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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. Magnetic properties of single-phase MnBi grown from MnBi49 melt

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The single-phase NiAs-type MnBi, embedded in Bi matrix, was grown from homogeneous MnBi49 melt at low temperatures to prevent the formation of Mn1.08Bi. 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.

  5. High-pressure behavior of the ternary bismuth oxides Bi{sub 2}Al{sub 4}O{sub 9}, Bi{sub 2}Ga{sub 4}O{sub 9} and Bi{sub 2}Mn{sub 4}O{sub 10}

    SciTech Connect

    Lopez-de-la-Torre, Laura; Friedrich, Alexandra; Juarez-Arellano, Erick A.; Winkler, Bjoern; Wilson, Dan J.; Bayarjargal, Lkhamsuren; Hanfland, Michael; Burianek, Manfred; Muehlberg, Manfred; Schneider, Hartmut

    2009-04-15

    The high-pressure behavior of Bi{sub 2}Al{sub 4}O{sub 9}, Bi{sub 2}Mn{sub 4}O{sub 10} and Bi{sub 2}Ga{sub 4}O{sub 9} was investigated by in situ powder synchrotron X-ray diffraction. Pressures up to 35 GPa were generated using the diamond anvil cell technique. Complementary data of the pressure dependence of Bi{sub 2}Ga{sub 4}O{sub 9} were obtained by density functional theory-based model calculations. Bi{sub 2}Al{sub 4}O{sub 9} and Bi{sub 2}Mn{sub 4}O{sub 10} are structurally stable to the highest pressures obtained. In contrast, a reversible phase transition is observed in Bi{sub 2}Ga{sub 4}O{sub 9} at approximately 16 GPa. A fit of a 3rd-order Birch-Murnaghan equation of state to the p-V data results in V{sub 0}=356.93(9)A{sup 3}, B{sub 0}=122(2)GPa and B{sup '}=4.9(3) for Bi{sub 2}Al{sub 4}O{sub 9}; V{sub 0}=372.27(1)A{sup 3}, B{sub 0}=138(2)GPa and B{sup '}=4.2(2) for Bi{sub 2}Mn{sub 4}O{sub 10}; and V{sub 0}=388.63(3)A{sup 3}, B{sub 0}=102(8)GPa and B{sup '}=3.8(2) for Bi{sub 2}Ga{sub 4}O{sub 9}. The most compressible axis is the a axis for all the compounds. This behavior can be rationalized in terms of the inflexible polyhedra connections parallel to the b and c axes. - The influence of cation substitution on the high-pressure behavior of ternary bismuth oxides was investigated by powder X-ray diffraction using the diamond anvil cell technique. While Bi{sub 2}Ga{sub 4}O{sub 9} shows a reversible phase transition at approximately 16 GPa, Bi{sub 2}Al{sub 4}O{sub 9} and Bi{sub 2}Mn{sub 4}O{sub 10} are structurally stable up to 29 and 35 GPa, respectively. Complementary density functional theory-based model calculations were performed on Bi{sub 2}Ga{sub 4}O{sub 9}.

  6. Development of MnBi permanent magnet: Neutron diffraction of MnBi powder

    SciTech Connect

    Cui, J.; Choi, J. P.; Li, G.; Polikarpov, E.; Darsell, J.; Kramer, M. J.; Zarkevich, N. A.; Wang, L. L.; Johnson, D. D.; Marinescu, M.; Huang, Q. Z.; Wu, H.; Vuong, N. V.; Liu, J. P.

    2014-05-07

    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 powder. The result shows that the purity of the obtained powder is about 91 wt. % at 300 K, 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.

  7. 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.

  8. Synthesis and Structure of BiMnVO 5 and BiMnAsO 5

    NASA Astrophysics Data System (ADS)

    Xun, X.; Yokochi, A.; Sleight, A. W.

    2002-10-01

    The isostructural compounds BiMnVO 5 and BiMnAsO 5 have been prepared for the first time. Their structures were determined from single-crystal X-ray diffraction data in space group Poverline1 with Z=2. For the vanadate a=6.912(4) Å, b=6.991(2) Å, c=5.354(1) Å, α=108.55(2)°, β=95.98(4)° and r=109.73(4)°. For the arsenate a=6.868(1) Å, b=6.905(2) Å, c=5.360(1) Å, α=109.47(2)°, β=95.91(2)°, and γ=109.32(2)°. The structures are based on MnO 6 octahedra sharing one edge to form Mn 2O 10 groups, Bi 2O 8 groups, and MO 4 tetrahedra with M=As or V. The same moieties are found in the BiMnPO 5 structure, which has monoclinic symmetry. However, the triclinic structures for BiMnVO 5 and BiMnAsO 5 cannot be regarded as distorted versions of the monoclinic BiMnPO 5 structure because the connectivity of the moieties is distinctly different.

  9. 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.

  10. 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.

  11. Photoemission study of some novel materials: Rare earth/transition metal interface, Ba*(0.6)*K*(0.4)*BiO3* and AlPdMn

    NASA Astrophysics Data System (ADS)

    Wu, Xilin

    1995-02-01

    Synchrotron radiation photoemission spectroscopy and low energy electron diffraction (LEED) are applied to explore several novel materials: (1) Ce epitaxial growth on W (110) surfaces; (2) Eu epitaxial growth on Ta (110) surfaces; (3) Sm epitaxial growth on Ta (110) surfaces; (4) quasicrystalline AlPdMn; and (5) superconducting Ba(1-x)K(x)BiO3. In the case of rare earth overlayers on transition metal surface, resonance photoemission spectroscopy is used to enhance the 4f features. The metal surface phase transition is investigated on an atomic-scale. In the case of quasicrystalline AlPdMn and superconducting Ba(1-x)K(x)BiO3 the electronic structures are investigated by angle-resolved photoemission.

  12. 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.

  13. Control of anisotropy and magnetism of MnBi nanomaterials

    NASA Astrophysics Data System (ADS)

    Zhang, Wenyong; Sellmyer, David

    2015-03-01

    High-anisotropy MnBi nanostructures have been fabricated by in-situ annealing of Bi/Mn/Bi multilayers and magnetic-field annealing of melt-spun MnxBi100-x ribbons. The ratio of Mn to Bi affects the concentration of NiAs-type MnBi, the degree of c-axis orientation, and phase distribution. For x = 50, the MnxBi100-x film exhibits the optimum nanostructure in which MnBi grains are uniformly separated by a thin layer of Bi. This has produced a record value of (BH)max = 16.3 MGOe for this compound. A good c-axis texture has been developed for Mn50Bi50 ribbons with a remanence ratio of 0.94 after magnetic-field annealing and this result subsequently leads to (BH)max = 9.2 MGOe, the highest value for bulk MnBi materials. The reason for the much higher energy product for the Mn50Bi50 film compared to the Mn50Bi50 ribbon is that the ribbon has a comparatively lower coercivity induced by inhomogeneous distribution of intergranular Bi. The effect of element doping, optimization of preparation parameters, and temperature dependence of properties also will be discussed. This work was supported by US DOE/BES (DE-FG2-04ER46152) and NCMN.

  14. Microstructure Of MnBi/Bi Eutectic Alloy

    NASA Technical Reports Server (NTRS)

    Wilcox, William R.; Eisa, G. F.; Baskaran, B.; Richardson, Donald C.

    1988-01-01

    Collection of three reports describes studies of directional solidification of MnBi/Bi eutectic alloy. Two of the reports, "Influence of Convection on Lamellar Spacing of Eutectics" and "Influence of Convection on Eutectic Microstructure," establish theoretical foundation for remaining document. Reports seek to quantify effect of convection on concentration field of growing lamellar eutectic. Remaining report, "Study of Eutectic Formation," begins by continuing theoretical developments. New technique under development by one of the authors helps to reveal three-dimensional microstructures of alloys.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

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

    PubMed Central

    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

    2015-01-01

    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. PMID:25766744

  2. 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.

  3. Bonding, moment formation, and magnetic interactions in Ca14MnBi11 and Ba14MnBi11

    NASA Astrophysics Data System (ADS)

    Sánchez-Portal, D.; Martin, Richard M.; Kauzlarich, S. M.; Pickett, W. E.

    2002-04-01

    ``14-1-11'' phase compounds, based on magnetic Mn ions and typified by Ca14MnBi11 and Ba14MnBi11, show an unusual magnetic behavior, but the large number (104) of atoms in the primitive cell has precluded any previous full electronic structure study. Using an efficient, local-orbital-based method within the local-spin-density approximation to study the electronic structure, we find a gap between a bonding valence-band complex and an antibonding conduction-band continuum. The bonding bands lack one electron per formula unit of being filled, making them low carrier density p-type metals. The hole resides in the MnBi4 tetrahedral unit, and partially compensates for the high-spin d5 Mn moment, leaving a net spin near 4μB that is consistent with experiment. These manganites are composed of two disjoint but interpenetrating ``jungle gym'' networks of spin-4/2 MnBi9-4 units with ferromagnetic interactions within the same network, and weaker couplings between the networks whose sign and magnitude is sensitive to materials parameters. Ca14MnBi11 is calculated to be ferromagnetic as observed, while for Ba14MnBi11 (which is antiferromagnetic) the ferromagnetic and antiferromagnetic states are calculated to be essentially degenerate. The band structure of the ferromagnetic states is very close to half metallic.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Studies of directionally solidified eutectic Bi/MnBi at low growth velocities

    NASA Technical Reports Server (NTRS)

    Pirich, R. G.

    1984-01-01

    The (lambda-squared)(V) deviation for diffusion-only rod eutectic growth, where lambda is the interrod spacing and V is the growth velocity, was studied at growth velocities less than 5 cm/h in directionally solidified eutectic Bi-Mn (Bi/MnBi). At lower growth velocities, (V less than 0.5 cm/h) morphological instability occurred which resulted in nonaligned, irregularly dispersed MnBi fibers. The (lambda-squared)(V) relation was experimentally determined over a range of growth velocities between 0.1 and 50 cm/h, thermal gradients in the liquid at the liquid-solid interface that varied from 40 to 120 C/cm and solidification orientation with respect to the direction of gravity. Naturally induced, convective instabilities are suggested as a possible growth velocity limit for cooperative growth in the Bi-Mn and related alloy systems.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Control of magnetic properties of MnBi and MnBiCu thin films by Kr{sup +} ion irradiation

    SciTech Connect

    Xu Qianqian; Kanbara, Ryutarou; Kato, Takeshi; Iwata, Satoshi; Tsunashima, Shigeru

    2012-04-01

    Mn{sub 52}Bi{sub 48} (15 nm) and Mn{sub 54}Bi{sub 24}Cu{sub 21} (15 nm) thin films were prepared by the magnetron sputtering and vacuum annealing at 350 deg. C, and the variations of their structures and magnetic properties with 30 keV Kr{sup +} ion irradiation were studied. The MnBi and MnBiCu films exhibited saturation magnetizations M{sub s} of 180 emu/cc and 210 emu/cc, the coercivities H{sub c} of 10 kOe and 3.4 kOe, respectively. The M{sub s} and H{sub c} of the MnBi abruptly vanished by the irradiation of ion dose at 3 x 10{sup 14} ions/cm{sup 2}, while those of the MnBiCu film gradually decreased with increasing the ion dose and became zero at 5 x 10{sup 13} ions/cm{sup 2}. The different trend on the ion irradiation between MnBi and MnBiCu films is understood by the surface structure of the film, i.e., the MnBi has convex islands on its surface, which protect the underneath NiAs-type MnBi from the irradiation, while the MnBiCu has rather flat surface, and its crystal structure was uniformly modified by the irradiation. From the surface flatness and the uniformity of the MnBiCu film, as well as the low annealing temperature of 350 deg. C, it was concluded that the MnBiCu film is one of the attractive materials for high-density ion irradiation bit patterned media.

  16. 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.

  17. Solidifying Mn/Bi in a Magnetic Field

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    Report describes experiments in directional solidification of eutectic Mn/Bi in magnetic field. Study determines whether effects of gravitationally-induced convection reduced or eliminated by magnetic field. Morphological, thermal, and magnetic analyses done on samples grown at various speeds and various applied strengths. Magnetic effects similar to those of low gravity.

  18. Anomalous electron transport in ferromagnetic MnBi films

    NASA Astrophysics Data System (ADS)

    Kharel, Parashu; Sellmyer, D. J.

    2011-03-01

    Materials having high spin polarization, large perpendicular magnetic anisotropy and high Curie temperature hold great potential for a range of spintronic applications. MnBi has the hexagonal NiAs structure and possesses strong permanent magnet and magneto-optical properties. Our recent research shows that MnBi exhibits a high transport spin polarization of 63%, so it is useful to investigate the electron transport properties of this material. We have found that MnBi is a metallic conductor but the resistivity shows an anomalous temperature dependence at low temperature. Analysis of the Hall data for various samples shows that the extraordinary Hall effect is the dominant part in the transverse Hall effect and a Hall angle of 2.8% has been measured. An experimental investigation on the origin of the observed large extraordinary Hall effect in MnBi thin films will be discussed. This research is supported by NSF-MRSEC Grant DMR-0820521, the DOE Grant DE-FG02-04ER46152 and NCMN. S. Mangin, D. Ravelosona, J. A. Katine, M. J. Carey, B. D. Terris and Eric E. Fullerton, Nature Mater. 5, 210 (2006).

  19. 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).

  20. 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.

  1. 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.

  2. 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.

  3. 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

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

    PubMed

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

    2016-11-16

    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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Effect of convection on the microstructure of the MnBi/Bi eutectic

    NASA Technical Reports Server (NTRS)

    Eisa, Gaber Faheem; Wilcox, william R.; Busch, Garrett

    1986-01-01

    For the quasi-regular fibrous microstructure of MnBi formed at freezing rates of 9 mm/h and above, good agreement between experimental and theoretical results for fiber spacing, freezing rate, radial position, and ampoule rotation rate is found. For the irregular blade-like microstructure formed at lower freezing rates, convection is found to coarsen the microstructure somwhat more than predicted. The volume fraction of MnBi was also shown to depend on ampoule rotation and radial position, even in the absence of ampoule rotation. The two-fold finer microstructure observed in space-processed material could not be explained by the elimination of buoyancy-driven natural convection.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. Structural and Ferromagnetic Properties of an Orthorhombic Phase of MnBi Stabilized with Rh Additions

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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). To date, 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 -xRhx Bi [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 3 μB/f .u . at low temperatures. 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.

  17. The Ternary Alkaline-Earth Metal Manganese Bismuthides Sr2MnBi2 and Ba2Mn1-xBi2 (x ≈ 0.15).

    PubMed

    Ovchinnikov, Alexander; Saparov, Bayrammurad; Xia, Sheng-Qing; Bobev, Svilen

    2017-10-02

    Two new ternary manganese bismuthides have been synthesized and their structures established based on single-crystal X-ray diffraction methods. Sr2MnBi2 crystallizes in the orthorhombic space group Pnma (a = 16.200(9) Å, b = 14.767(8) Å, c = 8.438(5) Å, V = 2018(2) Å(3); Z = 12; Pearson index oP60) and is isostructural to the antimonide Sr2MnSb2. The crystal structure contains corrugated layers of corner- and edge-shared [MnBi4] tetrahedra and Sr atoms enclosed between these layers. Electronic structure calculations suggest that Sr2MnBi2 is a magnetic semiconductor possessing Mn(2+) (high-spin d(5)) ions, and its structure can be rationalized within the Zintl concept as [Sr(2+)]2[Mn(2+)][Bi(3-)]2. The temperature dependence of the resistivity shows behavior consistent with a degenerate semiconductor/poor metal, and magnetic susceptibility measurements reveal a high degree of frustration resulting from the two-dimensional nature of the structure. The compositionally similar Ba2Mn1-xBi2 (x ≈ 0.15) crystallizes in a very different structure (space group Imma, a = 25.597(8) Å, b = 25.667(4) Å, c = 17.128(3) Å, V = 11253(4) Å(3); Z = 64; Pearson index oI316) with its own structure type. The complex structure boasts Mn atoms in a variety of coordination environments and can be viewed as consisting of two interpenetrating 3D frameworks, linked by Bi-Bi bonds. Ba2Mn1-xBi2 can be regarded as a highly reduced compound with anticipated metallic behavior.

  18. 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.

  19. 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.

  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. 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.

  3. 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.

  4. Effect of composition and heat treatment on MnBi magnetic materials

    SciTech Connect

    Cui, Jun; Choi, Jung-Pyung; Polikarpov, Evgueni; Bowden, Mark E; Xie, Wei; Li, Guosheng; Nie, Zimin; Zarkevich, Nikolai; Kramer, Matthew J; Johnson, Duane

    2014-10-01

    The metallic compound MnBi is a promising rare-earth-free permanent magnet material, unique among all candidates for its high intrinsic coercivity (Hci) and its large positive temperature coefficient. The Hci of MnBi in thin-film or powder form can exceed 12 and 26 kOe at 300 and 523 K, respectively. Such a steep rise in Hci with increasing temperature is unique to MnBi. Consequently, MnBi is a highly sought-after hard phase for exchange coupling nanocomposite magnets. However, the reaction between Mn and Bi is peritectic, and hence Mn tends to precipitate out of the MnBi liquid during the solidification process. As result, when the alloy is prepared using conventional induction or arc-melting casting methods, additional Mn is required to compensate the precipitation of Mn. In addition to composition, post-casting annealing plays an important role in obtaining a high content of MnBi low-temperature phase (LTP) because the annealing encourages the Mn precipitates and the unreacted Bi to react, forming the desired LTP phase. Here we report a systematic study of the effect of composition and heat treatments on the phase content and magnetic properties of Mn–Bi alloys. In this study, 14 compositions were prepared using conventional metallurgical methods, and the compositions, crystal structures, phase content and magnetic properties of the resulting alloys were analyzed. The results show that the composition with 55 at.% Mn exhibits both the highest LTP content (93 wt.%) and magnetization (74 emu g-1 with 9 T applied field at 300 K).

  5. 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.

  6. Magnetic properties in MnBi alloy of small crystallites for permanent magnet devices

    SciTech Connect

    Sharma, S. K.; Prakash, H. R.; Ram, S.

    2016-05-06

    A rare-earth free alloy like MnBi is a potential candidate for developing small magnets and devices. In a commercially viable method, a MnBi alloy was prepared by arc melting Mn and Bi metals in a 1:1 ratio. In terms of the X-ray diffraction a single crystalline MnBi phase is formed of the as prepared alloy. FESEM images delineate thin MnBi layers (25 – 40 nm thickness) of average EDX composition throughout the specimen. A large coercivity 5.501 kOe (6.5 emu/g magnetization) observed in an M-H at 300 K is decreased to 0.171 (9.0 emu/g magnetization) at 100 K in decreasing upon cooling.

  7. 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.

  8. 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

  9. 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

  10. 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.

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

    DOE PAGES

    Zhang, Anmin; Liu, Changle; Yi, Changjiang; ...

    2016-12-16

    Dirac materials exhibit intriguing low-energy carrier dynamics that offer a fertile ground for novel physics discovery. Something of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. 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 drivesmore » a charge-gap opening along the Dirac locus. These 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. Our results also hold great promise for applications in magnetic Dirac devices.« less

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

  18. Synthesis and characterization of Mn intercalated Mg-Al hydrotalcite.

    PubMed

    Yang, Chengxue; Liao, Libing; Lv, Guocheng; Wu, Limei; Mei, Lefu; Li, Zhaohui

    2016-10-01

    Mn intercalated hydrotalcite was prepared using a reconstruction method. And Mn intercalation was confirmed by XRD, FTIR, and thermal analyses. The different valences of Mn were present as determined by XPS. Calcination slightly promoted the isomorphic replacement of Mn(2+) and Mn(3+) for Mg(2+) and Al(3+), especially the replacement of Mn(2+) for Mg(2+) and Al(3+), and to some extent, reduced Mn intercalation. Ultrasonic treatment significantly increased Mn intercalation in permanganate form (Mn(7+)), and promoted the replacement of Mn(2+) for Mg(2+) and Al(3+). XRF analysis showed that ultrasonic treatment decreased the unbalanced layer charge of Mn intercalated hydrotalcite, while prolonged calcination increased it. These results may provide guidance on the preparation and application of Mn intercalated hydrotalcite. Extended calcination time and ultrasonic vibration increased the interlayer spacing of hydrotalcite, as a result of reduction in layer charge. As the layer charge was not completely balanced after Mn intercalation, a certain amount of CO3(2-) was re-adsorbed into the interlayer space. Mn-hydrotalcites with different layer charges, different contents of Mn with varying valences are expected to have different performances in the process of adsorption, degradation, and catalysis. Copyright © 2016 Elsevier Inc. All rights reserved.

  19. 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).

  20. 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.

  1. 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.

