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Sample records for magnetically ordered materials

  1. A new class of natural magnetic materials - The ordering alloys

    NASA Technical Reports Server (NTRS)

    Wasilewski, Peter

    1988-01-01

    It is shown that tetrataenite (approximately FeNi), found in many meteorites, and Josephinite (approximately FeNi3), found in many serpentinized peridotites and possibly in Allende, are atomically ordered alloys. Data are presented, showing magnetic hysteresis loops, coercivity-temperature behavior at cryogenic temperatures, and thermomagnetic curves, that show that these ordered magnetic materials have unique magnetic properties and do not fit the conventional rock magnetism paradigms represented by Fe3O4 serpentinites. The ordered state is characterized by induced magnetic anisotropy, reaching the extreme for the tetragonal truly uniaxial anisotropy in FeNi. It is suggested that these ordered magnetic alloys should be considered a new class of natural magnetic materials.

  2. NMR study of domain wall pinning in a magnetically ordered material

    NASA Astrophysics Data System (ADS)

    Pleshakov, I. V.; Popov, P. S.; Kuz'min, Yu. I.; Dudkin, V. I.

    2016-01-01

    The use of nuclear magnetic resonance in the form of spin echo in combination with magnetic field pulses applied to a magnetically ordered material sample offers a convenient tool for studying characteristics of the centers of domain-wall pinning. Possibilities of this method have been demonstrated in experiments with lithium-zinc ferrite.

  3. Magnetically responsive ordered mesoporous materials: A burgeoning family of functional composite nanomaterials

    NASA Astrophysics Data System (ADS)

    Deng, Yonghui; Cai, Yue; Sun, Zhenkun; Zhao, Dongyuan

    2011-06-01

    Magnetic mesoporous materials, as a family of novel functional nanomaterials, have attracted increasing attention due to their unique properties. Much work has been done to synthesize these materials and to explore applications in various fields, such as catalysis, separation, hyperthermia, drug delivery, and MR imaging. This Letter reviews the synthesis approaches, which can be grouped into three categories, i.e. sol-gel coating, post-loading, and nanocasting approaches. Emphasis is placed on the elucidation of the design principles, synthesis strategies and the properties-applications relationship of the mesoporous materials.

  4. Kambersky Damping in L10 Magnetic Materials of Ordered and Disordered States with Substitutional Defects

    NASA Astrophysics Data System (ADS)

    Qu, Tao; Victora, Randall

    2015-03-01

    L10 phase alloys with high magnetic anisotropy play a key role in spintronic devices. The damping constant α represents the elimination of the magnetic energy and affects the efficiency of devices. However, the intrinsic Kambersky damping reported experimentally differs among investigators and the effect of defects on α is never investigated. Here, we apply Kambersky's torque correlation technique, within the tight-binding method, to L10 ordered and disordered alloys FePt, FePd,CoPt and CoPd. In the ordered phase, CoPt has the largest damping of 0.067 while FePd has the minimum value of 0.009 at room temperature. The calculated damping value of FePt and FePd agrees well with experiment. Artificially shifting Ef, as might be accomplished by doping with impurity atoms, shows that α follows the density of states (DOS) at Ef in these four L10 alloys. We introduce lattice defects through exchanging the positions of 3d and non-3d transition elements in 36 atom supercells. The damping increases with reduced degree of chemical order, owing to the enhanced spin-flip channel allowed by the broken symmetry. This prediction is confirmed by measurements in FePt. It is demonstrated that this corresponds to an enhanced DOS at the Fermi level, owing to the rounding of the DOS with loss of long-range order. This work was supported primarily by C-SPIN (one of the six SRC STAR-net Centers) and partly by the MRSEC Program under Contract No. DMR-0819885.

  5. Unmixing Multi-Component Magnetic Mixtures in Geologic Materials Using First Order Reversal Curve Diagrams

    NASA Astrophysics Data System (ADS)

    Lascu, I.; Harrison, R. J.; Li, Y.; Muraszko, J.; Channell, J. E. T.; Piotrowski, A. M.; Hodell, D. A.; Necula, C.; Panaiotu, C. G.

    2015-12-01

    We have developed a magnetic unmixing method based on principal component analysis (PCA) of first-order reversal curve (FORC) diagrams. PCA provides an objective and robust statistical framework for unmixing, because it represents data variability as a linear combination of a limited number of principal components that are derived purely on the basis of natural variations contained within the dataset. For PCA we have resampled FORC distributions on grids that capture diagnostic signatures of magnetic domain states. Individual FORC diagrams were then recast as linear combinations of end-member (EM) FORC diagrams, located at user-defined positions in PCA space. The EM selection is guided by constraints derived from physical modeling, and is imposed by data scatter. To test our model, we have investigated temporal variations of two EMs in bulk North Atlantic sediment cores collected from the Rockall Trough and the Iberian Continental Margin. Sediments from these sites contain a mixture of magnetosomes and granulometrically distinct detrital magnetite. We have also quantified the spatial variation of three EM components in surficial sediments along the flow path of the North Atlantic Deep Water (NADW). These samples were separated into granulometric fractions, which also assisted in constraining EM definition. The unmixing model reveals systematic variations in EM relative abundance as a function of distance along NADW flow. Finally, we have applied PCA to the combined dataset of Rockall Trough and NADW sediments, which can be recast as a four-EM mixture, providing enhanced discrimination between components. Our method forms the foundation of a general solution to the problem of unmixing multi-component magnetic mixtures, a fundamental task of rock magnetic studies.

  6. Study of multi-layer active magnetic regenerators using magnetocaloric materials with first and second order phase transition

    NASA Astrophysics Data System (ADS)

    Lei, T.; Engelbrecht, K.; Nielsen, K. K.; Neves Bez, H.; Bahl, C. R. H.

    2016-09-01

    Magnetocaloric materials (MCM) with a first order phase transition (FOPT) usually exhibit a large, although sharp, isothermal entropy change near their Curie temperature, compared to materials with a second order phase transition (SOPT). Experimental results of applying FOPT materials in recent magnetocaloric refrigerators (MCR) demonstrated the great potential for these materials, but a thorough study on the impact of the moderate adiabatic temperature change and strong temperature dependence of the magnetocaloric effect (MCE) is lacking. Besides, comparing active magnetic regenerators (AMR) using FOPT and SOPT materials is also of fundamental interest. We present modeling results of multi-layer AMRs using FOPT and SOPT materials based on a 1D numerical model. First the impact of isothermal entropy change, adiabatic temperature change and shape factor describing the temperature dependence of the MCE are quantified and analyzed by using artificially built magnetocaloric properties. Then, based on measured magnetocaloric properties of La(Fe,Mn,Si)13H y and Gd, an investigation on how to layer typical FOPT and SOPT materials with different temperature spans is carried out. Moreover, the sensitivity of variation in Curie temperature distribution for both groups of AMRs is investigated. Finally, a concept of mixing FOPT and SOPT materials is studied for improving the stability of layered AMRs with existing materials.

  7. Symmetry of Magnetically Ordered Quasicrystals

    NASA Astrophysics Data System (ADS)

    Lifshitz, Ron

    1998-03-01

    The notion of magnetic symmetry is reexamined in light of the recent observation of long-range magnetic order in icosahedral quasicrystals [Charrier et al., Phys. Rev. Lett. 78, 4637 (1997)]. The relation between the symmetry of a magnetically ordered (periodic or quasiperiodic) crystal, given in terms of a ``spin space group,'' and its neutron diffraction diagram is established. In doing so, an outline of a symmetry classification scheme for magnetically ordered quasiperiodic crystals, is provided. Predictions are given for the expected diffraction patterns of magnetically ordered icosahedral crystals, provided their symmetry is well described by icosahedral spin space groups.

  8. Magnetic ordering in the ultrapure site-diluted spin chain materials SrCu1 -xNixO2

    NASA Astrophysics Data System (ADS)

    Simutis, G.; Thede, M.; Saint-Martin, R.; Mohan, A.; Baines, C.; Guguchia, Z.; Khasanov, R.; Hess, C.; Revcolevschi, A.; Büchner, B.; Zheludev, A.

    2016-06-01

    The muon spin rotation technique is used to study magnetic ordering in ultrapure samples of SrCu1 -xNixO2 , an archetypical S =1 /2 antiferromagnetic Heisenberg chain system with a small number of S =1 defects. The ordered state in the parent compound is shown to be highly homogeneous, contrary to a previous report [M. Matsuda et al., Phys. Rev. B 55, R11953 (1997), 10.1103/PhysRevB.55.R11953]. Even a minute number of Ni impurities results in inhomogeneous order and a decrease of the transition temperature. At as little as 0.5 % Ni concentration, magnetic ordering is entirely suppressed. The results are compared to previous theoretical studies of weakly coupled spin chains with site defects.

  9. Magnetic order and electronic properties of Li2Mn2(MoO4)3 material for lithium-ion batteries: ESR and magnetic susceptibility studies

    NASA Astrophysics Data System (ADS)

    Suleimanov, N. M.; Prabaharan, S. R. S.; Khantimerov, S. M.; Nizamov, F. A.; Michael, M. S.; Drulis, H.; Wisniewski, P.

    2016-08-01

    We describe the application of electron spin resonance (ESR) and magnetic susceptibility methods to study the magnetic properties and valence state of transition metal ions in Li2Mn2(MoO4)3 polyanion compound previously studied for its cathode-active properties in lithium containing batteries. ESR measurements of Li2Mn2(MoO4)3 have shown the presence of Mn2+ ions in the octahedral environment of oxygen ions. It is found that the part of manganese ions occupy the anti-site positions in lithium sublattice. The absence of the ESR signal from molybdenum ions indicates that they are non-magnetic and adopt the 6+ valence state. Considerable overlapping between 3d orbitals of transition metal and 2p oxygen orbitals has been experimentally established. This leads to the indirect exchange interaction and antiferromagnetic ordering of manganese ions at 1.4 K.

  10. Comparison of the order of magnetic phase transitions in several magnetocaloric materials using the rescaled universal curve, Banerjee and mean field theory criteria

    SciTech Connect

    Burrola-Gándara, L. A. Santillan-Rodriguez, C. R.; Rivera-Gomez, F. J.; Saenz-Hernandez, R. J.; Botello-Zubiate, M. E.; Matutes-Aquino, J. A.

    2015-05-07

    Magnetocaloric materials with second order phase transition near the Curie temperature can be described by critical phenomena theory. In this theory, scaling, universality, and renormalization are key concepts from which several phase transition order criteria are derived. In this work, the rescaled universal curve, Banerjee and mean field theory criteria were used to make a comparison for several magnetocaloric materials including pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, MnFeP{sub 0.46}As{sub 0.54}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3}. Pure Gd, SmCo{sub 1.8}Fe{sub 0.2}, and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}MnO{sub 3} present a collapse of the rescaled magnetic entropy change curves into a universal curve, which indicates a second order phase transition; applying Banerjee criterion to H/σ vs σ{sup 2} Arrot plots and the mean field theory relation |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3} for the same materials also determines a second order phase transition. However, in the MnFeP{sub 0.46}As{sub 0.54} sample, the Banerjee criterion applied to the H/σ vs σ{sup 2} Arrot plot indicates a first order magnetic phase transition, while the mean field theory prediction for a second order phase transition, |ΔS{sub M}| ∝ (μ{sub 0}H/T{sub c}){sup 2/3}, describes a second order behavior. Also, a mixture of first and second order behavior was indicated by the rescaled universal curve criterion. The diverse results obtained for each criterion in MnFeP{sub 0.46}As{sub 0.54} are apparently related to the magnetoelastic effect and to the simultaneous presence of weak and strong magnetism in Fe (3f) and Mn (3g) alternate atomic layers, respectively. The simultaneous application of the universal curve, the Banerjee and the mean field theory criteria has allowed a better understanding about the nature of the order of the phase transitions in different magnetocaloric materials.

  11. Spin Projection of Empty Partial Density of States by Resonant X-ray Scattering (RXS): Application to Materials with Different Magnetic Ordering

    SciTech Connect

    Draeger, Guenter; Machek, Pavel

    2003-01-24

    We report the first experimental spin projections of empty partial density of states in antiferromagnetic NiO and CuO, paramagnetic MnO and in ferrimagnetic Dy3Fe5O12 by means of resonant X-ray scattering (RXS). Resolving resonantly scattered K{alpha}1,2 , K{beta}1,3 , L{alpha}1 and L1 core line spectra into their spin-up and spin-down components the spin character of the dipole- and quadrupole-excited conduction band states can quantitatively be analyzed. Since the method employs spin conservation in the RXS process and local spin references, it needs neither circularly polarized radiation nor sample magnetization for measuring the spectra. Hence, antiferro- and paramagnetic materials can be investigated as well. In the paper, the basic idea of the novel method, its experimental realization and the data treatment are reported including the spectra decomposition into the spin-up and spin-down components by using Principal Component Analysis (PCA). New and unambiguous results will be presented providing the opportunity to verify experimentally the results of spin-dependent (LSDA+U) calculations. So we argue the new spectroscopy complements X-ray magnetic dichroism, which is silent for antiferro- and paramagnetic materials. In fact, the novel method gives insight into the spin polarization of conduction band states in correlated materials, independently on their magnetic ordering.

  12. Topological excitations in magnetic materials

    NASA Astrophysics Data System (ADS)

    Bazeia, D.; Doria, M. M.; Rodrigues, E. I. B.

    2016-05-01

    In this work we propose a new route to describe topological excitations in magnetic systems through a single real scalar field. We show here that spherically symmetric structures in two spatial dimensions, which map helical excitations in magnetic materials, admit this formulation and can be used to model skyrmion-like structures in magnetic materials.

  13. Experiments on Magnetic Materials

    ERIC Educational Resources Information Center

    Schneider, C. S.; Ertel, John P.

    1978-01-01

    Describes the construction and use of a simple apparatus to measure the magnetization density and magnetic susceptibility of ferromagnetic, paramagnetic, and the diamagnetic solids and liquids. (Author/GA)

  14. Magnetic Materials in sustainable energy

    NASA Astrophysics Data System (ADS)

    Gutfleisch, Oliver

    2012-02-01

    A new energy paradigm, consisting of greater reliance on renewable energy sources and increased concern for energy efficiency in the total energy lifecycle, has accelerated research in energy-related technologies. Due to their ubiquity, magnetic materials play an important role in improving the efficiency and performance of devices in electric power generation, conversion and transportation. Magnetic materials are essential components of energy applications (i.e. motors, generators, transformers, actuators, etc.) and improvements in magnetic materials will have significant impact in this area, on par with many ``hot'' energy materials efforts. The talk focuses on the state-of-the-art hard and soft magnets and magnetocaloric materials with an emphasis on their optimization for energy applications. Specifically, the impact of hard magnets on electric motor and transportation technologies, of soft magnetic materials on electricity generation and conversion technologies, and of magnetocaloric materials for refrigeration technologies, will be discussed. The synthesis, characterization, and property evaluation of the materials, with an emphasis on structure-property relationships, will be examined in the context of their respective markets as well as their potential impact on energy efficiency. Finally, considering future bottle-necks in raw materials and in the supply chain, options for recycling of rare-earth metals will be analyzed.ootnotetextO. Gutfleisch, J.P. Liu, M. Willard, E. Bruck, C. Chen, S.G. Shankar, Magnetic Materials and Devices for the 21st Century: Stronger, Lighter, and More Energy Efficient (review), Adv. Mat. 23 (2011) 821-842.

  15. Materials with low DC magnetic susceptibility for sensitive magnetic measurements

    NASA Astrophysics Data System (ADS)

    Khatiwada, R.; Dennis, L.; Kendrick, R.; Khosravi, M.; Peters, M.; Smith, E.; Snow, W. M.

