic semiconductor alloys [1]. Here, we report the low temperature molecular beam epitaxy of (In_0.5Ga_0.5)_1-xMn_xAs and (In_0.5Al_0.5)_1-xMn_xAs epilayers, heterostructures and superlattices. Electron and x-ray diffraction studies show that the samples have structural quality similar to that of the more extensively studied (In,Mn)As and (Ga,Mn)As ferromagnetic semiconductors. Electron probe microanalysis measurements indicate that up to ˜ 11 % of Mn can be incorporated in the alloys. Magnetization measurements with a superconducting quantum interference device show that (In_0.5Ga_0.5)_0.89Mn_0.11As and (In_0.5Al_0.5)_0.89Mn_0.11As epilayers have a Curie temperature (T_C) ranging up to 95 K and 25 K, respectively. The consistently lower values of TC in (In_0.5Al_0.5)_1-xMn_xAs compared to (In_0.5Ga_0.5)_1-xMn_xAs are attributed to a reduced hole density caused by an enhanced acceptor activation energy. Work supported by grants from DARPA, ONR and NSF. 1. S. Ohya, H. Kobayashi, M. Tanaka, Appl. Phys. Lett. 83, 2175 (2003).

  18. Enhancement of tetragonal anisotropy and stabilisation of the tetragonal phase by Bi/Mn-double-doping in BaTiO3 ferroelectric ceramics

    PubMed Central

    Yabuta, Hisato; Tanaka, Hidenori; Furuta, Tatsuo; Watanabe, Takayuki; Kubota, Makoto; Matsuda, Takanori; Ifuku, Toshihiro; Yoneda, Yasuhiro

    2017-01-01

    To stabilise ferroelectric-tetragonal phase of BaTiO3, the double-doping of Bi and Mn up to 0.5 mol% was studied. Upon increasing the Bi content in BaTiO3:Mn:Bi, the tetragonal crystal-lattice-constants a and c shrank and elongated, respectively, resulting in an enhancement of tetragonal anisotropy, and the temperature-range of the ferroelectric tetragonal phase expanded. X-ray absorption fine structure measurements confirmed that Bi and Mn were located at the A(Ba)-site and B(Ti)-site, respectively, and Bi was markedly displaced from the centrosymmetric position in the BiO12 cluster. This A-site substitution of Bi also caused fluctuations of B-site atoms. Magnetic susceptibility measurements revealed a change in the Mn valence from +4 to +3 upon addition of the same molar amount of Bi as Mn, probably resulting from a compensating behaviour of the Mn at Ti4+ sites for donor doping of Bi3+ into the Ba2+ site. Because addition of La3+ instead of Bi3+ showed neither the enhancement of the tetragonal anisotropy nor the stabilisation of the tetragonal phase, these phenomena in BaTiO3:Mn:Bi were not caused by the Jahn-Teller effect of Mn3+ in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi3+. PMID:28367973

  19. XPS and EELS characterization of Mn2SiO4, MnSiO3 and MnAl2O4

    NASA Astrophysics Data System (ADS)

    Grosvenor, A. P.; Bellhouse, E. M.; Korinek, A.; Bugnet, M.; McDermid, J. R.

    2016-08-01

    X-ray Photoelectron Spectroscopy (XPS) and Electron Energy Loss Spectroscopy (EELS) are strong candidate techniques for characterizing steel surfaces and substrate-coating interfaces when investigating the selective oxidation and reactive wetting of advanced high strength steels (AHSS) during the continuous galvanizing process. However, unambiguous identification of ternary oxides such as Mn2SiO4, MnSiO3, and MnAl2O4 by XPS or EELS, which can play a significant role in substrate reactive wetting, is difficult due to the lack of fully characterized standards in the literature. To resolve this issue, samples of Mn2SiO4, MnSiO3 and MnAl2O4 were synthesized and characterized by XPS and EELS. The unique features of the XPS and EELS spectra for the Mn2SiO4, MnSiO3 and MnAl2O4 standards were successfully derived, thereby allowing investigators to fully differentiate and identify these oxides at the surface and subsurface of Mn, Si and Al alloyed AHSS using these techniques.

  20. Growth and magnetic properties of multiferroic LaxBi1-xMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Gajek, M.; Bibes, M.; Wyczisk, F.; Varela, M.; Fontcuberta, J.; Barthélémy, A.

    2007-05-01

    A comparative study of LaxBi1-xMnO3 thin films grown on SrTiO3 substrates is reported. It is shown that these films grow epitaxially in a narrow pressure-temperature range. A detailed structural and compositional characterization of the films is performed within the growth window. The structure and the magnetization of this system are investigated. We find a clear correlation between the magnetization and the unit-cell volume that we ascribe to Bi deficiency and the resultant introduction of a mixed valence on the Mn ions. On these grounds, we show that the reduced magnetization of LaxBi1-xMnO3 thin films compared to the bulk can be explained quantitatively by a simple model, taking into account the deviation from nominal composition and the Goodenough-Kanamori-Anderson rules of magnetic interactions.

  1. Lattice dynamics of Ni-Mn-Al Heusler alloys

    SciTech Connect

    Moya, Xavier; Manosa, Lluis; Planes, A.; Krenke, T.; Acet, Mehmet; Wassermann, E. F.; Morin, M.; Garlea, Vasile O; Lograsso, Tom; Zarestky, Jerel L.

    2008-01-01

    We have studied the lattice dynamics of a Ni54Mn23Al23 (at.%) Heusler single-crystalline alloy by means of neutron scattering and ultrasonic techniques. Results show the existence of a number of precursor phenomena. We have found an anomaly (dip) in the low TA2 phonon branch at the wave number 0.33 (in reciprocal lattice units) that becomes more pronounced (phonon softening) with decreasing temperature. We have also observed softening of the associated shear elastic constant (C ) with decreasing temperature. Ultrasonic measurements under applied magnetic field, both isothermally and varying the temperature show that the values of elastic constants depend on magnetic order thus evidencing magnetoelastic coupling.

  2. Subsolidus phase equilibria and properties in the system Bi 2O 3:Mn 2O 3±x:Nb 2O 5

    NASA Astrophysics Data System (ADS)

    Vanderah, T. A.; Lufaso, M. W.; Adler, A. U.; Levin, I.; Nino, J. C.; Provenzano, V.; Schenck, P. K.

    2006-11-01

    Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn 2+, Mn 3+, and Mn 4+ were all observed. Ternary compound formation was limited to pyrochlore (A 2B 2O 6O'), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi 2(Mn,Nb) 2O 7) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn 2+). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi 2O 3:Mn 2O 3±x:Nb 2O 5 using neutron powder diffraction data is reported with the A and O' atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn 2+ on A-sites and Mn 3+ on B-sites (Bi 1.6Mn 2+0.4(Mn 3+0.8Nb 1.2)O 7, Fd3¯m (♯227), a=10.478(1) Å); evidence of A or O' vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi 1.5Zn 0.92Nb 1.5O 6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi 1.600Mn 1.200Nb 1.200O 7 was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi 1.5Zn 0.92Nb 1.5O 6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.

  3. Morphological evolution and strengthening behavior of α-Al(Fe,Mn)Si in Al-6Si-2Fe-xMn alloys

    NASA Astrophysics Data System (ADS)

    Gao, Tong; Hu, Kaiqi; Wang, Longshuai; Zhang, Bangran; Liu, Xiangfa

    β-Al5FeSi is preferred to form in Al-Si-Fe alloys, normally exhibiting needlelike, which is harmful for the mechanical properties. In this paper, with the addition of 1%, 1.5% and 3% Mn into an Al-6Si-2Fe alloy, β-Al5FeSi phase was found to transform to skeleton, flower-like and coarse dendritic α-Al(Fe,Mn)Si, respectively. The novel flower-like α-Al(Fe,Mn)Si crystals contain developed branches with the average diameter of ∼200 nm, performing strengthening effect on the tensile property. Detailed morphologies of α-Al(Fe,Mn)Si phase and the formation mechanism were discussed.

  4. Reversing ferroelectric polarization in multiferroic DyMn{sub 2}O{sub 5} by nonmagnetic Al substitution of Mn

    SciTech Connect

    Zhao, Z. Y.; Liu, M. F.; Li, X.; Wang, J. X.; Yan, Z. B.; Wang, K. F.; Liu, J.-M.

    2014-08-07

    The multiferroic RMn{sub 2}O{sub 5} family, where R is rare-earth ion or Y, exhibits rich physics of multiferroicity which has not yet well understood. DyMn{sub 2}O{sub 5} is a representative member of this family. The ferroelectric polarization of DyMn{sub 2}O{sub 5} is claimed to be magnetically relevant and have more than one component. Therefore, the polarization reversal upon the sequent magnetic transitions is expected. We investigate the evolution of the ferroelectric polarization upon a partial substitution of Mn{sup 3+} by nonmagnetic Al{sup 3+} in order to tailor the Mn{sup 3+}-Mn{sup 4+} interactions and then to modulate the polarization in DyMn{sub 2−x/2}Al{sub x/2}O{sub 5}. It is revealed that the polarization can be successfully reversed by Al-substitution via substantially suppressing the Mn{sup 3+}-Mn{sup 4+} interactions, while the Dy{sup 3+}-Mn{sup 4+} interactions can sustain against the substitution until a level as high as x = 0.2. In addition, the independent Dy spin ordering is shifted remarkably down to an extremely low temperature due to the Al{sup 3+} substitution. The present work unveils the possibility of tailoring the Mn{sup 3+}-Mn{sup 4+} and Dy{sup 3+}-Mn{sup 4+} interactions independently, and thus reversing the ferroelectric polarization.

  5. XRD and XANES study of some Cu-doped MnBi materials

    NASA Astrophysics Data System (ADS)

    Mishra, Ashutosh; Patil, Harsha

    2016-10-01

    High purity MnBi low temperature phase has been prepared and analyzed using X- ray diffraction (XRD) and X-ray absorption near edge structure (XANES) measurements. The X-ray diffraction measurements were carried out using Bruker D8 Advance X-ray diffractometer. The X-rays were produced using a sealed tube and the wavelength of X-ray was 154 nm (Cu K-alpha). and X-rays were detected using a fast counting detector based on Silicon strip technology (Bruker LynxEye detector)[1]. and the X-ray absorption spectra has emerged as a powerful technique for local structure determination, which can be applied to any type of material. The X-ray absorption measurements of two Cu-doped MnBi alloys have been performed at the recently developed BL-8 Dispersive EXAFS beam line at 2.5 GeV Indus-2 synchrotron at RRCAT, Indore, India[2]. The X-ray absorption near edge structure (XANES) data obtained has been processed using data analysis program Athena. The energies of the K absorption edge, chemical shifts, edge-widths, shifts of the principal absorption maximum in the alloys have been determined.

  6. MnBi particles with high energy density made by spark erosion

    SciTech Connect

    Nguyen, PK; Jin, SH; Berkowitz, AE

    2014-05-07

    We report on the properties of low-temperature phase (LTP)-MnBi particles produced by the rapid-quenching technique of spark-erosion. The as-prepared powder consists of amorphous, crystalline, and superparamagnetic particles, mostly as porous aggregates. The major fraction of the powder consists of 20-30 nm particles. A short anneal crystallizes the amorphous particles producing a high moment, >90% of theoretical M-S, albeit with H-C of a few kOe. If lightly milled, the agglomerates are broken up to yield H-C of 1 T. These findings are supported by the x-ray diffraction pattern showing broadened peaks of the predominant LTP-MnBi phase. The combination of spark erosion, milling, and annealing has produced randomly oriented particles with (BH)(MAX) similar to 3.0 MGOe. The particles are expected to show record energy product when aligned along their crystallographic easy axes. (C) 2014 AIP Publishing LLC.

  7. MnBi particles with high energy density made by spark erosion

    SciTech Connect

    Nguyen, Phi-Khanh Jin, Sungho; Berkowitz, Ami E.

    2014-05-07

    We report on the properties of low-temperature phase (LTP)-MnBi particles produced by the rapid-quenching technique of spark-erosion. The as-prepared powder consists of amorphous, crystalline, and superparamagnetic particles, mostly as porous aggregates. The major fraction of the powder consists of 20–30 nm particles. A short anneal crystallizes the amorphous particles producing a high moment, >90% of theoretical M{sub S}, albeit with H{sub C} of a few kOe. If lightly milled, the agglomerates are broken up to yield H{sub C} of 1 T. These findings are supported by the x-ray diffraction pattern showing broadened peaks of the predominant LTP-MnBi phase. The combination of spark erosion, milling, and annealing has produced randomly oriented particles with (BH){sub MAX} ∼ 3.0 MGOe. The particles are expected to show record energy product when aligned along their crystallographic easy axes.

  8. Strain-modulated ferromagnetism and band gap of Mn doped Bi2Se3

    PubMed Central

    Qi, Shifei; Yang, Hualing; Chen, Juan; Zhang, Xiaoyang; Yang, Yingping; Xu, Xiaohong

    2016-01-01

    The quantized anomalous Hall effect (QAHE) have been theoretically predicted and experimentally confirmed in magnetic topological insulators (TI), but dissipative channels resulted by small-size band gap and weak ferromagnetism make QAHE be measured only at extremely low temperature (<0.1 K). Through density functional theory calculations, we systemically study of the magnetic properties and electronic structures of Mn doped Bi2Se3 with in-plane and out-of-plane strains. It is found that out-of-plane tensile strain not only improve ferromagnetism, but also enlarge Dirac-mass gap (up to 65.6 meV under 6% strain, which is higher than the thermal motion energy at room temperature ~26 meV) in the Mn doped Bi2Se3. Furthermore, the underlying mechanisms of these tunable properties are also discussed. This work provides a new route to realize high-temperature QAHE and paves the way towards novel quantum electronic device applications. PMID:27374782

  9. Strain-modulated ferromagnetism and band gap of Mn doped Bi2Se3

    NASA Astrophysics Data System (ADS)

    Qi, Shifei; Yang, Hualing; Chen, Juan; Zhang, Xiaoyang; Yang, Yingping; Xu, Xiaohong

    2016-07-01

    The quantized anomalous Hall effect (QAHE) have been theoretically predicted and experimentally confirmed in magnetic topological insulators (TI), but dissipative channels resulted by small-size band gap and weak ferromagnetism make QAHE be measured only at extremely low temperature (<0.1 K). Through density functional theory calculations, we systemically study of the magnetic properties and electronic structures of Mn doped Bi2Se3 with in-plane and out-of-plane strains. It is found that out-of-plane tensile strain not only improve ferromagnetism, but also enlarge Dirac-mass gap (up to 65.6 meV under 6% strain, which is higher than the thermal motion energy at room temperature ~26 meV) in the Mn doped Bi2Se3. Furthermore, the underlying mechanisms of these tunable properties are also discussed. This work provides a new route to realize high-temperature QAHE and paves the way towards novel quantum electronic device applications.

  10. Strain Localization in Thin Films of Bi(Fe,Mn)O3 Due to the Formation of Stepped Mn(4+)-Rich Antiphase Boundaries.

    PubMed

    MacLaren, I; Sala, B; Andersson, S M L; Pennycook, T J; Xiong, J; Jia, Q X; Choi, E-M; MacManus-Driscoll, J L

    2015-12-01

    The atomic structure and chemistry of thin films of Bi(Fe,Mn)O3 (BFMO) films with a target composition of Bi2FeMnO6 on SrTiO3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn(4+)-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 Å. Outside the area enclosed by the antiphase boundaries, the out-of-plane lattice parameter is much closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO3 on the SrTiO3 substrate to minimise any Mn-Ti interactions.

  11. Strain localization in thin films of Bi(Fe,Mn)O3 due to the formation of stepped Mn4+-rich antiphase boundaries

    DOE PAGES

    MacLaren, I.; Sala, B.; Andersson, S. M. L.; ...

    2015-10-17

    Here, the atomic structure and chemistry of thin films of Bi(Fe,Mn)O3 (BFMO) films with a target composition of Bi2FeMnO6 on SrTiO3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn4+-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 Å. Outside the area enclosed by the antiphase boundaries, the out-of-plane lattice parameter is muchmore » closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO3 on the SrTiO3 substrate to minimise any Mn-Ti interactions.« less

  12. Bi-quadratic interlayer exchange coupling in Co{sub 2}MnSi/Ag/Co{sub 2}MnSi pseudo spin-valve

    SciTech Connect

    Goripati, Hari S.; Hono, K.; Hayashi, Masamitsu; Furubayashi, T.; Taniguchi, T.; Sukegawa, H.; Takahashi, Y. K.

    2011-12-15

    Bi-quadratic interlayer exchange coupling is found below 100 K in a Co{sub 2}MnSi/Ag/Co{sub 2}MnSi current-perpendicular-to-plane pseudo spin valves. The bi-quadratic coupling constant J{sub 2} was estimated to be {approx}-0.30 erg/cm{sup 2} at 5 K and the strong temperature dependence of the coupling strength points its likely origin to the ''loose spin'' model. Application of current of {approx}2 x 10{sup 7} A/cm{sup 2} below 100 K leads to an increase in the magnetoresistance (MR), indicating current induced antiparallel alignment of the two magnetic layers. These results strongly suggest that the presence of the bi-quadratic interlayer exchange coupling causes the reduction of the magnetoresistance at low temperature and illustrates the importance of understanding the influence of interlayer exchange coupling on magnetization configuration in magnetic nanostructures.

  13. Mn substitution-driven structural and magnetic phase evolution in Bi1-xSmxFeO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Troyanchuk, I. O.; Kovetskaya, M. I.; Paixão, J. A.

    2012-01-01

    X-ray diffraction and magnetization measurements of the Bi0.9Sm0.1Fe1-yMnyO3 and Bi0.86Sm0.14 Fe1-zMnzO3 (y ≤ 0.4, z ≤ 0.3) series were carried out in order to follow the effect of Mn doping on the room temperature crystal structure and magnetic properties of Sm-substituted BiFeO3. Initially polar rhombohedral Bi0.9Sm0.1FeO3 compound (space group R3c) was shown to undergo the Mn-substitution driven structural transformation into the orthorhombic Pnam phase at y ˜ 0.2. Further increasing of the Mn content stabilizes the modified structural phase demonstrating the features of incommensurability. In the Bi0.86Sm0.14Fe1-zMnzO3 series, the initially dominant antipolar orthorhombic Pnam phase transforms toward the nonpolar Pnma structure (z ˜ 0.3). Changes of the main magnetic state (from mixed antiferromagnetic/weak ferromagnetic to weak ferromagnetic) were found to correlate with the rhombohedral-to-orthorhombic transition; however, within the compositional range of the orthorhombically distorted compounds, the room temperature spontaneous magnetization rapidly decreases with increasing Mn content.

  14. Synthesis, composition, and structure of sillenite-type solid solutions in the Bi2O3-SiO2-MnO2 system.

    PubMed

    Mel'nikova, Tatyana I; Kuz'micheva, Galina M; Rybakov, Victor B; Bolotina, Nadezhda B; Dubovsky, Alexander B

    2011-03-07

    Individual compounds and solid solutions are obtained under hydrothermal conditions in the Bi(2)O(3)-SiO(2)-MnO(2) system in the form of faceted crystals and epitaxial films on the Bi(24)Si(2)O(40) substrate. The crystals have the shape of a cube (for the molar ratio of the starting components Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O > 1), a tetrahedron (for Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O < 1), or a tetrahedron-cube combination (for Na(2)SiO(3)·9H(2)O:Mn(NO(3))(2)·6H(2)O = 1). Crystal-chemical analysis based on the data of single-crystal and powder X-ray diffraction, IR spectra, and the results of calculation of the local balance by the bond-valence method reveals formation of the Bi(24)(Si(4+),Mn(4+))(2)O(40) phases, which probably include Mn(5+) ions (epitaxial films), as well as the Bi(24)(Si(4+),Bi(3+),Mn(4+))(2)O(40) and Bi(24)(Si(4+),Mn(4+))(2)O(40) phases in the (1 - x)Bi(3+)(24)Si(4+)(2)O(40) - x(Bi(3+)(24)Mn(4+)(2)O(40)) system and the Bi(24)(Bi(3+),Mn(4+))(2)O(40) phase in the (1 - x)Bi(3+)(24)Bi(3+)(2)(O(39)ⁱ(1)) - x(Bi(3+)(24)Mn(4+)(2)O(40)) system. Precision X-ray diffraction studies of single crystals of the Bi(24)(Bi,Si,Mn)(2)O(40) general composition show that these sillenites crystallize in space group P23 and not I23 as the Bi(24)Si(2)O(40) phase. The dissymmetrization of sillenite phases is observed for the first time. It is explained by a kinetic (growth) phase transition of the order-disorder type due to population of a crystallographic site by atoms with different crystal-chemical properties and quasi-equilibrium conditions of crystal growth in the course of a hydrothermal synthesis below 400 °C at unequal molar amounts of the starting components in the batch.

  15. Direct observation of a gap opening in topological interface states of MnSe/Bi{sub 2}Se{sub 3} heterostructure

    SciTech Connect

    Matetskiy, A. V. Kibirev, I. A.; Saranin, A. A.; Hirahara, T.; Hasegawa, S.; Zotov, A. V.

    2015-08-31

    High-quality MnSe(111) film was bilayer-by-bilayer grown epitaxially onto the Bi{sub 2}Se{sub 3}(111) surface using molecular beam epitaxy. Reversal scenario with quintuple layer-by-layer growth of Bi{sub 2}Se{sub 3} onto the MnSe film was also realized. Angle-resolved photoemission spectroscopy measurements of Bi{sub 2}Se{sub 3} capped with two bi-layers of MnSe revealed that an energy gap of about 90 meV appears at the Dirac point of the original Bi{sub 2}Se{sub 3} surface, possibly due to breaking the time-reversal symmetry on the Bi{sub 2}Se{sub 3} surface by magnetic proximity effect from MnSe.

  16. First-principles study of structural and elastic properties of monoclinic and orthorhombic BiMnO3.

    PubMed

    Mei, Zhi-Gang; Shang, Shun-Li; Wang, Yi; Liu, Zi-Kui

    2010-07-28

    The structural and elastic properties of BiMnO(3) with monoclinic (C 2/c) and orthorhombic (Pnma) ferromagnetic (FM) structures have been studied by first-principles calculations within LDA + U and GGA + U approaches. The equilibrium volumes and bulk moduli of BiMnO(3) phases are evaluated by equation of state (EOS) fittings, and the bulk properties predicted by LDA + U calculations are in better agreement with experiment. The orthorhombic phase is found to be more stable than the monoclinic phase at ambient pressure. A monoclinic to monoclinic phase transition is predicted to occur at a pressure of about 10 GPa, which is ascribed to magnetism versus volume instability of monoclinic BiMnO(3). The single-crystal elastic stiffness constants c(ij)s of the monoclinic and orthorhombic phases are investigated using the stress-strain method. The c(46) of the monoclinic phase is predicted to be negative. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young's modulus, bulk modulus-shear modulus ratio, Poisson's ratio, and elastic anisotropy ratio are determined based on the calculated elastic constants. The presently predicted phase transition and elastic properties open new directions for investigation of the phase transitions in BiMnO(3), and provide helpful guidance for the future elastic constant measurements.

  17. Effect of Eu magnetism on the electronic properties of the candidate Dirac material EuMnBi2

    NASA Astrophysics Data System (ADS)

    May, Andrew F.; McGuire, Michael A.; Sales, Brian C.

    2014-08-01

    The crystal structure and physical properties of the layered material EuMnBi2 have been characterized by measurements on single crystals. EuMnBi2 is isostructural with the Dirac material SrMnBi2 based on single-crystal x-ray diffraction, crystallizing in the I4/mmm space group (No. 139). Magnetic susceptibility measurements suggest antiferromagnetic (AFM) ordering of moments on divalent Eu ions near TN=22 K. For low fields, the ordered Eu moments are aligned along the c axis, and a spin flop is observed near 5.4 T at 5 K. The moment is not saturated in an applied field of 13 T at 5 K, which is uncommon for compounds containing Eu2+. The magnetic behavior suggests an anisotropy enhancement via interaction between Eu and the Mn moments that appear to be ordered antiferromagnetically below ≈310 K. A large increase in the magnetoresistance is observed across the spin flop, with absolute magnetoresistance reaching ≈650% at 5 K and 12 T. Hall effect measurements reveal a decrease in the carrier density below TN, which implies a manipulation of the Fermi surface by magnetism on the sites surrounding the Bi square nets that lead to Dirac cones in this family of materials.

  18. Magnetic BiMn-α phase synthesis prediction: First-principles calculation, thermodynamic modeling and nonequilibrium chemical partitioning

    DOE PAGES

    Zhou, S. H.; Liu, C.; Yao, Y. X.; ...

    2016-04-29

    BiMn-α is promising permanent magnet. Due to its peritectic formation feature, there is a synthetic challenge to produce single BiMn-α phase. The objective of this study is to assess driving force for crystalline phase pathways under far-from-equilibrium conditions. First-principles calculations with Hubbard U correction are performed to provide a robust description of the thermodynamic behavior. The energetics associated with various degrees of the chemical partitioning are quantified to predict temperature, magnetic field, and time dependence of the phase selection. By assessing the phase transformation under the influence of the chemical partitioning, temperatures, and cooling rate from our calculations, we suggestmore » that it is possible to synthesize the magnetic BiMn-α compound in a congruent manner by rapid solidification. The external magnetic field enhances the stability of the BiMn-α phase. In conclusion, the compositions of the initial compounds from these highly driven liquids can be far from equilibrium.« less

  19. Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

    DOE PAGES

    Choi, Yongseong; Jiang, Xiujuan; Bi, Wenli; ...

    2016-11-28

    Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong uniaxial magnetic anisotropy above its ~ 90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) measurements at the Mn K and Bi L2,3 edges show induced magnetism in Bi, which is strongly coupled to the magnetism of Mn. Temperature- and pressure-dependent XMCD results reveal that hydrostatic pressure mimics the effect of temperature, driving a transition from uniaxial to in-plane anisotropy. The pressure and temperature transitions are shown to be connected to an anisotropic lattice contraction in NiAs-type structures. Temperature and pressure, hence, induce coupled structural and magnetic responses,more » highlighting the importance of both anisotropic lattice change and Mn-Bi hybridization in leading to the magnetic anisotropy change across the SRT. Lastly, the dependence of magnetic anisotropy on the anisotropic lattice change is confirmed by density functional theory.« less

  20. Bi-Mn mixed metal organic oxide: A novel 3d-6p mixed metal coordination network

    NASA Astrophysics Data System (ADS)

    Shi, Fa-Nian; Rosa Silva, Ana; Bian, Liang

    2015-05-01

    A new terminology of metal organic oxide (MOO) was given a definition as a type of coordination polymers which possess the feature of inorganic connectivity between metals and the direct bonded atoms and show 1D, 2D or 3D inorganic sub-networks. One such compound was shown as an example. A 3d-6p (Mn-Bi. Named MOOMnBi) mixed metals coordination network has been synthesized via hydrothermal method. The new compound with the molecular formula of [MnBi2O(1,3,5-BTC)2]n (1,3,5-BTC stands for benzene-1,3,5-tricarboxylate) was characterized via single crystal X-ray diffraction technique that revealed a very interesting 3-dimensional (3D) framework with Bi4O2(COO)12 clusters which are further connected to Mn(COO)6 fragments into a 2D MOO. The topology study indicates an unprecedented topological type with the net point group of {413.62}{413.68}{416.65}{418.610}{422.614}{43} corresponding to 3,6,7,7,8,9-c hexa-nodal net. MOOMnBi shows catalytic activity in the synthesis of (E)-α,β-unsaturated ketones.

  1. Neutron diffraction study of magnetic ordering of the manganese bismuth chloro-sulfide: MnBiS{sub 2}Cl

    SciTech Connect

    Doussier-Brochard, C.; Leone, P. Andre, G.; Moelo, Y.

    2009-04-02

    In quaternary compounds of Mn{sup 2+}PnQ{sub 2}X (Pn = Sb, Bi; Q = S, Se; X = Cl, Br, I), Mn atoms in octahedral coordination (4 Q and 2 X) form waved layers separated by Pn atoms. The magnetic structure of the manganese bismuth chloro-sulfide MnBiS{sub 2}Cl has been determined by neutron powder diffraction, revealing a magnetic ordering with an incommensurate wave-vector along b-axis (k = [0, 0.3978, 0]) at 1.6 K. Two modulation models, sinusoidal and helicoidal, give quite equivalent magnetic reliability factors (R{sub mag} = 0.0450 and 0.0481, respectively). The magnetic moment decreases with increasing temperature, to zero at T{sub N} = 32 K. The evolution of the propagation wave-vector shows an irregularity at about 28 K. It could evidence two-phase transitions in agreement with the specific heat measurements. These results are compared to those of manganese antimony chloro-sulfide MnSbS{sub 2}Cl, isotypic with MnBiS{sub 2}Cl.

  2. Anomalous Dilatometric Response in Fe-Mn-Al-Si Steel

    NASA Astrophysics Data System (ADS)

    Ghosh, S. K.

    2012-04-01

    The present study deals with the transformation of an aggregate consisting of ferrite and pearlite into austenite in a Fe-0.36C-1.98Mn-1.97Al-0.30Si (wt%) steel. The transformation phenomenon has been studied using dilatometry which confirms that austenite starts to nucleate due to dissolution of ferrite and pearlite and subsequently it commences to grow when the appropriate elevated temperature is reached. The austenite formation has been accompanied with the formation of a hump in the dilatation curve which is different with respect to the results reported earlier. The non-conventional behaviour associated with the austenite formation has been explained using the X-ray diffraction data, microstructural investigation and also with MT-DATA theoretical calculations.

  3. Recrystallization behavior of a supersaturated Al Mn alloy

    SciTech Connect

    Radhakrishnan, Balasubramaniam; Liu, W C

    2010-01-01

    The effect of concurrent precipitation on recrystallization behavior during the isothermal annealing of a supersaturated and deformed Al-Mn alloy was investigated. It is found that concurrent precipitation strongly affects the recrystallization behavior of this alloy. At low temperatures, concurrent precipitation retards recrystallization and results in large flat grains. The size of recrystallized grains decreases significantly with increasing temperature. The kinetics of recrystallization was determined by measurements of hardness. The JMAK exponent decreases from 3.0 to 0.8 as the annealing temperature increases from 371 C to 427 C. The activation energy for recrystallization of the alloy is about 456 kJ/mol. Concurrent precipitation enhances the activation energy for recrystallization of aluminum alloys.

  4. Magnetic structure and spin excitations in BaMn2Bi2

    DOE PAGES

    Calder, Stuart A.; Saparov, Bayrammurad I; Cao, H. B.; ...

    2014-02-19

    We present a single crystal neutron scattering study of BaMn2Bi2, a recently synthesized material with the same ThCr2Si2type structure found in several Fe-based unconventional superconducting materials. We show long range magnetic order, in the form of a G-type antiferromagnetic structure, to exist up to 390 K with an indication of a structural transition at 100 K. Utilizing inelastic neutron scattering we observe a spin-gap of 16 meV, with spin-waves extending up to 55 meV. We find these magnetic excitations are well fit to a J1-J2-Jc Heisenberg model and present values for the exchange interactions. The spin wave spectrum appears tomore » be unchanged by the 100 K structural phase transition.« less

  5. Magnetic and structural phase transitions of MnBi under high magnetic fields

    PubMed Central

    Koyama, Keiichi; Mitsui, Yoshifuru; Watanabe, Kazuo

    2008-01-01

    High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature TSR(=90 K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of TSR. By applying a magnetic field of 5 T, the parameter a increases by ∼0.05% when T

  6. Synthesis, characterization and electrochemical performance of Al-substituted Li₂MnO₃

    SciTech Connect

    Dhital, Chetan; Huq, Ashfia; Paranthaman, Mariappan Parans; Manivannan, Ayyakkannu; Torres-Castro, Loraine; Shojan, Jifi; Julien, Christian M.; Katiyar, Ram S.

    2015-08-08

    Li2MnO3 is known to be electrochemically inactive due to Mn in tetravalent oxidation state. Several compositions such as Li2MnO3 , Li1.5Al0.17MnO3, Li1.0Al0.33MnO3 and Li0.5Al0.5MnO3 were synthesized by a sol–gel Pechini method. All the samples were characterized with x-ray diffraction, Raman, x-ray photoelectron spectroscopy, scanning electron microscopy, Tap density and BET analyzer. X-ray diffraction patterns indicated the presence of monoclinic phase for pristine Li2MnO3and mixed monoclinic/spinel phases (Li2 - xMn1 - yAlx + yO3 + z) for Al-substituted Li2MnO3compounds. The Al substitution seems to occur both at Li and Mn sites, which could explain the presence of spinel phase. X-ray photoelectron spectroscopy for Mn 2p orbital reveals a significant decrease in binding energy for Li1.0Al0.33MnO3 and Li0.5Al0.5MnO3 compounds. Cyclic voltammetry, charge/discharge cycles and electrochemical impedance spectroscopy were also performed. A discharge capacity of 24 mAh g-1 for Li2MnO3, 68 mAh g-1 for Li1.5Al0.17MnO3, 58 mAh g-1 for Li1.0Al0.33MnO3 and 74 mAh g-1 for Li0.5Al0.5MnO3 were obtained. As a result, aluminum substitutions increased the formation of spinel phase which is responsible for cycling.

  7. Josephson effect in Al/Bi2Se3/Al coplanar hybrid devices

    NASA Astrophysics Data System (ADS)

    Galletti, L.; Charpentier, S.; Lucignano, P.; Massarotti, D.; Arpaia, R.; Tafuri, F.; Bauch, T.; Suzuki, Y.; Tagliacozzo, A.; Kadowaki, K.; Lombardi, F.

    2014-08-01

    The edge states of Topological Insulators (TI) are protected against backscattering, thanks to the topological properties arising from their band structure. Coupling a TI to a superconductor (S) can induce unconventional effects, including the creation of Majorana bound states (MBS). The fabrication of coplanar hybrid devices is a fundamental step to pave the way to the understanding of proximity effects in topologically non-trivial systems, and to a large variety of experiments aimed at the possible detection of MBS. We discuss the feasibility and some relevant properties of Al-Bi2Se3-Al coplanar proximity devices. Special attention is devoted to the design of the junction, aimed at enhancing the coupling between the electrodes and the TI.

  8. Fabrication of L10-Ordered MnAl Films for Observation of Tunnel Magnetoresistance Effect

    NASA Astrophysics Data System (ADS)

    Saruyama, Haruaki; Oogane, Mikihiko; Kurimoto, Yuta; Naganuma, Hiroshi; Ando, Yasuo

    2013-06-01

    We succeeded in fabricating L10-ordered MnAl films with a high perpendicular magnetic anisotropy energy of 107 erg/cm3 and a small average film roughness of 0.4 nm by using a molten Mn-Al sputtering alloyed target and optimizing the substrate temperature. In addition, we investigated the tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs) with the prepared L10-ordered MnAl electrode. The TMR effect was observed at RT in an MTJ with a very thin Co50Fe50 layer inserted into the MnAl electrode and MgO tunneling barrier interface. This is the first observation of the TMR effect in MTJs with an L10-ordered MnAl electrode.

  9. Elastocaloric effect in CuAlZn and CuAlMn shape memory alloys under compression.

    PubMed

    Qian, Suxin; Geng, Yunlong; Wang, Yi; Pillsbury, Thomas E; Hada, Yoshiharu; Yamaguchi, Yuki; Fujimoto, Kenjiro; Hwang, Yunho; Radermacher, Reinhard; Cui, Jun; Yuki, Yoji; Toyotake, Koutaro; Takeuchi, Ichiro

    2016-08-13

    This paper reports the elastocaloric effect of two Cu-based shape memory alloys: Cu68Al16Zn16 (CuAlZn) and Cu73Al15Mn12 (CuAlMn), under compression at ambient temperature. The compression tests were conducted at two different rates to approach isothermal and adiabatic conditions. Upon unloading at a strain rate of 0.1 s(-1) (adiabatic condition) from 4% strain, the highest adiabatic temperature changes (ΔTad) of 4.0 K for CuAlZn and 3.9 K for CuAlMn were obtained. The maximum stress and hysteresis at each strain were compared. The stress at the maximum recoverable strain of 4.0% for CuAlMn was 120 MPa, which is 70% smaller than that of CuAlZn. A smaller hysteresis for the CuAlMn alloy was also obtained, about 70% less compared with the CuAlZn alloy. The latent heat, determined by differential scanning calorimetry, was 4.3 J g(-1) for the CuAlZn alloy and 5.0 J g(-1) for the CuAlMn alloy. Potential coefficients of performance (COPmat) for these two alloys were calculated based on their physical properties of measured latent heat and hysteresis, and a COPmat of approximately 13.3 for CuAlMn was obtained.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

  10. Luminescent properties of Mn-doped Y3Al5O12 single crystalline films

    NASA Astrophysics Data System (ADS)

    Zorenko, Yu.; Gorbenko, V.; Zorenko, T.; Kuklinski, B.; Grinberg, M.; Wiśniewski, K.; Bilski, P.

    2014-08-01

    The absorption, cathodoluminescence and photoluminescence (PL) spectra as well as PL decay kinetics of Mn doped Y3Al5O12 (YAG:Mn) single crystalline films (SCF) with manganese concentration in the 0.002-0.2 at.% range, grown by the LPE method from PbO to B2O3 based flux onto YAG substrates, were analyzed in this work. The special goal was spectroscopic determination of valence states of manganese ions which are realized in these SCF depending on Mn content. In SCF with Mn content (0.002-0.02 at.%), the incorporation of Mn4+ and Mn2+ ions was found. The absorption and emission spectra of YAG:Mn SCF at higher (0.02-0.2 at.%) content confirmed that the main valence state of manganese ions is Mn3+ state.

  11. CaMn2Al10: Itinerant Mn magnetism on the verge of magnetic order

    SciTech Connect

    Steinke, L.; Simonson, J. W.; Yin, W. -G.; Smith, G. J.; Kistner-Morris, J. J.; Zellman, S.; Puri, A.; Aronson, M. C.

    2015-07-24

    We report the discovery of CaMn2Al10, a metal with strong magnetic anisotropy and moderate electronic correlations. Magnetization measurements find a Curie-Weiss moment of 0.83μB/Mn, significantly reduced from the Hund's rule value, and the magnetic entropy obtained from specific heat measurements is correspondingly small, only ≈ 9% of Rln2. These results imply that the Mn magnetism is highly itinerant, a conclusion supported by density functional theory calculations that find strong Mn-Al hybridization. Consistent with the layered nature of the crystal structure, the magnetic susceptibility χ is anisotropic below 20 K, with a maximum ratio of χ[010][001] ≈ 3.5. A strong power-law divergence χ(T) ~ T–1.2 below 20 K implies incipient ferromagnetic order, an Arrott plot analysis of the magnetization suggests a vanishing low Curie temperature TC ~ 0. Our experiments indicate that CaMn2Al10 is a rare example of a system where the weak and itinerant Mn-based magnetism is poised on the verge of order.

  12. Crystal structure and magnetic properties of the Cr-doped spiral antiferromagnet BiMnFe{sub 2}O{sub 6}

    SciTech Connect

    Batuk, Dmitry; De Dobbelaere, Christopher; Tsirlin, Alexander A.; Abakumov, Artem M.; Hardy, An; Van Bael, Marlies K.; Greenblatt, Martha; Hadermann, Joke

    2013-09-01

    Graphical abstract: - Highlights: • The substitution of Cr for Mn in BiMnFe{sub 2}O{sub 6} is possible by the solution–gel method. • The BiCr{sub x}Mn{sub 1−x}Fe{sub 2}O{sub 6} solid solution is obtained for the x values up to 0.3. • Increasing Cr content lowers the temperature of the antiferromagnetic ordering. - Abstract: We report the Cr{sup 3+} for Mn{sup 3+} substitution in the BiMnFe{sub 2}O{sub 6} structure. The BiCr{sub x}Mn{sub 1−x}Fe{sub 2}O{sub 6} solid solution is obtained by the solution–gel synthesis technique for the x values up to 0.3. The crystal structure investigation using a combination of X-ray powder diffraction and transmission electron microscopy demonstrates that the compounds retain the parent BiMnFe{sub 2}O{sub 6} structure (for x = 0.3, a = 5.02010(6)Å, b = 7.06594(7)Å, c = 12.6174(1)Å, S.G. Pbcm, R{sub I} = 0.036, R{sub P} = 0.011) with only a slight decrease in the cell parameters associated with the Cr{sup 3+} for Mn{sup 3+} substitution. Magnetic susceptibility measurements suggest strong similarities in the magnetic behavior of BiCr{sub x}Mn{sub 1−x}Fe{sub 2}O{sub 6} (x = 0.2; 0.3) and parent BiMnFe{sub 2}O{sub 6}. Only T{sub N} slightly decreases upon Cr doping that indicates a very subtle influence of Cr{sup 3+} cations on the magnetic properties at the available substitution rates.

  13. Influence of sp-d hybridization on the electronic structure of Al-Mn alloys

    SciTech Connect

    Shukla, A. K.; Biswas, C.; Dhaka, R. S.; Das, S. C.; Barman, S. R.; Krueger, P.

    2008-05-15

    The influence of sp-d hybridization on the electronic structure of different Al-Mn alloys has been studied by photoelectron spectroscopy. Experimental evidence of a pseudogap in a crystalline binary Hume-Rothery alloy is provided. The pseudogap varies systematically with Mn concentration. The sp-d hybridization alone, even in the absence of Hume-Rothery mechanism, can produce the pseudogap. Existence of the pseudogap, suppression of the Mn 2p satellite, and decrease in the Doniach-Sunjic asymmetry parameter are the consequences of the sp-d hybridization. An in situ method of preparing these alloys by annealing a Mn adlayer on Al(111) is presented.

  14. Influence of sp-d hybridization on the electronic structure of Al-Mn alloys

    NASA Astrophysics Data System (ADS)

    Shukla, A. K.; Biswas, C.; Dhaka, R. S.; Das, S. C.; Krüger, P.; Barman, S. R.

    2008-05-01

    The influence of sp-d hybridization on the electronic structure of different Al-Mn alloys has been studied by photoelectron spectroscopy. Experimental evidence of a pseudogap in a crystalline binary Hume-Rothery alloy is provided. The pseudogap varies systematically with Mn concentration. The sp-d hybridization alone, even in the absence of Hume-Rothery mechanism, can produce the pseudogap. Existence of the pseudogap, suppression of the Mn2p satellite, and decrease in the Doniach-Šunjić asymmetry parameter are the consequences of the sp-d hybridization. An in situ method of preparing these alloys by annealing a Mn adlayer on Al(111) is presented.

  15. Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

    PubMed

    Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

    2016-09-01

    A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal.

  16. Catalytic oxidation of toluene in contaminant emission control systems using Mn-Ce/gamma-Al2O3.

    PubMed

    Kim, H-J; Choi, S-W; Inyang, H I

    2008-05-01

    Toluene, the alkyl benzene, is a common constituent of contaminant streams emitted by hydrocarbon fuel combustion systems. The oxidation of toluene to less toxic compounds can be enhanced through catalysis. The capacity of Mn-Ce/gamma-Al2O3 to catalyze toluene oxidation was investigated using a fixed bed flow reactor, operating within a temperature range of 160-400 degrees C. Mono-metallic catalysts were prepared with the manganese and cerium contents of 1-21 wt% on gamma-Al2O3, support and bi-metallic catalysts were prepared with cerium (0.5-21 wt%/) on 18.2 wt% manganese. The results indicate that the 18.2 wt% Mn-10.0 wt% Ce catalyst combination had the best catalytic efficiency for toluene oxidation. Increase in cerium loading reduces the surface area of catalytic materials measured by BET, but increases catalytic activity. Data obtained through TGA (Thermogravimetric analysis), XRD (X-ray diffraction) and toluene-TPR (Temperature Programmed Reduction) measurements show that the reduction of the catalysts in the process of toluene oxidation is directly proportional to observed weight loss under hydrogen flow. From these results, it is concluded that cerium improves the catalytic role of manganese in toluene oxidation. Oxygen mobility is also promoted in a redox mechanism in which MnO2 serves as the active sites. These results are useful in the development of toluene emission control systems for hydrocarbon fuel combustion systems.

  17. Ferroelectric Sm-Doped BiMnO3 Thin Films with Ferromagnetic Transition Temperature Enhanced to 140 K

    PubMed Central

    2014-01-01

    A combined chemical pressure and substrate biaxial pressure crystal engineering approach was demonstrated for producing highly epitaxial Sm-doped BiMnO3 (BSMO) films on SrTiO3 single crystal substrates, with enhanced magnetic transition temperatures, TC up to as high as 140 K, 40 K higher than that for standard BiMnO3 (BMO) films. Strong room temperature ferroelectricity with piezoresponse amplitude, d33 = 10 pm/V, and long-term retention of polarization were also observed. Furthermore, the BSMO films were much easier to grow than pure BMO films, with excellent phase purity over a wide growth window. The work represents a very effective way to independently control strain in-plane and out-of-plane, which is important not just for BMO but for controlling the properties of many other strongly correlated oxides. PMID:25141031

  18. Contribution of an extrinsic mechanism for the electrical polarization in BiMn{sub 2}O{sub 5} ceramics

    SciTech Connect

    Fier, I.; Chinaglia, D. L.; Walmsley, L.; Pereira, E. C.; Rabelo, A. C.; Freitas, R. G.

    2012-12-15

    DC conductivity, frequency dependent dielectric constant and pyroelectric coefficients, obtained from thermal stimulated depolarization current curves, in BiMn{sub 2}O{sub 5} ceramics in the range of temperatures from 10 K to 320 K are reported. The data could be explained if it is assumed that a dipole defect is formed due to an oxygen vacancy and two manganese ions which have their valence changed to accept an electron.

  19. Structural, magnetic, and dielectric properties of solid solutions between BiMnO3 and YMnO3

    NASA Astrophysics Data System (ADS)

    Belik, Alexei A.

    2017-02-01

    Bi1-xYxMnO3 (0.1≤x≤0.9) solid solutions were prepared by the high-pressure high-temperature method at 6 GPa and 1573 K. They crystallize in the GdFeO3-type perovskite structure with the Pnma symmetry. Crystal structures of Bi0.9Y0.1MnO3 and Bi0.5Y0.5MnO3 are studied by synchrotron X-ray powder diffraction at room temperature. Only one Néel temperature, TN, is found in samples with 0.1≤x≤0.9 in comparison with two Néel temperatures observed in YMnO3 (TN=29 and 39 K). Samples with 0.5≤x≤0.9 have almost constant TN=44 K, while TN starts to increase linearly for other compositions: TN=46 K for x=0.3, TN=58 K for x=0.2, and TN=68 K for x=0.1. Field-induced transitions from canted-antiferromagnetic states to antiferromagnetic states are detected at about 30 kOe for x=0.2 and 70 kOe for x=0.1. Dielectric constant increases below TN in samples with 0.5≤x≤1, while it decreases below TN in samples with 0.1≤x≤0.3. Our data suggest that a magnetic structure changes near x=0.4. By extrapolation, we could estimate lattice parameters (a=5.9221 Å, b=7.5738 Å, and c=5.4157 Å) and TN=79 K for a hypothetical Pnma modification of BiMnO3.

  20. Mn-doping induced ferromagnetism and enhanced superconductivity in Bi4 -xMnxO4S3 (0.075 ≤x ≤0.15 )

    NASA Astrophysics Data System (ADS)

    Feng, Zhenjie; Yin, Xunqing; Cao, Yiming; Peng, Xianglian; Gao, Tian; Yu, Chuan; Chen, Jingzhe; Kang, Baojuan; Lu, Bo; Guo, Juan; Li, Qing; Tseng, Wei-Shiuan; Ma, Zhongquan; Jing, Chao; Cao, Shixun; Zhang, Jincang; Yeh, N.-C.

    2016-08-01

    We demonstrate that Mn doping in the layered sulfides Bi4O4S3 leads to stable Bi4-xMnxO4S3 compounds that exhibit both long-range ferromagnetism and enhanced superconductivity for 0.075 ≤x ≤0.15 , with a possible record superconducting transition temperature (Tc) ˜15 K among all BiS2-based superconductors. We conjecture that the coexistence of superconductivity and ferromagnetism may be attributed to Mn doping in the spacer Bi2O2 layers away from the superconducting BiS2 layers, whereas the enhancement of Tc may be due to excess electron transfer to BiS2 from the Mn4 +/Mn3 + substitutions in Bi2O2 . This notion is empirically corroborated by the increased electron-carrier densities upon Mn doping, and by further studies of the Bi4-xAxO4S3 compounds (A = Co, Ni; x =0.1 , 0.125), where the Tc values remain comparable to that of the undoped Bi4O4S3 system (˜4.5 K) due to lack of 4+ valences in either Co or Ni ions for excess electron transfer to the BiS2 layers. These findings therefore shed new light on feasible pathways to enhance the Tc values of BiS2-based superconductors, although complete elucidation of the interplay between superconductivity and ferromagnetism in these anisotropic layered compounds awaits the development of single crystalline materials for further investigation.

  1. Micromagnetic analysis of the hardening mechanisms of nanocrystalline MnBi and nanopatterned FePt intermetallic compounds.

    PubMed

    Kronmüller, H; Yang, J B; Goll, D

    2014-02-12

    The uniaxial intermetallic compounds of L10-FePt and the low temperature NiAs structure of MnBi are suitable alloys for application as high-density recording materials or as high-coercivity permanent magnets. Single domain particles of these materials are characterized by coercive fields above 1 T over a large temperature range. In particular MnBi shows a coercive field of 2 T at 450 K. Its extraordinary magnetic properties in the temperature range up to 600 K are due to an increase of the magnetocrystalline anisotropy constant from 1.2 MJ m(-3) at 300 K to 2.4 MJ m(-3) at 450 K. In spite of the large coercivities obtained for both type of materials their experimental values deviate considerably from the theoretical values Hc = 2K1/Js valid for a homogeneous rotation process in spherical particles. As is well known these discrepancies are due to the deteriorating effects of the microstructure. For an analysis of the coercive fields the Stoner-Wohlfarth theory has to be expanded with respect to higher anisotropy constants and to microstructural effects such as misaligned grains and grain surfaces with reduced anisotropy constants. It is shown that the temperature dependence and the angular dependence of Hc for FePt as well as MnBi can be quantitatively interpreted by taking into account the above mentioned intrinsic and microstructural effects.

  2. Time-reversal symmetry breaking type II Weyl state in YbMnBi2

    NASA Astrophysics Data System (ADS)

    Borisenko, Sergey

    Detection of Dirac, Majorana and Weyl fermions in real materials may significantly strengthen the bridge between high-energy and condensed-matter physics. While the presence of Dirac fermions is well established in graphene and topological insulators, Majorana particles have been reported recently and evidence for Weyl fermions in non-centrosymmetric crystals has been found only a couple of months ago, the ``magnetic'' Weyl fermions are still elusive despite numerous theoretical predictions and intense experimental search. In order to detect a time-reversal symmetry breaking Weyl state we designed two materials with Fermi velocities superior to that of graphene and I will present the experimental evidence of realization of such a state in one of them, YbMnBi2. We model the time reversal symmetry breaking observed by magnetization measurements by a canted antiferromagnetic state and find a number of Weyl points both above and below the Fermi level. Using angle-resolved photoemission, we directly observe these latter Weyl points and a hallmark of the exotic state - the arc of the surface states which connects these points. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties.