  2. Molecular beam epitaxy growth and structure of self-assembled Bi2Se3/Bi2MnSe4 multilayer heterostructures

    NASA Astrophysics Data System (ADS)

    Hagmann, Joseph A.; Li, Xiang; Chowdhury, Sugata; Dong, Si-Ning; Rouvimov, Sergei; Pookpanratana, Sujitra J.; Yu, Kin Man; Orlova, Tatyana A.; Bolin, Trudy B.; Segre, Carlo U.; Seiler, David G.; Richter, Curt A.; Liu, Xinyu; Dobrowolska, Margaret; Furdyna, Jacek K.

    2017-08-01

    We demonstrate that the introduction of an elemental beam of Mn during the molecular beam epitaxial growth of Bi2Se3 results in the formation of layers of Bi2MnSe4 that intersperse between layers of pure Bi2Se3. This study revises the assumption held by many who study magnetic topological insulators (TIs) that Mn incorporates randomly at Bi-substitutional sites during epitaxial growth of Mn:Bi2Se3. Here, we report the formation of thin film magnetic TI Bi2MnSe4 with stoichiometric composition that grows in a self-assembled multilayer heterostructure with layers of Bi2Se3, where the number of Bi2Se3 layers separating the single Bi2MnSe4 layers is approximately defined by the relative arrival rate of Mn ions to Bi and Se ions during growth, and we present its compositional, structural, and electronic properties. We support a model for the epitaxial growth of Bi2MnSe4 in a near-periodic self-assembled layered heterostructure with Bi2Se3 with corresponding theoretical calculations of the energetics of this material and those of similar compositions. Computationally derived electronic structure of these heterostructures demonstrates the existence of topologically nontrivial surface states at sufficient thickness.

  3. 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.

  4. 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.

  5. Magnetic properties of mechanically alloyed Mn-Al-C powders

    NASA Astrophysics Data System (ADS)

    Kohmoto, O.; Kageyama, N.; Kageyama, Y.; Haji, H.; Uchida, M.; Matsushima, Y.

    2011-01-01

    We have prepared supersaturated-solution Mn-Al-C alloy powders by mechanical alloying using a planetary high-energy mill. The starting materials were pure Mn, Al and C powers. The mechanically-alloyed powders were subjected to a two-step heating. Although starting particles are Al and Mn with additive C, the Al peak disappears with MA time. With increasing MA time, transition from α-Mn to β-Mn does not occur; the α-Mn structure maintains. At 100 h, a single phase of supersaturated-solution α-Mn is obtained. The lattice constant of α-Mn decreases with increasing MA time. From the Scherrer formula, the crystallite size at 500 h is obtained as 200Å, which does not mean amorphous state. By two-step heating, high magnetization (66 emu/g) was obtained from short-time-milled powders (t=10 h). The precursor of the as-milled powder is not a single phase α-Mn but contains small amount of fcc Al. After two-step heating, the powder changes to τ-phase. Although the saturation magnetization increases, the value is less than that by conventional bulk MnAl (88 emu/g). Meanwhile, long-time-milled powder of single α-Mn phase results in low magnetization (5.2 emu/g) after two-step heating.

  6. Layer-number dependence of the magnetic properties of MnBi films

    NASA Astrophysics Data System (ADS)

    Moon, Hongjae; Kim, Sumin; Jung, Hwaebong; Lee, Hyun-Sook; Lee, Wooyoung

    2017-10-01

    We present the effect of multilayer deposition on the magnetic properties of MnBi thin films. The multilayered MnBi films were fabricated with alternating deposition of Bi and Mn with N (N = 2-10) layers (L), followed by in situ thermal annealing. As N increases, the even-layered and odd-layered films show a similar layer-number-dependence of the magnetic properties, such as an increasing behavior for Hc and a concave-up behavior for Mr and (BH)max. Higher magnetic properties were obtained at 9L and 10L. According to the electron microscopy analyses, different morphologies and elemental distributions were observed at different N (e.g., smooth-surfaced MnBi film with Bi islands at 2L and uneven-surfaced MnBi film at 10L). The different distributions of microstructure and chemical components are associated with the layer-dependent magnetic properties of the MnBi films.

  7. 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

  8. 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.

  9. Migration kinetics of oxygen vacancies in Mn-modified BiFeO₃ thin films.

    PubMed

    Wu, Jiagang; Wang, John; Xiao, Dingquan; Zhu, Jianguo

    2011-07-01

    Migration kinetics of oxygen vacancies in BiFe(0.95)Mn(0.05)O(3) thin film were investigated by the temperature -dependent leakage current as well as the electric field and temperature-dependent impedance spectroscopy. The BiFe(0.95)Mn(0.05)O(3) is of an abnormal leakage behavior, and an Ohmic conduction is observed regardless of varied temperatures and electric fields. The temperature-dependent impedance spectroscopy under different resistance states is used to illuminate different leakage behavior between BiFe(0.95)Mn(0.05)O(3) and pure BiFeO(3). The impedance spectroscopy under a high resistance state shows that the first ionization of oxygen vacancies is responsible for the dielectric relaxation and electrical conduction of BiFe(0.95)Mn(0.05)O(3) in the whole temperature range of 294 to 474 K; the BiFeO(3) exhibits similar dielectric relaxation and electrical conduction behavior in the low-temperature range of 294-374 K, whereas the short-range motion of oxygen vacancies was involved in the high-temperature range of 374-474 K. The impedance spectroscopy under a low resistance state demonstrates that the dielectric relaxation and conduction mechanisms almost keep unchanged for BiFe(0.95)Mn(0.05)O(3), whereas the hopping electrons of Fe(2+)-V(O)(•)-Fe(3+) and Fe(2+)-Fe(3+) are responsible for its dielectric relaxation and conduction mechanism of BiFeO(3). Different impedance spectroscopy under low and high resistance states confirms that an abnormal leakage behavior of BiFe(0.95)Mn(0.05)O(3) is related to different migration kinetics of oxygen vacancies, obviously differing from that of BiFeO(3).

  10. 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.

  11. 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.

  12. 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.

  13. 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%.

  14. 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.

  15. 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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Adsorption-controlled growth of BiMnO3 films by molecular-beam epitaxy

    SciTech Connect

    Lee, H; Ke, X; Misra, R.; Ihlefeld, J.F.; Xu, Xiaoshan; Mei, Z.G.; Heeg, T.; Roeckerath, M.; Musfeldt, J.L.; Schiffer, P.; Schlom, D.G.

    2010-01-01

    We have developed the means to grow BiMnO3 thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO3 may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with rocking curve full width at half maximum values as narrow as 11 arc sec 0.003 . Optical absorption measurements reveal that BiMnO3 has a direct band gap of 1.1 0.1 eV.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Processing of MnBi bulk magnets with enhanced energy product

    DOE PAGES

    Poudyal, Narayan; Liu, Xubo; Wang, Wei; ...

    2016-02-23

    Here, we report magnetic properties and microstructure of high energy-product MnBi bulk magnets fabricated by low-temperature ball-milling and warm compaction technique. A maximum energy product (BH)max of 8.4 MGOe and a coercivity of 6.2 kOe were obtained in the bulk MnBi magnet at room temperature. Magnetic characterization at elevated temperatures showed an increase in coercivity to 16.2 kOe while (BH)max value decreased to 6.8 MGOe at 400 K. Microstructure characterization revealed that the bulk magnets consist of oriented uniform nanoscale grains with average size about 50 nm.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Combined effects of Bi deficiency and Mn substitution on the structural transformation and functionality of BiFeO{sub 3} films

    SciTech Connect

    Chen, Jingyi; Wang, Yao Deng, Yuan

    2014-11-07

    Mn-doped BiFeO{sub 3} 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 BiFeO{sub 3}. The crystal structure of Bi{sub 1−δ}Fe{sub 1−x}Mn{sub x}O{sub 3} 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 Bi{sub 1−δ}Fe{sub 1−x}Mn{sub x}O{sub 3} 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 BiFeO{sub 3} 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 BiFeO{sub 3} films. This study thus shows a simple and effective way to control the functionalities of BiFeO{sub 3} films.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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.

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

    SciTech Connect

    Williams, T. J. Taylor, A. E.; Lumsden, M. D.; Christianson, A. D.; Hahn, S. E.; Fishman, R. S.; Parker, D. S.; McGuire, M. A.; Sales, B. C.

    2016-05-09

    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 parametrize 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.

  8. 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.

  9. 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.

  10. Spin dynamics and magnetic interactions of Mn dopants in the topological insulator Bi2Te3

    NASA Astrophysics Data System (ADS)

    Zimmermann, S.; Steckel, F.; Hess, C.; Ji, H. W.; Hor, Y. S.; Cava, R. J.; Büchner, B.; Kataev, V.

    2016-09-01

    The magnetic and electronic properties of the magnetically doped topological insulator Bi2 -xMnxTe3 were studied using electron-spin resonance (ESR) and measurements of static magnetization and electrical transport. The investigated high-quality single crystals of Bi2 -xMnxTe3 show a ferromagnetic phase transition for x ≥0.04 at TC≈12 K. The Hall measurements reveal a p -type finite charge-carrier density. Measurements of the temperature dependence of the ESR signal of Mn dopants for different orientations of the external magnetic field give evidence that the localized Mn moments interact with the mobile charge carriers leading to Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a low-dimensional character of magnetic correlations that persist far above the ferromagnetic ordering temperature.

  11. 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.

  12. Effect of Mn and Fe on the Formation of Fe- and Mn-Rich Intermetallics in Al-5Mg-Mn Alloys Solidified Under Near-Rapid Cooling.

    PubMed

    Liu, Yulin; Huang, Gaoren; Sun, Yimeng; Zhang, Li; Huang, Zhenwei; Wang, Jijie; Liu, Chunzhong

    2016-01-29

    Mn was an important alloying element used in Al-Mg-Mn alloys. However, it had to be limited to a low level (<1.0 wt %) to avoid the formation of coarse intermetallics. In order to take full advantage of the benefits of Mn, research was carried out to investigate the possibility of increasing the content of Mn by studying the effect of cooling rate on the formation of Fe- and Mn-rich intermetallics at different content levels of Mn and Fe. The results indicated that in Al-5Mg-Mn alloy with low Fe content (<0.1 wt %), intermetallic Al₆(Fe,Mn) was small in size and amount. With increasing Mn content, intermetallic Al₆(Fe,Mn) increased, but in limited amount. In high-Fe-containing Al-5Mg-Mn alloys (0.5 wt % Fe), intermetallic Al₆(Fe,Mn) became the dominant phase, even in the alloy with low Mn content (0.39 wt %). Cooling rate played a critical role in the refinement of the intermetallics. Under near-rapid cooling, intermetallic Al₆(Fe,Mn) was extremely refined. Even in the high Mn and/or high-Fe-containing alloys, it still demonstrated fine Chinese script structures. However, once the alloy composition passed beyond the eutectic point, the primary intermetallic Al₆(Fe,Mn) phase displayed extremely coarse platelet-like morphology. Increasing the content of Fe caused intermetallic Al₆(Fe,Mn) to become the primary phase at a lower Mn content.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. Anomalous magneto-structural behavior of MnBi explained: A path towards an improved permanent magnet

    NASA Astrophysics Data System (ADS)

    Zarkevich, N. A.; Wang, L.-L.; Johnson, D. D.

    2014-03-01

    Low-temperature MnBi (hexagonal NiAs phase) exhibits anomalies in the lattice constants (a, c) and bulk elastic modulus (B) below 100 K, spin reorientation and magnetic susceptibility maximum near 90 K, and, importantly for high-temperature magnetic applications, an increasing coercivity (unique to MnBi) above 180 K. We calculate the total energy and magneto-anisotropy energy (MAE) versus (a, c) using DFT+U methods. We reproduce and explain all the above anomalies. We predict that coercivity and MAE increase due to increasing a, suggesting means to improve MnBi permanent magnets.

  18. 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.

  19. 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

  20. 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.

  1. Local and average structure of Mn- and La-substituted BiFeO3

    NASA Astrophysics Data System (ADS)

    Jiang, Bo; Selbach, Sverre M.

    2017-06-01

    The local and average structure of solid solutions of the multiferroic perovskite BiFeO3 is investigated by synchrotron X-ray diffraction (XRD) and electron density functional theory (DFT) calculations. The average experimental structure is determined by Rietveld refinement and the local structure by total scattering data analyzed in real space with the pair distribution function (PDF) method. With equal concentrations of La on the Bi site or Mn on the Fe site, La causes larger structural distortions than Mn. Structural models based on DFT relaxed geometry give an improved fit to experimental PDFs compared to models constrained by the space group symmetry. Berry phase calculations predict a higher ferroelectric polarization than the experimental literature values, reflecting that structural disorder is not captured in either average structure space group models or DFT calculations with artificial long range order imposed by periodic boundary conditions. Only by including point defects in a supercell, here Bi vacancies, can DFT calculations reproduce the literature results on the structure and ferroelectric polarization of Mn-substituted BiFeO3. The combination of local and average structure sensitive experimental methods with DFT calculations is useful for illuminating the structure-property-composition relationships in complex functional oxides with local structural distortions.

  2. 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.

  3. Atomistic simulation and XAS investigation of Mn induced defects in Bi{sub 12}TiO{sub 20}

    SciTech Connect

    Rezende, Marcos V dos S.; Santos, Denise J.; Jackson, Robert A.; Valerio, Mário E.G.; Macedo, Zélia S.

    2016-06-15

    This work reports an investigation of the valence and site occupancy of Mn dopants in Bi{sub 12}TiO{sub 20} (BTO: Mn) host using X-ray Absorption (XAS) and atomistic simulation techniques based on energy minimisation. X-ray Absorption Near Edge Structure (XANES) at the Mn K-edges gave typical results for Mn ions with mixed valences of 3+ and 4+. Extended X-ray Absorption Fine Structure (EXAFS) results indicated that Mn ions are probably substituted at Ti sites. Atomistic simulation was performed assuming the incorporation of Mn{sup 2+}, Mn{sup 3+} and Mn{sup 4+} ions at either Bi{sup 3+} or Ti{sup 4+} sites, and the results were compared to XANES and EXAFS measurements. Electrical conductivity for pure and doped samples was used to evaluate the consistency of the proposed model. - Graphical abstract: The structure of Bi{sub 12}TiO{sub 20} (BTO). Display Omitted - Highlights: • Pure and Mn-doped Bi{sub 12}TiO{sub 20} samples were studied by experimental techniques combined with atomistic simulation. • Good agreement between experimental and simulation results was obtained. • XANES results suggest a mixture of 3+ and 4+ valences for Mn, occupying the Ti4+ site in both cases. • Charge compensation by holes is most energetically favoured, explaining the enhancement observed in AC dark conductivity.

  4. Magnetic properties and structure of low temperature phase MnBi with island structure

    NASA Astrophysics Data System (ADS)

    Ito, Masashi; Tanaka, Yoshitomo; Satoh, Takuya; Mankey, Gary; Schad, Rainer; Suzuki, Takao

    2017-05-01

    The magnetic properties of the low temperature phase (LTP) MnBi thin films of islands structure are discussed. The LTP MnBi islands are formed onto silica substrates after the multilayers Bi(3.2nm)/Mn(2nm)x N are deposited and then annealed at 450C for 0.5hr, where N is the number of the repetition of a pair of Mn and Bi layer. Those islands are found to be of the LTP MnBi, with the c-axis orientation along the normal to the sample plane for N=10 ˜ 40. Their size vary from place to place, but are averagely of about a few hundred nm in height and a few μm in width for N from 10 to 40. For N=200, the elongated islands are formed densely, with the length of about a few tens of μm. The coverage of those islands increases with N. The temperature dependence of saturation magnetization Ms is qualitatively similar to that for bulk, though the absolute values for Ms are smaller by 20%. The magnetic anisotropy constants of Ku1 and Ku2 are evaluated for the samples with N=10 ˜ 40, where Ku1 and Ku2 are the magnetic anisotropy constants corresponding to the second and fourth power term in the uniaxial magnetic anisotropy energy expression. It is found that the Ku1 increases with T monotonously, reaching to about 1x107 erg/cc at 400K. On the other hand, the Ku2 remains nearly zero for temperatures below 300K, and then becomes negative, reaching to about 7 x 106 erg/cc at 400K. This is the first to report of the temperature dependence of Ku1 and Ku2 in the LTP MnBi of an island structure. It is also noted that the decrease of Ku for a temperature range beyond around 450 K is possibly due to the decrease of the Ku2 component, as demonstrated in the present study.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    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 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. The dependence of magnetic anisotropy on the anisotropic lattice change is confirmed by density functional theory.

  7. 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.

  8. Plasmon Enhancement of Photoinduced Resistivity Changes in Bi1-xCaxMnO3 Thin Films

    NASA Astrophysics Data System (ADS)

    Smolyaninova, Vera; Talanova, E.; Kolagani, Rajeswari; Yong, G.; Kennedy, R.; Steger, M.; Wall, K.

    2007-03-01

    Doped rare-earth manganese oxides (manganites) exhibit a wide variety of physical phenomena due to complex interplay of electronic, magnetic, orbital, and structural degrees of freedom and their sensitivity to external fields. A photoinduced insulator to conductor transition in charge-ordered manganites is especially interesting from the point of view of creating photonic devices. Thin films of Bi0.4Ca0.6MnO3 exhibit large photoinduced resistivity changes associated with melting of the charge ordering by visible light [1]. We have found a considerable increase of the photoinduced resistivity changes in the Bi0.4Ca0.6MnO3 thin film after depositing metal nanoparticles on the surface. This increase can be explained by enhancement of local electromagnetic field in the vicinity of the gold nanoparticle due to the plasmon resonance. The changes in lifetime of the photoinduced state will be reported, and the possible origin of these effects will be discussed. [1] V. N. Smolyaninova at al., Appl. Phys. Lett. 86, 071922 (2005).

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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

  17. 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.

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

    SciTech Connect

    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. Something of particular interest is the interplay of Dirac carriers with other quantum phenomena such as magnetism. 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. These 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. Our results also hold great promise for applications in magnetic Dirac devices.

  19. A Full View of the Segregation Evolution in Al-Bi Immiscible Alloy

    NASA Astrophysics Data System (ADS)

    Lu, Wenquan; Zhang, Shuguang; Zhang, Wei; Hu, Qiaodan; Yu, Jianding; Fu, Yanan; Li, Jianguo

    2017-06-01

    Using synchrotron radiography, in this study, we caught a full view of the segregation evolution of Al-10 wt pct Bi immiscible alloy during solidification. We provide the direct experimental evidence of surface segregation prior to liquid decomposition. And the Bi enrichment at the bottom part should come from melt flow rather than Soret effect. The Marangoni effect and Stokes effect dominate in separate stages in solidifying Al-Bi alloy. Further, the size distribution of Bi droplets obeys Gaussian distribution.

  20. 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.

  1. 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.

  2. 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.

  3. Discontinuous coarsening behavior of Ni(2)MnAl intermetallic compound during isothermal aging treatment of Fe-Mn-Ni-Al alloys.

    PubMed

    Heo, Yoon-Uk; Takeguchi, Masaki; Furuya, Kazuo; Lee, Hu-Chul

    2010-08-01

    The discontinuous reaction of the Ni(2)MnAl intermetallic phase was investigated during the aging of a solution-treated Fe-8.3Mn-8.2Ni-4.2Al alloy. During aging, Ni(2)MnAl lamellae formed at the prior austenite grain boundaries and twin boundaries and grew into the neighboring grains. The presence of continuously precipitated fine Ni(2)MnAl particles before the growth of the discontinuously precipitated lamellae was confirmed by dark-field transmission electron microscopy, and it was concluded that the present reaction is a type of discontinuous coarsening process, alpha' + Ni(2)MnAl (continuous precipitation) --> alpha + Ni(2)MnAl (discontinuous coarsening). The chemical driving force and the reduction of the total coherent strain energy were suggested to be the driving force for the discontinuous coarsening reaction.

  4. 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.

  5. 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.

  6. Optical investigation of the strong spin-orbit-coupled magnetic semimetal YbMnBi2

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Dipanjan; Cheng, Bing; Yaresko, Alexander; Gibson, Quinn D.; Cava, R. J.; Armitage, N. P.

    2017-08-01

    Strong spin-orbit coupling (SOC) can result in ground states with nontrivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of A MnBi2 (A = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of YbMnBi2, a newly discovered member of this family and a proposed Weyl semimetal (WSM) candidate with broken time reversal symmetry. Together with density functional theory (DFT) band-structure calculations, we show that the complex conductivity can be interpreted as the sum of an intraband Drude response and interband transitions. We argue that the canting of the magnetic moments that has been proposed to be essential for the realization of the WSM in an otherwise antiferromagnetically ordered system is not necessary to explain the optical conductivity. We believe our data is explained qualitatively by the uncanted magnetic structure with a small offset of the chemical potential from strict stochiometry. We find no definitive evidence of a bulk Weyl nodes. Instead, we see signatures of a gapped Dirac dispersion, common in other members of A MnBi2 family or compounds with similar 2D network of Bi atoms. We speculate that the evidence for a WSM seen in ARPES arises through a surface magnetic phase. Such an assumption reconciles all known experimental data.