    2016-02-01

    Materials with very low DC magnetic susceptibility have many scientific applications. To our knowledge however, relatively little research has been conducted with the goal to produce a totally nonmagnetic material. This phrase in our case means after spatially averaging over macroscopic volumes, it possesses an average zero DC magnetic susceptibility. We report measurements of the DC magnetic susceptibility of three different types of nonmagnetic materials at room temperature: (I) solutions of paramagnetic salts and diamagnetic liquids, (II) liquid gallium-indium alloys and (III) pressed powder mixtures of tungsten and bismuth. The lowest measured magnetic susceptibility among these candidate materials is in the order of 10-9 cgs volume susceptibility units, about two orders of magnitude smaller than distilled water. In all cases, the measured concentration dependence of the magnetic susceptibility is consistent with that expected for the weighted sum of the susceptibilities of the separate components within experimental error. These results verify the well-known Wiedemann additivity law for the magnetic susceptibility of inert mixtures of materials and thereby realize the ability to produce materials with small but tunable magnetic susceptibility. For our particular scientific application, we are also looking for materials with the largest possible number of neutrons and protons per unit volume. The gallium-indium alloys fabricated and measured in this work possess to our knowledge the smallest ratio of volume magnetic susceptibility to nucleon number density per unit volume for a room temperature liquid, and the tungsten-bismuth pressed powder mixtures possess to our knowledge the smallest ratio of volume magnetic susceptibility to nucleon number density per unit volume for a room temperature solid. This ratio is a figure of merit for a certain class of precision experiments that search for possible exotic spin-dependent forces of Nature.

  16. Ferroic nature of magnetic toroidal order.

    PubMed

    Zimmermann, Anne S; Meier, Dennis; Fiebig, Manfred

    2014-01-01

    Electric dipoles and ferroelectricity violate spatial inversion symmetry, and magnetic dipoles and ferromagnetism break time-inversion symmetry. Breaking both symmetries favours magnetoelectric charge-spin coupling effects of enormous interest, such as multiferroics, skyrmions, polar superconductors, topological insulators or dynamic phenomena such as electromagnons. Extending the rationale, a novel type of ferroic order violating space- and time-inversion symmetry with a single order parameter should exist. This existence is fundamental and the inherent magnetoelectric coupling is technologically interesting. A uniform alignment of magnetic vortices, called ferrotoroidicity, was proposed to represent this state. Here we demonstrate that the magnetic vortex pattern identified in LiCoPO4 exhibits the indispensable hallmark of such a ferroic state, namely hysteretic poling of ferrotoroidic domains in the conjugate toroidal field, along with a distinction of toroidal from non-toroidal poling effects. This consolidates ferrotoroidicity as fourth form of ferroic order. PMID:25190207

  17. Magnetic properties of ordered NiPt

    NASA Astrophysics Data System (ADS)

    Brommer, P. E.; Franse, J. J. M.

    1988-04-01

    Thermal expansion, forced volume magnetostriction and high magnetic field data are presented on the ordered equiatomic NiPt compound. Values are derived for the magnetovolume parameter κC (≃3 × 10 -6kg2A-2m-4), and for the electronic and lattice Grüneisen parameters (Γ e ≊ 5.6; Γ latt ≊ 2.5) . Ordering effects on the magnetoelastic properties are studied for alloys containing 40-60 at % Ni.

  18. Centimeter-order view for magnetic domain imaging with local magnetization direction by longitudinal Kerr effect

    NASA Astrophysics Data System (ADS)

    Meguro, Sakae; Akahane, Koichi; Saito, Shin

    2016-05-01

    An observation system of centimeter-order of view of magnetic domain with local magnetization direction was developed by designing a telecentric optical system of finite design through the extension of microscope technology. The field of view realized in the developed system was 1.40 × 1.05 cm as suppressing defocus and distortion. Detection of the local magnetization direction has become possible by longitudinal Kerr observation from the orthogonal two directions. This system can be applied to the domain observation of rough surface samples and time resolved analysis for soft magnetic materials such as amorphous foil strips and soft magnetic thin films.

  19. Magnetic and charge ordering in nanosized manganites

    SciTech Connect

    Zhang, T. Wang, X. P.; Fang, Q. F.; Li, X. G.

    2014-09-15

    Perovskite manganites exhibit a wide range of functional properties, such as colossal magneto-resistance, magnetocaloric effect, multiferroic property, and some interesting physical phenomena including spin, charge, and orbital ordering. Recent advances in science and technology associated with perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. The nanoscale perovskite manganites display novel magnetic and electronic properties that are different from their bulk and film counterparts. Understanding the size effects of perovskite manganites at the nanoscale is of importance not only for the fundamental scientific research but also for developing next generation of electronic and magnetic nanodevices. In this paper, the current understanding and the fundamental issues related to the size effects on the magnetic properties and charge ordering in manganites are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites. In addition to review the literatures, this article identifies the promising avenues for the future research in this area.

  20. Magnetic and charge ordering in nanosized manganites

    NASA Astrophysics Data System (ADS)

    Zhang, T.; Wang, X. P.; Fang, Q. F.; Li, X. G.

    2014-09-01

    Perovskite manganites exhibit a wide range of functional properties, such as colossal magneto-resistance, magnetocaloric effect, multiferroic property, and some interesting physical phenomena including spin, charge, and orbital ordering. Recent advances in science and technology associated with perovskite oxides have resulted in the feature sizes of microelectronic devices down-scaling into nanoscale dimensions. The nanoscale perovskite manganites display novel magnetic and electronic properties that are different from their bulk and film counterparts. Understanding the size effects of perovskite manganites at the nanoscale is of importance not only for the fundamental scientific research but also for developing next generation of electronic and magnetic nanodevices. In this paper, the current understanding and the fundamental issues related to the size effects on the magnetic properties and charge ordering in manganites are reviewed, which covers lattice structure, magnetic and electronic properties in both ferromagnetic and antiferromagnetic based manganites. In addition to review the literatures, this article identifies the promising avenues for the future research in this area.

  1. Magnetism in Parent Iron Chalcogenides: Quantum Fluctuations Select Plaquette Order

    NASA Astrophysics Data System (ADS)

    Ducatman, Samuel; Perkins, Natalia B.; Chubukov, Andrey

    2012-10-01

    We analyze magnetic order in Fe chalcogenide Fe1+yTe, the parent compound of the high-temperature superconductor Fe1+yTe1-xSex. Experiments show that magnetic order in this material contains components with momentum Q1=(π/2,π/2) and Q2=(π/2,-π/2) in the Fe only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works assumed that the ordered state has a single Q (either Q1 or Q2). In such a state, spins form double stripes along one of the diagonals breaking the rotational C4 symmetry. We show that quantum fluctuations actually select another order—a double Q plaquette state with equal weight of Q1 and Q2 components, which preserves C4 symmetry. We argue that the order in Fe1+yTe is determined by the competition between quantum fluctuations and magnetoelastic coupling.

  2. Multiferroicity Broken by Commensurate Magnetic Ordering in Terbium Orthomanganite.

    PubMed

    Zhang, Hao; Flacau, Roxana; Du, Xin; Manuel, Pascal; Cong, Junzhuang; Sun, Young; Sun, Junliang; Yang, Sihai; Li, Guobao; Liao, Fuhui; Lin, Jianhua

    2016-04-18

    TbMnO3 is an important multiferroic material with strong coupling between magnetic and ferroelectric orderings. Incommensurate magnetic ordering is suggested to be vital for this coupling in TbMnO3 , which can be modified by doping at the site of Tb and/or Mn. Our study shows that a self-doped solid solution Tb1-x Mny MnO3 (y≤x) can be formed with Mn doped into the site of Tb of TbMnO3 . When y is small Tb1-x Mny MnO3 shows both ferroelectric and incommensurate magnetic orders at low temperature, which is similar to TbMnO3 . However, if y is large enough, a commensurate antiferromagnetic ordering appears along with the incommensurate magnetic ordering to prevent the appearance of multiferroicity in Tb1-x Mny MnO3 . That is to say, the magnetoeletric coupling can be broken by the co-existence of a commensurate antiferromagnetic ordering. This finding may be useful to the study of TbMnO3 . PMID:26833883

  3. Magnetic spectroscopy and microscopy of functional materials

    SciTech Connect

    Jenkins, Catherine Ann

    2011-05-01

    Heusler intermetallics Mn2Y Ga and X2MnGa (X; Y =Fe, Co, Ni) undergo tetragonal magnetostructural transitions that can result in half metallicity, magnetic shape memory, or the magnetocaloric effect. Understanding the magnetism and magnetic behavior in functional materials is often the most direct route to being able to optimize current materials for todays applications and to design novel ones for tomorrow. Synchrotron soft x-ray magnetic spectromicroscopy techniques are well suited to explore the the competing effects from the magnetization and the lattice parameters in these materials as they provide detailed element-, valence-, and site-specifc information on the coupling of crystallographic ordering and electronic structure as well as external parameters like temperature and pressure on the bonding and exchange. Fundamental work preparing the model systems of spintronic, multiferroic, and energy-related compositions is presented for context. The methodology of synchrotron spectroscopy is presented and applied to not only magnetic characterization but also of developing a systematic screening method for future examples of materials exhibiting any of the above effects. The chapter progression is as follows: an introduction to the concepts and materials under consideration (Chapter 1); an overview of sample preparation techniques and results, and the kinds of characterization methods employed (Chapter 2); spectro- and microscopic explorations of X2MnGa/Ge (Chapter 3); spectroscopic investigations of the composition series Mn2Y Ga to the logical Mn3Ga endpoint (Chapter 4); and a summary and overview of upcoming work (Chapter 5). Appendices include the results of a Think Tank for the Graduate School of Excellence MAINZ (Appendix A) and details of an imaging project now in progress on magnetic reversal and domain wall observation in the classical Heusler material Co2FeSi (Appendix B).

  4. High Spin-Chern Insulators with Magnetic Order

    PubMed Central

    Ezawa, Motohiko

    2013-01-01

    As a topological insulator, the quantum Hall (QH) effect is indexed by the Chern and spin-Chern numbers and . We have only in conventional QH systems. We investigate QH effects in generic monolayer honeycomb systems. We search for spin-resolved characteristic patterns by exploring Hofstadter's butterfly diagrams in the lattice theory and fan diagrams in the low-energy Dirac theory. It is shown that the spin-Chern number can takes an arbitrary high value for certain QH systems. This is a new type of topological insulators, which we may call high spin-Chern insulators. Samples may be provided by graphene on the SiC substrate with ferromagnetic order, transition-metal dichalcogenides with ferromagnetic order, transition-metal oxide with antiferromagnetic order and silicene with ferromagnetic order. Actually high spin-Chern insulators are ubiquitous in any systems with magnetic order. Nevertheless, the honeycomb system would provide us with unique materials for practical materialization. PMID:24310394

  5. High Spin-Chern Insulators with Magnetic Order

    NASA Astrophysics Data System (ADS)

    Ezawa, Motohiko

    2013-12-01

    As a topological insulator, the quantum Hall (QH) effect is indexed by the Chern and spin-Chern numbers and . We have only in conventional QH systems. We investigate QH effects in generic monolayer honeycomb systems. We search for spin-resolved characteristic patterns by exploring Hofstadter's butterfly diagrams in the lattice theory and fan diagrams in the low-energy Dirac theory. It is shown that the spin-Chern number can takes an arbitrary high value for certain QH systems. This is a new type of topological insulators, which we may call high spin-Chern insulators. Samples may be provided by graphene on the SiC substrate with ferromagnetic order, transition-metal dichalcogenides with ferromagnetic order, transition-metal oxide with antiferromagnetic order and silicene with ferromagnetic order. Actually high spin-Chern insulators are ubiquitous in any systems with magnetic order. Nevertheless, the honeycomb system would provide us with unique materials for practical materialization.

  6. Nanostructured magnetic networks: a materials comparison

    NASA Astrophysics Data System (ADS)

    Weston, James L.; Butera, Alejandro; Otte, Dietmar; Barnard, John A.

    1999-03-01

    One method to achieve the enhanced coercivity necessary for the next generation of ultra high density recording media is to use a patterned substrate to nanostructure the magnetic material. By sputter-depositing a magnetic film onto the surface of a nanoporous substrate, unique magnetic properties result from the reduced dimension and topography of the film. The resultant "network" film has a coercivity nearly two orders of magnitude higher than a continuous thin film of the same thickness. This increase in coercivity has been attributed primarily to shape anisotropy due to the proportional relationship observed between the coercivity and the moment of the deposited network. To better understand the effect of the shape anisotropy, a number of different classes of magnetic materials of varying moment and magnetocrystalline anisotropy were deposited onto porous templates and compared. In general, these materials show a peak coercivity in the thickness range of 15-20 nm. In this thickness the range a linear relationship between the coercivity and moment is observed confirming the influence of shape anisotropy. A simple model assuming coherent reversal of a magnetized ellipsoid gives a ratio of 1.1 between the short and long axes. This value is significantly smaller than what it is observed by direct imaging. However, if a more realistic model of magnetization reversal is employed (such as fanning) the ratio obtained is in close agreement with the experiments.

  7. Detecting magnetic ordering with atomic size electron probes

    DOE PAGESBeta

    Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Cantoni, Claudia; Lupini, Andrew R.

    2016-05-27

    While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setupmore » presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.« less

  8. Cryogenic structural materials for superconducting magnets

    SciTech Connect

    Dalder, E.N.C.; Morris, J.W. Jr.

    1985-02-22

    This paper reviews research in the United States and Japan on structural materials for high-field superconducting magnets. Superconducting magnets are used for magnetic fusion energy devices and for accelerators that are used in particle-physics research. The cryogenic structural materials that we review are used for magnet cases and support structures. We expect increased materials requirements in the future.

  9. Iron-cobalt based soft magnetic materials

    NASA Astrophysics Data System (ADS)

    Basu, Sujit

    FeCo-based alloys with high Tc and low magnetic anisotropy are the most promising soft magnetic materials for high temperature application such as turbine and electric vehicles. Present commercially available Hiperco alloys do not meet very well the high temperature application requirements. To develop new generation of soft magnets, firstly, the relationship among magnetic properties, mechanical properties and microstructure should been studied and clarified. At high temperature, the evolution of microstructure of FeCo is very complicated, including the change of defects, ordering parameter, the amount of precipitates, and the grain size. All of these factors significantly affect the high temperature properties. In our study, a big effort was focused on the separation of these individual effects. We are now able to understand the mechanism of these effects on the magnetic and mechanical properties. Based on this understanding, new magnets have been tentatively developed by using Electrodeposition technique. This involves fiber matrix composites where the magnetic properties are borne by the magnetic matrix and the mechanical properties by the composite fibers.