  3. Effect of Mn doping on ultrafast carrier dynamics in thin films of the topological insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    Glinka, Yuri D.; Babakiray, Sercan; Holcomb, Mikel B.; Lederman, David

    2016-04-01

    Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface-coupled topological insulator Bi2-x Mn x Se3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x  =  0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x  =  0.013-0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn2+ acceptors and their dimers. The shortest decay-time (~0.75 ps) measured for the film with x  =  0.27 suggests a great potential of Mn-doped Bi2Se3 films for applications in high-speed optoelectronic devices. Using Raman spectroscopy exploiting similar laser photon energy (1.58 eV), we demonstrate that due to indirect intersurface coupling in the films, the photoexcited electron trapping in the bulk enhances the electron-phonon interaction strength in Dirac surface states.

  4. Structural transitions and enhanced ferroelectricity in Ca and Mn co-doped BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Huang, Ji-Zhou; Shen, Yang; Li, Ming; Nan, Ce-Wen

    2011-11-01

    Ca and Mn co-doped BiFeO3 (BFO) thin films were fabricated on (111) Pt/Ti/SiO2/Si substrates via a simple solution approach. Enhanced ferroelectric properties were obtained in these Ca and Mn co-doped BFO films, e.g., large remnant polarization value (Pr ˜ 89 μC/cm2) and large remnant polarization to saturated polarization ratio (Pr/Ps ˜ 0.84) for Bi0.90Ca0.10Fe0.90Mn0.10O3 film. X-ray diffraction and Raman spectra of these films showed that B-site Mn doping causes substantial structural transition toward orthorhombic phase and A-site Ca doping facilitates an evolution to tetragonal phase with higher crystal symmetry. The structural transitions are in favor of enhanced ferroelectric properties in the BFO films. The approach of A and B site co-doping is proved to be effective in enhancing ferroelectric performance in multiferroic BFO films.

  5. Oxidation behavior of cubic phases formed by alloying Al3Ti with Cr and Mn

    NASA Technical Reports Server (NTRS)

    Parfitt, L. J.; Nic, J. P.; Mikkola, D. E.; Smialek, J. L.

    1991-01-01

    Gravimetric, SEM, and XRD data are presented which document the significant improvement obtainable in the oxidation resistance of Al3Ti-containing alloys through additions of Cr. The L1(2) Al(67)Cr(8)Ti25 alloy exhibited excellent cyclic oxidation resistance at 1473 K, with the primary oxide formed being the ideally protective alpha-Al2O3. The Al(67)Mn(8)Ti(25) alloy also tested for comparison exhibited poor cyclic oxidation resistance, with substantial occurrence of TiO2 in the protective scales. Catastrophic oxidation was also encountered in the quaternary alloy Al(67)Mn(8)Ti(22)V(3).

  6. Amorphization of Al[sub 6]Mn phase in an Al-14 a/o Mn alloy during low energy helium ion bombardment

    SciTech Connect

    Nair, K.G.M.; Krishan, K. . Materials Science Division); Vijayalakshmi, M. . Metallurgy Division)

    1993-10-01

    Amorphization of ordered intermetallic compounds has been observed during ion, electron and neutron irradiations. Investigations have been carried out in a number of systems. It has been generally observed that intermetallic compounds with a narrow range of homogeneity (line compounds) amorphize on irradiation. The present paper reports the observation of irradiation-induced amorphization in the Al[sub 6]Mn phase in an Al-14 a/o Mn alloy. The dose and energy dependence of the amorphization process are discussed. The present studies suggest that the defects produced during irradiation rather than the implanted atoms (helium) play a major role in the crystalline to amorphous transition.

  7. Interactions in Ternary Mixtures of MnO2, Al2O3, and Natural Organic Matter (NOM) and the Impact on MnO2 Oxidative Reactivity.

    PubMed

    Taujale, Saru; Baratta, Laura R; Huang, Jianzhi; Zhang, Huichun

    2016-03-01

    Our previous work reported that Al2O3 inhibited the oxidative reactivity of MnO2 through heteroaggregation between oxide particles and surface complexation of the dissolved Al ions with MnO2 (S. Taujale and H. Zhang, "Impact of interactions between metal oxides to oxidative reactivity of manganese dioxide" Environ. Sci. Technol. 2012, 46, 2764-2771). The aim of the current work was to investigate interactions in ternary mixtures of MnO2, Al2O3, and NOM and how the interactions affect MnO2 oxidative reactivity. For the effect of Al ions, we examined ternary mixtures of MnO2, Al ions, and NOM. Our results indicated that an increase in the amount of humic acids (HAs) increasingly inhibited Al adsorption by forming soluble Al-HA complexes. As a consequence, there was less inhibition on MnO2 reactivity than by the sum of two binary mixtures (MnO2+Al ions and MnO2+HA). Alginate or pyromellitic acid (PA)-two model NOM compounds-did not affect Al adsorption, but Al ions increased alginate/PA adsorption by MnO2. The latter effect led to more inhibition on MnO2 reactivity than the sum of the two binary mixtures. In ternary mixtures of MnO2, Al2O3, and NOM, NOM inhibited dissolution of Al2O3. Zeta potential measurements, sedimentation experiments, TEM images, and modified DLVO calculations all indicated that HAs of up to 4 mg-C/L increased heteroaggregation between Al2O3 and MnO2, whereas higher amounts of HAs completely inhibited heteroaggregation. The effect of alginate is similar to that of HAs, although not as significant, while PA had negligible effects on heteroaggregation. Different from the effects of Al ions and NOMs on MnO2 reactivity, the MnO2 reactivity in ternary mixtures of Al2O3, MnO2, and NOM was mostly enhanced. This suggests MnO2 reactivity was mainly affected through heteroaggregation in the ternary mixtures because of the limited availability of Al ions.

  8. Fabrication of L10-MnAl perpendicularly magnetized thin films for perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Hosoda, Masaki; Oogane, Mikihiko; Kubota, Miho; Kubota, Takahide; Saruyama, Haruaki; Iihama, Satoshi; Naganuma, Hiroshi; Ando, Yasuo

    2012-04-01

    Structural and magnetic properties of MnAl thin films with different composition, growth temperature, and post-annealing temperature were investigated. The optimum condition for fabrication of L10-MnAl perpendicularly magnetized thin film deposited on Cr-buffered MgO single crystal substrate was revealed. The results of x ray diffraction indicated that the MnAl films annealed at proper temperature had a (001)-orientation and L10-ordered structure. The L10-ordered films were perpendicularly magnetized and had a large perpendicular anisotropy. In addition, low surface roughness was achieved. For the optimized fabrication condition, the saturation magnetization Ms of 600 emu/cm3 and perpendicular magnetic anisotropy Ku of 1.0 × 107 erg/cm3 was obtained using the Mn48Al52 target at deposition temperature of 200 °C and post-annealing temperature of 450 °C.

  9. Development of Rare-Earth Free Mn-Al Permanent Magnet Employing Powder Metallurgy Route

    NASA Astrophysics Data System (ADS)

    Singh, N.; Shyam, R.; Upadhyay, N. K.; Dhar, A.

    2015-02-01

    Most widely used high-performance permanent magnets are currently based on intermetallics of rare-earths in combination with Fe and Co. Rare-earth elements required for these magnets are getting expensive by the day. Consequently, there is a thrust worldwide to develop economical rare-earth free permanent magnets. It is acknowledged that the phase in Mn-Al alloys possesses magnetic properties without the presence of ferromagnetic elements such as Fe, Co, and Ni. In the present study, we report the synthesis of magnetic phase of Mn54Al46 alloy synthesized using mechanical alloying followed by solutionizing and annealing to obtain the desired magnetic phase. It is well known that Al dissolves partially in Mn matrix hence supersaturated solid solution of Mn54Al46 alloy powder was obtained by mechanical alloying using a planetary high-energy ball mill. For this purpose elemental Mn and Al powders were ball-milled in Argon atmosphere at 400 rpm using stainless steel bowl with ball to powder ratio of 15:1. These mechanically alloyed Mn54Al46 powders were then consolidated using spark plasma sintering at 550°C for 20 min. followed by solution treatment at 1050°C for 5 hrs and then water quenched to retain high temperature phase. Subsequently, the Mn54Al46 samples were annealed in the temperature range 450°C-650°C to obtain the magnetic phase. These samples were characterized by XRD and SEM and the magnetic properties were measured using a vibrating sample magnetometer (VSM). It was observed that the magnetization and coercivity of MnAl magnets exhibited strong dependence on annealing temperature and annealing time.

  10. Antiferromagnetic interaction between A'-site Mn spins in A-site-ordered perovskite YMn3Al4O12.

    PubMed

    Tohyama, Takenori; Saito, Takashi; Mizumaki, Masaichiro; Agui, Akane; Shimakawa, Yuichi

    2010-03-01

    The A-site-ordered perovskite YMn(3)Al(4)O(12) was prepared by high-pressure synthesis. Structural analysis with synchrotron powder X-ray diffraction data and the Mn L-edges X-ray absorption spectrum revealed that the compound has a chemical composition Y(3+)Mn(3+)(3)Al(3+)(4)O(2-)(12) with magnetic Mn(3+) at the A' site and non-magnetic Al(3+) at the B site. An antiferromagnetic interaction between the A'-site Mn(3+) spins is induced by the nearest neighboring Mn-Mn direct exchange interaction and causes an antiferromagnetic transition at 34.3 K.

  11. Improved tunneling magnetoresistance in (Ga,Mn)As/AlOx/CoFeB magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Yu, G. Q.; Chen, L.; Rizwan, Syed; Zhao, J. H.; XU, K.; Han, X. F.

    2011-06-01

    We fabricated (Ga,Mn)As/AlOx/Co40Fe40B20 magnetic tunnel junctions with ferromagnetic semiconductor/insulator/ferromagnetic metal (S/I/F) structure. The treatments of pre-annealing and post-plasma cleaning on the (Ga,Mn)As film were introduced before the growth of the subsequent layers. A high tunneling magnetoresistance (TMR) ratio of 101% is achieved at 2 K, and the spin polarization of (Ga,Mn)As, P = 56.8%, is deduced from Jullière's formula. The improved TMR ratio is primarily due to the improved magnetism of (Ga,Mn)As layer by low-temperature annealing and cleaned interface between (Ga,Mn)As and AlOx attained by subsequent plasma cleaning process.

  12. Effect of Ni content on microwave absorbing properties of MnAl powder

    NASA Astrophysics Data System (ADS)

    Wang, Zhen-zhong; Lin, Pei-hao; Huang, Wei-chao; Pan, Shun-kang; Liu, Ye; Wang, Lei

    2016-09-01

    MnAlNi powder was prepared by the process of vacuum levitation melting and high-energy ball milling, The morphology and phase structure of the powder were analyzed by Scanning Electron Microscope(SEM), X-ray diffraction(XRD) and the effect of the Ni content on microwave absorbing properties of MnAl powder was investigated by an vector network analyzer. The addition of Ni, which improved the microwave absorbing properties of MnAl powder but not changed the composition of Al8Mn5 alloy. The minimum reflectivity of (Al8Mn5)0.95Ni0.05 powder with a coating thickness (d) of 1.8 mm was about -40.8 dB and has better bandwidth effect, the absorbing mechanism of AlMnNi powders on the electromagnetic was related to the electromagnetic loss within the absorbing coatings and the effect of coating thickness on the interference loss of electromagnetic wave.

  13. Electronic diffuse reflectance spectra of Bi-V-Sb-Al catalysts for oxidative ammonolysis

    SciTech Connect

    Rizaev, R.G.; Akhverdiev, R.B.; Alieva, T.C.; Efendiev, M.R.; Krylov, O.V.; Magerranova, Z.Y.

    1986-10-01

    Diffuse reflectance spectra of monocomponent, binary, and tricomponent Bi-VSb-Al catalysts for the oxidative ammonolysis of aromatic compounds were taken in the 200- to 850-nm region and interpreted. It was established that vanadium ions in two valence states, V/sup 4 +/ and V/sup 5 +/, exist on the surface of ..gamma..-Al/sub 2/O/sub 3/. On treatment of V-Sb-Al with a reaction mixture of C/sub 7/H/sub 6/Cl/sub 2/ + O/sub 2/ + NH/sub 3/, V/sup 5 +/ ions are reduced to V/sup 4 +/ and Sb/sup 3 +/ ions are oxidized to Sb/sup 5 +/. This is also characteristic of the V-Al and Sb-Al oxide systems. In the case of V-Bi-Al, treatment with the reaction mixture does not lead to the reduction of V/sup 5 +/ ions. After treatment of Sb-Bi-Al with the reaction mixture, the presence of three phases, Sb/sub 2/O/sub 3/, Sb/sub 2/O/sub 5/, and Bi/sub 2/O/sub 3/ was detected spectroscopically. After treatment of the Bi-V-Sb-Al with the reaction mixture, the formation of a chemical compound of the bismuth vanadate type in which the V/sup 5 +/ ions are tightly held and resistant to oxidation was observed. The phases Sb/sub 2/O/sub 3/ and Sb/sub 2/O/sub 5/ were also found.

  14. Structure and magnetic properties of low-temperature phase Mn-Bi nanosheets with ultra-high coercivity and significant anisotropy

    SciTech Connect

    Liu, Rongming E-mail: shenbg@iphy.ac.cn; Zhang, Ming; Niu, E; Li, Zhubai; Zheng, Xinqi; Wu, Rongrong; Zuo, Wenliang; Shen, Baogen; Hu, Fengxia; Sun, Jirong

    2014-05-07

    The microstructure, crystal structure, and magnetic properties of low-temperature phase (LTP) Mn-Bi nanosheets, prepared by surfactant assistant high-energy ball milling (SA-HEBM) with oleylamine and oleic acid as the surfactant, were examined with scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. Effect of ball-milling time on the coercivity of LTP Mn-Bi nanosheets was systematically investigated. Results show that the high energy ball milling time from tens of minutes to several hours results in the coercivity increase of Mn-Bi powders and peak values of 14.3 kOe around 10 h. LTP Mn-Bi nanosheets are characterized by an average thickness of tens of nanometers, an average diameter of ∼1.5 μm, and possess a relatively large aspect ratio, an ultra-high room temperature coercivity of 22.3 kOe, a significant geometrical and magnetic anisotropy, and a strong (00l) crystal texture. Magnetization and demagnetization behaviors reveal that wall pinning is the dominant coercivity mechanism in these LTP Mn-Bi nanosheets. The ultrafine grain refinement introduced by the SA-HEBM process contribute to the ultra-high coercivity of LTP Mn-Bi nanosheets and a large number of defects put a powerful pinning effect on the magnetic domain movement, simultaneously. Further magnetic measurement at 437 K shows that a high coercivity of 17.8 kOe and a strong positive temperature coefficient of coercivity existed in the bonded permanent magnet made by LTP Mn-Bi nanosheets.

  15. Structure and Magnetic Properties of Mechanical Alloyed Mn-15at.%Al

    NASA Astrophysics Data System (ADS)

    Hannora, Ahmed E.; Hanna, Faried F.; Marei, Lotfy K.

    2013-04-01

    Mechanical alloying (MA) method has been used to produce nanocrystallite Mn-15at.%Al alloy. X-ray diffraction (XRD) patterns for the as-milled elemental α-Mn and aluminum powder samples show a mixture of α + β-MnAl phases after 20 h of milling and changes to a dominant β-MnAl phase structure after 50 h. An average crystallite size of 40 nm was determined from Hall-Williamson method analysis after 5 h of milling. Moreover, the thermal analysis results using differential thermal analysis (DTA), suggested a possible phase transformation after 20 h of milling. Isothermal treatments are carried in the temperature range of 450°C to 1000°C. Room-temperature vibrating sample magnetometer (VSM) measurements of the hysteretic response revealed that the saturation magnetization Bs and coercivity Hc for 10 h ball milled sample are 2.1 emu/g and 92 Oe, respectively.

  16. Crystal, magnetic, and electronic structures, and properties of new BaMnPnF (Pn = As, Sb, Bi).

    PubMed

    Saparov, Bayrammurad; Singh, David J; Garlea, Vasile O; Sefat, Athena S

    2013-01-01

    New BaMnPnF (Pn = As, Sb, Bi) are synthesized by stoichiometric reaction of elements with BaF₂. They crystallize in the P4/nmm space group, with the ZrCuSiAs-type structure, as indicated by X-ray crystallography. Electrical resistivity results indicate that Pn = As, Sb, and Bi are semiconductors with band gaps of 0.73 eV, 0.48 eV and 0.003 eV (extrinsic value), respectively. Powder neutron diffraction reveals a G-type antiferromagnetic order below T(N) = 338(1) K for Pn = As, and below T(N) = 272(1) K for Pn = Sb. Magnetic susceptibility increases with temperature above 100 K for all the materials. Density functional calculations find semiconducting antiferromagnetic compounds with strong in-plane and weaker out-of-plane exchange coupling that may result in non-Curie Weiss behavior above TN. The ordered magnetic moments are 3.65(5) μ(B)/Mn for Pn = As, and 3.66(3) μ(B)/Mn for Pn = Sb at 4 K, as refined from neutron diffraction experiments.

  17. Robust paramagnetism in Bi2- xMxRu2O7 (M=Mn,Fe,Co,Ni,Cu) pyrochlore

    NASA Astrophysics Data System (ADS)

    Haas, M. K.; Cava, R. J.; Avdeev, M.; Jorgensen, J. D.

    2002-09-01

    We report magnetic susceptibility, resistivity, and Seebeck coefficients for Bi2-xMxRu2O7 pyrochlore. The solid solution exists up to x=0.5 for M=Cu,Ni,Co and up to x=0.1 for M=Fe,Mn. The doped materials do not exhibit ferromagnetism or any localized ruthenium moment behavior. Instead we find the Ru-O and Bi-O sublattices to be essentially independent, with any magnetism resulting from the unpaired first-row transition metal dopant spins. Cobalt substitution for bismuth results in localized Co2+ and low-temperature spin-glass transitions in several cases. Nickel moments on the pyrochlore lattice display properties intermediate to localized and itinerant. Finally, copper doping results in an enhancement of the Pauli metallic density of states.

  18. Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions.

    PubMed

    Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro

    2016-01-01

    For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm(2)/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.

  19. Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions

    PubMed Central

    Masuda, Hidetoshi; Sakai, Hideaki; Tokunaga, Masashi; Yamasaki, Yuichi; Miyake, Atsushi; Shiogai, Junichi; Nakamura, Shintaro; Awaji, Satoshi; Tsukazaki, Atsushi; Nakao, Hironori; Murakami, Youichi; Arima, Taka-hisa; Tokura, Yoshinori; Ishiwata, Shintaro

    2016-01-01

    For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm2/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials. PMID:27152326

  20. Transformation of α-Al(Fe,Mn)Si in Al-7Si-0.4Mg cast alloys after solution heat treatment

    NASA Astrophysics Data System (ADS)

    Han, Sang Won

    2013-01-01

    The α-Al(Fe,Mn)Si compound in an Al-7Si-0.35Mg-0.2Fe-xMn cast alloy has two shapes, a needle-like shape and a Chinese script shape. These two kinds of compounds are tinged with either white or gray tones irrespective of their shape. Unlike compounds with a white tone, during solution heat treatment, all α-Al (Fe,Mn)Si compounds with a gray tone experience severe dissolution. Concerning white-tinged α-Al (Fe,Mn)Si compounds, unlike the needle-like α-Al(Fe,Mn)Si, α-Al(Fe,Mn)Si that resembles Chinese script is rarely transformed.

  1. Leakage current phenomena in Mn-doped Bi(Na,K)TiO3-based ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Walenza-Slabe, J.; Gibbons, B. J.

    2016-08-01

    Mn-doped 80(Bi0.5Na0.5)TiO3-20(Bi0.5K0.5)TiO3 thin films were fabricated by chemical solution deposition on Pt/TiO2/SiO2/Si substrates. Steady state and time-dependent leakage current were investigated from room temperature to 180 °C. Undoped and low-doped films showed space-charge-limited current (SCLC) at high temperatures. The electric field marking the transition from Ohmic to trap-filling-limited current increased monotonically with Mn-doping. With 2 mol. % Mn, the current was Ohmic up to 430 kV/cm, even at 180 °C. Modeling of the SCLC showed that all films exhibited shallow trap levels and high trap concentrations. In the regime of steady state leakage, there were also observations of negative differential resistivity and positive temperature coefficient of resistivity near room temperature. Both of these phenomena were confined to relatively low temperatures (below ˜60 °C). Transient currents were observed in the time-dependent leakage data, which was measured out to several hundred seconds. In the undoped films, these were found to be a consequence of oxygen vacancy migration modulating the electronic conductivity. The mobility and thermal activation energy for oxygen vacancies was extracted as μion ≈ 1.7 × 10-12 cm2 V-1 s-1 and EA,ion ≈ 0.92 eV, respectively. The transient current displayed different characteristics in the 1 mol. % Mn-doped films which were not readily explained by oxygen vacancy migration.

  2. Site-mixing effect on the XMCD spectrum in double perovskite Bi2FeMnO6

    NASA Astrophysics Data System (ADS)

    Ahmed, Towfiq; Chen, Aiping; McFarland, Brian; Wang, Qiang; Ohldag, Hendrik; Sandberg, Richard; Jia, Quanxi; Yarotski, Dmitry A.; Zhu, Jian-Xin

    2016-06-01

    We investigate magnetization in double perovskite multiferroic Bi2FeMnO6 (BFMO) thin film using density functional theory (DFT) simulations, and X-ray magnetic circular dichroism (XMCD) measurements. The exchange interaction between Fe and Mn sites gives rise to a ferrimagnetic ordering in BFMO. When grown without structural defects, distinct XMCD signal is expected from this system. The site resolved magnetization, thus, can be extracted using XMCD sum rules. Although our theoretical calculations are consistent with this expectation for the ideal BFMO system, experimental measurements find evidence of anomalous peak for the L2 and L3 edges of XMCD signals, and thus, the XMCD sum rules are no longer valid. We theoretically explain this phenomenon by considering both tetragonal (near interface), and monoclinic (bulk) phases of BFMO system, with Fe and Mn ions interchanged between their respective sites. Such site-mixing between magnetic cations are commonly found during the synthesis process. Our DFT calculations of XMCD for site interchanged Fe and Mn ions in the bulk phase (monoclinic) of BFMO are in good agreement with experimental XMCD signal and reproduce the anomalous peak features at L2/L3 edges.

  3. Fabrication of Bi Nanowire Array into Nanoporous Film Made from Phase-Separated Al-Si Film

    NASA Astrophysics Data System (ADS)

    Fukutani, Kazuhiko; Den, Tohru

    2008-04-01

    Ultrahigh-pore-density nanoporous films with a pore diameter less than 10 nm and a pore density exceeding 1016 pores/m2 have been fabricated by the phase separation of an Al-Si system and the subsequent removal of Al cylinders, for use in the template-assisted growth of Bi nanowire arrays. Bi was used to fill the pores of template films by electrodeposition. The temperature dependence of the resistance of the obtained Bi nanowires with a diameter of 9 nm, parallel to the Bi nanowire growth direction, exhibits a semimetal-to-semiconductor transition due to the quantum confinement effect.

  4. Electronic and Optical Properties of Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) Antiperovskite Compounds

    NASA Astrophysics Data System (ADS)

    Iqbal, Samad; Murtaza, G.; Khenata, R.; Mahmood, Asif; Yar, Abdullah; Muzammil, M.; Khan, Matiullah

    2016-08-01

    The electronic and optical properties of cubic antiperovskites Ca3MN (M = Ge, Sn, Pb, P, As, Sb and Bi) were investigated by applying the full potential linearized augmented plane wave plus local orbitals (FP-LAPW + lo) scheme based on density functional theory. Different exchange correlation potentials were adopted for the calculations. The results of band structure and density of states show that, by changing the central anion of Ca3MN, the nature of the materials change from metallic (Ca3GeN, Ca3SnN, Ca3PbN) to semiconducting with small band gaps (Ca3SbN and Ca3BiN) to insulating (Ca3PN and Ca3AsN). The optical properties such as dielectric function, absorption coefficient, optical conductivity, reflectivity and refractive indices have also been calculated. The results reveal that all the studied compounds are optically active in the visible and ultraviolet energy regions, and therefore can be effectively utilized for optoelectronic devices.

  5. Oxygen vacancy effects on double perovskite Bi2FeMnO6: A first-principles study

    NASA Astrophysics Data System (ADS)

    Ghosh, Ayana; Ahmed, Towfiq; Yarotski, Dzmitry A.; Nakhmanson, Serge M.; Zhu, Jian-Xin

    2016-12-01

    Double perovskite Bi2FeMnO6 (BFMO) is a potential candidate for the highly sought single-phase multiferroic system. The large orbital radius of the Bi 6s2 lone pairs is responsible for BFMO to exhibit low symmetries and spontaneous polarization, whereas B-site ordering of Mn and Fe contributes to its magnetic properties. In this work, we study both electronic correlation and oxygen vacancy effects on magnetic, electronic and optical properties of BFMO by performing first-principles simulations using density functional theory within the local spin-density approximation (LSDA) and the LSDA+U method. We have numerically demonstrated that a strong on-site Hubbard interaction is critical for the gap opening in a pristine BFMO. We have performed calculations on a supercell constructed with eight chemical formula units of BFMO, from which oxygen atoms were removed incrementally. We showed that the average magnetization decreases with the increase of oxygen vacancy concentration. From the calculated band structure and optical conductivity, an insulator-metal transition or crossover was identified with oxygen in BFMO.

  6. Synthesis and Magnetic Properties of τ-MnAlC Powders.

    PubMed

    Moon, Ki-Woong; Lee, Gyu-Tae; Jeon, Kwang-Won; Kim, Jongryoul

    2015-11-01

    In order to improve the hard magnetic properties of MnAl alloy, it is critical to fabricate fine τ phase MnAl powders. In addition, a rapid cooling process and an addition of stabilization elements are required to fabricate a homogeneous phase because a τ phase is a metastable structure. In this study, τ-Mn54Al(46-x)C(x) (x = 0, 1, 2) powders were prepared by melt-spinning and subsequent annealing and milling processes. As a result, a main phase was revealed as a high temperature e phase in melt spun MnAI ribbons. And a subsequent annealing in the temperature range of 450-650 degrees C resulted in the formation of a τ phase. A maximum saturation magnetization (M(s)) value of 96.56 emu/g was obtained when the melt-spun τ-Mn54Al44C2 ribbons were annealed at 500 degrees C for 10 min. However, a milling process increased the coercivity up to 3804 Oe but simultaneously reduced M(s) down to 60.34 emu/g.

  7. Perpendicular magnetic anisotropy in Mn{sub 2}CoAl thin film

    SciTech Connect

    Sun, N. Y.; Zhang, Y. Q.; Che, W. R.; Shan, R.; Fu, H. R.; You, C. Y.

    2016-01-15

    Heusler compound Mn{sub 2}CoAl (MCA) is attracting more attentions due to many novel properties, such as high resistance, semiconducting behavior and suggestion as a spin-gapless material with a low magnetic moment. In this work, Mn{sub 2}CoAl epitaxial thin film was prepared on MgO(100) substrate by magnetron sputtering. The transport property of the film exhibits a semiconducting-like behavior. Moreover, our research reveals that perpendicular magnetic anisotropy (PMA) can be induced in very thin Mn{sub 2}CoAl films resulting from Mn-O and Co-O bonding at Mn{sub 2}CoAl/MgO interface, which coincides with a recent theoretical prediction. PMA and low saturation magnetic moment could lead to large spin-transfer torque with low current density in principle, and thus our work may bring some unanticipated Heusler compounds into spintronics topics such as the domain wall motion and the current-induced magnetization reversal.

  8. Electrochemical deposition and microstructural characterization of AlCrFeMnNi and AlCrCuFeMnNi high entropy alloy thin films

    NASA Astrophysics Data System (ADS)

    Soare, V.; Burada, M.; Constantin, I.; Mitrică, D.; Bădiliţă, V.; Caragea, A.; Târcolea, M.

    2015-12-01

    Al-Cr-Fe-Mn-Ni and Al-Cr-Cu-Fe-Mn-Ni high entropy alloy thin films were prepared by potentiostatic electrodeposition and the microstructure of the deposits was investigated. The thin films were co-deposited in an electrolyte based on a DMF (N,N-dimethylformamide)-CH3CN (acetonitrile) organic compound. The energy dispersive spectrometry investigation (EDS) indicated that all the five respectively six elements were successfully co-deposited. The scanning electron microscopy (SEM) analysis revealed that the film consists of compact and uniform particles with particle sizes of 500 nm to 4 μm. The X-ray diffractometry (XRD) patterns indicated that the as-deposited thin films were amorphous. Body-centered-cubic (BCC) structures were identified by XRD after the films were annealed at various temperatures under inert Ar atmosphere. The alloys adhesion on the substrate was determined by the scratch-testing method, with higher values obtained for the Al-Cr-Cu-Fe-Mn-Ni alloy.

  9. The ultraviolet and visible luminescence of Bi3+ in the orthorhombic perovskite, GdAlO3

    NASA Astrophysics Data System (ADS)

    Srivastava, A. M.; Comanzo, H. A.

    2017-01-01

    The spectroscopic properties of the Bi3+ ion as a function of its concentration is examined to clarify the nature of optical transitions that are responsible for the ultraviolet (333 nm) and visible emission of GdAlO3:Bi3+. The UV band which is characterized by small Stokes shift (0.52 eV) is ascribed to emission from isolated Bi3+ ions (3P0,1 → 1S0 transition). The peak emission wavelength and the width of the visible band depend on the Bi3+ concentration. This emission is ascribed to pairs or cluster of Bi3+ ions in the perovskite lattice. The spectroscopic properties of the pair emission in GdAlO3 are contrasted with the impurity trapped excitonic emission in CaSnO3. A comparative study of the behavior of Bi3+ luminescence in a series of materials with the orthorhombic perovskite structure is presented.

  10. Dynamical x-ray diffraction from an icosahedral Al-Pd-Mn quasicrystal

    SciTech Connect

    Kycia, S.

    1996-04-23

    Primary extinction effects in diffraction from single grains of Al-Pd- Mn, and presumably many other FCI alloys, may be significant and should be corrected for prior to use of diffraction data in structural determinations. Probes based on dynamical diffraction effects, such as x-ray standing wave fluorescence, multiple beam interference, and x-ray transmission topographs, may now be used to study the bulk and surface structure of some quasicrystals. The observation of dynamical diffraction from icosahedral Al-Pd-Mn is a striking confirmation of the fact that quasicrystals can present a degree of structural perfection comparable to that found in the best periodic intermetallic crystals.

  11. Perpendicularly magnetized τ-MnAl (001) thin films epitaxied on GaAs

    NASA Astrophysics Data System (ADS)

    Nie, S. H.; Zhu, L. J.; Lu, J.; Pan, D.; Wang, H. L.; Yu, X. Z.; Xiao, J. X.; Zhao, J. H.

    2013-04-01

    Perpendicularly magnetized τ-MnAl films have been epitaxied on GaAs (001) by molecular-beam epitaxy. Crystalline quality and magnetic properties of the samples were strongly dependent on growth temperature. The highest coercivity of 10.7 kOe, saturation magnetization of 361.4 emu/cm3, perpendicular magnetic anisotropy constant of 13.65 Merg/cm3, and magnetic energy product of 4.44 MGOe were achieved. These tunable magnetic properties make MnAl films valuable as excellent and cost-effective alternative for not only high density perpendicular magnetic recording storage and spintronics devices but also permanent magnets.

  12. High pressure spectroscopy study of SCF Tb3Al5O12:Mn

    NASA Astrophysics Data System (ADS)

    Wiśniewski, K.; Zorenko, Y. U.; Gorbenko, V.; Zorenko, T.; Kukliński, B.; Grinberg, M.

    2010-11-01

    Single crystal film of Tb3Al5O12:Mn, with concentration of Mn approximately equal to 0.07 at%, has been grown by liquid phase epitaxy on Y3Al5O12 substrate. We have measured the absorption, luminescence, luminescence excitation spectra and luminescence kinetics of the film. To analyze the energetic structure and to estimate the crystal field strength we have measured the photoluminescence spectra under high hydrostatic pressure applied in diamond anvil cell up to 110 kbar. The Mn emission was consisted with the band peaked at 16800 cm-1 that shifts toward the lower energy with increasing pressure with the rate -9 cm-1/kbar. To characterize the Mn charge state we performed calculations of Tanabe -Sugano diagrams for 3d5, 3d4 and 3d3 system. The negative pressure shift of the 16800 cm-1 band yields attribution of this band to the 4T1 →6A1 transition in dodecahedrally coordinated Mn2+ ion. We have estimated quantity of Dq/B equal to 1.8 ±0.2. The configurational coordinate diagram of the Mn2+(3d5) has been calculated to analyze the nonradiative deexcitation processes 4T1 → 2T2 →6A1.

  13. On the quasi-1D magnetic behavior of Ba 2MnCoAl 2F 14, Ba 2MnCuAl 2F 14 and related compounds

    NASA Astrophysics Data System (ADS)

    le Lirzin, A.; Darriet, J.; Georges, R.; Soubeyroux, J. L.

    1992-02-01

    Two new fluorides Ba 2MnCoAl 2F 14 and Ba 2MnCoAl 2F 14, isostructural with the natural compound usovite Ba 2CaMgAl 2F 14, have been synthesized. The nuclear structures of both compounds, refined from neutron diffraction data, give evidence for strongly disordered bimetallic chains MnCu or MnCo along the b-axis: two new theoretical treatments are suggested in order to account for the magnetic behavior of each compound but, due to their intrinsic limitations, they are in fact applied here to solid solutions between the parent compound and BaMnAlF 7, namely Ba 2Mn 1+ yCu 1- yAl2F14 and Ba 2Mn1+ yCo1- yAl 2F 14, leading to a rather good agreement with the measured values of the susceptibilities.

  14. Development of spin-gapless semiconductivity and half metallicity in Ti2MnAl by substitutions for Al

    NASA Astrophysics Data System (ADS)

    Lukashev, Pavel; Gilbert, Simeon; Staten, Bradley; Hurley, Noah; Fuglsby, Ryan; Kharel, Parashu; Huh, Yung; Valloppilly, Shah; Zhang, Wenyong; Yang, K.; Sellmyer, David J.

    In recent years, ever increasing interest in spin-based electronics has resulted in the search for a new class of materials that can provide a high degree of spin polarized electron transport. An ideal candidate would act like insulator for one spin channel and a conductor or semiconductor for the opposite spin channel (e.g., half metal (HM), spin-gapless semiconductor (SGS)). Here, we present the combined computational, theoretical, and experimental study of Ti2MnAl, a Heusler compound with potential application in the field of spintronics. We show that in the ground state this material is metallic, however it becomes a SGS when 50% of Al is substituted with In (e.g., Ti2MnAl0.5In0.5) , and a HM when 50% of Al is substituted with Sn (e.g., Ti2MnAl0.5Sn0.5) . Detailed study of the structural, electronic, and magnetic properties of these materials is presented. Financial support: DOE/BES (DE-FG02-04ER46152); NSF NNCI: 1542182; NRI; Academic and Scholarly Excellence Funds, Office of Academic Affairs, SDSU; UNI Faculty Summer Fellowship; Program for Outstanding Innovative Talents in Hohai University.

  15. Influence of Mn concentration on magnetic topological insulator MnxBi2−xTe3 thin-film Hall-effect sensor

    SciTech Connect

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; Hadimani, R. L.; Jiles, D. C.

    2015-06-11

    Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as that of the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.

  16. Structural properties of Bi{sub 2−x}Mn{sub x}Se{sub 3} thin films grown via molecular beam epitaxy

    SciTech Connect

    Babakiray, Sercan; Johnson, Trent A.; Borisov, Pavel; Holcomb, Mikel B.; Lederman, David; Marcus, Matthew A.; Tarafder, Kartick

    2015-07-28

    The effects of Mn doping on the structural properties of the topological insulator Bi{sub 2}Se{sub 3} in thin film form were studied in samples grown via molecular beam epitaxy. Extended x-ray absorption fine structure measurements, supported by density functional theory calculations, indicate that preferential incorporation occurs substitutionally in Bi sites across the entire film volume. This finding is consistent with x-ray diffraction measurements which show that the out of plane lattice constant expands while the in plane lattice constant contracts as the Mn concentration is increased. X-ray photoelectron spectroscopy indicates that the Mn valency is 2+ and that the Mn bonding is similar to that in MnSe. The expansion along the out of plane direction is most likely due to weakening of the Van der Waals interactions between adjacent Se planes. Transport measurements are consistent with this Mn{sup 2+} substitution of Bi sites if additional structural defects induced by this substitution are taken into account.

  17. Core and valence level photoemission and photoabsorption study of icosahedral Al Pd Mn quasicrystals

    NASA Astrophysics Data System (ADS)

    Horn, K.; Theis, W.; Paggel, J. J.; Barman, S. R.; Rotenberg, E.; Ebert, Ph; Urban, K.

    2006-01-01

    The electronic structure of quasicrystalline Al-Pd-Mn is investigated by means of valence and core level photoelectron spectroscopy. Variations of the photoionization cross section in the constituents' valence electronic levels as a function of photon energy are used to identify contributions from the different atomic species, in particular near the Pd 4d Cooper minimum. Resonant photoemission at the Mn 2p absorption edge shows the contribution of the Mn 3d states to the density of states in a region near the Fermi level. The asymmetry of Pd 3d and Mn 2p core level photoemission lines, and its difference for emission from metallic and quasicrystalline phases, are utilized to infer the contributions of the different constituents to the density of states at the Fermi level.

  18. A study of Fe2+xMn1-xAl alloys: Structural and magnetic properties

    NASA Astrophysics Data System (ADS)

    Paduani, C.; Migliavacca, A.; Pöttker, W. E.; Schaf, J.; Krause, J. C.; Ardisson, J. D.; Samudio Pérez, C. A.; Takeuchi, A. Y.; Yoshida, M. I.

    2007-08-01

    The Fe2+xMn1-xAl alloys were studied experimentally to assess the effect of variations of composition around stoichiometric on the structural and magnetic properties of this system. The results indicate that the ordered L21(X2YZ) structure of full Heusler alloys can be stabilized with small deviations of composition from the stoichiometric 2:1:1. The saturation magnetization is strongly composition dependent and decreases with the increase of the Mn concentration, in spite of the fact that the Mn atoms carry the largest moment in the ordered phase. The highest Curie temperature was observed for the Fe-richer alloy. Magnetic measurements suggest that atomic disorder and competition of the antiferromagnetic Fe-Mn and Mn-Mn interactions with the ferromagnetic Fe-Fe, Mn-Mn and Fe-Mn interactions lead to a frustrated couplings ending in a reentrant spin-glass behavior at low temperature.

  19. Effect of the thickness of BiFeO3 layers on the magnetic and electric properties of BiFeO3/La0.7Sr0.3MnO3 heterostructures

    NASA Astrophysics Data System (ADS)

    Wang, Le; Wang, Zhen; Jin, Kui-juan; Li, Jian-qi; Yang, Huai-xin; Wang, Can; Zhao, Rui-qiang; Lu, Hui-bin; Guo, Hai-zhong; Yang, Guo-zhen

    2013-06-01

    BiFeO3 layers with various thicknesses were fabricated on La0.7Sr0.3MnO3 covered SrTiO3 substrates by a laser molecular-beam epitaxy system. The ferromagnetic transition temperature (Tc) and magnetic coercive field (Hc) of BiFeO3/La0.7Sr0.3MnO3 heterostructures are larger than those of the La0.7Sr0.3MnO3 film. With increasing the thickness of the BiFeO3 layer, Tc, Hc, and ferroelectric coercive field of the BiFeO3/La0.7Sr0.3MnO3 heterostructures decrease, while the dielectric permittivity, remanent polarization, and resistance ratio of the ON and OFF states increase. The variations of the magnetic and electric properties with the thickness could be due to the effects of the epitaxial strain and the interface layer.

  20. Three-dimensionally Ordered Macroporous Structure Enabled Nanothermite Membrane of Mn2O3/Al

    NASA Astrophysics Data System (ADS)

    Zheng, Guoqiang; Zhang, Wenchao; Shen, Ruiqi; Ye, Jiahai; Qin, Zhichun; Chao, Yimin

    2016-03-01

    Mn2O3 has been selected to realize nanothermite membrane for the first time in the literature. Mn2O3/Al nanothermite has been synthesized by magnetron sputtering a layer of Al film onto three-dimensionally ordered macroporous (3DOM) Mn2O3 skeleton. The energy release is significantly enhanced owing to the unusual 3DOM structure, which ensures Al and Mn2O3 to integrate compactly in nanoscale and greatly increase effective contact area. The morphology and DSC curve of the nanothermite membrane have been investigated at various aluminizing times. At the optimized aluminizing time of 30 min, energy release reaches a maximum of 2.09 kJ•g‑1, where the Al layer thickness plays a decisive role in the total energy release. This method possesses advantages of high compatibility with MEMS and can be applied to other nanothermite systems easily, which will make great contribution to little-known nanothermite research.

  1. Three-dimensionally Ordered Macroporous Structure Enabled Nanothermite Membrane of Mn2O3/Al

    PubMed Central

    Zheng, Guoqiang; Zhang, Wenchao; Shen, Ruiqi; Ye, Jiahai; Qin, Zhichun; Chao, Yimin

    2016-01-01

    Mn2O3 has been selected to realize nanothermite membrane for the first time in the literature. Mn2O3/Al nanothermite has been synthesized by magnetron sputtering a layer of Al film onto three-dimensionally ordered macroporous (3DOM) Mn2O3 skeleton. The energy release is significantly enhanced owing to the unusual 3DOM structure, which ensures Al and Mn2O3 to integrate compactly in nanoscale and greatly increase effective contact area. The morphology and DSC curve of the nanothermite membrane have been investigated at various aluminizing times. At the optimized aluminizing time of 30 min, energy release reaches a maximum of 2.09 kJ∙g−1, where the Al layer thickness plays a decisive role in the total energy release. This method possesses advantages of high compatibility with MEMS and can be applied to other nanothermite systems easily, which will make great contribution to little-known nanothermite research. PMID:26935405

  2. New type of Schottky diode-based Cu-Al-Mn-Cr shape memory material films

    NASA Astrophysics Data System (ADS)

    Aksu Canbay, C.; Dere, A.; Mensah-Darkwa, Kwadwo; Al-Ghamdi, Ahmed; Karagoz Genç, Z.; Gupta, R. K.; Yakuphanoglu, F.

    2016-07-01

    Cr-doped CuAlMn shape memory alloys were produced by arc melting method. The effects of Cr content on microstructure and transformation parameters of were investigated. The alloys were characterized by X-ray analysis, optical microscope observations and differential scanning calorimetry measurements. The grain size of the alloys was decreased by the addition of Cr into CuAlMn alloy system. The martensite transformation temperature was shifted both the lower temperature and higher temperature with the addition of chromium. This change was explained on the basis of the change in the thermodynamics such as enthalpy, entropy and activation energy values. The obtained results indicate that the phase transformation temperatures of the CuAlMn alloy system can be controlled by addition of Cr. We fabricated a Schottky barrier diode and observed that ideality factor and barrier height increase with increasing temperature. The diodes exhibited a thermal sensor behavior. This indicates that Schottky diode-based Cu-Al-Mn-Cr shape memory material films can be used as a sensor in high-temperature measurement applications.

  3. Dislocations in nanostructured two-phase Fe30Ni20Mn20Al30.

    PubMed

    Wu, X; Baker, I

    2013-03-01

    In a previous study, the dislocations in Fe(30)Ni(20)Mn(25)Al(25) (at. %), which consist of 50 nm wide alternating b.c.c. and B2 phases, were shown to have a/2<111> Burgers vectors after room temperature deformation. The dislocations were found to glide in pairs on both {110} and {112} slip planes and were relatively widely separated in the b.c.c. phase, where the dislocations were uncoupled, and closely spaced in the B2 phase, where the dislocations were connected by an anti-phase boundary. In this article, we analyze the dislocations in the two ~5 nm-wide B2 phases in a related two-phase alloy Fe(30)Ni(20)Mn(20)Al(30), with compositions Fe-23Ni-21Mn-24Al and Fe-39Ni-12Mn-34Al, compressed to ~3% strain at a strain rate 5 × 10(-4) s(-1) at 873 K (the lowest temperature at which substantial plastic flow was observed). It is shown that slip occursby the glide of a<100> dislocations. A review of the literature suggests that the differences in the observed slip vector between these B2 phases could be due to the differences in composition, differences in deformation temperature, or possibly both.

  4. A transition in the magneto-transport in the L10 MnAl thin films

    NASA Astrophysics Data System (ADS)

    Luo, Linqiang; Lu, Jiwei; Dao, Nam; Cui, Yishen; Wolf, Stuart A.

    2015-03-01

    In this talk we will report on L10 MnAl thin films with perpendicular magnetic anisotropy prepared on single crystal MgO substrates by co-sputtering Mn and Al targets. A Cr seeding layer enabled the epitaxial growth of the MnAl films. The magneto-resistance (MR) of these films was measured using a Hall bar structure. When the external magnetic field was applied perpendicular to the thin film surface, a change of the sign of MR was observed as will be discussed below. Above 175K, a negative magnetoresistance was observed with two maxima occuring at the coercivity fields of the MnAl thin films. Below 175K, the MR became positive, and the MR ratio increased with decreasing temperature. The possible mechanisms for the transition in the MR will be discussed in detail in this talk. They include the effects of inhomogeneity, chemical ordering and the underlying domain structure. The authors gratefully acknowledge financial support provided by INSPIRE program.

  5. Al-Mn coating electrodeposited from ionic liquid on NdFeB magnet with high hardness and corrosion resistance

    NASA Astrophysics Data System (ADS)

    Ding, Jingjing; Xu, Bajin; Ling, Guoping

    2014-06-01

    Al-Mn coatings were electrodeposited on sintered NdFeB permanent magnet in MnCl2-AlCl3-1-ethyl-3-methylim-idazolium chloride (MnCl2-AlCl3-EMIC) ionic liquid at room temperature. The coatings were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The adhesion strength of the coating on NdFeB substrate was evaluated by thermal shock and scratch test. The hardness and corrosion behavior of Al-Mn coating were measured by a Knoop microhardness tester, immersion test and neutral salt spray test respectively. The results showed that the amorphous structure of the deposits was obtained at the current density of 6 mA/cm2, while higher current densities resulted in a mixed structure of amorphous and crystalline. The Al-Mn coating showed excellent adhesion strength on NdFeB substrate with the thermal shock test over 30 cycles and Lc > 80 N. The hardness of Al-Mn coating was up to 5.4 GPa. The amorphous Al-Mn coating showed an anodic sacrificial protection with a low corrosion rate for NdFeB. Meanwhile, the magnetic properties measured by an AMT-4 magnetic measurement device showed that Al-Mn coating did not deteriorate the magnetic property of NdFeB.

  6. Anomalous magnetic configuration of Mn{sub 2}NiAl ribbon and the role of hybridization in the martensitic transformation of Mn{sub 50}Ni{sub 50−x}Al{sub x} ribbons

    SciTech Connect

    Zhao, R. B.; Zhao, D. W.; Li, G. K.; Ma, L. E-mail: houdenglu@mail.hebtu.edu.cn; Zhen, C. M.; Hou, D. L. E-mail: houdenglu@mail.hebtu.edu.cn; Wang, W. H.; Liu, E. K.; Chen, J. L.; Wu, G. H.

    2014-12-08

    The magnetic configuration of Mn{sub 2}NiAl ribbon has been investigated. In contrast to Ni{sub 2}MnAl, the compound Mn{sub 2}NiAl with considerable disorder does exhibit ferromagnetism and, due to exchange interaction competition, both ferromagnetic and antiferromagnetic moment orientations can coexist between nearest neighbor Mn atoms. This is unexpected in Heusler alloys. Regarding the mechanism of the martensitic transformation in Mn{sub 50}Ni{sub 50−x}Al{sub x}, it is found that increasing the Al content results in an unusual change in the lattice constant, a decrease of the transformation entropy change, and enhancement of the calculated electron localization. These results indicate that the p-d covalent hybridization between Mn (or Ni) and Al atoms gradually increases at the expense of the d-d hybridization between Ni and Mn atoms. This leads to an increased stability of the austenite phase and a decrease of the martensitic transformation temperature. For 11 ≤ x ≤ 14, Mn{sub 50}Ni{sub 50−x}Al{sub x} ferromagnetic shape memory alloys are obtained.

  7. Temperature-dependent first-order reversal curve measurements on unusually hard magnetic low-temperature phase of MnBi

    NASA Astrophysics Data System (ADS)

    Muralidhar, Shreyas; Gräfe, Joachim; Chen, Yu-Chun; Etter, Martin; Gregori, Giuliano; Ener, Semih; Sawatzki, Simon; Hono, Kazuhiro; Gutfleisch, Oliver; Kronmüller, Helmut; Schütz, Gisela; Goering, Eberhard J.

    2017-01-01

    We have performed first-order reversal curve (FORC) measurements to investigate the irreversible magnetization processes in the low-temperature phase of MnBi. Using temperature-dependent FORC analysis, we are able to provide a clear insight into the effects of microstructural parameters such as grain diameter, shape, and surface composition on the coercivity of nucleation hardened permanent magnet MnBi. FORC diagrams of MnBi show a unique broadening and narrowing of the coercive field distribution with increasing temperature. We were able to microscopically identify the reason for this behavior, based on the shift in the single domain critical diameter from nearly 1 to 2 μ m , thereby changing the dependence of coercivity with particle size. This is based on a strong increase in the uniaxial anisotropy constant with increasing temperature. Furthermore, the results also give an additional confirmation that the magnetic hardening in low-temperature phase MnBi occurs due to nucleation mechanisms. In our case, we show that temperature-dependent FORC measurements provide a powerful tool for the microscopic understanding of high-performance permanent magnet systems.

  8. Preparation and characterization of MnZn/FeSiAl soft magnetic composites

    NASA Astrophysics Data System (ADS)

    Li, Jing; Peng, Xiaoling; Yang, Yanting; Ge, Hongliang

    2017-03-01

    In this paper, MnZn ferrites were used as coating agents to prepare MnZn/FeSiAl soft magnetic composites (SMCs) in order to improve the magnetic property, because of the higher permeability of magnetic MnZn ferrites than that of traditional coatings which are always nonmagnetic. The effects of molding pressure, annealing temperature, and content of insulation on the soft magnetic properties of MnZn/FeSiAl SMCs were studied. With increasing molding pressure, the effective permeability of the SMCs increased firstly and then decreased, while the core loss decreased firstly and then increased, and both have the best performance at 1.6 GPa. The permeability increased with increasing temperature, reached the maximum value at 660 °C and then decreased, while the core loss decreased with increasing temperature to 700 °C and then increased. The permeability increased with increasing MnZn content from 0.1 to 3% and then decreased, while the D-C bias property continuously increased.

  9. Strain localization in thin films of Bi(Fe,Mn)O3 due to the formation of stepped Mn4+-rich antiphase boundaries

    SciTech Connect

    MacLaren, I.; Sala, B.; Andersson, S. M. L.; Pennycook, T. J.; Xiong, Jia; Jia, Q. X.; Choi, E. -M.; MacManus-Driscoll, J. L.