  7. 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.

  8. 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.

  9. 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.

  10. 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; hide

    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.

  11. 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.

  12. 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.

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

    DOE PAGES

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

    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 themore » importance of the anisotropic lattice change and Mn-Bi hybridization to the magnetic anisotropy change across the SRT.« less

  14. 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.

  15. Ferroelectricity in BiMO (M=Al and Ga) with the γ-BiO structure

    NASA Astrophysics Data System (ADS)

    Mangalam, R. V. K.; Ranjith, R.; Iyo, A.; Sundaresan, A.; Krupanidhi, S. B.; Rao, C. N. R.

    2006-10-01

    We report on the dielectric properties of bismuth aluminate and gallate with Bi:Al(Ga) ratio of 1:1 and 12:1 prepared at high temperature and ambient pressure. These compounds crystallize in a noncentrosymmetric body-centered cubic structure (space group I23) with a˜10.18 Å rather than in the perovskite structure. This cubic phase is related to the γ-BiO structure which has the actual chemical formula Bi243+(BiBi)O. In the aluminates and gallates studied by us, the Al and Ga ions are distributed over the 24f and 2a sites. These compounds exhibit ferroelectric hysteresis at room temperature with a weak polarization.

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

    PubMed

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

    2013-12-21

    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.

  17. 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.

  18. 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.

  19. Superplasticity in a lean Fe-Mn-Al steel.

    PubMed

    Han, Jeongho; Kang, Seok-Hyeon; Lee, Seung-Joon; Kawasaki, Megumi; Lee, Han-Joo; Ponge, Dirk; Raabe, Dierk; Lee, Young-Kook

    2017-09-29

    Superplastic alloys exhibit extremely high ductility (>300%) without cracks when tensile-strained at temperatures above half of their melting point. Superplasticity, which resembles the flow behavior of honey, is caused by grain boundary sliding in metals. Although several non-ferrous and ferrous superplastic alloys are reported, their practical applications are limited due to high material cost, low strength after forming, high deformation temperature, and complicated fabrication process. Here we introduce a new compositionally lean (Fe-6.6Mn-2.3Al, wt.%) superplastic medium Mn steel that resolves these limitations. The medium Mn steel is characterized by ultrafine grains, low material costs, simple fabrication, i.e., conventional hot and cold rolling, low deformation temperature (ca. 650 °C) and superior ductility above 1300% at 850 °C. We suggest that this ultrafine-grained medium Mn steel may accelerate the commercialization of superplastic ferrous alloys.Research in new alloy compositions and treatments may allow the increased strength of mass-produced, intricately shaped parts. Here authors introduce a superplastic medium manganese steel which has an inexpensive lean chemical composition and which is suited for conventional manufacturing processes.

  20. 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

  1. 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

  2. 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.

  3. Pressure induced superconductivity in the antiferromagnetic Dirac material BaMnBi2.

    PubMed

    Chen, Huimin; Li, Lin; Zhu, Qinqing; Yang, Jinhu; Chen, Bin; Mao, Qianhui; Du, Jianhua; Wang, Hangdong; Fang, Minghu

    2017-05-09

    The so-called Dirac materials such as graphene and topological insulators are a new class of matter different from conventional metals and (doped) semiconductors. Superconductivity induced by doing or applying pressure in these systems may be unconventional, or host mysterious Majorana fermions. Here, we report a successfully observation of pressure-induced superconductivity in an antiferromagnetic Dirac material BaMnBi2 with T c of ~4 K at 2.6 GPa. Both the higher upper critical field, μ 0 H c2(0) ~ 7 Tesla, and the measured current independent of T c precludes that superconductivity is ascribed to the Bi impurity. The similarity in ρ ab (B) linear behavior at high magnetic fields measured at 2 K both at ambient pressure (non-superconductivity) and 2.6 GPa (superconductivity, but at the normal state), as well as the smooth and similar change of resistivity with pressure measured at 7 K and 300 K in zero field, suggests that there may be no structure transition occurred below 2.6 GPa, and superconductivity observed here may emerge in the same phase with Dirac fermions. Our findings imply that BaMnBi2 may provide another platform for studying SC mechanism in the system with Dirac fermions.

  4. 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

  5. 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.

  6. Effects of frit addition on the surface morphology and structural properties of ZnO-Bi2O3-Mn2O3 discs

    NASA Astrophysics Data System (ADS)

    Shahardin, Ahmad Hajidi; Mahmud, Shahrom; Sendi, Rabab Khalid

    2015-04-01

    ZnO-Bi2O3-Mn2O3 discs were prepared using conventional ceramic processing method and sintered at 1000°C. The different percentages of frit on the ZnO-Bi2O3-Mn2O3 discs were 0.0%, 0.5%, 1.0% and 3.0%. From FESEM observation, the grain structure and grain growth were more uniformly constructed and well distributed. Frit addition was found to cause a big drop in the average grain size from 4.59 µm to 2.76 µm even with an addition of 0.5 mol%. The Si and Al content in the frit recipe might have played a role as inhibiting agents in grain growth during sintering. RAMAN intensity and phase shifting were not affected by frit addition except at 3 mol%. Frit addition did not affect the formation of secondary phases. Frit addition below 3 mol% in ZnO-Bi2O3-Mn2O3 varistor discs can be used as a method in controlling grain size without affecting other properties.

  7. 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

  8. 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.

  9. 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%.

  10. Effect of applied magnetic fields during directional solidification of eutectic Bi-Mn

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    Samples of rod eutectics Bi/MnBi were directionally solidified in a growth-up Bridgman-Stockbarger configuration in the presence of a transverse magnetic field up to 3 kg to determine whether gravity-driven convective effects could be reduced or eliminated. The experiments were carried out over a range of furnace velocities, V, of 0.2 to 50 cm per hour with a thermal gradient at the liquid-solid interface of 100 C/cm and 150 C/cm. Morphological, thermal and magnetic analyses were carried out on samples grown with and without an applied magnetic field. For samples grown at V greater than 3 cm per hour in a transverse magnetic field, reduced mean rod diameter and interrod spacing occurred as well as undercooling and increased coercive strength. The data agreed with that obtained for low-g growth at 50 cm per hour and 30 cm per hour.

  11. Exchange bias between ferromagnetic metals and multiferroic BiFeO3, LuMnO3, and TbMnO3

    NASA Astrophysics Data System (ADS)

    Murakami, Makoto; Fujino, S.; Hattrick-Simpers, J.; Lim, S.-H.; Salamanca-Riba, L.; Kundaliya, D.; Ogale, S.; Venkatesan, T.; Higgins, J.; Wuttig, M.; Takeuchi, I.; Lofland, S.; Cheong, S.-W.

    2007-03-01

    We are using exchange bias at ferromagnet layer/multiferroic interfaces to study the nature of magnetism in multiferroic materials. Co 5 nm layers have been deposited by sputtering on surfaces of epitaxial BiFeO3 and TbMnO3 thin films and on LuMnO3 single crystals. Epitaxial BiFeO3 and TbMnO3 films were prepared by PLD. Magnetic properties of the Co/multiferroic bilayers are measured using SQUID, VSM, MOKE and XMCD. In BiFeO3, we find that the bilayers exhibit exchange bias even at room temperature. In the TbMnO3 system, increasing of coercive field and exchange bias was also clearly observed below the N'eel temperature. In LuMnO3, we observe positive exchange bias as well as switching of the sign of the exchange bias depending on the cooling procedure. This behavior may be related to the frustration in Mn spins. Difference in the exchange bias behavior between different multiferroic materials will be discussed. The effect of electric field on exchange bias is currently under investigation. Supported by ONR N000140110761, ONR N000140410085, NSF DMR 0094265, DMR 0231291, MRSEC DMR-00-0520471, and the W. M. Keck Foundation.

  12. 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.

  13. 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.

  14. 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).

  15. 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

  16. 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.

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

    PubMed

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

    2017-04-03

    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 Ti(4+) sites for donor doping of Bi(3+) into the Ba(2+) site. Because addition of La(3+) instead of Bi(3+) 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 Mn(3+) in the MnO6 octahedron, but caused by the Bi-displacement, probably resulting from the effect of the 6 s lone-pair electrons in Bi(3+).

  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. 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.

  20. 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.

  1. Effects of CuZnAl Particles on Properties and Microstructure of Sn-58Bi Solder

    PubMed Central

    Yang, Fan; Zhang, Liang; Liu, Zhi-quan; Zhong, Su Juan; Ma, Jia; Bao, Li

    2017-01-01

    With the purpose of improving the properties of the Sn-58Bi lead-free solder, micro-CuZnAl particles ranging from 0 to 0.4 wt % were added into the low temperature eutectic Sn-58Bi lead-free solder. After the experimental testing of micro-CuZnAl particles on the properties and microstructure of the Sn-58Bi solders, it was found that the wettability of the Sn-58Bi solders was obviously improved with addition of CuZnAl particles. When the addition of CuZnAl particles was 0.2 wt %, the wettability of the Sn-58Bi solder performed best. At the same time, excessive addition of CuZnAl particles led to poor wettability. However, the results showed that CuZnAl particles changed the melting point of the Sn-58Bi solder slightly. The microstructure of the Sn-58Bi solder was refined by adding CuZnAl particles. When the content of CuZnAl addition was between 0.1 and 0.2 wt %, the refinement was great. In addition, the interfacial IMC layer between new composite solder and Cu substrate was thinner than that between the Sn-58Bi solder and Cu substrate. PMID:28772917

  2. Adsorption-controlled growth of BiMnO{sub 3} films by molecular-beam epitaxy

    SciTech Connect

    Lee, J. H.; Ke, X.; Misra, R.; Schiffer, P.; Ihlefeld, J. F.; Mei, Z. G.; Liu, Z. K.; Xu, X. S.; Musfeldt, J. L.; Heeg, T.; Schlom, D. G.; Roeckerath, M.; Schubert, J.

    2010-06-28

    We have developed the means to grow BiMnO{sub 3} thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO{sub 3} may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with omega rocking curve full width at half maximum values as narrow as 11 arc sec (0.003 deg. ). Optical absorption measurements reveal that BiMnO{sub 3} has a direct band gap of 1.1+-0.1 eV.

  3. 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.

  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. 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.

  6. 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.

  7. Structural, magnetic, and electron transport properties of MnBi:Fe thin films

    SciTech Connect

    Kharel, P.; Skomski, R.; Sellmyer, D. J.; Li, X. Z.; Shah, V. R.; Al-Aqtash, N.; Tarawneh, K.; Sabirianov, R. F.

    2012-04-01

    The structural, magnetic, and electron transport properties of Mn{sub 55-x}Fe{sub x}Bi{sub 45} (x = 0, 2, 4, 5, 8, 11, 13, 16) films prepared by multilayer deposition and annealing using e-beam evaporation have been investigated. Fe doping has produced a significant change in the magnetic properties of the samples including the decrease in saturation magnetization and magnetocrystalline anisotropy and increase in coercivity. Although the magnetization shows a smooth decrease with increasing Fe concentration, the coercivity jumps abruptly from 8.5 kOe to 22 kOe as Fe content changes from 4% to 5%, but the change in coercivity is small as the concentration goes beyond 5%. The temperature dependence of resistivity shows that the samples with low Fe concentration ({<=}4%) are metallic, but the resistivity increases unexpectedly as the concentration reaches 5%, where the resistance increases with decreasing temperature below 300 K. First-principle calculations suggest that the observed magnetic properties can be understood as the consequences of competing ferromagnetic and antiferromagnetic exchange interactions between the interstitial atom and the rest of the MnBi lattice.

  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. 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.

  10. 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.

  11. 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.

  12. An optical investigation of the Magnetic Weyl semi-metal candidate YbMnBi2

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Dipanjan; Cheng, Bing; Gibson, Quinn D.; Cava, Robert J.; Armitage, N. Peter

    The discovery of Dirac and Weyl fermions in condensed matter systems has sparked tremendous interest in both condensed matter and high energy physics communities alike. While the existence of Dirac electrons in graphene and topological insulator materials is now well established, only a handful of experiments provide direct evidence of Weyl fermions in non-centrosymmetric systems. Moreover, the theoretically predicted Weyl fermions in magnetic materials with strong spin-orbit coupling have continued to be elusive. A potent candidate for a Weyl semimetal with broken time reversal symmetry (TRS) and antiferromagnetic ordering is the newly discovered YbMnBi2 compound. Although the complete magnetic structure of this material is still unknown, preliminary ARPES measurements are consistent with TRS breaking and a Weyl fermionic band dispersion. In this work, we investigate YbMnBi2 single crystal with FTIR spectroscopy and study its low energy electrodynamic response. The energy scale of IR light is ideally suited to probe for the linear band dispersion of these materials close to the Weyl points. Temperature dependent optical conductivity calculations reveal crucial information on the fundamental scattering processes in these materials.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. Effects of an applied magnetic field on directional solidification of off-eutectic Bi-Mn alloys

    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. 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 field. Conductivity gradients in the melt are suggested as a possible mechanism for the observed results.

  18. Diffusivity of Cd in beta-Mn and beta-Mn(Al) measured by PAC

    NASA Astrophysics Data System (ADS)

    Zacate, Matthew O.; Collins, Gary S.

    2003-03-01

    Beta-Mn is a high-temperature allotrope stable between 720-1080 C with 20 atoms per unit cell on two inequivalent sites. Earlier perturbed angular correlation (PAC) measurements by M. Rots et al. showed that In/Cd impurities occupy the 12d site. It can be shown that jumps from one site to one of six neighboring 12d sites leads to reorientation of the electric-field gradient (efg) by angles close to 90^o. Jump frequencies of atoms were obtained by fitting the dynamically relaxed perturbation function using the method of Baudry and Boyer for N=3 orientations of the efg, with diffusivities proportional to jump frequencies. PAC measurements carried out on pure beta-Mn lead to D= 1.1(2) x 10-12 m^2/s at the lower phase boundary. Measurements were also made on alloys containing a few percent of aluminum, for which the diffusivity was found to be a factor of four lower. An Arrhenius plot for the alloy yielded an activation energy Q= 0.71(5) eV and prefactor D_0= 2(1) x 10-9 m^2/s. We are unaware of any previous measurement of diffusion in beta-Mn for comparison.

  19. Two-carrier transport in SrMnBi2 thin films

    NASA Astrophysics Data System (ADS)

    Yan, Xiao; Zhang, Cheng; Liu, Shan-Shan; Liu, Yan-Wen; Zhang, David Wei; Xiu, Fa-Xian; Zhou, Peng

    2017-06-01

    Monocrystalline SrMnBi2 thin films were grown by molecular beam epitaxy (MBE), and their transport properties were investigated. A high and unsaturated linear magnetoresistance (MR) was observed, which exhibited a transition from a semi-classical weak-field B 2 dependence to a high-field linear dependence. An unusual nonlinear Hall resistance was also observed because of the anisotropic Dirac fermions. The two-carrier model was adopted to analyze the unusual Hall resistance quantitatively. The fitting results yielded carrier densities and mobilities of 3:75 × 1014 cm-2 and 850 cm2·V-1·s-1, respectively, for holes, and 1.468 × 1013 cm2, 4118 cm2×V-1·s-1, respectively, for electrons, with a hole-dominant conduction at 2.5 K. Hence, an effective mobility can be achieved, which is in reasonable agreement with the effective hole mobility of 1800 cm2×V-1×s-1, extracted from the MR. Further, the angle-dependent MR, proportional to cos θ, where θ is the angle between the external magnetic field and the perpendicular orientation of the sample plane, also implies a high anisotropy of the Fermi surface. Our results about SrMnBi2 thin films, as one of a new class of AEMnBi2 and AEMnSb2 (AE = Ca, Sr, Ba, Yb, Eu) materials, suggest that they have a lot of exotic transport properties to be investigated, and that their high mobility might facilitate electronic device applications.

  20. 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.

  1. 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.

  2. Electronic structure and magnetism of Mn 2CuAl: A first-principles study

    NASA Astrophysics Data System (ADS)

    Li, S. T.; Ren, Z.; Zhang, X. H.; Cao, C. M.

    2009-07-01

    The electronic structure and magnetism of a new Mn-based Heusler alloys Mn 2CuAl has been studied by first-principles calculations. The calculations suggest that Mn 2CuAl crystallizes in the Hg 2CuTi type of structure, in which the Cu atoms have Al as nearest neighbors. As a consequence, the Mn atoms occupy two nearest neighbor sublattices A and B. Like the well known Heusler alloy Cu 2MnAl, the magnetic moment of Mn 2CuAl also comes from the two Mn atoms in the lattice, while the Cu atom is almost nonmagnetic. At equilibrium lattice constant, Mn 2CuAl is a ferrimagnet with moment of 0.22μ B. The partial spin moments of Mn (A) and Mn (B) are -3.52μ B and 3.74μ B, respectively. The small total moment comes from the antiparallel configurations of the Mn partial moments. With a small contraction of the lattice, the total moment becomes near zero and a half-metallic antiferromagnetic state is observed.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Effects of Mn and Al on the Intragranular Acicular Ferrite Formation in Rare Earth Treated C-Mn Steel

    NASA Astrophysics Data System (ADS)

    Song, Mingming; Song, Bo; Yang, Zhanbing; Zhang, Shenghua; Hu, Chunlin

    2017-07-01

    The influence of Al, Mn and rare earth (RE) on microstructure of C-Mn steel was investigated. The capacities of different RE inclusions to induce intragranular acicular ferrite (AF) formation were compared. Result shows that RE treatment could make C-Mn steel from large amounts of intragranular AF. Al killed is detrimental to the formation of intragranular AF in RE-treated C-Mn steel. An upper bainite structure would replace the AF when Al content increased to 0.027 mass %. The optimal Mn content to form AF is about 0.75-1.31 mass %. The effective RE inclusion which could induce AF nucleation is La2O2S. When patches of MnS are attached on the surface of La2O2S inclusion, AF nucleation capacity of RE-containing inclusion could enlarge obviously. The existence of manganese-depleted zone and low lattice misfit would be the main reason of La-containing inclusion inducing AF nucleation in C-Mn steel.

  10. 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.

  11. 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

  12. Magnetic and ferroelectric ordering in BiMn{sub 2}O{sub 5} oxide

    SciTech Connect

    Menshenin, V. V.

    2016-01-15

    A group-theoretical analysis of the magnetic phase of BiMn{sub 2}O{sub 5} oxide is performed using the space symmetry group of the compound. Using the projection operator method, we determine the basis functions of the irreducible representation of the space group, which are expressed in terms of the magnetic vector components. This representation can govern two phase transitions from the paramagnetic state to the antiferromagnetic phase with close temperatures and ordering of the spins of manganese ions in two crystallographic positions. It is found from renorm group analysis of these transitions that when these transitions occur as second- order transitions, the electric polarization does not appear in the system because spin fluctuations in this case elevate the symmetry of the system. Polarization appears when at least one of these transitions becomes a first-order transition as a result of spin fluctuations.

  13. 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

  14. 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.

  15. 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'. © 2016 The Author(s).

  16. 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.

  17. Crystal structure, homogeneity range and electronic structure of rhombohedral γ-Mn5Al8

    DOE PAGES

    Thimmaiah, Srinivasa; Turner, Zachary; Lamichhane, Tej; ...

    2017-04-07

    The γ-region of the Mn–Al phase diagram between 45 and 70 at.% Al was re-investigated by a combination of powder and single crystal X-ray diffraction as well as EDS analysis to establish the distribution of Mn and Al atoms. Single crystals of γ-Mn5–x Al8+x were grown using Sn-flux at 650 °C. The crystal structure, atomic coordinates and site occupancy parameters of γ-Mn5−x Al8+x phases were refined from single crystal X-ray data. The γ-Mn5-x Al8+x phase adopts the rhombohedral Cr5Al8-type structure rather than a cubic γ-brass structure. The refined compositions from two crystals extracted from the Al-rich and Mn-rich sides are,more » respectively, Mn4.76Al8.24(2) (I) and Mn6.32Al6.68(2) (II). The structure was refined in the acentric R3m space group (No.160, Z=6), in order to compare with other reported rhombohedral γ-brasses. In addition, according to X-ray powder diffraction analysis, at the Al-rich side the γ-phase coexists with LT–Mn4Al11 and, at the Mn-rich side, with a hitherto unknown phase. The refined lattice parameters from powder patterns fall in the range a=12.6814(7)−12.6012(5) Å and c=7.9444(2)−7.9311(2) Å from Al-rich to Mn-rich loadings, and the corresponding rhombohedral angles distorted from a pseudo-cubic cell were found to be 89.1(1)°−88.9(1)°. Magnetic susceptibility and magnetization studies of Mn4.92Al8.08(2) are consistent with moment bearing Mn and suggest a spin glass state below 27 K. Tight-binding electronic structure calculations (LMTO-ASA with LSDA) showed that the calculated Fermi level for γ-“Mn5Al8” falls within a pseudogap of the density of states, a result which is in accordance with a Hume-Rothery stabilization mechanism γ-brass type phases.« less

  18. 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.