  10. Testing of a First Order AC Magnetic Susceptometer

    NASA Astrophysics Data System (ADS)

    Fukuda, Ryan; Sunny, Smitha; Ho, Pei-Chun

    2011-11-01

    A first-order AC magnetic susceptometer has been constructed and tested to find the magnetic response of strongly correlated electron materials. The instrument works by using a primary coil to apply a small AC magnetic field of .104 Oe to a sample with a cylindrical coil space of length .635 cm and diameter .355 cm. A lock-in amplifier is used to monitor the induced voltage from a set of secondary coils. By coupling a temperature-controlled system with this instrument, the change in the magnetic signal with respect to temperature is measured. Monitoring the signal changes may indicate the temperature that causes the material to transition to either a ferromagnetic, anti-ferromagnetic, or superconducting state. A 122.47 mg Gd polycrystal was used to test our susceptometer. The data qualitatively agrees with the previous results of magnetization vs. temperature of Gd single crystals by Nigh et al. [1]: there is a steep increase in the pick-up signal at 300 K where Gd becomes ferromagnetic and a peak at 210 K [1]. This susceptometer will be used for our future investigation of magnetic properties of rare earth compounds and nanoparticles in the temperature range of 10 K to 300 K. [4pt] [1] H. E. Nigh, S. Legvold, and F. H. Spedding, Physical Review 132, 1092 (1963)

  11. Magnetic ordering in lanthanide-molybdenum oxide nanostructure arrays

    NASA Astrophysics Data System (ADS)

    Hagmann, Joseph; Le, Son; Schneemeyer, Lynn; Olsen, Patti; Besara, Tiglet; Siegrist, Theo; Seiler, David; Richter, Curt

    Reduced ternary molybdenum oxides, or bronzes, offer an attractive materials platform to study a wide variety of remarkable physical phenomena in a system with highly varied structural chemistry. Interesting electronic behaviors, such as superconductivity, charge density waves, and magnetism, in these materials arise from the strong hybridization of the 4d states of high-valent Mo with O p orbitals. We investigate a series of molybdenum bronze materials with Lanthanide-Mo16O44 composition that can be described as a three-dimensional array of metallic Mo8O32 nanostructures computationally predicted to contain a single charge with spin 1/2 separated by insulating MoO4 tetrahedra. This study reveals novel magnetic ordering in Lanthanide-Mo16O44 systems arising, not from the inclusion of magnetic elements, but rather from an exchange interaction between cubic Mo8O32 units. Here, we report the magnetometry and transport behaviors of a series of Lanthanide-Mo16O44 materials, emphasizing an observed low-temperature phase transition signifying the onset of antiferromagnetic ordering between the arrayed nanostructures, and relate these behaviors to their experimentally-characterized structures to reveal the intriguing physics of these correlated electronic systems.

  12. Magnetic ordering in frustrated antiferromagnets on the pyrochlore lattice

    NASA Astrophysics Data System (ADS)

    Chern, Gia-Wei

    Pyrochlore antiferromagnet is one of the most studied examples of strongly-interacting systems. The conflict between the lattice geometry and the local spin correlations favored by their interactions precludes the simple Neel ordering and creates an extensive degeneracy of the classical ground state. This, in turn, renders the magnet susceptible to nominally small perturbations such as quantum fluctuations, anisotropies, and dipolar interactions. Of particular interest is the classical Heisenberg spins on the pyrochlore lattice with exchange interactions restricted to the nearest neighbors. It has been demonstrated by analytical arguments and numerical simulations that the spin system remains disordered down to the lowest temperatures. In this thesis I study how magnetic ordering is induced by residual perturbations in such a system. Apart from the theoretical interest, the work presented in this thesis is mainly motivated by experimental observations of real materials. Three mechanisms of breaking the ground-state degeneracy are considered here: (1) order by distortion, (2) further-neighbor exchange interactions, and (3) the orbital degrees of freedom. In the first part, we present a theoretical model describing the lattice distortion and incommensurate magnetic order in the compound CdCr2O 4, which belongs to a class of chromium spinels exhibiting the magnetoelastic phase transitions. The magnetic frustration is relieved through the spin-driven Jahn-Teller effect involving a phonon doublet with odd parity. The distortion stabilizes a collinear magnetic order with the propagation wavevector q = 2pi(0, 0, 1). The crystal structure becomes chiral due to the lack of inversion symmetry. The handedness is transferred to the magnetic system by the relativistic spin-orbit coupling: the collinear state is twisted into a long spiral with the spins in the ac plane and q shifted to 2pi(0, delta, 1), consistent with the experiments. In the second part, we examine the effects

  13. Magnetic Cluster States in Nanostructured Materials

    SciTech Connect

    Diandra Leslie-Pelecky

    2008-06-13

    The goal of this work is to fabricate model nanomaterials with different types of disorder and use atomic-scale characterization and macroscopic magnetization measurements to understand better how specific types of disorder affects macroscopic magnetic behavior. This information can be used to produce magnetic nanomaterials with specific properties for applications such as permanent magnets, soft magnetic material for motors and biomedical applications.

  14. Pressure-Induced Order in the Gapped Quantum Magnet DTN

    NASA Astrophysics Data System (ADS)

    Mannig, Alexandra; Moeller, Johannes; Zheludev, Andrey; Garlea, V. Ovidiu; Dela Cruz, Clarina; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio

    We present muon-spin relaxation, neutron diffraction and magnetic susceptibility data under applied hydrostatic pressure on the organometallic S = 1 quantum magnet NiCl2 . 4 [ SC(NH2)2 ] . The material consists of weakly coupled antiferromagnetic chains and has a spin gap resulting from a large single-ion anisotropy. Our muon spin rotation experiments provide local field dependencies on temperature as well as pressure and allow for the mapping of a detailed phase diagram up to 22kbar. Thus, we demonstrate that the compound may be driven through two subsequent pressure-induced transitions into apparently distinct magnetically ordered phases. Neutron diffraction and susceptibility measurements support those results and show the potential of low-pressure transitions to be investigated by various techniques.

  15. Magnetic Stirling cycles - A new application for magnetic materials

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1977-01-01

    There is the prospect of a fundamental new application for magnetic materials as the working substance in thermodynamic cycles. Recuperative cycles which use a rare-earth ferromagnetic material near its Curie point in the field of a superconducting magnet appear feasible for applications from below 20 K to above room temperature. The elements of the cycle, advanced in an earlier paper, are summarized. The basic advantages include high entropy density in the magnetic material, completely reversible processes, convenient control of the entropy by the applied field, the feature that heat transfer is possible during all processes, and the ability of the ideal cycle to attain Carnot efficiency. The mean field theory is used to predict the entropy of a ferromagnet in an applied field and also the isothermal entropy change and isentropic temperature change caused by applying a field. Results are presented for J = 7/2 and g = 2. The results for isentropic temperature change are compared with experimental data on Gd. Coarse mixtures of ferromagnetic materials with different Curie points are proposed to modify the path of the cycle in the T-S diagram in order to improve the efficiency or to increase the specific power.

  16. PREFACE: Soft Magnetic Materials 8

    NASA Astrophysics Data System (ADS)

    Pfützner, H.

    1988-01-01

    The Conference "Soft Magnetic Materials 8" was held from 1 to 4 September 1987 at the Congress Centre Badgastein, Austria. It was organized by the Division of Bioelectricity and Magnetism and by the Institute of Applied and Technical Physics of the University of Technology, Vienna. The Conference was the eighth in the bi-annual series which commenced in Turin, Italy. It was attended by about 130 scientists from universities and industrial companies from 19 countries. The theme of the Conference was the recent progress in industrial applications and developments of soft magnetic alloys including magnetic measurements and field computation problems as well as fundamental aspects. In five sessions, 13 invited papers were presented in oral form. In addition, the program of poster sessions included 122 contributed papers. Regrettably, some of them were not presented when authors (especially from Eastern European countries as well as from China) were unable to be present. A clear emphasis of papers was laid on characteristics and applications of amorphous materials. As confirmed by the delegates, the spacious Congress Centre—well aerated by the near-by waterfall—provided an effective environment for informal discussions. The Conference Dinner as well as the Mountain Lodge Evening were utilized for general communications in an intensive form. However, a slight mishap of this Conference should not be concealed: Due to a thunder storm, one delegate spent a long frosty night on a rock peak of Badgasteins mountains. Still, next day he presented his excellent paper in top condition. The next Conference, SMM9, is planned to be held in El Escorial, Spain, in 1989.

  17. De Magnete et Meteorite: Cosmically Motivated Materials

    SciTech Connect

    Lewis, LH; Pinkerton, FE; Bordeaux, N; Mubarok, A; Poirier, E; Goldstein, JI; Skomski, R; Barmak, K

    2014-01-01

    Meteorites, likely the oldest source of magnetic material known to mankind, are attracting renewed interest in the science and engineering community. Worldwide focus is on tetrataenite, a uniaxial ferromagnetic compound with the tetragonal L1(0) crystal structure comprised of nominally equiatomic Fe-Ni that is found naturally in meteorites subjected to extraordinarily slow cooling rates, as low as 0.3 K per million years. Here, the favorable permanent magnetic properties of bulk tetrataenite derived from the meteorite NWA 6259 are quantified. The measured magnetization approaches that of Nd-Fe-B (1.42 T) and is coupled with substantial anisotropy (1.0-1.3 MJ/m(3)) that implies the prospect for realization of technologically useful coercivity. A highly robust temperature dependence of the technical magnetic properties at an elevated temperature (20-200 degrees C) is confirmed, with a measured temperature coefficient of coercivity of -0.005%/ K, over one hundred times smaller than that of Nd-Fe-B in the same temperature range. These results quantify the extrinsic magnetic behavior of chemically ordered tetrataenite and are technologically and industrially significant in the current context of global supply chain limitations of rare-earth metals required for present-day high-performance permanent magnets that enable operation of a myriad of advanced devices and machines.

  18. Collective osmotic shock in ordered materials

    NASA Astrophysics Data System (ADS)

    Zavala-Rivera, Paul; Channon, Kevin; Nguyen, Vincent; Sivaniah, Easan; Kabra, Dinesh; Friend, Richard H.; Nataraj, S. K.; Al-Muhtaseb, Shaheen A.; Hexemer, Alexander; Calvo, Mauricio E.; Miguez, Hernan

    2012-01-01

    Osmotic shock in a vesicle or cell is the stress build-up and subsequent rupture of the phospholipid membrane that occurs when a relatively high concentration of salt is unable to cross the membrane and instead an inflow of water alleviates the salt concentration gradient. This is a well-known failure mechanism for cells and vesicles (for example, hypotonic shock) and metal alloys (for example, hydrogen embrittlement). We propose the concept of collective osmotic shock, whereby a coordinated explosive fracture resulting from multiplexing the singular effects of osmotic shock at discrete sites within an ordered material results in regular bicontinuous structures. The concept is demonstrated here using self-assembled block copolymer micelles, yet it is applicable to organized heterogeneous materials where a minority component can be selectively degraded and solvated whilst ensconced in a matrix capable of plastic deformation. We discuss the application of these self-supported, perforated multilayer materials in photonics, nanofiltration and optoelectronics.

  19. Collective osmotic shock in ordered materials.

    PubMed

    Zavala-Rivera, Paul; Channon, Kevin; Nguyen, Vincent; Sivaniah, Easan; Kabra, Dinesh; Friend, Richard H; Nataraj, S K; Al-Muhtaseb, Shaheen A; Hexemer, Alexander; Calvo, Mauricio E; Miguez, Hernan

    2012-01-01

    Osmotic shock in a vesicle or cell is the stress build-up and subsequent rupture of the phospholipid membrane that occurs when a relatively high concentration of salt is unable to cross the membrane and instead an inflow of water alleviates the salt concentration gradient. This is a well-known failure mechanism for cells and vesicles (for example, hypotonic shock) and metal alloys (for example, hydrogen embrittlement). We propose the concept of collective osmotic shock, whereby a coordinated explosive fracture resulting from multiplexing the singular effects of osmotic shock at discrete sites within an ordered material results in regular bicontinuous structures. The concept is demonstrated here using self-assembled block copolymer micelles, yet it is applicable to organized heterogeneous materials where a minority component can be selectively degraded and solvated whilst ensconced in a matrix capable of plastic deformation. We discuss the application of these self-supported, perforated multilayer materials in photonics, nanofiltration and optoelectronics. PMID:22120413

  20. Magnetic order the iron spins in NdOFeAs

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Lynn, J. W.; Li, J.; Li, G.; Chen, G. F.; Luo, J. L.; Wang, N. L.; Dai, Pengcheng; Dela Cruz, C.; Mook, H. A.

    2009-03-01

    Polarized and unpolarized powder neutron-diffraction measurements have been carried out to investigate the iron magnetic order in the parent compound of one of the highest Tc system, NdFeAsO. Antiferromagnetic order is observed below 141 K [1], which is in close proximity to the structural distortion observed in this material [2]. The magnetic structure consists of chains of parallel spins that are arranged antiparallel between chains, which is the same in-plane spin arrangement as observed in all the other iron oxypnictide materials. Nearest-neighbor spins along the c axis are antiparallel like LaFeAsO [3]. The ordered moment is 0.25 (7) μB, which is the smallest ordered moment found so far in these systems. [3pt] [1]Ying Chen, J. W. Lynn, J. Li, G. Li, G. F. Chen, J. L. Luo, N. L. Wang, Pengcheng Dai, C. dela Cruz and H. A. Mook, Phys. Rev. B 78, 064515 2008. [0pt] [2]Y. Qiu, W. Bao, Q. Huang, T. Yildirim, J. M. Simmons, M. A. Green, J.W. Lynn, Y.C. Gasparovic, J. Li, T. Wu, G. Wu, and X.H. Chen, arXiv:0806.2195 (Phys. Rev. Lett. accepted). [0pt] [3] C. dela Cruz, Q. Huang, J. W. Lynn, J. Li, W. Ratcliff II, J. L. Zarestky, H. A. Mook, G. F. Chen, J. L. Luo, N. L. Wang, and P. Dai, Nature 453, 899 (2008).

  1. From hidden order to magnetic order: Optical conductivity reveals new behavior in URu2Si2

    NASA Astrophysics Data System (ADS)

    Hall, Jesse; Kanchanavatee, Noravee; Janoschek, Marc; Huang, Kevin; Butch, Nicholas; Maple, Brian; Timusk, Thomas

    2013-03-01

    As a new generation of experimental techniques is brought to bear against the heavy-Fermion compound URu2Si2, striking new details about the electronic structure changes at the mysterious hidden order (HO) transition are becoming clear. Far infrared optical conductivity measurements were performed on oriented samples of URu2Si2 doped with both Fe and Re. While Re-doping pushes the material towards ferromagnetism, Fe-doping substitutes for hydrostatic pressure and enhances the temperature of the HO transition slightly before pushing the material into antiferromagnetism. Optical conductivity measurements have revealed new information about the charge dynamics at the transition, and how these evolve with doping. Both the structure and energy of the gap are altered as the material is pushed towards magnetic ordering. Comparison is made between the gap seen in optical conductivity and the charge gaps seen in scanning tunneling spectroscopy and ARPES, as well as the gaps in the magnetic excitation spectrum seen in neutron scattering. This work supported by the Natural Science and Engineering Research Council of Canada and US DOE (Grant No. DE FG02-04ER46105)

  2. Advanced Magnetic Materials and Transducers: Enabling Information Explosion and Magnetic Nanotechnology

    NASA Astrophysics Data System (ADS)

    Wang, Shan

    2003-03-01

    Advanced magnetic materials and transducers are critical building blocks in numerous engineering devices such as bio-magnetic sensors, magnetic hard disk drives, magnetic inductors, electronic article survrence, and magnetic levitation trains. They are essential for the explosive growth in the storage capacity of hard drives at least by two orders of magnitude in the 1990s. The use of magnetic media with ever higher coercivities requires write heads to deliver more intense magnetic field, which in turn requires higher saturation magnetization of the soft magnetic material used in write heads. As an example, the talk will describe films of a new soft magnetic material based on Fe-Co-N with a saturation magnetization of 24 kG, exceeding that of any currently available soft magnetic material, with a superior permeability of over 1000 up to 1.2 GHz. They are very promising for extending the superparamagnetic limit in magnetic recording while achieving a data rate of over 2.4 Gbit/s, as well as for applications in gigahertz integrated inductors and other electromagnetic devices. Rapid development in giant magnetoresistive materials and novel spin-dependent devices has enabled read heads to detect ever-smaller bits written in hard disk drives. In search of new magnetoresistive materials, we encounter many interesting scientific questions. The talk will describe work on electron specular reflection and specular spin valves using an in-situ resistance and magnetoresistance probe. The challenges in utilizing spin valves and spin-dependent tunnel junctions for future generations of hard disk drives will also be discussed. Finally, new applications of advanced magnetic materials and transducers are emerging in magnetic nanotechnologies and magnetoelectronics. As an example, bio-magnetic sensing and DNA detection based on spin valve sensors and magnetic nanoparticle labels will be described.