    2015-10-17

    Here, the atomic structure and chemistry of thin films of Bi(Fe,Mn)O3 (BFMO) films with a target composition of Bi2FeMnO6 on SrTiO3 are studied using scanning transmission electron microscopy imaging and electron energy loss spectroscopy. It is shown that Mn4+-rich antiphase boundaries are locally nucleated right at the film substrate and then form stepped structures that are approximately pyramidal in three dimensions. These have the effect of confining the material below the pyramids in a highly strained state with an out-of-plane lattice parameter close to 4.1 Å. Outside the area enclosed by the antiphase boundaries, the out-of-plane lattice parameter is much closer to bulk values for BFMO. This suggests that to improve the crystallographic perfection of the films whilst retaining the strain state through as much of the film as possible, ways need to be found to prevent nucleation of the antiphase boundaries. Since the antiphase boundaries seem to form from the interaction of Mn with the Ti in the substrate, one route to perform this would be to grow a thin buffer layer of pure BiFeO3 on the SrTiO3 substrate to minimise any Mn-Ti interactions.

  10. Anomalous Hall effect in MnAl/W bilayers: Modification from strong spin Hall effect of W

    NASA Astrophysics Data System (ADS)

    Meng, K. K.; Miao, J.; Xu, X. G.; Wu, Y.; Zhao, J. H.; Jiang, Y.

    2017-04-01

    We report systematic measurements of anomalous Hall effect (AHE) in MnAl/W bilayers modified by strong spin Hall effect (SHE) of the heavy metals, in which a single L10-MnAl epitaxial layer reveals obvious orbital two-channel Kondo (2CK) effect. The results are compared with the AHE in MnAl/Cu with weak spin orbit coupling. As increasing the thickness of W, the strong SHE has gradually suppressed the orbital 2CK effect and modified the AHE of MnAl. A scaling involving multiple competing scattering mechanisms has been used to distinguish different contributions to the modified AHE. The direct observation of spin-orbit torque induced magnetization switching confirms that the result is a combination of the AHE of MnAl and SHE of W.

  11. Observation of Precipitation Evolution in Fe-Ni-Mn-Ti-Al Maraging Steel by Atom Probe Tomography

    NASA Astrophysics Data System (ADS)

    Pereloma, E. V.; Stohr, R. A.; Miller, M. K.; Ringer, S. P.

    2009-12-01

    We describe the full decomposition sequence in an Fe-Ni-Mn-Ti-Al maraging steel during isothermal annealing at 550 °C. Following significant pre-precipitation clustering reactions within the supersaturated martensitic solid solution, (Ni,Fe)3Ti and (Ni,Fe)3(Al,Mn) precipitates eventually form after isothermal aging for ~60 seconds. The morphology of the (Ni,Fe)3Ti particles changes gradually during aging from predominantly plate-like to rod-like, and, importantly, Mn and Al were observed to segregate to these precipitate/matrix interfaces. The (Ni,Fe)3(Al,Mn) precipitates occurred at two main locations: uniformly within the matrix and at the periphery of the (Ni,Fe)3Ti particles. We relate this latter mode of precipitation to the Mn-Al segregation.

  12. Observation of Precipitation Evolution in Fe-Ni-Mn-Ti-Al Maraging Steel using Atom Probe Tomography

    SciTech Connect

    Pereloma, E. V.; Stohr, R A; Miller, Michael K; Ringer, S. P.

    2009-01-01

    We describe the full decomposition sequence in an Fe-Ni-Mn-Ti-Al maraging steel during isothermal annealing at 550 C. Following significant pre-precipitation clustering reactions within the supersaturated martensitic solid solution, (Ni,Fe){sub 3}Ti and (Ni,Fe){sub 3}(Al,Mn) precipitates eventually form after isothermal aging for {approx}60 seconds. The morphology of the (Ni,Fe){sub 3}Ti particles changes gradually during aging from predominantly plate-like to rod-like, and, importantly, Mn and Al were observed to segregate to these precipitate/matrix interfaces. The (Ni,Fe){sub 3}(Al,Mn) precipitates occurred at two main locations: uniformly within the matrix and at the periphery of the (Ni,Fe){sub 3}Ti particles. We relate this latter mode of precipitation to the Mn-Al segregation.

  13. Structural and magnetic characterization of BiFe{sub x}Mn{sub 2-x}O{sub 5} oxides (x=0.5, 1.0)

    SciTech Connect

    Retuerto, M.; Martinez-Lope, M.J.; Krezhov, K.; Fernandez-Diaz, M.T.; Alonso, J.A.

    2011-09-15

    The title compounds have been synthesized by a citrate technique followed by thermal treatments in air (BiFe{sub 0.5}Mn{sub 1.5}O{sub 5}) or under high oxygen pressure conditions (BiFeMnO{sub 5}), and characterized by X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization measurements. The crystal structures have been refined from NPD data in the space group Pbam at 295 K. These phases are isostructural with RMn{sub 2}O{sub 5} oxides (R=rare earths) and contain infinite chains of Mn{sup 4+}O{sub 6} octahedra sharing edges, linked together by (Fe,Mn){sup 3+}O{sub 5} pyramids and BiO{sub 8} units. These units are strongly distorted with respect to those observed in other RFeMnO{sub 5} compounds, due to the presence of the electronic lone pair on Bi{sup 3+}. It is noteworthy the certain level of antisite disorder exhibited in both samples, where the octahedral positions are partially occupied by Fe cations, and vice versa. BiFe{sub x}Mn{sub 2-x}O{sub 5} (x=0.5, 1.0) are short-range magnetically ordered below 20 K for x=0.5 and at 40 K for x=1.0. The main magnetic interactions seem to be antiferromagnetic (AFM); however, the presence of a small hysteresis in the magnetization cycles indicates the presence of some weak ferromagnetic (FM) interactions. - Graphical Abstract: BiFe{sub x}Mn{sub 2-x}O{sub 5} (x=0.5, 1.0) samples are isostructural with BiMn{sub 2}O{sub 5}, belonging to the Pbam space group. The crystal structure contains infinite chains of edge-sharing Mn{sup 4+}O{sub 6} octahedra, interconnected by dimer units of Fe{sup 3+}O{sub 5} square pyramids. These units are strongly distorted due to the presence of the electronic lone pair on Bi{sup 3+}. They are magnetically ordered at low temperatures. The main magnetic interactions seem to be antiferromagnetic with the presence of some weak ferromagnetic response. Highlights: > Two new compounds of formula BiFe{sub x}Mn{sub 2-x}O{sub 5} (x=0.5, 1.0) have been obtained. > Their crystallographic

  14. Influence of Mn concentration on magnetic topological insulator MnxBi2−xTe3 thin-film Hall-effect sensor

    DOE PAGES

    Ni, Y.; Zhang, Z.; Nlebedim, I. C.; ...

    2015-06-11

    Hall-effect (HE) sensors based on high-quality Mn-doped Bi2Te3 topological insulator (TI) thin films have been systematically studied in this paper. Improvement of Hall sensitivity is found after doping the magnetic element Mn into Bi2Te3. The sensors with low Mn concentrations, MnxBi2-xTe3, x = 0.01 and 0.08 show the linear behavior of Hall resistance with sensitivity about 5 Ω/T. And their Hall sensitivity shows weak dependence on temperature. For sensors with high Mn concentration (x = 0.23), the Hall resistance with respect to magnetic field shows a hysteretic behavior. Moreover, its sensitivity shows almost eight times as high as that ofmore » the HE sensors with low Mn concentration. The highest sensitivity can reach 43 Ω/T at very low magnetic field. This increase of Hall sensitivity is caused by the occurrence of anomalous HE (AHE) after ferromagnetic phase transition. Our work indicates that the magnetic-element-doped TIs with AHE are good candidates for HE sensors.« less

  15. EPR, optical absorption and photoluminescence properties of MnO 2 doped 23B 2O 3-5ZnO-72Bi 2O 3 glasses

    NASA Astrophysics Data System (ADS)

    Prakash Singh, Shiv; Chakradhar, R. P. S.; Rao, J. L.; Karmakar, Basudeb

    2010-05-01

    Electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), optical absorption and photoluminescence (PL) spectroscopic measurements are performed on Mn 2+ doped high bismuth containing zinc-bismuth-borate glasses. TEM images reveal homogeneously dispersed Bi o nanoparticles (NPs) of spherical shape with size about 5 nm. EPR spectra exhibit predominant signals at g≈2.0 and 4.3 with a sextet hyperfine structure. The resonance signal at g≈2.0 is due to Mn 2+ ions in an environment close to octahedral symmetry, where as the resonance at g≈4.3 is attributed to the rhombic surrounding of the Mn 2+ ions. The hyperfine splitting constant ( A) indicates that Mn 2+ ions in these glasses are moderately covalent in nature. The zero-field splitting parameter D has been calculated from the allowed hyperfine lines. The optical absorption spectrum exhibits a single broad band centered at 518 nm (19,305 cm -1) is assigned to the 6A 1g(S)→ 4T 1g(G) transition of Mn 2+ ions. The visible and near infrared (NIR) luminescence bands at 548, 652 and 804 nm have been observed when excited at 400 and 530 nm, respectively. These luminescence centers are supposed to be caused by the lower valence state of bismuth, such as Bi 2+ and Bi + ions, generated during melting process.

  16. Atomic-Scale Electronic Spectra across BiFeO3/La0.7Sr0.3MnO3 Complex Oxide Heterointerfaces

    NASA Astrophysics Data System (ADS)

    Chiu, Ya-Ping; Huang, Bo-Chao; Yu, Pu; Ramesh, Ramamoorthy; Chu, Ying-Hao

    2014-03-01

    Atomic-scale evolution of electronic structures across BiFeO3/La0.7Sr0.3MnO3 complex oxide heterointerfaces has been revealed using cross-sectional scanning tunneling microscopy and spectroscopy. Analysis of scanning tunneling spectroscopy results exploits the interfacial valence mismatch to influence the electrostatic configurations across the BiFeO3/La0.7Sr0.3MnO0.3 heterointerfaces. Spatially unit-cell-by-unit-cell resolved electronic states at the atomic level reveal how the control of material interfaces at the atomic level to determine the ferroelectric polarization in BiFeO3. Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.

  17. Processing of Mn-Al nanostructured magnets by spark plasma sintering and subsequent rapid thermal annealing

    NASA Astrophysics Data System (ADS)

    Saravanan, P.; Vinod, V. T. P.; Černík, Miroslav; Selvapriya, A.; Chakravarty, Dibyendu; Kamat, S. V.

    2015-01-01

    The potential of spark plasma sintering (SPS) in combination with rapid thermal annealing (RTA) for the processing of Mn-Al nanostructured magnets is explored in this study. Ferromagnetic α-Mn alloy powders were processed by high-energy ball milling using Mn (56 at%) and Al (44 at%) as constituent metal elements. The alloying action between Mn and Al due to intensive milling was studied by X-ray diffraction and field-emission scanning electron microscope; while the phase transformation kinetics was investigated using differential scanning calorimetry. The evolution of ferromagnetic properties in the as-milled powders was studied by superconducting quantum interference device (SQUID). Among the Mn-Al alloy powders collected at various milling intervals, the 25 h milled Mn-Al powders showed a good combination of coercivity, Hc (11.3 kA/m) and saturation magnetization, Ms (5.0 A/m2/kg); accordingly, these powders were chosen for SPS. The SPS experiments were conducted at different temperatures: 773, 873 and 973 K and its effect on the density, phase composition and magnetic properties of the Mn-Al bulk samples were investigated. Upon increasing the SPS temperature from 773 to 973 K, the bulk density was found to increase from 3.6 to 4.0 g/cm3. The occurrence of equilibrium β-phase with significant amount of γ2-phase was obvious at all the SPS temperatures; however, crystallization of some amount of τ-phase was evident at 973 K. Irrespective of the SPS temperatures, all the samples demonstrated soft magnetic behavior with Hc and Ms values similar to those obtained for the 25 h milled powders. The magnetic properties of the SPSed samples were significantly improved upon subjecting them to RTA at 1100 K. Through the RTA process, Hc values of 75, 174 and 194 kA/m and Ms values of 19, 21 and 28 A/m2/kg were achieved for the samples SPSed at 773, 873 and 973 K, respectively. The possible reasons for the observed improvement in the magnetic properties of the SPSed

  18. Elevated Temperature Deformation of Fe-39.8Al and Fe-15.6Mn-39.4Al

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel

    2004-01-01

    The elevated temperature compressive properties of binary Fe-39.8 at % Al and Fe-15.6Mn-39.4Al have been measured between 1000 and 1300 K at strain rates between 10(exp 7) and 10(exp 3)/ s. Although the Mn addition to iron aluminide did not change the basic deformation characteristics, the Mn-modified alloy was slightly weaker. In the regime where deformation of FeAl occurs by a high stress exponent mechanism (n = 6), strength increases as the grain size decreases at least for diameters between approx. 200 and approx. 10 microns. Due to the limitation in the grain size-flow stress-temperature-strain rate database, the influence of further reductions of the grain size on strength is uncertain. Based on the appearance of subgrains in deformed iron aluminide, the comparison of grain diameters to expected subgrain sizes, and the grain size exponent and stress exponent calculated from deformation experiments, it is believed that grain size strengthening is the result of an artificial limitation on subgrain size as proposed by Sherby, Klundt and Miller.

  19. Large low-field magnetodielectric response in multiferroic Bi2NiMnO6 thin film

    NASA Astrophysics Data System (ADS)

    Rathi, A.; Anshul, Avneesh; Gupta, Anurag; Rout, P. K.; Maurya, K. K.; Kotnala, R. K.; Pant, R. P.; Basheed, G. A.

    2017-04-01

    Single-phase multiferroics exhibiting a large low-field magnetodielectric effect (MDE) are of great interest for the practical realization of multifunctional devices, as existing multiferroics demand large magnetic fields to cause any significant MDE. Here, we report remarkably large MDE \\equiv Δ {{\\varepsilon}\\prime} /{{\\varepsilon}\\prime}∼ 6 % at very low fields (H≤slant 5 kOe) near T C in multiferroic Bi2NiMnO6 thin film. More importantly, the insensitivity of {{\\varepsilon}\\prime} to temperature and frequency variations, and pronounced change in {{\\varepsilon}\\prime} near T C in zero magnetic field attribute the observed large MDE to the inherent exchange magnetoelectric interactions.

  20. First principles calculations of magnetism, dielectric properties and spin-phonon coupling in double perovskite Bi(2)CoMnO(6).

    PubMed

    Bhattacharjee, Satadeep; Eriksson, Olle; Sanyal, Biplab

    2012-07-25

    First principles electronic structure calculations have been performed for the double perovskite Bi(2)CoMnO(6) in its non-centrosymmetric polar state using the generalized gradient approximation plus the Hubbard U approach. We find that the ferromagnetic state is more favored compared to the ferrimagnetic state with both Co and Mn in high spin states. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. The magnetic structure dependent phonon frequencies indicate the presence of a weak spin-phonon coupling. Using the Berry phase method, we obtain a spontaneous ferroelectric polarization of 5.88 μC cm(-2), which is close to the experimental value observed for a similar compound, Bi(2)NiMnO(6).

  1. Energy transfer between Eu-Mn and photoluminescence properties of Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ solid solution

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yuhua; Liu, Bitao; Li, Feng

    2010-08-01

    In order to evaluate the energy transfer between Eu-Mn in Ba0.75Al11O17.25-BaMgAl10O17 solid solution, Ba0.75Al11O17.25-BaMgAl10O17:Eu2+,Mn2+ phosphors were prepared by flux method. The crystal structure and the morphology of the solid solution were demonstrated by x-ray dirrfactometer and scanning electron microscopy. The photoluminescence mechanisms were explained by the energy transfer of Eu2+ to Mn2+ and the Dexter theory. A redshift of green emission peak and a decrease in decay time with the increase in Mn2+ concentration were observed. These phenomena are attributed to the formation of Mn2+ paired centers after analysis by a method of Pade approximations.

  2. Magnetic and transport properties of the ferromagnetic semiconductor heterostructures (In,Mn)As/(Ga,Al)Sb

    NASA Astrophysics Data System (ADS)

    Oiwa, A.; Endo, A.; Katsumoto, S.; Iye, Y.; Ohno, H.; Munekata, H.

    1999-02-01

    We have investigated the magnetic and transport properties of (In,Mn)As thin films grown on a (Ga,Al)Sb layer. Strong perpendicular magnetic anisotropy is observed for the (In,Mn)As layer, the thickness of which is less than the critical value required for relaxation of lattice-mismatch-induced strain. The anomalous Hall coefficient is found to be approximately proportional to the square of resistivity in the low-field region. Large negative magnetoresistance is found to occur over a magnetic field range significantly wider than that for the ferromagnetic hysteresis loop.

  3. Stability, sub-gap current, 1/f-noise, and elemental depth profiling of annealed Al:Mn-AlOX-Al normal metal-insulator-superconducting tunnel junctions

    NASA Astrophysics Data System (ADS)

    Julin, J. K.; Chaudhuri, S.; Laitinen, M.; Sajavaara, T.; Maasilta, I. J.

    2016-12-01

    In this paper we report a study of the effect of vacuum annealing at 400°C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, aluminum as the superconductor and amorphous aluminum oxide as the tunneling barrier (Al:Mn-AlOx-Al). The annealing treatment improves the stability of the junctions, increases their tunneling resistance and does not have a negative impact on the low-temperature current-voltage characteristics. The measured 1/f resistance noise of the junctions also changes after annealing, in the best case decreasing by over an order of magnitude. All these observations show that annealing is a viable route to improve NIS junction devices after the sample has been fabricated.

  4. Ab initio study of Fe{sub 2}MnZ (Al, Si, Ge) Heusler alloy using GGA approximation

    SciTech Connect

    Jain, Vivek Kumar Jain, Vishal Lakshmi, N. Venugopalan, K.

    2014-04-24

    Density functional theory based on FP-LAPW method used to investigate the electronic structure of Fe{sub 2}MnZ, shows that the total spin magnetic moment shows a trend consistent with the Slater–Pauling curve. The Fe and Mn magnetic moment depend on choice of Z element although the magnetic moment of Z element is negative and less than 0.1 μ{sub B}. Spin polarization calculations evidence 100% spin polarization for Fe{sub 2}MnSi. Fe{sub 2}MnAl and Fe{sub 2}MnGe show metallic behavior with 93%, 98% spin polarization.

  5. Effect of Pr- and Nd- doping on structural, dielectric, and magnetic properties of multiferroic Bi0.8La0.2Fe0.9Mn0.1O3

    NASA Astrophysics Data System (ADS)

    Singh, Rahul; Dwivedi, G. D.; Shahi, P.; Kumar, D.; Prakash, Om; Ghosh, A. K.; Chatterjee, Sandip

    2014-04-01

    Bi0.8La0.15RE0.05Fe0.9Mn0.1O3 (where RE = Pr and Nd) have been prepared via conventional solid state route. The Rietveld refinement of X-ray diffraction patterns shows that both systems crystallize in orthorhombic Pnma space group. Raman modes observed for these two systems indicate that both systems are very close to orthorhombic Pnma structure. Appearance of prominent A1-3 and weak E-2 modes in Bi0.8La0.15Nd0.05Fe0.9Mn0.1O3 indicate the presence of chemically more active Bi-O covalent bonds (which favors stereochemical activity of Bi lone pair electrons) in comparison to Bi0.8La0.15Pr0.05Fe0.9Mn0.1O3. Moreover, Bi0.8La0.15Nd0.05Fe0.9Mn0.1O3 system shows higher dielectric constant, low dielectric loss, and higher magnetization value in comparison to Bi0.8La0.15Pr0.05Fe0.9Mn0.1O3 system. Ferroelectric transition temperature decreases to 460 °C for both systems in comparison to 710 °C of Bi0.8La0.2Fe0.9Mn0.1O3. The improved dielectric and magnetic response suggests Bi0.8La0.15Nd0.05Fe0.9Mn0.1O3 a better multiferroic system than Bi0.8La0.15Pr0.05Fe0.9Mn0.1O3.

  6. Charge defects and highly enhanced multiferroic properties in Mn and Cu co-doped BiFeO3 thin films

    NASA Astrophysics Data System (ADS)

    Dong, Guohua; Tan, Guoqiang; Luo, Yangyang; Liu, Wenlong; Xia, Ao; Ren, Huijun

    2014-06-01

    Pure BiFeO3 (BFO) and Mn, Cu co-doped BiFeO3 (BFMCO) thin films were deposited on fluorine doped tin oxide (FTO) substrates by a chemical solution deposition method. Detailed investigations were made on the effects of Mn and Cu co-doping on the crystal structure, the defect chemistry, multiferroic properties of the BFO thin films. With the co-doping of Mn and Cu, a structural transition from the rhombohedral (R3c:H) to the biphasic structure (R3c:H + P1) is confirmed by XRD, Rietveld refinement and Raman analysis. X-ray photoelectron spectroscopy (XPS) analysis shows that the coexistence of Fe2+/Fe3+ and Mn2+/Mn3+ ions in the co-doping films are demonstrated. Meanwhile, the way of the co-doping at B-sits is conducive to suppress Fe valence state of volatility and to decrease oxygen vacancies and leakage current. It's worth noting that the co-doping can induce the superior ferroelectric properties (a huge remanent polarization, 2Pr ∼ 220 μC/cm2 and a relatively low coercive field, 2Ec ∼ 614 kV/cm). The introduction of Mn2+ and Cu2+ ions optimizes the magnetic properties of BFO thin films by the biphasic structure and the destruction of spin cycloid.

  7. Composition Optimization of Al-DOPING Lithium Manganese Oxide from Al2O3-Li2CO3-MnO2 Ternary System

    NASA Astrophysics Data System (ADS)

    He, Gang; Sun, Xinyan; Hong, Jianhe; He, Mingzhong

    2013-07-01

    In order to synthesize eutectic compound of Al doping lithium manganese oxide which can be used as cathode material in lithium battery, using γ-Al2O3, Li2CO3 and MnO2 as starting raw materials, the composition optimization research work has been done by the solid state synthesis method. A limited composition range was found in Al2O3-Li2CO3-MnO2 ternary system, in which the synthesized Al doping lithium manganese oxides have single spinel structure and good electrochemical performance. The results showed that the LiAl0.04Mn1.96O4 material presented better charge-discharge cycling behavior than pure LiMn2O4, and showed the best electrochemistry property among the compounds in the Al2O3-Li2O-Mn2O3 ternary system. LiAl0.04Mn1.96O4 still kept perfect cubic structure, but LiMn2O4 kept the coexistence of the cubic and tetragonal phases after 50 charge-discharge cycles.

  8. Antisite-induced half-metallicity and fully-compensated ferrimagnetism in Co-Mn-V-Al alloy

    NASA Astrophysics Data System (ADS)

    Wang, L. Y.; Dai, X. F.; Wang, X. T.; Cui, Y. T.; Liu, E. K.; Wang, W. H.; Wu, G. H.; Liu, G. D.

    2015-10-01

    We predicted that Co-Mn-V-Al alloy is a fully-compensated half-metallic ferrimagnet in CoVMnAl-type atomic arrangement with 25% ˜ 50% Co-Mn antisites using band structure calculations. The CoVMnAl-type atomic arrangement with about 30% Co-Mn antisites was successfully synthesized. The measurements of magnetic properties and electronic transport properties confirmed the half-metallicity and fully-compensated ferrimagnetism. We argued that the half-metallicity and ferrimagnetism in Co-Mn-V-Al compounds originate from the antisite between the Co and Mn atoms, which implies a new way to search for half-metallic material in Heusler alloys.

  9. Mono-, bi-, and trinuclear bis-hydrated Mn(2+) complexes as potential MRI contrast agents.

    PubMed

    Forgács, Attila; Regueiro-Figueroa, Martín; Barriada, José Luis; Esteban-Gómez, David; de Blas, Andrés; Rodríguez-Blas, Teresa; Botta, Mauro; Platas-Iglesias, Carlos

    2015-10-05

    We report a series of ligands containing pentadentate 6,6′-((methylazanediyl)bis(methylene))dipicolinic acid binding units that form mono- (H2dpama), di- (mX(H2dpama)2), and trinuclear (mX(H2dpama)3) complexes with Mn2+ containing two coordinated water molecules per metal ion, which results in pentagonal bipyramidal coordination around the metal ions. In contrast, the hexadentate ligand 6,6′-((ethane-1,2-diylbis(azanediyl))bis(methylene))dipicolinic acid (H2bcpe) forms a complex with distorted octahedral coordination around Mn2+ that lacks coordinated water molecules. The protonation constants of the ligands and the stability constants of the Mn2+, Cu2+, and Zn2+ complexes were determined using potentiometric and spectrophotometric titrations in 0.15 M NaCl. The pentadentate dpama2– ligand and the di- and trinucleating mX(dpama)24– and mX(dpama)36– ligands provide metal complexes with stabilities that are very similar to that of the complex with the hexadentate ligand bcpe2–, with log β101 values in the range 10.1–11.6. Cyclic voltammetry experiments on aqueous solutions of the [Mn(bcpe)] complex reveal a quasireversible system with a half-wave potential of +595 mV versus Ag/AgCl. However, [Mn(dpama)] did not suffer oxidation in the range 0.0–1.0 V, revealing a higher resistance toward oxidation. A detailed 1H NMRD and 17O NMR study provided insight into the parameters that govern the relaxivity for these systems. The exchange rate of the coordinated water molecules in [Mn(dpama)] is relatively fast, kex298 = (3.06 ± 0.16) × 108 s–1. The trinuclear [mX(Mn(dpama)(H2O)2)3] complex was found to bind human serum albumin with an association constant of 1286 ± 55 M–1 and a relaxivity of the adduct of 45.2 ± 0.6 mM–1 s–1 at 310 K and 20 MHz.

  10. Electric and adhesion properties of an interface between Sn1 - x Mn x Te single crystals and Bi-Sn alloys

    NASA Astrophysics Data System (ADS)

    Alieva, T. D.; Akhundova, N. M.; Abdinova, G. D.; Bagieva, G. Z.; Abdinov, D. Sh.

    2016-05-01

    The adhesion and electric properties of an interface between Sn1 - x Mn x Te single crystals and a 57 wt % Bi and 43 wt % Sn alloy in a temperature range of ˜77-300 K are studied. It is shown that the Bi-Sn alloy and the above single crystals form an ohmic contact that exhibits fairly high work of adhesion and strength of adhesion, along with low contact resistance. The deposition of the Bi-Sn alloy on the end faces of the crystals results in the formation of such intermediate phases as Bi2Te3 and SnTe at the interface, the doping of the near-contact region of the crystal, and the filling of vacancies in the tin sublattice in this region with diffusing atoms of the contact alloy components.

  11. Experimental Investigation on Thermoresistance between AlN, Bi-2223 and OFHC in High Tc- Direct Cooling Technology

    NASA Astrophysics Data System (ADS)

    Wang, H. L.; Rao, R. S.; Wang, J.

    2014-12-01

    In the development of high temperature superconducting (HTS) direct cooling technology, the high electric insulation high heat conducting AlN has become one of the important components. The thermal contact resistance between AlN, Bi-2223 and OFHC is investigated by experiment with a G-M cryocooler as the source of cooling. The heat conductivity of AlN is measured between 29 and 160 K temperatures. When the temperature on the interface layer side of Bi-2223 is 55 K, under the action of the contact pressure of 0.5469 MPa, the thermal contact resistance between AlN and Bi-2223 is 38.86 times to the thermal conduction resistance of a 10 mm thick AlN pad. Baced on micro-nanocryogenics, it is proposed that the thermal contact resistance is one of the crucial techniques to be attacked in HTS direct cooling technology.

  12. Dynamic mechanical analyze of superelastic CuMnAl shape memory alloy

    NASA Astrophysics Data System (ADS)

    (Dragoș Ursanu, A. I.; Stanciu, S.; Pricop, B.; Săndulache, F.; Cimpoeșu, N.

    2016-08-01

    A new shape memory alloy was obtain from high purity Cu, Mn and Al elements using a induce furnace. The intelligent material present negative transformation temperatures and an austenite like state at room temperature. The austenite state of CuMnAl shape memory alloy present superelasticity property. Five kilograms ingot was obtain of Cu10Mn10Al alloy. From the base material (melted state) were cut samples with 6 mm thickness using a mechanical saw. After an homogenization heat treatment the samples were hot rolled through four passes with a reduction coefficient of 20%. Experimental lamellas were obtained with 1.5 mm thickness and 90x10 mm length and width. After the hot rolled treatment the materials were heat treated at 800°C for 20 minutes and chilled in water. Four samples, one just laminated and three heat treated by aging, were analyzed with a Netzsch DMA equipment to establish the elastic modulus and the internal friction values of the materials. Metallic materials microstructure was analyzed using a scanning electron microscope Vega Tescan LMH II type. After the aging heat treatment a decrease of internal friction is observed on the entire analyze range which is assigned to formation of Al-based precipitates that block the internal movement of the alloy characteristic phases.

  13. Quaternary aluminum silicides grown in Al flux: RE5Mn4Al(23-x)Si(x) (RE = Ho, Er, Yb) and Er44Mn55(AlSi)237.

    PubMed

    Calta, Nicholas P; Kanatzidis, Mercouri G

    2013-09-03

    Four novel intermetallic silicides, RE5Mn4Al(23-x)Si(x) (x = 7.9(9), RE = Ho, Er, Yb) and Er44Mn55(AlSi)237, have been prepared by reaction in aluminum flux. Three RE5Mn4Al(23-x)Si(x) compounds crystallize in the tetragonal space group P4/mmm with the relatively rare Gd5Mg5Fe4Al(18-x)Si(x) structure type. Refinement of single-crystal X-ray diffraction data yielded unit cell parameters of a = 11.3834(9)-11.4171(10) Å and c = 4.0297(2)-4.0575(4) Å with volumes ranging from 522.41(5) to 528.90(8) Å(3). Structure refinements on single-crystal diffraction data show that Er44Mn55(AlSi)237 adopts a new cubic structure type in the space group Pm3n with a very large unit cell edge of a = 21.815(3) Å. This new structure is best understood when viewed as two sets of nested polyhedra centered on a main group atom and a manganese atom. These polyhedral clusters describe the majority of the atomic positions in the structure and form a perovskite-type network. We also report the electrical and magnetic properties of the title compounds. All compounds except the Ho analogue behave as normal paramagnetic metals without any observed magnetic transitions above 5 K and exhibit antiferromagnetic correlations deduced from the value of their Curie constants. Ho5Mn4Al(23-x)Si(x) exhibits a ferromagnetic transition at 20 K and an additional metamagnetic transition at 10 K, suggesting independent ordering temperatures for two distinct magnetic sublattices.

  14. The nature of Mn4+ luminescence in the orthorhombic perovskite, GdAlO3

    NASA Astrophysics Data System (ADS)

    Srivastava, A. M.; Brik, M. G.

    2017-01-01

    In this paper we report on the spectroscopic properties of Mn4+ (3d3) ion in the orthorhombic perovskite, GdAlO3 and calculate the energy levels using the exchange charge model of crystal-field theory. The calculated Mn4+ energy levels are in good agreement with the experimental data. The results of our calculations yield the crystal-field splitting and Racah parameters of Dq = 2083 cm-1, B = 780 cm-1 and C = 2864 cm-1, with C/B = 3.67. The emission spectrum is composed of the zero phonon line (2Eg → 4A2g transition) with dominating intensity and its vibrational sidebands. We have also calculated Mulliken atomic charges and bond populations for three isostructural perovskites (GdAlO3, LaGaO3 and CaZrO3) to seek correlation between the energy position of the Mn4+2E level and the covalence of Mn4+sbnd O2- chemical bonding.

  15. Redox mediated synthesis of hierarchical Bi2O3/MnO2 nanoflowers: a non-enzymatic hydrogen peroxide electrochemical sensor.

    PubMed

    Ray, Chaiti; Dutta, Soumen; Roy, Anindita; Sahoo, Ramkrishna; Pal, Tarasankar

    2016-03-21

    Uniform hierarchical Bi2O3/MnO2 nanoflowers (BM NFs) are fabricated via a reaction strategy by combining redox reaction and hydrothermal treatment. This wet chemical method reports for the first time a one pot synthesis of Bi2O3/MnO2 nanoflowers via a thermodynamically allowed galvanic reaction between Bi(0) and KMnO4 in aqueous solution under modified hydrothermal (MHT) conditions. The Bi2O3/MnO2 NF composites are then applied as a catalyst for electrochemical hydrogen peroxide detection. Exceedingly high H2O2 detection sensitivity (0.914 μA μM(-1) cm(-2)) lies in a wide linear range of 0.2-290 μM and the detection limit goes down to 0.05 μM (S/N = 3) for non-enzymatic detection of H2O2 in solution. This prototype sensor demonstrates an admirable analytical performance considering its long-term stability, good reproducibility and acceptable selectivity against common interfering species. The employment of the stable nanocomposite for real sample analysis makes it a deliverable for H2O2 sensing.

  16. Microstructure and Phase Analysis in Mn-Al and Zr-Co Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Lucis, Michael J.

    In America's search for energy independence, the development of rare-earth free permanent magnets is one hurdle that still stands in the way. Permanent magnet motors provide a higher efficiency than induction motors in applications such as hybrid vehicles and wind turbines. This thesis investigates the ability of two materials, Mn-Al and Zr-Co, to fill this need for a permanent magnet material whose components are readily available within the U.S. and whose supply chain is more stable than that of the rare-earth materials. This thesis focuses on the creation and optimization of these two materials to later be used as the hard phase in nanocomposites with high energy products (greater than 10 MGOe). Mn-Al is capable of forming the pure L10 structure at a composition of Mn54Al43C3. When Mn is replaced by Fe or Cu using the formula Mn48Al43C3T6 the anisotropy constant is lowered from 1.3·107 ergs/cm3 to 1.0·107 ergs/cm3 and 0.8·10 7 ergs/cm3 respectively. Previous studies have reported a loss in magnetization in Mn-Al alloys during mechanical milling. The reason for this loss in magnetization was investigated and found to be due to the formation of the equilibrium beta-Mn phase of the composition Mn3Al2 and not due to oxidation or site disorder. It was also shown that fully dense Mn-Al permanent magnets can be created at hot pressing temperatures at or above 700°C and that the epsilon-phase to tau-phase transition and consolidation can be combined into a single processing step. The addition of small amounts of Cu to the alloy, 3% atomic, can increase the compaction density allowing high densities to be achieved at lower pressing temperatures. While the structure is still under debate, alloys at the composition Zr2Co11 in the Zr-Co system have been shown to have hard magnetic properties. This thesis shows that multiple structures exist at this Zr2Co11 composition and that altering the cooling rate during solidification of the alloy affects the ratio of the phase

  17. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

    NASA Astrophysics Data System (ADS)

    Zhu, L. J.; Zhao, J. H.

    2017-02-01

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T1/2 dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn.

  18. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films.

    PubMed

    Zhu, L J; Zhao, J H

    2017-02-20

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T(1/2) dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn.

  19. Strength of "Light" Ferritic and Austenitic Steels Based on the Fe - Mn - Al - C System

    NASA Astrophysics Data System (ADS)

    Kaputkina, L. M.; Svyazhin, A. G.; Smarygina, I. V.; Kindop, V. E.

    2017-01-01

    The phase composition, the hardness, the mechanical properties at room temperature, and the resistance to hot (950 - 1000°C) and warm (550°C) deformation are studied for cast deformable "light" ferritic and austenitic steels of the Fe - (12 - 25)% Mn - (0 - 15)% Al - (0 - 2)% C system alloyed additionally with about 5% Ni. The high-aluminum high-manganese low-carbon and carbonless ferritic steels at a temperature of about 0.5 T melt have a specific strength close to that of the austenitic steels and may be used as weldable scale-resistant and wear-resistant materials. The high-carbon Fe - (20 - 24)% Mn - (5 - 9)% Al - 5% Ni - 1.5% C austenitic steels may be applied as light high-strength materials operating at cryogenic temperatures after a solution treatment and as scale- and heat-resistant materials in an aged condition.

  20. Fabrication of MnAl thin films with perpendicular anisotropy on Si substrates

    NASA Astrophysics Data System (ADS)

    Huang, Efrem Y.; Kryder, Mark H.

    2015-05-01

    For the first time, perpendicularly magnetized L10-ordered MnAl thin films were demonstrated using a MgO seed layer on Si substrates, which is critical to making spintronic devices. Fabrication conditions were selected by systematically varying sputtering parameters (film thickness, DC sputtering power, in situ substrate temperature, and post-annealing temperature) and investigating structural and magnetic properties. Strong perpendicular magnetic anisotropy with coercivity Hc of 8 kOe, Ku of over 6.5 × 106 erg/cm3, saturation magnetization Ms of 300 emu/cm3, and out-of-plane squareness Mr/Ms of 0.8 were achieved. These MnAl film properties were obtained via DC magnetron sputtering at 530 °C, followed by 350 °C annealing under a 4 kOe magnetic field oriented perpendicular to the film plane.

  1. Anomalous resistivity upturn in epitaxial L21-Co2MnAl films

    PubMed Central

    Zhu, L. J.; Zhao, J. H.

    2017-01-01

    Despite of the great scientific and technology interest, highly ordered full-Heusler L21-Co2MnAl films have remained a big challenge in terms of the availability and the electrical transport. Here we report the controllable growth and the intriguing transport behavior of epitaxial L21-Co2MnAl films, which exhibit a low-temperature (T) resistivity upturn with a pronounced T1/2 dependence, a robust independence of magnetic fields, and a close relevance to structural disorder. The resistivity upturn turns out to be qualitatively contradictory to weak localization, particle-particle channel electron-electron interaction (EEI), and orbital two-channel Kondo effect, leaving a three-dimensional particle-hole channel EEI the most likely physical source. Our result highlights a considerable tunability of the structural and electronic disorder of magnetic films by varying growth temperature, affording unprecedented insights into the origin of the resistivity upturn. PMID:28218300

  2. Raman spectroscopic study of MnAl2O4 galaxite at various pressures and temperatures

    NASA Astrophysics Data System (ADS)

    Zhai, Shuangmeng; Yin, Yuan; Shieh, Sean R.; Chang, Yun-Yuan; Xie, Tianqi; Xue, Weihong

    2017-03-01

    The vibrational properties of synthetic galaxite, MnAl2O4, were investigated at various pressures (0-29.7 GPa) and temperatures (80-973 K), respectively. The Raman frequencies of all observed bands for galaxite continuously increase with increasing pressure and decrease with increasing temperature, respectively. The quantitative analysis shows that the lowest frequency T 2 g mode has the smallest isothermal mode Grüneisen parameter. Combined with previous studies, the thermal Grüneisen parameter of galaxite is determined to be 1.23(5). The quantitative analysis of temperature dependences of Raman bands yields that the lowest frequency T 2 g mode has the largest isobaric mode Grüneisen parameter. The intrinsic anharmonic mode parameters are also calculated and nonzero, indicating an existence of intrinsic anharmonicity for MnAl2O4 spinel.

  3. Solubility and magnetic properties enhancement in bi-phase nanostructure Cu-Fe-Mn alloy

    NASA Astrophysics Data System (ADS)

    Mondal, B. N.; Basumallick, A.; Nath, D. N.; Chattopadhyay, P. P.

    2013-09-01

    In order to improve solubility and magnetic properties, the ball milling technology was used for the production of 50Cu-40Fe-10Mn (wt%) alloy. The effect of Mn content on the microstructure and magnetic properties of Cu-Fe alloy was also investigated in detail. Microstructure and magnetic properties of the alloy were analyzed by X-ray diffraction, differential scanning calorimetry, high resolution transmission electron microscopy and superconducting quantum interface device magnetometry. The results showed that a complete solid solution of the alloy was produced after 30 h of milling. Quantitative phase analysis of X-ray diffraction data revealed that the milled alloy obtained after isothermal annealing at 550 °C for 1 h consisted of Cu (54.52 wt%), α-Fe (36.49 wt%) and MnO (8.99 wt%). The milled alloy obtained after annealing at 450 °C for 1 h leads to the maximum values of magnetic properties such as coercivity=438 Oe, remanent magnetization=14.3 emu/g, and saturation magnetization=51 emu/g.

  4. Investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al alloy with Ag and Mn additions

    SciTech Connect

    Silva, R.A.G.; Paganotti, A.; Gama, S.; Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A.

    2013-01-15

    The investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al, Cu-11%Al-3%Ag, Cu-11%Al-10%Mn and Cu-11%Al-10%Mn-3%Ag alloys was made using microhardness measurements, differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field measurement. The results indicated that the Mn addition changes the phase stability range, the microhardness values and makes undetectable the eutectoid reaction in annealed Cu-11%Al and Cu-11%Al-3%Ag alloys while the presence of Ag does not modify the phase transformation sequence neither microhardness values of the annealed Cu-11%Al and Cu-11%Al-10%Mn alloys, but it increases the magnetic moment of this latter at about 2.7 times and decreases the rates of eutectoid and peritectoid reactions of the former. - Highlights: Black-Right-Pointing-Pointer The microstructure of Cu-Al alloy is modified in the Ag presence. Black-Right-Pointing-Pointer ({alpha} + {gamma}) phase is stabilized down to room temperature when Ag is added to Cu-Al alloy. Black-Right-Pointing-Pointer Ag-rich phase modifies the magnetic characteristics of Cu-Al-Mn alloy.

  5. The effects of Ni, Mo, Ti and Si on the mechanical properties of Cr free Mn steel (Fe-25Mn-5Al-2C)

    NASA Technical Reports Server (NTRS)

    Schuon, S. R.

    1982-01-01

    The FeMnAlC alloys may hold potential as Cr-free replacements for high strategic material iron base superalloys, but little is known about their intermediate temperature (650 C to 870 C) mechanical properties. The effects of alloying elements on the mechanical properties of model FeMnAlC alloys were studied. Results showed that modified FeMnAlC alloys had promising short term, intermediate temperature properties but had relatively poor stress rupture lives at 172 MPa and 788 C. Room temperature and 788 C tensile strength of FeMnAlC alloys were better than common cast stainless steels. Changes in room temperature tensile and 788 C tensile strength and ductility, and 788 C stress rupture life were correlated with changes in Ni, Mo, Ti, and Si levels due to alloying effects on interstitial carbon levels and carbide morphology. Fe-25Mn-5Al-2C had a very poor stress rupture life at 172 MPa and 788 C. Addition of carbide-forming elements improved the stress rupture life.

  6. Structural, magnetic, and superconducting properties of pulsed-laser-deposition-grown La<mn>1.85mn> Sr<mn>0.15mn> CuO<mn>4mn> / La<mn>2mn>/>3mn> Ca<mn>1mn>/>3mn> MnO>3mn> superlattices on (001)-oriented LaSrAlO>4mn> substrates

    SciTech Connect

    Das, S.; Sen, K.; Marozau, I.; Uribe-Laverde, M. A.; Biskup, N.; Varela, M.; Khaydukov, Y.; Soltwedel, O.; Keller, T.; Döbeli, M.; Schneider, C. W.; Bernhard, C.

    2014-03-12

    Epitaxial La<mn>1.85mn> Sr<mn>0.15mn> CuO<mn>4mn> / La<mn>2mn>/>3mn> Ca<mn>1mn>/>3mn> MnO>3mn> (LSCO/LCMO) superlattices (SL) on (001)- oriented LaSrAlO4 substrates have been grown with pulsed laser deposition (PLD) technique. Their structural, magnetic and superconducting properties have been determined with in-situ reflection high energy electron diffraction (RHEED), x-ray diffraction, specular neutron reflectometry, scanning transmission electron microscopy (STEM), electric transport, and magnetization measurements. We find that despite the large mismatch between the in-plane lattice parameters of LSCO (a = 0.3779 nm) and LCMO (a = 0.387 nm) these superlattices can be grown epitaxially and with a high crystalline quality. While the first LSCO layer remains clamped to the LSAO substrate, a sizeable strain relaxation occurs already in the first LCMO layer. The following LSCO and LCMO layers adopt a nearly balanced state in which the tensile and compressive strain effects yield alternating in-plane lattice parameters with an almost constant average value. No major defects are observed in the LSCO layers, while a significant number of vertical antiphase boundaries are found in the LCMO layers. The LSCO layers remain superconducting with a relatively high superconducting onset temperature of Tconset ≈ 36 K. The macroscopic superconducting response is also evident in the magnetization data due to a weak diamagnetic signal below 10 K for H ∥ ab and a sizeable paramagnetic shift for H ∥ c that can be explained in terms of a vortex-pinning-induced flux compression. The LCMO layers maintain a

  7. Effect of Mn Substitution for Multiferroic BiFeO3 Probed by High-Resolution Soft-X-Ray Spectroscopy

    SciTech Connect

    Higuchi, Tohru; Higuchi, T.; Hattori, T.; Sakamoto, W.; Itoh, N.; Shimura, T.; Yogo, T.; Yao, P.; Liu, Y.; Glans, P.; Chang, C.; Wu, Z.; Guo, Jinghua

    2008-07-11

    The electronic structures of BiFeO{sub 3} (BF) and Mn-doped BiFeO{sub 3} (BF(Mn)) have been studied by X-ray absorption spectroscopy (XAS) and soft-X-ray emission spectroscopy (SXES). The BF and BF(Mn) have the mixed valence state of Fe{sup 2+} and Fe{sup 3+}. The valence band is mainly composed of O 2p state hybridized with the majority-spin t{sub 2g} and e{sub g} orbitals of Fe 3d state. The conduction band is composed of the minority-spin t{sub 2g} and e{sub g} orbitals of Fe 3d. The band gaps of BF and BF(Mn) are estimated to be 1.3 eV and 2.7 eV, respectively. The increase of band gap with Mn substitution contributes to the change of bandwidth of valence band.

  8. 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.

  9. Liquid-liquid phase equilibrium and core-shell structure formation in immiscible Al-Bi-Sn alloys

    NASA Astrophysics Data System (ADS)

    Li, Mingyang; Jia, Peng; Sun, Xiaofei; Geng, Haoran; Zuo, Min; Zhao, Degang

    2016-04-01

    In this paper, the liquid-phase separation of ternary immiscible Al45Bi19.8Sn35.2 and Al60Bi14.4Sn25.6 melts was studied with resistivity and thermal analysis methods at different temperature. The resistivity-temperature curves appear abrupt and anomalously change with rising temperature, corresponding to the anomalous and low peak of melting process in DSC curves, indicative of the occurrence of the liquid-phase separation. The anomalous behavior of the resistivity temperature dependence is attributable to concentration-concentration fluctuations. The effect of composition and melt temperature on the liquid-phase separation and core-shell structure formation in immiscible Al-Bi-Sn alloys was studied. The liquid-phase separation and formation of the core-shell structure in immiscible Al-Bi-Sn alloys are readily acquired when the alloy compositions fall into liquid miscibility gap. What's more, the cross-sectional structure changes from irregular, dispersed to core-type shapes under the actions of Marangoni motion with increasing melt temperature. This study provides some clues for the preparation of core-shell microspheres of immiscible Al-Bi-Sn alloys via liquid-phase separation.

  10. Mechanical, electrical, and thermal properties of the directionally solidified Bi-Zn-Al ternary eutectic alloy

    NASA Astrophysics Data System (ADS)

    Şahin, M.; Çadırlı, E.

    2014-10-01

    A Bi-2.0Zn-0.2Al (wt%) ternary eutectic alloy was prepared using a vacuum melting furnace and a casting furnace. The samples were directionally solidified upwards at a constant growth rate ( V = 18.4 μm/s) under different temperature gradients ( G = 1.15-3.44 K/mm) and at a constant temperature gradient ( G = 2.66 K/mm) under different growth rates ( V = 8.3-500 μm/s) in a Bridgman-type directional solidification furnace. The dependence of microstructure parameter ( λ) on the solidification parameters ( G and V) and that of the microhardness (Hv) on the microstructure and solidification parameters were investigated. The resistivity ( ρ) measurements of the studied alloy were performed using the standard four-point-probe method, and the temperature coefficient of resistivity ( α) was calculated from the ρ- T curve. The enthalpy (Δ H) and the specific heat ( C p ) values were determined by differential scanning calorimetry analysis. In addition, the thermal conductivities of samples, obtained using the Wiedemann-Franz and Smith-Palmer equations, were compared with the experimental results. The results revealed that, the thermal conductivity values obtained using the Wiedemann-Franz and Smith-Palmer equations for the Bi-2.0Zn-0.2Al (wt%) alloy are in the range of 5.2-6.5 W/Km and 15.2-16.4 W/Km, respectively.

  11. Maxwell-Wagner relaxation and magnetodielectric properties of Bi0.5La0.5MnO3 ceramics

    NASA Astrophysics Data System (ADS)

    Turik, A. V.; Pavlenko, A. V.; Reznichenko, L. A.

    2016-08-01

    The complex permittivity ɛ = ɛ'- iɛ″ of manganite bismuth-lanthanum Bi0.5La0.5MnO3 ceramics has been measured at temperature T = 78 K in the frequency range f = 200-105 Hz and in the magnetic induction range B = 0-5 T. Dielectric relaxation and the pronounced magnetodielectric effect have been detected. The explanation based on the superposition of Maxwell-Wagner relaxation and the magnetoresistance effect has been proposed.

  12. Activity of MnO in MnO-CaO-SiO2-Al2O3-MgO Molten Slags

    NASA Astrophysics Data System (ADS)

    Yan, Baijun; Chen, Xuexin; Tao, Jun

    2016-12-01

    The activities of MnO in the MnO-CaO-SiO2-Al2O3 (10, 20, and 30 mass pct)-MgO (5 mass pct) melts at 1873 K (1600 °C) were measured by equilibrating the melts with liquid copper under an oxygen partial pressure controlled by CO/CO2 gas mixture with a volume ratio of 99/1. Over the investigated composition range, MnO shows a negative deviation from Raoultian behavior. On the basis of the experimental data, the activity coefficient of MnO in this multicomponent melts was evaluated using the following quadratic formalism based on regular solution model: RT ln {γ_{MnO(s)} = sumlimits_j {{α_{ij}}x_j^2} + sumlimits_j {sumlimits_k {( {{α_{ij}} + {α_{ik}} - {α_{jk}}}){x_j}{x_k} + I{^' } . The values of the conversion factor, I', for the melts containing 10, 20, and 30 mass pct Al2O3 were determined to be 6950, 2715, and 12092 J/mol, respectively. Iso-activity contours for MnO in the five component system were calculated using the quadratic formalism, and they showed a good agreement with the experimental data.