  19. 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.

  20. Enhanced ferro- and piezoelectric performances through interface control in BiFe0.99W0.01O3/BiFe0.95Mn0.05O3/BiFe0.99W0.01O3 thin film

    NASA Astrophysics Data System (ADS)

    Jiang, Xiaomei; Yan, Jing; Hu, Guangda

    2017-08-01

    By eliminating domain backswitching, the severe aging problem of BiFe0.95Mn0.05O3, as a volume effect, was solved through an interface control method. A BiFe0.95Mn0.05O3 thin film sandwiched by BiFe0.99W0.01O3 layers (BiFe0.99W0.01O3/BiFe0.95Mn0.05O3/BiFe0.99W0.01O3) was prepared on a Pt(111)/Ti/SiO2/Si substrate using a metal organic decomposition method. BiFeO3, BiFe0.95Mn0.05O3, BiFe0.99W0.01O3, (top)BiFe0.99W0.01O3/BiFe0.95Mn0.05O3, and BiFe0.95Mn0.05O3/BiFe0.99W0.01O3(bottom) films were fabricated for comparison. All the films show well-saturated and rectangular hysteresis loops. Most importantly, the BiFe0.99W0.01O3/BiFe0.95Mn0.05O3/BiFe0.99W0.01O3 film exhibits the largest piezoresponse (˜220 pm/V). This interface control method, by inhibiting the nucleation of domains with the opposite direction at the interfaces, opens up a promisingly feasible way to solve the aging problem of ferroelectric films and to achieve desired ferroelectric and piezoelectric properties.

  1. 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.

  2. 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.

  3. Sr and Mn co-doped sol-gel derived BiFeO3 ceramics with enhanced magnetism and reduced leakage current

    NASA Astrophysics Data System (ADS)

    Sharma, Nandni; Kumar, Sanjeev; Mall, Ashish Kumar; Gupta, Rajeev; Garg, Ashish

    2017-01-01

    In this manuscript, we report the effect of Sr and Mn doping on the electrical and magnetic characteristics of BiFeO3 nanoparticles, synthesized by sol-gel technique. While powder diffraction analysis of the samples suggested absence of any structural distortion in both Sr-doped and Sr and Mn co-doped BiFeO3 nanoparticles, Rietveld refinement of the data suggested that the unit cell volume decreases with doping. Room temperature Raman studies of the samples confirmed the incorporation of Sr and Mn in BiFeO3. It was seen that Sr doping of BiFeO3 showed substantial reduction in the leakage current whilst co-doping with Sr and Mn led to lower reduction in the leakage current through offering better performance over undoped BiFeO3, due to changes brought in the defect chemistry upon doping. Additionally, Sr and Mn co-doped BiFeO3 samples exhibit enhanced magnetization in comparison to undoped and Sr doped BiFeO3, possibly due to interruptions in the spin cycloid of BiFeO3.

  4. Synthesis of MnO{sub 2} phases from LiMn{sub 2}O{sub 4} in aqueous acidic media. Mechanisms of phase transformations, reactivity, and effect of Bi species

    SciTech Connect

    Larcher, D.; Courjal, P.; Gerand, B.; Blyr, A.; Pasquier, A. du; Tarascon, J.M.; Urbina, R.H.

    1998-10-01

    The nature of the phases obtained by acid digestion of LiMn{sub 2}O{sub 4} phases prepared at 800 C from a mixture of MnO{sub 2} (EMD) and Li{sub 2}CO{sub 3} was investigated. The authors found that the complete transformation toward {alpha}-MnO{sub 2} and then {gamma}-MnO{sub 2} observed for LiMn{sub 2}O{sub 4} treated in 2.5 M H{sub 2}SO{sub 4} for 24 h at 95 C is highly dependent on the amount of water in the reaction medium. The {lambda} {yields} {alpha}/{gamma} transformation was found to be the result of a dissolution-crystallization mechanism that can be completely avoided by adding a soluble Bi, Pb, or Tl salt to the reaction medium. By coupling energy dispersive spectroscopy analysis, infrared spectroscopy, and potentiometric titration, the authors demonstrated the presence of Bi species adsorbed at the surface of the {lambda}-MnO{sub 2} oxide thus modifying its reactivity. In addition, the kinetics of the {lambda} {yields} {alpha}/{gamma} phase transformation was found to depend on the amount of added Bi salt, suggesting the complexing role of Bi toward Mn (Bi-Mn complexes), thereby affecting the crystallization step of the reaction. The same treatment was applied to LiMn{sub 2}O{sub 4} in the presence of a Bi salt in anhydrous electrolyte (LiPF{sub 6}/ethylene carbonate/dimethyl carbonate). In this case, the spinel oxide dissolution slows down and BiF{sub 3} precipitates. With respect to recent findings about the mechanisms involved in the electrochemical capacity failure at elevated temperature in Li-ion LiMn{sub 2}O{sub 4} cells, these results open new alternatives to solve this recurrent problem.

  5. 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.

  6. 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.

  7. 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.

  8. Electronic Structure and Half-Metallicity of Heusler Alloy Mn2RhAl

    NASA Astrophysics Data System (ADS)

    Li, Songtao; Liu, Yang; Ren, Zhi; Zhang, Xiaohong; Liu, Guodong

    2013-10-01

    The site preference, electronic structure and magnetic properties of Mn2RhAl have been studied by first-principles calculations. Both the Cu2MnAl-structure and the Hg2CuTi-type have been tested. For the compound Mn2RhAl, the Hg2CuTi structure is the more stable one with a lattice parameter of 5.80 Å. The Mn2RhAl alloy is predicted to be a half-metal with 100% spin polarization of the conduction electrons at the Fermi level (EF). The calculated total magnetic moment is 2.00 μB per unit cell, which is in line with the Slater-Pauling curve of Mt = Zt-24. The Mn(A) and Mn(B) atom-projected spin moments are -1.54 μB and 3.16 μB, respectively. The resulting moment is mainly determined by the antiparallel aligned Mn(A) and Mn(B) spin moment. Whereas, the small spin magnetic moment of Rh is small and only 0.38 μB and the Al atom is almost nonmagnetic. Such an alloy may be a promising material for future spintronics devices.

  9. 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

  10. The roles of Zr and Mn in processing and superplasticity of Al-Mg alloys

    NASA Technical Reports Server (NTRS)

    Mcnelley, Terry R.; Hales, S. J.

    1990-01-01

    Processing studies have been conducted on two alloys, of nominal compositions Al-10Mg-0.1Zr or Al-10Mg-0.5Mn, in order to clarify the role of the dispersoid forming Zr or Mn additions. Mechanical property data reveal that the Mn-containing alloy has a lower maximum elongation but exhibits superplastic response over a broader range of temperature. Microstructural investigations and texture analyses were utilized to assess the effect of the presence of Al8Mg5 precipitates in combination with either Al3Zr or Al6Mn dispersoid particles during isothermal rolling at 300 C and subsequent tensile deformation at temperatures from 200-425 C.

  11. Interfacial exchange interactions and magnetism of Ni2MnAl /Fe bilayers

    NASA Astrophysics Data System (ADS)

    Yanes, R.; Simon, E.; Keller, S.; Nagyfalusi, B.; Khmelevsky, S.; Szunyogh, L.; Nowak, U.

    2017-08-01

    Based on multiscale calculations combining ab initio methods with spin dynamics simulations, we perform a detailed study of the magnetic behavior of Ni2MnAl /Fe bilayers. Our simulations show that such a bilayer exhibits a small exchange bias effect when the Ni2MnAl Heusler alloy is in a disordered B2 phase. Additionally, we present an effective way to control the magnetic structure of the Ni2MnAl antiferromagnet, in the pseudo-ordered B2-I as well as the disordered B2 phases, via a spin-flop coupling to the Fe layer.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Bismuth Quantum Dots in Annealed GaAsBi/AlAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Butkutė, Renata; Niaura, Gediminas; Pozingytė, Evelina; Čechavičius, Bronislovas; Selskis, Algirdas; Skapas, Martynas; Karpus, Vytautas; Krotkus, Arūnas

    2017-06-01

    Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, the Bi nanoparticles experience a transition to the direct-bandgap semiconducting state.

  17. Bismuth Quantum Dots in Annealed GaAsBi/AlAs Quantum Wells.

    PubMed

    Butkutė, Renata; Niaura, Gediminas; Pozingytė, Evelina; Čechavičius, Bronislovas; Selskis, Algirdas; Skapas, Martynas; Karpus, Vytautas; Krotkus, Arūnas

    2017-12-01

    Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, the Bi nanoparticles experience a transition to the direct-bandgap semiconducting state.

  18. Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser

    NASA Astrophysics Data System (ADS)

    Ludewig, P.; Knaub, N.; Hossain, N.; Reinhard, S.; Nattermann, L.; Marko, I. P.; Jin, S. R.; Hild, K.; Chatterjee, S.; Stolz, W.; Sweeney, S. J.; Volz, K.

    2013-06-01

    The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of ˜947 nm. These results from broad area devices show great promise for developing efficient IR laser diodes based on this emerging materials system.

  19. Growth and ferroelectric properties of La and Al codoped BiFeO3 epitaxial films

    NASA Astrophysics Data System (ADS)

    Izumi, Hirokazu; Yoshimura, Takeshi; Fujimura, Norifumi

    2017-05-01

    Preparation of La and Al codoped BiFeO3 ((Bi1-xLax)(Fe1-xAlx)O3 (x = 0, 0.1, 0.2, 0.3, and 0.4): BFO-LA) thin films on Nb doped SrTiO3 (001) substrates was attempted by using a pulsed laser deposition (PLD) method. All obtained BFO-LA films grew epitaxially with a cube-on-cube relationship with the substrate. Upon La and Al codoping, the crystal system of the films changed from the rhombohedral-like monoclinic (MA) phase to the tetragonal phase, and the unit cell volume decreased monotonically. Although the ferroelectricity of the films was degraded by more than 20% La and Al codoping, 10% La and Al codoped BiFeO3 showed a larger remanent polarization than non-doped BiFeO3. The piezoelectric d constant (d33(AFM)) of the 10% La and Al codoped films was slightly reduced, in contrast to the drastic reduction observed for La doped BiFeO3.

  20. Ferroelectric photovoltaic properties of Ce and Mn codoped BiFeO3 thin film

    NASA Astrophysics Data System (ADS)

    Gupta, Surbhi; Tomar, Monika; Gupta, Vinay

    2014-01-01

    Photovoltaic properties of multiferroic (Ce, Mn) codoped BiFeO3 (BCFMO) thin films grown on low cost ITO coated corning glass substrate have been investigated. The transient response of photovoltaic current of the BCFMO thin film in metal-multiferroic-metal (MMM) capacitor configuration is found to be strongly dependent on both the intensity of incident laser light (λ = 405 nm) varying from 15 mW/cm2 to 160 mW/cm2 and thickness of the BCFMO film (110 to 305 nm). Current density-voltage (J-V) measurement shows an exponential increase in photoinduced open circuit voltage and linear increase in short circuit photocurrent with increase in intensity of illuminating light. Almost 240 fold enhancement in photo-induced current is observed in BCFMO thin film of 110 nm thickness. Present work suggests that multiferroic BCFMO thin film deposited on ITO coated corning glass substrate using chemical solution deposition technique exhibits strong photovoltaic response that can be exploited efficiently for the light harvesting and photosensitive device application.

  1. Photoelectrochemical properties of BiMnO3 thin films and nanostructures

    NASA Astrophysics Data System (ADS)

    Chakrabartty, Joyprokash; Barba, David; Jin, Lei; Benetti, Daniele; Rosei, Federico; Nechache, Riad

    2017-10-01

    We report and compare the properties of BiMnO3 (BMO) nanostructures and thin films as photoanodes in photoelectrochemical solar cells. BMO films are grown on Niobium doped SrTiO3 crystalline substrates using pulse laser deposition. Nanoscale patterns of BMO are obtained by depositing through nanostencils, namely shadow masks with nanometer-scale circular apertures. We demonstrate that BMO nanostructures exhibit superior photoelectrochemical properties, compared to BMO thin films when used as photoelectrodes in cells for hydrogen production. A photocurrent density of ∼0.9 mA cm-2 at 0.8 V vs Ag/AgCl (1.38 V vs RHE) under 1 Sun is recorded for BMO nanostructures. On the other hand, BMO films exhibit a photocurrent density of ∼40 μA cm-2 at 0.4 V vs Ag/AgCl (0.98 V vs RHE) under 2 Sun which is four times higher than that recorded under 1 Sun illumination (∼10 μA cm-2 at 0.4 V vs Ag/AgCl). Mott-Schottky analysis evidences n-type characteristics for both BMO thin films and nanostructures. According to band alignment with respect to the redox potential of water, we conclude that both types of photoelectrodes are suitable for oxygen evolution reaction.

  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. 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).

  4. 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).

  5. 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.

  6. 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.

  7. 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.

  8. Microstructure and mechanical behavior of Fe30Ni 20Mn35Al15 and modified Fe30Ni 20Mn35Al15 alloys

    NASA Astrophysics Data System (ADS)

    Meng, Fanling

    A novel alloy with nominal composition Fe30Ni 20Mn35Al15 has been found to show good room-temperature strength and significant ductility. The current project is to study the wear properties of as-cast Fe30Ni20Mn35Al 15 and discuss the possibility of further improving the mechanical properties of this alloy. The dry sliding wear of as-cast Fe30Ni20Mn 35Al15 was studied in in four different environments, i.e. air, dry oxygen, dry argon and a 4% hydrogen/nitrogen mixture. Two-body and three-body abrasive wear mechanism was found for tests in oxygen-containing environments, while plastic flow mechanisms dominated the wear behavior for tests in argon. Hydrogen embrittlement led to 1000% increase of wear loss by causing more rapid crack nucleation of the asperities. The effects of different additions of chromium (≤ 8 at. %) on both microstructure and fracture behavior of Fe30Ni20Mn 35Al15 were investigated. All alloys consisted of (Ni, Al)-rich B2 and (Fe, Mn)-rich f.c.c. phases with most of the Cr residing in the f.c.c. phase. The addition of 6 at. % Cr not only increased the room temperature ductility, but also completely suppressed the environmental embrittlement observed in the Cr-free alloy at low strain rates. The effects of varying the Al concentration on the microstructures and tensile properties of six two-phase FeNiMnAl alloys with a composition close to Fe30Ni20Mn35Al15 were studied. The increase in f.c.c. volume fraction and f.c.c. lamellar width led to an increase in ductility and a decrease in yield strength. The correlation between the yield stress and f.c.c. lamellar spacing lambda obeyed a Hall-Petch-type relationship, i.e. sigmay=252+0.00027lambda-1, where the units for sigmay and lambda are MPa and meter, respectively. FeNiMnAl alloy with B2 and f.c.c. phases aligned along was reported to show high strength at room temperature. The mechanical properties of Fe 28Ni18Mn33Al21, consisting of (Ni, Al)-enriched B2 and (Fe, Mn)-enriched f.c.c. phases with

  9. 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.

  10. Microstructure and mechanical properties of 980MPa grade Fe-Mn-Al-C lightweight steel

    NASA Astrophysics Data System (ADS)

    Jiang, Yinghua; Xie, Chunqian

    2017-06-01

    Fe-Mn-Al-C lightweight high strength steel, adding more Mn, Al and C elements into conventional AHSS, shows amazing mechanical properties, corrosion resistant and weight reduction than conventional AHSS. The mechanical properties and microstructure of Fe-15Mn-6.8Al-0.9C-0.2Ti steel after annealing process were investigated. The results show that the microstructures consisted of secondary phases TiC precipitate and ferrite in the austenite matrix. The tensile strength and elongation of the steel are 985MPa and 36%, respectively. The density is 6.86g/cm3. Continuous strain hardening behavior provides Fe-Mn-Al-C lightweight steel with perfect combination of strength and ductility.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Red-emitting AlN:Mn2+ phosphors prepared by combustion synthesis

    NASA Astrophysics Data System (ADS)

    Shi, Zhongqi; Zou, Yongyong; Jing, Ruifeng; Zhang, Kuo; Qiao, Guanjun; Wang, Hongjie

    2015-12-01

    Red-emitting Mn2+-doped AlN(AlN:Mn2+) phosphors were successfully prepared by a highly effective combustion synthesis method. The phase purity, morphology, element-composition and luminescence properties of the synthesized phosphors were investigated. X-ray diffraction (XRD) results show that the Mn2+-doped into the AlN host did not induce a second phase and distort the structure significantly. Scanning electron microscopy (SEM) images display that the phosphors have an irregular shape with a particle size in the range of 1-5 μm. X-ray photoelectron spectroscopy (XPS) spectrum indicates that Mn ions are divalent state. The synthesized AlN:Mn2+ phosphors exhibit a strong red emission centered at 600 nm, which is ascribe to the 4T1(4G)-6A1(6S) transition of Mn2+ under ultraviolet excitation. The emission intensity reaches its maximum when Mn2+-doped concentration is 3 mol%.

  16. 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.

  17. Structural and morphological studies on Bi{sub 1-x}Ca{sub x}MnO{sub 3} thin films grown by RF magnetron sputtering

    SciTech Connect

    Pugazhvadivu, K. S.; Santhiya, M.; Tamilarasan, K.; Balakrishnan, L.

    2016-05-23

    Bi{sub 1-x}Ca{sub x}MnO{sub 3} (0 ≤ X ≤ 0.4) thin films are deposited on n–type Si (100) substrate at 800 °C by RF magnetron sputtering. X-ray diffraction pattern shows that the films are crystallized in monoclinic structure with C2 space group. The crystallite size and induced strain in the prepared films are measured by W-H plot. The cell parameters and texture coefficient of the films are calculated. The surface morphology of the films is examined by atomic force microscope. The study confirms the optimum level of calcium doping is 20 at. % in Bi site of BiMnO{sub 3} film, these findings pave the way for further research in the Ca modified BiMnO{sub 3} films towards device fabrication.

  18. Multiferroics BiMn1-xAlxO3 nanoparticles: Synthesis, characterization and evaluation of various structural, physical, electrical and dielectric parameters

    NASA Astrophysics Data System (ADS)

    Ahmad, Bashir; Raissat, Rabia; Mumtaz, Saleem; Ahmad, Zahoor; Sadiq, Imran; Ashiq, Muhammad Naeem; Najam-ul-Haq, Muhammad

    2017-07-01

    The aluminium substituted bismuth based manganates with nominal composition BiMn1-xAlxO3 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) were prepared by the simple microemulsion method. The alteration in their structural, electrical and dielectric parameters due to Al substitution has been investigated. The X-ray diffraction analysis (XRD) confirms the formation of single phase orthorhombic with crystallite size ranges from 32 to 52 nm. The morphological features and particle size were determined by using scanning electron microscopy (SEM). The dc electrical resistivity increased from 6 × 108 to 8 × 109 Ω cm with the increase in substituent concentration. The dielectric constant, dielectric loss tangent and dielectric loss factor decreased with the increase in frequency. The increase in electrical resistivity makes the synthesized materials paramount over other materials and can be useful for technological applications in microwave devices.

  19. The Effects of Addition of Al on Electrical Degradation of ZnO Varistors

    NASA Astrophysics Data System (ADS)

    Satoi, Yohei; Yoshikado, Shinzo

    The effects of addition of Al on the electrical degradation of the Bi, Mn, and Al added ZnO varistors and the Bi, Co, and Al added ZnO varistors were investigated by V-I, C-V, ICTS, and XPS methods. The optimum quantity of Al additive to prevent the electrical degradation is approximately 5ppm in the case of Bi-Mn-Al added ZnO varistor and approximately 10ppm in the case of Bi-Co-Al added ZnO varistor. For each optimum quantity of Al content for Bi-Mn-Al or Bi-Co-Al added varistor, the distribution of values of the energies of the trap levels became narrowest. On the other hand, values of the full width at half maximum of Mn-2p and Co-2p orbits became largest.

  20. 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.

  1. 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.

  2. Toluene removal by sequential adsorption-plasma catalytic process: Effects of Ag and Mn impregnation sequence on Ag-Mn/γ-Al2O3.