  3. Magnetic stirling cycles: A new application for magnetic materials

    NASA Technical Reports Server (NTRS)

    Brown, G. V.

    1977-01-01

    The elements of the cycle are summarized. The basic advantages include high entropy density in the magnetic material, completely reversible processes, convenient control of the entropy by the applied field, the feature that heat transfer is possible during all processes, and the ability of the ideal cycle to attain Carnot efficiency. The mean field theory is used to predict the entropy of a ferromagnet in an applied field and also the isothermal entropy change and isentropic temperature change caused by applying a field. The results for isentropic temperature change are compared with experimental data on Gd. Coarse mixtures of ferromagnetic materials with different Curie points are proposed to modify the path of the cycle in the T-S diagram in order to improve the efficiency or to increase the specific power.

  4. Structure, magnetic order and excitations in the 245 family of Fe-based superconductors.

    PubMed

    Bao, Wei

    2015-01-21

    Elastic neutron scattering simultaneously probes both the crystal structure and magnetic order in a material. Inelastic neutron scattering measures phonons and magnetic excitations. Here, we review the average composition, crystal structure and magnetic order in the 245 family of Fe-based superconductors and in related insulating compounds from neutron diffraction works. A three-dimensional phase-diagram summarizes various structural, magnetic and electronic properties as a function of the sample composition. A high pressure phase diagram for the superconductor is also provided. Magnetic excitations and the theoretic Heisenberg Hamiltonian are provided for the superconductor. Issues for future works are discussed. PMID:25427222

  5. Application peculiarities of magnetic materials for protection from magnetic fields

    NASA Astrophysics Data System (ADS)

    Wai, P.; Dmitrenko, V.; Grabchikov, S.; Vlasik, K.; Novikov, A.; Petrenko, D.; Trukhanov, V.; Ulin, S.; Uteshev, Z.; Chernysheva, V.; Shustov, A.

    2016-02-01

    In different materials for magnetic shields, the maximum permeability is achieved for different values of the magnetic field. This determines the choice of material. So for protection from magnetic fields strength of 10 - 150 A/m it is advisable to apply the amorphous ribbon 84KXCP. For stronger fields (more than 400 A/m) it is recommended to use MFS based on Ni20Fe80. Use of these materials allows creating an effective shield working in a wide range of magnetic field strengths.

  6. Magnetic Ordering In Superconducting Nb-doped Bi2Se3

    NASA Astrophysics Data System (ADS)

    Corbae, Paul; Lawson, Benjamin; Li, Gang; Yu, Fan; Asaba, Tomoya; Tinsman, Colin; Qui, Yusheng; Hor, Yew San; Li, Lu

    Coexistence of superconductivity and magnetic order has been suggested by early studies of topological superconductor candidate, niobium doped Bi2Se3. In order to elucidate the interesting physics of this coexistence, we performed highly sensitive torque magnetometry to study the material's magnetization. We observed a bump feature in the magnetization around 8 Tesla in both the superconducting and non-superconducting samples. This is distinct from the paramagnetic torque response of the parent compound, Bi2Se3, suggesting some interesting magnetic order in Nb-doped Bi2Se3.

  7. Magnetic Moment Distribution in Layered Materials

    NASA Astrophysics Data System (ADS)

    Nicholson, D. M. C.; Zhang, X.-G.; Wang, Y.; Shelton, W. A.; Butler, W. H.; Stocks, G. M.; MacLaren, J. M.

    1996-03-01

    Thin layers of magnetic material surrounded by non-magnetic layers display a reduced moment per atom relative to the bulk magnetic material. Plots of sturation magnetization versus magnetic layer thickness can be explained in terms of magnetically dead layers at interfaces. First principles calculations indicate a more complex distribution of magnetic moments. Moment distributions calculated in the local density approximation restricted to colinear spins and with unrestricted spin orientations will be presented for Cu/Ni/Cu, Cu/permalloy/Cu, and Mo/Ni/Mo structures. Work supported by Division of Materials Science, the Mathematical Information and Computational Science Division of the Office of Computational Technology Research, and by the Assistant Secretary of Defence Programs, Technology Management Group, Technology Transfer Initiative, US DOE under subcontract DEAC05-84OR21400 with Martin-Marietta Energy Systems, Inc.

  8. Phase transformations in shock compacted magnetic materials

    NASA Astrophysics Data System (ADS)

    Wehrenberg, Christopher

    Shock compaction experiments were performed on soft magnetic phases Fe 4N and Fe16N2, and hard magnetic phases Nd 2Fe14B and Sm2Fe17N3 in order to determine their thermo-mechanical stability during shock loading and explore the possibility of fabricating a textured nanocomposite magnet. Gas gun experiments performed on powders pressed in a three capsule fixture showed phase transformations occurring in Fe4N, Fe16N 2, and Nd2Fe14B, while Sm2Fe17 N3 was observed to be relatively stable. Shock compaction of FCC Fe4N resulted in a partial transformation to HCP Fe3N, consistent with previous reports of the transition occurring at a static pressure of ~3 GPa. Shock compaction of Fe16N 2 produced decomposition products α-Fe, Fe4N, and FeN due to a combination of thermal effects associated with dynamic void collapse and plastic deformation. Decomposition of Nd-Fe-B, producing α-Fe and amorphous Nd-Fe-B, was observed in several shock consolidated samples and is attributed to deformation associated with shock compaction, similar to decomposition reported in ball milled Nd-Fe-B. No decomposition was observed in shock compacted samples of Sm-Fe-N, which is consistent with literature reports showing decomposition occurring only in samples compacted at a pressure above ~15 GPa. Nd-Fe-B and Sm-Fe-N were shown to accommodate deformation primarily by grain size reduction, especially in large grained materials. Hard/Soft composite magnetic materials were formed by mixing single crystal particles of Nd-Fe-B with iron nanoparticles, and the alignment-by-magnetic-field technique was able to introduce significant texture into green compacts of this mixture. While problems with decomposition of the Nd2Fe14B phase prevented fabricating bulk magnets from the aligned green compacts, retention of the nanoscale morphology of the α-Fe particles and the high alignment of the green compacts shows promise for future development of textured nanocomposite magnets through shock compaction.

  9. Magnetic field effects on microwave absorbing materials

    NASA Technical Reports Server (NTRS)

    Goldberg, Ira; Hollingsworth, Charles S.; Mckinney, Ted M.

    1991-01-01

    The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

  10. Simulating functional magnetic materials on supercomputers.

    PubMed

    Gruner, Markus Ernst; Entel, Peter

    2009-07-22

    The recent passing of the petaflop per second landmark by the Roadrunner project at the Los Alamos National Laboratory marks a preliminary peak of an impressive world-wide development in the high-performance scientific computing sector. Also, purely academic state-of-the-art supercomputers such as the IBM Blue Gene/P at Forschungszentrum Jülich allow us nowadays to investigate large systems of the order of 10(3) spin polarized transition metal atoms by means of density functional theory. Three applications will be presented where large-scale ab initio calculations contribute to the understanding of key properties emerging from a close interrelation between structure and magnetism. The first two examples discuss the size dependent evolution of equilibrium structural motifs in elementary iron and binary Fe-Pt and Co-Pt transition metal nanoparticles, which are currently discussed as promising candidates for ultra-high-density magnetic data storage media. However, the preference for multiply twinned morphologies at smaller cluster sizes counteracts the formation of a single-crystalline L1(0) phase, which alone provides the required hard magnetic properties. The third application is concerned with the magnetic shape memory effect in the Ni-Mn-Ga Heusler alloy, which is a technologically relevant candidate for magnetomechanical actuators and sensors. In this material strains of up to 10% can be induced by external magnetic fields due to the field induced shifting of martensitic twin boundaries, requiring an extremely high mobility of the martensitic twin boundaries, but also the selection of the appropriate martensitic structure from the rich phase diagram. PMID:21828528

  11. Numerical modeling of higher order magnetic moments in UXO discrimination

    USGS Publications Warehouse

    Sanchez, V.; Yaoguo, L.; Nabighian, M.N.; Wright, D.L.

    2008-01-01

    The surface magnetic anomaly observed in unexploded ordnance (UXO) clearance is mainly dipolar, and consequently, the dipole is the only magnetic moment regularly recovered in UXO discrimination. The dipole moment contains information about the intensity of magnetization but lacks information about the shape of the target. In contrast, higher order moments, such as quadrupole and octupole, encode asymmetry properties of the magnetization distribution within the buried targets. In order to improve our understanding of magnetization distribution within UXO and non-UXO objects and to show its potential utility in UXO clearance, we present a numerical modeling study of UXO and related metallic objects. The tool for the modeling is a nonlinear integral equation describing magnetization within isolated compact objects of high susceptibility. A solution for magnetization distribution then allows us to compute the magnetic multipole moments of the object, analyze their relationships, and provide a depiction of the anomaly produced by different moments within the object. Our modeling results show the presence of significant higher order moments for more asymmetric objects, and the fields of these higher order moments are well above the noise level of magnetic gradient data. The contribution from higher order moments may provide a practical tool for improved UXO discrimination. ?? 2008 IEEE.

  12. Magnetic ordering of the polar airglow

    NASA Technical Reports Server (NTRS)

    Frederick, J. E.; Hays, P. B.

    1978-01-01

    The visible airglow experiment on the Atmosphere Explorer-C satellite has gathered sufficient data over the earth's polar regions to allow one to map the geographic distribution of particle precipitation using emissions at 3371 and 5200 A. Both of these features exhibit large variations in space and time. The 3371 A emission of N2(C cubed pi), excited by low energy electrons, indicates substantial energy inputs on the dayside in the vicinity of the polar cusp. More precipitation occurs in the morning than evening for the sample reported here, while the entire night sector between magnetic latitudes 65 and 77.5 deg is subjected to particle fluxes. Regions of enhanced 5200 A emission from N(D-2) are larger in horizontal extent than those at 3371 A. This smearing effect is due to ionospheric motions induced by magnetospheric convection.

  13. Uniaxial Pressure Dependence of Magnetic Order in MnSi.

    PubMed

    Chacon, A; Bauer, A; Adams, T; Rucker, F; Brandl, G; Georgii, R; Garst, M; Pfleiderer, C

    2015-12-31

    We report comprehensive small angle neutron scattering measurements complemented by ac susceptibility data of the helical order, conical phase, and Skyrmion lattice phase (SLP) in MnSi under uniaxial pressures. For all crystallographic orientations uniaxial pressure favors the phase for which a spatial modulation of the magnetization is closest to the pressure axis. Uniaxial pressures as low as 1 kbar applied perpendicular to the magnetic field axis enhance the Skyrmion lattice phase substantially, whereas the Skyrmion lattice phase is suppressed for pressure parallel to the field. Taken together we present quantitative microscopic information on how strain couples to magnetic order in the chiral magnet MnSi. PMID:26765018

  14. Magnetic material arrangement in oriented termites: a magnetic resonance study

    NASA Astrophysics Data System (ADS)

    Alves, O. C.; Wajnberg, E.; de Oliveira, J. F.; Esquivel, D. M. S.

    2004-06-01

    Temperature dependence of the magnetic resonance is used to study the magnetic material in oriented Neocapritermes opacus (N.o.) termite, the only prey of the migratory ant Pachycondyla marginata (P.m.). A broad line in the g=2 region, associated to isolated nanoparticles shows that at least 97% of the magnetic material is in the termite's body (abdomen + thorax). From the temperature dependence of the resonant field and from the spectral linewidths, we estimate the existence of magnetic nanoparticles 18.5 ± 0.3 nm in diameter and an effective magnetic anisotropy constant, Keff between 2.1 and 3.2 × 10 4 erg/cm 3. A sudden change in the double integrated spectra at about 100 K for N.o. with the long body axis oriented perpendicular to the magnetic field can be attributed to the Verwey transition, and suggests an organized film-like particle system.

  15. Magnetically driven suppression of nematic order in an iron-based superconductor.

    PubMed

    Avci, S; Chmaissem, O; Allred, J M; Rosenkranz, S; Eremin, I; Chubukov, A V; Bugaris, D E; Chung, D Y; Kanatzidis, M G; Castellan, J-P; Schlueter, J A; Claus, H; Khalyavin, D D; Manuel, P; Daoud-Aladine, A; Osborn, R

    2014-01-01

    A theory of superconductivity in the iron-based materials requires an understanding of the phase diagram of the normal state. In these compounds, superconductivity emerges when stripe spin density wave (SDW) order is suppressed by doping, pressure or atomic disorder. This magnetic order is often pre-empted by nematic order, whose origin is yet to be resolved. One scenario is that nematic order is driven by orbital ordering of the iron 3d electrons that triggers stripe SDW order. Another is that magnetic interactions produce a spin-nematic phase, which then induces orbital order. Here we report the observation by neutron powder diffraction of an additional fourfold-symmetric phase in Ba1-xNaxFe2As2 close to the suppression of SDW order, which is consistent with the predictions of magnetically driven models of nematic order. PMID:24848521

  16. Magnetism in Non-Traditional Materials

    SciTech Connect

    Menon, Madhu

    2013-09-17

    complimentary to the hole defects appear to be the pentagons along the curved surface of the drum. Charge oscillations found in the nano-drum are minimized in the nanoribbons. But more importantly, the hole edge atoms in the nano-drums retain significant magnetic moments; almost twice those of the corresponding ones in hydrogenated graphene nanoribbons (H-GNRs). These results suggest that the topological defects in the nano-drums may act like blocks to keep magnetic moments from ?leaking? out from the hole defects. This may have significant implications for the the use of nano-drums in magnetic storage technology where the ratio, magnetic-moment/weight, is of paramount importance in any futuristic device applications. One of the basic problems of the DFT/LSDA+U theory is the efficient evaluation of the U-term. With this in mind we proposed an alternative approach for its calculation which is based on the knowledge of the Hartree-Fock wave functions of the system under consideration. As a result, the proposed approach is closer to the basic definition of the DFT/LSDA+U scheme and its hybrid-DFT nature. According to our approach, the U value is obtained in a consistent and ab-initio way using the self-consistently calculated wave functions of the given system at the level of the HF approximation. Our method is applicable for systems which include more than one type of elements with localized d-orbitals. The method has been applied the case of the doped Zn(Co)O systems successfully. Currently, theories based on conventional superexchange or double-exchange interactions cannot explain long range magnetic order at concentrations below percolation threshold in dilute magnetic semiconductors. On the other hand, the codoping induced magnetism, which can justify magnetic interactions below percolation threshold, has eluded explanation. With this in mind, we proposed that defect-induced magnetism in codoped non-magnetic materials can be viewed within a molecular generalization of the

  17. Magnetic order in rare earth bromates below 0. 1 K

    SciTech Connect

    Xu, Jingchun; Corruccini, L.R. )

    1989-08-01

    Magnetic order inferred from dc susceptibility measurements is reported for Gd, Er, and Yb bromates. No order is seen in Nd bromate at temperatures above {approximately}6.5 mK. Erbium bromate orders in a fashion outwardly similar to the structurally related Er ethyl sulfate.

  18. Beam loss reduction by magnetic shielding using beam pipes and bellows of soft magnetic materials

    NASA Astrophysics Data System (ADS)

    Kamiya, J.; Ogiwara, N.; Hotchi, H.; Hayashi, N.; Kinsho, M.