  13. Activity of MnO in MnO-CaO-SiO2-Al2O3-MgO Molten Slags

    NASA Astrophysics Data System (ADS)

    Yan, Baijun; Chen, Xuexin; Tao, Jun

    2017-04-01

    The activities of MnO in the MnO-CaO-SiO2-Al2O3 (10, 20, and 30 mass pct)-MgO (5 mass pct) melts at 1873 K (1600 °C) were measured by equilibrating the melts with liquid copper under an oxygen partial pressure controlled by CO/CO2 gas mixture with a volume ratio of 99/1. Over the investigated composition range, MnO shows a negative deviation from Raoultian behavior. On the basis of the experimental data, the activity coefficient of MnO in this multicomponent melts was evaluated using the following quadratic formalism based on regular solution model: RT ln {γ_{{{MnO}}({{s}})}} = \\sum\\limits_j {{α_{ij}}x_j^2} + \\sum\\limits_j {\\sum\\limits_k {( {{α_{ij}} + {α_{ik}} - {α_{jk}}}){x_j}{x_k} + I{^' } . The values of the conversion factor, I', for the melts containing 10, 20, and 30 mass pct Al2O3 were determined to be 6950, 2715, and 12092 J/mol, respectively. Iso-activity contours for MnO in the five component system were calculated using the quadratic formalism, and they showed a good agreement with the experimental data.

  14. Poling-Written Ferroelectricity in Bulk Multiferroic Double-Perovskite BiFe0.5Mn0.5O3.

    PubMed

    Delmonte, Davide; Mezzadri, Francesco; Gilioli, Edmondo; Solzi, Massimo; Calestani, Gianluca; Bolzoni, Fulvio; Cabassi, Riccardo

    2016-06-20

    We present a comprehensive study of the electrical properties of bulk polycrystalline BiFe0.5Mn0.5O3, a double perovskite synthesized in high-pressure and high-temperature conditions. BiFe0.5Mn0.5O3 shows an antiferromagnetic character with TN = 288 K overlapped with an intrinsic antiferroelectricity due to the Bi(3+) stereochemical effect. Beyond this, the observation of a semiconductor-insulator transition at TP ≈ 140 K allows one to define three distinct temperature ranges with completely different electrical properties. For T > TN, electric transport follows an ordinary thermally activated Arrhenius behavior; the system behaves as a paramagnetic semiconductor. At intermediate temperatures (TP < T < TN), electric transport is best described by Mott's variable range hopping model with lowered dimensionality D = 1, stabilized by the magnetic ordering process and driven by the inhomogeneity of the sample on the B site of the perovskite. Finally, for T < TP, the material becomes a dielectric insulator, showing very unusual poling-induced soft ferroelectricity with high saturation polarization, similar to the parent compound BiFeO3. Under external electric poling, the system irreversibly evolves from antiferroelectric to polar arrangement.

  15. Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites.

    PubMed

    Boona, Stephen R; Vandaele, Koen; Boona, Isabel N; McComb, David W; Heremans, Joseph P

    2016-12-12

    Transverse thermoelectric devices produce electric fields perpendicular to an incident heat flux. Classically, this process is driven by the Nernst effect in bulk solids, wherein a magnetic field generates a Lorentz force on thermally excited electrons. The spin Seebeck effect also produces magnetization-dependent transverse electric fields. It is traditionally observed in thin metallic films deposited on electrically insulating ferromagnets, but the films' high resistance limits thermoelectric conversion efficiency. Combining Nernst and spin Seebeck effect in bulk materials would enable devices with simultaneously large transverse thermopower and low electrical resistance. Here we demonstrate experimentally that this is possible in composites of conducting ferromagnets (Ni or MnBi) containing metallic nanoparticles with strong spin-orbit interactions (Pt or Au). These materials display positive shifts in transverse thermopower attributable to inverse spin Hall electric fields in the nanoparticles. This more than doubles the power output of the Ni-Pt materials, establishing proof of principle that the spin Seebeck effect persists in bulk nanocomposites.

  16. Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites

    NASA Astrophysics Data System (ADS)

    Boona, Stephen R.; Vandaele, Koen; Boona, Isabel N.; McComb, David W.; Heremans, Joseph P.

    2016-12-01

    Transverse thermoelectric devices produce electric fields perpendicular to an incident heat flux. Classically, this process is driven by the Nernst effect in bulk solids, wherein a magnetic field generates a Lorentz force on thermally excited electrons. The spin Seebeck effect also produces magnetization-dependent transverse electric fields. It is traditionally observed in thin metallic films deposited on electrically insulating ferromagnets, but the films' high resistance limits thermoelectric conversion efficiency. Combining Nernst and spin Seebeck effect in bulk materials would enable devices with simultaneously large transverse thermopower and low electrical resistance. Here we demonstrate experimentally that this is possible in composites of conducting ferromagnets (Ni or MnBi) containing metallic nanoparticles with strong spin-orbit interactions (Pt or Au). These materials display positive shifts in transverse thermopower attributable to inverse spin Hall electric fields in the nanoparticles. This more than doubles the power output of the Ni-Pt materials, establishing proof of principle that the spin Seebeck effect persists in bulk nanocomposites.

  17. Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites

    PubMed Central

    Boona, Stephen R.; Vandaele, Koen; Boona, Isabel N.; McComb, David W.; Heremans, Joseph P.

    2016-01-01

    Transverse thermoelectric devices produce electric fields perpendicular to an incident heat flux. Classically, this process is driven by the Nernst effect in bulk solids, wherein a magnetic field generates a Lorentz force on thermally excited electrons. The spin Seebeck effect also produces magnetization-dependent transverse electric fields. It is traditionally observed in thin metallic films deposited on electrically insulating ferromagnets, but the films' high resistance limits thermoelectric conversion efficiency. Combining Nernst and spin Seebeck effect in bulk materials would enable devices with simultaneously large transverse thermopower and low electrical resistance. Here we demonstrate experimentally that this is possible in composites of conducting ferromagnets (Ni or MnBi) containing metallic nanoparticles with strong spin–orbit interactions (Pt or Au). These materials display positive shifts in transverse thermopower attributable to inverse spin Hall electric fields in the nanoparticles. This more than doubles the power output of the Ni-Pt materials, establishing proof of principle that the spin Seebeck effect persists in bulk nanocomposites. PMID:27941927

  18. Electron spin resonance studies of Bi0.6Ca(0.4-x)SrxMnO3

    NASA Astrophysics Data System (ADS)

    Kurian, Joji; Singh, R.

    2010-05-01

    The temperature dependent electron spin resonance (ESR) studies were carried out on Bi0.6Ca(0.4-x)SrxMnO3 (0≤x≤0.4). The variation of charge ordering temperature, TCO, and Néel temperature, TN, are obtained from plots of double integrated (DI) intensity and linewidth (ΔH) of the ESR signal as a function of temperature. In the temperature range T>TCO, the sample is in the paramagnetic phase and the magnetic interactions are dominated by ferromagnetic (FM) spin correlations. In the range TN

  19. X-ray magnetic spectroscopy of MBE-grown Mn-doped Bi{sub 2}Se{sub 3} thin films

    SciTech Connect

    Collins-McIntyre, L. J.; Watson, M. D.; Zhang, S. L.; Coldea, A. I.; Hesjedal, T.; Baker, A. A.; Harrison, S. E.; Pushp, A.; Kellock, A. J.; Parkin, S. S. P.; Laan, G. van der

    2014-12-15

    We report the growth of Mn-doped Bi{sub 2}Se{sub 3} thin films by molecular beam epitaxy (MBE), investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), SQUID magnetometry and x-ray magnetic circular dichroism (XMCD). Epitaxial films were deposited on c-plane sapphire substrates by co-evaporation. The films exhibit a spiral growth mechanism typical of this material class, as revealed by AFM. The XRD measurements demonstrate a good crystalline structure which is retained upon doping up to ∼7.5 atomic-% Mn, determined by Rutherford backscattering spectrometry (RBS), and show no evidence of the formation of parasitic phases. However an increasing interstitial incorporation of Mn is observed with increasing doping concentration. A magnetic moment of 5.1 μ{sub B}/Mn is obtained from bulk-sensitive SQUID measurements, and a much lower moment of 1.6 μ{sub B}/Mn from surface-sensitive XMCD. At ∼2.5 K, XMCD at the Mn L{sub 2,3} edge, reveals short-range magnetic order in the films and indicates ferromagnetic order below 1.5 K.

  20. Al-Si-Mn Alloy Coating on Aluminum Substrate Using Cold Metal Transfer (CMT) Welding Technique

    NASA Astrophysics Data System (ADS)

    Rajeev, G. P.; Kamaraj, M.; Bakshi, S. R.

    2014-06-01

    The cold metal transfer (CMT) process was explored as a weld overlay technique for synthesizing Al-Si-Mn alloy coating on a commercially pure Al plate. The effect of welding speed on the bead geometry, deposition rate, and the dilution were studied and the best parameter was used to synthesize the coatings. The CMT process can be used to produce thick coatings (>2.5 mm) without porosity and with low dilution levels. The Vickers hardness number of the Al substrate increased from 28 in the bulk to 57 in the coating. It is suggested that the CMT process can be an effective and energy-efficient technique for depositing thick coatings and is useful in weld repair of aluminum alloy components.

  1. Stabilization of a Metastable Fibrous Bi21.2(1)(Mn1–xCox )20 Phase with Pseudo-Pentagonal Symmetry Prepared Using a Bi Self-Flux

    DOE PAGES

    Thimmaiah, Srinivasa; Taufour, Valentin; Saunders, Scott; ...

    2016-11-15

    Bi21.2(1)(Mn1–xCox )20 is a new metastable phase which is synthesized via Bi self-flux, adopts a highly fibrous morpholo-gy, and decomposes endothermically near 168 °C. It crystallizes in the orthorhombic space group Imma with unit cell parameters α = 19.067(4) Å, $b$ = 4.6071(10) Å and c = 11.583(4) Å, adopting a low-temperature modification of BiNi-type structure by forming columns along the b-axis. Wave-length-dispersive X-ray spectroscopy (WDS) confirms the presence of Co in the structure, which is found to be 7 at.%. In each column, the transition metal (T) and Bi atoms construct a double-walled nanotubular arrangement of atoms around themore » disordered central Bi atoms. Electronic structure calculations (LMTO-ASA, LSDA) show that the calculated Fermi level falls into a pseudogap and also indicate a possible low-temperature magnetic ordering in the phase.« less

  2. Thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73)

    SciTech Connect

    Barczak, S.A.; Downie, R.A.; Popuri, S.R.; Decourt, R.; Pollet, M.; Bos, J.W.G.

    2015-07-15

    Two series of Fe and Al double substituted MnSi{sub γ} chimney ladders with a nominal valence electron count, VEC=14 per transition metal were prepared (γ=1.75). Simultaneous replacement of Mn with Fe and Si with Al yielded the Mn{sub 1−x}Fe{sub x}Si{sub 1.75−x}Al{sub x} series while the second Mn{sub 1−x}Fe{sub x}Si{sub 1.75–1.75x}Al{sub 2x} series follows the pseudo-binary between MnSi{sub 1.75} and FeAl{sub 2}. Scanning electron microscopy and elemental mapping revealed that ~60% of the nominal Al content ends up in the product with the remainder lost to sublimation, and that up to 7% Al can be substituted in the main group sublattice. Profile analysis of X-ray powder diffraction data revealed gradual changes in the cell metrics, consistent with the simultaneous substitution of Fe and Al in a fixed ratio. All samples are p-type with VEC≈13.95 from the structural data and ~1×10{sup 21} holes cm{sup −3} from variable temperature Seebeck measurements. The substituted samples have lower electrical resistivities (ρ{sub 300} {sub K}=2–5 mΩ cm) due to an improved microstructure. This leads to increased thermoelectric power factors (largest S{sup 2}/ρ=1.95 mW m{sup −1} K{sup −2}) compared to MnSi{sub γ}. The thermal conductivity for the Mn{sub 0.95}Fe{sub 0.05}Si{sub 1.66}Al{sub 0.1} sample is 2.7 W m{sup −1} K{sup −1} between 300 and 800 K, and is comparable to literature data for the parent material. - Graphical abstract: The crystal structure, microstructure and thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73) have been investigated. - Highlights: • Up to 7% Al can be substituted in MnSi{sub γ} when co-doped with Fe. • Improved microstructure and reduced electrical resistivities for Al substituted samples. • Largest power factor 1.95 mW m{sup −1} K{sup −2} and best estimated ZT=0.5.

  3. Microstructural Developments and Tensile Properties of Lean Fe-Mn-Al-C Lightweight Steels

    NASA Astrophysics Data System (ADS)

    Sohn, S. S.; Lee, S.; Lee, B.-J.; Kwak, J.-H.

    2014-09-01

    Concepts of Fe-Al-Mn-C-based lightweight steels are fairly simple, but primary metallurgical issues are complicated. In this study, recent studies on lean-composition lightweight steels were reviewed, summarized, and emphasized by their microstructural development and mechanical properties. The lightweight steels containing a low-density element of Al were designed by thermodynamic calculation and were manufactured by conventional industrial processes. Their microstructures consisted of various secondary phases as κ-carbide, martensite, and austenite in the ferrite matrix according to manufacturing and annealing procedures. The solidification microstructure containing segregations of C, Mn, and Al produced a banded structure during the hot rolling. The (ferrite + austenite) duplex microstructure was formed after the annealing, and the austenite was retained at room temperature. It was because the thermal stability of austenite nucleated from fine κ-carbide was quite high due to fine grain size of austenite. Because these lightweight steels have outstanding properties of strength and ductility as well as reduced density, they give a promise for automotive applications requiring excellent properties.

  4. Numerical Study of Microstructural Evolution During Homogenization of Al-Si-Mg-Fe-Mn Alloys

    NASA Astrophysics Data System (ADS)

    Priya, Pikee; Johnson, David R.; Krane, Matthew J. M.

    2016-09-01

    Microstructural evolution during homogenization of Al-Si-Mg-Fe-Mn alloys occurs in two stages at different length scales: while holding at the homogenization temperature (diffusion on the scale of the secondary dendrite arm spacing (SDAS) in micrometers) and during quenching to room temperature (dispersoid precipitation at the nanometer to submicron scale). Here a numerical study estimates microstructural changes during both stages. A diffusion-based model developed to simulate evolution at the SDAS length scale predicts homogenization times and microstructures matching experiments. That model is coupled with a Kampmann Wagner Neumann-based precipitate nucleation and growth model to study the effect of temperature, composition, as-cast microstructure, and cooling rates during posthomogenization quenching on microstructural evolution. A homogenization schedule of 853 K (580 °C) for 8 hours, followed by cooling at 250 K/h, is suggested to optimize microstructures for easier extrusion, consisting of minimal α-Al(FeMn)Si, no β-AlFeSi, and Mg2Si dispersoids <1 μm size.

  5. Substitution effect on the magnetic and transport properties of CeNi{sub 0.8−x}Mn{sub x}Bi{sub 2}

    SciTech Connect

    Kim, Soo-Whan; Lee, Kyujoon; Jung, Myung-Hwa; Adroja, D. T.; Demmel, F.; Taylor, J. W.

    2014-08-21

    We report the results of Mn substitution for Ni in CeNi{sub 0.8}Bi{sub 2} (i.e., CeNi{sub 0.8−x}Mn{sub x}Bi{sub 2}). All the samples have an antiferromagnetic ordered state below T{sub N} = 5.0 K due to localized 4f-magnetic moment on the Ce ions. Besides this antiferromagnetic ordering caused by Ce, the magnetic and transport properties are abruptly changed with increasing Mn contents at the boundary composition of x = 0.4. The magnetic state is changed into a ferromagnetic state around 200 K for x > 0.4, where the electrical resistivity is strongly suppressed to become simple metallic. These results of ferromagnetism and metallicity can be explained by the double exchange mechanism, rather than the simple picture of Doniach phase diagram. The mixed valence states of Ni and Mn ions are confirmed by X-ray photoelectron spectroscopy. For x ≤ 0.4, the initial Ni{sup 3+} state gradually changes to the Ni{sup 2+} state with increasing x up to 0.4. On further increase of x > 0.4, the Ni{sup 2+} state is replaced by the Mn{sup 2+} state, which gradually changes to the final Mn{sup 3+} state. We also present an inelastic neutron scattering (INS) measurements on CeNi{sub 0.8}Bi{sub 2} (i.e., x = 0) between 1.2 and 12 K. The high energy INS study reveals the presence of two well-defined crystal electric field (CEF) excitations near 9 meV and 19 meV at 1.2 K and 6 K, while the low energy INS study reveals the presence of quasielastic scattering above 4 K. We will discuss our INS results of CeNi{sub 0.8}Bi{sub 2} based on the CEF model.

  6. Tunneling magnetoresistance in (Ga,Mn)As/Al-O/CoFeB hybrid structures

    NASA Astrophysics Data System (ADS)

    Du, G. X.; Babu, M. Ramesh; Han, X. F.; Deng, J. J.; Wang, W. Z.; Zhao, J. H.; Wang, W. D.; Tang, Jinke

    2009-04-01

    Tunneling magnetoresistance (TMR) in Ga0.92Mn0.08As/Al-O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field |H|≤2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 μA. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented.

  7. A Study of Al-Mn Transition Edge Sensor Engineering for Stability

    SciTech Connect

    George, E. M.; et al.

    2013-11-10

    The stability of Al-Mn transition edge sensor (TES) bolometers is studied as we vary the engineered TES transition, heat capacity, and/or coupling between the heat capacity and TES. We present thermal structure measurements of each of the 39 designs tested. The data is accurately fit by a two-body bolometer model, which allows us to extract the basic TES parameters that affect device stability. We conclude that parameters affecting device stability can be engineered for optimal device operation, and present the model parameters extracted for the different TES designs.

  8. Fast magnetization precession for perpendicularly magnetized MnAlGe epitaxial films with atomic layered structures

    NASA Astrophysics Data System (ADS)

    Mizukami, S.; Sakuma, A.; Kubota, T.; Kondo, Y.; Sugihara, A.; Miyazaki, T.

    2013-09-01

    Epitaxial growth and magnetization precessional dynamics for tetragonal MnAlGe films are investigated. The films are grown on MgO (100) with c axis parallel to the film normal and well-ordered layered structures. The film exhibits rectangular hysteresis loop with perpendicular magnetic anisotropy constant of 4.7 Merg/cm3 and saturation magnetization of 250 emu/cm3. Magnetization precession with precession frequency of ˜100 GHz is observed by time-resolved magneto-optical Kerr effect. Further, the Gilbert damping constant is found to be less than ˜0.05, which is much larger than that obtained using the first principles calculations.

  9. Improved optical storage properties of NaAlSiO4: Tb3+ induced by Bi3+

    NASA Astrophysics Data System (ADS)

    Zhou, Junhe; Yu, Xue; Wang, Ting; Zhou, Dacheng; Qiu, Jianbei

    2016-07-01

    NaAlSiO4: Tb3+, Bi3+ phosphor was synthesized with green long persistent luminescence (LPL) and photo-stimulated luminescence (PSL) observed. The influence of metal ion Bi3+ on the optical storage properties of NaAlSiO4: Tb3+ was investigated in detail. The emitter Tb3+ introduced two kinds of traps located at 350 K (TA) and 440 K (TB) in the thermoluminescence (TL) glow curve. Bi3+ as a codopant ion introduced a new trap peaking at 390 K (TC), which contributed to the improved LPL properties. Besides, owing to the existence of deep and stable trap TB, green PSL can still be observed after 72 h since the excitation was stopped. Accordingly, the mechanism of LPL and PSL process was discussed briefly.

  10. Investigating the effect of Cd-Mn co-doped nano-sized BiFeO3 on its physical properties

    NASA Astrophysics Data System (ADS)

    Ishaq, B.; Murtaza, G.; Sharif, S.; Azhar Khan, M.; Akhtar, Naeem; Will, I. G.; Saleem, Murtaza; Ramay, Shahid M.

    This work deals with the investigation of different effects on the structural, magnetic, electronic and dielectric properties of Cd and Mn doped Bi0.75Cd0.25Fe1-xMnxO3 multiferroic samples by taking fixed ratios of Cd and varying the Mn ratio with values of x = 0.0, 0.5, 0.10 and 0.15. Cd-Mn doped samples were synthesized chemically using a microemulsion method. All the samples were finally sintered at 700 °C for 2 h to obtain the single phase perovskites structure of BiFeO3 materials. The synthesized samples were characterized by different techniques, such as X-ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), LCR meter and magnetic properties using VSM. XRD results confirm BFO is a perovskite structure having crystallite size in the range of 24-54 nm. XRD results also reveal observed structural distortion due to doping of Cd at the A-site and Mn at the B-site of BFO. SEM results depict that, as the substitution of Cd-Mn increases in BFO, grain size decreases up to 30 nm. FTIR spectra showed prominent absorption bands at 555 cm-1 and 445 cm-1 corresponding to the stretching vibrations of the metal ions complexes at site A and site B, respectively. Variation of dielectric constant (ɛ‧) and loss tangent (tan δ) at room temperature in the range of 1 MHz to 3 GHz have been investigated. Results reveal that with Cd-Mn co doping a slight decrease in dielectric constant have been observed. Magnetic properties of Cd-Mn doped pure BFO samples have been studied at 300 K. Results reveal that undoped BiFeO3 exhibits weak ferromagnetic ordering due to the canting of its spin. Increase in magnetization and decrease in coercivity is a clear indication that a material can be used in high density recording media and memory devices.

  11. Effect of progressive substitution of Bi3+ by La3+ on the structural, magnetic, and transport properties of Bi0.6Ca0.4MnO3

    NASA Astrophysics Data System (ADS)

    Zhang, R. R.; Kuang, G. L.; Yin, L. H.; Sun, Y. P.

    2010-11-01

    Structural, magnetic, and electronic transport properties of Bi0.6-xLaxCa0.4MnO3 (0≤x≤0.6) manganites have been studied systematically. The parent compound exhibits robust charge ordered antiferrromagnetic (COAFM) phase with TCO˜293 K and AFM Néel temperature TN˜149 K. The sample with x =0.1 show a M(T ) curve of "arch bridge" form between 142 and 253 K, which is attributed to the AFM peak embedded in the broad transition of the CO. For the middle doping samples (0.2≤x≤0.4), although the CO peaks disappear as a result of the suppression of the long range CO state, AFM superexchange coupling has been strengthened with the increasing of La doping level. The Bi0.1La0.5Ca0.4MnO3 sample shows interesting phenomena such as magnetization steps and magnetic memory effect. The resistivity of the samples exhibits insulating behavior in our measured temperature range for x ≤0.4. While both x =0.5 and x =0.6 compounds exhibit metal-insulator transition. Furthermore, large low field magnetoresistance (MR) and hysteresis appears only in the MR(H) curve of x =0.5 sample. These results are discussed in terms of the charge localization caused by the lattice distortion due to the character of the 6s2 lone pair of Bi3+ ions.

  12. Structural, dielectric, and ferroelectric properties of the (1-x)PbTiO₃-xBiAlO₃ solid solution.

    PubMed

    Yu, Huichun; Ren, Wei; Ye, Zuo-Guang

    2010-10-01

    Ferroelectric ceramics derived from the solid solution of (1-x)PbTiO₃-xBiAlO₃ (x = 0, 0.05, 0.10, 0.15, and 0.18) have been synthesized by solid-state reactions. A pure perovskite phase is formed for 0 ≤ x ≤ 0.15. The tetragonality (c/a) of the solid solution decreases with the increasing amount of BiAlO₃. Scanning electron microscopic images reveal a microstructure with a fine grain size of less than 1 μm for the solid solution ceramics (x ≥ 0.05). Compared with pure PbTiOPbTiO₃ ceramics whose high conductivity and poor densification were harmful to their dielectric performance, the ceramics of (1-x)PbTiO₃-xBiAlO₃ are well-densified (with a relative density of up to 93%) and their dielectric and ferroelectric properties are significantly improved with the addition of BiAlO₃, exhibiting reduced dielectric losses, well-developed P-E hysteresis loops (for x = 0.05, 0.10, and 0.15) and a high remnant polarization (P(r)) of 64 μC/cm² (for x = 0.15).

  13. The effects of alloying elements Al and In on Ni-Mn-Ga shape memory alloys, from first principles.

    PubMed

    Chen, Jie; Li, Yan; Shang, Jia-Xiang; Xu, Hui-Bin

    2009-01-28

    The electronic structures and formation energies of the Ni(9)Mn(4)Ga(3-x)Al(x) and Ni(9)Mn(4)Ga(3-x)In(x) alloys have been investigated using the first-principles pseudopotential plane-wave method based on density functional theory. The results show that both the austenite and martensite phases of Ni(9)Mn(4)Ga(3) alloy are stabilized by Al alloying, while they become unstable with In alloying. According to the partial density of states and structural energy analysis, different effects of Al and In alloying on the phase stability are mainly attributed to their chemical effects. The formation energy difference between the austenite and martensite phases decreases with Al or In alloying, correlating with the experimentally reported changes in martensitic transformation temperature. The shape factor plays an important role in the decrease of the formation energy difference.

  14. Synthesis of Waste Form in the Gd-Fe-Al-Ni-Mn-Cr-O System

    SciTech Connect

    Chae, S.C.; Jang, Y.N.; Bae, I.K.; Ryu, K.W.

    2006-07-01

    Poly-phase waste form which was the mixture of Gd{sub 3}Fe{sub 2}Al{sub 3}O{sub 12} and (Ni{sub x}Mn{sub 1-x})(Fe{sub y}Cr{sub 1-y}){sub 2}O{sub 4} was synthesized. Also, we are intended to examine phase relation and physicochemical properties of coexisted phases in the compositions and to confirm accommodation relation of elements and phases. Two types of phase series were observed: Garnet-perovskite-spinel and Garnet-spinel. The compositions of garnets and spinels were nonstoichiometric, and especially, this poly-phase ceramics may be in a good waste form. The excessive Gd in garnets indicated the immobilization of higher content of actinides. The nonstoichiometric compositions of garnet and spinel were attributed to the formation of perovskite in that perovskite contained Gd, Fe and Al from garnet and Cr from spinel. (authors)

  15. Structural model of quasiperiodic Pb monolayer deposited on fivefold i-Al-Pd-Mn surface

    NASA Astrophysics Data System (ADS)

    Krajčí, M.; Hafner, J.; Ledieu, J.; Fournée, V.

    2010-04-01

    On the basis of analysis of experimental STM images and ab-initio calculations we propose a structural model of the quasiperiodic Pb monolayer grown on the fivefold i-Al-Pd-Mn surface at a coverage close to the saturation. The skeleton of the Pb monolayer can be seen as a network of the "star-fish" (SF) clusters. The atomic structure of the monolayer is based on a decorated P1 tiling. The model can reproduce also the experimentally observed quasiperiodic τ-scaled P1 ordering (τ is the golden mean). The bright spots seen in STM images appear at Pb atoms in the centers of those SF clusters where the substrate has Al atoms at these positions.

  16. Observation of the TWIP + TRIP Plasticity-Enhancement Mechanism in Al-Added 6 Wt Pct Medium Mn Steel

    NASA Astrophysics Data System (ADS)

    Lee, Seawoong; Lee, Kyooyoung; De Cooman, Bruno C.

    2015-06-01

    The intercritically annealed Fe-0.15 pctC-6.0 pctMn-1.5 pctSi-3.0 pctAl and Fe-0.30 pctC-6.0 pctMn-1.5 pctSi-3.0 pctAl medium Mn steels were found to have improved mechanical properties due to the TWIP and TRIP plasticity-enhancing mechanisms being activated in succession during tensile deformation. The increase of the C content from 0.15 to 0.30 pct resulted in ultra-high strength properties and a strength-ductility balance of approximately 65,000 MPa-pct, i.e., equivalent to the strength-ductility balance of high Mn TWIP steel with a fully austenitic microstructure.

  17. Realization of spin gapless semiconductors: the Heusler compound Mn2CoAl.

    PubMed

    Ouardi, Siham; Fecher, Gerhard H; Felser, Claudia; Kübler, Jürgen

    2013-03-08

    Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and half-metallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a band gap in one of the spin channels and a zero band gap in the other and thus allow for tunable spin transport. Here, we report the first experimental verification of the spin gapless magnetic semiconductor Mn(2)CoAl, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of 2 μ(B). Below 300 K, the compound exhibits nearly temperature-independent conductivity, very low, temperature-independent carrier concentration, and a vanishing Seebeck coefficient. The anomalous Hall effect is comparatively low, which is explained by the symmetry properties of the Berry curvature. Mn(2) CoAl is not only suitable material for room temperature semiconductor spintronics, the robust spin polarization of the spin gapless semiconductors makes it very promising material for spintronics in general.

  18. Plasma Nitriding Behavior of Fe-C-M (M = Al, Cr, Mn, Si) Ternary Martensitic Steels

    NASA Astrophysics Data System (ADS)

    Tomio, Yusaku; Kitsuya, Shigeki; Oh-ishi, Keilchiro; Hono, Kazuhiro; Miyamoto, Goro; Furuhara, Tadashi

    2014-01-01

    Change in surface hardness and nitrides precipitated in Fe-0.6C binary and Fe-0.6 mass pct C-1 mass pct M (M = Al, Cr, Mn, Si) ternary martensitic alloys during plasma nitriding were investigated. Surface hardness was hardly increased in the Fe-0.6C binary alloy and slightly increased in Fe-0.6C-1Mn and Fe-0.6C-1Si alloys. On the other hand, it was largely increased in Fe-0.6C-1Al and Fe-0.6C-1Cr alloys. In all the Fe-0.6C-1M alloys except for the Si-added alloy, fine platelet alloy nitrides precipitated inside martensite laths. In the Fe-0.6C-1Si alloy, Si-enriched film was observed mainly at a grain boundary and an interface between cementite and matrix. Crystal structure of nitrides observed in the martensitic alloys was similar to those in Fe-M binary ferritic alloys reported previously. However, there was a difference in hardening behavior between ferrite and martensite due to a high density of dislocations acting as a nucleation site of the nitrides and partitioning of an alloying element between martensite and cementite changing the driving force of precipitation of the nitrides.

  19. Application of Cu-Al-Mn superelastic alloy bars as reinforcement elements in concrete beams

    NASA Astrophysics Data System (ADS)

    Shrestha, Kshitij C.; Araki, Yoshikazu; Nagae, Takuya; Yano, Hayato; Koetaka, Yuji; Omori, Toshihiro; Sutou, Yuji; Kainuma, Ryosuke; Ishida, Kiyohito

    2012-04-01

    Experimental works are done to assess the seismic behavior of concrete beams reinforced with superelastic alloy (SEA) bars. Applicability of newly developed Cu-Al-Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, have been proposed as partial replacements for conventional steel bars in order to reduce residual deformations in structures during and after intense earthquakes. Four-point reverse-cyclic bending tests were done on 1/3 scale concrete beams comprising three different types of specimens - conventional steel reinforced concrete (ST-RC), SEA reinforced concrete (SEA-RC), and SEA reinforced concrete with pre-tensioning (SEA-PC). The results showed that SEA reinforced concrete beams demonstrated significant enhancement in crack recovery capacity in comparison to steel reinforced beam. Average recovery of cracks for each of the specimens was 21% for ST-RC, 84% for SEA-RC, and 86% for SEA-PC. In addition, SEA-RC and SEA-PC beams demonstrated strong capability of recentering with comparable normalized strength and ductility relative to conventional ST-RC beam specimen. ST-RC beam, on the other hand, showed large residual cracks due to progressive reduction in its re-centering capability with each cycle. Both the SEA-RC and SEA-PC specimens demonstrated superiority of Cu-Al-Mn SEA bars to conventional steel reinforcing bars as reinforcement elements.

  20. Formation of quasicrystalline phase in Al70-x Ga x Pd17Mn13 alloys

    NASA Astrophysics Data System (ADS)

    Yadav, T. P.; Singh, Devinder; Shahi, Rohit R.; Shaz, M. A.; Tiwari, R. S.; Srivastava, O. N.

    2011-07-01

    In the present investigation, the formation and stability of icosahedral phase in Al70- x Ga x Pd17Mn13 alloys has been explored using X-ray diffraction, scanning, transmission electron microscopy and energy dispersive X-ray analysis. Cast alloys and melt-spun ribbons with x = 2.5, 5, 7.5, 10, 12.5, 15 and 20 have been investigated. In both cases, the alloys up to 5 at% Ga exhibit the formation of pure icosahedral phase. However, for x ≥5 at% Ga content, the cast alloy exhibits the formation of multiphase material, consisting of an icosahedral phase along with AlPd-type B2 and ξ‧ crystalline (orthorhombic structure with unit cell a = 23.5 Å, b = 16.6 Å and c = 12.4 Å) phases. In the case of the melt spun ribbon for x = 5 at% Ga, only an icosahedral phase has been found, but for 15 > x > 5 at% Ga, an icosahedral phase is the majority phase with AlPd-type B2 phase being the minority component. For x = 15 at% Ga, a Al3Pd2-type hexagonal phase together with a small amount of quasicrystalline phase is formed. However, for x = 20, only a hexagonal Al3Pd2 phase results.

  1. Atomic-Scale Tunneling Spectra across BiFeO3/La0.7Sr0.3MnO3 Heterointerfaces

    NASA Astrophysics Data System (ADS)

    Chiu, Ya-Ping; Huang, Bo-Chao; Yu, Pu; Chang, Chia-Seng; Chu, Ying-Hao

    2015-03-01

    Atomic-level evolution of electronic structures across BiFeO3/La0.7Sr0.3MnO3 complex oxide heterointerfaces has been demonstrated by cross-sectional scanning tunneling microscopy and spectroscopy in this work. Analysis of scanning tunneling spectroscopy results exploits how the change in the terminated interface brings the influence to the electrostatic configurations across the BiFeO3/La0.7Sr0.3MnO3 heterointerfaces. Spatially unit-cell-by-unit-cell resolved electronic states at the atomic level reveal that the control of material interfaces at the atomic level determines the ferroelectric polarization in BiFeO3. The precise electronic information therefore provides a clear realization about the electronic state at these complex-oxide heterointerfaces, which is crucial to understand and design a host of novel functionalities at complex oxide heterointerfaces. Affilication 2: Department of Physics, National Sun Yat-sen University, Kaohsiung 804, Taiwan.

  2. Environmentally assisted cracking of two-phase Fe-Mn-Al alloys in NaCl solution

    NASA Astrophysics Data System (ADS)

    Shih, S.-T.; Tsu, I.-F.; Perng, T.-P.

    1993-02-01

    Three two-phase Fe-Mn-Al alloys with nominal compositions, Fe-24Mn-9Al, Fe-27Mn-9Al-3Cr,. and Fe-27Mn-9Al-6Cr, were prepared in the solution-treated and cold-rolled conditions. The fractions of ferrite in the solution-treated condition were controlled at 46 to 60 pct, mainly by adjusting the carbon content and the relative amounts of Mn and Al. The ferrite fractions were reduced to 30 to 37 pct after 75 pct deformation by cold-rolling. Specimens were tensile tested at open circuit in aerated 3.5 pct NaCl solution at slow strain rates ranging from 4 × 10-7 to 4 × 10-5 s-1 at room temperature. All of the alloys were quite susceptible to environmentally assisted cracking (EAC). The deformed specimens showed less susceptibility, presumably because the plasticity was already too limited. The EAC appeared to occur at or after the onset of plastic deformation. In this alloy system, the ferritic phase was less resistant to EAC than the austenitic phase, in contrast to the Fe-Cr-Ni stainless steels. The crack propagated preferentially through the ferrite grains or along the ferrite/austenite grain boundaries. The addition of up to 6 pct Cr did not improve the EAC resistance.

  3. The effects of annealing on the microstructure and mechanical properties of Fe28Ni18Mn33Al21

    DOE PAGES

    Meng, Fanling; Qiu, Jingwen; Baker, Ian; ...

    2015-08-20

    In this paper, As-cast Fe28Ni18Mn33Al21, which consists of aligned, 50 nm, (Ni, Al)-rich B2, and (Fe, Mn)-rich f.c.c. phases, was annealed at a variety of temperatures up to 1423 K and the microstructure and mechanical properties were examined. It was shown that the as-cast microstructure arises from a eutectoid transformation at ~1300 K. Annealing at temperatures ≤1073 K produces β-Mn-structured precipitates and hardness values up to 816 HV, while annealing at temperatures >1073 K leads to dramatic coarsening of the two-phase B2/f.c.c. microstructure (up to 5.5 µm after 50 h at 1273 K), but does not lead to β-Mn precipitation.more » Interestingly, annealing at temperatures >1073 K delays the onset of β-Mn precipitation during subsequent anneals at lower temperatures. Coarsening the B2/f.c.c. lamellar structure by annealing at higher temperatures softens it and leads to increases in ductility from fracture before yield to ~8 % elongation. Finally, the presence of β-Mn precipitates makes the very fine, brittle B2/f.c.c. microstructures even more brittle, but significant ductility (8.4 % elongation) is possible even with β-Mn precipitates present if the B2/f.c.c. matrix is coarse and, hence, more ductile.« less

  4. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    DOE PAGES

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; ...

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  5. Room temperature ferrimagnetism and ferroelectricity in strained, thin films of BiFe 0.5 Mn 0.5 O 3

    SciTech Connect

    Choi, Eun -Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J.; Arena, Darío; Sahonta, Suman -Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun -Sik; Wang, Haiyan; Langridge, Sean; Kim, Young -Min; Borisevich, Albina Y.; MacLaren, Ian; Ramasse, Quentin M.; Blamire, Mark G.; Jia, Quanxi; MacManus-Driscoll, Judith L.

    2014-10-14

    Highly strained films of BiFe0.5Mn0.5O₃ (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ~ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (~ 0.58 μB/f.u) on high quality (001) SrTiO₃. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe³⁺ and Mn³⁺. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.

  6. Room temperature ferrimagnetism and ferroelectricity in strained, thin films of BiFe 0.5 Mn 0.5 O 3

    DOE PAGES

    Choi, Eun -Mi; Fix, Thomas; Kursumovic, Ahmed; ...

    2014-10-14

    Highly strained films of BiFe0.5Mn0.5O₃ (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ~ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (~ 0.58 μB/f.u) on high quality (001) SrTiO₃. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe³⁺ and Mn³⁺. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain statemore » in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.« less

  7. Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin Films of BiFe0.5Mn0.5O3.

    PubMed

    Choi, Eun-Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J; Arena, Darío; Sahonta, Suman-Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun-Sik; Wang, Haiyan; Langridge, Sean; Kim, Young-Min; Borisevich, Albina Y; MacLaren, Ian; Ramasse, Quentin M; Blamire, Mark G; Jia, Quanxi; MacManus-Driscoll, Judith L

    2014-12-01

    Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS ) of up to 90 emu/cc (∼ 0.58 μB /f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe(3+) and Mn(3+). While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above.

  8. Room Temperature Ferrimagnetism and Ferroelectricity in Strained, Thin Films of BiFe0.5Mn0.5O3

    PubMed Central

    Choi, Eun-Mi; Fix, Thomas; Kursumovic, Ahmed; Kinane, Christy J; Arena, Darío; Sahonta, Suman-Lata; Bi, Zhenxing; Xiong, Jie; Yan, Li; Lee, Jun-Sik; Wang, Haiyan; Langridge, Sean; Kim, Young-Min; Borisevich, Albina Y; MacLaren, Ian; Ramasse, Quentin M; Blamire, Mark G; Jia, Quanxi; MacManus-Driscoll, Judith L

    2014-01-01

    Highly strained films of BiFe0.5Mn0.5O3 (BFMO) grown at very low rates by pulsed laser deposition were demonstrated to exhibit both ferrimagnetism and ferroelectricity at room temperature and above. Magnetisation measurements demonstrated ferrimagnetism (TC ∼ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (∼ 0.58 μB/f.u) on high quality (001) SrTiO3. X-ray magnetic circular dichroism showed that the ferrimagnetism arose from antiferromagnetically coupled Fe3+ and Mn3+. While scanning transmission electron microscope studies showed there was no long range ordering of Fe and Mn, the magnetic properties were found to be strongly dependent on the strain state in the films. The magnetism is explained to arise from one of three possible mechanisms with Bi polarization playing a key role. A signature of room temperature ferroelectricity in the films was measured by piezoresponse force microscopy and was confirmed using angular dark field scanning transmission electron microscopy. The demonstration of strain induced, high temperature multiferroism is a promising development for future spintronic and memory applications at room temperature and above. PMID:26213531

  9. Pressure-enhanced superconductivity in Eu<mn>3mn>Bi>2mn>S<mn>4mn>F<mn>4mn>

    SciTech Connect

    Luo, Yongkang; Zhai, Hui -Fei; Zhang, Pan; Xu, Zhu -An; Cao, Guang -Han; Thompson, J. D.

    2014-12-17

    The pressure effect on the newly discovered charge-transferred BiS2-based superconductor, Eu3Bi2S4F4, with a Tc of 1.5 K at ambient pressure, is investigated by transport and magnetic measurements. Accompanied with the enhancement of metallicity under pressures, the onset superconducting transition temperature increases abruptly around 1.0 GPa, reaching ~10.0 K at 2.26 GPa. Alternating current magnetic susceptibility measurements indicate that a new superconducting phase with a higher Tc emerges and dominates at high pressures. In the broad pressure window of 0.68GPa≤p≤2.00 GPa, the high-Tc phase coexists with the low-Tc phase. Hall effect measurements reveal a significant difference in electronic structures between the two superconducting phases. As a result, our work devotes the effort to establish the commonality of pressure effect on the BiS2-based superconductors, and also uncovers the importance of electron carrier density in the high-Tc phase.

  10. Revisiting the ground state of CoAl>2mn>O<mn>4mn> : Comparison to the conventional antiferromagnet MnAl>2mn>O<mn>4mn>

    SciTech Connect

    MacDougall, Gregory J.; Aczel, Adam A.; Su, Yixi; Schweika, Werner; Faulhaber, E.; Schneidewind, A.; Christianson, Andrew D.; Zarestky, Jerel L.; Zhou, H. D.; Mandrus, David; Nagler, Stephen E.

    2016-11-17

    The A-site spinel material CoAl2O4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or “spin-spiral-liquid” ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a “kinetically inhibited” antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This study provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited order is unaffected by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T=2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl2O4, which acts as an unfrustrated analog to CoAl2O4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at TN=39 K. Direct comparison between the two compounds indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. Finally, the higher level of cation inversion in the MnAl2O4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.

  11. First-principles investigation of structural and magnetic disorder in CuNiMnAl and CuNiMnSn Heusler alloys

    NASA Astrophysics Data System (ADS)

    Aron-Dine, S.; Pomrehn, G. S.; Pribram-Jones, A.; Laws, K. J.; Bassman, L.

    2017-01-01

    Two quaternary Heusler alloys, equiatomic CuNiMnAl and CuNiMnSn, are studied using density functional theory to understand their tendency for atomic disorder on the lattice and the magnetic effects of disorder. Disordered structures with antisite defects of atoms of the same and different sublattices are considered, with the level of atomic disorder ranging from 3% to 25%. Formation energies and magnetic moments are calculated relative to the ordered ground state and combined with a simple thermodynamical model to estimate temperature effects. We predict the relative levels of disordering in the two equiatomic alloys with good correlation to experimental x-ray diffraction results. The effect of swaps involving Mn is also discussed.

  12. Temporal variability of bioavailable Cd, Hg, Zn, Mn and Al in an upwelling regime.

    PubMed

    Lares, M Lucila; Flores, Muñoz Gilberto; Lara-Lara, Ruben

    2002-01-01

    Monthly variability of Cd, Hg, Zn, Mn and Al concentrations in mussels (Mytilus californianus) soft tissue and brown seaweed (Macrocystis pyrifera) was studied at a pristine rocky shore off San Quintin Bay, Baja California, México. The results were related to climatic and hydrographic conditions and to the physiological state of the mussels (condition index) by correlation analysis and principal component analysis (PCA). A "normalization" to account for the variability induced by the physiological state of the mussel was performed. The PCA was performed in two ways to relate the environmental variables and the condition index to: (1) the metal concentrations in mussels, and (2) the "normalized" mussel concentrations. The association of the variability of Cd with the upwelling season was revealed in both PCAs. The temporal variability of this metal in mussels was highly correlated to that in seaweed, suggesting that the dissolved phase determined the variability of Cd in mussels. However, for Hg, Zn, Mn and Al the results from both PCAs were different. The first PCA showed the relationship of these metals to pluvial precipitation and to the condition index. The PCA for the normalized mussel concentrations showed that, after eliminating the effect of the condition index, only Al was related to pluvial precipitation. Manganese, and to a less degree Zn, were related to these metals in seaweed. Because zinc is an essential element in mussels, some regulation of their internal concentrations is likely. Mercury was not detected in seaweed, but because of its reactive nature, it is not expected that the dissolved fraction could be a significant pathway; therefore, it can be concluded that its temporal variability was determined by the variability in the condition index only.

  13. Calculations of structural, elastic, electronic, magnetic and phonon properties of FeNiMnAl by the first principles

    SciTech Connect

    Uğur, Şule; İyigör, Ahmet

    2014-10-06

    The electronic, elastic and dynamical properties of the quaternary alloy FeNiMnAl have been investigated using a pseudopotential plane wave method within the generalized gradient approximation (GGA). We determined the lattice parameters and the bulk modulus B. In addition, the elastic properties such as elastic constans (C{sub 11}, C{sub 12} and C{sub 44}), the shear modulus G, the young modulus E, the poisson's ratio σ and the B/G ratio are also given. The FeNiMnAl Heusler alloy exhibit a ferromagnetic half-metallic behavior with the total magnetic moment of 4.02 μ{sub B}. The phonon dispersion of FeNiMnAl has been performed using the density functional theory and the direct method with 2×2×2 supercell.

  14. Giant magnetocaloric effect in GdAlO3 and a comparative study with GdMnO3

    NASA Astrophysics Data System (ADS)

    Mahana, Sudipta; Manju, U.; Topwal, D.

    2017-01-01

    The magnetic properties and magnetocaloric effect of polycrystalline GdAlO3 and GdMnO3 have been investigated to assess their potential usage as magnetic refrigerants at cryogenic temperatures. These compounds undergo antiferromagnetic transitions at low temperatures which are associated with the giant magnetic entropy change effect (-\\bigtriangleup {{S}M} )  ˜40.9 J Kg · K-1 under a field change of 0-9 T for GdAlO3 while the moderate effect of 18 J Kg · K-1 is observed for polycrystalline GdMnO3. Though the relative cooling power of both the stated materials is similar however, the absence of magnetic and thermal hysteresis makes GdAlO3 a more efficient magnetic refrigerant than GdMnO3.

  15. Robust antiferromagnetism preventing superconductivity in pressurized (Ba0.61K0.39)Mn2Bi2

    SciTech Connect

    Gu, Dachun; Dai, Xia; Le, Congcong; Sun, Liling; Wu, Qi; Saparov, Bayrammurad; Guo, Jing; Gao, Peiwen; Zhang, Shan; Zhou, Yazhou; Zhang, Chao; Jin, Shifeng; Xiong, Lun; Li, Rui; Li, Yanchun; Li, Xiaodong; Liu, Jing; Sefat, Athena S.; Hu, Jiangping; Zhao, Zhongxian

    2014-12-05

    BaMn2Bi2 possesses an iso-structure of iron pnictide superconductors and similar antiferromagnetic (AFM) ground state to that of cuprates, therefore, it receives much more attention on its properties and is expected to be the parent compound of a new family of superconductors. When doped with potassium (K), BaMn2Bi2 undergoes a transition from an AFM insulator to an AFM metal. Consequently, it is of great interest to suppress the AFM order in the K-doped BaMn2Bi2 with the aim of exploring the potential superconductivity. Here, we report that external pressure up to 35.6 GPa cannot suppress the AFM order in the K-doped BaMn2Bi2 to develop superconductivity in the temperature range of 300 K–1.5 K, but induces a tetragonal (T) to an orthorhombic (OR) phase transition at ~20 GPa. Theoretical calculations for the T and OR phases, on basis of our high-pressure XRD data, indicate that the AFM order is robust in the pressurized Ba0.61K0.39Mn2Bi2. Utlimately, both of our experimental and theoretical results suggest that the robust AFM order essentially prevents the emergence of superconductivity.

  16. Influence of MnC2O4 microadditives on combustion characteristics of CuO/Al nanoenergetics

    NASA Astrophysics Data System (ADS)

    Painuly, Madhusudan; Patel, Vinay Kumar; Bhattacharya, Shantanu

    2016-05-01

    In this work, we have investigated the catalytic effect of MnC2O4 microrods on combustion characteristics of CuO/nAl nanoenergetic composites. CuO nanorods were prepared by solid state synthesis method using the nonionic surfactant of poly(ethylene)glycol of molecular weight 400 (PEG400). The crystal information and microstructure of CuO/nAl nanoenergetics were studied by X-ray diffractometry and Transmission Electron microscopy. Microrods shaped manganese oxalate (MnC2O4) were fabricated by using mild thermal precipitation and aging process and confirmed by energy dispersive X-ray spectroscopy (EDS). The microstructures of MnC2O4 microrods and the nanoenergetic composites of CuO/nAl/MnC2O4 were characterized by Field emission scanning electron microscopy (FE-SEM) imaging. The addition of MnC2O4 microrods has demonstrated a significant enhancement in dynamic pressure-time characteristics of CuO/nAl nanoenergetics.

  17. New SrAl 2B 2O 7:Eu 2+, Mn 2+ phosphors for white light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhou, Liya; Yi, Linghong; Feng, Xiaoming

    2011-12-01

    A series of Eu 2+ and Mn 2+ co-doped SrAl 2B 2O 7 phosphors were prepared by solid-state reaction method. X-ray powder diffraction (XRD) and photoluminescence excitation and emission were employed to characterize the phosphors. The results show that energy transfers between Eu 2+and Mn 2+ ions. As the content of Ca 2+ ions in Ca xSr 0.92- xAl 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphors increased, the CIE coordinates decreased and close to the white color standard mandated by the National Television Standard Committee (NTSC). Meanwhile, a white LED (light-emitting diode) was fabricated by combining the Ca 0.5Sr 0.42Al 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphors with a 370 nm InGaN chip. The color coordinate of the fabricated white LED was also close to the white color standard, indicating that the Ca 0.5Sr 0.42Al 2B 2O 7:Eu 2+0.06, Mn 2+0.02 phosphor is a promising single-host phosphor that can be used in white LEDs.

  18. New SrAl2B2O7:Eu2+, Mn2+ phosphors for white light-emitting diodes.

    PubMed

    Zhou, Liya; Yi, Linghong; Feng, Xiaoming

    2011-12-01

    A series of Eu(2+) and Mn(2+) co-doped SrAl(2)B(2)O(7) phosphors were prepared by solid-state reaction method. X-ray powder diffraction (XRD) and photoluminescence excitation and emission were employed to characterize the phosphors. The results show that energy transfers between Eu(2+)and Mn(2+) ions. As the content of Ca(2+) ions in Ca(x)Sr(0.92-x)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors increased, the CIE coordinates decreased and close to the white color standard mandated by the National Television Standard Committee (NTSC). Meanwhile, a white LED (light-emitting diode) was fabricated by combining the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphors with a 370 nm InGaN chip. The color coordinate of the fabricated white LED was also close to the white color standard, indicating that the Ca(0.5)Sr(0.42)Al(2)B(2)O(7):Eu(2+)(0.06), Mn(2+)(0.02) phosphor is a promising single-host phosphor that can be used in white LEDs.

  19. Free energy landscape approach to aid pure phase synthesis of transition metal (X=Cr, Mn and Fe) doped bismuth titanate (Bi2Ti2O7)

    NASA Astrophysics Data System (ADS)

    Mayfield, Cedric L.; Huda, Muhammad N.