    PubMed

    Qin, Caihong; Huang, Xuemin; Dang, Xiaoqing; Huang, Jiayu; Teng, Jingjing; Kang, Zhongli

    2016-11-01

    A series of Ag-Mn/γ-Al2O3 were prepared under different Ag/Mn impregnation sequence and tested in the sequential adsorption-plasma catalytic removal of toluene. When Mn was impregnated first, the resulting catalyst, Ag-Mn(F)/γ-Al2O3, had longer breakthrough time, gave less emission of toluene, had higher CO2 selectivity, and had better carbon balance and COx yield compared to catalysts prepared via other impregnation sequences. After 120 min of NTP treatment, the carbon balance of Ag-Mn(F)/γ-Al2O3 was 91%, with 87% as COx contributions. A Brunauer-Emmett-Teller (BET) analysis and X-ray photoelectron spectroscopy (XPS) results show that, the impregnation sequence impacts the BET surface area and the ratio and existing state of Ag on the surface of the catalysts. The longer breakthrough time when using Ag-Mn(F)/γ-Al2O3 as catalyst is attributed to the large amount of Ag(+) on the surface. Ag(+) is a new active site for toluene adsorption. When Ag was impregnated first (Ag(F)-Mn/γ-Al2O3) or Ag and Mn co-impregnated (Ag-Mn-C/γ-Al2O3), the predominant specie was Ag(+). Both Ag(0) and Ag(+) species were detected on Ag-Mn(F)/γ-Al2O3. Ag(0) cooperation with MnOx may promote the migration of surface active oxygen. This would facilitate the oxidation of adsorbed toluene with CC bond already weakened by Ag(+) and would result in higher CO2 selectivity and better carbon balance as seen in the Ag-Mn(F)/γ-Al2O3 system. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Magnetic ordering in perovskites A1 - xMnO3 + y (A=La, Bi, rare earth ion) (abstract)

    NASA Astrophysics Data System (ADS)

    Troyanchuk, I. O.; Kasper, N. V.; Szymczak, H.; Nabialek, A.

    1997-04-01

    In order to clarify the mechanism of exchange interactions in orthomanganites with perovskite structure a magnetic study of parent compounds as a function of stoichiometry has been made. It was shown that the LaMnO2.99 is a weak ferromagnet with TN=147 K while LaMnO3.13 and La0.9MnO3.05 are ferromagnets with TC=160 and 240 K, respectively. The magnetic data indicate that the mixed magnetic state involving ferro- and antiferromagnetic domains is realized in the intermediate range of oxygen content. The RMnO3+y (R=Nd, Sm, Eu, Gd) are inhomogeneous antiferromagnets. The temperatures of start of magnetic moments freezing inside ferromagnetic clusters depend slightly on stoichiometry and for y˜0 are equal 83, 65, 47, and 22 K, respectively. The coercive field for LaMnO3 is 6 kOe at 4.2 K while that for EuMnO3 is much higher—26 kOe. It is worth noting that the Neel temperatures of RMnO3(R=Eu, Gd, Tb, Dy) are estimated to be about 40 K independently of the type of rare-earth ion. Magnetic moments of Gd, Tb, and Dy in the rare-earth sublattice are antiferromagnetically ordered below 6-7 K. Applying external fields induces the antiferromagnet-ferromagnet transition in rare-earth sublattice. Hcr at 2 K for RMnO3(R=Gd, Tb, Dy) are measured to be about 5, 12, and 10 kOe, respectively. In contrast to rare-earth compounds, the BiMnO3 is ferromagnet below 98 K. The deviation from stoichiometry as well as replacement of Bi ions by Sr, Ca, or La ions leads to the suppression of the long-range ferromagnetic order. Magnetic properties are discussed in terms of super exchange interactions between manganese ions via oxygen taking into account the 3d-orbital ordering that occurs in LaMnO3 and TbMnO3 at 400 and 1200°C, respectively.

  4. 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.

  5. Influence of the Bi3+ electron lone pair in the evolution of the crystal and magnetic structure of La(1-x)Bi(x)Mn2O5 oxides.

    PubMed

    Retuerto, M; Muñoz, A; Martínez-Lope, M J; Garcia-Hernandez, M; André, G; Krezhov, K; Alonso, J A

    2013-05-29

    La(1-x)Bi(x)Mn2O5 (x = 0, 0.2, 0.4, 0.6, 0.8 and 1) oxides are members of the RMn2O5 family. The entire series has been prepared in polycrystalline form by a citrate technique. The evolution of their magnetic and crystallographic structures has been investigated by neutron powder diffraction (NPD) and magnetization measurements. All the samples crystallize in an orthorhombic structure with space group Pbam containing infinite chains of Mn(4+)O6 octahedra sharing edges, linked together by Mn(3+)O5 pyramids and (La/Bi)O8 units. These units become strongly distorted as the amount of Bi increases, due to the electron lone pair of Bi(3+). All the members of the series are magnetically ordered below TN = 25-40 K and they present different magnetic structures. For the samples with low Bi content (x = 0.2 and 0.4) the magnetic structure is characterized by the propagation vector k = (0,0,1/2). The magnetic moments of the Mn(4+) ions placed at octahedral sites are ordered according to the basis vectors (Gx, Ay, 0) whereas the Mn(3+) moments, located at pyramidal sites, are ordered according to the basis vectors (0, 0, Cz). When the content of Bi increases, two different propagation vectors are needed to explain the magnetic structure: k1 = (0,0,1/2) and k2 = (1/2,0,1/2). For x = 0.6 and 0.8, k2 is predominant over k1 and for this propagation vector (k2) the magnetic arrangement is defined by the basis vectors (Gx, Ay,0) and (Fx, Cy, 0) for Mn(4+) and Mn(3+) ions, respectively.

  6. Optical and magnetic measurements of Mn+-implanted AlN

    NASA Astrophysics Data System (ADS)

    Li, M. K.; Li, C. B.; Liu, C. S.; Fan, X. J.; Fu, D. J.; Shon, Y.; Kang, T. W.

    2004-01-01

    AlN films were prepared by medium-frequency reactive magnetron sputtering and subsequently implanted with 200 keV Mn+ ions with a dose of 5×1016cm-2. The properties of Mn+-implanted AlN films were investigated by optical and magnetic measurements. Cathodoluminescence (CL) measurements showed a peak at 2.07 eV in AlN and a broad luminescence band around 2.0-3.4 eV in the implanted samples. Fitting of the CL data reveals three peaks, among which the main peak is located at 2.6 eV and attributed to a donor-to-Mn2+ transition. The magnetic measurement showed a transition temperature of 100 K in the implanted AlN annealed at 500 °C for 30 min. Clear ferromagnetic hysteresis was observed at 77 K, with a coercive field of 212.7 Oe.

  7. 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.

  8. First-principles study of Mn adsorption on Al4C3(0 0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Yao, L. F.; Li, K.; Zhou, N. G.

    2016-02-01

    First-principle calculation based on the density functional theory was adopted to investigate the adsorption energy, stability, electronic structure and bonding of Mn atom adsorption on Al-terminated and C-terminated Al4C3(0 0 0 1) surface under 0.25 ML and 0.5 ML. Results show that the structure of Mn adsorption on C-terminated Al4C3(0 0 0 1) surface is more stable than that on Al-terminated surface according to the formation energy calculation. For Mn adsorption on Al-terminated surface, Mn is more favorable to reside at the site H1 comparing with other sites. As well, for Mn adsorption on C-terminated surface, the structure of Mn adsorption at site H‧1 is the most stable one. By analyzing the electronic structure and bonding, it is found that the mixed metallic/covalent bonds are formed between Mn atoms and Al-terminated surface, while the covalent bonds are formed between Mn atoms and C-terminated surface. According to the interlayer spacing calculation, Al4C3(0 0 0 1) surfaces are reconstructed after Mn adsorption, which in turn affect the following stacking of Mg atoms on Al4C3(0 0 0 1) surface. The above analysis provided effective theoretical support to the experimental phenomenon that high Mn content has negative influence on the heterogeneous nucleation of Al4C3 particles for α-Mg grains.

  9. 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.

  10. 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.

  11. 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

  12. Single-Crystal Elastic Properties of the Spinel (MgAl2O4) - Galaxite (MnAl2O4) Solid Solution Series

    NASA Astrophysics Data System (ADS)

    Speziale, S.; Bruschini, E.; Andreozzi, G. B.; Bosi, F.; Hålenius, U.

    2014-12-01

    Spinels are a subject of intense research in solid state physics, materials science and geosciences. Their general formula is T(A1-i)M(AiB2-i)X4 (A and B are cations, X are anions, T and M indicate tetrahedrally- and octahedrally-coordinated sites and i is the inversion degree). They are ideal materials to study the interplay between chemical substitutions, structure and the physical properties of solids. As spinel-structured ringwoodite (Mg,Fe)2SiO4 is the most abundant mineral in the lower transition zone, understanding the effect of chemical substitution on the elastic properties of spinels is of crucial for geophysics. We have experimentally studied the variation of the elastic properties along the join MgAl2O4 - MnAl2O4. Crystals of 4 compositions along the join were synthesized at the very same experimental conditions and their crystal chemistry was fully characterized. Single-crystal elastic constants Cij of all the samples were measured by Brillouin spectroscopy at ambient conditions. For compositions with Mn/Mg < 0.5 C11 remains constant, then it decreases of ~4% for higher Mn contents. From MgAl2O4 to MnAl2O4 C12 lineraly increases ~ 5% and C44 decreases ~ 20% . The bulk modulus KS is almost constant, whereas the shear modulus G decreases ~ 18% across the join. The elastic constants of MnAl2O4 are C11 = 271.3 (± 1.3) GPa, C12 = 164.8 (± 1.3) GPa and C44 = 124.9 (5) GPa. Using the empirical polyhedral approach [1] we have inferred the effectve polyhedral bulk moduli of Mg, Mn and Al in T and M sites. We observe that KMnM < KMgM < KMgT ≈ KMnT < KAlM << KAlT. The relationship between polyhedral moduli and ionic potential IP [2] can be expressed as Ki j (GPa) = 20 ( ± 2) × IP + 108 (± 10), where i is the cation, j is the site and IP is in units of (e/Å). Using our correlation and atomic radii from [3] we successfully reproduced the bulk modulus of different oxide spinels with bi- and tri-valent cations. Our preliminary results confirm that empirical

  13. Structural, dielectric and magnetic studies on BiPbSr{sub 2}MnO{sub 6}

    SciTech Connect

    Sahu, B.; Mohapatra, S. R.; Singh, A. K. E-mail: sahubinayak.magnon@gmail.com; Kaushik, S. D.; Siruguri, V.

    2015-06-24

    We have investigated structural, room temperature dielectric and magnetic properties of BiPbSr{sub 2}MnO{sub 6} as a potential candidate to show magnetoelectric coupling. The X-ray diffraction study shows the crystal structure is noncentrosymmetrical with orthorhombic space group A2aa while neutron diffraction study demonstrates the above structure is centrosymmetrical with orthorhombic space group Amaa. The DC susceptibility measurement performed on polycrystalline powders exhibits antiferromagnetic ordering below transition temperature ∼ 190K. The frequency dependent dielectric measurement at room temperature displays the normal polar dielectric behavior.

  14. A comparison of τ-MnAl particulates produced via different routes.

    PubMed

    Chaturvedi, Anurag; Yaqub, Rumana; Baker, Ian

    2014-02-12

    MnAl alloys are very promising rare-earth-free permanent magnets. Nanocrystalline microstructures can have beneficial effects on the properties of magnetic MnAl alloys. In the present work we examined multiple routes to process MnAl alloys and studied the effects of milling on Mn-46 at.% Al powders. Mn54Al46 was produced via gas atomization, melt spinning, and rapid solidification rate processing. It was then mechanically milled using a water-cooled Union Process attritor for times up to 20 h. X-ray diffraction patterns showed the presence of mostly the high-temperature ε-phase with significant amounts of the equilibrium γ2 and β phases in both the cast and milled particulates. The powders were annealed for various temperatures and times in order to obtain the ferromagnetic τ-phase. Magnetic measurements of the optimally annealed powders showed a coercivity of 3.62 kOe and saturation magnetization of 59.8 emu g(-1) for mechanically milled gas-atomized powder annealed at 500 °C for 30 min.

  15. 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.

  16. Leakage current phenomena in Mn-doped Bi(Na,K)TiO{sub 3}-based ferroelectric thin films

    SciTech Connect

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

    2016-08-28

    Mn-doped 80(Bi{sub 0.5}Na{sub 0.5})TiO{sub 3}-20(Bi{sub 0.5}K{sub 0.5})TiO{sub 3} thin films were fabricated by chemical solution deposition on Pt/TiO{sub 2}/SiO{sub 2}/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 μ{sub ion} ≈ 1.7 × 10{sup −12} cm{sup 2} V{sup −1} s{sup −1} and E{sub A,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.

  17. 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.

  18. 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.

  19. Microstructure Formation in AlSi4MgMn and AlMg5Si2Mn High-Pressure Die Castings

    NASA Astrophysics Data System (ADS)

    Otarawanna, S.; Gourlay, C. M.; Laukli, H. I.; Dahle, A. K.

    2009-07-01

    Understanding microstructure formation during high-pressure die casting (HPDC) is important for the effective quality control of high-pressure diecast aluminum-alloy components for high-integrity applications. In this study, two HPDC-specific aluminum alloys, AlSi4MgMn and AlMg5Si2Mn, were cast into tensile test bars by cold-chamber (CC) HPDC. The microstructures of the tensile bar specimens were characterized at different length scales, from the scale of the casting to the scale of the eutectic interlamellar spacing. The results show that the salient as-cast microstructural features, e.g., externally solidified crystals (ESCs), defect bands, the surface layer, grain size distribution, porosity, and hot tears were similar for both alloys. The formation of these features can be understood by considering the influence of flow and solidification during each stage of the HPDC process.

  20. One step preparation of pure 𝝉-MnAl phase with high magnetization using strip casting method

    NASA Astrophysics Data System (ADS)

    Shao, Zhuyin; Zhao, Hui; Zeng, Jiling; Zhang, Yinfeng; Yang, Wenyun; Lai, Youfang; Guo, Shuai; Du, Honglin; Wang, Changsheng; Yang, Yingchang; Yang, Jinbo

    2017-05-01

    Ferromagnetic phase of Mn-Al exhibits great potential in the rare-earth free permanent magnetic materials due to its high magnetocrystalline anisotropy, high magnetization, high Curie temperature and low cost. In this work, the strip casting technique was applied to prepare MnAl magnetic phase. X-ray diffraction and energy dispersive X-ray analyses indicate that the as-prepared Mn54Al46 strip sample consists of pure τ-MnAl magnetic phase. It is found that the composition of Mn54Al46 is suitable to prepare τ-MnAl phase during the strip casting process. The Mn54Al46 strip sample synthesized through the strip casting exhibits a fairly high magnetization of 114 emu/g under a field of 5 T, while the coercivity of iHc = 2.8 kOe, magnetization of M5T = 63.9 emu/g at room temperature can be obtained for Mn54Al46 powder sample. This preparation method can produce a large amount of τ-phase MnAl alloy and promote mass industrialized production.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Effect of Thermomagnetic Treatment on Structure and Properties of Cu-Al-Mn Alloy

    NASA Astrophysics Data System (ADS)

    Titenko, A. N.; Demchenko, L. D.; Perekos, A. O.; Gerasimov, O. Yu

    2017-04-01

    The paper studies the influence of magnetic field on magnetic and mechanical properties of Cu-Mn-Al alloy under annealing. The comparative analysis of the magnetic field orientation impact on solid solution decomposition processes in a fixed annealing procedure is held using the methods of low-field magnetic susceptibility, specific magnetization, and microhardness test. The paper highlights changes in the magnetic and mechanical properties of Cu-Al-Mn alloy as the result of change in a critical size of forming precipitated ferromagnetic phase and determines correlation in the behavior of magnetic and mechanical properties of the alloy, depending on a critical nucleus size of forming precipitated ferromagnetic phase.

  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. 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.

  11. 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.

  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. Electrical properties of medium field, chem-prep varistors. [ZnO doped with Co, Mn, or Al

    SciTech Connect

    Tuttle, B.A.; Voigt, J.A.; Binasiewicz, E.J.; Kimball, K.M.

    1988-01-01

    Medium field, chem-prep, ZnO varistors were synthesized and electrically tested. Eight formulations were used with three dopants: (1) Co (0, 0.25, 0.5 mol %), (2) Mn (0, 0.25, 0.5 mol %) and (3) Al (0, 125, and 150 ppM by weight). Al doping produced two dramatic effects: (1) an increase in the electric switching field by factors of 5 to 10, and (2) a significant enhancement of the high current density nonlinearity coefficient. Firing temperatures of 800, 900 and 1000/sup 0/C were used to densify materials and produce varistors with electrical switching fields in the 3 to 10 kV/cm range. Current density vs electric field measurements were made from 1 ..mu..A/cm/sup 2/ to 10 A/cm/sup 2/ using dc and pulse techniques. The varistor with the largest nonlinearity coefficient over this extended current density range was fired at 1000/sup 0/C and contained 0.25 Co, 0.25 Mn, 0.56 Bi (mol %) and 150 ppM Al (by weight). The nonlinearity coefficient was 14 at low current densities (0.1 mA/cm/sup 2/ to 5 mA/cm/sup 2/) and 28 for high current densities (0.1 to 10 A/cm/sup 2/). Because of the large nonlinearity coefficient, this varistor is the best candidate for Sandia applications of all varistors we synthesized. Further, the varistor had an electrical switch field of 5 kV/cm at 10 A/cm/sup 2/ and was greater than 96% of theoretical density. Low field dielectric properties and J vs. E characteristics as a function of temperature were measured for this varistor. 7 tabs.

  14. 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.

  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. Rashba-Dresselhaus spin-splitting in the bulk ferroelectric oxide BiAlO3

    NASA Astrophysics Data System (ADS)

    da Silveira, Luiz Gustavo Davanse; Barone, Paolo; Picozzi, Silvia

    2016-06-01

    It has been recently suggested that the coexistence of ferroelectricity and Rashba-like spin-splitting effects due to spin-orbit coupling in a single material may allow for a nonvolatile electric control of spin degrees of freedom. In the present work, we compared the structural and ferroelectric properties of tetragonal and rhombohedral phases of ferroelectric BiAlO3 by means of density-functional calculations. In both phases, we carefully investigated Rashba and Dresselhaus effects, giving rise to spin-splitting in their bulk electronic structure, particularly near the conduction band minimum, supplementing our first-principles results with an effective k .p model analysis. The full reversal of the spin texture with ferroelectric polarization switching was also predicted. BiAlO3 can therefore be considered as the first known oxide to exhibit a coexistence of ferroelectricity and Rashba-Dresselhaus effects.

  18. Hardness and microstructural variation of Al-Mg-Mn-Sc-Zr alloy.

    PubMed

    Ikeshita, Sumiha; Strodahs, Ansis; Saghi, Zineb; Yamada, Kazuhiro; Burdet, Pierre; Hata, Satoshi; Ikeda, Ken-Ichi; Midgley, Paul A; Kaneko, Kenji

    2016-03-01

    Variations of Vickers hardness were observed in Al-Mg-Mn alloy and Al-Mg-Mn-Sc-Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al-Mg-Mn-Sc-Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al3Sc1-xZrx and also block-shaped Al3Sc precipitates growing along <100>Al with facets {100} and {110} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al3Sc. Copyright © 2015 Elsevier Ltd. All rights reserved.

  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. 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.

  1. 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.

  2. 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.

  3. 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.

  4. In situ Observation of Phase Transformation in MnAl(C) Magnetic Materials.

    PubMed

    Si, Ping-Zhan; Qian, Hui-Dong; Choi, Chul-Jin; Park, Jihoon; Han, Sangho; Ge, Hong-Liang; Shinde, Kiran P

    2017-08-31

    The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was observed by in situ transmission electron microscopy. The exact temperature range for different phase transformation modes was determined by magnetic measurements. The displacive growth of ε→τ in Mn54Al46 (or Mn54Al46C2.44) occurs at temperatures below 650 K (or 766 K), above which both modes coexist. One-third or less of the ε-phase can be transformed into τ-phase via displacive mode while the remaining two-thirds or more via massive mode. In bulk τ-phase, most τ-nanocrystals formed via displacive mode are distributed in the matrix of large τ-grains that formed via massive mode. The typical massive growth rate of the τ-phase is 8-60 nm/s, while the displacive growth rate is low. A more complete understanding of the ε→τ phase transformations in the MnAl-based magnets was provided in this work, based on which the annealing process for ε→τ was optimized and thus high purity τ-phase with high saturation magnetization was obtained.

  5. 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

  6. 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.

  7. 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.