    2014-11-01

    One of the main sources of beam loss in high power accelerators is unwanted stray magnetic fields from magnets near the beam line, which can distort the beam orbit. The most effective way to shield such magnetic fields is to perfectly surround the beam region without any gaps with a soft magnetic high permeability material. This leads to the manufacture of vacuum chambers (beam pipes and bellows) with soft magnetic materials. A Ni-Fe alloy (permalloy) was selected for the material of the pipe parts and outer bellows parts, while a ferritic stainless steel was selected for the flanges. An austenitic stainless steel, which is non-magnetic material, was used for the inner bellows for vacuum tightness. To achieve good magnetic shielding and vacuum performances, a heat treatment under high vacuum was applied during the manufacturing process of the vacuum chambers. Using this heat treatment, the ratio of the integrated magnetic flux density along the beam orbit between the inside and outside of the beam pipe and bellows became small enough to suppress beam orbit distortion. The outgassing rate of the materials with this heat treatment was reduced by one order magnitude compared to that without heat treatment. By installing the beam pipes and bellows of soft magnetic materials as part of the Japan Proton Accelerator Research Complex 3 GeV rapid cycling synchrotron beam line, the closed orbit distortion (COD) was reduced by more than 80%. In addition, a 95.5% beam survival ratio was achieved by this COD improvement.

  19. Composite, ordered material having sharp surface features

    DOEpatents

    D'Urso, Brian R.; Simpson, John T.

    2006-12-19

    A composite material having sharp surface features includes a recessive phase and a protrusive phase, the recessive phase having a higher susceptibility to a preselected etchant than the protrusive phase, the composite material having an etched surface wherein the protrusive phase protrudes from the surface to form a sharp surface feature. The sharp surface features can be coated to make the surface super-hydrophobic.

  20. Magnetic ordering in Ho2Fe2Si2C

    NASA Astrophysics Data System (ADS)

    Susilo, R. A.; Cadogan, J. M.; Cobas, R.; Hutchison, W. D.; Avdeev, M.; Campbell, S. J.

    2015-05-01

    We have used neutron diffraction and 57Fe Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho2Fe2Si2C. We have established that Ho2Fe2Si2C orders antiferromagnetically below TN = 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k =[0 0 1/2 ] . 57Fe Mössbauer spectra collected below TN show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the 57Fe spectra below TN, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice.

  1. Cross coupling between electric and magnetic orders in a multiferroic metal-organic framework.

    PubMed

    Tian, Ying; Stroppa, Alessandro; Chai, Yisheng; Yan, Liqin; Wang, Shouguo; Barone, Paolo; Picozzi, Silvia; Sun, Young

    2014-01-01

    The coexistence of both electric and magnetic orders in some metal-organic frameworks (MOFs) has yielded a new class of multiferroics beyond inorganic materials. However, the coupling between two orders in multiferroic MOFs has not been convincingly verified yet. Here we present clear experimental evidences of cross coupling between electric and magnetic orders in a multiferroic MOF [(CH3)2NH2]Fe(HCOO)3 with a perovskite structure. The dielelectric constant exhibit a hump just at the magnetic ordering temperature TN. Moreover, both the direct (magnetic field control of dielectric properties) and converse (electric field control of magnetization) magnetoelectric effects have been observed in the multiferroic state. This work opens up new insights on the origin of ferroelectricity in MOFs and highlights their promise as magnetoelectric multiferroics. PMID:25317819

  2. Development of electroplated magnetic materials for MEMS

    NASA Technical Reports Server (NTRS)

    Myung, N. V.; Sumadjo, P. T. A.; Park, D. Y.

    2002-01-01

    Soft ferromagnetic materials have thus far found the most utility in magnetic-MEMS, because the technologies necessary for depositing and micromachining them have been well developed previously by the data storage industry.

  3. High-strength magnetic materials

    NASA Technical Reports Server (NTRS)

    Detert, K.

    1970-01-01

    Two new precipitation-hardened magnetic alloys are suitable for operation in 800 to 1600 deg F range. One is a martensitic alloy and the other a cobalt-based alloy. They possess improved creep resistance and have application in high temperature inductors and alternators.

  4. Driving magnetic order in a manganite by ultrafast lattice excitation

    NASA Astrophysics Data System (ADS)

    Först, M.; Tobey, R. I.; Wall, S.; Bromberger, H.; Khanna, V.; Cavalieri, A. L.; Chuang, Y.-D.; Lee, W. S.; Moore, R.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Trigo, M.; Zheng, H.; Mitchell, J. F.; Dhesi, S. S.; Hill, J. P.; Cavalleri, A.

    2011-12-01

    Femtosecond midinfrared pulses are used to directly excite the lattice of the single-layer manganite La0.5Sr1.5MnO4. Magnetic and orbital orders, as measured by femtosecond resonant soft x-ray diffraction with an x-ray free-electron laser, are reduced within a few picoseconds. This effect is interpreted as a displacive exchange quench, a prompt shift in the equilibrium value of the magnetic- and orbital-order parameters after the lattice has been distorted. Control of magnetism through ultrafast lattice excitation may be of use for high-speed optomagnetism.

  5. Magnetic ordering temperature of nanocrystalline Gd: enhancement of magnetic interactions via hydrogenation-induced "negative" pressure.

    PubMed

    Tereshina, E A; Khmelevskyi, S; Politova, G; Kaminskaya, T; Drulis, H; Tereshina, I S

    2016-01-01

    Gadolinium is a nearly ideal soft-magnetic material. However, one cannot take advantage of its properties at temperatures higher than the room temperature where Gd loses the ferromagnetic ordering. By using high-purity bulk samples with grains ~200 nm in size, we present proof-of-concept measurements of an increased Curie point (TC) and spontaneous magnetization in Gd due to hydrogenation. From first-principles we explain increase of TC in pure Gd due to the addition of hydrogen. We show that the interplay of the characteristic features in the electronic structure of the conduction band at the Fermi level in the high-temperature paramagnetic phase of Gd and "negative" pressure exerted by hydrogen are responsible for the observed effect. PMID:26931775

  6. Replacing critical rare earth materials in high energy density magnets

    NASA Astrophysics Data System (ADS)

    McCallum, R. William

    2012-02-01

    High energy density permanent magnets are crucial to the design of internal permanent magnet motors (IPM) for hybride and electric vehicles and direct drive wind generators. Current motor designs use rare earth permanent magnets which easily meet the performance goals, however, the rising concerns over cost and foreign control of the current supply of rare earth resources has motivated a search for non-rare earth based permanent magnets alloys with performance metrics which allow the design of permanent magnet motors and generators without rare earth magnets. This talk will discuss the state of non-rare-earth permanent magnets and efforts to both improve the current materials and find new materials. These efforts combine first principles calculations and meso-scale magnetic modeling with advance characterization and synthesis techniques in order to advance the state of the art in non rare earth permanent magnets. The use of genetic algorithms in first principle structural calculations, combinatorial synthesis in the experimental search for materials, atom probe microscopy to characterize grain boundaries on the atomic level, and other state of the art techniques will be discussed. In addition the possibility of replacing critical rare earth elements with the most abundant rare earth Ce will be discussed.

  7. Location of laccase in ordered mesoporous materials

    NASA Astrophysics Data System (ADS)

    Mayoral, Álvaro; Gascón, Victoria; Blanco, Rosa M.; Márquez-Álvarez, Carlos; Díaz, Isabel

    2014-11-01

    The functionalization with amine groups was developed on the SBA-15, and its effect in the laccase immobilization was compared with that of a Periodic Mesoporous Aminosilica. A method to encapsulate the laccase in situ has now been developed. In this work, spherical aberration (Cs) corrected scanning transmission electron microscopy combined with high angle annular dark field detector and electron energy loss spectroscopy were applied to identify the exact location of the enzyme in the matrix formed by the ordered mesoporous solids.

  8. Cation Ordering in Li[NixMnxCo(1-2x)]O2-Layered Cathode Materials: A Nuclear Magnetic Resonance (NMR), Pair Distribution Function, X-ray Absorption Spectroscopy, and Electrochemical Study

    SciTech Connect

    Zeng,D.; Cabana, J.; Breger, J.; Yoon, W.; Grey, C.

    2007-01-01

    Several members of the compositional series Li[NixMnxCo(1-2x)]O2 (0.01 = x = 1/3) were synthesized and characterized. X-ray diffraction results confirm the presence of the layered a-NaFeO2-type structure, while X-ray absorption near-edge spectroscopy experiments verify the presence of Ni2+, Mn4+, and Co3+. Their local environment and short-range ordering were investigated by using a combination of 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and neutron pair distribution function (PDF) analysis, associated with reverse Monte Carlo (RMC) calculations. The 6Li MAS NMR spectra of compounds with low Ni/Mn contents (x = 0.10) show several well-resolved resonances, which start to merge when the amount of Ni and Mn increases, finally forming a broad resonance at high Ni/Mn contents. Analysis of the 6Li MAS NMR 6Li[Ni0.02Mn0.02Co0.96]O2 spectrum, is consistent with the formation of Ni2+ and Mn4+ clusters within the transition-metal layers, even at these low-doping levels. The oxidation state of Ni in this high Co content sample strongly depends upon the Li/transition metal ratio of the starting materials. Neutron PDF analysis of the highest Ni/Mn content sample Li[Ni1/3Mn1/3Co1/3]O2 shows a tendency for Ni cations to be close to Mn cations in the first coordination shell; however, the Co3+ ions are randomly distributed. Analysis of the intensity of the 'LiCoO2' resonance, arising from Li surrounded by Co3+ in its first two cation coordination shells, for the whole series provides further evidence for a nonrandom distribution of the transition-metal cations. The presence of the insulator-to-metal transition seen in the electrochemical profiles of these materials upon charging correlates strongly with the concentration of the 'LiCoO2' resonance.

  9. Interactions of Plutonium and Lanthanides with Ordered Mesoporous Materials

    NASA Astrophysics Data System (ADS)

    Parsons-Moss, Tashi

    Ordered mesoporous materials are porous solids with a regular, patterned structure composed of pores between 2 and 50 nm wide. Such materials have attracted much attention in the past twenty years because the chemistry of their synthesis allows control of their unique physicochemical properties, which can be tuned for a variety of applications. Generally, ordered mesoporous materials have very high specific surface areas and pore volumes, and offer unique structures that are neither crystalline nor amorphous. The large tunable interface provided by ordered mesoporous solids may be advantageous in applications involving sequestration, separation, or detection of actinides and lanthanides in solution. However, the fundamental chemical interactions of actinides and lanthanides must be understood before applications can be implemented. This dissertation focuses primarily on the fundamental interactions of plutonium with organically modified mesoporous silica, as well as several different porous carbon materials, both untreated and chemically oxidized. A method for functionalizing mesoporous silica by self assembly and molecular grafting of functional organosilane ligands was optimized for the 2D-hexagonal ordered mesoporous silica known as SBA-15 (Santa Barbara amorphous silica). Four different organically-modified silica materials were synthesized and characterized with several techniques. To confirm that covalent bonds were formed between the silane anchor of the ligand and the silica substrate, functionalized silica samples were analyzed with 29Si nuclear magnetic resonance spectroscopy. Infrared spectroscopy was used in combination with 13C and 31P nuclear magnetic resonance spectroscopy to verify the molecular structures of the ligands after they were synthesized and grafted to the silica. The densities of the functional silane ligands on the silica surface were estimated using thermogravimetric analysis. Batch sorption experiments were conducted with solutions of

  10. Dynamic magnetic susceptibility of systems with long-range magnetic order

    SciTech Connect

    Vannette, Matthew Dano

    2009-01-01

    The utility of the TDR as an instrument in the study of magnetically ordered materials has been expanded beyond the simple demonstration purposes. Results of static applied magnetic field dependent measurements of the dynamic magnetic susceptibility, χ, of various ferromagnetic (FM) and antiferromagnetic (AFM) materials showing a range of transition temperatures (1-800 K) are presented. Data was collected primarily with a tunnel diode resonator (TDR) at different radio-frequencies (~10-30 MHz). In the vicinity of TC local moment ferromagnets show a very sharp, narrow peak in χ which is suppressed in amplitude and shifted to higher temperatures as the static bias field is increased. Unexpectedly, critical scaling analysis fails for these data. It is seen that these data are frequency dependent, however there is no simple method whereby measurement frequency can be changed in a controllable fashion. In contrast, itinerant ferromagnets show a broad maximum in χ well below TC which is suppressed and shifts to lower temperatures as the dc bias field is increased. The data on itinerant ferromagnets is fitted to a semi-phenomenological model that suggests the sample response is dominated by the uncompensated minority spins in the conduction band. Concluding remarks suggest possible scenarios to achieve frequency resolved data using the TDR as well as other fields in which the apparatus may be exploited.

  11. Location of laccase in ordered mesoporous materials

    SciTech Connect

    Mayoral, Álvaro; Gascón, Victoria; Blanco, Rosa M.; Márquez-Álvarez, Carlos; Díaz, Isabel

    2014-11-01

    The functionalization with amine groups was developed on the SBA-15, and its effect in the laccase immobilization was compared with that of a Periodic Mesoporous Aminosilica. A method to encapsulate the laccase in situ has now been developed. In this work, spherical aberration (C{sub s}) corrected scanning transmission electron microscopy combined with high angle annular dark field detector and electron energy loss spectroscopy were applied to identify the exact location of the enzyme in the matrix formed by the ordered mesoporous solids.

  12. Microscopic Materials on a Magnet

    NASA Technical Reports Server (NTRS)

    2008-01-01

    These images show a comparison of the weak magnet OM7 from the Optical Microscope on NASA's Phoenix Mars Lander before (left) and after (right) soil deposition.

    The microscope took the left image during Phoenix's Sol 15 (June 10, 2008) and the right image during Sol 21 (Jun 16, 2008).

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  13. Deflagration, fronts of tunneling, and dipolar ordering in molecular magnets

    NASA Astrophysics Data System (ADS)

    Garanin, Dmitry

    2011-03-01

    Although there is no exchange interaction in crystals of molecular magnets characterized by a giant effective spin S (S = 10 for Mn 12 , and Fe 8) , magnetic field B (D) generated by magnetic moments g μ B S of magnetic molecules creates energy bias W (D) = 2 Sg μ BB (D) on a molecule that largely exceeds the tunnelling splitting Δ of matching quantum states on different sides of the anisotropy barrier. Thus the dipolar field has a profound influence on the processes of tunnelling and relaxation in molecular magnets. Both theoretical and experimental works showed a slow non-exponential relaxation of the magnetization in both initially ordered and completely disordered states since most of the spins are off tunneling resonance at any time. Recently a new mode of relaxation via tunneling has been found, the so-called fronts of tunneling, in which (within a 1 d theoretical model) dipolar field adjusts so that spins are on resonance within the broad front core. In this ``laminar'' regime fronts of tunnelling are moving fast at speeds that can exceed that of the temperature-driven magnetic deflagration, if a sufficiently strong transverse field is applied. However, a ``non-laminar'' regime has also been found in which instability causes spins to go off resonance and the front speed drops. In a combination with magnetic deflagration, the laminar regime becomes more stable and exists in the whole dipolar window 0 <= W <=W (D) on the external bias W , where the deflagration speed strongly increases. Another dipolar effect in molecular magnets is dipolar ordering below 1 K that has recently been shown to be non-uniform because of formation of magnetic domains. An object of current research is possible non-uniformity of magnetic deflagration and tunneling fronts via domain instability that could influence their speed.

  14. Levitating a Magnet Using a Superconductive Material.

    ERIC Educational Resources Information Center

    Juergens, Frederick H.; And Others

    1987-01-01

    Presented are the materials and a procedure for demonstrating the levitation of a magnet above a superconducting material. The demonstration can be projected with an overhead projector for a large group of students. Kits to simplify the demonstration can be purchased from the Institute for Chemical Education of the University of Wisconsin-Madison.…

  15. Magnetic Levitational Assembly for Living Material Fabrication.

    PubMed

    Tasoglu, Savas; Yu, Chu Hsiang; Liaudanskaya, Volha; Guven, Sinan; Migliaresi, Claudio; Demirci, Utkan

    2015-07-15

    Functional living materials with microscale compositional topographies are prevalent in nature. However, the creation of biomaterials composed of living micro building blocks, each programmed by composition, functionality, and shape, is still a challenge. A powerful yet simple approach to create living materials using a levitation-based magnetic method is presented. PMID:25872008

  16. Search for magnetic monopoles in lunar material

    NASA Technical Reports Server (NTRS)

    Alvarez, L. W.; Eberhard, P. H.; Ross, R. R.; Watt, R. D.