    2016-06-01

    A density functional theory study of Cr, Mn and Fe substitutions in Bi2Ti2O7 (BTO) photocatalysts is presented. We performed a stability analysis from our total energy calculations and have determined formations of dopant inspired phases are detrimental to the overall photocatalytic performance of X-doped BTO. From our calculated formation energies and electronic structures it is shown that X substitution of Ti is least stable and should be associated with formation of secondary phases more so than X substitution of Bi. This result contradicts the many experimental studies which suggest transition metal dopants always substitute Ti in BTO, but on the other hand, explains the poor photocatalytic response beyond what has become known as the critical dopant concentration.

  20. Magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganite

    NASA Astrophysics Data System (ADS)

    Daivajna, Mamatha D.; Rao, Ashok

    2016-11-01

    Near room temperature, magnetocaloric effect in pristine and Bi-doped Pr0.6Sr0.4MnO3 manganites has been studied using in-field heat capacity measurements. The Debye temperature (θD) for the pristine sample was estimated to be 522 K and its value increases to 530 K for the Bi-doped sample with x=0.05. The entropy associated with paramagnetic (PM) to ferromagnetic (FM) transition is found to be 2.4 J/mol K and 2.3 J/mol K for x=0 and 0.05 compositions respectively. The estimated values of adiabatic temperature ∆Tad for the samples with x=0 and x=0.05 are respectively 2.2 K and 1.9 K for 0-6 Tesla. The maximum isothermal change in entropy, ∆SM for the sample Pr0.6Sr0.4MnO3 with transition temperature 306 K is found to be 2.7 J/kg-K with application of external magnetic field of 2 T and for Bi-doped sample (with x=0.05) the isothermal change in entropy reduces to 2.0 J/kg-K. The calculated maximum values of the isothermal entropy changes, ∆SM for the pristine sample, vary in the range 1.7-3.9 J/kg-K for a magnetic field change of 1-6 T. The present results suggest that these compounds can be possible candidates as magnetic refrigerants. This results in a large relative cooling power (RCP) around 93.5 J kg-1 K for the pristine sample under an application of magnetic field of 2 T. On contrary, with Bi-doping, RCP decreases to 56 J kg-1 K at external field of 2 T.

  1. Application of a bi-stable chain model for the analysis of jerky twin boundary motion in NiMnGa

    NASA Astrophysics Data System (ADS)

    Benichou, Itamar; Faran, Eilon; Shilo, Doron; Givli, Sefi

    2013-01-01

    The "jerky" motion of a twin boundary in the ferromagnetic shape memory alloy NiMnGa is studied experimentally and theoretically. We employ a bi-stable chain model in order to interpret macroscopic stress-strain experiments and extract important micro-level properties. The analysis reveals the existence of a periodic barrier for type I twin boundary motion with an average distance of 19 μm and amplitude of 0.16 J/m2. Further, we show that the macroscopic mechanical response depends on the length of the crystal and predict a significant decrease of the hysteresis in sub-mm length specimens.

  2. Effect of grain size on charge and spin correlations in Bi0.5Ca0.5MnO3 manganite nanoparticles

    NASA Astrophysics Data System (ADS)

    Ade, Ramesh; Singh, Rajender

    2016-11-01

    In this work we report the electron spin resonance (ESR) and magnetization (M) studies to understand the effect of grain size (GS) on the charge ordering and spin correlations in Bi0.5Ca0.5MnO3 manganite synthesized by sol-gel method. The suppression of charge ordering (CO), long-range antiferromagnetic (AFM) state, shifting of ferromagnetic (FM)-cluster glass (CG) transition towards higher temperatures and evolution of different magnetic correlations with decrease in GS are discussed in view of the changes in surface to volume ratio of nano-grains.

  3. Neither Goodenough ionic model nor Zener polaron model for Bi 0.5Ca 0.5Mn 1- xNi xO 3- δ system

    NASA Astrophysics Data System (ADS)

    Toulemonde, O.; Skovsen, I.; Mesguich, F.; Gaudin, E.

    2008-04-01

    The magnetic susceptibilities of three Bi 0.5Ca 0.5MnO 3- δ compounds synthesised by three different methods were characterised and analysed. Large magnetic Mn x clusters ( x ≥ 4) were considered to explain the high value of the Curie-Weiss constant. Unlike previous studies on similar systems, Goodenough ionic model or Zener polaron model is not suitable. In all cases, cluster behaviour is observed at low field and at low temperature. The influence of the oxygen stoichiometry and the homogeneity of the cation distribution depending on the method of the synthesis used is discussed. Finally, the effects of nickel doping on the magnetic properties were studied and the cluster behaviour was confirmed. The distribution in size of the clusters depends on the amount of nickel and it induces a glassy magnetic behaviour.

  4. Microstructural Evolution and Functional Properties of Fe-Mn-Al-Ni Shape Memory Alloy Processed by Selective Laser Melting

    NASA Astrophysics Data System (ADS)

    Niendorf, Thomas; Brenne, Florian; Krooß, Philipp; Vollmer, Malte; Günther, Johannes; Schwarze, Dieter; Biermann, Horst

    2016-06-01

    In the current study, a Fe-Mn-Al-Ni shape memory alloy is processed by additive manufacturing for the first time. Microstructural evolution upon processing is strongly affected by thermal gradients and solidification velocity and, thus, by processing parameters and the actual specimen geometry. By single-step solutionizing heat treatment pronounced grain growth is initiated leading to microstructures showing good reversibility. The compressive stress-strain response revealed maximum reversible pseudo-elastic strain of about 7.5 pct. Critical steps toward further optimization of additively manufactured Fe-Mn-Al-Ni shape memory alloys are discussed.

  5. Ferromagnetism and antiferromagnetism in Ni 2+ x+ yMn 1- xAl 1- y alloys

    NASA Astrophysics Data System (ADS)

    Paduani, C.; Migliavacca, A.; Sebben, M. L.; Ardisson, J. D.; Yoshida, M. I.; Soriano, S.; Kalisz, M.

    2007-01-01

    The magnetic behavior of Ni 2+ xMn 1- xAl alloys around the stoichiometric 2:1:1 composition was investigated with several experimental techniques. The results of low-temperature magnetization measurements indicate that a competition mechanism between ferromagnetism and antiferromagnetism is expected in off-stoichiometric alloys. Although the Curie temperature is strongly dependent on the composition, the saturation magnetization has an unsystematic variation for deviations from the stoichiometric Ni 2MnAl alloy. A reentrant-spin-glass behavior is observed below 50 K.

  6. Polar and nonpolar phases of BiMO{sub 3}: A review

    SciTech Connect

    Belik, Alexei A.

    2012-11-15

    Simple Bi-based compounds, BiMO{sub 3}, are quite interesting materials. They offer large variations in crystal symmetries, polarity, and properties. Their chemical simplicity makes them ideal systems for materials fabrications, theoretical understanding, and thin-film growths. They can only be prepared at high-pressure high-temperature conditions (except for BiFeO{sub 3}) in a bulk form. Some of them can be stabilized in thin films (M=Al, Sc, Cr, Mn, and Fe). In this review, we collect and analyze the recent experimental and theoretical results on BiMO{sub 3} with M=Al, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Ga, In, and Rh. In addition, unresolved problems and desirable future experiments are emphasized especially for the highly controversial compound BiMnO{sub 3}. - Graphical abstract: Crystal symmetries in which BiMO{sub 3} compounds crystallize. Highlights: Black-Right-Pointing-Pointer BiMO{sub 3} compounds offer large variations in crystal symmetries, polarity, and properties. Black-Right-Pointing-Pointer Experimental and theoretical results on BiMO{sub 3} were reviewed. Black-Right-Pointing-Pointer Unresolved problems and desirable future experiments are emphasized. Black-Right-Pointing-Pointer Special attention is paid on the highly controversial compound BiMnO{sub 3}.

  7. Magnetization reversal processes in hot-extruded τ-MnAl-C

    NASA Astrophysics Data System (ADS)

    Thielsch, J.; Bittner, F.; Woodcock, T. G.

    2017-03-01

    The magnetic domain structure of hot-extruded bulk τ-Mn53Al45C2 was studied by Kerr microscopy under application of a magnetic field in-situ. The microstructure consists of recrystallized, fine-grained regions and large non-recrystallized grains which contain a high density of twins. Within these large polytwinned grains, a clear pinning interaction of magnetic domain walls at twin boundaries was observed but with a rather small pinning force. The smaller, recrystallized grains show a higher resistance to magnetization reversal. The critical single domain particle size of this material was estimated at 773 nm and the fine, recrystallized grains are in the range of this size. Demagnetizing the sample following saturation using a 3 T field pulse revealed that individual fine grains reverse independently from their neighbours.

  8. Thermoelectric and mechanical properties of gapless Zr2MnAl compound

    NASA Astrophysics Data System (ADS)

    Yousuf, Saleem; Gupta, Dinesh C.

    2017-01-01

    We present the study of elastic and magnetic properties of Zr2MnAl full-Heusler alloys within the first-principles density functional theory. The lattice constant, magnetic moment, bulk modulus and density of states are calculated using the full potential linearized augmented plane wave method in the generalized gradient approximation scheme. The thermoelectric properties are studied between the temperature range of 50-800 K. Seebeck coefficient (S) measurements indicate the material as n-type with large S value of -83.06 μV/K at 400 K. The material shows higher efficiency for thermoelectric use with figure of merit equal to 0.92 at 400 K relatively higher in comparison for the other full Heusler compounds in these temperature ranges. The behaviour of gapless character is mainly responsible for the anomalous transport properties of the material required for the thermoelectric applications.

  9. Permanent magnet properties of Mn-Al-C between -50 C and +150 C

    NASA Technical Reports Server (NTRS)

    Abdelnour, Z. A.; Mildrum, H. F.; Strnat, K. J.

    1981-01-01

    Anisotropic Mn-Al-C (Ni) magnets are potential substitutes for Alnico 5 and 8. The limited machinability of the alloy and the fact that it is cobalt-free made it particularly interesting. The low Curie point and the costly warm extrusion process needed for grain orientation are drawbacks. The objective of this study was a detailed magnetic characterization of the material for possible use in electric machinery. The principal subjects of the study were the largest extruded bars presently available, of 31 mm diameter. Easy and hard axis magnetization curves and second-quadrant recoil loop fields were measured at various temperatures ranging from -50 C to +150 C. Property variations over the cross section of a bar were also studied.

  10. Lattice Dynamics and Phonon Softening in NiMnAl Heusler Alloys

    SciTech Connect

    Moya, Xavier; Manosa, L.; Planes, A.; Krenke, T.; Acet, Mehmet; Garlea, Vasile O; Lograsso, Tom; Schlagel, D. L.; Zarestky, Jarel

    2006-01-01

    Inelastic and elastic neutron scattering have been used to study a single crystal of the Ni{sub 54}Mn{sub 23}Al{sub 23} Heusler alloy over a broad temperature range. The paper reports the experimental determination of the low-lying phonon dispersion curves for this alloy system. We find that the frequencies of the TA2 modes are relatively low. This branch exhibits an anomaly (dip) at a wave number {xi}{sub 0}=1/3{approx}0.33, which softens with decreasing temperature. Associated with this anomalous dip at {xi}{sub 0}, an elastic central peak scattering is also present. We have also observed satellites due to the magnetic ordering.

  11. Large exchange-bias in Ni55Mn19Al24Si2 polycrystalline ribbons

    NASA Astrophysics Data System (ADS)

    Singh, Rohit; Ingale, Babita; Varga, Lajos K.; Khovaylo, Vladimir V.; Chatterjee, Ratnamala

    2014-09-01

    The crystal structure, phase transition and exchange bias effect in induction melted polycrystalline ribbons of Ni55Mn19Al24Si2 have been studied using room temperature x-ray diffraction (XRD), differential scanning calorimetry (DSC) and magnetic measurements. The sample was found to show structural transformation temperatures such as austenite start (As)=306 K, austenite finish (Af)=316 K, martensite start (Ms)=305 K and martensite finish (Mf)=294 K all above room temperature. The room temperature structure evaluated as orthorhombic 14 M with lattice parameters a=4.14 Å, b=29.84 Å, and c=5.72 Å. Importantly at 2 K, the sample showed a large exchange bias field of about 2520 Oe, which is the maximum value ever reported among the Heusler alloy samples.

  12. Chemical zoning and diffusion of Ca, Al, Mn, and Cr in olivine of springwater pallasite

    NASA Technical Reports Server (NTRS)

    Zhou, Y.; Steele, Ian M.

    1993-01-01

    The pallasites, consisting mainly of Fe-Ni metal and olivine, are thought to represent the interior of a planetary body which slowly cooled from high temperature. Although the olivines are nearly homogeneous, ion microprobe studies revealed variations of Ca, Ti, Co, Cr, and Ni near grain edges. These variations were thought to represent diffusion in response to falling temperature of the parent body. Pallasite cooling rates have been estimated based on kamacite taenite textures but results differ by x100. In principle elemental profiles in olivine can allow estimates of cooling rate if diffusion coefficients are known; in addition, given a cooling rate, diffusion coefficients could be derived. Data are presented which show that apparent diffusion profiles can be measured for Al, Ca, Cr, and Mn which qualitatively agree with expected diffusion rates and have the potential of providing independent estimates of pallasite cooling rates.

  13. Icosahedral quasicrystal decoration models. II. Optimization under realistic Al-Mn potentials

    SciTech Connect

    Mihalkovic, M. |; Zhu, W.; Henley, C.L.; Phillips, R.

    1996-04-01

    We have constructed and relaxed over 200 different finite structure models for the quasicrystal {ital i}-AlMn based on decorations of the {open_quote}{open_quote}canonical-cell tiling.{close_quote}{close_quote} We adopted {ital ab} {ital initio}-based pair potentials with strong Friedel oscillations, which reproduce the phase diagram of real Al-Mn intermetallic crystal structures fairly well. Our various decoration rules encompass cases with face-centered icosahedral (FCI) symmetry and with simple icosahedral (SI) symmetry, and include additional variations in the occupancy and/or chemistry of certain site types. Each decoration was applied to 11 distinct periodic approximants of the tiling. We found that (i) the relaxed atomic positions of each site type can be closely approximated by fixed positions on each tile type, even though the environments (beyond the first neighbor) are inequivalent. (ii) Models with simple icosahedral (SI) space-group symmetry were better than those with face-centered icosahedral (FCI) space-group symmetry. (iii) {open_quote}{open_quote}Loose{close_quote}{close_quote} decorations, containing voids almost large enough for an atom, were better than the {open_quote}{open_quote}dense{close_quote}{close_quote} decorations which were suggested by packing considerations. (iv) Our results depended on using the realistic potentials; {ital short}-range potentials favor the {open_quote}{open_quote}dense{close_quote}{close_quote} structures, and many details depend on the second or further oscillations in the potentials. (v) For our best model, there is relatively little variation of the energy when tiles are rearranged, i.e., a {ital random}-{ital tiling} {ital model} is a good zero-order description of the system. {copyright} {ital 1996 The American Physical Society.}

  14. Surface topography and roughness of high-speed milled AlMn1Cu

    NASA Astrophysics Data System (ADS)

    Wang, Zhenhua; Yuan, Juntang; Yin, Zengbin; Hu, Xiaoqiu

    2016-10-01

    The aluminum alloy AlMn1Cu has been broadly applied for functional parts production because of its good properties. But few researches about the machining mechanism and the surface roughness were reported. The high-speed milling experiments are carried out in order to improve the machining quality and reveal the machining mechanism. The typical topography features of machined surface are observed by scan electron microscope(SEM). The results show that the milled surface topography is mainly characterized by the plastic shearing deformation surface and material piling zone. The material flows plastically along the end cutting edge of the flat-end milling tool and meanwhile is extruded by the end cutting edge, resulting in that materials partly adhere to the machined surface and form the material piling zone. As the depth of cut and the feed per tooth increase, the plastic flow of materials is strengthened and the machined surface becomes rougher. However, as the cutting speed increases, the plastic flow of materials is weakened and the milled surface becomes smoother. The cutting parameters (e.g. cutting speed, feed per tooth and depth of cut) influencing the surface roughness are analyzed. It can be concluded that the roughness of the machined surface formed by the end cutting edge is less than that by the cylindrical cutting edge when a cylindrical flat-end mill tool is used for milling. The proposed research provides the typical topography features of machined surface of the anti-rust aluminum alloy AlMn1Cu in high speed milling.

  15. Resistivity Changes Due to Precipitation Effects in Fibre Reinforced Mg-Al-Zn-Mn Alloy

    NASA Astrophysics Data System (ADS)

    Kiehn, J.; Kainer, K. U.; Vostrý, P.; Stulíková, I.

    1997-05-01

    The change of electrical properties of alumina short fibre reinforced Mg-Al-Zn-Mn alloy AZ91D during isochronal annealing up to 300 °C is discussed. The Saffil® fibres were incorporated into the magnesium alloy by direct squeeze casting. The fibre distribution is random planar parallel to the flat faces of the dc four-point resistivity specimens machined from the solution treated castings. A sharp drop of resistivity between 140 and 260 °C is explained by the formation of incoherent -phase particles. Some practical recommendations concerning the use of alumina short fibre reinforced AZ91 alloy are made on the basis of the results obtained. Es werden die Änderungen der elektrischen Eigenschaften der aluminiumoxid-kurzfaserverstärkten Mg-Al-Zn-Mn Legierung AZ91D während isochroner Wärmebehandlungen bis 300 °C diskutiert. Das direkte Preßgießverfahren diente zur Herstellung der Saffil®-Faser Magnesium Verbundwerkstoffe. Die Proben zur Widerstandsmessung nach der Vier-Punkt Methode wurden durch spanende Bearbeitung aus den lösungsgeglühten Preßgußstücken herausgearbeitet, so daß sie regellose Faserverteilung in den Ebenen parallel zu den flachen Probenseiten aufwiesen. Ein starker Abfall des elektrischen Widerstands im Temperaturbereich zwischen 140 und 260 °C wird durch die Bildung inkohärenter β-Phase erklärt. Auf Grundlage der Ergebnisse werden einige Empfehlungen zur Anwendung der kurzfaserverstärkten Legierung AZ91 gegeben.

  16. Investigation on electronic and magnetic properties of Mn2NiAl by ab initio calculations and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Masrour, R.; Jabar, A.; Hlil, E. K.; Hamedoun, M.; Benyoussef, A.; Hourmatallah, A.; Rezzouk, A.; Bouslykhane, K.; Benzakour, N.

    2017-04-01

    Self-consistent ab initio calculations, based on Density Functional Theory (DFT) approach and using Full potential Linear Augmented Plane Wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the Mn2NiAl. Magnetic moment considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for Monte Carlo simulations to compute other magnetic parameters. Also, the magnetic properties of Mn2NiAl are studied using the Monte Carlo simulations. The variation of magnetization and magnetic susceptibility with the reduced temperature of Mn2NiAl are investigated. The transition temperature of this system is deduced for different values exchange interaction and crystal field. The thermal total magnetization has been obtained, and the magnetic hysteresis cycle is established. The total magnetic moment is superior to those obtained by the other method and is mainly determined by the antiparallel aligned MnI, MnII and Ni spin moments. The superparamagnetic phase is found at the neighborhood of transition temperature.

  17. Al-26-production rates and Mn-53/Al-26 production rate ratios in nonantarctic chondrites and their application to bombardment histories

    NASA Astrophysics Data System (ADS)

    Herpers, U.; Englert, P.

    1983-11-01

    The long-lived spallogenic radionuclides Al-26 and Mn-53 were systematically studied in a large number of nonantarctic meteorites by nondestructive gamma-gamma-coincidence technique and neutron activation, respectively. From the Al-26-activities normalized to the main target element, silicon, an average production rate of 298 + or - 55 (dpm/kg Si/equ/) was derived. Baed on 15 chondrites with exposure ages equal to or greater than 12,000,000 a and depth profiles of Dhurmsala and Keyes, an average production rate ratio (Mn-53/Al-26)(prod) = 1.48 + or - 0.15 (dpm/kg Fe / dpm/kg Si/equ/) was calculated, which seems to be depth-independent for meteorites with preatmospheric radii R less than 35 cm. Mn-53/Al-26-radiation ages for 29 stones with short exposure ages were determined. A comparison of the results with the respective Mn-53 and Ne-21-exposure ages generally shows a good agreement. The cosmic ray bombardment age scale covered by this method is the range for T(rad) from 1,000,000 to 10,000,000 a.

  18. Resonant state due to Bi in the dilute bismide alloy GaAs<mn>1mn>-xBix

    SciTech Connect

    Joshya, R. S.; Ptak, A. J.; France, R.; Mascarenhas, A.; Kini, R. N.

    2014-10-01

    It has been theoretically predicted that isolated Bi forms a resonant state in the valence band of the dilute bismide alloy, GaAs1-xBix. We present ultrafast pump-probe reflectivity measurements of this interesting alloy system, which provide experimental evidence for the resonant state. The reflectivity transients for pump/probe wavelengths λ ~ 860–900 nm have negative amplitude, which we attribute to the absorption of the probe pulse by the pump induced carriers that are localized at the Bi-resonant state. Our measurements show that the lifetime of carriers localized at the resonant state is ~200 ps at 10 K.

  19. Effect of MnO2 doping and temperature treatment on optical energy band gap properties in Zn-Bi-Ti-O varistor ceramics

    NASA Astrophysics Data System (ADS)

    Ghazali, M. S. M.; Abdullah, W. R. W.; Zakaria, A.; Kamari, H. M.; Rizwan, Z.

    2016-11-01

    In this study, the optical band-gap energy (Eg) was investigated with respect to MnO2 and sintering temperatures on ZnO based varistor ceramics. Eg of the ceramic (99-x) mol% ZnO + 0.5 mol% Bi2O3 + 0.5 mol% TiO2 + × MnO2 where × = 0, 0.2, 0.4, 0.6 and 0.8 mol%, were determined using UV-Vis spectrophotometer. The samples was prepared through solid-state route and sintered at the sintering temperature from 1110, 1140 and 1170 °C for 45 and 90 min in open air. At no doping of MnO2, the values of Eg are 2.991 ± 0.001, 2.989 ± 0.001 eV for 45 and 90 min sintering time; respectively. Eg was decreased to 2.192 ± 0.001 eV at 1140 °C at 45 min sintering time. Similar result of Eg was observed at longer heat treatment. Further addition of dopant causing the Eg decreases rapidly to 2.099 and 2.106 ± 0.001 eV at 45 and 90 min sintering time; respectively. XRD analysis indicates that there is hexagonal ZnO and secondary phases, Zn2MnO4, Bi4Ti3O12 and Zn2Ti3O8. The relative density of the sintered ceramics decreased or remain constant with the increase of MnO2 concentration for 45 min sintering time, however, further prolong sintering time; the relative density decreases form 90.25 to 88.35%. This indicates the pores are increasing with the increase of heat treatment. The variation of sintering temperatures to the optical band gap energy of based ZnO varistor doped with MnO2 due to the formation of interface states.

  20. B2+L2{sub 1} ordering in Co{sub 2}MnAl Heusler alloy

    SciTech Connect

    Vinesh, A.; Sudheesh, V. D.; Lakshmi, N.; Venugopalan, K.

    2014-04-24

    Magnetic and structural properties of B2 ordered Co{sub 2}MnAl Heusler alloy have been studied by X-ray diffraction and DC magnetization techniques. X-ray diffractogram shows the structure is of B2 type with preferential site disorder between Mn and Al atoms and presence of a small L2{sub 1} phase. DC magnetization studies at low temperature establish that the antiferromagnetic nature arises mainly due to the antiparallel coupling of spin moments of 3d electrons of Co with Mn atoms. Curie temperature (T{sub c}) is 733 K which is close to T{sub c} of the L2{sub 1} phase.

  1. Intrinsic quantum spin Hall and anomalous Hall effects in h-Sb/Bi epitaxial growth on a ferromagnetic MnO2 thin film.

    PubMed

    Zhou, Jian; Sun, Qiang; Wang, Qian; Kawazoe, Yoshiyuki; Jena, Puru

    2016-06-07

    Exploring a two-dimensional intrinsic quantum spin Hall state with a large band gap as well as an anomalous Hall state in realizable materials is one of the most fundamental and important goals for future applications in spintronics, valleytronics, and quantum computing. Here, by combining first-principles calculations with a tight-binding model, we predict that Sb or Bi can epitaxially grow on a stable and ferromagnetic MnO2 thin film substrate, forming a flat honeycomb sheet. The flatness of Sb or Bi provides an opportunity for the existence of Dirac points in the Brillouin zone, with its position effectively tuned by surface hydrogenation. The Dirac points in spin up and spin down channels split due to the proximity effects induced by MnO2. In the presence of both intrinsic and Rashba spin-orbit coupling, we find two band gaps exhibiting a large band gap quantum spin Hall state and a nearly quantized anomalous Hall state which can be tuned by adjusting the Fermi level. Our findings provide an efficient way to realize both quantized intrinsic spin Hall conductivity and anomalous Hall conductivity in a single material.

  2. Revealing the Formation Mechanism and Effect of Pressure on the Magnetic Order of Multiferroic BiMn2O5 Through Neutron Powder Diffraction

    NASA Astrophysics Data System (ADS)

    Dang, N. T.; Kozlenko, D. P.; Kichanov, S. E.; Jabarov, S. G.; Mammadov, A. I.; Mekhtieva, R. Z.; Phan, T. L.; Smotrakov, V. G.; Eremkin, V. V.; Savenko, B. N.

    2017-02-01

    The crystal and magnetic structures of the strong magnetoelectric BiMn2O5 have been studied as a function of pressure up to 5.7 GPa in the temperature range from 10 K to 60 K by means of neutron powder diffraction. The results reveal that the Pbam orthorhombic crystal structure remains unchanged in the investigated thermodynamic range. At ambient pressure, a long-range commensurate antiferromagnetic (AFM) phase with propagation vector q = (1/2, 0, 1/2) formed below T N = 41(2) K, accompanied by anomalies in the temperature dependence of structural parameters including the lattice parameters, interatomic distances, and bond angles. This AFM phase remained stable in the studied pressure range, and the relevant pressure coefficient of the Néel temperature was determined to be 3.0(4) K/GPa. No incommensurate AFM phase was detected. The magnetic properties of BiMn2O5 and their difference from most other RMn2O5 compounds were analyzed in terms of competing exchange interactions.

  3. Visible light activity of pulsed layer deposited BiVO4/MnO2 films decorated with gold nanoparticles: The evidence for hydroxyl radicals formation

    NASA Astrophysics Data System (ADS)

    Trzciński, Konrad; Szkoda, Mariusz; Sawczak, Mirosław; Karczewski, Jakub; Lisowska-Oleksiak, Anna

    2016-11-01

    Thin films containing BiVO4 and MnO2 deposited on FTO and modified by Au nanoparticles were studied towards their photoelectrochemical and photocatalytical activities in an aqueous electrolyte. Electrodes were prepared by the pulsed laser deposition (PLD) method. The surfactant-free ablation process was used for preparation of the gold nanoparticles (GNP) water suspension. Obtained layers of varied thicknesses (27-115 nm) were characterized using Raman spectroscopy, UV-vis spectroscopy and scanning electron microscopy. Electrochemical methods such as electrochemical impedance spectroscopy, linear voltammetry and chronoamperometry under visible light illumination and in the dark were applied to characterize layers as photoanodes. Simple modification of the BiVO4 + MnO2 layer by drop-casting of small amount of colloidal gold (1.5 × 10-14 mol of GNP on 1 cm2) leads to enhancement of the generated photocurrent recorded at E = 0.5 V vs. Ag/AgCl (0.1 M KCl) from 63 μA/cm2 to 280 μA/cm2. Photocatalytical studies were also exploited towards decomposition of methylene blue (MB). A possible mechanism of MB photodegradation was proposed. The formation of hydroxyl radicals was detected by photoluminescence spectra using terephthalic acid as the probe molecule.

  4. Magnetization switching in the BiFe0.9Mn0.1O3 thin films modulated by resistive switching process

    NASA Astrophysics Data System (ADS)

    Chen, Guangyi; Bi, Guifeng; Song, Lin; Weng, Yakui; Pan, Danfeng; Li, Yongchao; Dong, Shuai; Tang, Tao; Liu, Jun-ming; Wan, Jian-guo

    2016-09-01

    Polycrystalline BiFe0.9Mn0.1O3 thin films have been prepared on Pt/Ti/SiO2/Si wafers by a sol-gel process. The film exhibits typical resistive switching (RS) effect. Moreover, accompanied with the RS process, remarkable magnetization switching (MS) behaviors happen, i.e., at low resistance state the film shows high saturation magnetization, while showing low saturation magnetization at high resistance state. We revealed that such a MS effect mainly originates from the conversion of Fe ion valence state between Fe2+ and Fe3+ during the RS process, which was confirmed by the x-ray photoelectron spectroscopy measurements. The further first-principle calculations showed that the doping of Mn into the BiFeO3 could induce an impurity energy level which makes it facile to achieve the conversion of Fe ion valence state. Based on the conductive filament model, a possible mechanism of tuning the MS effect by RS process is proposed, which is closely related to the conversion of Fe ion valence state along with the forming and rupture of conduction filaments. This work provides us a promising avenue to design switchable multistate devices with both electric and magnetic functionalities.

  5. Experimental study of the valence band of Bi>2mn>Se>3mn>

    SciTech Connect

    Gao, Yi-Bin; He, Bin; Parker, David; Androulakis, Ioannis; Heremans, Joseph P.

    2014-09-26

    The valence band of Bi2Se3 is investigated with Shubnikov - de Haas measurements, galvanomagnetic and thermoelectric transport. At low hole concentration, the hole Fermi surface is closed and box-like, but at higher concentrations it develops tube-like extensions that are open. The experimentally determined density-of-states effective mass is lighter than density-functional theory calculations predict; while we cannot give a definitive explanation for this, we suspect that the theory may lack sufficient precision to compute room-temperature transport properties, such as the Seebeck coefficient, in solids in which there are Van der Waals interlayer bonds.

  6. Unoccupied electronic states of icosahedral Al-Pd-Mn quasicrystals: Evidence of image potential resonance and pseudogap

    SciTech Connect

    Maniraj, M; Rai, Abhishek; Barman, S R; Krajci, M; Schlagel, Deborah L; Lograsso, Thomas A; Horn, K

    2014-09-01

    We study the unoccupied region of the electronic structure of the fivefold symmetric surface of an icosahedral (i) Al-Pd-Mn quasicrystal. A feature that exhibits parabolic dispersion with an effective mass of (1.15±0.1)me and tracks the change in the work function is assigned to an image potential resonance because our density functional calculation shows an absence of band gap in the respective energy region. We show that Sn grows pseudomorphically on i-Al-Pd-Mn as predicted by density functional theory calculations, and the energy of the image potential resonance tracks the change in the work function with Sn coverage. The image potential resonance appears much weaker in the spectrum from the related crystalline Al-Pd-Mn surface, demonstrating that its strength is related to the compatibility of the quasiperiodic wave functions in i-Al-Pd-Mn with the free-electron-like image potential states. Our investigation of the energy region immediately above EF provides unambiguous evidence for the presence of a pseudogap, in agreement with our density functional theory calculations.

  7. Electrical and photoresponse properties of vacuum deposited Si/Al:ZnSe and Bi:ZnTe/Al:ZnSe photodiodes

    NASA Astrophysics Data System (ADS)

    Rao, Gowrish K.

    2017-04-01

    The paper reports fabrication and characterization of Bi:ZnTe/Al:ZnSe and Si/Al:ZnSe thin film photodiodes. The characteristics of the devices were studied under dark and illuminated conditions. The normalized spectral response, speed of photoresponse and variation of photocurrent with power density were studied in detail. Many vital parameters, such as diode ideality factor, barrier height, the thickness of the depletion region, trap depth, rise and decay times of photocurrent, were determined. Conduction mechanism in the photodiodes is discussed with the help of widely accepted theoretical models.

  8. An experimental investigation of innovative bridge columns with engineered cementitious composites and Cu-Al-Mn super-elastic alloys

    NASA Astrophysics Data System (ADS)

    Hosseini, F.; Gencturk, B.; Lahpour, S.; Ibague Gil, D.

    2015-08-01

    Recent strong earthquakes have shown that reinforced concrete (RC) bridge columns constructed using conventional materials and techniques suffer from major damage and permanent deformations. The yielding of the longitudinal reinforcement as the main source of energy absorption, and cracking and spalling of concrete results in a dysfunctional bridge structure that does not support the post-disaster recovery efforts. This paper investigates the use of engineered cementitious composites (ECCs) and Cu-Al-Mn super-elastic alloys (SEAs) to improve the performance of bridge columns under seismic loads. A new column design is proposed, which is composed of a pre-fabricated ECC tube that encompasses the longitudinal and transverse steel reinforcement (rebar). The rebar in the plastic hinge region of the cantilever columns was totally or partially replaced with Cu-Al-Mn SEA bars. The tube was filled with conventional concrete after it was placed inside the rebar cage of the foundation. ECC exhibits superior tensile ductility, bonding with steel, energy absorption and shear resistance, in addition to lower permeability and reduced crack widths compared to conventional concrete. Cu-Al-Mn SEA bars are capable of recovering large inelastic deformations exceeding 12% strain. The proposed approach capitalizes on the deformability of ECC with reduced damage, and the energy absorption capacity of Cu-Al-Mn SEA bars without permanent deformation. A total of six column specimens were constructed and tested under simulated seismic loading. The number of rebars replaced with Cu-Al-Mn SEA bars, ECC mixture design, and the ratio of the concrete core area to total column cross-sectional area were the variables investigated in the test program. A comparison of the results indicated that the proposed concept with no Cu-Al-Mn SEA bars provides higher lateral strength, similar energy absorption and reduced damage compared to conventional RC columns; however, similar to a conventional column, it

  9. The effect of Mn on the mechanical behavior of Al alloys

    NASA Astrophysics Data System (ADS)

    Nam, Soo Woo; Lee, Duck Hee

    2000-02-01

    Manganese has been known to be an alloying element of Al alloys that contributes to uniform deformation. Recently, it was found that as the manganese content increases over 0.5 wt.% in such aluminum alloys as the 6000, and 7000 series alloys, both yield and ultimate tensile strength increase significantly without decreasing ductility. The added manganese forms a manganese dispersoid of Al6Mn. This dispersoid has an incoherent structural relationship with respect to the matrix, FCC, in retarding the motion of dislocations that increase strength. Once the dislocation is blocked by the dispersoid, it tends to change the slip system by means of cross-slip. This cross-slip allows the deformation to maintain uniformly good ductility. TEM observation has proven the above mentioned activities of dislocation by analyzing the characters of the dislocations around and away from the dispersoids. Adding manganese to aluminum alloys not only enhances tensile strength but also significantly improves low-cycle fatigue resistance. Corrosion resistance is also measurable improved by the addition of manganese. After extrusion, the recrystallization is also retarded so that a very small grain size is maintained, contributing to an improvement in the mechanical properties.

  10. Mn-53 and Al-26 evidence for solar cosmic ray constancy - An improved model for interpretation

    NASA Technical Reports Server (NTRS)

    Russ, G. P., III; Emerson, M. T.

    1980-01-01

    A general, numerical method for calculating activities of solar cosmic ray produced radionuclides at any point within an irregularly shaped lunar rock of known surface contour and lunar surface orientation is described. This method is then used to predict the activities of Mn-53 andAl-26 as a function of postion within lunar rock 68815 for various assumed values of solar cosmic ray flux (J), rigidity (R sub 0), and rock erosion rate (ER). The predicted activities agree with the measured activities of Kohl et al. (1978) when values of R sub 0 = 100 MV, J = 70 p/sq cm-sec (4 pi, E greater than 10 MeV), ER not greater than 1 mm/m.y. and a total exposure time of 2 m.y. are assumed. These values are in agreement with those found for rocks exposed for not less than 10 m.y. and provide no evidence for variation of the average solar cosmic ray parameters between the last 2 and 10 m.y. intervals. When interpreted with the improved model the activity vs. depth profiles for three faces of 68815 show no evidence of SCR anisotropy or differential erosion.

  11. Hard magnetic properties of melt-spun Mn-Al-C alloys

    NASA Astrophysics Data System (ADS)

    Pasko, A.; Mazaleyrat, F.; LoBue, M.; Fazakas, E.; Varga, L. K.

    2013-01-01

    Structural and magnetic characterization of Mnx-yAl100-x-yC2y (x = {50, 55}; y = {0, 1}) melt­spun ribbons is reported. To obtain the metastable ferromagnetic τ­phase, rapidly solidified alloys were annealed either in a vacuum furnace at 823 K or directly in the vibrating sample magnetometer under applied magnetic field. Optimal magnetic properties were demonstrated by Mn54Al44C2 samples proved to be single­phase with a coercivity of 0.19 T measured in both cases. For this composition the structural ɛ→τ phase transformation has been magnetically detected at 786 K, Curie temperature of τ­phase (Tc = 592 K, Tp = 610 K) has been determined using mean field approximations in ferromagnetic and paramagnetic regions. Rietveld refinement of X­ray diffraction spectra was employed to analyse the phase constitution of annealed alloys, lattice parameters as a function of chemical composition and mean grain size for the phases involved.

  12. Mechanical Properties and Microstructure of TIG and FSW Joints of a New Al-Mg-Mn-Sc-Zr Alloy

    NASA Astrophysics Data System (ADS)

    Xu, Guofu; Qian, Jian; Xiao, Dan; Deng, Ying; Lu, Liying; Yin, Zhimin

    2016-04-01

    A new Al-5.8%Mg-0.4%Mn-0.25%Sc-0.10%Zr (wt.%) alloy was successfully welded by tungsten inert gas (TIG) and friction stir welding (FSW) techniques, respectively. The mechanical properties and microstructure of the welded joints were investigated by microhardness measurements, tensile tests, and microscopy methods. The results show that the ultimate tensile strength, yield strength, and elongation to failure are 358, 234 MPa, and 27.6% for TIG welded joint, and 376, 245 MPa and 31.9% for FSW joint, respectively, showing high strength and superior ductility. The TIG welded joint fails in the heat-affected zone and the fracture of FSW joint is located in stirred zone. Al-Mg-Mn-Sc-Zr alloy is characterized by lots of dislocation tangles and secondary coherent Al3(Sc,Zr) particles. The superior mechanical properties of the TIG and FSW joints are mainly derived from the Orowan strengthening and grain boundary strengthening caused by secondary coherent Al3(Sc,Zr) nano-particles (20-40 nm). For new Al-Mg-Mn-Sc-Zr alloy, the positive effect from secondary Al3(Sc, Zr) particles in the base metal can be better preserved in FSW joint than in TIG welded joint.

  13. Correlation of martensitic transformation temperatures of Ni- Mn-Ga/Al-X alloys to non-bonding electron concentration

    NASA Astrophysics Data System (ADS)

    Ramudu, M.; Satish Kumar, A.; Seshubai, V.; Rajasekharan, T.

    2015-02-01

    The martensitic transformation TM of the alloys of Ni-Mn-Ga and Ni-Mn-Al show a general trend of increase with electron per atom ratio (e/a) calculated from the total number of electrons outside the rare gas shell of the atoms. However prediction of TM fails among iron substituted Ni-Mn-Ga alloys and those with In doped for Ga, due to the absence of a useful trend. A scheme of computing modified electron concentration is presented considering only the non-bonding electrons per atom Ne/a of the compounds, based on Pauling's ideas on the electronic structure of metallic elements. Systematic variation of TM with Ne/a is reproduced for a large number of alloys of Ni-Mn-Ga and the anomaly observed for Fe containing alloys with e/a disappears. The non-bonding electron concentration is thus demonstrated to be effective in predicting TM of shape memory alloys of Ni-Mn-Ga-X system including the isoelectronic compounds of Ni-Mn-Ga-In.

  14. Magnetic inhomogeneity and Griffiths phase in Bi substituted La0.65-xBixCa0.35MnO3 manganites

    NASA Astrophysics Data System (ADS)

    Manjunatha, S. O.; Rao, Ashok; Poornesh, P.; Lin, W. J.; Kuo, Y.-K.

    2016-10-01

    In the present communication, we report the effect of Bi substitution on structural, magneto-transport, magnetic and thermal properties of La0.65-xBixCa0.35MnO3 (0≤x≤0.2) compounds. Rietveld refined XRD patterns confirm that all the samples are single phase and crystallize in rhombohedral symmetry with R-3C space group. It was observed from electrical and magnetic studies that with increasing Bi content both the metal-insulator transition temperature (TMI) and ferromagnetic-paramagnetic (FM-PM) transition temperature (TC) shift towards lower temperatures. Deviation of the temperature dependence of inverse susceptibility curves from the Curie-Weiss law suggests the existence of Griffiths-like phase. The electrical resistivity data were analyzed by utilizing various theoretical models. It is revealed that the electron-electron scattering is dominating in the metallic region, while the insulating region is well-described by the polaron hopping model. Analysis of thermoelectric power data further reveals that the small polaron hopping (SPH) mechanism is operative in the high-temperature insulating regime. The entropy change associated with the FM-PM transition is found to decrease with increasing x, which is presumably due to the increase in magnetic inhomogeneity with increasing Bi content.

  15. Element specific and depth-resolved interface magnetism in BiFeO3/La0.67Sr0.33MnO3 thin films

    NASA Astrophysics Data System (ADS)

    Bertinshaw, Joel; Brück, Sebastian; Fritzsche, Helmut; Khaydukov, Yury; Soltwedel, Olaf; Keller, Thomas; Goering, Eberhard; Audehm, Patrick; Hutchison, Wayne; Maran, Ronald; Valanoor, Nagarajan; Klose, Frank; Ulrich, Clemens

    2013-03-01

    In recent years significant research has been conducted to probe the emergent physics of atomically sharp transition metal oxide layered systems. The spin, orbital and charge state at the interface has a drastic impact on the exhibited emergent physics. We have investigated epitaxial bi-layers of multiferroic BiFeO3 (BFO) / ferromagnetic La0.67Sr0.33MnO3 (LSMO). Polarized Neutron Reflectivity conducted at ANSTO, Chalk River, and FRM-II provided the absolute magnetic moment at the interface and X-ray Resonant Magnetic Reflectivity performed at BESSY II provided element specific magnetic information. We determined the precise magnetic properties of the bi-layer interface region, which indicated a region of depleted magnetization extending ~25Å into the LSMO at the interface, despite no FM in the BFO and in contrast to previous results on an inverse LSMO/BFO system. The importance of this result extends to the study and functionality of all strongly correlated thin film systems.

  16. Structural modifications in a Mn54Al43C3 melt-spun alloy induced by mechanical milling and subsequent annealing investigated by atom probe tomography

    SciTech Connect

    Le Breton, JM; Bran, J; Folcke, E; Lucis, M; Larde, R; Jean, M; Shield, JE

    2013-12-25

    The structural changes upon milling and subsequent annealing of a Mn54Al43C3 alloy containing the intermetallic tetragonal L1(0) MnAl phase (tau phase) as the major phase were investigated by X-ray diffraction and atom probe tomography. The analyses show that milling the starting powder for 10 h leads to the nanostructuration of the sample. The milled sample is partly oxidised and contains both non oxidised Mn60 +/- 5Al40 +/- 5 regions and oxidised regions. Annealing the powder for 1 h at 500 degrees C leads to enrichment in Al of the oxidised regions, and to the phase transformation of the non-oxidised regions into a nano-structured beta-Mn-like phase with a composition close to Mn3Al2. (C) 2013 Elsevier B. V. All rights reserved.

  17. Electronic, structural, and magnetic properties of the quaternary Heusler alloy NiCoMnZ (Z=Al, Ge, and Sn)

    NASA Astrophysics Data System (ADS)

    Halder, Madhumita; Mukadam, M. D.; Suresh, K. G.; Yusuf, S. M.

    2015-03-01

    The electronic, magnetic, and structural properties of the Heusler alloys NiCoMnZ (Z=Al, Ge, and Sn) have been investigated both theoretically and experimentally. NiCoMnGe and NiCoMnSn have ordered cubic Heusler structure (with a possible disorder between Ni and Co), while NiCoMnAl has a B2 type disordered Heusler structure with random occupancy between Mn and Al atom at their crystallographic sites. Electronic structure calculation shows that NiCoMnGe and NiCoMnSn are normal ferromagnets, whereas NiCoMnAl is nearly half metallic (~100% spin polarization) in nature with its magnetic moment close to an integer value following the Slater-Pauling rule. Ab-initio calculations show ~56% and ~60% spin polarization for NiCoMnGe and NiCoMnSn, respectively. Magnetization measurements show all the three compounds have a high Curie temperature (>583 K).

  18. Magnetic coupling in Epitaxial BiFeO3-La0.7Sr0.3MnO3 Heterostructures Integrated on Si(100)

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Prater, J. T.; Wu, Fan; Shelton, C. T.; Maria, J.-P.; Narayan, J.

    2014-03-01

    We present and discuss the magnetic characteristic of BiFeO3 (BFO)/La0.7Sr0.3MnO3 (LSMO) heterostructure, integrated on Si (100) using pulsed laser deposition (PLD) via the domain matching epitaxy (DME) paradigm. The magnetic behavior of this heterostructure, in which a d5 system (Fe3+) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn3+/Mn4+ in LSMO exhibits interesting magneto electric coupling phenomenon. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetization and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of exchange coupling when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetization and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom.

  19. Interdiffusion between the L1(2) trialuminides Al66Ti25Mn9 and Al67Ti25Cr8

    NASA Technical Reports Server (NTRS)

    Kumar, K. S.; Whittenberger, J. D.

    1992-01-01

    Concentration-distance profiles obtained from Al66Ti25Mn9/Al67Ti25Cr8 diffusion couples are used to determine the interdiffusion coeffients in the temperature range 1373-1073 K. The couples are treated as pseudobinaries, and the diffusion coefficients are determined using the Matano approach. The results are then used to compute the activation energies for diffusion, and a comparison is made with some existing data for the activation energy for creep of Al22Ti8Fe3.

  20. Luminescent properties of BaAl2Si2O8:Eu2+, Mn2+ phosphor for white LED

    NASA Astrophysics Data System (ADS)

    Shen, Changyu; Li, Ke

    2010-10-01

    BaAl2Si2O8:xEu2+, yMn2+ was prepared by high-temperature solid state reaction and X-ray powder diffraction analysis confirmed the formation of it. It was found experimentally that, its emission peaks situated at 420 nm and 570 nm respectively under excitation of 380 nm irradiation. The emission peaks at 420 nm originate from the transition 5d to 4f of Eu2+ ions that occupy the Ba2+ sites in the crystal of BaAl2Si2O8, while the 580nm emission is attributed to the energy transfer from Eu2+ ions to Mn2+ ions. The white light can be obtained by combining the 380 nm chip with the phosphor. When the concentrations of the Eu2+ ions and Mn2+ ions were 0.05 mol and 0.35 mol respectively, the sample presented intense white emitting. The near-ultraviolet InGaN-based BaAl2Si2O8:0.05Eu2+, 0.35Mn2+ LED achieves good color rendering of 85 with the CIE coordinate of (0.3183, 0.3036).

  1. Application of a novel flash-milling procedure for coercivity development in nanocrystalline MnAl permanent magnet powders

    NASA Astrophysics Data System (ADS)

    Rial, J.; Villanueva, M.; Céspedes, E.; López, N.; Camarero, J.; Marshall, L. G.; Lewis, L. H.; Bollero, A.

    2017-03-01

    This study shows the possibility of dramatically tuning microstructure and magnetic properties of gas-atomized Mn54Al46 particles by milling for an unprecedented duration of 30 s. This flash-milling procedure avoids the high temperatures typically achieved in lengthy conventional ball milling experiments, and is efficient to reduce the crystallite size to the nanometer scale, induce microstructural strain and ease phase transformations. This leads to the creation of the τ-MnAl phase providing magnetization, and the β-Mn phase operating in the mechanism for coercivity development. Post-annealing at 355 °C for 10 min results in a coercivity about three times larger than that of the annealed starting material, and thus reduces the optimum processing temperature in 75 °C by comparison with that needed for the latter to achieve the best combination of magnetic properties. A maximum obtained coercivity exceeding 5 kOe compares to the highest values reported to date for isotropic MnAl powders attained after milling for times above 20 h. This high coercivity is of additional relevance for further consideration of this material as a hard magnetic phase in the preparation of nanocomposite permanent magnets. The combination of the cost-efficient synthesis technique (gas-atomization) and novel processing route (flash-milling) for the production of low-cost isotropic nanocrystalline MnAl powders, opens new paths to the possible mass production of these materials as an alternative to permanent magnets containing critical raw materials.

  2. Aluminum Deoxidation Equilibria in Liquid Iron: Part III—Experiments and Thermodynamic Modeling of the Fe-Mn-Al-O System

    NASA Astrophysics Data System (ADS)

    Paek, Min-Kyu; Do, Kyung-Hyo; Kang, Youn-Bae; Jung, In-Ho; Pak, Jong-Jin

    2016-10-01

    Deoxidation equilibria in high-Mn- and high-Al-alloyed liquid steels were studied over the entire Fe-Mn-Al composition range by both experiments and thermodynamic modeling. Effect of Mn on the Al deoxidation equilibria in liquid iron was measured by the different experimental techniques depending on the Al content. In order to confirm the reproducibility of the experimental results, the deoxidation experiments were carried out reversibly from high oxygen state by addition of Al as a deoxidizer, and from low oxygen state by addition of Fe2O3 or MnO as an oxygen source. For the Al-rich side, CaO flux was added on top of liquid iron in order to remove suspended Al2O3 inclusions in the melt. Based on the present experimental result and available critically evaluated literature data, the Al deoxidation equilibria in Fe-Mn-Al-O liquid alloy were thermodynamically modeled. The Modified Quasichemical Model was used in order to take into account a strong short-range ordering of atoms in molten state. Deoxidation equilibria and inclusion stability diagram for entire Fe-Mn-Al melt were successfully reproduced by the present model.

  3. Room temperature electromechanical and magnetic investigations of ferroelectric Aurivillius phase Bi5Ti3(FexMn1-x)O15 (x = 1 and 0.7) chemical solution deposited thin films

    NASA Astrophysics Data System (ADS)

    Keeney, Lynette; Groh, Claudia; Kulkarni, Santosh; Roy, Saibal; Pemble, Martyn E.; Whatmore, Roger W.