  8. Directly obtained τ-phase MnAl, a high performance magnetic material for permanent magnets

    SciTech Connect

    Fang, Hailiang; Kontos, Sofia; Ångström, Jonas; Cedervall, Johan; Svedlindh, Peter; Gunnarsson, Klas; Sahlberg, Martin

    2016-05-15

    The metastable tetragonal τ-phase has been directly obtained from casting Mn{sub 0.54}Al{sub 0.46} and (Mn{sub 0.55}Al{sub 0.45}){sub 100}C{sub 2} using the drop synthesis method. The as-casted samples were ball milled to decrease the particle size and relaxed at 500 °C for 1 h. The phase composition, crystallographic parameters, magnetic properties and microstructure were systematically studied. The results reveal that the τ-phase could be directly obtained from drop synthesis. The highest M{sub s} of 117 emu/g was achieved in the (Mn{sub 0.55}Al{sub 0.45}){sub 100}C{sub 2} where the τ-phase was stabilized by doping with carbon. Carbon doping increased the c/a ratio of the τ-phase as it occupies specific interstitial positions (½, ½, 0) in the structure. Furthermore, ball milling increases the coercivity (H{sub c}) at the expense of a decrease in magnetic saturation (M{sub s}). The increase in coercivity is explained by a decrease of grain size in conjunction with domain wall pinning due to defects introduced during the ball milling process. - Graphical abstract: The tetragonal τ-phase has been directly obtained from casting Mn{sub 0.54}Al{sub 0.46} and (Mn{sub 0.55}Al{sub 0.45}){sub 100}C{sub 2} using the drop synthesis method. The phase composition, crystallographic parameters, magnetic properties and microstructure were systematically studied. The highest M{sub s} of 117 emu/g was achieved for (Mn{sub 0.55}Al{sub 0.45}){sub 100}C{sub 2} ball milling increases the coercivity (H{sub c}) at the expense of a decrease in magnetic saturation (M{sub s}). - Highlights: • The ferromagnetic τ-phase has been directly obtained from casting. • The highest M{sub s} of 117 emu/g was achieved for (Mn{sub 0.55}Al{sub 0.45}){sub 100}C{sub 2}. • Ball milling increases the coercivity but decreases the magnetic saturation.

  9. First-principles study of MnAl for its application in MgO-based perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Zhang, Xuan; Tao, L. L.; Zhang, Jia; Liang, S. H.; Jiang, Leina; Han, X. F.

    2017-06-01

    MnAl, as a prospective candidate of magnetic electrode materials for MgO-based magnetic tunnel junctions, possesses several advantages including the spin polarized Δ 1 band, relatively low Gilbert damping factor, and large perpendicular magnetic anisotropy. Here, we report a thorough first-principles investigation on MnAl/MgO/MnAl-magnetic tunnel junctions (MTJs). It is found that the bulk anisotropy density is 17.39 Merg/cm3, while the interfacial anisotropy contribution is evaluated to be 0.12 erg/cm2 and 0.44 erg/cm2 for Mn- and Al-terminated structures, respectively. The large anisotropy can be attributed to dyz and d z 2 orbits. Furthermore, the formation of a Mn-O bond on the interface of MnAl/MgO is shown to be detrimental for the improvement of perpendicular anisotropy. On the other hand, a giant zero-bias tunneling magnetoresistance ratio is predicted and can be maintained over 2000% even for a bias up to 0.6 V for Mn-terminated MTJs. The in-plane spin transfer torque for Mn-terminated MTJs increases linearly with a bias up to 0.6 V due to the large net spin-polarized current. This work paves the way for the further application of MnAl-based perpendicular magnetic tunnel junctions.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Pulsed Laser Deposition of Bi0.4Ca0.6MnO3 Epitaxial Films on SrTiO3 Buffered Silicon

    NASA Astrophysics Data System (ADS)

    Yong, Grace; Smolyaninova, Vera; Adhikari, Sanjay; Hofmann, Benjamin; Kolagani, Rajeswari; Liang, Yong

    2010-03-01

    Bi0.4Ca0.6MnO3 is a photo-responsive material. Upon illumination with visible light, the resistivity of Bi0.4Ca0.6MnO3 epitaxial thin films on oxide substrates decreases significantly in a wide temperature range due to the destruction of charge ordering, with the resistivity (ρ) recovering upon subsequent blocking of the light. We demonstrate that Bi0.4Ca0.6MnO3 can be grown epitaxially (by PLD) on SrTiO3 buffered Si(001). (The Si was buffered with ˜ 100å epitaxial SrTiO3 grown via a Motorola Molecular Beam Epitaxy process). In general, epitaxy on silicon is needed for integration of a detector component with complementary MOS readout. Epitaxial growth on Si also opens up the possibility of fabricating a free-standing, strain-free Bi0.4Ca0.6MnO3 membrane via standard Si micromachining techniques. Such a free standing film may be expected to have properties similar to that of the bulk single crystal which exhibit permanent photoinduced reflectivity changes attractive for photonic device application.

  15. 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.

  16. 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

  17. Al-doped spinel LiAl 0.1Mn 1.9O 4 with improved high-rate cyclability in aqueous electrolyte

    NASA Astrophysics Data System (ADS)

    Yuan, Anbao; Tian, Lei; Xu, Wanmei; Wang, Yuqin

    To improve the cyclability of spinel LiMn 2O 4 in aqueous electrolyte, Al-doped LiAl xMn 2- xO 4 (x = 0.05, 0.1, 0.15) materials are prepared using a room-temperature solid-state grinding reaction followed by calcination at different temperatures for different durations, respectively. Their phase structures and morphologies are characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Electrochemical performances of the materials are investigated by cyclic voltammetry and galvanostatic charge/discharge methods. XRD results reveal that the crystallinity of the LiAl 0.1Mn 1.9O 4 increases with increasing calcination temperature and calcination time. However, when the calcination temperature is increased to 800 °C, a small amount of Mn 3O 4 impurity phase is detected in the product calcined for 12 h, due to the decomposition of LiAl 0.1Mn 1.9O 4, while the product calcined for a shorter time of 3 or 6 h is found to be LiAl 0.1Mn 1.9O 4 single phase. TEM results confirm that the grain size of the materials increases with increasing calcination temperature. Electrochemical experiments demonstrate that the charge/discharge cyclability of the LiAl 0.1Mn 1.9O 4 increases with increase in calcination temperature and calcination time. Compared with the pristine LiMn 2O 4, the Al-doped LiAl xMn 1- xO 4 show the obviously improved cyclability, especially for the LiAl 0.1Mn 1.9O 4 calcined at an elevated temperature for 12 h.

  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. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Weyl points in the ferromagnetic Heusler compound Co2MnAl

    NASA Astrophysics Data System (ADS)

    Kübler, J.; Felser, C.

    2016-05-01

    The anomalous Hall conductivity (AHC) in some ferromagnetic and antiferromagnetic Heusler compounds was theoretically and experimentally found to be exceptionally large. For the case of ferromagnetic Co2MnAl we here argue that the large AHC is connected with the appearance of Weyl points near the Fermi energy. We find four Weyl points slightly above the Fermi edge. We describe our analysis for a magnetization being in the (110)-direction. For the possible (100)-direction we find at least four Weyl points, too. We predict that Co2MnGa also possesses Weyl points near or at the Fermi energy.

  8. 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.

  9. Magnetic structure and spin excitations in BaMn2Bi2

    SciTech Connect

    Calder, Stuart A.; Saparov, Bayrammurad I; Cao, H. B.; Niedziela, Jennifer L.; Lumsden, Mark D.; Sefat, Athena Safa; Christianson, Andrew D.

    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 to be unchanged by the 100 K structural phase transition.

  10. 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).

  11. 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.

  12. 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.

  13. 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.

  14. Structural and electrical properties of polycrystalline Bi(Fe0.6Mn0.4)O3 thin films

    NASA Astrophysics Data System (ADS)

    Kim, S. W.; Kim, W. J.; Lee, M. H.; Song, T. K.; Do, D.

    2013-12-01

    A 40% Mn-substituted BiFeO3 (BFMO) thin film was deposited on a Pt(111)/Ti/SiO2/Si(100) substrate by using a pulsed laser deposition method. The coexistence of rhombohedral and orthorhombic structures in the BFMO thin film was confirmed by using X-ray diffraction and Raman spectra investigation. The leakage current density of the BFMO thin film was larger than that of a pure polycrystalline BiFeO3 (BFO) thin film. In order to understand the leakage current behaviors, was investigated the leakage current mechanisms. The leakage current mechanism of the BFO thin film was found to be space-charge-limited conduction (SCLC), followed by trap-filled conduction causal by the increasing electric field strength. On the other hand, trap-filled conduction was not observed in the BFMO thin film. A leaky ferroelectric hysteresis loop was observed in the BFMO thin film, but not in the BFO thin film.

  15. Removal of aqueous Pb(II) by adsorption on Al2O3-pillared layered MnO2

    NASA Astrophysics Data System (ADS)

    Zhang, Haipeng; Gu, Liqin; Zhang, Ling; Zheng, Shourong; Wan, Haiqin; Sun, Jingya; Zhu, Dongqiang; Xu, Zhaoyi

    2017-06-01

    In the present study, Al2O3-pillared layered MnO2 (p-MnO2) was synthesized using δ-MnO2 as precursor and Pb(II) adsorption on p-MnO2 and δ-MnO2 was investigated. To clarify the adsorption mechanism, Al2O3 was also prepared as an additional sorbent. The adsorbents were characterized by X-ray fluorescence analysis, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and N2 adsorption-desorption. Results showed that in comparison with pristine δ-MnO2, Al2O3 pillaring led to increased BET surface area of 166.3 m2 g-1 and enlarged basal spacing of 0.85 nm. Accordingly, p-MnO2 exhibited a higher adsorption capacity of Pb(II) than δ-MnO2. The adsorption isotherms of Pb(II) on δ-MnO2 and Al2O3 pillar fitted well to the Freundlich model, while the adsorption isotherm of Pb(II) on p-MnO2 could be well described using a dual-adsorption model, attributed to Pb(II) adsorption on both δ-MnO2 and Al2O3. Additionally, Pb(II) adsorption on δ-MnO2 and p-MnO2 followed the pseudo second-order kinetics, and a lower adsorption rate was observed on p-MnO2 than δ-MnO2. The Pb(II) adsorption capacity of p-MnO2 increased with solution pH and co-existing cation concentration, and the presence of dissolved humic acid (10.2 mg L-1) did not markedly impact Pb(II) adsorption. p-MnO2 also displayed good adsorption capacities for aqueous Cu(II) and Cd(II). Findings in this study indicate that p-MnO2 could be used as a highly effective adsorbent for heavy metal ions removal in water.

  16. 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.

  17. Al/C/MnO2 sandwich nanowalls with highly porous surface for electrochemical energy storage

    NASA Astrophysics Data System (ADS)

    He, Shuijian; Zhang, Ruizhong; Zhang, Chunmei; Liu, Minmin; Gao, Xiaohui; Ju, Jian; Li, Lei; Chen, Wei

    2015-12-01

    Hierarchical materials supported on metal substrates present promising applications in flexible energy storage and conversion devices. Compared to Au, Ag, Cu, Ni, Ti, W and their alloys, Al, the most abundant metal in the crust has been less used in supercapacitors due to its high activity which makes it unstable in acid and base electrolytes. In this paper, we explore a novel Al/C/MnO2 sandwich structured material for the first time for supercapacitor. Owing to the highly porous and open surface structure and the highly conductive Al/C double core current collector on nanoscale, the Al/C/MnO2 sandwich nanowall arrays supported on Al foil show excellent capacitance performance with a maximum area specific capacitance of 1008.3 mF cm-2 and a high energy density of 35.2 μWh cm-2 at 2 mA cm-2. Moreover, a supercapacitor device with 4 supercapacitors connected in series can power a LED lamp. The present study demonstrates a novel electrode architecture based on Al foil with remarkably high area specific capacitance and stability for promising supercapacitor applications. Our strategy provides a new approach to the fabrication of hierarchical electrode materials from Al metal (could also be extend to other metal substrates) for supercapacitors and other energy storage and conversion devices.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Aluminium and Phosphate Uptake by Phragmites australis: the Role of Fe, Mn and Al Root Plaques

    PubMed Central

    BATTY, LESLEY C.; BAKER, ALAN J. M.; WHEELER, BRYAN D.

    2002-01-01

    Aluminium, a potentially phytotoxic metal, is an important constituent of many mine water discharges but has largely been neglected in the literature. The behaviour of this element in the rhizosphere of the wetland plant Phragmites australis was investigated in the laboratory in the presence and absence of Mn and Fe root plaques. Electron microscopy and chemical extraction techniques were utilized to determine the physico‐chemical properties of the plaques and any association of Al. Both Mn and Fe plaques occurred as amorphous coatings on root surfaces with uneven distributions. Al was not adsorbed onto the surface of either plaque type but formed a separate phosphate deposit closely resembling the Fe and Mn plaques. Phosphorus was also found to be adsorbed to the surface of the Fe plaques (but not the Mn plaques). Both mechanisms were found to immobilize P at the root surface but this did not significantly reduce the concentration of P in aerial plant tissues that was sufficient to ensure adequate growth. PMID:12096805

  6. 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

  7. Giant tunable Rashba spin splitting in a two-dimensional BiSb monolayer and in BiSb/AlN heterostructures

    NASA Astrophysics Data System (ADS)

    Singh, Sobhit; Romero, Aldo H.

    2017-04-01

    The search for novel two-dimensional giant Rashba semiconductors is a crucial step in the development of the forthcoming nanospintronic technology. Using first-principles calculations, we study a stable two-dimensional crystal phase of BiSb having buckled honeycomb lattice geometry, which is yet unexplored. The phonon, room temperature molecular dynamics, and elastic constant calculations verify the dynamical and mechanical stability of the monolayer at 0 K and at room temperature. The calculated electronic band structure reveals the direct band gap semiconducting nature of a BiSb monolayer with the presence of a highly mobile two-dimensional electron gas (2DEG) near the Fermi level. Inclusion of spin-orbit coupling yields the giant Rashba spin-splitting of a 2DEG near the Fermi level. The calculated Rashba energy and Rashba splitting constant are 13 meV and 2.3 eVÅ, respectively, which are amongst the largest yet known Rashba spin splitting parameters in 2D materials. We demonstrate that the strength of the Rashba spin splitting can be significantly tuned by applying in-plane biaxial strain on the BiSb monolayer. The presence of the giant Rashba spin splitting together with the large electronic band gap (1.6 eV) makes this system of peculiar interest for optoelectronics applications. Furthermore, we study the electronic properties of BiSb/AlN heterostructures having a lattice mismatch of 1.3% at the interface. Our results suggest that a BiSb monolayer and BiSb/AlN heterostructure systems could be potentially used to develop highly efficient spin field-effect transistors, optoelectronics, and nanospintronic devices. Thus, this comprehensive study of two-dimensional BiSb systems can expand the range of possible applications in future spintronic technology.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Magnetic properties of Mn-Al-C alloy powders produced by mechanical grinding

    NASA Astrophysics Data System (ADS)

    Saito, Tetsuji

    2005-05-01

    The saturation magnetization of the milled powders gradually decreased as the milling time increased due to the transformation of the magnetic τ phase into the amorphous phase. On the other hand, the coercivity of the milled powders increased to a peak value of 4.35kOe, then decreased with increasing milling time. When the amorphous powders were annealed at relatively high temperatures, the annealed powders consisted mostly of the magnetic τ phase. The optimally annealed Mn-Al-C-Ni powders exhibited a high remanence of 60emu/g with a coercivity of 1.95kOe, which is comparable to those of the gas-atomized Mn-Al-C-Ni powders.

  15. 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

  16. 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.

  17. Effect of Copper on Corrosion of Forged AlSi1MgMn Automotive Suspension Components

    NASA Astrophysics Data System (ADS)

    Koktas, Serhan; Gokcil, Emre; Akdi, Seracettin; Birol, Yucel

    2017-08-01

    Recently, modifications in the alloy composition and the manufacturing process cycle were proposed to achieve a more uniform structure with no evidence of coarse grains across the section of the AlSi1MgMn alloys. Cu was added to the AlSi1MgMn alloy to improve its age hardening capacity without a separate solution heat treatment. However, Cu addition degrades the corrosion resistance of this alloy due to the formation of Al-Cu precipitates along the grain boundaries that are cathodic with respect to the aluminum matrix and thus encourage intergranular corrosion. The present work was undertaken to identify the impact of Cu addition on the corrosion properties of AlSi1MgMn alloys with different Cu contents. A series of AlSi1MgMn alloys with 0.06-0.89 wt.% Cu were tested in order to identify an optimum level of Cu addition.

  18. Electronic structure and photocatalytic water splitting of lanthanum-doped Bi{sub 2}AlNbO{sub 7}

    SciTech Connect

    Li Yingxuan; Chen Gang Zhang Hongjie; Li Zhonghua

    2009-04-02

    Bi{sub 2-x}La{sub x}AlNbO{sub 7} (0 {<=} x {<=} 0.5) photocatalysts were synthesized by the solid-state reaction method and characterized by powder X-ray diffraction (XRD), infrared (IR) spectra and ultraviolet-visible (UV-vis) spectrophotometer. The band gaps of the photocatalysts were estimated from absorption edge of diffuse reflectance spectra, which were increased by the doping of lanthanum. It was found from the electronic band structure study that orbitals of La 5d, Bi 6p and Nb 4d formed a conduction band at a more positive level than Bi 6p and Nb 4d orbitals, which results in increasing the band gap. Photocatalytic activity for water splitting of Bi{sub 1.8}La{sub 0.2}AlNbO{sub 7} was about 2 times higher than that of nondoped Bi{sub 2}AlNbO{sub 7}. The increased photocatalytic activity of La-doped Bi{sub 2}AlNbO{sub 7} was discussed in relation to the band structure and the strong absorption of OH groups at the surface of the catalyst.

  19. 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.

  20. Tensile Fracture Modes in Fe-22Mn-0.6C and Fe-30Mn-3Si-3Al Twinning-Induced Plasticity (TWIP) Steels

    NASA Astrophysics Data System (ADS)

    Yang, H. K.; Tian, Y. Z.; Zhang, Z. J.; Yang, C. L.; Zhang, P.; Zhang, Z. F.

    2017-10-01

    Tensile tests were carried out to investigate the differences in fracture mechanisms between Fe -22Mn -0.6C and Fe -30Mn -3Si -3Al (wt pct) twinning-induced plasticity steels. Although both steels possess a strong twinning capability during tensile deformation, they display different tensile fracture modes of shear and necking. The Portevin -le Chatelier band is proposed as the key factor influencing the different fracture mechanisms.

  1. 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.

  2. Directly obtained τ-phase MnAl, a high performance magnetic material for permanent magnets

    NASA Astrophysics Data System (ADS)

    Fang, Hailiang; Kontos, Sofia; Ångström, Jonas; Cedervall, Johan; Svedlindh, Peter; Gunnarsson, Klas; Sahlberg, Martin

    2016-05-01

    The metastable tetragonal τ-phase has been directly obtained from casting Mn0.54Al0.46 and (Mn0.55Al0.45)100C2 using the drop synthesis method. The as-casted samples were ball milled to decrease the particle size and relaxed at 500 °C for 1 h. The phase composition, crystallographic parameters, magnetic properties and microstructure were systematically studied. The results reveal that the τ-phase could be directly obtained from drop synthesis. The highest Ms of 117 emu/g was achieved in the (Mn0.55Al0.45)100C2 where the τ-phase was stabilized by doping with carbon. Carbon doping increased the c/a ratio of the τ-phase as it occupies specific interstitial positions (½, ½, 0) in the structure. Furthermore, ball milling increases the coercivity (Hc) at the expense of a decrease in magnetic saturation (Ms). The increase in coercivity is explained by a decrease of grain size in conjunction with domain wall pinning due to defects introduced during the ball milling process.

  3. Effect of Additional Element on Hybrid Laser Weldability in Al-Mn Alloys

    NASA Astrophysics Data System (ADS)

    Suzuki, Kenta; Hori, Hisashi; Kanamori, Keiji; Mizushima, Kazumitsu; Kinoshita, Junichi; Murata, Tooru

    Hybrid laser welding have been carried out, with bead-on-plate and butt welding setting, on Al-Mn and Al-Mn-Mg alloys, to evaluate the welding defects morphology. On bead-on-plate welding, keyhole mode was achieved without the welding defects at 60mm/s traveling speed with 2.12kW pulsed laser in Al-Mn alloy. The increase of maximum power of pulsed laser and Mg content caused a rise of welding defects, that is, porosities and cracks. Simultaneously, both penetration depth and bead width became larger, and aspect ratio of fusion zone (depth to width) also increased. X ray tomography clearly evaluated internal welding defects such as porosity. Morphology of fusion zone and welding defects were influenced by an incorrect root gap in butt welding. An increase in the root gap tended to reduce the porosity, and achieved higher aspect ratio of fusion zone, which was deeper penetration depth and wider bead width. On the other hand, underfill, as superficial welding defect, was clearly formed in both alloys. The root gap in butt welding was one of sensitive factors on the laser weldability besides Mg content and pulsed laser power.