    1972-01-01

    Magnetic monopoles in 19.8 kg. of lunar material returned by Apollo 11, 12 and 14 missions were investigated. The search was done with a detector which is capable of detecting any single monopole of any charge equal to or larger than the minimum value compatible with Dirac's theory. Two experiments were performed, each one with different lunar material. In each experiment the lunar material was divided into several measurement samples. No monopole was found. The magnetic charge of each sample was consistent with zero.

  17. Magnetic properties of Martian surface material

    NASA Technical Reports Server (NTRS)

    Hargraves, R. B.

    1984-01-01

    The hypothesis that the magnetic properties of the Martian surface material are due to the production of a magnetic phase in the clay mineral nontronite by transient shock heating is examined. In the course of the investigation a magnetic material is produced with rather unusual properties. Heating from 900 C to 1000 C, of natural samples of nontronite leads first to the production of what appears to be Si doped maghemite gamma (-Fe2O3). Although apparently metastable, the growth of gamma -Fe2O3 at these temprtures is unexpected, and its relative persistence of several hours at 1000 C is most surprising. Continued annealing of this material for longer periods promote the crystallization of alpha Fe2O3 and cristobalite (high temperature polymorph of SiO2). All available data correlate this new magnetic material with the cristobalite hence our naming it magnetic ferri cristobalite. Formation of this magnetic cristobalite, however, may require topotactic growth from a smectite precursor.

  18. Magnetic properties of Martian surface material

    NASA Astrophysics Data System (ADS)

    Hargraves, R. B.

    1984-06-01

    The hypothesis that the magnetic properties of the Martian surface material are due to the production of a magnetic phase in the clay mineral nontronite by transient shock heating is examined. In the course of the investigation a magnetic material is produced with rather unusual properties. Heating from 900 C to 1000 C, of natural samples of nontronite leads first to the production of what appears to be Si doped maghemite gamma (-Fe2O3). Although apparently metastable, the growth of gamma -Fe2O3 at these temprtures is unexpected, and its relative persistence of several hours at 1000 C is most surprising. Continued annealing of this material for longer periods promote the crystallization of alpha Fe2O3 and cristobalite (high temperature polymorph of SiO2). All available data correlate this new magnetic material with the cristobalite hence our naming it magnetic ferri cristobalite. Formation of this magnetic cristobalite, however, may require topotactic growth from a smectite precursor.

  19. Electrically tuned magnetic order and magnetoresistance in a topological insulator.

    PubMed

    Zhang, Zuocheng; Feng, Xiao; Guo, Minghua; Li, Kang; Zhang, Jinsong; Ou, Yunbo; Feng, Yang; Wang, Lili; Chen, Xi; He, Ke; Ma, Xucun; Xue, Qikun; Wang, Yayu

    2014-01-01

    The interplay between topological protection and broken time reversal symmetry in topological insulators may lead to highly unconventional magnetoresistance behaviour that can find unique applications in magnetic sensing and data storage. However, the magnetoresistance of topological insulators with spontaneously broken time reversal symmetry is still poorly understood. In this work, we investigate the transport properties of a ferromagnetic topological insulator thin film fabricated into a field effect transistor device. We observe a complex evolution of gate-tuned magnetoresistance, which is positive when the Fermi level lies close to the Dirac point but becomes negative at higher energies. This trend is opposite to that expected from the Berry phase picture, but is intimately correlated with the gate-tuned magnetic order. The underlying physics is the competition between the topology-induced weak antilocalization and magnetism-induced negative magnetoresistance. The simultaneous electrical control of magnetic order and magnetoresistance facilitates future topological insulator based spintronic devices. PMID:25222696

  20. Magnetic behavior in an ordered Co nanorod array

    NASA Astrophysics Data System (ADS)

    Wang, T.; Wang, Y.; Fu, Y.; Hasegawa, T.; Oshima, H.; Itoh, K.; Nishio, K.; Masuda, H.; Li, F. S.; Saito, H.; Ishio, S.

    2008-11-01

    The magnetization reversal process of an ordered Co nanorod array is shown using the images obtained from successive in-field magnetic force microscope (MFM) measurements. The magnetization reversal model is discussed according to local and whole magnetization reversal properties measured by the polar magneto-optical Kerr effect (PMOKE) and an alternating gradient magnetometer (AGM), respectively. Additionally, the dipolar field was probed using in-field MFM measurements. By removing the effect of the dipolar field, an intrinsic switching field distribution (SFD) is shown in a map with a hexagonal array. A detailed study of the dipolar field in ordered nanorod arrays with various diameters and pitches was carried out by numerical calculations.

  1. Low Temperature Magnetic Ordering of the Magnetic Ionic Plastic Crystal, Choline[FeCl4

    NASA Astrophysics Data System (ADS)

    de Pedro, I.; García-Saiz, A.; Andreica, D.; Fernández Barquín, L.; Fernández-Díaz, M. T.; Blanco, J. A.; Amato, A.; Rodríguez Fernández, J.

    2015-11-01

    We report on the nature of the low temperature magnetic ordering of a magnetic ionic plastic crystal, Choline[FeCl4]. This investigation was carried out using heat capacity measurements, neutron diffraction experiments and muon spin relaxation (μSR) spectroscopy. The calorimetric measurements show the onset of an unusual magnetic ordering below 4 K with a possible second magnetic phase transition below 2 K. Low temperature neutron diffraction data reveal a three dimensional antiferromagnetic ordering at 2 K compatible with the previous magnetometry results. The analysis of μSR spectra indicates a magnetic phase transition below 2.2 K. At 1.6 K, the analysis of the shape of the μSR spectra suggests the existence of an additional magnetic phase with features of a possible incommensurate magnetic structure.

  2. Porphyrins as Second Order Nonlinear Optical Materials

    NASA Astrophysics Data System (ADS)

    Chou, Homer

    Because of the unusually high thermal and chemical stability of porphyrins as well as their very large pi-conjugated systems, three classes of high beta-value push-pull porphyrins were synthesized and subsequently successfully engineered into Langmuir-Blodgett (LB) films for a systematic evaluation of porphyrins as chi^{(2)} materials. Class I explored the effects of the number of donor-acceptor groups on the porphyrin periphery (i.e., H_2(an_3P), H_2 (cis-a_2n_2P), H_2(a_3nP), H _2(a_4P) where a = 4-(N-octadecylamido)phenyl or 4-(N-octadecyl-amino)phenyl; n = 4-nitrophenyl; P = 5,10,15,20 substituted tetraarylporphyrinate (2-).). Class II examined the effect of varying the strength of cis-substituted donor-acceptor pairs on the porphyrin periphery (i.e., H_2(cis-a_2n _2P), H_2(cis-c _2p_2P), and H_2 (cis-h_2py_2P) where c = 4-(2-cholesteryloxy)-ethoxyphenyl; h = 4-hydroxyphenyl or 4-methoxyphenyl; and py = 4-pyridyl or 4-(N-octadecyl) pyridiniumyl). Class III looked at the respone of a heterosubstituted bis- push-pull cerium sandwich porphyrin complex, (Ce ^{IV}(TPyP)(TMeP)) ^{4+}I_4 (where Py = 4-(N-octadecyl)pyridiniumyl and Me = 4-methoxyphenyl). Characterization of the porphyrin LB films reveals rather surprising behavior. The isotherm data show that the mean molecular area of the porphyrins increase smoothly from 80-200A as the number of aliphatic chains increase around the porphyrin periphery from one to four. In addition, based on UV-visible linear dichroism, all of the porphyrin films possess C _{infty v} symmetry and adopt a tilt angle, theta, of about 33^circ with respect to the fused quartz substrate. The proposed fixed orientation model suggests that the interporphyrin pi -pi interactions dominate the porphyrin orientation while the number of aliphatic chains around the porphyrin periphery determines the porphyrin's packing density in the LB film. After these monolayers were transferred to fused quartz substrates, the chi^{(2)} response of these

  3. Magnetic and Superconducting Materials at High Pressures

    SciTech Connect

    Struzhkin, Viktor V.

    2015-03-24

    The work concentrates on few important tasks in enabling techniques for search of superconducting compressed hydrogen compounds and pure hydrogen, investigation of mechanisms of high-Tc superconductivity, and exploring new superconducting materials. Along that route we performed several challenging tasks, including discovery of new forms of polyhydrides of alkali metal Na at very high pressures. These experiments help us to establish the experimental environment that will provide important information on the high-pressure properties of hydrogen-rich compounds. Our recent progress in RIXS measurements opens a whole field of strongly correlated 3d materials. We have developed a systematic approach to measure major electronic parameters, like Hubbard energy U, and charge transfer energy Δ, as function of pressure. This technique will enable also RIXS studies of magnetic excitations in iridates and other 5d materials at the L edge, which attract a lot of interest recently. We have developed new magnetic sensing technique based on optically detected magnetic resonance from NV centers in diamond. The technique can be applied to study superconductivity in high-TC materials, to search for magnetic transitions in strongly correlated and itinerant magnetic materials under pressure. Summary of Project Activities; development of high-pressure experimentation platform for exploration of new potential superconductors, metal polyhydrides (including newly discovered alkali metal polyhydrides), and already known superconductors at the limit of static high-pressure techniques; investigation of special classes of superconducting compounds (high-Tc superconductors, new superconducting materials), that may provide new fundamental knowledge and may prove important for application as high-temperature/high-critical parameter superconductors; investigation of the pressure dependence of superconductivity and magnetic/phase transformations in 3d transition metal compounds, including

  4. Ferromagnetic ordering in NpAl2: Magnetic susceptibility and 27Al nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Martel, L.; Griveau, J.-C.; Eloirdi, R.; Selfslag, C.; Colineau, E.; Caciuffo, R.

    2015-08-01

    We report on the magnetic properties of the neptunium based ferromagnetic compound NpAl2. We used magnetization measurements and 27Al NMR spectroscopy to access magnetic features related to the paramagnetic and ordered states (TC=56 K). While very precise DC SQUID magnetization measurements confirm ferromagnetic ordering, they show a relatively small hysteresis loop at 5 K reduced with a coercive field HCo~3000 Oe. The variable offset cumulative spectra (VOCS) acquired in the paramagnetic state show a high sensitivity of the 27Al nuclei spectral parameters (Knight shifts and line broadening) to the ferromagnetic ordering, even at room temperature.

  5. Final Technical Progress Report NANOSTRUCTURED MAGNETIC MATERIALS

    SciTech Connect

    Charles M. Falco

    2012-09-13

    This report describes progress made during the final phase of our DOE-funded program on Nanostructured Magnetic Materials. This period was quite productive, resulting in the submission of three papers and presentation of three talks at international conferences and three seminars at research institutions. Our DOE-funded research efforts were directed toward studies of magnetism at surfaces and interfaces in high-quality, well-characterized materials prepared by Molecular Beam Epitaxy (MBE) and sputtering. We have an exceptionally well-equipped laboratory for these studies, with: Thin film preparation equipment; Characterization equipment; Equipment to study magnetic properties of surfaces and ultra-thin magnetic films and interfaces in multi-layers and superlattices.

  6. Magnetism, Magnetic Materials and their Applications III - Proceedings of the III Latin American Workshop

    NASA Astrophysics Data System (ADS)

    Leccabue, F.; Sagredo, V.

    1996-08-01

    The Table of Contents for the full book PDF is as follows: * Preface * Section I: Fundamental, Techniques and Materials * Magnetism in finite size Ising aggregates * Magnetic anisotropy in thin films * Magnetocrystalline anisotropy in rare earth intermetallics * Ferromagnetism vs Kondo effect in normal and superconducting CeTyX4-y * Magnetic phase transition and magnetocrystalline anisotropy of rare-earth transition-metal alloys * Giant magnetoresistance and related effects in multilayer and granular magnetic materials for practical applications * Magnetic properties of dilute PdMn alloys * TbFe amorphous thin films. Structural, magnetic and magnetoelastic studies * Nanophase exchange coupled alloys with enhanced hard magnetic properties * Exchange interactions in ferrimagnetic rare earth-transition metal multilayers * Superparamagnetic relaxation in interacting γ-Fe2O3 particles * Magnetic circular X-ray dichroism * Non-frustrated domains in Ising lattices with competing interactions * Thermomagnetic and X-ray diffraction analysis of Nd3Fe29-xTix and (Nd1-xYx)3Fe27.3Ti1.7 alloys * Electron paramagnetic resonance above the ordering temperature in La1-xCaxMnO3+δ * Spin-polarisation at Cr/Fe and Mn/Fe interfaces * Interplay of segregation, phase separation and magnetism in cobalt-copper slabs * High temperature behaviour of amorphous and nanocrystalline soft magnetic materials * Preparation of magnetic oxide thin films * Magnetic interactions in enhanced-remanence permanent magnets * Section II: Poster Session : Fundamental, Techniques and Materials * Magnetic properties in inorganic materials * Thermoreflactance measurements on Cd1-xCoxSe magnetic semiconductors * Analytical solutions of the NCA equations for the Coqblin-Schrieffer model in the zero temperature limit * Magneto-structural and spectroscopic investigation of MnxCd1-xIn2Te4 solid solutions * Magnetic after-effect processes in barium hexagonal ferrites * Electron paramagnetic resonance in PtFe alloys

  7. Structure and magnetism in novel group IV element-based magnetic materials

    SciTech Connect

    Tsui, Frank

    2013-08-14

    The project is to investigate structure, magnetism and spin dependent states of novel group IV element-based magnetic thin films and heterostructures as a function of composition and epitaxial constraints. The materials systems of interest are Si-compatible epitaxial films and heterostructures of Si/Ge-based magnetic ternary alloys grown by non-equilibrium molecular beam epitaxy (MBE) techniques, specifically doped magnetic semiconductors (DMS) and half-metallic Heusler alloys. Systematic structural, chemical, magnetic, and electrical measurements are carried out, using x-ray microbeam techniques, magnetotunneling spectroscopy and microscopy, and magnetotransport. The work is aimed at elucidating the nature and interplay between structure, chemical order, magnetism, and spin-dependent states in these novel materials, at developing materials and techniques to realize and control fully spin polarized states, and at exploring fundamental processes that stabilize the epitaxial magnetic nanostructures and control the electronic and magnetic states in these complex materials. Combinatorial approach provides the means for the systematic studies, and the complex nature of the work necessitates this approach.

  8. Multiferroic BaCoF4 in Thin Film Form: Ferroelectricity, Magnetic Ordering, and Strain.

    PubMed

    Borisov, Pavel; Johnson, Trent A; García-Castro, Andrés Camilo; KC, Amit; Schrecongost, Dustin; Cen, Cheng; Romero, Aldo H; Lederman, David

    2016-02-01

    Multiferroic materials have simultaneous magnetic and ferroelectric long-range orders and can be potentially useful for a wide range of applications. Conventional ferroelectricity in oxide perovskites favors nonmagnetic electronic configurations of transition metal ions, thus limiting the number of intrinsic multiferroic materials. On the other hand, this is not necessarily true for multiferroic fluorides. Using molecular beam epitaxy, we demonstrate for the first time that the multiferroic orthorhombic fluoride BaCoF4 can be synthesized in thin film form. Ferroelectric hysteresis measurements and piezoresponse force microscopy show that the films are indeed ferroelectric. From structural information, magnetic measurements, and first-principles calculations, a modified magnetic ground state is identified which can be represented as a combination of bulk collinear antiferromagnetism with two additional canted spin orders oriented along orthogonal axes of the BaCoF4 unit cell. The calculations indicate that an anisotropic epitaxial strain is responsible for this unusual magnetic ground state. PMID:26745210

  9. High performance electrical, magnetic, electromagnetic and electrooptical devices enabled by three dimensionally ordered nanodots and nanorods

    DOEpatents

    Goyal, Amit , Kang; Sukill

    2012-02-21

    Novel articles and methods to fabricate same with self-assembled nanodots and/or nanorods of a single or multicomponent material within another single or multicomponent material for use in electrical, electronic, magnetic, electromagnetic and electrooptical devices is disclosed. Self-assembled nanodots and/or nanorods are ordered arrays wherein ordering occurs due to strain minimization during growth of the materials. A simple method to accomplish this when depositing in-situ films is also disclosed. Device applications of resulting materials are in areas of superconductivity, photovoltaics, ferroelectrics, magnetoresistance, high density storage, solid state lighting, non-volatile memory, photoluminescence, thermoelectrics and in quantum dot lasers.