    2012-07-01

    Aurivillius phase thin films of Bi5Ti3(FexMn1-x)O15 with x = 1 (Bi5Ti3FeO15) and 0.7 (Bi5Ti3Fe0.7Mn0.3O15) on SiO2-Si(100) and Pt/Ti/SiO2-Si substrates were fabricated by chemical solution deposition. The method was optimized in order to suppress formation of pyrochlore phase Bi2Ti2O7 and improve crystallinity. The structural properties of the films were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Optimum crystallinity and pyrochlore phase suppression was achieved by the addition of 15 to 25 mol. % excess bismuth to the sols. Based on this study, 17.5 mol. % excess bismuth was used in the preparation of Bi2Ti2O7-free films of Bi5Ti3FeO15 on SrTiO3(100) and NdGaO3(001) substrates, confirming the suppression of pyrochlore phase using this excess of bismuth. Thirty percent of the Fe3+ ions in Bi5Ti3FeO15 was substituted with Mn3+ ions to form Bi2Ti2O7-free thin films of Bi5Ti3Fe0.7Mn0.3O15 on Pt/Ti/SiO2-Si, SiO2-Si(100), SrTiO3(100), and NdGaO3(001) substrates. Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15 thin films on Pt/Ti/SiO2-Si and SiO2-Si(100) substrates were achieved with a higher degree of a-axis orientation compared with the films on SrTiO3(100) and NdGaO3(001) substrates. Room temperature electromechanical and magnetic properties of the thin films were investigated in order to assess the potential of these materials for piezoelectric, ferroelectric, and multiferroic applications. Vertical piezoresponse force microscopy measurements of the films demonstrate that Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15 thin films are piezoelectric at room temperature. Room temperature switching spectroscopy-piezoresponse force microscopy measurements in the presence and absence of an applied bias demonstrate local ferroelectric switching behaviour (180°) in the films. Superconducting quantum interference device magnetometry measurements do not show any room temperature ferromagnetic hysteresis down to an upper detection limit of 2.53 × 10

  4. Field-dependent magnetization of BiFeO3 in ultrathin La0.7Sr0.3MnO3/BiFeO3 superlattice

    DOE PAGES

    Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra; ...

    2015-12-02

    We report the observation of field-induced magnetization of BiFeO3 (BFO) in an ultrathin La0.7Sr0.3MnO3 (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μB/Fe) for ultrathin BFO layermore » (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).« less

  5. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    PubMed Central

    Zhu, L. J.; Nie, S. H.; Xiong, P.; Schlottmann, P.; Zhao, J. H.

    2016-01-01

    The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- to square-root temperature dependence and deviation from it in three distinct temperature regimes. Our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons. PMID:26905518

  6. Interfacial segregation and deformation of superplastically deformed Al-Mg-Mn alloys

    SciTech Connect

    Vetrano, J.S.; Lavender, C.A.; Bruemmer, S.M.

    1995-03-01

    Microstructural and microchemical studies have been carried out on superplastically deformed Al-Mg-Mn (AA5083-type) alloys. Grain boundary composition was measured using a Scanning Auger Microprobe (SAM) and an Analytical Transmission Electron Microscope (ATEM), while conventional TEM was used for microstructural evaluation. Non-equilibrium segregation of Si to grain boundaries following deformation was measured by both techniques. Significant interfacial Si enrichment was only detected in gage sections of tensile specimens after uniaxial strains from 50 to 200%. Grip regions which experience identical thermal histories, but without plastic deformation, did not reveal Si segregation. Selected samples also showed a slight depletion of Mg at grain boundaries after deformation. The only reproducible observation of equilibrium segregation was in Zr-modified alloys, where Sn was detected by SAM in both the deformed and undeformed sections of the sample. Microstructural analysis documented subgrain formation and subgrain-precipitate interactions during superplastic deformation. In addition, many grain boundaries and precipitate interfaces contained small (5 to 20 nm) voids. Compositional analysis of these nano-voids revealed that they were enriched in Mg with the adjacent boundary regions correspondingly depleted.

  7. Orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films

    DOE PAGES

    Zhu, L. J.; Nie, S. H.; Xiong, P.; ...

    2016-02-24

    The orbital two-channel Kondo effect displaying exotic non-Fermi liquid behaviour arises in the intricate scenario of two conduction electrons compensating a pseudo-spin-1/2 impurity of two-level system. Despite extensive efforts for several decades, no material system has been clearly identified to exhibit all three transport regimes characteristic of the two-channel Kondo effect in the same sample, leaving the interpretation of the experimental results a subject of debate. Here we present a transport study suggestive of a robust orbital two-channel Kondo effect in epitaxial ferromagnetic L10-MnAl films, as evidenced by a magnetic field-independent resistivity upturn with a clear transition from logarithmic- tomore » square-root temperature dependence and deviation from it in three distinct temperature regimes. Lastly, our results also provide an experimental indication of the presence of two-channel Kondo physics in a ferromagnet, pointing to considerable robustness of the orbital two-channel Kondo effect even in the presence of spin polarization of the conduction electrons.« less

  8. Magneto-trions in a GaMnAs/Ga0.6Al0.4As Quantum Dot

    NASA Astrophysics Data System (ADS)

    Lalitha, D.; Peter, A. John; Lee, Chang Woo

    2014-09-01

    Magneto bound exciton and the charged exciton in a GaMn0.02As/Ga0.6Al0.4As quantum dot are reported with the spatial confinement effect. The numerical calculations are carried out with the inclusion of exchange interaction between the carrier and the magnetic impurities. The binding energies of exciton and the trions and the optical transition energy are obtained as a function of dot radius. Numerical computations are followed using exact diagonalization method. The spin polaronic energy of the exciton and the charged excitons are obtained using a mean field theory in the presence of magnetic field strength. The magnetization of Mn ion impurities as a function of dot radius is investigated. The effective g-factor of conduction (valence) band electron (hole) is obtained in the GaMnAs quantum dot. The magnetic field induced size dependence of effective Landé g-factor is computed. The result shows that (i) the geometrical dependence on sp-d exchange interaction in the GaMn0.02As/Ga0.6Al0.4As quantum dot has great influence with the geometrical confinement, (ii) the monotonic behavior of effective g-factor with the reduction of dot radius is observed, (iii) the Landé factor is more sensitive if the geometrical confinement effect is included and (iv) the value of effective g-factor increases when the spatial confinement is enhanced for all the dot radii. Our results show that the effective Landé g-factor can be manipulated negative to positive values in the GaMn0.02As/Ga0.4Al0.6As quantum dot.

  9. Improvement of impact toughness of 5Mn-1Al-0.5Ti steel by intercritical annealing

    NASA Astrophysics Data System (ADS)

    Yi, Il-Cheol; Ha, Yumi; Lee, Hakcheol; Zargaran, A.; Kim, Nack J.

    2017-02-01

    The present study is aimed at improving the impact toughness of 5Mn-1Al-0.5Ti steel by incorporating ferrite-martensite dual phase microstructure by intercritical annealing. Although (8-12)Mn martensitic steels usually show very low impact toughness due to the occurrence of intergranular fracture, the martensitic structure of the present 5Mn-1Al-0.5Ti steel fails by transgranular cleavage fracture due to higher grain boundary strength than matrix strength incurred by reduced Mn content and segregation of Ti along grain boundaries. Nevertheless, it still shows very poor impact toughness at room temperature due to its coarse grain size. The application of intercritical annealing, i.e., formation of dual phase microstructure, is shown to significantly decrease ductile-to-brittle transition temperature (DBTT), with only a small degradation of tensile properties; however, microstructural examinations show that most of ferrite/martensite interfaces have a character of low angle boundaries and therefore such decrease in DBTT is not necessarily due to the formation of ferrite-martensite dual phase structure, but rather to the refinement of grain size by low temperature annealing.

  10. Improvement of impact toughness of 5Mn-1Al-0.5Ti steel by intercritical annealing

    NASA Astrophysics Data System (ADS)

    Yi, Il-Cheol; Ha, Yumi; Lee, Hakcheol; Zargaran, A.; Kim, Nack J.

    2017-03-01

    The present study is aimed at improving the impact toughness of 5Mn-1Al-0.5Ti steel by incorporating ferrite-martensite dual phase microstructure by intercritical annealing. Although (8-12)Mn martensitic steels usually show very low impact toughness due to the occurrence of intergranular fracture, the martensitic structure of the present 5Mn-1Al-0.5Ti steel fails by transgranular cleavage fracture due to higher grain boundary strength than matrix strength incurred by reduced Mn content and segregation of Ti along grain boundaries. Nevertheless, it still shows very poor impact toughness at room temperature due to its coarse grain size. The application of intercritical annealing, i.e., formation of dual phase microstructure, is shown to significantly decrease ductile-to-brittle transition temperature (DBTT), with only a small degradation of tensile properties; however, microstructural examinations show that most of ferrite/martensite interfaces have a character of low angle boundaries and therefore such decrease in DBTT is not necessarily due to the formation of ferrite-martensite dual phase structure, but rather to the refinement of grain size by low temperature annealing.

  11. Phase transformation induced by electric field and mechanical stress in Mn-doped (Bi1/2Na1/2)TiO3-(Bi1/2K1/2)TiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Ehara, Yoshitaka; Novak, Nikola; Ayrikyan, Azatuhi; Geiger, Philipp T.; Webber, Kyle G.

    2016-11-01

    Electric-field- and stress-induced phase transformations were investigated in polycrystalline 0.5 mol. % Mn-doped (1-x)(Bi1/2Na1/2)TiO3-x(Bi1/2K1/2)TiO3 (x = 0.1, 0.2). To characterize the effect of electric field and stress on the stability of the ferroelectric and relaxor states, polarization- and current density-electric field curves, as well as the stress-strain response as a function of temperature were characterized. Analogous to the observed electrical behavior, the macroscopic mechanical constitutive behavior showed a closed hysteresis at elevated temperatures, indicating a reversible stress-induced relaxor-to-ferroelectric transformation. The electrical and mechanical measurements were used to construct electric field-temperature and stress-temperature phase diagrams, which show similar characteristics. These data show that a mechanical compressive stress, similarly to an electric field, can induce long-range ferroelectric order in a relaxor ferroelectric.

  12. Dynamic magnetic interaction in La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/BiFeO{sub 3} heterostructure

    SciTech Connect

    Guo, H. Y.; Lin, J. G.; Yang, Jan Chi; Chu, Y. H.

    2014-09-15

    The La{sub 2/3}Sr{sub 1/3}MnO{sub 3}/BiFeO{sub 3} (LSMO/BFO) heterostructure is studied as probed by temperature-dependent ferromagnetic resonance (FMR). Consistent with the structure analysis, two FMR modes are found for both a single LSMO layer and a LSMO/BFO bilayer grown on DyScO{sub 3}, corresponding to the strained and relaxed phases of LSMO. The FMR linewidth intensity vs temperature curve shows two maxima at 200 K and 140 K in the strained phase of LSMO/BFO bilayer, which is related to the magnetic excitations in BFO. Our results demonstrate a dynamic spin interaction between LSMO and BFO, suggesting an effective route to manipulate the magnetic properties of oxide heterostructures.

  13. Structural, dielectric and magnetic properties of Bi0.8Ba0.2Fe0.6Mn0.4O3 ceramic

    NASA Astrophysics Data System (ADS)

    Rangi, Manisha; Sanghi, S.; Agarwal, A.; Kaswan, K.; Jangra, S.; Singh, O.

    2016-05-01

    Polycrystalline Bi0.8Ba0.2Fe0.6Mn0.4O3 ceramic was synthesized via conventional two stage solid state reaction method. The crystal structure is examined via powder x-ray diffraction and Rietveld refinement revealed that the sample has a rhombohedral crystal structure (space group R3c). The dielectric response of the sample was analyzed in the frequency range 10 Hz to 5 MHz at different temperature. The values of dielectric constant (ɛ') and dielectric loss factor (tan δ) increases with increasing temperature at different frequencies which may be the result of increase in the number of charge carriers and their mobilities due to the thermal activation. M-H hysteresis loop was recorded at room temperature up to a field of 15 kOe which shows that there is slightly enhancement in magnetization with co-doping.

  14. Correlation between electrical and magnetic properties of polycrystalline La0.5Ca0.5Mn0.98Bi0.02O3

    NASA Astrophysics Data System (ADS)

    Krichene, A.; Bourouina, M.; Venkateshwarlu, D.; Solanki, P. S.; Rayaprol, S.; Ganesan, V.; Boujelben, W.; Kuberkar, D. G.

    2016-06-01

    We have reported in this work the study of correlation between electrical transport and magnetic properties of La0.5Ca0.5Mn0.98Bi0.02O3 polycrystalline sample prepared by solid state method. Structural analysis reveals that presently studied compound crystallizes in the orthorhombic structure with Pnma space group. Temperature dependence of magnetization indicates that our studied compound undergoes a paramagnetic-ferromagnetic transition at Curie temperature TC=237 K. Magnetotransport analysis was successfully carried out using percolation model in the temperature range 40-300 K for magnetic field values up to 14 T. Strong correlation between electrical and magnetic properties was observed along with the absence of charge ordering inside the structure of our sample.

  15. Structural, magnetic and magnetocaloric properties of layered perovskite La1.1Bi0.3Sr1.6Mn2O7

    NASA Astrophysics Data System (ADS)

    Oubla, M.; Lamire, M.; Boutahar, A.; Lassri, H.; Manoun, B.; Hlil, E. K.

    2016-04-01

    The La1.1Bi0.3Sr1.6Mn2O7 sample was synthesized by coprecipitation method. Its structure has been characterized by X-ray powder diffraction. The diffraction patterns are consistent with the I4/mmm symmetry, with tetragonal lattice parameters a=3.8750±0.0001 Å and c=20.0456±0.0002 Å. Magnetic measurements have shown a ferromagnetic like ordering with second order magnetic phase transition to paramagnetic states. The magnetic entropy change caused by a magnetic field, (-∆Smax), was estimated on the basis of the Maxwell relation. The maximum magnetic entropy change (-∆Smax) and the relative cooling power (RCP) are, 1.65 J kg-1K-1 and 134.4 J kg-1 respectively, for a 5 T magnetic field change at 340 K.

  16. Mechanism of Fluorescence Enhancement of Biosynthesized XFe2O4-BiFeO3 (X = Cr, Mn, Co, or Ni) Membranes

    NASA Astrophysics Data System (ADS)

    Bian, Liang; Li, Hai-long; Dong, Hai-liang; Dong, Fa-qin; Song, Mian-xin; Wang, Li-sheng; Hou, Wen-ping; Gao, Lei; Zhang, Xiao-yan; Zhou, Tian-liang; Sun, Guang-ai; Li, Xin-xi; Xie, Lei

    2016-12-01

    Ferrites-bismuth ferrite is an intriguing option for medical diagnostic imaging device due to its magnetoelectric and enhanced near-infrared fluorescent properties. However, the embedded XFO nanoparticles are randomly located on the BFO membranes, making implementation in devices difficult. To overcome this, we present a facile bio-approach to produce XFe2O4-BiFeO3 (XFO-BFO) (X = Cr, Mn, Co, or Ni) membranes using Shewanella oneidensis MR-1. The perovskite BFO enhances the fluorescence intensity (at 660 and 832 nm) and surface potential difference (-469 385 meV and -80 525 meV) of the embedded spinel XFO. This mechanism is attributed to the interfacial coupling of the X-Fe (e- or h+) and O-O (h+) interfaces. Such a system could open up new ideas in the design of environmentally friendly fluorescent membranes.

  17. Effect of grain size on charge and magnetic ordering in Bi{sub 0.67}Ca{sub 0.33}MnO{sub 3}

    SciTech Connect

    Ade, Ramesh Singh, R.

    2014-04-24

    In the present work we report the electron spin resonance(ESR) and magnetic measurements to understand the effect of grain size on the charge ordering (CO), orbital ordering (OO), long range anti ferromagnetic (AFM) ordering in Bi{sub 0.67}Ca{sub 0.33}MnO{sub 3} manganite synthesized by sol-gel method. The temperature dependence of linewidth (ΔH) of the ESR signal and magnetization have been used to get information about magnetic interactions. The CO is suppressed and AFM ordering remains unaffected with increase in grain size of the sample. The competition between FM and AFM correlations is strongly dependent on the grain size of the sample.

  18. Rare-Earth-Free Permanent Magnets for Electrical Vehicle Motors and Wind Turbine Generators: Hexagonal Symmetry Based Materials Systems Mn-Bi and M-type Hexaferrite

    SciTech Connect

    Hong, Yang-Ki; Haskew, Timothy; Myryasov, Oleg; Jin, Sungho; Berkowitz, Ami

    2014-06-05

    The research we conducted focuses on the rare-earth (RE)-free permanent magnet by modeling, simulating, and synthesizing exchange coupled two-phase (hard/soft) RE-free core-shell nano-structured magnet. The RE-free magnets are made of magnetically hard core materials (high anisotropy materials including Mn-Bi-X and M-type hexaferrite) coated by soft shell materials (high magnetization materials including Fe-Co or Co). Therefore, our research helps understand the exchange coupling conditions of the core/shell magnets, interface exchange behavior between core and shell materials, formation mechanism of core/shell structures, stability conditions of core and shell materials, etc.

  19. Magneto-transport properties of oriented Mn{sub 2}CoAl films sputtered on thermally oxidized Si substrates

    SciTech Connect

    Xu, G. Z.; Du, Y.; Zhang, X. M.; Liu, E. K.; Wang, W. H. Wu, G. H.; Zhang, H. G.

    2014-06-16

    Spin gapless semiconductors are interesting family of materials by embracing both magnetism and semiconducting due to their unique band structure. Its potential application in future spintronics requires realization in thin film form. In this Letter, we report fabrication and transport properties of spin gapless Mn{sub 2}CoAl films prepared on thermally oxidized Si substrates by magnetron sputtering deposition. The films deposited at 673 K are well oriented to (001) direction and display a uniform-crystalline surface. Magnetotransport measurements on the oriented films reveal a semiconducting-like resistivity, small anomalous Hall conductivity, and linear magnetoresistance representative of the transport signatures of spin gapless semiconductors. The magnetic properties of the films have also been investigated and compared to that of bulk Mn{sub 2}CoAl, showing small discrepancy induced by the composition deviation.

  20. Conditions for spin-gapless semiconducting behavior in Mn{sub 2}CoAl inverse Heusler compound

    SciTech Connect

    Galanakis, I.; Özdoğan, K.; Şaşıoğlu, E.; Blügel, S.

    2014-03-07

    Employing ab initio electronic structure calculations, we investigate the conditions for spin-gapless semiconducting (SGS) behavior in the inverse Mn{sub 2}CoAl Heusler compound. We show that tetragonalization of the lattice, which can occur during films growth, keeps the SGS character of the perfect cubic compound. On the contrary, atomic swaps even between sites with different local symmetry destroy the SGS character giving rise to a half-metallic state. Furthermore, the occurrence of Co-surplus leads also to half-metallicity. Thus, we propose that in order to achieve SGS behavior during the growth of Mn{sub 2}CoAl (and similar SGS Heusler compounds) thin films, one should minimize the occurrence of defects, while small deformations of the lattice, due to the lattice mismatch with the substrate, do not play a crucial role.

  1. Ab initio explanation of disorder and off-stoichiometry in Fe-Mn-Al-C κ carbides

    NASA Astrophysics Data System (ADS)

    Dey, Poulumi; Nazarov, Roman; Dutta, Biswanath; Yao, Mengji; Herbig, Michael; Friák, Martin; Hickel, Tilmann; Raabe, Dierk; Neugebauer, Jörg

    2017-03-01

    Carbides play a central role for the strength and ductility in many materials. Simulating the impact of these precipitates on the mechanical performance requires knowledge about their atomic configuration. In particular, the C content is often observed to substantially deviate from the ideal stoichiometric composition. In this work, we focus on Fe-Mn-Al-C steels, for which we determined the composition of the nanosized κ carbides (Fe,Mn)3AlC by atom probe tomography in comparison to larger precipitates located in grain boundaries. Combining density functional theory with thermodynamic concepts, we first determine the critical temperatures for the presence of chemical and magnetic disorder in these carbides. Second, the experimentally observed reduction of the C content is explained as a compromise between the gain in chemical energy during partitioning and the elastic strains emerging in coherent microstructures.

  2. Magnetic properties of Co50-xNixMn25Al25 alloys with B2 structure

    NASA Astrophysics Data System (ADS)

    Okubo, A.; Xu, X.; Umetsu, R. Y.; Kanomata, T.; Ishida, K.; Kainuma, R.

    2011-04-01

    Magnetic properties of the B2 phase in Co50-xNixMn25Al25 alloys were investigated. Spontaneous magnetization Ms measured at 4.2 K increases linearly with increasing x in the region of x ≤ 30 in accordance with following the generalized Slater-Pauling (GSP) line. However, Ms abruptly decreases with increasing x and deviates from the GSP line in the Ni-rich region of x > 30, suggesting a drastic change in the density of states at the Fermi energy. The Curie temperature TC decreases monotonically with increasing x and significantly decreases in the region of x > 30. Antiferromagnetic evidence is clearly observed at x > 45, and the Néel temperature TN increases with increasing x, in reaching the value of the B2 phase in Ni2MnAl.

  3. Characteristic chemical shift of quasicrystalline alloy Al53Si27Mn20 studied by EELS and SXES

    NASA Astrophysics Data System (ADS)

    Koshiya, S.; Terauchi, M.; Tsai, A. P.

    2011-06-01

    Chemical shifts of all constituent atoms for amorphous (Am), quasicrystalline (QC) and crystalline (Cryst) alloys of Al53Si27Mn20 were investigated for the first time by high energy-resolution electron energy-loss spectroscopy (EELS) and soft-X-ray emission spectroscopy (SXES). Among Al L-shell excitation EELS spectra of Am, QC and Cryst alloys, only QC alloy showed an apparent chemical shift to the larger binding energy side by 0.4 eV. In Al-Kα and Si-Kα emission SXES spectra of these alloys, only QC alloy showed a chemical shift to the larger binding energy side by 4 eV for Al-Kα and 6 eV for Si-Kα. These chemical shift values are comparable to those of corresponding metal oxides. This indicates a smaller amount of valence charge at Al and Si atomic sites in QC alloy. On the other hand, Mn-L SXES spectra did not show any chemical shift. Therefore, the decreased charge from Al and Si sites should be distributed between atomic sites, indicating the presence of covalent bonding nature for QC ordered alloy.

  4. Nanoindentation Mechanical Properties of a Bi-phase Cu29Zr32Ti15Al5Ni19 Alloy

    NASA Astrophysics Data System (ADS)

    Pi, JinHong; Wang, ZhangZhong; He, XianCong; Bai, YunQiang

    2016-01-01

    Mechanical properties of cylindrical bi-phasic high-entropy alloy Cu29Zr32Ti15Al5Ni19 (3 mm in diameter) were characterized by nanoindentation test in each phase. The results show that the constituent FCC phase is of low nanohardness (2.35 GPa) and modulus (60.9 GPa), while another constituent phase in the alloy, the HCP phase, shows much higher nanohardness (6.5 GPa) and modulus (115.3 GPa). Creep occurs in both phases during the indentation.

  5. Shock Equation of State of Multi-Phase Epoxy-Based Composite (Al-MnO2-Epoxy)

    DTIC Science & Technology

    2010-10-01

    There are several studies in the literature regarding the equation of state of alumina-epoxy composites. Although these single component systems...paper presents the shock equation of state results on a multi-phase composite Al-MnO2-epoxy. Equation of state experiments were conducted using three...The experimental equation of state data is compared to volume averaged and mesoscale mixture models.

  6. A Mössbauer effect study of the Fe2+ x Mn1- x Al Heusler alloys

    NASA Astrophysics Data System (ADS)

    Paduani, C.; Samudio Pérez, C. A.; Schaf, J.; Ardisson, J. D.; Takeuchi, A. Y.; Yoshida, M. I.

    2010-01-01

    In this work the Mössbauer spectroscopy has been used to study the magnetic properties of Fe2 + x Mn1 - x Al alloys with small deviations of composition from the stoichiometric 2:1:1. The Mössbauer parameters obtained for the L21 phase indicate H hf fields of about 25 T and 30 T at 80 K for Fe atoms at X sites in the ordered X2YZ structure of the L21 full Heusler alloys.

  7. White luminescence and energy transfer process in Bi3+,Sm3+ co-doped Ca3Al2O6 phosphors

    NASA Astrophysics Data System (ADS)

    Wang, LongJun; Guo, Hai; Wei, YunLe; Noh, Hyeon Mi; Jeong, Jung Hyun

    2015-04-01

    Ca3Al2O6:Bi3+,Sm3+ phosphors were synthesized by conventional solid state reaction method and their luminescent properties were systemically investigated by excitation, emission spectra and decay curves measurement. Through an efficient energy transfer process from Bi3+ to Sm3+, the obtained phosphors exhibit emission from Bi3+ and Sm3+ with considerable intensity under near-ultraviolet excitation (300 nm). Tuning the content of Sm3+ can generate the varied hues from blue green to white. Our research will extend the understanding of interactions between Bi3+ and rare earth ions and show the potential application of Bi3+,Sm3+ co-doped phosphors in W-LEDs field.

  8. Evolution of Intermetallics, Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

    NASA Astrophysics Data System (ADS)

    Liu, K.; Chen, X.-G.

    2016-12-01

    Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al6(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1-0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.

  9. Magnetism-Structure Correlations during the epsilon ->tau Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

    SciTech Connect

    Jimenez-Villacorta, F; Marion, JL; Oldham, JT; Daniil, M; Willard, MA; Lewis, LH

    2014-01-21

    Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn55Al45 ribbons from the as-quenched metastable antiferromagnetic (AF) epsilon-phase to the target ferromagnetic (FM) L1(0) tau-phase are investigated. The as-solidified material exhibits a majority hexagonal epsilon-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature T-B similar to 95 K (H-ex similar to 13 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature T-anneal approximate to 568 K (295 degrees C) promotes the nucleation of the metastable L1(0) tau-MnAl phase at the expense of the parent epsilon-phase, donating an increasingly hard ferromagnetic character. The onset of the epsilon ->tau transformation occurs at a temperature that is similar to 100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy.

  10. Engineering the polar magneto-optical Kerr effect in strongly strained L10-MnAl films

    NASA Astrophysics Data System (ADS)

    Zhu, Lijun; Brandt, Liane; Zhao, Jianhua

    2016-10-01

    We report the engineering of the polar magnetooptical (MO) Kerr effect in perpendicularly magnetized L10-MnAl epitaxial films with remarkably tuned magnetization, strain, and structural disorder by varying substrate temperature (T s) during molecular-beam epitaxy growth. The Kerr rotation was enhanced by a factor of up to 5 with T s increasing from 150 to 350 °C as a direct consequence of the improvement of the magnetization. A similar remarkable tuning effect was also observed on the Kerr ellipticity and the magnitude of the complex Kerr angle, while the phase of the complex Kerr angle appears to be independent of the magnetization. The combination of the good semiconductor compatibility, the moderate coercivity of 0.3-8.2 kOe, the tunable polar MO Kerr effect of up to ~0.034°, and giant spin precession frequencies of up to ~180 GHz makes L10-MnAl films a very interesting MO material. Our results give insights into both the microscopic mechanisms of the MO Kerr effect in L10-MnAl alloys and their scientific and technological application potential in the emerging spintronics and ultrafast MO modulators.

  11. Aurivillius phases of PbBi{sub 4}Ti{sub 4}O{sub 15} doped with Mn{sup 3+} synthesized by molten salt technique: Structure, dielectric, and magnetic properties

    SciTech Connect

    Zulhadjri; Prijamboedi, B.; Nugroho, A.A.; Mufti, N.; Fajar, A.; Palstra, T.T.M.; Ismunandar

    2011-05-15

    Doping of manganese (Mn{sup 3+}/Mn{sup 4+}) into the Aurivillius phase Pb{sub 1-x}Bi{sub 4+x}Ti{sub 4-x}Mn{sub x}O{sub 15} was carried out using the molten salt technique for various Mn concentrations (x=0, 0.2, 0.4, 0.6, 0.8, and 1). Single phase samples could be obtained in the composition range with x up to 0.6 as confirmed by X-ray and neutron diffraction analysis. Dielectric measurements show a peak at 801, 803, 813 and 850 K for samples with x=0, 0.2, 0.4, and 0.6, respectively, related to the ferroelectric transition temperature (T{sub c}). The main contribution of the in-plane polarization for x{<=}0.2 which was calculated from the atomic positions obtained by the structure analysis is the dipole moment in the Ti(1)O{sub 6} layer; however, for x{>=}0.4 the polarization originates from the dipole moment in the Ti(2)O{sub 6} layer. Mn doping in the Pb{sub 1-x}Bi{sub 4+x}Ti{sub 4-x}Mn{sub x}O{sub 15} does not show any long range magnetic ordering. -- Graphical abstract: The dipole moment of TiO{sub 6} dependence of x in Pb{sub 1-x}Bi{sub 4+x}Ti{sub 4-x}Mn{sub x}O{sub 15} (0{<=}x{<=}0.6): (a) along a-axis and (b) on the ab plane. This figure indicated that polarization in the ab-plane contribute to the total polarization. Display Omitted Highlights: {yields} We have prepared Pb{sub 1-x}Bi{sub 4+x}Ti{sub 4-x}Mn{sub x}O{sub 15}, 0{<=}x{<=}1 by the molten-salt method. {yields} The oxides adopted A2{sub 1}am space group. {yields} Dipole moments of the inner Ti(1)O{sub 6} are the main polarization contributor for x{<=}0.2. {yields} Dipole moments of the outer Ti(2)O{sub 6} are the main polarization contributor for x>0.2. {yields} Ferromagnetic interactions show the contribution of mixed valence of Mn{sup 3+}/Mn{sup 4+}.

  12. 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.

  13. Site engineering in chemical solution deposited Na1/2Bi1/2TiO3 thin films using Mn acceptor

    NASA Astrophysics Data System (ADS)

    Feng, Chao; Yang, Changhong; Geng, Fangjuan; Lv, Panpan; Yao, Qian

    2016-02-01

    A series of Mn doped Na1/2Bi1/2TiO3 (NBT) thin films with dopant concentrations from 0 to 4 at% (NBTMn x , x = 0, 0.01, 0.02, 0.04) were fabricated on the indium tin oxide/glass substrates by chemical solution deposition. The effects of Mn doping content on crystalline, ferroelectric and dielectric properties were investigated. All thin films exhibit phase-pure polycrystalline perovskite structures. For the insulating measurement, at low electric field, space charge limited conduction or a grain boundary limited behavior is responsible for the leakage behavior of NBTMn x thin films, whereas at the high electric field, the dominant mechanism is changed to the interface-limited Fowler-Nordheim tunneling except NBTMn0.04. The leakage current density is reduced by more than three orders of magnitude in NBTMn0.02 compared with that of NBT thin film. Also, the enhanced ferroelectric properties of NBTMn0.02 thin film can be observed in polarization-electric filed hysteresis loop with P r of 38 μC cm-2, which is consistent with the result of the normalized capacitance-voltage curve. The dielectric constant and dissipation factor of NBTMn0.02 thin film are 501 and 0.04, respectively at 100 kHz. These electrical property improvements are attributed to the decrease of oxygen vacancy-induced leakage current.

  14. Phase transition and enhanced magneto-dielectric response in BiFeO{sub 3}-DyMnO{sub 3} multiferroics

    SciTech Connect

    Tripathy, Satya N. Pradhan, Dillip K.; Pradhan, Dhiren K.; Palai, Ratnakar; Katiyar, Ram S.; Mishra, Karuna K.; Sen, Shrabanee; Paulch, Marian; Scott, James F.

    2015-04-14

    We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO{sub 3}-x DyMnO{sub 3} (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn2{sub 1}a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO{sub 3} substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H = 2 T for x = 0.2.

  15. Effect of annealing temperature on the structural reorganization of Eu3+ optical centers in Al2O3-Eu2O3-BiOF gel films

    NASA Astrophysics Data System (ADS)

    Malashkevich, G. E.; Kornienko, A. A.; Dunina, E. B.; Prusova, I. V.; Shevchenko, G. P.; Bokshits, Yu. V.

    2007-06-01

    The dependence of the structural reorganization of Eu3+ optical centers in Al2O3-Eu2O3-BiOF films on the annealing temperature has been investigated. It is shown by the methods of crystal field theory and computer simulation that the increase in the annealing temperature from 700 to 1100 °C leads to removal of bismuth from Eu-O-Bi complex centers with the C 3V symmetry in the Al2O3 structure and the change in symmetry from D 3 to O h for a large fraction of EuAlO3 centers.

  16. Synthèse et structure cristalline d'un matériau noir AgMn(II) 3(Mn(III) 0,26Al0,74)(MoO4)5.

    PubMed

    Bouzidi, Chahira; Frigui, Wafa; Zid, Mohamed Faouzi

    2015-03-01

    A new silver aluminium trimangan-ese penta-molybdate {silver(I) trimanganese(II) aluminium penta-kis-[tetra-oxidomolybdate(VI)]}, AgMn(II) 3(Mn(III) 0,26Al0,74)(MoO4)5, has been synthesized using solid-state methods. The structure is composed of M 2O10 dimers, M 3O14 (M = Mn, Al) trimers and MoO4 tetra-hedra sharing corners and forming three types of layers A, B and B'. The sequence of the constituting layers is A-BB'-A-BB', with B' obtained from B by inversion symmetry, forming a three-dimensional structure with large channels in which the positionally disordered and partially occupied Ag(+) ions reside. The Mn(III) and Al(III) atoms share the same site, M. AgMn(II) 3(Mn(III) 0,26Al0,74)(MoO4)5 is isotypic with the NaMg3 X(MoO4)5 (X = Al, In) family and with NaFe4(MoO4)5. A comparative structural description is provided between the structure of the title compound and those of related phases containing dimers, trimers and tetra-mers.

  17. Synthèse et structure cristalline d’un matériau noir AgMnII 3(MnIII 0,26Al0,74)(MoO4)5

    PubMed Central

    Bouzidi, Chahira; Frigui, Wafa; Zid, Mohamed Faouzi

    2015-01-01

    A new silver aluminium trimangan­ese penta­molybdate {silver(I) trimanganese(II) aluminium penta­kis­[tetra­oxidomolybdate(VI)]}, AgMnII 3(MnIII 0,26Al0,74)(MoO4)5, has been synthesized using solid-state methods. The structure is composed of M 2O10 dimers, M 3O14 (M = Mn, Al) trimers and MoO4 tetra­hedra sharing corners and forming three types of layers A, B and B′. The sequence of the constituting layers is A–BB′–A–BB′, with B′ obtained from B by inversion symmetry, forming a three-dimensional structure with large channels in which the positionally disordered and partially occupied Ag+ ions reside. The MnIII and AlIII atoms share the same site, M. AgMnII 3(MnIII 0,26Al0,74)(MoO4)5 is isotypic with the NaMg3 X(MoO4)5 (X = Al, In) family and with NaFe4(MoO4)5. A comparative structural description is provided between the structure of the title compound and those of related phases containing dimers, trimers and tetra­mers. PMID:25844193

  18. Interface magnetism in epitaxial BiFeO3-La0.7Sr0.3MnO3 heterostructures integrated on Si(100).

    PubMed

    Rao, S S; Prater, J T; Wu, Fan; Shelton, C T; Maria, J-P; Narayan, J

    2013-01-01

    We report on the heteroepitaxial growth of ferroelectric (FE)-antiferromagnetic (AFM) BiFeO3 (BFO) on ferromagnetic La0.7Sr0.3MnO3 (LSMO), integrated on Si(100) using pulsed laser deposition via the domain matching epitaxy paradigm. The BFO/LSMO films were epitaxially grown on Si(100) by introducing epitaxial layers of SrTiO3/MgO/TiN. X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photo absorption spectroscopy, and atomic force microscopy were employed to fully characterize the samples. Furthermore, we have investigated the magnetic behavior of this five layer heterostructure, in which a d(5) system (Fe(3+)) manifested in FE-AFM BFO is epitaxially conjoined at the interface to a multivalent transition metal ion such as Mn(3+)/Mn(4+) in LSMO. The temperature- and magnetic field-dependent magnetization measurements reveal an unexpected enhancement in magnetic moment and improved magnetic hysteresis squareness originating from the BFO/LSMO interface. We observe a stronger temperature dependence of HEB when the polarity of field cooling is negative as compared to positive field cooling. We believe such an enhancement in magnetic moment and magnetic coupling is likely directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom, similar to what has previously been reported in the literature. Future work will involve the linearly polarized X-ray absorption measurements to prove this hypothesis. This work represents a starting step toward the realization of magneto-electronic devices integrated with Si(100).

  19. Theoretical Predictions of Structural, Electronic, and Optical Properties of Dilute Bismide AlN1- x Bi x in Zinc-Blend Structures

    NASA Astrophysics Data System (ADS)

    Alaya, R.; Slama, S.; Hashassi, M.; Mbarki, M.; Rebey, A.; Alaya, S.

    2017-04-01

    We report the results of first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW + lo) method to explore the effects of alloying under the non-conventional AlN III-V compound with bismuth. We have calculated the structural and electronic properties of the binary compounds AlN and AlBi in the zinc blend structure. We have found a good agreement between our results and the experimental and theoretical results available for that binary compounds which may be a support for the results of the ternary alloys. For the AlNBi ternary alloys, we have found a rapid reduction of the energy gap by 1.31 eV/%Bi accompanied by a strong increase in the spin-orbit splitting energy (Δso) with increasing Bi composition. We have also shown that the Δso becomes greater than the energy gap for composition of Bi about 4.2% (Δso > E g). This result is significant due to the possibility of suppressing Auger recombination, which is expected to improve the high temperature performance and thermal stability of light emitting devices. Finally, we have calculated the variation of the optical properties of AlNBi compounds, such as dielectric function and refractive index versus Bi composition.

  20. Gallium-enhanced phase contrast in atom probe tomography of nanocrystalline and amorphous Al-Mn alloys.

    PubMed

    Ruan, Shiyun; Torres, Karen L; Thompson, Gregory B; Schuh, Christopher A

    2011-07-01

    Over a narrow range of composition, electrodeposited Al-Mn alloys transition from a nanocrystalline structure to an amorphous one, passing through an intermediate dual-phase nanocrystal/amorphous structure. Although the structural change is significant, the chemical difference between the phases is subtle. In this study, the solute distribution in these alloys is revealed by developing a method to enhance phase contrast in atom probe tomography (APT). Standard APT data analysis techniques show that Mn distributes uniformly in single phase (nanocrystalline or amorphous) specimens, and despite some slight deviations from randomness, standard methods reveal no convincing evidence of Mn segregation in dual-phase samples either. However, implanted Ga ions deposited during sample preparation by focused ion-beam milling are found to act as chemical markers that preferentially occupy the amorphous phase. This additional information permits more robust identification of the phases and measurement of their compositions. As a result, a weak partitioning tendency of Mn into the amorphous phase (about 2 at%) is discerned in these alloys.

  1. Site-sensitive energy transfer modes in Ca3Al2O6: Ce(3+)/Tb(3+)/Mn(2+) phosphors.

    PubMed

    Zhang, Jilin; He, Yani; Qiu, Zhongxian; Zhang, Weilu; Zhou, Wenli; Yu, Liping; Lian, Shixun

    2014-12-28

    Ce(3+)/Eu(2+), Tb(3+) and Mn(2+) co-doping in single-phase hosts is a common strategy to achieve white-light phosphors via energy transfer, which provides a high color rendering index (CRI) value and good color stability. However, not all hosts are suitable for white-light phosphors due to inefficient energy transfer. In this study, the site-sensitive energy transfer from different crystallographic sites of Ce(3+) to Tb(3+)/Mn(2+) in Ca3Al2O6 has been investigated in detail. The energy transfer from purplish-blue Ce(3+) to Tb(3+) is an electric dipole-dipole mode, and the calculated critical distance (Rc) suggests the existence of purplish-blue Ce(3+)-Tb(3+) clusters. No energy transfer is observed from purplish-blue Ce(3+) to Mn(2+). In co-doped phosphors based on greenish-blue Ce(3+), however, the radiative mode dominates the energy transfer from Ce(3+) to Tb(3+), and an electric dipole-quadrupole interaction is responsible for the energy transfer from Ce(3+) to Mn(2+). A detailed discussion on the site-sensitive energy transfer modes might provide a new aspect to discuss and understand the possibilities and mechanisms of energy transfer, according to certain crystallographic sites in a complex host with different cation sites, as well as provide a possible approach in searching for single-phase white-light-emitting phosphors.

  2. Internal energy transfer phenomenon and light-emission properties of γ-LiAlO2 phosphor doped with Mn2+

    NASA Astrophysics Data System (ADS)

    Wang, Bai-Bin; Chang, Chi-Fen; Yang, Wein-Duo

    2013-07-01

    γ-LiAlO2:Mn2+ phosphor was synthesized using the cellulose-citric acid sol-gel method, and its light emission and energy transfer properties were investigated. Excitation and emission spectrum analysis revealed a decrease in intensity of the spectrum as the amount of Mn2+ doping increased. Blasse's equation determined the maximum distance for energy transfer between Mn2+ ions as 4.3142 nm. Dexter's theory verifies that the mechanism of energy transfer between Mn2+ ions conforms to an electric dipole and electric quadrupole interaction.

  3. Magnetic properties of Mn1-xAl1-yNi alloys in the B2 (CsCl-type) structure

    NASA Astrophysics Data System (ADS)

    Paduani, C.; Schaf, J.; Ardisson, J. D.; Takeuchi, A. Y.

    2010-02-01

    In this work is investigated structural and magnetic properties of ferromagnetic Mn1-xAl1-yNi alloys in the κ phase which has a B2 (CsCl-type) structure. The Curie temperatures are above room temperature and decrease with the substitution of Ni for Mn. The magnetic measurements indicate the existence of ferrimagnetism originated from Mn atoms which carry unequal and opposite magnetic moments in different sublattices. A larger average magnetic moment is observed in the Ni-doped system, as compared to the Fe-system, which is due to the formation of larger moment on Mn atoms at the cube corners.

  4. Spectroscopic properties of oxygen vacancies in LaAlO>3mn>

    SciTech Connect

    Dicks, Oliver A.; Shluger, Alexander L.; Sushko, Peter V.; Littlewood, Peter B.

    2016-04-25

    Oxygen vacancies in LaAlO3 (LAO) play an important role in the formation of the two-dimensional electron gas observed at the LaAlO3/SrTiO3 interface and affect the performance of MOSFETs using LAO as a gate dielectric. However, their spectroscopic properties are still poorly understood, which hampers their experimental identification. Here we predict the absorption spectra and ESR parameters of oxygen vacancies in LAO using periodic and embedded cluster methods and density functional theory (DFT). The structure, charge distribution, and spectroscopic properties of the neutral (V 0 O) and charged (V + O and V 2+ O ) oxygen vacancies in cubic and rhombohedral LaAlO3 are investigated. The highest intensity optical transitions [calculated using time-dependent DFT (TDDFT)], from the oxygen vacancy states to the conduction-band states have onsets at 3.5 and 4.2 eV for V 0 O and 3.6 eV for V + O in rhombohedral LAO and 3.3 and 4.0 eV for V 0 O and 3.4 eV for V + O in cubic LAO, respectively. Also reported are the isotropic g value (2.004026) and hyperfine coupling constants of V + O , which are compared to the experimental data obtained using electron spin resonance (ESR) spectroscopy, and accurately predict both the position and the width (3 mT) of its ESR signature. These results may further facilitate the experimental identification of oxygen vacancies in LAO and help to establish their role at the LAO/STO interfaces and in nanodevices using LAO.

  5. Spectroscopic properties of oxygen vacancies in LaAlO>3mn>

    SciTech Connect

    Dicks, Oliver A.; Shluger, Alexander L.; Sushko, Peter V.; Littlewood, Peter B.

    2016-04-01

    Oxygen vacancies in LaAlO3 (LAO) play an important role in the formation of the 2-dimensional electron gas observed at the LaAlO3/SrTiO3 interface and affect the performance of MOSFETs using LAO as a gate dielectric. However, their spectroscopic properties are still poorly understood, which hampers their experimental identification. Here we predict the absorption spectra and ESR parameters of oxygen vacancies in LAO using periodic and embedded cluster models and Density Functional Theory (DFT). The structure, charge distribution, and spectroscopic properties of the neutral (V0O) and charged (V+O and V2+O ) oxygen vacancies in cubic and rhombohedral LaAlO3 are investigated. The highest intensity optical transitions (calculated using time dependent DFT (TDDFT)), from the oxygen vacancy states to the conduction band states have onsets at 3.5 and 4.2 eV for V0O and 3.6 eV for V+O in rhombohedral LAO and 3.3 and 4.0 eV for V 0O and 3.4 eV for V+O in cubic LAO, respectively. Also reported are the isotropic g-value (2.004026) and hyperfine coupling constants of V+O which are compared to the experimental data obtained using electron spin resonance (ESR) spectroscopy, and accurately predict both the position and the width (3 mT) of its ESR signature. These results may further facilitate the experimental identification of oxygen vacancies in LAO and help to establish their role at the LAO/STO interfaces and in nanodevices using LAO.

  6. First principles study on the structural, magnetic, electronic and optical properties of un-doped and La-doped BiFe0.75Mn0.125Ti0.125O3

    NASA Astrophysics Data System (ADS)

    Zhang, Ren; Chen, Wei; Gao, Ning; Zhu, Yiyi; Mao, Weiwei; Chu, Liang; Zhang, Jian; Yang, Jianping; Li, Xing'ao; Huang, Wei

    2016-10-01

    Based on the generalized gradient approximation (GGA), the structural, magnetic, electronic and optical properties of BiFe0.75Ti0.125Mn0.125O3 (TM) and Bi1 - yLayFe0.75Ti0.125Mn0.125O3 (y = 0.125, 0.25) (LTM) were researched by the first principles. Compared with the pure BiFeO3 (zero magnetic moment), the magnetic moment of TM gets improved greatly and the value computed here is ∼ 3μB, while La doping almost has no effect on that of TM. Ti and Mn co-doping converts the indirect band gap of BiFeO3 (2.20 eV) to a direct band gap of TM (0.95 eV). The bandwidth of TM is similar to that of LTM1 (1 La atom, y = 0.125) within the tolerance, but smaller than that of LTM2 (2 La atoms, y = 0.25). This is consistent with their gradually increased absorption edges to infrared region, and suggests that doping La into the B sites of TM makes it more potential application on photovoltaic. According to the results of reflectivity, (Ti, Mn)-codoped BiFeO3 is transparent, while LTM is nontransparent in the visible light region which indicates more potential valuable for visible-light-responsive devices. To gain some insight into the optical properties of the samples, three relationships have been discussed: (1) the reflectivity and energy loss function, (2) the extinction coefficient and the imaginary part of the dielectric function, and (3) the refractive index and the real part of the dielectric function.

  7. [Research on SCR denitrification of MnOx/Al2O3 modified by CeO2 and its mechanism at low temperature].

    PubMed

    Guo, Jing; Li, Cai-Ting; Lu, Pei; Cui, Hua-Fei; Peng, Dun-Liang; Wen, Qing-Bo

    2011-08-01

    The Al2O3,which has large specific surface area and is used as carrier,was prepared by sol-gel method in this study. Series catalysts of MnOx, CeO2 plus MnOx supported on Al2O3 by isometric impregnation method. The SCR denitrification experimental conditions were as follows: NH3 as reductive agent, certain gas velocity and suitable ratio of gas mixed was setup. Furthermore, the experiments of BET, XRD and SEM were also carried out respectively in order to obtain physicochemical properties of the prepared catalysts. The experimental results showed that the loading of active component and calcination temperature made a big difference to the catalysts' performance. With appropriate addition of CeO2, MnOx/Al2O3 exhibits better activity and stability. For MnOx/Al2O3, the catalytic activity on NO was greatly influenced by its loaded content, and 7% MnOx/Al2O3 showed superior catalytic activity among the MnOx/Al2O3. The addition of CeO2 could greatly improve the dispersibility of MnOx on the carrier and increase its catalytic activity. The 4% CeO2 addition was the optimum loaded mass precent. Forthermore, 550 degrees C is the best calcination temperature, as MnOx formed different crystalline phases with temperature, at the same time, the addition of CeO2 could affect MnOx crystalline phase. The catalytic mechanism of SCR on NO was also discussed.

  8. A single-component white-emitting CaSr2Al2O6:Ce3+, Li+, Mn2+ phosphor via energy transfer.

    PubMed

    Li, Yanyan; Shi, Yurong; Zhu, Ge; Wu, Quansheng; Li, Hao; Wang, Xicheng; Wang, Qian; Wang, Yuhua

    2014-07-21

    A series of single-component Ce(3+), Li(+), Mn(2+) ions codoped color-tunable CaSr2Al2O6 phosphors were synthesized by a high-temperature solid-state reaction, and the photoluminescence properties as well as the energy transfer mechanism from Ce(3+) to Mn(2+) ions have been investigated in detail. The Ce(3+) activated phosphors have strong absorption in the range of 250-420 nm and can give a blue emission centered at about 460 nm. When Mn(2+) ions are codoped, the emission of CaSr2Al2O6:Ce(3+), Li(+), Mn(2+) phosphors can be tuned from blue to red through adjusting the doping concentration of the Mn(2+) ions, under the irradiation of 358 nm. When the concentration of Mn(2+) is increased to 0.02, a warm-white light can be obtained with good CIE coordinates of (0.388, 0.323) and a low CCT of 3284 K. The energy transfer mechanism from the Ce(3+) to Mn(2+) ions is demonstrated to be a quadrupole-quadrupole interaction based on the analysis of the decay curves of the phosphors. The thermal quenching stability was also investigated. The results indicate that CaSr2Al2O6:Ce(3+), Li(+), Mn(2+) samples might have potential applications in w-LEDs.

  9. Catalytic oxidation of elemental mercury over the modified catalyst Mn/alpha-Al2O3 at lower temperatures.

    PubMed

    Li, Jianfeng; Yan, Naiqiang; Qu, Zan; Qiao, Shaohua; Yang, Shijian; Guo, Yongfu; Liu, Ping; Jia, Jinping

    2010-01-01

    In order to facilitate the removal of elemental mercury (Hg(0)) from coal-fired flue gas, catalytic oxidation of Hg(0) with manganese oxides supported on inert alumina (alpha-Al2O3) was investigated at lower temperatures (373-473 K). To improve the catalytic activity and the sulfur-tolerance of the catalysts at lower temperatures, several metal elements were employed as dopants to modify the catalyst of Mn/alpha-Al2O3. The best performance among the tested elements was achieved with molybdenum (Mo) as the dopant in the catalysts. It can work even better than the noble metal catalyst Pd/alpha-Al2O3. Additionally, the Mo doped catalyst displayed excellent sulfur-tolerance performance at lower temperatures, and the catalytic oxidation efficiency for Mo(0.03)-Mn/alpha-Al2O3 was over 95% in the presence of 500 ppm SO2 versus only about 48% for the unmodified catalyst. The apparent catalytic reaction rate constant increased by approximately 5.5 times at 423 K. In addition, the possible mechanisms involved in Hg(0) oxidation and the reaction with the Mo modified catalyst have been discussed.

  10. Electromagnetic and microwave absorbing properties of the composites containing flaky FeSiAl powders mixed with MnO2 in 1-18 GHz

    NASA Astrophysics Data System (ADS)

    Xu, Haibing; Bie, Shaowei; Jiang, Jianjun; Yuan, Wei; Chen, Qian; Xu, Yongshun

    2016-03-01

    The flaky FeSiAl/ irregular shaped MnO2 composite with the different mass ratios were prepared by using a two-roll mixer and a vulcanizing machine. The morphologies of the composite absorbers were characterized by a scanning electron microscope. The microwave electromagnetic properties of the composites were measured using a vector network analyzer in the range of 1-18 GHz. The effect of the mass ratio of FeSiAl/MnO2 on the microwave loss properties of the composites was investigated. The results show that the reflection loss (RL) values exceeding -20 dB from 3.5 to 16.5 GHz can be obtained for the flaky FeSiAl/MnO2 mass ratio of 1:1 from 1.5 mm to 5 mm. In addition, the FeSiAl/MnO2 composite with the FeSiAl/MnO2 mass ratio of 7:3 has -10 dB bandwidth of 6.6 GHz (from 11.4-18 GHz) with a thickness of 1.5 mm. It is found that the flaky FeSiAl/MnO2 composites can be potential microwave absorption materials.