  4. 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

  5. Early Stages of Precipitation Process in Al-(Mn-)Sc-Zr Alloy Characterized by Positron Annihilation

    NASA Astrophysics Data System (ADS)

    Vlach, Martin; Cizek, Jakub; Melikhova, Oksana; Stulikova, Ivana; Smola, Bohumil; Kekule, Tomas; Kudrnova, Hana; Gemma, Ryota; Neubert, Volkmar

    2015-04-01

    Thermal effects on the precipitation stages in as-cast Al-0.70 at. pct Mn-0.15 at. pct Sc-0.05 at. pct Zr alloy were studied. The role of lattice defects was elucidated by positron annihilation spectroscopy (lifetime and coincidence Doppler broadening) enabling investigation of solutes clustering at the atomic scale. This technique has never been used in the Al-Sc- and/or Al-Zr-based alloys so far. Studies by positron annihilation were combined with resistometry, hardness measurements, and microstructure observations. Positrons trapped at defects are preferentially annihilated by Sc electrons. Lifetime of trapped positrons indicates that Sc atoms segregate at dislocations. Maximum fraction of positrons annihilated by Sc electrons occurring at 453 K (180 °C) suggests that clustering of Sc bound with vacancies takes place. It is followed by peak of this fraction at 573 K (300 °C). A rise of the contribution of trapped positrons annihilated by Zr electrons starting at 513 K (240 °C) and attaining maximum also at 573 K (300 °C) confirms that Zr participates in precipitation of the Al3Sc particles already at these temperatures. The pronounced hardening at 573 K (300 °C) has its nature in the precipitation of the Al3Sc particles with a Zr-rich shell. The contribution of trapped positrons annihilated by Mn electrons was found to be negligible.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Effect of Zn and Mn Additions on the Wear Resistance of Cast Alloy Mg - 5% Al - 1% Si

    NASA Astrophysics Data System (ADS)

    Cug, Harun; Ahlatci, Hayrettin

    2017-07-01

    The effect of additions of Zn and Mn (from 0.5 to 4%) on the microstructure of alloy Mg - 5% Al - 1% Si is studied by the methods of x-ray diffractometry and light and scanning electron microscopy. The strength parameters are determined in tensile and wear tests. It is shown that particles of Mg2Si precipitate in the matrix and particles of Mg17Al12 precipitate on grain boundaries upon the introduction of low contents of Zn and Mn. Phases MgZn and Al6Mn precipitate at a high content of the additions. An optimum concentration of Zn and Mn is chosen for raising the wear resistance of alloy Mg - 5% Al - 1% Si.

  11. Structural, magnetic, and dielectric studies of the Aurivillius compounds SrBi{sub 5}Ti{sub 4}MnO{sub 18} and SrBi{sub 5}Ti{sub 4}Mn{sub 0.5}Co{sub 0.5}O{sub 18}

    SciTech Connect

    Yuan, B.; Yang, J. Zuo, X. Z.; Tang, X. W.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Song, D. P.; Sun, Y. P.

    2015-01-14

    We have successfully synthesized the Aurivillius compounds SrBi{sub 5}Ti{sub 4}MnO{sub 18} and SrBi{sub 5}Ti{sub 4}Mn{sub 0.5}Co{sub 0.5}O{sub 18} using a modified Pechini method. Both samples have an orthorhombic structure with the space group B2cb. The valence state of Mn is suggested to be +3 and the doped Co ions exist in the form of Co{sup 2+} and Co{sup 3+} based on the results of x-ray photoelectron spectroscopy. The sample SrBi{sub 5}Ti{sub 4}MnO{sub 18} exhibits a dominant paramagnetic state with the existence of superparamagnetic state as evidenced by the electron paramagnetic resonance results, whereas SrBi{sub 5}Ti{sub 4}Mn{sub 0.5}Co{sub 0.5}O{sub 18} undergoes a ferrimagnetic transition at 161 K originating from the antiferromagnetic coupling of Co-based and Mn-based sublattices, and a ferromagnetic transition at 45 K arising from the Mn{sup 3+}-O-Co{sup 3+} (low spin) interaction. The sample SrBi{sub 5}Ti{sub 4}Mn{sub 0.5}Co{sub 0.5}O{sub 18} exhibits two dielectric anomalies. One corresponds to a relaxor-like dielectric relaxation which follows the Vogel-Fulcher function and the other dielectric relaxation obeys the Arrhenius law arising from the collective motion of oxygen vacancies. In addition, the sample SrBi{sub 5}Ti{sub 4}Mn{sub 0.5}Co{sub 0.5}O{sub 18} exhibits a magnetodielectric effect caused by the Maxwell-Wagner effect because of the conductivity of the sample. This is demonstrated by the fact that the activation energy in dielectric loss process is close to that for dc conductivity and the magnetodielectric effect is sensitive to the measured frequency.

  12. Molecular structure of Mg-Al, Mn-Al and Zn-Al halotrichites-type double sulfates--an infrared spectroscopic study.

    PubMed

    Palmer, Sara J; Frost, Ray L

    2011-05-01

    Near infrared (NIR), X-ray diffraction (XRD) and infrared (IR) spectroscopy have been applied to halotrichites of the formula MgAl(2)(SO(4))(4)·22H(2)O, MnAl(2)(SO(4))(4)·22H(2)O and ZnAl(2)(SO(4))(4)·22H(2)O. Comparison of the halotrichites in different spectral regions has shown that the incorporation of a divalent transition metal into the halotrichite structure causes a shift in OH stretching band positions to lower wavenumbers. Therefore, an increase of the hydrogen bond strength of the bonded water is observed for divalent cations with a larger molecular mass. XRD has confirmed the formation of halotrichite for all three samples and characteristic peaks of halotrichite have been identified for each halotrichite-type compound. It has been observed that Mg-Al and Mn-Al halotrichite are very similar in structure, while Zn-Al showed several differences particularly in the NIR spectra. This work has shown that compounds with halotrichite structures can be synthesised and characterised by infrared and NIR spectroscopy. Copyright © 2011 Elsevier B.V. All rights reserved.

  13. Iron-base superalloys - A phase analysis of the multicomponent system (Fe-Mn-Cr-Mo-Nb-Al-Si-C)

    NASA Technical Reports Server (NTRS)

    Gupta, H.; Nowotny, H.; Lemkey, F. D.

    1988-01-01

    In the course of studies on the iron-rich multicomponent system Fe-Mn-Cr-Mo-Nb-Al-Si-C, work was concentrated on pertinent quinary and six-component combinations namely Fe-Mn-Al-Si-C, Fe-Cr-Al-Si-C and Fe-Mn-Cr-Al-Si-C which had been elaborated at 65, 72, and 80 wt pct Fe. Manganese acts as a strong stabilizer for the cementite carbide. Chromium seems to stabilize the iron aluminide Fe2Al5 which forms in a considerable amount within an alloy of nominal composition Fe(65)Mn(15)Cr(12)Al(5)Si(2)C(1) (percent by weight). Although the Mn3AlC carbide is, like Fe3AlC, a perovskite carbide, manganese does not appear to favor the formation of the perovskite carbide. Because of the relatively low sintering temperature (700 C), for al large portion of the samples equilibria conditions are not always reached.

  14. 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.

  15. 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.

  16. 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.

  17. Precipitation behavior of dispersoids in Al-Mg-Si-Cu-Mn-Cr alloy during homogenization annealing

    NASA Astrophysics Data System (ADS)

    Han, Yi; Ma, Ke; Wang, Chuyan; Nagaumi, Hiromi

    The precipitation behavior of dispersoids containing Mn and Cr in Al-Mg-Si-Cu-Mn-Cr alloy during homogenization annealing with different heating rate was investigated in this paper. Scanning transmission electron microscopy (STEM) was used to measure the difference in the size and number density of dispersoids after the two treatments. The effect of homogenization treatment on the recrystallization fraction and grain size was determined by examining hot forged and solution treated specimens using electron back-scatter diffraction (EBSD). It was found that the slow homogenization heating rate promotes to an increase in the average dispersoid number density and decrease in particle size. The enhanced dispersoids distribution resulting from the slow homogenization heating rate leads to a reduction in the recrystallization fraction (24 29% lower) and grain size (18 22% smaller).

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. Realizing semiconductivity by a large bandgap tuning in Bi4Ti3O12 via inserting La1-xSrxMnO3 perovskite layers

    NASA Astrophysics Data System (ADS)

    Wang, Jianlin; Chen, Zezhi; Huang, Haoliang; Cui, Jiameng; Zhang, Wenhua; Fu, Zhengping; Peng, Ranran; Yan, Wensheng; Lu, Yalin

    2017-05-01

    Bismuth layer structured Aurivillius oxides have long been considered as traditional ferroelectric dielectrics, and they are feasible platforms incubating magnetic, ferroelectric, photonic, microwave, etc. properties for many important applications. It has been a longstanding challenge to achieve a certain charge carrier concentration and to narrow the bandgap in such transition metal complex oxides, yet realizing that semiconductivity is necessary for potential integration functions such as junctions in oxide optoelectronic devices. By inserting La1-xSrxMnO3 into the typical Bi4Ti3O12 ferroelectric host, we demonstrate semiconductivity and large bandgap tuning in Bi4Ti3O12-La1-xSrxMnO3 (0.3 ≤ x ≤ 0.7) solid solutions, in which a minimum resistivity value of ρ = 5021 Ω.cm and an optical bandgap value of Eg = 1.97 eV are obtained. Soft X-ray absorption spectra provide Mn and Ti charge valence states, indicating an almost constant Mn3.2+ state and an increase towards Ti4+ when raising the La/Sr ratio.

  6. 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.

  7. 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.

  8. 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.

  9. 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; Iowa State Univ., Ames, IA; ...

    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

  10. Deformation Twinning in Nb-Microalloyed Fe-Mn-C-Al Twinning-Induced Plasticity Steel

    NASA Astrophysics Data System (ADS)

    Kwon, Eui Pyo; Kim, Dae Young; Park, Hyun Kyeong

    2017-09-01

    Work hardening and deformation twinning in microalloyed Fe-Mn-C-Al twinning-induced plasticity (TWIP) steel with Nb were investigated in this study, and it was found that the addition of Nb affected the work-hardening behavior of TWIP steel. Moreover, the quantitative characterization of twinning was performed on the deformed microstructure by electron backscattering diffraction analysis, and the results indicate that the addition of Nb causes a reduction in twinning kinetics. The decrease in deformation twinning in TWIP steel with added Nb can be attributed to the effect of fine grain, dislocations in non-recrystallized grains, and the formation of twins on a particular grain orientation.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Prediction of half-metallic properties for the Heusler alloys Mn 2CrZ (Z=Al, Ga, Si, Ge, Sb): A first-principles study

    NASA Astrophysics Data System (ADS)

    Luo, Hongzhi; Zhu, Zhiyong; Liu, Guodong; Xu, Shifeng; Wu, Guangheng; Liu, Heyan; Qu, Jingping; Li, Yangxian

    First-principles FLAPW calculations were performed on the Mn 2CrZ ( Z=Al, Ga, Si, Ge and Sb) alloys. Based on these results we predict two half-metallic ferromagnets (HMFs) namely Mn 2CrAl and Mn 2CrSb, and also find an energy gap in Mn 2CrGa which lies near the Fermi level. The energy gap lies in the majority spin band for Mn 2CrAl and Mn 2CrGa, whereas in the minority one for Mn 2CrSb. The calculated total spin magnetic moments Mtcal are -1 μB per unit cell for Mn 2CrAl and Mn 2CrGa, +1 μB per unit cell for Mn 2CrSb and zero for Mn 2CrSi and Mn 2CrGe, which agree with the Slater-Pauling rule. The calculation indicates a large and localized magnetic moment of Cr at B site. This is meaningful for searching for new half-metallic antiferromagnets in Heusler alloys. The magnetic moment of Cr is found to increase with increasing atomic number of Z and is antiparallel to that of Mn. The change of Mn and Cr spin moments compensates each other and keeps the total spin moment as an integer when the Z atom is changed.

  16. 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.

  17. 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.

  18. 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.

  19. 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).

  20. 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.

  1. Self-Poling-Induced Magnetoelectric Effect in Highly Strained Epitaxial BiFeO3/La0.67Sr0.33MnO3-δ Multiferroic Heterostructures.

    PubMed

    Li, Dong; Zheng, Dongxing; Gong, Junlu; Zheng, Wanchao; Jin, Chao; Bai, Haili

    2017-07-19

    Highly strained epitaxial BiFeO3/La0.67Sr0.33MnO3-δ (BFO/LSMO) heterostructures were fabricated on LaAlO3 substrates by magnetron sputtering. The as-grown downward self-polarization of BFO capping layers was confirmed by piezoelectric force microscopy. Using the electrostatic field-induced charge screening, a hole depletion state was induced in ultrathin (8 nm) LSMO films. As a result of the interfacial charge coupling, appreciable saturated magnetization (MS) increase of about 500 and 100% can be observed in LSMO with BFO capping at 5 and 300 K, respectively. Besides, LSMO phase translations can be revealed by the BFO thickness-related exchange bias field (HE) and MS of the BFO/LSMO heterostructures. The results established a new approach in achieving interfacial magnetoelectric couplings with thin self-polarized multiferroic layers.

  2. 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.

  3. 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)

  4. 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.

  5. 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.

  6. 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.

  7. Compensated Ferrimagnetism in the Zero-Moment Heusler Alloy Mn3Al

    NASA Astrophysics Data System (ADS)

    Jamer, Michelle E.; Wang, Yung Jui; Stephen, Gregory M.; McDonald, Ian J.; Grutter, Alexander J.; Sterbinsky, George E.; Arena, Dario A.; Borchers, Julie A.; Kirby, Brian J.; Lewis, Laura H.; Barbiellini, Bernardo; Bansil, Arun; Heiman, Don

    2017-06-01

    While antiferromagnets have been proposed as components to limit stray magnetic fields, their inability to be spin polarized inhibits their use in spintronic devices. Compensated ferrimagnets are a unique solution to this dilemma since they have zero net moment, but their nonsymmetric density of states allows the achievement of high spin polarization. Density-functional theory predicts Mn3Al in the D 03 structure to be fully compensated and retain half-metallicity at room temperature. In this work, 50-nm Mn3Al thin films are synthesized using molecular beam epitaxy and annealed at various temperatures in order to investigate their magnetic properties. Magnetometry measurements confirm the high Curie temperature of 605 K. Polarized-neutron reflectometry (PNR) indicates a low net magnetic moment, along with depth profiles of the structure and magnetization. From the PNR data, a saturation moment of 0.11 ±0.04 μB/f .u . is extracted, confirming the nominal zero moment present in these thin films.

  8. 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.

  9. The environment assisted cracking of Fe-32Mn-9Al alloys

    SciTech Connect

    Chang, S.C.; Liu, J.Y.; Juang, H.K.

    1994-12-31

    Stress corrosion cracking (SCC) behaviors of four austenitic Fe-32Mn-9Al containing approximately 1 wt% carbon alloys were studied in this work. All of the four alloys are susceptible to stress corrosion cracking in room temperature and 160C NaCl solution. The SCC can be enhanced by applying anodic potential. The mechanism of SCC is mainly active path corrosion. The crack path is transgranular. The addition of 1.23% Mo or 1.27% Si to the austenitic Fe-32Mn-V/ 9Al alloy does not change the SCC mechanism and crack path. The addition of 1.27% Si makes the alloy more susceptible to SCC but no such effect was observed with 1.23% Mo. All four alloys studied are susceptible to hydrogen embrittlement in 3.5% NaCl solution at negative enough cathodic applied potential. The addition of Mo, Cr or Si in the alloy displaces the embrittlement potential to a more cathodic range.

  10. Polymerization of catechin catalyzed by Mn-, Fe- and Al-oxides.

    PubMed

    Chen, Yue Min; Tsao, Tsung Ming; Liu, Cheng Chung; Huang, Pan Ming; Wang, Ming Kuang

    2010-11-01

    The role of short-range order (SRO) metal oxides, which are common in acid soils and associated environments, in influencing the abiotic transformations of catechin, which is common in the soil of tea plantations, still remains poorly understood. The aim of this study was to investigate the catalytic power of SRO Mn(IV)-, Fe(III)- and Al-oxides in influencing the abiotic transformations of catechin. At the end of a 90-h reaction period, the release of CO(2) in all the oxide-catechin systems is higher than that for the system with only catechin. Polymerization of catechin is catalyzed and enhanced by SRO-oxides, as is indicated by the absorbance values of the supernatants, which were obtained via visible adsorption spectroscopy, and the yields of humic polymers. The sequence of the oxides that increased the yield of total humic polymers in these systems under ambient atmosphere is: Fe(III)-oxide>Mn(IV)-oxide>Al-oxide>no catalyst (catechin). The electron spin resonance (ESR) and Fourier transformation infrared absorption spectrometry (FT-IR) of humic polymers formed in the oxide-catechin systems were similar to the spectra obtained from the humic polymers extracted from the soil. The catalytic power of SRO-oxides in promoting the oxidative polymerization of catechin, the resultant formation of humic substances, and C turnover in acid soils thus merit attention. Copyright (c) 2010. Published by Elsevier B.V.

  11. 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.

  12. 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

  13. Effect of controlled Mn doping on transition of oxygen vacancies in Bi2Ti2O7 thin films: An electrochemical study

    NASA Astrophysics Data System (ADS)

    Kang, Leeseung; An, HyeLan; Kim, Tae Hyung; Lee, Duk-Hee; Park, Kyung-Soo; Swain, Basudev; Lee, Chan Gi; Nahm, Sahn

    2017-09-01

    Crystalline pyrochlore Bi2Ti2O7 (B2T2) thin films were well formed at 300 °C under 740 mTorr of oxygen partial pressure using pulsed laser deposition. In order to improve the electrical properties of the dielectric B2T2 films, Mn ions were doped into the films and their influence was investigated. Improvement in electrical behavior, especially leakage current density were revealed via impedance spectroscopy and electrochemical studies. Mn doping at an appropriate level improved the electrical properties of the films by affording extrinsic oxygen vacancies that reduced the number of intrinsic oxygen vacancies acting as electron trap sites at the interface between the Pt electrode and the B2T2 film. Schottky emission was posited as the leakage current mechanism in the 10 mol% Mn doped B2T2 (Mn:B2T2) films. The barrier height between the Pt electrode and the Mn:B2T2 film was approximately 1.46 eV, but decreased to 0.51 eV for the non-doped film due to large numbers of intrinsic oxygen vacancies.

  14. 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.

  15. High-resolution electron microscope observation of interface microstructure of a cast Al-Mg-Si-Bi-Pb(6262)/Al2O3p composite.

    PubMed

    Zhou, Z.; Fan, Z.; Peng, H. X.; Li, D. X.

    2001-02-01

    High-resolution electron microscopy was employed to characterize the interface structure of a cast Al-Mg-Si-Bi-Pb aluminium(6262)-based composite reinforced by alpha alumina particles with a trace of beta alumina in order to investigate the behaviour of alloying elements in cast composites. Except for a few primary Mg2Si particles, few reaction products were detected at the interface of Al/alpha-Al2O3 due to the unfavourable reaction kinetics during the squeeze-casting process. The Mg2Si particle has an orientation relationship with alpha-Al2O3 of [011]Mg2Si//[1210]alpha-Al2O3 (111)Mg2Si//(0006)alpha-Al2O3. A significant amount of MgAl2O4 was found on the surface of the beta-Al2O3 particles, which is in contrast to the small degree of reaction found on alpha-Al2O3 particles. MgAl2O4 and beta-Al2O3 particles have the following orientation relationship: [011]MgAl2O4//[1210]beta-Al2O3 (111) MgAl2O4//(0006)beta-Al2O3. The similar crystal structure of beta-Al2O3 to MgAl2O4 favours MgAl2O4 nucleation and growth on the surface of beta-Al2O3. Interfacial energy minimization dominates the atomic structure of the interface with the result that close packed planes and directions in the Al2O3 reinforcement and reaction products are parallel to the interfaces. Bi and Pb were found in the form of metallic nanometre particles between Al2O3 particles, or between the MgAl2O4 and Al2O3 particles, or in the open channels of beta-Al2O3 filled by the Al matrix.

  16. 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.

  17. First-principles investigation of structural and magnetic disorder in CuNiMnAl and CuNiMnSn Heusler alloys

    DOE PAGES

    Aron-Dine, S.; Pomrehn, G. S.; Pribram-Jones, A.; ...

    2017-01-10

    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.more » In conclusion, the effect of swaps involving Mn is also discussed.« less

  18. 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.

  19. New Kagomé Metal Sc3Mn3Al7Si5--Quantum Spin-Liquid Candidate?

    NASA Astrophysics Data System (ADS)

    He, Hua; Miiller, Wojciech; Aronson, Meigan

    2014-03-01

    While most of the reported Kagomé systems are semiconductors or insulators, in which the magnetic moments have a highly localized character, here we present a new intermetallic compound, Sc3Mn3Al7Si5, as a rare example of a Kagomé metal. The structure of the compound was established by single-crystal X-ray diffraction, and it crystallizes with a hexagonal structure (Sc3Ni11Si4 type) with Mn atoms forming the Kagomé lattice. The dc magnetic susceptibility measurements find a Curie-Weiss moment of ~ 0.51 μB/Mn, however, no magnetic order is found for temperatures as low as 1.8 K. Electrical resistivity and heat capacity measurements show that this compound is definitively metallic, with an enhanced specific heat Sommerfeld coefficient below 10K, indicating strong electronic correlations. Intriguingly, these features have revealed Sc3Mn3Al7Si5 as a possible quantum spin liquid. The role of the geometrically frustrated structure and Mn-ligand hybridization in the magnetism of Sc3Mn3Al7Si5 is also discussed. We acknowledge the Office of Assistant Secretary of Defense for Research and Engineering for providing the NSSEFF funds that supported this research.