  10. Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments

    PubMed Central

    Freitas, Jair C. C.; Scopel, Wanderlã L.; Paz, Wendel S.; Bernardes, Leandro V.; Cunha-Filho, Francisco E.; Speglich, Carlos; Araújo-Moreira, Fernando M.; Pelc, Damjan; Cvitanić, Tonči; Požek, Miroslav

    2015-01-01

    The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at 13C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18–21 T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials. PMID:26434597

  11. Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments

    NASA Astrophysics Data System (ADS)

    Freitas, Jair C. C.; Scopel, Wanderlã L.; Paz, Wendel S.; Bernardes, Leandro V.; Cunha-Filho, Francisco E.; Speglich, Carlos; Araújo-Moreira, Fernando M.; Pelc, Damjan; Cvitanić, Tonči; Požek, Miroslav

    2015-10-01

    The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at 13C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21 T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials.

  12. Determination of the hyperfine magnetic field in magnetic carbon-based materials: DFT calculations and NMR experiments.

    PubMed

    Freitas, Jair C C; Scopel, Wanderlã L; Paz, Wendel S; Bernardes, Leandro V; Cunha-Filho, Francisco E; Speglich, Carlos; Araújo-Moreira, Fernando M; Pelc, Damjan; Cvitanić, Tonči; Požek, Miroslav

    2015-01-01

    The prospect of carbon-based magnetic materials is of immense fundamental and practical importance, and information on atomic-scale features is required for a better understanding of the mechanisms leading to carbon magnetism. Here we report the first direct detection of the microscopic magnetic field produced at (13)C nuclei in a ferromagnetic carbon material by zero-field nuclear magnetic resonance (NMR). Electronic structure calculations carried out in nanosized model systems with different classes of structural defects show a similar range of magnetic field values (18-21 T) for all investigated systems, in agreement with the NMR experiments. Our results are strong evidence of the intrinsic nature of defect-induced magnetism in magnetic carbons and establish the magnitude of the hyperfine magnetic field created in the neighbourhood of the defects that lead to magnetic order in these materials. PMID:26434597

  13. NMR study of new ruthenates with high magnetic ordering

    NASA Astrophysics Data System (ADS)

    Paulose, P. L.; Chakrabarty, Tanmoy

    The Ru based compounds, Ca3LiRuO6 and Ca3NaRuO6 show unusually high magnetic ordering temperature. Extended super exchange model is invoked to explain the magnetic behavior in the isostructural compound Ca3LiOsO6. We have carried out NMR investigation on these two Ru-based compounds. Ca3LiRuO6 is a weak ferromagnet with a magnetic ordering temperature (TC) of 115 K which is explored by the temperature dependence of 7Li NMR line shift, line-width and spin-lattice relaxation rate (1/T1) . Above TC, a broad maximum is observed in the evolution of line-width of the spectra. We speculate that this feature might be attributed to some low-dimensional magnetic behavior. Contrastingly, Ca3NaRuO6 with similar structure and local geometry of the Ru5+ ions is a conventional antiferromagnet with a transition temperature of 90 K. The temperature dependence of 23Na NMR line shift and 1/T1 is studied across magnetic transition in Ca3NaRuO6. The temperature variation of line-width is found to be different compared to Ca3LiRuO6. In both these systems, 1/T1 decreases significantly below ordering temperature, characteristic of many antiferromagnetic systems.

  14. Magnetic Alignment and Charge Transport Improvement in Functional Soft Materials

    NASA Astrophysics Data System (ADS)

    Majewski, Pawel W.

    The realization of nanostructured functional materials by self-assembly in polymers and polymer nanocomposites is adversely affected by persisting structural defects which greatly diminish the performance of the material. The use of magnetic fields to impose long-range order is investigated in three distinct systems - ion-conducting block copolymers, semiconducting nanowire-polymer composites and lyotropic surfactant mesophases. The alignment process is quantitatively studied with X-ray scattering and microscopic methods. Time and temperature resolved data collected in situ during the magnetic experiments provide an insight into the thermodynamic and kinetic aspects of the process. These data together with simultaneous electrical conductivity measurements allow relating fundamental structural properties (e.g., morphology and long-range order) to transport properties (i.e., conductivity). In particular, it is demonstrated that magnetic fields offer a viable route for improvement of electric conductivity in these systems. More than an order of magnitude increase in conductivity is recorded in magnetically-annealed materials. The resulting aligned nanostructured systems are attractive for ordered solid polymer electrolyte membranes, heterojunction photovoltaic devices and generally help to understand charge transport mechanisms in anisotropic heterogeneous systems.

  15. Magnetic field induced 1st order transitions: Recent studies, and some new concepts

    NASA Astrophysics Data System (ADS)

    Chaddah, P.

    2015-05-01

    Phase transitions are caused by varying temperature, or pressure, or magnetic field. The observation of 1st order magneto-structural transitions has created application possibilities based on magnetoresistance, magnetocaloric effect, magnetic shape memory effect, and magneto-dielectric effect. Magnetic field induced transitions, and phase coexistence of competing magnetic phases down to the lowest temperature, gained prominence over a decade ago with theoretical models suggesting that the ground state is not homogeneous. Researchers at Indore pushed an alternative view that this phase coexistence could be due to glasslike "kinetic arrest" of a disorder-broadened first-order magnetic transition between two states with long-range magnetic order, resulting in phase coexistence down to the lowest temperatures. The CHUF (cooling and heating in unequal field) protocol created at Indore allows the observation of `devitrification', followed by `melting'. I show examples of measurements establishing kinetic arrest in various materials, emphasizing that glasslike arrest of 1st order magnetic transitions may be as ubiquitous as glass formation following the arrest of 1st order structural transitions.

  16. Chemisorption and magnetization: a bond order-rigid band model

    NASA Astrophysics Data System (ADS)

    Fournier, R.; Salahub, D. R.

    1990-11-01

    We briefly review and analyze results of self-consistent LSD calculations on the effect of chemisorption of CO, H, O and C on the magnetism of nickel clusters. Guided by the similarities in these four cases, we propose a model which relates the change in magnetization of a ferromagnetic surface, caused by a chemisorbed species, to magnetic properties of the clean surface and to a qualitative description of the adsorbate-surface bond. The two key quantities in this model are the adsorbate-surface bond order and the spin polarization of the states at the Fermi energy. In the simplest version of this model, the bond order determines the number of electrons that will fill the metal band. In turn, the polarization of states at the Fermi energy determines how the electrons will partition in up and down spins. We contrast our model with the bond number model. Comparisons with experiments are made at a semi-quantitative level.

  17. Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron

    SciTech Connect

    Chui, C. P.; Zhou, Yan

    2014-03-15

    Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD) simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

  18. Emergent long-range magnetic ordering in manganite superlattices

    NASA Astrophysics Data System (ADS)

    Burganov, Bulat; Macke, Sebastian; Monkman, Eric; Adamo, Carolina; Shai, Daniel; Schlom, Darrell; Sawatzky, George; Shen, Kyle

    2015-03-01

    Complex oxides composed into atomically precise heterostructures host a plethora of new phenomena driven by interface effects, dimensionality, correlations and strain. An example is emergent ferromagnetism in the superlattices (SL) of LaMnO3/SrMnO3 and the dimensionality-driven metal insulator transition, still not well understood theoretically. We use soft x-ray scattering combined with SQUID magnetometry to determine the magnetic and orbital ordering in the (LaMnO3)2n /(SrMnO3)n SL for n =1,2,3,4. By composition this system is close to colossal-magnetoresistive La2/3Sr1/3MnO3, an FM metal below 400K. The system undergoes a metal-insulator transition with higher n and is believed to have a complex magnetic ordering. We observe an unexpected long-range order in the n =4 sample where the magnetic period is equal to two chemical periods. The observed half-order Bragg peaks show strong linear and no circular dichroism. The temperature and polarization dependence of reflectometry points towards alignment between A-type AFM orders in the neighboring LaMnO3 layers, which is very unusual and indicates a long range interaction acting across the thick SrMnO3 layers with nominally G-type spin configuration. We simulate the reflectometry data for several model spin configurations to further elucidate the nature of this ordering.

  19. Magnetization and magnetostriction in highly magnetostrictive materials

    SciTech Connect

    Thoelke, J.B.

    1993-05-26

    The majority of this research has been in developing a model to describe the magnetostrictive properties of Terfenol-D, Tb{sub 1{minus}x}Dy{sub x}Fe{sub y} (x = 0.7-0.75 and y = 1.8--2.0), a rare earth-iron alloy which displays much promise for use in device applications. In the first chapter an introduction is given to the phenomena of magnetization and magnetostriction. The magnetic processes responsible for the observed magnetic properties of materials are explained. An overview is presented of the magnetic properties of rare earths, and more specifically the magnetic properties of Terfenol-D. In the second chapter, experimental results are presented on three composition of Tb{sub 1{minus}x}Dy{sub x}Fe{sub y} with x = 0.7, y= 1.9, 1.95, and x= 0.73, y= 1.95. The data were taken for various levels of prestress to show the effects of composition and microstructure on the magnetic and magnetostrictive properties of Terfenol-D. In the third chapter, a theoretical model is developed based on the rotation of magnetic domains. The model is used to explain the magnetic and magnetostrictive properties of Terfenol-D, including the observed negative strictions and large change in strain. The fourth chapter goes on to examine the magnetic properties of Terfenol-D along different crystallographic orientations. In the fifth chapter initial data are presented on the time dependence of magnetization in nickel.

  20. Magnetic field induced third order susceptibility of third order harmonic generation in a ZnMgSe strained quantum well

    SciTech Connect

    Mark, J. Abraham Hudson Peter, A. John

    2014-04-24

    Third order susceptibility of third order harmonic generation is investigated in a Zn{sub 0.1}Mg{sub 0.9}Se/Zn{sub 0.8}Mg{sub 0.2}Se/Zn{sub 0.1}Mg{sub 0.9}Se quantum well in the presence of magnetic field strength. The confinement potential is considered as the addition of energy offsets of the conduction band (or valence band) and the strain-induced potential in our calculations. The material dependent effective mass is followed throughout the computation because it has a high influence on the electron energy levels in low dimensional semiconductor systems.

  1. Quantifying Nanoscale Order in Amorphous Materials via Fluctuation Electron Microscopy

    ERIC Educational Resources Information Center

    Bogle, Stephanie Nicole

    2009-01-01

    Fluctuation electron microscopy (FEM) has been used to study the nanoscale order in various amorphous materials. The method is explicitly sensitive to 3- and 4-body atomic correlation functions in amorphous materials; this is sufficient to establish the existence of structural order on the nanoscale, even when the radial distribution function…

  2. Giant magnetoresistance materials for magnetic recording technology

    SciTech Connect

    Heffner, R.H.; Adams, C.D.; Brosha, E.L.

    1997-12-01

    This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work focused on a class of transition-metal-oxide (TMO) materials (LaMnO{sub 3} doped with Ca, Ba, or Sr) that exhibits an insulator-to-metal transition near a ferromagnetic phase transition temperature. This yields a very large magnetoresistance; thus these materials may have important uses as magnetic sensors in a variety of applications, ranging from automobiles to read heads for magnetic storage. In addition, the transport current in the ferromagnetic state is likely to be very highly polarized, which means that additional device applications using the phenomena of spin-polarized tunneling can be envisioned. Use of these materials as magnetic sensors depends upon learning to control the synthesis parameters (principally temperature, pressure and composition) to achieve a specific carrier concentration and/or mobility. A second challenge is the high magnetic fields ({ge}1 Tesla) currently required to achieve a large change in resistance. The authors began an investigation of two novel approaches to this field-sensitivity problem, involving the development of multilayer structures of the TMO materials. Finally, they began to explore the use of epitaxial strain as a means of changing the transport properties in thin-film multilayers.

  3. Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots

    NASA Astrophysics Data System (ADS)

    Bustingorry, S.; Pomiro, F.; Aurelio, G.; Curiale, J.

    2016-06-01

    The so-called Arrott plot, which consists in plotting H /M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T* is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T* corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetrical second-order critical points at finite magnetic field (Tc,±Hc) . We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimental data on La2 /3Ca1 /3MnO3 and discuss an estimate for the location of the triple point and the second-order critical points.

  4. Dynamic Characterization of Thin Film Magnetic Materials

    NASA Astrophysics Data System (ADS)

    Gu, Wei

    A broadband dynamic method for characterizing thin film magnetic material is presented. The method is designed to extract the permeability and linewidth of thin magnetic films from measuring the reflection coefficient (S11) of a house-made and short-circuited strip line testing fixture with or without samples loaded. An adaptive de-embedding method is applied to remove the parasitic noise of the housing. The measurements were carried out with frequency up to 10GHz and biasing magnetic fields up to 600 Gauss. Particular measurement setup and 3-step experimental procedures are described in detail. The complex permeability of a 330nm thick continuous FeGaB, 435nm thick laminated FeGaB film and a 100nm thick NiFe film will be induced dynamically in frequency-biasing magnetic field spectra and compared with a theoretical model based on Landau-Lifshitz-Gilbert (LLG) equations and eddy current theories. The ferromagnetic resonance (FMR) phenomenon can be observed among these three magnetic materials investigated in this thesis.

  5. Phonon induced magnetism in ionic materials

    NASA Astrophysics Data System (ADS)

    Restrepo, Oscar D.; Antolin, Nikolas; Jin, Hyungyu; Heremans, Joseph P.; Windl, Wolfgang

    2014-03-01

    Thermoelectric phenomena in magnetic materials create exciting possibilities in future spin caloritronic devices by manipulating spin information using heat. An accurate understanding of the spin-lattice interactions, i.e. the coupling between magnetic excitations (magnons) and lattice vibrations (phonons), holds the key to unraveling their underlying physics. We report ab initio frozen-phonon calculations of CsI that result in non-zero magnetization when the degeneracy between spin-up and spin-down electronic density of states is lifted for certain phonon displacement patterns. For those, the magnetization as a function of atomic displacement shows a sharp resonance due to the electronic states on the displaced Cs atoms, while the electrons on indium form a continuous background magnetization. We relate this resonance to the generation of a two-level system in the spin-polarized Cs partial density of states as a function of displacement, which we propose to be described by a simple resonant-susceptibility model. Current work extends these investigations to semiconductors such as InSb. ODR and WW are supported by the Center for Emergent Materials, an NSF MRSEC at OSU (Grant DMR-0820414).HJ and JPH are supported by AFOSR MURI Cryogenic Peltier Cooling, Contract #FA9550-10-1-0533.

  6. Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field.