  11. Enhancement of Curie temperature and transition temperature range induced by Al doping in Mn1-xAlxCoGe

    NASA Astrophysics Data System (ADS)

    Si, Xiaodong; Liu, Yongsheng; Lei, Wei; Xu, Juan; Du, Wenlong; Lin, Jia; Zhou, Tao; Lu, Xiaofei

    2016-12-01

    Mn1-xAlxCoGe alloys with a second order transition were produced by arc-melting method. The substitution of Mn by Al increased the Curie temperature (TC) from 260.5 K to 300.8 K, the magnetic entropy change (|ΔSM|) decreased from 3.78 J·Kg-1K-1 to 2.35 J·Kg-1K-1 under a field change of Δμ0H=5 T. In addition, the |ΔSM| well linearly depends on the H2/3 around TC. Furthermore, the relative cooling power (RCP) can reach 242.3 J·Kg-1 with a large full width at half maximum of |ΔSM| (75.5 K) for x=0.02. The decrease of |ΔSM| is explained by the corresponding monotonical decrease of magnetic moment per formula unit.

  12. Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

    NASA Astrophysics Data System (ADS)

    Li, Meng-long; Wang, Fu-ming; Li, Chang-rong; Yang, Zhan-bing; Meng, Qing-yong; Tao, Su-fen

    2015-06-01

    The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s-1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al (Als), while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s-1 and 0.43°C·s-1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

  13. The role of tree uprooting dynamics on the dynamics of Fe (Mn, Al and Si) forms in different forest soils

    NASA Astrophysics Data System (ADS)

    Tejnecký, V.; Samonil, P.; Boruvka, L.; Nikodem, A.; Drabek, O.; Valtera, M.

    2013-12-01

    Tree uprooting dynamics plays an important role in the development of forest ecosystems. This process causes bioturbation of soils and creates new microenvironments which consist of pits and mounds. These microtopographical forms could persist for some thousands of years. Pits and mounds undergo different pedogenesis in comparison to adjacent undisturbed soils. The stage of pedogenesis can be assessed according to the results of fractionation of Fe and also partially Mn, Al and Si. The main aim of this contribution is to assess the fractionation of Fe, Mn, Al and Si for three different soil regions. Soil samples were collected at three localities occurred along hypothetical gradient of soil weathering and leaching processes: The first was a (spruce)-fir-beech natural forest in the Razula region. The second location is the same type of natural forest in Zofin; however it has contrasting lithology. Both these natural forests are located in the Czech Republic (CZ). The third forest was a northern hardwood forest in Upper Peninsula, Michigan, USA. The prevailing soil types - Haplic Cambisols have formed on flysch parent materials in the Razula reserve; Entic Podzols have developed on granite residuum at the Zofin reserve, and Albic Podzols occurred in outwash parent materials at the Michigan sites (Šamonil et al., in press). In total 790 soil samples were analysed. These samples were collected from 5 depths (0-10, 15, 30, 50 and 100 cm) within the pit, mound and control, currently undisturbed position. For each sample, content of Fe (and Mn, Al, Si) forms: exchangeable, crystalline, and amorphous together with organically complexed Fe were determined. We generally observed an increased content of Fe soil forms in the pits of studied treethrows. The content of Fe forms increased along depth gradient at the disturbed sites. However, exchangeable Fe was most abundant in the 0-10cm layer which corresponds to the A horizon. Naturally, if present, the E horizon exhibited

  14. Effect of precipitate structure on hot deformation of Al-Mg-Mn alloys

    SciTech Connect

    Vetrano, J.S.; Lavender, C.A.; Smith, M.T.; Bruemmer, S.M.

    1993-10-01

    The size and nature of precipitates have strong effects on microstructural evolution from the cold-worked state through the course of deformation at high temperatures. Through selected heat treatments and minor alloying alterations the precipitate structure of AA5083 has been manipulated. Minor additions of Zr have been used to create fine (50 to 100 nm) precipitates. The number and size distribution of medium-sized (<1 {mu}m) Mn-rich precipitates were modified by increasing the Mn concentration in conjunction with several heat treatment paths. Effects of these precipitates on the dislocation structure, recrystallization behavior and grain growth during high-temperature deformation have been elucidated.

  15. Microstructural evolution and hardness of TiAl3 and TiAl2 phases on Ti-45Al-2Nb-2Mn-1B by plasma pack aluminizing

    NASA Astrophysics Data System (ADS)

    Rastkar, Ahmad Reza; Parseh, Pejman; Darvishnia, Naser; Hadavi, Seyed Mohammad Mehdi

    2013-07-01

    The surface of Ti-45Al-2Nb-2Mn-1B (at%) titanium aluminide was aluminized in a so called plasma pack aluminizing by packing the substrate in a mixture of aluminum copper alloy and application of an 18 kHz pulsed DC glow discharge plasma in argon gas. The plasma energy provided the necessary heat for melting and mutual diffusion of titanium and aluminum at the surface of titanium aluminide alloy in less than 1 h without any further heat treatment. The microstructure and hardness of different phases on the surface of Ti-45Al-2Nb-2Mn-1B alloy were characterized using optical and electron microscopy, X-ray diffraction (XRD), EDX analysis and Vickers microhardness tests. The thickness of the surface layers was up to 300 μm. The surface layers consisted mainly of TiAl3 and TiAl2 compounds. These compounds appeared in blocky and round shapes with different micrometer sizes in a matrix of aluminum alloy phase. The hardness of the surface layers was up to 600 HV0.1, which was higher than that of Ti-45Al-2Nb-2Mn-1B substrate (330 HV0.1).

  16. Revisiting the ground state of CoAl2O4 : Comparison to the conventional antiferromagnet MnAl2O4

    DOE PAGES

    MacDougall, Gregory J.; Aczel, Adam A.; Su, Yixi; ...

    2016-11-17

    The A-site spinel material CoAl2O4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or “spin-spiral-liquid” ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a “kinetically inhibited” antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This study provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited order is unaffectedmore » by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T=2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl2O4, which acts as an unfrustrated analog to CoAl2O4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at TN=39 K. Direct comparison between the two compounds indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. Finally, the higher level of cation inversion in the MnAl2O4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.« less

  17. Revisiting the ground state of CoAl2O4 : Comparison to the conventional antiferromagnet MnAl2O4

    NASA Astrophysics Data System (ADS)

    MacDougall, G. J.; Aczel, A. A.; Su, Yixi; Schweika, W.; Faulhaber, E.; Schneidewind, A.; Christianson, A. D.; Zarestky, J. L.; Zhou, H. D.; Mandrus, D.; Nagler, S. E.

    2016-11-01

    The A -site spinel material CoAl2O4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or "spin-spiral-liquid" ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a "kinetically inhibited" antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This paper provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited order is unaffected by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T =2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl2O4 , which acts as an unfrustrated analog to CoAl2O4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at TN=39 K. Direct comparison between the two compounds indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. The higher level of cation inversion in the MnAl2O4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.

  18. Characterization of phase development in non-isothermally annealed mould-cast and heat-treated Al-Mn-Sc-Zr alloys

    SciTech Connect

    Vlach, M. Stulikova, I.; Smola, B.; Zaludova, N.

    2010-12-15

    The effect of Mn addition on microstructure and mechanical properties during isochronal annealing in the temperature range of 20 deg. C - 570 deg. C of the mould-cast and heat-treated Al-Sc-Zr alloys with a various content of Mn and Zr was studied. The electrical resistometry together with the microhardness (HV0.3) measurements were compared to microstructure development. The microstructure development was examined by scanning electron microscopy, transmission electron microscopy and electron diffraction. Relative resistivity changes and the microhardness of the mould-cast and heat-treated Al-Mn-Sc-Zr alloys exhibit similar dependence on annealing temperature. Precipitation of the Al{sub 3}Sc particles is responsible for the peak microhardness in all these alloys. The microhardness decrease is slightly delayed during the isochronal annealing and during the high temperature heat treatment in the mould-cast alloy with the higher Zr-content due to a higher oversaturation of Zr. The decomposition sequence of the oversaturated solid solution of the studied Al-Mn-Sc-Zr alloys is compatible with the recently published decomposition sequence of the Al-Sc-Zr system and also with the formation of Mn,Fe-containing particles. It seems very probable that the addition of Mn does not influence the decomposition of solid solution of the ternary Al-Sc-Zr system. - Research Highlights: {yields} Al{sub 3}Sc particles are responsible for the peak microhardness in all the studied alloys. {yields} The microhardness decrease is delayed in the alloy with the higher Zr-content. {yields} The peak hardening of the heat-treated alloys is shifted to higher temperatures. {yields} Mn does not influence the decomposition sequence of the Al-Sc-Zr system.

  19. The effect of Mn and B on the magnetic and structural properties of nanostructured Fe60Al40 alloys produced by mechanical alloying.

    PubMed

    Rico, M M; Alcázar, G A Pérez; Zamora, L E; González, C; Greneche, J M

    2008-06-01

    The effect of Mn and B on the magnetic and structural properties of nanostructured samples of the Fe60Al40 system, prepared by mechanical alloying, was studied by 57Fe Mössbauer spectrometry, X-ray diffraction and magnetic measurements. In the case of the Fe(60-x)Mn(x)Al40 system, 24 h milling time is required to achieve the BCC ternary phase. Different magnetic structures are observed according to the temperature and the Mn content for alloys milled during 48 h: ferromagnetic, antiferromagnetic, spin-glass, reentrant spin-glass and superparamagnetic behavior. They result from the bond randomness behaviour induced by the atomic disorder introduced by the MA process and from the competitive interactions of the Fe-Fe ferromagnetic interactions and the Mn-Mn and Fe-Mn antiferromagnetic interactions and finally the presence of Al atoms acting as dilutors. When B is added in the Fe60Al40 alloy and milled for 12 and 24 hours, two crystalline phases were found: a prevailing FeAl BCC phase and a Fe2B phase type. In addition, one observes an additional contribution attributed to grain boundaries which increases when both milling time and boron composition increase. Finally Mn and B were added to samples of the Fe60Al40 system prepared by mechanical alloying during 12 and 24 hours. Mn content was fixed to 10 at.% and B content varied between 0 and 20 at.%, substituting Al. X-ray patterns show two crystalline phases, the ternary FeMnAl BCC phase, and a (Fe,Mn)2B phase type. The relative proportion of the last phase increases when the B content increases, in addition to changes of the grain size and the lattice parameter. Such behavior was observed for both milling periods. On the other hand, the magnetic hyperfine field distributions show that both phases exhibit chemical disorder, and that the contribution attributed to the grain boundaries is less important when the B content increases. Coercive field values of about 10(2) Oe slightly increase with boron content

  20. Laboratory study on the adsorption of Mn(2+) on suspended and deposited amorphous Al(OH)(3) in drinking water distribution systems.

    PubMed

    Wang, Wendong; Zhang, Xiaoni; Wang, Hongping; Wang, Xiaochang; Zhou, Lichuan; Liu, Rui; Liang, Yuting

    2012-09-01

    Manganese (II) is commonly present in drinking water. This paper mainly focuses on the adsorption of manganese on suspended and deposited amorphous Al(OH)(3) solids. The effects of water flow rate and water quality parameters, including solution pH and the concentrations of Mn(2+), humic acid, and co-existing cations on adsorption were investigated. It was found that chemical adsorption mainly took place in drinking water with pHs above 7.5; suspended Al(OH)(3) showed strong adsorption capacity for Mn(2+). When the total Mn(2+) input was 3 mg/L, 1.0 g solid could accumulate approximately 24.0 mg of Mn(2+) at 15 °C. In drinking water with pHs below 7.5, because of H(+) inhibition, active reaction sites on amorphous Al(OH)(3) surface were much less. The adsorption of Mn(2+) on Al(OH)(3) changed gradually from chemical coordination to physical adsorption. In drinking water with high concentrations of Ca(2+), Mg(2+), Fe(3+), and HA, the removal of Mn(2+) was enhanced due to the effects of co-precipitation and adsorption. In solution with 1.0 mg/L HA, the residual concentration of Mn(2+) was below 0.005 mg/L, much lower than the limit value required by the Chinese Standard for Drinking Water Quality. Unlike suspended Al(OH)(3), deposited Al(OH)(3) had a much lower adsorption capacity of 0.85 mg/g, and the variation in flow rate and major water quality parameters had little effect on it. Improved managements of water age, pipe flushing and mechanical cleaning were suggested to control residual Mn(2+).

  1. Half-metallic ferromagnetism in Mn-doped zigzag AlN nanoribbon from first-principles

    NASA Astrophysics Data System (ADS)

    Aghili, S.; Beiranvand, R.; Elahi, S. M.; Abolhasani, M. R.

    2016-12-01

    Based on first-principles calculations, we investigate the effect of Mn impurity on the electronic and magnetic properties of H-terminated zigzag AlN nanoribbons (ZAlNNRs), using the band structure results obtained through the full potential linearized augmented plane wave method within the density functional theory. The calculated results show that the H-terminated ZAlNNR is semiconducting and non magnetic material with a direct band gap of about 2.78 eV. Density of state analyses shows that the top of the valence band is mainly contributed by N atoms, while just beside the conduction band the whole DOS is mainly contributed by Al atoms. The main result is a transition from non-magnetic semiconducting character to half-metallic features upon doping. The Mn-doped ZAlNNR shows complete (100%) spin polarization at the Fermi level and the charge transport is totally originated from Manganese spin up electrons in the nanoribbon. These results propose potential application for the development of AlN nanoribbon-based in magneto-electronic devices.

  2. Disorder - driven phase transition in La{sub 0.37}Bi{sub 0.15}Sm{sub 0.15}Ca{sub 0.33}MnO{sub 3}

    SciTech Connect

    Ade, Ramesh; Singh, R.

    2015-06-24

    We report the effect of disorder on the properties of La{sub 0.37}Bi{sub 0.15}Sm{sub 0.15}Ca{sub 0.33}MnO{sub 3} manganite synthesized by sol – gel method. The critical properties were investigated through various techniques such as modified - Arrott plot, Kouvel - Fisher method and critical isotherm analysis. The sample show second- order phase transition near critical point. The decrease in magnetization (M), Curie temperature (T{sub C}), evolution of spin or cluster glass behavior and the nature of phase transition compared to first - order transition in La{sub 0.67}Ca{sub 0.33}MnO{sub 3} are ascribed to the disorder caused by the size mismatch of the A-site cations with Bi and Sm doping at La- site.

  3. Performance of Al-0.5 Mg-0.02 Ga-0.1 Sn-0.5 Mn as anode for Al-air battery in NaCl solutions

    NASA Astrophysics Data System (ADS)

    Ma, Jingling; Wen, Jiuba; Gao, Junwei; Li, Quanan

    2014-05-01

    In this research, metal-air battery based on Al, Zn, Al-0.5 Mg-0.02 Ga-0.1 Sn and Al-0.5 Mg-0.02 Ga-0.1 Sn-0.5 Mn (wt%) is prepared and the battery performance is investigated by constant current discharge test in 2 mol L-1 NaCl solutions. The characteristics of the anodes after discharge are investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM). The corrosion behavior of the anodes is studied by self-corrosion rate measurement and potentiodynamic polarization measurement. The results show that Al-Mg-Ga-Sn-Mn is more active than Al, Zn and Al-Mg-Ga-Sn anodes. The self-corrosion rate is found to be in the order: Al < Al-Mg-Ga-Sn-Mn < Al-Mg-Ga-Sn < Zn. It has been observed that the Al-air battery based on Al-Mg-Ga-Sn-Mn offers higher operating voltage and anodic utilization than those with others. SEM and EIS results of the alloy are in good agreement with corrosion characteristics.

  4. Comparison of the Effect of Individual and Combined Zr and Mn Additions on the Fracture Behavior of Al-Cu-Li Alloy AA2198 Rolled Sheet

    NASA Astrophysics Data System (ADS)

    Tsivoulas, Dimitrios; Prangnell, Philip B.

    2013-11-01

    The effect of individual and combined addition of dispersoid-forming alloying elements Zr and Mn on the fracture behavior of the Al-Cu-Li alloy 2198 has been investigated by the Kahn tear test. Overall, the standard baseline 2198 alloy containing only Zr exhibited the best performance, while the alloy with the combined presence of Zr and Mn was slightly inferior. The lowest properties were seen for a Zr-free 2198-0.4Mn alloy variant. In the T351 temper fracture initiated at coarse constituent particles that formed large cavities and microvoid sheets linked the initial sites of void growth. In the Mn-containing alloys microvoids clearly nucleated at the coarser Al20Cu2Mn3 dispersoids within the microstructure, while this was not identifiable for the finer coherent Al3Zr dispersoids. However, this difference in the mechanism of cavity linkage had little effect on the overall toughness of the materials, which was more closely related to the effect of Mn and Zr on the level of recrystallization. Extended artificial aging promoted grain boundary decohesion due to the precipitation of high densities of T1 particles on GBs and favored a cleavage fracture mode. Particle decohesive fracture was also promoted by T1 precipitation on the Mn dispersoids.

  5. Disorder and complexity in the atomic structure of the perfect icosahedral alloy of Al-Pd-Mn

    SciTech Connect

    de Boissieu, M.; Stephens, P. ); Boudard, M.; Janot, C. ); Chapman, D.L. ); Audier, M. )

    1994-05-30

    The atomic structure of the perfect Al-Pd-Mn icosahedral phase has been studied on single grain samples. Using anomalous x-ray diffraction close to the Pd edge, the partial structure factor [ital F][sub Pd] has been extracted. In the six-dimensional description of its structure, we find that the atomic surface cannot be described by an object with a sharp boundary. A phason Debye-Waller term has been introduced to fully account for the data. It is interpreted as resulting from random phason disorder and nonsphericity of the atomic surfaces.

  6. Photo-luminescent properties and synthesis of Ca3Al4ZnO10:Mn4+ deep red-emitting phosphor

    NASA Astrophysics Data System (ADS)

    Cao, Renping; Zhang, Jinlong; Wang, Wudi; Chen, Ting; Gou, Qingdong; Wen, Yufeng; Xiao, Fen; Luo, Zhiyang

    2017-04-01

    Novel deep red-emitting Ca3Al4ZnO10:Mn4+ (CAZO:Mn4+) phosphor is synthesized by high-temperature solid-state reaction method in air. The crystal structures and optical characterizations of the phosphors are described. X-ray diffraction patterns indicate that all samples are a pure phase. CAZO:Mn4+ phosphor with excitation 330 and 465 nm exhibits strong deep red emission in the range of 650-790 nm. CAZO:Mn4+ phosphor can be efficiently excited by near-ultraviolet and blue light from 300 to 500 nm. The optimal Mn4+ ion concentration in CAZO:Mn4+ phosphor is ∼0.6 mol%. Lifetimes of CAZO:xMn4+ (0.3 ≤ x ≤ 1.8 mol%) phosphors decrease from 1.95 to 1.56 ms with increasing Mn4+ ion concentration in the range of 0.3-1.8 mol%. The paper content is help to develop other Mn4+ ion doped luminescence materials.

  7. Intriguing photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates.

    PubMed

    Sung, Kil Dong; Lee, Tae Kwon; Jung, Jong Hoon

    2015-01-01

    To date, electric fields have been widely used to control the magnetic properties of BiFeO3-based antiferromagnet/ferromagnet heterostructures through application of an exchange bias. To extend the applicability of exchange bias, however, an alternative mechanism to electric fields is required. Here, we report the photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on an SrTiO3 substrate. Through an ex situ pulsed laser deposition technique, we successfully synthesized epitaxial BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates. By measuring magnetoresistance under light illumination, we investigated the effect of light illumination on resistance, exchange bias, and coercive field in BiFeO3/La2/3Sr1/3MnO3 thin films. After illumination of red and blue lights, the exchange bias was sharply reduced compared to that measured in the dark. With increasing light intensity, the exchange bias under red and blue lights initially decreased to zero and then appeared again. It is possible to reasonably explain these behaviors by considering photo-injection from SrTiO3 and the photo-conductivity of La2/3Sr1/3MnO3. This study may provide a fundamental understanding of the mechanism underlying photo-controlled exchange bias, which is significant for the development of new functional spintronic devices.

  8. Compression, bend, and tension studies on forged Al67Ti25Cr8 and Al66Ti25Mn(g) L1(2) compounds

    NASA Technical Reports Server (NTRS)

    Kumar, K. S.; Brown, S. A.; Whittenberger, J. D.

    1991-01-01

    Cast, homogenized, and isothermally forged aluminum-rich L1(2) compounds Al67Ti25Cr8 and Al66Ti25Mn(g) were tested in compression as a function of temperature and as a function of strain rate at elevated temperatures (1000 K and 1100 K). Three-point bend specimens were tested as a function of temperature in the range 300 K to 873 K. Strain gages glued on the tensile side of the ambient and 473 K specimens enabled direct strain measurements. A number of 'buttonhead' tensile specimens were electro-discharge machined, fine polished, and tested between ambient and 1073 K for yield strength and ductility as a function of temperature. Scanning electron microscope (SEM) examination of fracture surfaces from both the bend and tensile specimens revealed a gradual transition from transgranular cleavage to intergranular failure with increasing temperature.

  9. Structure and physical properties of ternary W 5Si 3-type antimonides and bismuthides Zr 5M1-xPn 2+x ( M=Cr, Mn; Pn=Sb, Bi)

    NASA Astrophysics Data System (ADS)

    Tkachuk, Andriy V.; Mar, Arthur

    2004-11-01

    Four new ternary compounds Zr 5M1-xPn 2+x ( M=Cr, Mn; Pn=Sb, Bi) were synthesized by arc-melting and annealing at 800 °C. They crystallize in the tetragonal W 5Si 3-type structure. The crystal structure of Zr 5Cr 0.49(2)Sb 2.51(2) was refined from powder X-ray diffraction data by the Rietveld method (Pearson symbol tI32, tetragonal, space group I4/ mcm, Z=4, a=11.1027(6) Å, c=5.5600(3) Å). Four-probe electrical resistivity measurements on sintered polycrystalline samples indicated metallic behavior. Magnetic susceptibility measurements between 2 and 300 K revealed temperature-independent Pauli paramagnetism for Zr 5Cr 1-xSb 2+x and Zr 5Cr 1-xBi 2+x, but a strong temperature dependence for Zr 5Mn 1-xSb 2+x and Zr 5Mn 1-xBi 2+x which was fit to the Curie-Weiss law for the latter with θ=-11.3 K and μeff=1.81(1) μ. Band structure calculations for Zr 5Cr 0.5Sb 2.5 support a structural model in which Cr and Sb atoms alternate within the chain of interstitial sites formed at the centers of square antiprismatic Zr 8 clusters.

  10. Strain-tuned enhancement of ferromagnetic TC to 176 K in Sm-doped BiMnO3 thin films and determination of magnetic phase diagram

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Kleibeuker, Josée E.; MacManus-Driscoll, Judith L.

    2017-03-01

    BiMnO3 is a promising multiferroic material but it’s ferromagnetic TC is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (TC) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO3 thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak TC of up to 176 K, more than 70 K higher than for bulk BiMnO3, was achieved through precise strain tuning. The TC was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling.

  11. Strain-tuned enhancement of ferromagnetic TC to 176 K in Sm-doped BiMnO3 thin films and determination of magnetic phase diagram

    PubMed Central

    Choi, Eun-Mi; Kleibeuker, Josée E.; MacManus-Driscoll, Judith L.

    2017-01-01

    BiMnO3 is a promising multiferroic material but it’s ferromagnetic TC is well below room temperature and the magnetic phase diagram is unknown. In this work, the relationship between magnetic transition temperature (TC) and the substrate induced (pseudo-) tetragonal distortion (ratio of out-of-plane to in-plane lattice parameters, c/a) in BiMnO3 thin films, lightly doped to optimize lattice dimensions, was determined. For c/a > 0.99, hidden antiferromagnetism was revealed and the magnetisation versus temperature curves showed a tail behaviour, whereas for c/a < 0.99 clear ferromagnetism was observed. A peak TC of up to 176 K, more than 70 K higher than for bulk BiMnO3, was achieved through precise strain tuning. The TC was maximised for strong tensile in-plane strain which produced weak octahedral rotations in the out-of-plane direction, an orthorhombic-like structure, and strong ferromagnetic coupling. PMID:28256606

  12. Experimental determination of coexisting iron titanium oxides in the systems FeTiAlO, FeTiAlMgO, FeTiAlMnO, and FeTiAlMgMnO at 800 and 900°C, 1 4 kbar, and relatively high oxygen fugacity

    NASA Astrophysics Data System (ADS)

    Evans, Bernard W.; Scaillet, Bruno; Kuehner, Scott M.

    2006-08-01

    A synthetic, low-melting rhyolite composition containing TiO2 and iron oxide, with further separate additions of MgO, MnO, and MgO + MnO, was used in hydrothermal experiments to crystallize Ilm-Hem and Usp-Mt solid solutions at 800 and 900°C under redox conditions slightly below nickel nickel oxide (NNO) to ≈ 3 log_{10} f_{{{text{O}}2}} units above the NNO oxygen buffer. These experiments provide calibration of the FeTi-oxide thermometer + oxygen barometer at conditions of temperature and oxygen fugacity poorly covered by previous equilibrium experiments. Isotherms for our data in Roozeboom diagrams of projected %usp vs. %ilm show a change in slope at ≈ 60% ilm, consistent with the second-order transition from FeTi-ordered Ilm to FeTi-disordered Ilm-Hem. This feature of the system accounts for some, but not all, of the differences from earlier thermodynamic calibrations of the thermobarometer. In rhyolite containing 1.0 wt.% MgO, 0.8 wt.% MnO, or MgO + MnO, Usp-Mt crystallized with up to 14% of aluminate components, and Ilm-Hem crystallized with up to 13% geikielite component and 17% pyrophanite component. Relative to the FeTiAlO system, these components displace the ferrite components in Usp-Mt, and the hematite component in Ilm-Hem. As a result, projected contents of ulvöspinel and ilmenite are increased. These changes are attributed to increased non-ideality along joins from end-member hematite and magnetite to their respective Mg- and Mn-bearing titanate and aluminate end-members. The compositional shifts are most pronounced in Ilm-Hem in the range Ilm50 80, a solvus region where the chemical potentials of the hematite and ilmenite components are nearly independent of composition. The solvus gap widens with addition of Mg and even further with Mn. The Bacon Hirschmann correlation of Mg/Mn in Usp-Mt and coexisting Ilm-Hem is displaced toward increasing Mg/Mn in ilmenite with passage from ordered ilmenite to disordered hematite. Orthopyroxene and biotite

  13. In situ synchrotron study of liquid phase separation process in Al-10 wt.% Bi immiscible alloys by radiography and small angle X-ray scattering

    NASA Astrophysics Data System (ADS)

    Lu, W. Q.; Zhang, S. G.; Li, J. G.

    2016-03-01

    Liquid phase separation process of immiscible alloys has been repeatedly tuned to create special structure for developing materials with unique properties. However, the fundamental understanding of the liquid phase separation process is still under debate due to the characteristics of immiscible alloys in opacity and high temperature environment of alloy melt. Here, the liquid phase separation process in solidifying Al-Bi immiscible alloys was investigated by synchrotron radiography and small angle X-ray scattering. We provide the first direct evidence of surface segregation prior to liquid decomposition and present that the time dependence on the number of Bi droplets follows Logistic curve. The liquid decomposition results from a nucleation and growth process rather than spinodal decomposition mechanism because of the positive deviation from Porod's law. We also found that the nanometer-sized Bi-rich droplets in Al matrix melt present mass fractal characteristics.

  14. Achieving superwide-color-gamut display by using narrow-band green-emitting γ-AlON:Mn,Mg phosphor

    NASA Astrophysics Data System (ADS)

    Yoshimura, Kenichi; Fukunaga, Hiroshi; Izumi, Makoto; Takahashi, Kohsei; Xie, Rong-Jun; Hirosaki, Naoto

    2017-04-01

    The display backlight generated using sharp β-sialon:Eu (green) and K2SiF6:Mn (red) phosphors shows a very wide color gamut that mostly covers the whole National Television System Committee (NTSC) triangle. In this work, an alternative green phosphor is investigated to further improve the display color gamut. γ-AlON:Mn,Mg is a green phosphor that shows a shorter and narrower emission spectrum than sharp β-silaon:Eu. The display color gamut in the blue-green region is thus widened greatly by substituting γ-AlON:Mn,Mg for sharp β-sialon:Eu. The color gamut of displays with γ-AlON:Mn,Mg and K2SiF6:Mn exceeds 100% of the NTSC standard both in the CIE 1931 and the CIE 1976 color spaces. Furthermore, the white LEDs with γ-AlON:Mn,Mg have excellent stability that is comparable to those of LEDs with sharp β-sialon:Eu.

  15. Friction-Stir Welding - Heavy Inclusions in Bi-metallic welds of Al 2219/2195

    NASA Technical Reports Server (NTRS)

    Rietz, Ward W., Jr.

    2008-01-01

    Heavy Inclusions (HI) were detected for the first time by radiographic examination in aluminum alloy 2219forging/2195plate (advancing/retreating side) Friction Sir Welds (FSW) for the Space Shuttle External Tank (ET) Program. Radiographic HI indications appear as either small (approx.0.005"-0.025") individual particles or clusters of small particles. Initial work was performed to verify that the HI was not foreign material or caused by FSW pin tool debris. That and subsequent elemental analysis determined that the HI were large agglomerations of Al2Cu (theta phase), which is the strengthening precipitate in Al2219. A literature search on that subject determined that the agglomeration of phase has also been found in Al2219 bead on plate FSW [Ref. 1]. Since this was detected in ET space flight hardware, an investigative study of the effect of agglomerated theta phase particles in FSW Al2219f/2195p was performed. Numerous panels of various lengths were welded per ET weld procedures and radiographically inspected to determine if any HI was detected. Areas that had HI were sampled for room temperature and cyclic cryogenic (-423F) tensile testing and determined no significant adverse affect on mechanical properties when compared to test specimens without HI and historical data. Fracture surface examination using the Scanning Electron Microscope (SEM) revealed smaller phase agglomerations undetectable by radiographic inspection dispersed throughout the Al2219f/2195p FSW. This indicates that phase agglomeration is inherent to the Al2219f/2195p FSW process and only rarely creates agglomerations large enough to be detected by radiography. HI has not been observed in FSW of plate to plate material for either Al2219 or AL2195.

  16. Ferromagnetic-Antiferromagnetic Coupling by Distortion of Fe/Mn Oxygen Octahedrons in (BiFeO3 )m (La0.7 Sr0.3 MnO3 )n Superlattices.

    PubMed

    Xiong, Jie; Lei, Tianyu; Chu, Junwei; Yang, Chao; Wei, Jiake; Zhuo, Mujin; Choi, Eun-Mi; Tao, Bowan; Zhang, Wanli; Wang, Yongqiang; Li, Yanrong

    2017-03-10

    Interface enhanced magnetism attracts much attention due to its potential use in exploring novel structure devices. Nevertheless, the magnetic behavior at interfaces has not been quantitatively determined. In this study, abnormal magnetic moment reduction is observed in La0.7 Sr0.3 MnO3 (LSMO)/BiFeO3 (BFO) superlattices, which is induced by ferromagnetic (FM)/antiferromagnetic (AFM) coupling in the interface. With reduced repetition of the superlattice's unit cell [(LSMO)n /(BFO)n ]60/n (n = 1, 2, 5, 10) on a SrTiO3 substrate, magnetic moment reduction from 25.5 emu cc(-1) ([(LSMO)10 /(BFO)10 ]6 ) to 1.5 emu cc(-1) ([(LSMO)1 /(BFO)1 ]60 ) is obtained. Ab initio simulations show that due to the different magnetic domain formation energies, the magnetic moment orientation tends to be paramagnetic in the FM/AFM interface. The work focuses on the magnetic domain formation energy and provides a pathway to construct artificial heterostructures that can be an effective way to tune the magnetic moment orientation and control the magnetization of ultrathin films.

  17. Relationship Between Sulfide Capacity and Structure of MnO-SiO2-Al2O3-Ce2O3 System

    NASA Astrophysics Data System (ADS)

    Jeong, Se Ji; Kim, Tae Sung; Park, Joo Hyun

    2017-02-01

    Sulfide capacity of the MnO-SiO2-Al2O3-Ce2O3 system was measured at 1873 K (1600 °C), and the structural analysis was carried out using micro-Raman spectroscopy to understand the role of Ce2O3 in the sulfur dissolution behavior. Sulfide capacity of the basic melts (MnO/SiO2 = 2.2(±0.14)) decreased with increasing content of Ce2O3 to approx. 4 mol pct, beyond which it increased. Sulfide capacity continuously decreased in the less basic system (MnO/SiO2 = 1.0(±0.15)), whereas it was hardly affected by Ce2O3 in the relatively acidic composition (MnO/SiO2 = 0.3(±0.05)). There was a significant increase in the intensity of Raman band at 600 cm-1 by Ce2O3 addition in high MnO/SiO2 (=2.2) system, which originated from the transition from [(Al,Mn0.5)O4]-tetrahedron to [(Al,Ce)O6]-octahedron due to strong attraction between Al2O3 and Ce2O3. Combining thermodynamic and structural information, the effect of Ce2O3 on the sulfide capacity of Mn-aluminosilicate melts can be explained by the following factors: (1) Activity of MnO in the melts decreased by addition of Ce2O3; (2) Free oxygen was consumed in the structure modification from [(Al,Mn0.5)O4] to [(Al,Ce)O6] unit by addition of Ce2O3; and 3) When the Ce3+ content was greater than critical value (approx. 4 mol pct) in high MnO/SiO2 (=2.54) melts, excess Ce3+ and Mn2+ ions competitively reacted with S2- ions, resulting in an increase of sulfide capacity.

  18. Carbides in iron-rich Fe-Mn-Cr-Mo-Al-Si-C systems

    NASA Technical Reports Server (NTRS)

    Lemkey, F. D.; Gupta, H.; Nowotny, H.; Wayne, S. F.

    1984-01-01

    The optimization of high carbon iron-base superalloy properties with duplex microstructure gamma + M7C3 carbide requires analysis in the context of a seven-component system. Data are first provided here for the Fe-Mn-Cr-Mo-C quinary system, at 30 at. pct carbon. A characterization of competing carbides, according to a pseudoternary phase diagram at 35 wt pct iron, is made from isothermal sections. It is noted that while M7C3 and M3C carbides' occurrences are respectively favored at the Cr and Mn corners, the M2C carbide and molybdenum cementite are predominant with increasing amounts of Mo. Lattice parameters are reported for the various carbides.

  19. Investigation of the Enthalpy/Entropy Variation and Structure of Cu-Al-Mn-Fe Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Canbay, C. Aksu; Gudeloglu, S.; Genc, Z. Karagoz

    2015-04-01

    Cu-based Cu-Al-Mn-Fe shape memory alloys were produced in an arc melter under vacuum. The crystal structure of the fabricated alloys were determined by means of X-ray diffraction (XRD). The XRD analysis results indicated that the martensitic phase of the samples have an M18R structure. The characteristic transformation temperatures, thermodynamic parameters, and the activation energy values of the samples according to Kissinger and Ozawa methods were determined by differential scanning calorimetry measurements. The austenite transformation temperatures of the samples were found as , respectively. Also, the calculated activation energy values of the samples according to Kissinger and Ozawa methods are compared with each other. The effect of the presence of Al and Fe in the samples on the thermodynamic parameters is studied in this work.

  20. Investigation of spin-gapless semiconductivity and half-metallicity in Ti2MnAl-based compounds

    NASA Astrophysics Data System (ADS)

    Lukashev, P.; Kharel, P.; Gilbert, S.; Staten, B.; Hurley, N.; Fuglsby, R.; Huh, Y.; Valloppilly, S.; Zhang, W.; Yang, K.; Skomski, R.; Sellmyer, D. J.

    2016-04-01

    The increasing interest in spin-based electronics has led to a vigorous search for new materials that can provide a high degree of spin polarization in electron transport. An ideal candidate would act as an insulator for one spin channel and a conductor or semiconductor for the opposite spin channel, corresponding to the respective cases of half-metallicity and spin-gapless semiconductivity. Our first-principle electronic-structure calculations indicate that the metallic Heusler compound Ti2MnAl becomes half-metallic and spin-gapless semiconducting if half of the Al atoms are replaced by Sn and In, respectively. These electronic structures are associated with structural transitions from the regular cubic Heusler structure to the inverted cubic Heusler structure.

  1. Processing of CuAlMn Shape Memory Foams with Open Spherical Pores by Silica-Gel Beads Infiltration Method

    NASA Astrophysics Data System (ADS)

    Li, Hua; Yuan, Bin; Gao, Yan

    2016-10-01

    A molten metal infiltration process with amorphous SiO2 (silica-gel) beads as space holders was used to prepare Cu-based shape memory foams in this article. We found that the silica-gel beads with micropores inside expanded when being heated to elevated temperatures and that proper control of the expansion of silica-gel beads helped form necks between the beads with different bonding extent, which had been taken advantage of to have a good control of the foam morphology and porosity, by carefully designing suitable procedures and choosing proper parameters for the process. In addition, we studied in detail the effect of heating temperature, silica-gel bead density, and infiltration pressure of the present process on the morphology and porosity of CuAlMn shape memory foams. By coordinating these three key parameters, CuAlMn shape memory foams with open spherical pores and adjustable porosity from 66 to 85 pct were reliably produced.

  2. Microstructure and Mechanical Properties of Pulsed Laser Beam Welded Ti-2Al-1.5Mn Titanium Alloy Joints

    NASA Astrophysics Data System (ADS)

    Fang, Xiuyang; Liu, Hong; Zhang, Jianxun

    2014-06-01

    The microstructure and mechanical properties in the pulsed laser beam welded joints of Ti-2Al-1.5Mn titanium alloy thin sheet were investigated in this study. The results show that the original α + β-phases and the transformed α + α'-phases are found in the partially transformed heat-affected zone (HAZ) together with the remaining β-phase, and the microhardness gradually enhances in the region as the result of the increase of α'-phase. The martensitic α'-phase and the remaining β-phase are detected in the fully transformed HAZ and the fusion zone (FZ), and the highest microhardness is found in these regions in virtue of the dominant α'-phase structure. The fine α'-phase appeared in the FZ results in higher average microhardness at high welding speed. Moreover, similar to the results of microhardness test, the tensile test results mean that the HAZ and FZ are stronger than the base metal (BM). Therefore, pulsed laser beam welding is feasible for joining thin sheet of Ti-2Al-1.5Mn titanium alloy.

  3. Crystal Structure, Piezoelectric and Dielectric Properties of (Li, Ce)4+, Nb5+ and Mn2+ Co-doped CaBi4Ti4O15 High-Temperature Ceramics

    NASA Astrophysics Data System (ADS)

    Xin, Deqiong; Chen, Qiang; Wu, Jiagang; Bao, Shaoming; Zhang, Wen; Xiao, Dingquan; Zhu, Jianguo

    2016-07-01

    Bismuth-layered structured ceramics Ca0.85(Li,Ce)0.075Bi4Ti4- x Nb x O15-0.01MnCO3 were prepared by the conventional solid-state reaction method. The evolution of microstructure and corresponding electrical properties were studied. All the samples presented a single bismuth layered-structural phase with m = 4, indicating that (Li, Ce)4+, Nb5+ and Mn2+ adequately enter into the pseudo-perovskite structure and form solid solutions. It was found that Ca0.85(Li,Ce)0.075Bi4Ti3.98Nb0.02O15-0.01MnCO3 (CBTLCM-0.02Nb) ceramics possess the optimum electrical properties. The piezoelectric coefficient d 33, dielectric constant ɛ r, loss tan δ, planar electromechanical coupling factor k p and Curie-temperature T C of CBTLCM-0.02Nb ceramics were found to be ˜19.6 pC/N, 160, 0.16%, 8.1% and 767°C, respectively. Furthermore, the thermal depoling behavior demonstrates that the d 33 value of x = 0.02 content remains at 16.8 pC/N after annealing at 500°C. These results suggest that the (Li, Ce)4+-, Nb5+- and Mn2+-doped CBT-based ceramics are promising candidates for high-temperature piezoelectric applications.

  4. Phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics

    SciTech Connect

    Peng, Wei; Mao, Chaoliang; Liu, Zhen; Dong, Xianlin; Cao, Fei; Wang, Genshui

    2015-03-02

    The phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} lead-free ceramics were investigated systematically. The loss tangent of poled sample shows a broad peak when heating to about 80 °C, i.e., depolarization temperature T{sub d}. The polarization-electric field hysteresis loops at different temperature exhibit the feature of ferroelectric (FE)- antiferroelectric (AFE) phase transition and the co-existence of FE and AFE phase. The pyroelectric coefficients curve confirms its diffusion behaviors. The initial hysteresis loop and switching current curves under T{sub d} indicate the co-existence of FE and AFE phase. The domain morphology of transmission electron microscopy supports the co-existence of FE and AFE phase. Our work not only exhibit that the FE and AFE phase characteristics of 0.92Bi{sub 0.5}Na{sub 0.5}TiO{sub 3}-0.08BiAlO{sub 3} ceramics but also they may be helpful for further investigation on lead-free ceramics.

  5. First-principles study on the band structure, magnetic and elastic properties of half-metallic Cr2MnAl

    NASA Astrophysics Data System (ADS)

    Qi, Santao; Zhang, Chuan-Hui; Chen, Bao; Shen, Jiang

    2015-08-01

    In this study, we have investigated the structural, electronic, magnetic and elastic properties of the full-Heusler Cr2MnAl alloy in the framework of density functional theory with generalized gradient approximation (GGA). The calculated results showed that Cr2MnAl was stable in ferrimagnetic configuration and crystallized in the Hg2CuTi-type structure. From the band structure and density of states calculation results, we concluded that Cr2MnAl belongs to a kind of half-metallic compound with an indirect band gap of 0.37 eV. Immediately thereafter, we have analyzed the origin of half-metallic band gap. The total magnetic moment of Cr2MnAl at the stable state is - 2μB per formula unit, obeying the Slater-Pauling rule Mt = Zt - 24. In addition, various mechanical properties have been obtained and discussed based on the three principle elastic tensor elements C11,C12 and C44 for the first time in the present work. We expect that our calculated results may trigger the application of Cr2MnAl in future spintronics field.

  6. Enhancing the Photocatalytic Activity of Sr4 Al14 O25 :Eu(2+) ,Dy(3+) Persistent Phosphors by Codoping with Bi(3+) ions.

    PubMed

    García, Carlos R; Oliva, Jorge; Romero, Maria Teresa; Diaz-Torres, Luis A

    2016-01-20

    The photocatalytic activity of Bismuth codoped Sr4 Al14 O25 : Eu(2+) ,Dy(3+) persistent phosphors is studied by monitoring the degradation of the blue methylene dye UV light irradiation. Powder phosphors are obtained by a combustion synthesis method and a post-annealing process in reductive atmosphere. The XRD patterns show a single orthorhombic phase of Sr4 Al14 O25 : Eu(2+) ,Dy(3+) ,Bi(3+) phosphors even at high Bismuth dopant concentrations of 12 mol%, suggesting that Bi ions are well incorporated into the host lattice. SEM micrographs show irregular micro grains with sizes in the range of 0.5-20 μm. The samples present an intense greenish-blue fluorescence and persistent emissions at 495 nm, attributed to the 5d-4f allowed transitions of Eu(2+) . The fluorescence decreases as Bi concentration increases; that suggest bismuth induced traps formation that in turn quench the luminescence. The photocatalytic evaluation of the powders was studied under both 365 nm UV and solar irradiations. Sample with 12 mol% of Bi presented the best MB degradation activity; 310 min of solar irradiation allow 100% MB degradation whereas only 62.49% MB degradation is achieved under UV irradiation. Our Results suggest that codoping the persistent phosphors with Bi(3+) can be an alternative to enhance their photocatalytic activity. This article is protected by copyright. All rights reserved.

  7. Investigation of magnetic properties and electronic structure of layered-structure borides AlT{sub 2}B{sub 2} (T=Fe, Mn, Cr) and AlFe{sub 2–x}Mn{sub x}B{sub 2}

    SciTech Connect

    Chai, Ping; Stoian, Sebastian A.; Tan, Xiaoyan; Dube, Paul A.; Shatruk, Michael

    2015-04-15

    The ternary phases AlT{sub 2}B{sub 2} (T=Fe, Mn, Cr) and quaternary phases AlFe{sub 2–x}Mn{sub x}B{sub 2} have been synthesized by arc-melting and characterized by powder X-ray diffraction, magnetic measurements, Mössbauer spectroscopy, and electronic band structure calculations. All the compounds adopt the AlFe{sub 2}B{sub 2}-type structure, in which infinite zigzag chains of B atoms are connected by Fe atoms into [Fe{sub 2}B{sub 2}] slabs that alternate with layers of Al atoms along the b axis. The magnetic measurements reveal that AlFe{sub 2}B{sub 2} is a ferromagnet with T{sub C}=282 K while AlMn{sub 2}B{sub 2} and AlCr{sub 2}B{sub 2} do not show magnetic ordering in the studied temperature range of 1.8–400 K. A systematic investigation of solid solutions AlFe{sub 2−x}Mn{sub x}B{sub 2} showed a non-linear change in the structural and magnetic behavior. The ferromagnetic ordering temperature is gradually decreased as the Mn content (x) increases. The Mössbauer spectra reveal the presence of non-magnetic (NM) and ferromagnetic (FM) spectral components in all Mn-containing samples, with the amount of NM fraction increasing as the Mn content increases. While for the AlFe{sub 2−x}Mn{sub x}B{sub 2} samples with x=0.0 and 0.4 the hyperfine splitting of the FM spectral component collapses at temperatures close to the Curie temperatures determined from the magnetic measurements, for the x=1.2 and 1.6 samples the FM fraction exhibits a sizable unquenched hyperfine splitting at room temperature, a finding that is inconsistent with the observed magnetic properties. Along with the increase in the amount of the NM fraction, this observation suggests formation of Fe-rich and Mn-rich regions in the structure of the solid solutions. Quantum-chemical calculations and crystal orbital Hamilton population analysis provide a clear explanation of the distinction in properties for this series of compounds and also reveal the importance of electronic factors in modifying the

  8. Atomic moments in Mn2CoAl thin films analyzed by X-ray magnetic circular dichroism

    SciTech Connect

    Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D. A.; Heiman, D.

    2014-12-05

    Spin gapless semiconductors are known to be strongly affected by structural disorder when grown epitaxially as thin films. The magnetic properties of Mn2CoAl thin films grown on GaAs (001) substrates are investigated here as a function of annealing. This study investigates the atomic-specific magnetic moments of Mn and Co atoms measured through X-ray magnetic circular dichroism as a function of annealing and the consequent structural ordering. Results indicate that the structural distortion mainly affects the Mn atoms as seen by the reduction of the magnetic moment from its predicted value.

  9. High-pressure synthesis and characterization of BiCu{sub 3}(Mn{sub 4−x}Fe{sub x})O{sub 12} (x=0, 1.0, 2.0) complex perovskites

    SciTech Connect

    Kayser, P.; Martínez-Lope, M.J.; Alonso, J.A.; Sánchez-Benítez, J.; Fernández, M.T.

    2013-08-15

    We have studied the series of nominal composition BiCu{sub 3}(Mn{sub 4−x}Fe{sub x})O{sub 12} (x=0, 1.0, 2.0) where Mn is replaced by Fe cations in the ferrimagnetic perovskite BiCu{sub 3}Mn{sub 4}O{sub 12}. These compounds have been prepared from citrate precursors under moderate pressure conditions (3.5 GPa) and 1000 °C in the presence of KClO{sub 4} as oxidizing agent. All the samples have been studied by x-ray and neutron powder diffraction (NPD) at room temperature and 4 K. The crystal structure has been defined in a cubic Im3{sup ¯} (No. 204) space group with a 2a{sub 0}×2a{sub 0}×2a{sub 0} unit-cell. The doubling of the unit-cell occurs due to the ordering of Bi{sup 3+} and Cu{sup 2+} cations over A sites of the AA′{sub 3}B{sub 4}O{sub 12} structure. The A-site accommodates 12-fold coordinated Bi{sup 3+} ions and, at the A′-site, Jahn–Teller Cu{sup 2+} ions form pseudo-square planar units aligned perpendicular to each other. Mn{sup 4+}/Fe{sup 3+} cations randomly occupy the centre of slightly distorted octahedra. These materials have also been characterized by magnetic and magnetotransport measurements. We found that all the samples are ferrimagnetic and show a progressive decrease of T{sub C} as the Fe content increases, since Fe ions disturb the ferromagnetic interactions within the B magnetic sublattice. In fact, the Curie temperature diminishes from T{sub C}=360 K (x=0) to T{sub C}=219 K (x=2). The magnetic structures, studied by low-temperature NPD data, correspond to an antiferromagnetic arrangement of spins at 8c and 6b sites; the ordered moments are in excellent agreement with those obtained from the saturation magnetization at 4 K. A significant magnetoresistant effect is determined for the x=1.0 oxide, with low-field values as high as 5% at 300 K and 1 T. Highlights: • BiCu{sub 3}(Mn{sub 4−x}Fe{sub x})O{sub 12} perovskites have been prepared under high pressure conditions. • They have been characterized by NPD, magnetic and

  10. Ab-initio study of structural, elastic, thermal, electronic and magnetic properties of quaternary Heusler alloys CoMnCrZ (Z = Al, As, Si, Ge)

    NASA Astrophysics Data System (ADS)

    Mohamedi, Mohamed Walid; Chahed, Abbes; Amar, Amina; Rozale, Habib; Lakdja, Abdelaziz; Benhelal, Omar; Sayede, Adlane

    2016-12-01

    First-principles approach is used to study the structural, electronic and magnetic properties of CoMnCrZ (Z = Al, Si, Ge and As) quaternary Heusler compounds, using full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation (GGA). The computed equilibrium lattice parameters agree well with the available theoretical data. The obtained negative formation energy shows that CoMnCrZ (Z = Al, Si, Ge, As) compounds have strong structural stability. The elastic constants Cij are calculated using the total energy variation with strain technique. The polycrystalline elastic moduli (namely: the shear modulus, Young's modulus, Poisson's ratio, sound velocities, Debye temperature and melting temperature were derived from the obtained single-crystal elastic constants. The ductility mechanism for the studied compounds is discussed via the elastic constants Cij. Our calculations with the GGA approximation predict that CoMnCrGe, CoMnCrAl, CoMnCrSi and CoMnCrAs are half-metallic ferrimagnets (HMFs) with a half-metallic gap EHM of 0.03 eV, 0.19 eV, 0.34 eV and 0.50 eV for, respectively. We also find that the half-metallicity is maintained on a wide range of lattice constants.

  11. Distribution of Be, Al, Se and Bi in the surface waters of the western North Atlantic and Caribbean

    NASA Astrophysics Data System (ADS)

    Measures, C. I.; Grant, B.; Khadem, M.; Lee, D. S.; Edmond, J. M.