  20. Capacitive and magnetoresistive origin of magnetodielectric effects in Sm-substituted spiral antiferromagnet BiMnFe{sub 2}O{sub 6}

    SciTech Connect

    Ghara, Somnath; Sundaresan, A.; Yoo, Kyongjun; Kim, Kee Hoon

    2015-10-28

    BiMnFe{sub 2}O{sub 6} exhibits a spiral antiferromagnetic ordering below 212 K and a reentrant spin glass transition at 34 K. Further, magnetic and dielectric anomalies occur at the same temperature (T = 170 K) with a significant magnetodielectric effect. Upon substitution of Sm{sup 3+} for Bi{sup 3+} ions in Bi{sub 1−x}Sm{sub x}MnFe{sub 2}O{sub 6} (x = 0.1 and 0.2), the dielectric anomaly shifts to low temperatures (T = 135 and 72 K, respectively), whereas the magnetic anomaly develops into a weak ferromagnetism. For x = 0.2, the weak ferromagnetism occurs in a wide temperature range (90–201 K). Below 90 K, it undergoes a transition to an antiferromagnetic state. In contrast to the parent compound (x = 0), the magnetodielectric effect is observed both in the antiferromagnetic region (T < 90 K) with a maximum at the dielectric anomaly (72 K) and also in the weak ferromagnetic region. It has been shown that the magnetodielectric effect in the antiferromagnetic region has an intrinsic capacitive origin while that observed at the weak ferromagnetic region originates from magnetoresistance.

  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. Magnetic ordering in perovskites A{sub 1{minus}x}MnO{sub 3+y} (A=La, Bi, rare earth ion) (abstract)

    SciTech Connect

    Troyanchuk, I.O.; Kasper, N.V.; Szymczak, H.; Nabialek, A.

    1997-04-01

    In order to clarify the mechanism of exchange interactions in orthomanganites with perovskite structure a magnetic study of parent compounds as a function of stoichiometry has been made. It was shown that the LaMnO{sub 2.99} is a weak ferromagnet with T{sub N}=147 K while LaMnO{sub 3.13} and La{sub 0.9}MnO{sub 3.05} are ferromagnets with T{sub C}=160 and 240 K, respectively. The magnetic data indicate that the mixed magnetic state involving ferro- and antiferromagnetic domains is realized in the intermediate range of oxygen content. The RMnO{sub 3+y} (R=Nd, Sm, Eu, Gd) are inhomogeneous antiferromagnets. The temperatures of start of magnetic moments freezing inside ferromagnetic clusters depend slightly on stoichiometry and for y{approximately}0 are equal 83, 65, 47, and 22 K, respectively. The coercive field for LaMnO{sub 3} is 6 kOe at 4.2 K while that for EuMnO{sub 3} is much higher{emdash}26 kOe. It is worth noting that the Neel temperatures of RMnO{sub 3} (R=Eu, Gd, Tb, Dy) are estimated to be about 40 K independently of the type of rare-earth ion. Magnetic moments of Gd, Tb, and Dy in the rare-earth sublattice are antiferromagnetically ordered below 6{endash}7 K. Applying external fields induces the antiferromagnet{endash}ferromagnet transition in rare-earth sublattice. H{sub cr} at 2 K for RMnO{sub 3} (R=Gd, Tb, Dy) are measured to be about 5, 12, and 10 kOe, respectively. In contrast to rare-earth compounds, the BiMnO{sub 3} is ferromagnet below 98 K. The deviation from stoichiometry as well as replacement of Bi ions by Sr, Ca, or La ions leads to the suppression of the long-range ferromagnetic order. Magnetic properties are discussed in terms of super exchange interactions between manganese ions via oxygen taking into account the 3d-orbital ordering that occurs in LaMnO{sub 3} and TbMnO{sub 3} at 400 and 1200{degree}C, respectively. {copyright} {ital 1997 American Institute of Physics.}

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. Room temperature ferrimagnetism and ferroelectricity in strained, thin films of BiFe0.5Mn 0.5O3

    DOE PAGES

    Choi, Eun -Mi; Fix, Thomas; Kursumovic, Ahmed; ...

    2014-10-14

    In this study, 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. Magnetization measurements demonstrated ferrimagnetism (TC ~ 600K), with a room temperature saturation moment (MS) of up to 90 emu/cc (~0.58μB/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 themore » 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.« less

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Influence of Al and C on Mechanical Properties of Sub-Rapidly Solidified Fe-20Mn-xAl-yC Low-Density Steels

    NASA Astrophysics Data System (ADS)

    Liu, Libing; Shen, Zhengyan; Yang, Yang; Song, Changjiang; Zhai, Qijie

    Fe-Mn-Al-C low density steels with high manganese and high aluminum content have received much attention recently because their potential of more than 10wt.% reduction of density, excellent mechanical properties and multiphase microstructures. For present study, sub-rapidly solidified Fe-20Mn-xAl-yC low-density steels with different Al (5, 9,12wt.%) and C(0.4, 0.6, 0.8, 1.0,wt.%) have been produced to understand the influence of Al and C on phases content and mechanical properties. These near-net shaped Fe-20Mn-xA-yC steels all revealed duplex phases (δ+γ) during sub-rapid solidification, and some ordered DO3 phases formed in -ferrite. The changes of aluminum and carbon content lead to the volume fractions changes of -ferrite, and the dissolved aluminum content have a vital influence on tensile properties, but there is no clear relationship between phase proportions and tensile properties. The yield strength, ultimate tensile strength and total elongation of 9Al-0.8C steel are 593MPa, 952 MPa, and 46%, respectively, which shows the best comprehensive performance of these sub-rapidly solidified Fe-20Mn-xA-yC steels.

  16. 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.

  17. 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.

  18. Anisotropic grain growth of ZnO grain in the varistor system ZnO-Bi sub 2 O sub 3 -MnO-TiO sub 2

    SciTech Connect

    Sung, Gun Yong; Kim, Chong Hee )

    1988-11-01

    From the analysis of selected-area electron diffraction patterns through transmission electron microscopy, the crystallographic orientation of anisotropic ZnO grain growth by the addition of TiO{sub 2} to the varistor system ZnO-Bi{sub 2}O{sub 3}-MnO was determined to be the (10{anti 1}0) and ({anti 2}110) directions. The behavior of anisotropic grain growth was interpreted by the epitaxial growth of prism planes (resulting from the favorable atomic arrangement on these planes compared with other planes) and the increase in reactivity of the Bi-rich liquid phase toward the ZnO grain by the addition of TiO{sub 2}.

  19. Induced magnetization in La0.7Sr0.3MnO3/BiFeO3 superlattices.

    PubMed

    Singh, Surendra; Haraldsen, J T; Xiong, J; Choi, E M; Lu, P; Yi, D; Wen, X-D; Liu, J; Wang, H; Bi, Z; Yu, P; Fitzsimmons, M R; MacManus-Driscoll, J L; Ramesh, R; Balatsky, A V; Zhu, Jian-Xin; Jia, Q X

    2014-07-25

    Using polarized neutron reflectometry, we observe an induced magnetization of 75 ± 25 kA/m at 10 K in a La(0.7)Sr(0.3)MnO(3) (LSMO)/BiFeO(3) superlattice extending from the interface through several atomic layers of the BiFeO(3) (BFO). The induced magnetization in BFO is explained by density functional theory, where the size of band gap of BFO plays an important role. Considering a classical exchange field between the LSMO and BFO layers, we further show that magnetization is expected to extend throughout the BFO, which provides a theoretical explanation for the results of the neutron scattering experiment.

  20. Effect of heat treatments on the microstructure and formability of Al-Mg-Mn-Sc-Zr alloy.

    PubMed

    Miyake, Yudai; Sato, Yukio; Teranishi, Ryo; Kaneko, Kenji

    2017-10-01

    Microstructures and formability of scandium and zirconium added Al-Mg-Mn alloy sheets with various heating conditions were examined to improve their mechanical properties. Formability of these samples were judged by the Lankford value, r-value. It was possible to fabricate mechanically balanced Al-Mg-Mn-Sc-Zr alloy with high hardness 76.2 Hv and with high formability with r=1.2, by not only adding scandium and zirconium but also optimizing the heat treatment conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. 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.

  2. Alloy Design, Combinatorial Synthesis, and Microstructure-Property Relations for Low-Density Fe-Mn-Al-C Austenitic Steels

    NASA Astrophysics Data System (ADS)

    Raabe, D.; Springer, H.; Gutierrez-Urrutia, I.; Roters, F.; Bausch, M.; Seol, J.-B.; Koyama, M.; Choi, P.-P.; Tsuzaki, K.

    2014-09-01

    We present recent developments in the field of austenitic steels with up to 18% reduced mass density. The alloys are based on the Fe-Mn-Al-C system. Here, two steel types are addressed. The first one is a class of low-density twinning-induced plasticity or single phase austenitic TWIP (SIMPLEX) steels with 25-30 wt.% Mn and <4-5 wt.% Al or even <8 wt.% Al when naturally aged. The second one is a class of κ-carbide strengthened austenitic steels with even higher Al content. Here, κ-carbides form either at 500-600°C or even during quenching for >10 wt.% Al. Three topics are addressed in more detail, namely, the combinatorial bulk high-throughput design of a wide range of corresponding alloy variants, the development of microstructure-property relations for such steels, and their susceptibility to hydrogen embrittlement.

  3. Multi-state resistive switching memory with secure information storage in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Yao, Y. P.; Liu, Y. K.; Dong, S. N.; Yin, Y. W.; Yang, S. W.; Li, X. G.

    2012-05-01

    The ferroelectric polarization dependent bipolar and conductive filament related unipolar resistive switching behaviors are investigated systematically in Au/BiFe0.95Mn0.05O3/La5/8Ca3/8MnO3 heterostructure. The results show that after conductive filaments are formed, the ferroelectric state previously polarized will keep almost unchanged. By combining the two resistive switching mechanisms together under appropriate programming conditions, a tri-state-like resistive switching behavior is realized, finding effective routes in designing high-density storage. According to these distinctive characteristics, a prototype memory device with secure information storage is properly designed as an example of promising applications.

  4. 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.

  5. 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.

  6. 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.

  7. FAST TRACK COMMUNICATION: Electronic transport properties of charge-ordered Bi0.4Ca0.6MnO3 film

    NASA Astrophysics Data System (ADS)

    Chen, Y. Z.; Sun, J. R.; Wang, D. J.; Liang, S.; Wang, J. Z.; Han, Y. N.; Han, B. S.; Shen, B. G.

    2007-11-01

    The electronic transport properties of charge-ordered Bi0.4Ca0.6MnO3 films grown on a (110) SrTiO3 substrate are experimentally studied. Special attention has been paid to the Hall effect around the charge-ordering (CO) transition. The charge carriers are found to be electron-like, and the carrier density n exhibits a significant change upon the CO transition: it is nearly constant above the transition temperature Tco, ~0.36 electrons/Mn, and reduces with decrease of the temperature below Tco following the formula n \\propto \\exp (-E_{\\mathrm {H}}/k_{\\mathrm {B}}T) , with an activation energy EH of ~0.13 eV. In contrast, no obvious signatures of thermal activation for Hall mobility were observed. Meanwhile, it is revealed that magnetic field affects the resistivity by enhancing the carrier mobility of the film in the course of the CO transition.

  8. 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.

  9. Cyclic Degradation Behavior of < 001 \\rangle -Oriented Fe-Mn-Al-Ni Single Crystals in Tension

    NASA Astrophysics Data System (ADS)

    Vollmer, M.; Kriegel, M. J.; Krooß, P.; Martin, S.; Klemm, V.; Weidner, A.; Chumlyakov, Y.; Biermann, H.; Rafaja, D.; Niendorf, T.

    2017-08-01

    In the present study, functional fatigue behavior of a near 〈001〉-oriented Fe-Mn-Al-Ni single crystal was investigated under tensile load. An incremental strain test up to 3.5% strain and cyclic tests up to 25 cycles revealed rapid pseudoelastic degradation. Progressive microstructural degradation was studied by in situ scanning electron microscopy. The results show a partially inhibited reactivation of previously formed martensite and proceeding activation of untransformed areas in subsequent cycles. The preferentially formed martensite variants were identified by means of Schmid factor calculation and the Kurdjumov-Sachs relationship. Post mortem transmission electron microscopy investigations shed light on the prevailing degradation mechanisms. Different types of dislocations were found promoting the progressive degradation during cyclic loading.

  10. 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.

  11. 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.

  12. Study of fatigue crack growth rate for austenitic Fe-Al-Mn alloys

    SciTech Connect

    Chang, Y.P.; Lee, S.C.; Tang, G.H.

    1995-10-01

    A study was made of the crack growth rate (da/dN) versus stress-intensity variation ({Delta}K) behavior of Fe-Al-Mn alloys with different percentages of carbon, aluminum, and manganese at ambient temperature. The experimental results are described with respect to a Paris equation, da/dN = C({Delta}K){sup n}, where the exponent n, index for crack growth resistance of materials, was strongly influenced by alloy composition. It was found that higher manganese content provided better crack growth resistance, and that carbon and aluminum had an opposite effect. Scanning electron microscopy, x-ray diffraction, and mechanical properties evaluation were performed and correlated to the change of n values.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Effect of MnO on Sintering and Microstructure of Al2O3-MgO-CaO Refractories

    NASA Astrophysics Data System (ADS)

    Yin, Xue-liang; Liu, Lei; Shen, Xiang; He, Mei-le; Xu, Lei; Wang, Nan; Chen, Min

    In the current study, Al2O3-MgO-CaO refractories were prepared at 1400-1600°Cby the addition of MnO micro-powders, and the effect of MnO addition on densification behavior of the refractory was discussed. The results showed that the doped MnO dissolved to MgAl2O4 phase, and promoted the growth of MgAl2O4 grains by the formation of MgAl2O4 solid solution. As a result, the dense microstructure was obtained, with the apparent porosity decreased from 19.2% to 5.4% and the bulk density increased from 2.78g/cm3 to 3.15g/cm3 after firing at 1600°C for 2h by the addition of 4% MnO. In addition, a texture microstructure was observed, which is considered to be favorable to improve mechanical properties and the service life of Al2O3-MgO-CaO system refractories.

  19. Cubic structure and canted antiferromagnetism of CaMn7O12 doped with trivalent cations (Fe, Al, Cr)

    NASA Astrophysics Data System (ADS)

    Motin Seikh, Md.; Caignaert, V.; Lebedev, O. I.; Raveau, B.

    2014-02-01

    In this study, we show the dramatic effect of the doping of the octahedral sites with M3+ cations (Fe3+, Al3+ and Cr3+) upon the structure and magnetism of the rhombohedral double perovskite CaMn7O12. In the oxides CaMn7-xMxO12, charge ordering between Mn3+ and Mn4+ octahedral sites is destroyed leading to the cubic structure (Im-3), whereas the initial magnetic properties (TN~90 K) have disappeared leading to canted antiferromagnetism (TN≈50-70 K) for small x values (x ~0.2-1). A spin glass like behaviour is also observed for larger values (x~1) in the case of Fe substitution.

  20. 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.

  1. 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.}

  2. 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.

  3. 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}.

  4. 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.

  5. 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.

  6. Mn2CoZ (Z=Al,Ga,In,Si,Ge,Sn,Sb) compounds: Structural, electronic, and magnetic properties

    NASA Astrophysics Data System (ADS)

    Liu, G. D.; Dai, X. F.; Liu, H. Y.; Chen, J. L.; Li, Y. X.; Xiao, Gang; Wu, G. H.

    2008-01-01

    We study the electronic structures and magnetic properties of Mn2CoZ (Z=Al,Ga,In,Si,Ge,Sn,Sb) compounds with Hg2CuTi -type structure using first-principles full-potential linearized-augmented plane-wave calculations. It is found that the compounds with Z=Al , Si, Ge, Sn, and Sb are half-metallic ferrimagnet. Experimentally, we successfully synthesized the Mn2CoZ (Z=Al,Ga,In,Ge,Sn,Sb) compounds. Using the x-ray diffraction method and Rietveld refinement, we confirm that these compounds form Hg2CuTi -type structure instead of the conventional L21 structure. Based on the analysis on the electronic structures, we find that there are two mechanisms to induce the minority-spin band gap near the Fermi level, but only the d-d band gap determines the final width of the band gap. The magnetic interaction is quite complex in these alloys. It is the hybridization between the Mn(C) and Co atom that dominates the magnitude of magnetic moment of the Co atom and the sign of the Mn(B)-Co exchange interaction. The Mn2CoZ alloys follow the Slater-Pauling rule MH=NV-24 with varying Z atom. It was further elucidated that the molecular magnetic moment MH increases with increasing valence concentration only by decreasing the antiparallel magnetic moment of Mn(C) , while the magnetic moments of Mn(B) and Co are unaffected.

  7. Ferroelectric and ferromagnetic properties of epitaxial BiFeO{sub 3}-BiMnO{sub 3} films on ion-beam-assisted deposited TiN buffered flexible Hastelloy

    SciTech Connect

    Xiong, J.; Matias, V.; Jia, Q. X.; Tao, B. W.; Li, Y. R.

    2014-05-07

    Growth of multifunctional thin films on flexible substrates is of great technological significance since such a platform is needed for flexible electronics. In this study, we report the growth of biaxially aligned (BiFeO{sub 3}){sub 0.5}:(BiMnO{sub 3}){sub 0.5} [BFO-BMO] films on polycrystalline Hastelloy by using a biaxially aligned TiN as a seed layer deposited by ion-beam-assisted deposited and a La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) as a buffer layer deposited by pulsed laser deposition. The LSMO is used not only as a buffer layer but also as the bottom electrode of the BFO-BMO films. X-ray diffraction showed that the BFO-BMO films are biaxially oriented along both in-plane and out-of-plane directions. The BFO-BMO films on flexible metal substrates showed a polarization of 22.9 μC/cm{sup 2}. The magnetization of the BFO-BMO/LSMO is 62 emu/cc at room temperature.

  8. 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.

  9. 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.

  10. 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.

  11. High Temperature Deformation of Twin-Roll Cast Al-Mn-Based Alloys after Equal Channel Angular Pressing

    PubMed Central

    Málek, Přemysl; Šlapáková Poková, Michaela; Cieslar, Miroslav

    2015-01-01

    Twin roll cast Al-Mn- and Al-Mn-Zr-based alloys were subjected to four passes of equal channel angular pressing. The resulting grain size of 400 nm contributes to a significant strengthening at room temperature. This microstructure is not fully stable at elevated temperatures and recrystallization and vast grain growth occur at temperatures between 350 and 450 °C. The onset of these microstructure changes depends on chemical and phase composition. Better stability is observed in the Al-Mn-Zr-based alloy. High temperature tensile tests reveal that equal channel angular pressing results in a softening of all studied materials at high temperatures. This can be explained by an active role of grain boundaries in the deformation process. The maximum values of ductility and strain rate sensitivity parameter m found in the Al-Mn-Zr-based alloy are below the bottom limit of superplasticity (155%, m = 0.25). However, some features typical for superplastic behavior were observed—the strain rate dependence of the parameter m, the strengthening with increasing grain size, and the fracture by diffuse necking. Grain boundary sliding is believed to contribute partially to the overall strain in specimens where the grain size remained in the microcrystalline range. PMID:28793667

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Crystalline and magnetic structures of La{sub 1-x}Bi{sub x}MnO{sub 3+{delta}} manganites

    SciTech Connect

    Khomchenko, V. A. Troyanchuk, I. O.; Mantytskaya, O. S.; Tovar, M.; Szymczak, H.

    2006-07-15

    The crystalline and magnetic structures and magnetic properties of La{sub 1-x}Bi{sub x}MnO{sub 3+{delta}} (0.4 {<=} x {<=} 0.6, 0 {<=} {delta} {<=} 0.06) manganites have been studied. The solid solutions having the stoichiometric oxygen content are shown to be orbitally ordered A-type antiferromagnets. An increase in the oxygen content above the stoichiometric value is found to cause Mn{sup 4+} ions in the perovskite lattice, to remove the cooperative Jahn-Teller distortions, and to form a long-range ferromagnetic order. This order becomes broken as the concentration of the tetravalent manganese ions increases further. The tendency toward breaking the ferromagnetic order increases with the bismuth content. The magnetic properties are interpreted in terms of superexchange interactions on the assumption of local lattice distortions induced by anisotropy of the 6s{sup 2}(Bi{sup 3+})-2p{sup 6}(O{sup 2-}) chemical bonds.

  19. 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.

  20. 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.