    1984-11-01

    The mixed layer distributions of several trace elements have been determined along a detailed transect from Rhode Island to the Panama Canal. When taken together with a new and existing profile data from the North Atlantic and North Pacific, some general inferences emerge as to the processes controlling their concentrations in the surface waters. The large enrichments in Be observed in the upper waters of the North Atlantic relative to the North Pacific appear to be sustained mainly by fluvial inputs. Those of Se are derived from atmospheric transport. Aluminium and Bi also appear to have an aeolian source in the Sargasso Sea. However, in the tropical eastern Pacific, the Al input may be fluvial On this cruise, Be, Al and the Se species were analyzed on board ship within a few hours of collection. The demonstration that this is feasible opens up the prospect of the application of large-scale chemical hydrography to the study of the processes controlling the distribution and water column variability of trace elements in the oceans.

  12. On the origin of near-IR luminescence in Bi-doped materials (II). Subvalent monocation Bi⁺ and cluster Bi₅³⁺ luminescence in AlCl₃/ZnCl₂/BiCl₃ chloride glass.

    PubMed

    Romanov, Alexey N; Fattakhova, Zukhra T; Veber, Alexander A; Usovich, Olga V; Haula, Elena V; Korchak, Vladimir N; Tsvetkov, Vladimir B; Trusov, Lev A; Kazin, Pavel E; Sulimov, Vladimir B

    2012-03-26

    Broadband NIR photoluminescence (from 1000 to 2500 nm) was observed from partially reduced AlCl₃/ZnCl₂/BiCl₃ glass, containing subvalent bismuth species. The luminescence consists of three bands, assigned to Bi⁺ , Bi₂⁴⁺, and Bi₅³⁺ ions. The physical and optical characteristics of these centers and possible contribution to NIR luminescence from bismuth-doped oxide glasses are discussed.

  13. Thermoelectric properties of n-type Bi2Te2.7Se0.3 with addition of nano-ZnO:Al particles

    NASA Astrophysics Data System (ADS)

    Song, Shaowei; Wang, Jueling; Xu, Bo; Lei, Xiaobo; Jiang, Hongchuan; Jin, Yingrong; Zhang, Qinyong; Ren, Zhifeng

    2014-09-01

    Nano Al-doped ZnO (AZO) particles were added into n-type Bi2Te2.7Se0.3 alloys by ball milling and hot pressing method. The power factor was improved by ˜22% with addition of nano-AZO particles, accompanied with a ˜40% decrease of lattice thermal conductivity, leading to peak ZT of ˜0.85 at 323 K for Bi2Te2.7Se0.3(AZO)0.005 sample. The effects of the addition of AZO nanoparticles on the microstructure and thermoelectric transport properties are discussed.

  14. Localization of electrons due to orbitally ordered bi-stripes in the bilayer manganite La(2-2x)Sr(1+2x)Mn2O7 (x ~ 0.59).

    PubMed

    Sun, Z; Wang, Q; Fedorov, A V; Zheng, H; Mitchell, J F; Dessau, D S

    2011-07-19

    Electronic phases with stripe patterns have been intensively investigated for their vital roles in unique properties of correlated electronic materials. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. By studying the electronic structure of La(2-2x)Sr(1+2x)Mn(2)O(7) (x ∼ 0.59) and in combination with earlier scattering measurements, we demonstrate the variation of electronic properties accompanying the melting of so-called bi-stripes in this material. The static bi-stripes can strongly localize the electrons in the insulating phase above T(c) ∼ 160 K, while the fraction of mobile electrons grows, coexisting with a significant portion of localized electrons when the static bi-stripes melt below T(c). The presence of localized electrons below T(c) suggests that the melting bi-stripes exist as a disordered or fluctuating counterpart. From static to melting, the bi-stripes act as an atomic-scale electronic valve, leading to a "colossal" metal-insulator transition in this material.

  15. Localization of electrons due to orbitally ordered bi-stripes in the bilayer manganite La2-2xSr1+2xMn2O7 (x ∼ 0.59)

    PubMed Central

    Sun, Z.; Wang, Q.; Fedorov, A. V.; Zheng, H.; Mitchell, J. F.; Dessau, D. S.

    2011-01-01

    Electronic phases with stripe patterns have been intensively investigated for their vital roles in unique properties of correlated electronic materials. How these real-space patterns affect the conductivity and other properties of materials (which are usually described in momentum space) is one of the major challenges of modern condensed matter physics. By studying the electronic structure of La2-2xSr1+2xMn2O7 (x ∼ 0.59) and in combination with earlier scattering measurements, we demonstrate the variation of electronic properties accompanying the melting of so-called bi-stripes in this material. The static bi-stripes can strongly localize the electrons in the insulating phase above Tc ∼ 160 K, while the fraction of mobile electrons grows, coexisting with a significant portion of localized electrons when the static bi-stripes melt below Tc. The presence of localized electrons below Tc suggests that the melting bi-stripes exist as a disordered or fluctuating counterpart. From static to melting, the bi-stripes act as an atomic-scale electronic valve, leading to a “colossal” metal-insulator transition in this material. PMID:21715662

  16. Oxygen octahedra distortion induced structural and magnetic phase transitions in Bi{sub 1−x}Ca{sub x}Fe{sub 1−x}Mn{sub x}O{sub 3} ceramics

    SciTech Connect

    Kumar, Pawan; Kar, Manoranjan; Shankhwar, Nisha; Srinivasan, A.

    2015-05-21

    The co-doping of Ca and Mn in respective Bi and Fe-sites of BiFeO{sub 3} lattice leads to structural transition from rhombohedral (R3c space group) to orthorhombic (Pbnm space group) crystal symmetry. The tilt angle for anti-phase rotation of the oxygen octahedra of BiFeO{sub 3} at room temperature is observed to be ∼13.8°. It decreases with the increase in the co-doping percentage which suggests the composition-driven structural phase transition. The remnant magnetization for sample with 15% of co-doping becomes about 16 times that of BiFeO{sub 3}. It may be attributed to the suppression of cycloid spin structure and uncompensated spins at the surface of nanocrystallites. Further increase in co-doping percentage results in the sharp reduction of remnant magnetization due to the dominant contribution from the collinear antiferromagnetic ordering in the Pbnm space group. The Arrott plot analysis clearly indicates the composition-driven crossover from the antiferromagnetic to weak ferromagnetic ordering and vice versa. Electron spin resonance results provide the evidence for the composition-driven phase transitions from an incommensurate spin cycloidal modulated state to one with nearly homogeneous spin order. The band gap (2.17 eV) of BiFeO{sub 3} measured using UV-Vis spectra was supported by the resonance Raman spectra.

  17. Non-local spin injection effects in coplanar La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}/ La{sub 0.7}Sr{sub 0.3}MnO{sub 3} tri-layer

    SciTech Connect

    Joseph, D. Paul; Lin, J. G.

    2015-06-24

    Non-local electrical properties of pulsed laser deposited La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}/La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (L-B-L) coplanar tri-layer is investigated under different wiring configurations. Long range super-current of Bi-2212 penetrating into LSMO is dependent on geometry of spin injection. From qualitative analysis of structural, magnetic and electrical data, long range super-current is suggested to pass through domain walls and/or grain boundaries of LSMO.

  18. Synthesis and optical properties of turquoise- and green-colored brownmillerite-type Ba2In2- x- y Mn x Al y O5+ x codoped with manganese and aluminum

    NASA Astrophysics Data System (ADS)

    Jiang, Peng; Yang, Wen-hui; Zhou, Yun-cheng; Kuang, Jian-lei; Li, Yong; Xiao, Ting

    2016-11-01

    Brownmillerite-type oxides Ba2In2- x- y Mn x Al y O5+ x (0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.5) were prepared at 1300°C through solid-state reaction. X-ray diffraction (XRD) analysis showed that the structure symmetry evolved from orthorhombic to cubic with increasing Mn and Al contents. When y was greater than 0.3, peaks associated with small amounts of BaAl2O4 and Ba2InAlO5 impurities were observed in the XRD patterns. When substituted with a small amount of Mn ( x ≤ 0.3), the Ba2In2- x- y Mn x Al y O5+ x samples exhibited an intense turquoise color. The color changed to green and dark-green with increasing Mn concentration. UV-vis absorbance spectra revealed that the color changed only slightly upon Al doping. The valence state of Mn ions in Ba2In2- x- y Mn x Al y O5+ x was confirmed to be +5 on the basis of X-ray photoelectron spectroscopic analysis. According to this analysis, the intense turquoise color of the Ba2In2- x- y Mn x Al y O5+ x samples is rooted in the existence of Mn5+; thus, the introduction of Al does not affect the optical properties of the compounds.

  19. AlM2B2 (M  =  Cr, Mn, Fe, Co, Ni): a group of nanolaminated materials

    NASA Astrophysics Data System (ADS)

    Kádas, K.; Iuşan, D.; Hellsvik, J.; Cedervall, J.; Berastegui, P.; Sahlberg, M.; Jansson, U.; Eriksson, O.

    2017-04-01

    Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono- and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.

  20. Evolution of a novel Si-18Mn-16Ti-11P alloy in Al-Si melt and its influence on microstructure and properties of high-Si Al-Si alloy

    NASA Astrophysics Data System (ADS)

    Zhou, Xiao-Lu; Zhu, Xiang-Zhen; Gao, Tong; Wu, Yu-Ying; Liu, Xiang-Fa

    A novel Si-18Mn-16Ti-11P master alloy has been developed to refine primary Si to 14.7 ± 1.3 μm, distributed uniformly in Al-27Si alloy. Comparing with traditional Cu-14P and Al-3P, Si-18Mn-16Ti-11P provided a much better refining effect, with in-situ highly active AlP. The refined Al-27Si alloy exhibited a CTE of 16.25 × 10-6/K which is slightly higher than that of Sip/Al composites fabricated by spray deposition. The UTS and elongation of refined Al-27Si alloy were increased by 106% and 235% comparing with those of unrefined alloy. It indicates that the novel Si-18Mn-16Ti-11P alloy is more suitable for high-Si Al-Si alloys and may be a candidate for refining hypereutectic Al-Si alloy for electronic packaging applications. Moreover, studies showed that TiP is the only P-containing phase in Si-18Mn-16Ti-11P master alloy. A core-shell reaction model was established to reveal mechanism of the transformation of TiP to AlP in Al-Si melts. The transformation is a liquid-solid diffusion reaction driven by chemical potential difference and the reaction rate is controlled by diffusion. It means sufficient holding time is necessary for Si-18Mn-16Ti-11P master alloy to achieve better refining effect.

  1. Galvanomagnetic properties of Fe{sub 2}YZ (Y = Ti, V, Cr, Mn, Fe, Ni; Z = Al, Si) heusler alloys

    SciTech Connect

    Kourov, N. I. Marchenkov, V. V.; Belozerova, K. A.; Weber, H. W.

    2015-11-15

    The Hall effect and the magnetoresistance of Fe{sub 2}YZ Heusler alloys, where Y = Ti, V, Cr, Mn, Fe, and Ni, are the 3d transition metals and Z = Al and Si are the s, p elements of the third period of the periodic table, are studied at T = 4.2 K in magnetic fields H ≤ 100 kOe. It is shown that, in the high-field limit (H > 10 kOe), the value and the sign of the normal (R{sub 0}) and anomalous (R{sub s}) Hall coefficients change anomalously during transition from paramagnetic (Y = Ti, V) to ferromagnetic (Y = Cr, Mn, Fe, Ni) alloys. These coefficients have different signs for all alloys. Constant R{sub s} in the ferromagnetic alloys is positive, proportional to the residual resistivity ratio (R{sub s} ∝ ρ{sub 0}{sup 3.1}), and inversely proportional to spontaneous magnetization. The magnetoresistance of the alloys is a few percent and has a negative sign. A positive addition to transverse magnetoresistance is only detected in high magnetic fields, H > 10 kOe.

  2. Galvanomagnetic properties of Fe2YZ (Y = Ti, V, Cr, Mn, Fe, Ni; Z = Al, Si) heusler alloys

    NASA Astrophysics Data System (ADS)

    Kourov, N. I.; Marchenkov, V. V.; Belozerova, K. A.; Weber, H. W.

    2015-11-01

    The Hall effect and the magnetoresistance of Fe2YZ Heusler alloys, where Y = Ti, V, Cr, Mn, Fe, and Ni, are the 3 d transition metals and Z = Al and Si are the s, p elements of the third period of the periodic table, are studied at T = 4.2 K in magnetic fields H ≤ 100 kOe. It is shown that, in the high-field limit ( H > 10 kOe), the value and the sign of the normal ( R 0) and anomalous ( R s ) Hall coefficients change anomalously during transition from paramagnetic (Y = Ti, V) to ferromagnetic (Y = Cr, Mn, Fe, Ni) alloys. These coefficients have different signs for all alloys. Constant R s in the ferromagnetic alloys is positive, proportional to the residual resistivity ratio ( R s ∝ ρ 0 3.1 ), and inversely proportional to spontaneous magnetization. The magnetoresistance of the alloys is a few percent and has a negative sign. A positive addition to transverse magnetoresistance is only detected in high magnetic fields, H > 10 kOe.

  3. Co-synthesized Y-stabilized Bi2O3 and Sr-substituted LaMnO3 composite anode for high performance solid oxide electrolysis cell

    NASA Astrophysics Data System (ADS)

    Yan, Jingbo; Zhao, Zhe; Shang, Lei; Ou, Dingrong; Cheng, Mojie

    2016-07-01

    In this study we report a nano-composite anode comprised of Y-stabilized Bi2O3 (YSB) and Sr-substituted LaMnO3 (LSM) for solid oxide electrolysis cell (SOEC). The composite powder with primary particle size ranging from 20 to 80 nm is co-synthesized via a simple citric-nitrate combustion method. X-ray diffraction examination confirms cubic fluorite YSB and rhombohedral perovskite LSM as the main phases in the composite. Temperature programmed O2 desorption identifies remarkable low temperature desorption at 330 °C. Similarly, temperature programmed H2 reduction reveals strong reduction at 385 °C. The facile oxygen evolution on YSB-LSM may result from the increased amount of oxygen vacancies and improved oxygen ion mobility. A cell employing YSB-LSM composite anode achieves current density of -1.52 A cm-2 at 800 °C and 1.28 V, 50% higher than conventional LSM-YSZ cell. Impedance results and analysis of distribution of relaxation times indicate that the rate-determining anode processes are effectively accelerated on YSB-LSM. The activation energy for oxygen evolution reaction on YSB-LSM is reduced to 0.65 eV, notably lower than on LSM-YSZ (1.29 eV). The high performance of YSB-LSM composite anode is attributed to the fast ion decorporation on YSB, the facile O2 formation on LSM, and the abundant phase boundaries that facilitate the two processes.

  4. Electronic structure and magnetic properties in T2AlB2 (T =Fe, Mn, Cr, Co, and Ni) and their alloys

    NASA Astrophysics Data System (ADS)

    Ke, Liqin; Harmon, Bruce N.; Kramer, Matthew J.

    2017-03-01

    The electronic structure and intrinsic magnetic properties of Fe2AlB2 -related compounds and their alloys have been investigated using density functional theory. For Fe2AlB2 , the crystallographic a axis is the easiest axis, which agrees with experiments. The magnetic ground state of Mn2AlB2 is found to be ferromagnetic in the basal a b plane, but antiferromagnetic along the c axis. All 3 d dopings considered decrease the magnetization and Curie temperature in Fe2AlB2 . Electron doping with Co or Ni has a stronger effect on the decreasing of Curie temperature in Fe2AlB2 than hole doping with Mn or Cr. However, a larger amount of Mn doping on Fe2AlB2 promotes the ferromagnetic to antiferromagnetic transition. A very anisotropic magnetoelastic effect is found in Fe2AlB2 : the magnetization has a much stronger dependence on the lattice parameter c than on a or b , which is explained by electronic-structure features near the Fermi level. Dopings of other elements on B and Al sites are also discussed.

  5. Electronic structure and magnetic properties in T2AlB2 (T = Fe, Mn, Cr, Co, and Ni) and their alloys

    DOE PAGES

    Ke, Liqin; Harmon, Bruce N.; Kramer, Matthew J.

    2017-03-20

    In this study, the electronic structure and intrinsic magnetic properties of Fe2AlB2-related compounds and their alloys have been investigated using density functional theory. For Fe2AlB2, the crystallographic a axis is the easiest axis, which agrees with experiments. The magnetic ground state of Mn2AlB2 is found to be ferromagnetic in the basal ab plane, but antiferromagnetic along the c axis. All 3d dopings considered decrease the magnetization and Curie temperature in Fe2AlB2. Electron doping with Co or Ni has a stronger effect on the decreasing of Curie temperature in Fe2AlB2 than hole doping with Mn or Cr. However, a larger amountmore » of Mn doping on Fe2AlB2 promotes the ferromagnetic to antiferromagnetic transition. A very anisotropic magnetoelastic effect is found in Fe2AlB2: the magnetization has a much stronger dependence on the lattice parameter c than on a or b, which is explained by electronic-structure features near the Fermi level. Dopings of other elements on B and Al sites are also discussed.« less

  6. New pressure induced phase transitions in mullite-type Bi2(Fe4-xMnx)O10-δ complex oxides

    SciTech Connect

    Kalita, Patricia E; Cornelius, Andrew L; Lipinska, Kristina E; Lufaso, Michael W; Kann, Zachary R; Sinogeikin, Stanislav; Hemmers, Oliver A; Schneider, Hartmut

    2016-07-29

    Single phased mullite-type Bi2Fe4-xMnxO10-δ mixed crystals (0.25 ± x ± 3.125) and the end-member Bi2Fe4O9, synthesized from the oxides by reaction sintering up to 825°C, were studied at high-pressures in order to probe their high-pressure behavior and any possible structural phase transitions. In-situ synchrotron radiation-based powder X-ray diffraction was carried out in a diamond anvil cell, under quasi-hydrostatic conditions, up to a pressure of about 20 GPa at room temperature for each sample. A pressure-induced phase transition was found in all samples. The transition appeared spread over a pressure range and was not completed at the top investigated pressure. This is the first report of a pressure-induced phase transition in Bi2Fe4-xMnxO10-δ mixed crystals.

  7. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy.

    PubMed

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-05-16

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm.

  8. Premartensitic transition and relevant magnetic effects in Ni50Mn34In15.5Al0.5 alloy

    PubMed Central

    Wu, Yuqin; Guo, Shaopu; Yu, Shuyun; Cheng, Hui; Wang, Ruilong; Xiao, Haibo; Xu, Lingfang; Xiong, Rui; Liu, Yong; Xia, Zhengcai; Yang, Changping

    2016-01-01

    Resistance measurement, in situ optical microscopic observation, thermal and magnetic measurements have been carried out on Ni50Mn34In15.5Al0.5 alloy. The existence of a pronounced premartensitic transition prior to martensitic transition can be characterized by microstructure evolution as well as exothermic peak and smooth decrease of resistance and magnetization with obvious hysteresis over a wide temperature range upon cooling. Consequently, the alloy undergoes two successive magneto-structural transitions consisting of premartensitic and martensitic transitions. Magnetoelastic coupling between magnetic and structural degrees of freedom would be responsible for the appearance of premartensitic transition, as evinced by the distinct shift of transitions temperatures to lower temperature with external applied field of 50 kOe. The inverse premartensitic transition induced by magnetic field results in large magnetoresistance, and contributes to the enhanced inverse magnetocaloric effect through enlarging the peak value and temperature interval of magnetic entropy change ΔSm. PMID:27183331

  9. Formation of a fine-grained microstructure in Al-Mg-Mn-Zr alloy by the conventional method

    NASA Astrophysics Data System (ADS)

    Kulitskiy, V.; Mogucheva, A.; Kaibyshev, R.

    2016-11-01

    The material is rolled at ambient temperature with the total reduction 80%, and then recrystallization annealing is carried out in the temperature interval 300-400°C for 2 hours. A partial recrystallization occurred after annealing at temperatures below 320°C. The annealing temperature increase from 320 to 400°C leads to the formation of a recrystallized equiaxed microstructure with the grain size of about 6-12 µm. Based on detailed microstructural examinations, a comparison of microstructure-strength relationships is carried out. The investigation of the fine microstructure reveals a low dislocation density and low fraction of low-angle boundaries (LABs). The analysis of transmission electron microscopy (TEM) micrographs shows a uniform distribution of Al6Mn particles and retention of the dispersoid size and morphology throughout the process. The increase in the recrystallization annealing temperature above 320°C has a slight effect on the alloy microhardness.

  10. Effect of Annealing in Magnetic Field on Ferromagnetic Nanoparticle Formation in Cu-Al-Mn Alloy with Induced Martensite Transformation.

    PubMed

    Titenko, Anatoliy; Demchenko, Lesya

    2016-12-01

    The paper considers the influence of aging of high-temperature phase on subsequent martensitic transformation in Cu-Al-Mn alloy. The morphology of behavior of martensitic transformation as a result of alloy aging under annealing in a constant magnetic field with different sample orientation relatively to the field direction and without field was studied for direct control of the processes of martensite induction at cooling. Temperature dependences of electrical resistance, magnetic susceptibility, and magnetization, as well as field dependences of magnetization, and phase composition were found. The tendency to the oriented growth of precipitated ferromagnetic phase nanoparticles in a direction of applied field and to an increase of their volume fraction under thermal magnetic treatment of material that favors a reversibility of induced martensitic transformation is observed.

  11. Testing of the permanent magnet material Mn-Al-C for potential use in propulsion motors for electric vehicles

    NASA Technical Reports Server (NTRS)

    Abdelnour, Z.; Mildrun, H.; Strant, K.

    1981-01-01

    The development of Mn-Al-C permanent magnets is reviewed. The general properties of the material are discussed and put into perspective relative to alnicos and ferrites. The traction motor designer's demands of a permanent magnet for potential use in electric vehicle drives are reviewed. Tests determined magnetic design data and mechanical strength properties. Easy axis hysteresis and demagnetization curves, recoil loops and other minor loop fields were measured over a temperature range from -50 to 150 C. Hysteresis loops were also measured for three orthogonal directions (the one easy and two hard axes of magnetization). Extruded rods of three different diameters were tested. The nonuniformity of properties over the cross section of the 31 mm diameter rod was studied. Mechanical compressive and bending strength at room temperature was determined on individual samples from the 31 mm rod.

  12. Testing of the permanent magnet material Mn-Al-C for potential use in propulsion motors for electric vehicles

    NASA Technical Reports Server (NTRS)

    Abdelnour, Z. A.; Mildrum, H. F.; Strnat, K. J.

    1980-01-01

    The development of Mn-Al-C permanent magnets is reviewed. The general properties of the material are discussed and put into perspective relative to alnicos and ferrites. The commercial material now available is described by the manufacturer's data. The traction motor designer's demands of a permanent magnet for potential use in electric vehicle drives are reviewed. From this, a list of the needed specific information is extracted. A plan for experimental work is made which would generate this information, or verify data supplied by the producer. The results of these measurements are presented in the form of tables and graphs. The tests determined magnetic design data and some mechanical strength properties. Easy axis hysteresis and demagnetization curves, recoil loops and other minor loop fields were measured over a temperature range from -50 C to +150 C. Hysteresis loops were also measured for three orthogonal directions (the easy and 2 hard axes of magnetization).

  13. Thickness dependence of magnetic anisotropy and intrinsic anomalous Hall effect in epitaxial Co2MnAl film

    NASA Astrophysics Data System (ADS)

    Meng, K. K.; Miao, J.; Xu, X. G.; Zhao, J. H.; Jiang, Y.

    2017-04-01

    We have investigated the thickness dependence of magnetic anisotropy and intrinsic anomalous Hall effect (AHE) in single-crystalline full-Heusler alloy Co2MnAl (CMA) grown by molecular-beam epitaxy on GaAs(001). The magnetic anisotropy is the interplay of uniaxial and the fourfold anisotropy, and the corresponding anisotropy constants have been deduced. Considering the thickness of CMA is small, we ascribe it to the influence from interface stress. The AHE in CMA is found to be well described by a proper scaling. The intrinsic anomalous conductivity is found to be smaller than the calculated one and is thickness dependent, which is ascribed to the influence of chemical ordering by affecting the band structure and Fermi surface.

  14. Anomalous Hall effect in L 10-MnAl films with controllable orbital two-channel Kondo effect

    NASA Astrophysics Data System (ADS)

    Zhu, L. J.; Nie, S. H.; Zhao, J. H.

    2016-05-01

    The anomalous Hall effect (AHE) in strongly disordered magnetic systems has been buried in persistent confusion despite its long history. We report the AHE in perpendicularly magnetized L 10-MnAl epitaxial films with a variable orbital two-channel Kondo (2CK) effect arising from the strong coupling of conduction electrons and the structural disorders of two-level systems. The AHE is observed to excellently scale with ρAH/f =a0ρx x 0+b ρxx 2 at high temperatures where phonon scattering prevails. In contrast, significant deviation occurs at low temperatures where the orbital 2CK effect becomes important, suggesting a negative AHE contribution. The deviation of the scaling agrees with the orbital 2CK effect in the breakdown temperatures and deviation magnitudes.

  15. Formation of deoxidization products in iron ingot by the addition of Al, Si, and/or Mn (M-5)

    NASA Technical Reports Server (NTRS)

    Fukazawa, Akira

    1993-01-01

    The objective of this work is to examine the morphology, composition, and distribution of deoxidation products in iron and iron-10 percent Ni alloy ingots. The deoxidation agents Si, Mn, Al, and their mixtures are selected to investigate the formation mechanism of the deoxidation products and to compare the differences of oxide formation among these agents in microgravity. After the experiment in space, the tested specimens are going to be analyzed by the use of the latest physical and/or chemical analytical equipment, and the information obtained will be a great help for the comprehension of the formation of oxide inclusion in steel for practical purposes, and also for the study of the solidification mechanism theory in the theoretical field.

  16. Morphology and photoluminescence of BaAl12O19:Mn2+ green phosphor prepared by flux method

    NASA Astrophysics Data System (ADS)

    Zhou, Jun; Wang, Yu-Hua; Liu, Bi-Tao; Liu, Ji-Di

    2010-12-01

    This paper reports that the green phosphor BaAl11.9O19:0.1Mn2+ is prepared by a flux assisted solid state reaction method. The effect of flux systems on the crystal structure, morphology and luminescent properties of the phosphor are studied in detail. The samples are characterized by the application of x-ray diffraction patterns, scanning electron microscopy patterns, luminescent spectra and decay curves. The results show that a pure phase BaAl12O19 can be achieved at the firing temperature above 1300 °C by adding the proper flux system, the firing temperature is reduced at least 200 °C in comparison with the conventional solid state reaction method. Maximum photoluminescence emission intensity is observed at 517 nm for (AlF3+Li2CO3) flux system under vacuum ultraviolet region (147 nm) excitation. The photoluminescence emission intensity and the decay time of these phosphor is found to be more superior to that of the corresponding sample prepared by the conventional solid state reaction method implying the suitability of this route for the preparation of display device worthy phosphor materials.

  17. Growth and electronic structure of alkali-metal adlayers on icosahedral Al{sub 70.5}Pd{sub 21}Mn{sub 8.5}

    SciTech Connect

    Shukla, A. K.; Dhaka, R. S.; Biswas, C.; Banik, S.; Barman, S. R.; Horn, K.; Ebert, Ph.; Urban, K.

    2006-02-01

    We report x-ray photoelectron spectroscopy (XPS) study of Na and K adlayers on icosahedral Al{sub 70.5}Pd{sub 21}Mn{sub 8.5} (i-Al-Pd-Mn) quasicrystal. The Na 1s core-level exhibits a continuous linear shift of 0.8 eV towards lower binding energies (BE) with increasing coverage up to one monolayer (ML) saturation coverage. In the case of K/i-Al-Pd-Mn, a similar linear shift in the K 2p spectra towards lower BE is observed. In both cases, the plasmon related loss features are observed only above 1 ML. The substrate core-level peaks, such as Al 2p, do not exhibit any shift with the adlayer deposition up to the highest coverage. Based on these experimental observations and previous studies of alkali metal growth on metals, we conclude that below 1 ML, both Na and K form a dispersed phase on i-Al-Pd-Mn and there is hardly any charge transfer to the substrate. The variation of the adlayer and substrate core-level intensities with coverage indicates layer by layer growth.

  18. Pressure-induced phase transition in La<mn>1mn>xSmxO<mn>0.5mn>F<mn>0.5mn>BiS>2mn>

    SciTech Connect

    Fang, Y.; Yazici, D.; White, B. D.; Maple, M. B.

    2015-09-15

    Electrical resistivity measurements on La1–xSmxO0.5F0.5BiS2 (x = 0.1, 0.3, 0.6, 0.8) have been performed under applied pressures up to 2.6 GPa from 2 K to room temperature. The superconducting transition temperature Tc of each sample significantly increases at a Sm-concentration dependent pressure Pt, indicating a pressure-induced phase transition from a low-Tc to a high-Tc phase. At ambient pressure, Tc increases dramatically from 2.8 K at x = 0.1 to 5.4 K at x = 0.8; however, the Tc values at P > Pt decrease slightly with x and Pt shifts to higher pressures with Sm substitution. In the normal state, semiconducting-like behavior is suppressed and metallic conduction is induced with increasing pressure in all of the samples. Furthermore, these results suggest that the pressure dependence of Tc for the BiS2-based superconductors is related to the lattice parameters at ambient pressure and enable us to estimate the evolution of Tc for SmO0.5F0.5BiS2 under pressure.

  19. Microstructural Influence on Dynamic Properties of Age Hardenable FeMnAl Alloys

    DTIC Science & Technology

    2011-04-01

    dependent on the separation distance between the two crystal slabs and modeled using the universal binding energy relation ( UBER ) 28, 29: GC (x... UBER fit results for pure Fe3AlC gave a cleavage energy of GC=5.04 J/m2 and an ideal stress ζ max=40 GPa with the maximum stress and separation...distance λ at 163 0.46 Å, which corresponds to an ideal strain of 12.3%. The UBER fit results for a phosphorus doped Fe3AlC supercell showed that the

  20. The electronic structure and spin polarization of Co2Mn0.75(Gd, Eu)0.25Z (Z=Si, Ge, Ga, Al) quaternary Heusler alloys

    NASA Astrophysics Data System (ADS)

    Berri, Saadi

    2016-03-01

    A first-principles approach is used to study the electronic and magnetic properties of Co2Mn0.75(Gd, Eu)0.25Z(Z=Si, Ge, Ga, Al) quaternary Heusler alloys. The investigation was done using the (FP-LAPW) method where the exchange-correlation potential was calculated with the frame of GGA-WC. At ambient conditions our calculated results of band structures reveal that for Co2Mn0.75(Gd, Eu)0.25Z(Z=Si, Ge) has a half-metallic (HM) band structure profile showing 100% spin polarization at the Fermi level. In contrast, Co2Mn0.75(Gd, Eu)0.25Z(Z=Ga, Al) alloys are found to be metallic. Finally, the half metallic compounds found in some structures of this series might be useful in spintronic devices.

  1. Stabilization of a Metastable Fibrous Bi21.2(1)(Mn1–xCox )20 Phase with Pseudo-Pentagonal Symmetry Prepared Using a Bi Self-Flux

    SciTech Connect

    Thimmaiah, Srinivasa; Taufour, Valentin; Saunders, Scott; March, Stephen; Zhang, Yuemei; Kramer, Matthew J.; Canfield, Paul C.; Miller, Gordon J.

    2016-11-15

    Bi21.2(1)(Mn1–xCox )20 is a new metastable phase which is synthesized via Bi self-flux, adopts a highly fibrous morpholo-gy, and decomposes endothermically near 168 °C. It crystallizes in the orthorhombic space group Imma with unit cell parameters α = 19.067(4) Å, $b$ = 4.6071(10) Å and c = 11.583(4) Å, adopting a low-temperature modification of BiNi-type structure by forming columns along the b-axis. Wave-length-dispersive X-ray spectroscopy (WDS) confirms the presence of Co in the structure, which is found to be 7 at.%. In each column, the transition metal (T) and Bi atoms construct a double-walled nanotubular arrangement of atoms around the disordered central Bi atoms. Electronic structure calculations (LMTO-ASA, LSDA) show that the calculated Fermi level falls into a pseudogap and also indicate a possible low-temperature magnetic ordering in the phase.

  2. Mn(2+)-Ion Site Distribution of Zeolite Y (FAU, Si/Al = 1.56) Depending on the Ion-Exchange Ratio.

    PubMed

    Seo, Sung Man; Moon, Dae Jun; Suh, Jeong Min; Zhu, John; Lim, Woo Taik

    2016-05-01

    To investigate the tendency of Mn(2+)-ion exchange into zeolite Y, four single crystals of fully dehydrated Mn2+, Na(+)-exchanged zeolite Y (Si/Al = 1.56) were prepared by the exchange of Na75-Y (INa75I[Si117Al75,O384]-FAU) with aqueous of various concentrations by Mn2+ and Na+ in a total 0.05 M for molar ratios of 1:1 (crystal 1), 1:25 (crystal 2), 1:50 (crystal 3), and 1:100 (crystal 4), respectively, followed by vacuum dehydration at 400 degrees C. Their single-crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd3(-)m and were refined to the final error indices R1/wR2 = 0.0440/0.1545, 0.0369/0.1153, 0.0373/0.1091, and 0.0506/0.1667, respectively. Their unit-cell formulas are approximately LMn33.5Na8I[Si117Al75O384]-FAU, IMn20.5Na34I[Si117Al75O384]-FAU, IMn20.5Na34I[Si117Al75O384]-FAU, and IMn16.5Na42I[Si117Al75O384]-FAU, respectively. The degree of Mn2+-ion exchange increases from 44.3% to 89.1% with increasing the initial Mn2+ concentrations as Na+ content and the unit cell constant of the zeolite framework decrease.

  3. Magnetron deposited TiN coatings for protection of Al-Cu-Ag-Mg-Mn alloy

    NASA Astrophysics Data System (ADS)

    Stepanova, Tatiana V.; Kaziev, Andrey V.; Atamanov, Mikhail V.; Tumarkin, Alexander V.; Dolzhikova, Svetlana A.; Izmailova, Nelly Ph; Kharkov, Maxim M.; Berdnikova, Maria M.; Mozgrin, Dmitry V.; Pisarev, Alexander A.

    2016-09-01

    TiN coatings were deposited on a new Al super-alloy by magnetron sputtering in argon/nitrogen environment. The deposited layer structure, microhardness, adhesion, corrosion resistance, and fatigue life were investigated and tests demonstrated improved performance of the alloy.

  4. Evidence from x-ray and neutron powder diffraction patterns that the so-called icosahedral and decagonal quasicrystals of MnAl/sub 6/ and other alloys are twinned cubic crystals

    SciTech Connect

    Pauling, L.

    1987-06-01

    It is shown that the x-ray powder diffraction patterns of rapidly quenched MnAl/sub 6/ and Mg/sub 32/(Al,Zn)/sub 49/ and the neutron powder diffraction pattern of MnAl/sub 5/ are compatible with the proposed 820-atom primitive cubic structure. The values found for the edge of the unit cube are 23.365 A (x-ray) and 23.416 A (neutron) for MnAl/sub 6/ and 24.313 A (x-ray) for Mg/sub 32/(Al,Zn)/sub 49/.

  5. Crystal structure and dielectric properties of aurivillius phases A 0.5Bi4.5 B 0.5Ti3.5O15 ( A = Na, Ca, Sr, Pb; B = Cr, Co, Ni, Fe, Mn, Ga)

    NASA Astrophysics Data System (ADS)

    Vlasenko, V. G.; Zubkov, S. V.; Shuvaeva, V. A.; Abdulvakhidov, K. G.; Shevtsova, S. I.

    2014-08-01

    New polycrystalline Bi-containing layered perovskite-like oxides having the Aurivillius phase (AP) structure with the general formula A 0.5Bi4.5 B 0.5Ti3.5O15 ( A = Na, Ca, Sr, Pb; B = Cr, Co, Ni, Fe, Mn, Ga) have been synthesized. The unit cell parameters of the synthesized compounds have been determined by X-ray powder diffraction. All studied APs crystallize in the orthorhombic system (space group A21 am (36)). The degree of distortion of AP unit cells has been analyzed based on the obtained structural parameters. The temperature dependences of the permittivity have been measured and the Curie temperatures have been determined for all the samples. The significant difference in the values of the permittivity maxima for APs Sr0.5Bi4.5Co0.5Ti3.5O15 and Sr0.5Bi4.5Ni0.5Ti3.5O15 has been interpreted based on the electron microscopy data and explained by substantial changes in the porosity and crystal grain sizes of these ceramic samples.

  6. Room temperature magneto-structural transition in Al for Sn substituted Ni-Mn-Sn melt spun ribbons

    NASA Astrophysics Data System (ADS)

    Maziarz, W.; Czaja, P.; Szczerba, M. J.; Przewoźnik, J.; Kapusta, C.; Żywczak, A.; Stobiecki, T.; Cesari, E.; Dutkiewicz, J.

    2013-12-01

    Martensitic and magnetic transformations in Ni48Mn39.5Sn12.5-xAlx (x=0, 1, 2, 3) Heusler alloy ribbons were investigated. It is demonstrated that both magnetic and structural transformations occur in all of the studied samples. It is also shown that substitution of Sn with Al causes the martensitic transformation (MT) and the reverse martensitic transformation (RMT) temperatures to increase to room temperature (ΔTMT=49 K; ΔTRMT=43 K), whereas the Curie temperature of martensite TCM decreases (ΔT=36 K) and the Curie temperature of austenite TCA remains practically insensitive to Al introduction. This then allows to tune TCA and the MT temperature leading to their coincidence at ambient temperature. The austenite phase with the L21 type structure has been identified to exist in all the samples regardless of composition. On the other hand the structure of martensite has been shown to be sensitive to composition. It has been determined as the 10 M martensite with (32¯) stacking sequence in Al free samples and the 4O martensite with the stacking periodicity (31¯) in Al containing samples. In addition, the splitting of the field cooling (FC) and the field heating (FH) thermo-magnetic curves at low (50 Oe) magnetic field and below the TCM has been attributed to intermartensitic transition. The application of large magnetic field (50 kOe) has shown the existence of two distinct ferromagnetic states with a considerable hysteresis loop. The properties of these materials make them promising for magnetocaloric applications.

  7. Phase stability, band gap, and electronic and magnetic properties of quaternary heusler alloys FeMnScZ (Z = Al, Ga, In)

    NASA Astrophysics Data System (ADS)

    Gao, Y. C.; Zhang, Y.; Wang, X. T.

    2015-03-01

    By using the first-principles calculations, we have systematically investigated the phase stability, band gap, and electronic structures and magnetic properties of quaternary Heusler alloys FeMnScZ (Z = Al, Ga, In). We found that FeMnScZ (Z = Al, Ga, In) alloys are half-metallic ferrimagnets at their equilibrium lattice constants and retain a high spin polarization over a quite wide range of lattice distortions. The half-metallic band gap in the FeMnScZ (Z = Al, Ga, In) alloys arises from t 1u- t 2g splitting but not e u- t 1u splitting. The total magnetic moments are 3 µB per unit cell for FeMnScZ (Z = Al, Ga, In) alloys, following the Slater-Pauling rule with the total number of valence electrons minus 18 rather than 24. Moreover, all of these alloys have a negative formation energy, which implies that they can be synthesized experimentally.

  8. Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

    1988-01-01

    Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

  9. Peculiarities of excited state structure and photoluminescence in Bi(3+)-doped Lu(3)Al(5)O(12) single-crystalline films.

    PubMed

    Babin, V; Gorbenko, V; Krasnikov, A; Makhov, A; Nikl, M; Polak, K; Zazubovich, S; Zorenko, Yu

    2009-10-14

    Single-crystalline films of Lu(3)Al(5)O(12):Bi, prepared by the liquid phase epitaxy method from the melt-solution based on Bi(2)O(3) flux, have been studied at 4.2-400 K by time-resolved luminescence spectroscopy methods. Their emission spectra consist of two types of bands with strongly different characteristics. The ultraviolet emission band consists of two components, arising from the electronic transitions which correspond to the [Formula: see text] and [Formula: see text] transitions in a free Bi(3+) ion. At low temperatures, mainly the lower-energy component of this emission is observed, having the decay time∼10(-3) s at T<100 K and arising from the metastable (3)P(0) level. At T>100 K, the higher-energy emission component appears, arising from the thermally populated emitting (3)P(1) level. The visible emission spectrum consists of two dominant strongly overlapped broad bands with large Stokes shifts. At 4.2 K, their decay times are ∼10(-5) s and decrease with increasing temperature. Both of the visible emission bands are assumed to have an exciton origin. The lower-energy band is ascribed to an exciton, localized near a single Bi(3+) ion. The higher-energy band shows a stronger intensity dependence on the Bi(3+) content and is assumed to arise from an exciton localized near a dimer Bi(3+) center. The origin and structure of the corresponding excited states is considered and the processes, taking place in the excited states, are discussed.

  10. Investigation of magnetic spin glass property in La{sub 0.5}Bi{sub 0.5}MnO{sub 3} sample using non-linear AC susceptibility measurements

    SciTech Connect

    Kumar, Punith V. Manju, M. R. Dayal, Vijaylakshmi

    2014-04-24

    We present a comprehensive study on origin of Spin Glass (SG) property in polycrystalline La{sub 0.5}Bi{sub 0.5}MnO{sub 3} perovskite oxide using linear and higher order ac susceptibility (χ) measurements. The third order harmonic susceptibility (χ{sub 3}) vs. temperature (K) with varying magnetic fields from 0.95 to 9.45 Oe and the divergence in their χ{sub 3} (max) allows us to infer the SG behavior occurring in the sample possibly due to co-operative freezing of the spins.

  11. Magsimal-59, an AlMgMnSi-type squeeze-casting alloy designed for temper F

    SciTech Connect

    Hielscher, U.; Sternau, H.; Koch, H.; Franke, A.J.

    1996-10-01

    To get high mechanical properties using standard squeeze casting alloys (for example A356) it is indispensable to make a heat treatment. That means solution heat treatment and quenching and artificially aging. For this reason, the authors were challenged to develop an alloy that provides sophisticated mechanical properties without any heat treatment. Compared to A 356 T6 values in brackets, the new alloy has yield strength > 21 ksi (> 32 ksi) tensile strengths > 42 ksi (43 ksi) and elongation > 15% (10%) in temper F. fatigue strength (r = {minus}1, high frequency pulsation test) is > {+-} 16 ksi (13.5). To meet these properties, a casting process with high solidification velocity like squeeze casting or high pressure die-casting is necessary. Magsimal-59 is of the AlMgMnSi-type. The microstructure consists of {alpha}-Al and a very fine dispersed ternary eutectic. The microstructure and the influence of cooling rate on the mechanical properties will be discussed including some examples of castings.

  12. Lunar regolith dynamics based on analysis of the cosmogenic radionuclides Na-22, Al-26, and Mn-53

    NASA Technical Reports Server (NTRS)

    Fruchter, J. S.; Rancitelli, L. A.; Laul, J. C.; Perkins, R. W.

    1977-01-01

    Depth profiles of Na-22 and Al-26 in the upper portions of five lunar cores are analyzed. From the analyses, it is concluded that the natural gardening processes on the lunar surface result in mixing of the regolith to a depth of 2-3 cm over a time period which is short compared with the half-life of Al-26 (0.73 m.y.). It is also concluded that the rotary drill processes which were used to obtain the deep drill samples generally resulted in loss and/or mixing of the upper portions of the cores. In contrast, the near-surface regions of the drive tube cores appear to have a well-preserved stratigraphy. Analysis of Mn-53 in samples of six lunar rocks helps substantiate the accuracy of age date estimates by other means, and provides definite information that the total lunar surface exposure of two of these rocks has occurred during a single surface event which continued to their collection.

  13. Functioning mechanism of AlF3 coating on the Li- and Mn-rich cathode materials

    SciTech Connect

    Zheng, Jianming; Gu, Meng; Xiao, Jie; Polzin, Bryant; Yan, Pengfei; Chen, Xilin; Wang, Chong M.; Zhang, Jiguang

    2014-11-25

    Li- and Mn-rich (LMR) material is a very promising cathode for lithium ion batteries because of their high theoretical energy density (~900 Wh kg-1) and low cost. However, their poor long-term cycling stability, voltage fade, and low rate capability are significant barriers hindered their practical applications. Surface coating, e.g. AlF3 coating, can significantly improve the capacity retention and enhance the rate capability. However, the fundamental mechanism of this improvement and the microstructural evolution related to the surface coating is still not well understood. Here, we report systematic studies of the microstructural changes of uncoated and AlF3-coated materials before and after cycling using aberration-corrected scanning/transmission electron microscopy and electron energy loss spectroscopy. The results reveal that surface coating can reduce the oxidation of electrolyte at high voltage, thus suppressing the accumulation of SEI layer on electrode particle surface. Surface coating also enhances structural stability of the surface region (especially the electrochemically transformed spinel-like phase), and protects the electrode from severe etching/corrosion by the acidic species in the electrolyte, therefore limiting the degradation of the material. Moreover, surface coating can alleviate the undesirable voltage fade by minimize layered-spinel phase transformation in the bulk region of the materials. These fundamental findings may also be widely applied to explain the functioning mechanism of other surface coatings used in a broad range of electrode materials.

  14. A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

    NASA Astrophysics Data System (ADS)

    McKay, C. L.; Groeneveld, J.; Filipsson, H. L.; Gallego-Torres, D.; Whitehouse, M. J.; Toyofuku, T.; Romero, O. E.

    2015-09-01

    Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related to Marine Isotope Stage 3 (35-28 ka), the Last Glacial Maximum (28-19 ka), Heinrich Event 1 (18-15.5 ka), Bølling Allerød (15.5-13.5 ka) and the Younger Dryas (13.5-11.5 ka). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal

  15. Survey of trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) in retail samples of flavoured and bottled waters.

    PubMed

    Barroso, M F; Ramos, S; Oliva-Teles, M T; Delerue-Matos, C; Sales, M G F; Oliveira, M B P P

    2009-01-01

    Concentrations of eleven trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) were measured in 39 (natural and flavoured) water samples. Determinations were performed using graphite furnace electrothermetry for almost all elements (Al, As, Cd, Cr, Co, Mn, Ni, Pb, and Si). For Se determination hydride generation was used, and cold vapour generation for Hg. These techniques were coupled to atomic absorption spectrophotometry. The trace element content of still or sparkling natural waters changed from brand to brand. Significant differences between natural still and natural sparkling waters (p < 0.001) were only apparent for Mn. The Mann-Whitney U-test was used to search for significant differences between flavoured and natural waters. The concentration of each element was compared with the presence of flavours, preservatives, acidifying agents, fruit juice and/or sweeteners, according to the labelled composition. It was shown that flavoured waters generally increase the trace element content. The addition of preservatives and acidifying regulators had a significant influence on Mn, Co, As and Si contents (p < 0.05). Fruit juice can also be correlated to the increase of Co and As. Sweeteners did not provide any significant difference in Mn, Co, Se and Si content.

  16. High Redox Capacity of Al-Doped La1-x Srx MnO3-δ Perovskites for Splitting CO2 and H2 O at Mn-Enriched Surfaces.

    PubMed

    Ezbiri, M; Becattini, V; Hoes, M; Michalsky, R; Steinfeld, A

    2017-01-26

    Perovskites are attractive candidates for the solar-driven thermochemical redox splitting of CO2 and H2 O into CO and H2 (syngas) and O2 . This work investigates the surface activity of La1-x Srx Mn1-y Aly O3-δ (0≤x≤1, 0≤y≤1) and La0.6 Ca0.4 Mn0.6 Al0.4 O3-δ . At 1623 K and 15 mbar O2 , the oxygen non-stoichiometry of La0.2 Sr0.8 Mn0.8 Al0.2 O3-δ increases with the strontium content and reaches a maximum of δ=0.351. X-ray photoelectron spectroscopy analysis indicates that manganese is the only redox-active metal at the surface. All La1-x Srx Mn1-y Aly O3-δ compositions exhibit surfaces enriched in manganese and depleted in strontium. We discuss how these compositional differences of the surface from the bulk lead to the beneficially higher reduction extents and lower strontium carbonate concentrations at the aluminum-doped surfaces. Using first principles calculations, we validate the experimental reduction trends and elucidate the mechanism of the partial electronic charge redistribution upon perovskite reduction.

  17. Conduction phenomenon of Al3+ modified lead free (Na0.5Bi0.5)0.92Ba0.08TiO3 electroceramics

    NASA Astrophysics Data System (ADS)

    Borkar, Hitesh; Kumar, Ashok

    2016-05-01

    Choice of proper dopants at A or B-site of ABO3 perovskite structure can modify the morphotropic phase boundary (MPB), and hence functional properties of polar systems. The chemical nature of donor or acceptor will significantly influence the fundamental properties. Lead-free ferroelectrics have vast potential to replace the lead-based ceramics. The (Na0.5Bi0.5)1-xBaxTiO3 (NBT-BT) (at x=0.08) near MPB with small substitution of trivalent cations (Al3+) has been synthesized by solid state reaction route. The aim to choose the trivalent cations (Al3+) was its relatively smaller radii than that of Bi3+ cations to develop the antipolar phases in the ferroelectric ceramic. Structural, morphological and elemental compositional analyses were studied by X-ray diffraction (XRD), Secondary electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDAX), respectively. Ferroelectric studies were carried out on various compositions of (Na0.46Bi0.46-xAlxBa0.08)TiO3 (NBAT-BT) (x=0, 0.05, 0.07, 0.10) electroceramics. It was observed that with increase in concentration of Al the ferroelectricity state changes from soft to hard. Temperature dependent dielectric spectroscopy shows broad dielectric dispersion. The Al doping diminishes the relaxor behavior of NBT-BT ceramics. Impedance spectroscopy shows that electrical resistivity and relaxation frequency decreases with increase in Al-concentration. Modulus spectra indicate that Al significantly change the bulk capacitance of NBT-BT.

  18. Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 lead-free piezoceramic system

    PubMed Central

    Berik, Pelin; Maurya, Deepam; Kumar, Prashant; Kang, Min Gyu; Priya, Shashank

    2017-01-01

    Abstract This paper is concerned with the development of a piezoelectric d 15 shear-induced torsion actuator made of a lead-free piezoceramic material exhibiting giant piezoelectric shear stress coefficient (e 15) and piezoelectric transverse shear actuation force comparable to that of lead-based shear-mode piezoceramics. The Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO3 (NBT-BT-Mn) composition exhibited excellent properties as a torsional transducer with piezoelectric shear stress coefficient on the order of 11.6 C m–2. The torsional transducer, consisting of two oppositely polarized NBT-BT-Mn d 15 mode piezoceramic shear patches, provided a rate of twist of 0.08 mm m–1 V–1 under quasi-static 150 V drive. The high value of piezoelectric shear d 15 coefficient in NBT-BT-Mn sample further demonstrated its potential in practical applications. These results confirm that the lead-free piezoceramics can be as effective as their lead-based counterparts. PMID:28179958

  19. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery.

    PubMed

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-09-20

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

  20. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery

    PubMed Central

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-01-01

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm−2. At 1.0 V of cell voltage, a current density of 324 mA cm−2 is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm−2, and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte. PMID:27646032