    PubMed

    De France, Kevin J; Yager, Kevin G; Hoare, Todd; Cranston, Emily D

    2016-08-01

    Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0-1.2 T) and CNC concentration (1.65-8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = -0.499 where S = -0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = -0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected. PMID:27407001

  7. Orbital nematic order and interplay with magnetism in the two-orbital Hubbard model.

    PubMed

    Wang, Zhentao; Nevidomskyy, Andriy H

    2015-06-10

    Motivated by the recent angle-resolved photoemission spectroscopy (ARPES) on FeSe and iron pnictide families of iron-based superconductors, we have studied the orbital nematic order and its interplay with antiferromagnetism within the two-orbital Hubbard model. We used random phase approximation (RPA) to calculate the dependence of the orbital and magnetic susceptibilities on the strength of interactions and electron density (doping). To account for strong electron correlations not captured by RPA, we further employed non-perturbative variational cluster approximation (VCA) capable of capturing symmetry broken magnetic and orbitally ordered phases. Both approaches show that the electron and hole doping affect the two orders differently. While hole doping tends to suppress both magnetism and orbital ordering, the electron doping suppresses magnetism faster. Crucially, we find a realistic parameter regime for moderate electron doping that stabilizes orbital nematicity in the absence of long-range antiferromagnetic order. This is reminiscent of the non-magnetic orbital nematic phase observed recently in FeSe and a number of iron pnictide materials and raises the possibility that at least in some cases, the observed electronic nematicity may be primarily due to orbital rather than magnetic fluctuations. PMID:25988222

  8. First-order particle acceleration in magnetically driven flows

    DOE PAGESBeta

    Beresnyak, Andrey; Li, Hui

    2016-03-02

    In this study, we demonstrate that particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. Some examples of such flows include spontaneous turbulent reconnection and decaying magnetohydrodynamic turbulence, where a magnetic field relaxes to a lower-energy configuration and transfers part of its energy to kinetic motions of the fluid. We show that this energy transfer, which normally causes turbulent cascade and heating of the fluid, also results in a first-order acceleration of non-thermal particles. Since it is generic, this acceleration mechanism is likely to play a role in the production of non-thermal particle distribution inmore » magnetically dominant environments such as the solar chromosphere, pulsar magnetospheres, jets from supermassive black holes, and γ-ray bursts.« less

  9. First-Order Particle Acceleration in Magnetically-driven Flows

    NASA Astrophysics Data System (ADS)

    Beresnyak, Andrey; Li, Hui

    2016-03-01

    We demonstrate that particles are regularly accelerated while experiencing curvature drift in flows driven by magnetic tension. Some examples of such flows include spontaneous turbulent reconnection and decaying magnetohydrodynamic turbulence, where a magnetic field relaxes to a lower-energy configuration and transfers part of its energy to kinetic motions of the fluid. We show that this energy transfer, which normally causes turbulent cascade and heating of the fluid, also results in a first-order acceleration of non-thermal particles. Since it is generic, this acceleration mechanism is likely to play a role in the production of non-thermal particle distribution in magnetically dominant environments such as the solar chromosphere, pulsar magnetospheres, jets from supermassive black holes, and γ-ray bursts.

  10. Chemical and Magnetic Order in Vapor-Deposited Metal Films

    NASA Astrophysics Data System (ADS)

    Rooney, Peter Wiliam

    1995-01-01

    A stochastic Monte Carlo model of vapor deposition and growth of a crystalline, binary, A_3 B metallic alloy with a negative energy of mixing has been developed which incorporates deposition and surface diffusion in a physically correct manner and allows the simulation of deposition rates that are experimentally realizable. The effects of deposition rate and growth temperature on the development of short range order (SRO) in vapor-deposited films have been examined using this model. SRO in the simulated films increases with growth temperature up to the point at which the temperature corresponds to the energy of mixing, but we see no corresponding development of anisotropic SRO (preferential ordering of A-B pairs along the growth direction). Epitaxial (100) and (111) CoPt_3 films have been deposited over a range of growth temperatures from -50^circ C to 800^circC. Curie temperature (T_{rm c}) and saturation magnetization are dramatically enhanced in those films grown near 400^circ C over the values expected for the chemically homogeneous alloy. Magnetization data indicates that the high T _{rm c} films are inhomogeneous. These phenomena are interpreted as evidence of a previously unobserved magnetically driven miscibility gap in the Co-Pt phase diagram. Films grown near 400^circ C exhibit large uniaxial perpendicular magnetic anisotropy that cannot be accounted for by strain. The observed anisotropy coincides with the chemical phase separation and it seems likely that these two phenomena are related. Long range order (LRO) in the as-deposited films peaks at a growth temperature of 630^circC and then decreases with decreasing growth temperature. The decrease in LRO is either due to kinetic frustration or to competition from magnetically induced Co clustering. Theoretical phase diagrams based on the appropriate Blume-Emery-Griffiths Hamiltonian suggest the latter.

  11. Magnetic surface states in high polarization materials

    NASA Astrophysics Data System (ADS)

    Wu, Ning; Dowben, Peter A.

    2011-10-01

    Surfaces are often different materials, and typically have a different electronic structure from the bulk and since the dawn of surface science, surface-localized electronic states, surface states, have been extensively studied and investigated with growing accuracy. Of particular importance to spintronics are magnetic surface states. Interfaces will play a very important role in many spintronics devices, yet the interface properties are often ignored, poorly understood or badly characterized. For many nominally half metal materials, materials that in some ground state calculations exhibit 100% spin polarization, the magnetic surface states may significantly reduce the effective spin polarization. We review the magnetic surface states of several well known and often highly touted high spin polarized materials such as NiMnSb, Fe3O4, CoS2 and CrO2. Finally, we summarize surface state measurements of magnetoelectric antiferromagnets Cr2O3, which has electrically controllable net surface spins, a major complication to the study of CrO2 by photoemission.

  12. Magnetic mesoporous materials for removal of environmental wastes

    SciTech Connect

    Kim, Byoung Chan; Lee, Jinwoo; Um, Wooyong; Kim, Jaeyun; Joo, Jin; Lee, Jin Hyung; Kwak, Ja Hun; Kim, Jae Hyun; Lee, Changha; Lee, Hongshin; Addleman, Raymond S.; Hyeon, Taeghwan; Gu, Man Bock; Kim, Jungbae

    2011-09-15

    We have synthesized two different magnetic mesoporous materials that can be easily separated from aqueous solutions by applying a magnetic field. Synthesized magnetic mesoporous materials, Mag-SBA-15 (magnetic ordered mesoporous silica) and Mag-OMC (magnetic ordered mesoporous carbon), have a high loading capacity of contaminants due to high surface area of the supports and high magnetic activity due to the embedded iron oxide particles. Application of surface-modified Mag-SBA-15 was investigated for the collection of mercury from water. The mercury adsorption using Mag-SBA-15 was rapid during the initial contact time and reached a steady-state condition, with an uptake of approximately 97% after 7 hours. Application of Mag-OMC for collection of organics from water, using fluorescein as an easily trackable model analyte, was explored. The fluorescein was absorbed into Mag-OMC within minutes and the fluorescent intensity of solution was completely disappeared after an hour. In another application, Mag-SBA-15 was used as a host of tyrosinase, and employed as recyclable catalytic scaffolds for tyrosinase-catalyzed biodegradation of catechol. Tyrosinase aggregates in Mag-SBA-15, prepared in a two step process of tyrosinase adsorption and crosslinking, could be used repeatedly for catechol degradation with no serious loss of enzyme activity. Considering these results of cleaning up water from toxic inorganic, organic and biochemical contaminants, magnetic mesoporous materials have a great potential to be employed for the removal of environmental contaminants and potentially for the application in large-scale wastewater treatment plants.

  13. Size-Induced Chemical and Magnetic Ordering in Individual Fe-Au Nanoparticles

    SciTech Connect

    Mukherjee, Pinaki; Manchanda, Priyanka; Kumar, Pankaj; Zhou, Lin; Kramer, Matthew J; Kashyap, Arti; Skomski, Ralph; Sellmyer, David; Shield, Jeffrey E

    2014-08-26

    Formation of chemically ordered compounds of Fe and Au is inhibited in bulk materials due to their limited mutual solubility. However, here we report the formation of chemically ordered L12-type Fe3Au and FeAu3 compounds in Fe–Au sub-10 nm nanoparticles, suggesting that they are equilibrium structures in size-constrained systems. The stability of these L12-ordered Fe3Au and FeAu3 compounds along with a previously discovered L10-ordered FeAu has been explained by a size-dependent equilibrium thermodynamic model. Furthermore, the spin ordering of these three compounds has been computed using ab initio first-principle calculations. All ordered compounds exhibit a substantial magnetization at room temperature. The Fe3Au had a high saturation magnetization of about 143.6 emu/g with a ferromagnetic spin structure. The FeAu3 nanoparticles displayed a low saturation magnetization of about 11 emu/g. This suggests a antiferromagnetic spin structure, with the net magnetization arising from uncompensated surface spins. First-principle calculations using the Vienna ab initio simulation package (VASP) indicate that ferromagnetic ordering is energetically most stable in Fe3Au, while antiferromagnetic order is predicted in FeAu and FeAu3, consistent with the experimental results.

  14. Magnetism of directly ordered Sm-Co clusters

    SciTech Connect

    Balamurugan, B; Skomski, R; Li, XZ; Hadjipanayis, GC; Sellmyer, DJ

    2012-04-01

    Sm-Co bulk alloys have shown superior permanent-magnet properties, but research on Sm-Co nanoparticles is challenging because of the need to control particle size, size-distribution, crystalline ordering, and phase purity. In the present study, a cluster-deposition method was used to produce Sm-Co nanoparticles having desired crystal structures without the requirement of subsequent high-temperature thermal annealing. Poorly crystallized SmCo5 nanoparticles exhibit a low room-temperature coercivity of only 100 Oe, whereas crystalline SmCo5 and Sm2Co17 nanoparticles show room-temperature coercivities of 2000 and 750 Oe, respectively. The direct synthesis of Sm-Co nanoparticles having sizes of less than 10 nm and a high degree of atomic ordering is an important step toward creating nanoparticle building blocks for permanent-magnets and other significant applications. (C) 2012 American Institute of Physics. [doi:10.1063/1.3677668

  15. Emerging magnetic order in platinum atomic contacts and chains

    PubMed Central

    Strigl, Florian; Espy, Christopher; Bückle, Maximilian; Scheer, Elke; Pietsch, Torsten

    2015-01-01

    The development of atomic-scale structures revealing novel transport phenomena is a major goal of nanotechnology. Examples include chains of atoms that form while stretching a transition metal contact or the predicted formation of magnetic order in these chains, the existence of which is still debated. Here we report an experimental study of the magneto-conductance (MC) and anisotropic MC with atomic-size contacts and mono-atomic chains of the nonmagnetic metal platinum. We find a pronounced and diverse MC behaviour, the amplitude and functional dependence change when stretching the contact by subatomic distances. These findings can be interpreted as a signature of local magnetic order in the chain, which may be of particular importance for the application of atomic-sized contacts in spintronic devices of the smallest possible size. PMID:25649440

  16. Optimizing Energy Conversion: Magnetic Nano-materials

    NASA Astrophysics Data System (ADS)

    McIntyre, Dylan; Dann, Martin; Ilie, Carolina C.

    2015-03-01

    We present herein the work started at SUNY Oswego as a part of a SUNY 4E grant. The SUNY 4E Network of Excellence has awarded SUNY Oswego and collaborators a grant to carry out extensive studies on magnetic nanoparticles. The focus of the study is to develop cost effective rare-earth-free magnetic materials that will enhance energy transmission performance of various electrical devices (solar cells, electric cars, hard drives, etc.). The SUNY Oswego team has started the preliminary work for the project and graduate students from the rest of the SUNY 4E team (UB, Alfred College, Albany) will continue the project. The preliminary work concentrates on analyzing the properties of magnetic nanoparticle candidates, calculating molecular orbitals and band gap, and the fabrication of thin films. SUNY 4E Network of Excellence Grant.

  17. Magnetoresistance and magnetic ordering in praseodymium and neodymium hexaborides

    SciTech Connect

    Anisimov, M. A.; Bogach, A. V.; Glushkov, V. V.; Demishev, S. V.; Samarin, N. A.; Filipov, V. B.; Shitsevalova, N. Yu.; Kuznetsov, A. V.; Sluchanko, N. E.

    2009-11-15

    The magnetoresistance {Delta}{rho}/{rho} of single-crystal samples of praseodymium and neodymium hexaborides (PrB{sub 6} and NdB{sub 6}) has been measured at temperatures ranging from 2 to 20 K in a magnetic field of up to 80 kOe. The results obtained have revealed a crossover of the regime from a small negative magnetoresistance in the paramagnetic state to a large positive magnetoresistive effect in magnetically ordered phases of the PrB{sub 6} and NdB{sub 6} compounds. An analysis of the dependences {Delta}{rho}(H)/{rho} has made it possible to separate three contributions to the magnetoresistance for the compounds under investigation. In addition to the main negative contribution, which is quadratic in the magnetic field (-{Delta}{rho}/{rho} {proportional_to} H{sup 2}), a linear positive contribution ({Delta}{rho}/{rho} {proportional_to} H) and a nonlinear ferromagnetic contribution have been found. Upon transition to a magnetically ordered state, the linear positive component in the magnetoresistance of the PrB{sub 6} and NdB{sub 6} compounds becomes dominant, whereas the quadratic contribution to the negative magnetoresistance is completely suppressed in the commensurate magnetic phase of these compounds. The presence of several components in the magnetoresistance has been explained by assuming that, in the antiferromagnetic phases of PrB{sub 6} and NdB{sub 6}, ferromagnetic nanoregions (ferrons) are formed in the 5d band in the vicinity of the rareearth ions. The origin of the quadratic contribution to the negative magnetoresistance is interpreted in terms of the Yosida model, which takes into account scattering of conduction electrons by localized magnetic moments of rare-earth ions. Within the approach used, the local magnetic susceptibility {chi}{sub loc} has been estimated. It has been demonstrated that, in the temperature range T{sub N} < T < 20 K, the behavior of the local magnetic susceptibility {chi}{sub loc} for the compounds under investigation can

  18. Fingerprinting Magnetic Nanostructures by First Order Reversal Curves

    NASA Astrophysics Data System (ADS)

    Liu, Kai

    2007-03-01

    Realistic systems of magnetic nanostructures inevitably have inhomogeneities, which are manifested in distributions of magnetic properties, mixed magnetic phases, different magnetization reversal mechanisms, etc. The first order reversal curve (FORC) method [1-3] is ideally suited for ``fingerprinting'' such systems, both qualitatively and quantitatively. Here we present recent FORC studies on a few technologically important systems. In arrays of Fe nanodots [4], as the dot size decreases from 67 to 52nm, we have observed a vortex state to single-domain transition. Despite subtle changes in the major hysteresis loops, striking differences are seen in the FORC diagrams. The FORC method also gives quantitative measures of the magnetic phase fractions and vortex nucleation and annihilation fields. Furthermore, with decreasing temperature, it is more difficult to nucleate vortices within the dots and the single domain phase fraction increases. In exchange spring magnets [3], we have investigated the reversibility of the soft and hard layers and the interlayer exchange coupling. In FeNi/polycrystalline-FePt films, the FeNi and FePt layers reverse in a continuous process via a vertical spiral. In Fe/epitaxial-SmCo films, the reversal proceeds by a reversible rotation of the Fe soft layer, followed by an irreversible switching of the SmCo hard layer. As the SmCo partially demagnetizes, the Fe layer still remains reversible, as revealed by second order reversal curves (SORC). The exchange coupling between the two layers can be extracted as a function of the SmCo demagnetization state. These results demonstrate that FORC is a powerful method for magnetization reversal studies, due to its capability of capturing magnetic inhomogeneities, sensitivity to irreversible switching, and the quantitative phase information it can extract. Work done in collaboration with J. E. Davies, R. K. Dumas, J. Olamit, C. P. Li, I. V. Roshchin, I. K. Schuller, O. Hellwig, E. E. Fullerton, J. S

  19. Far-from-equilibrium magnetic granular layers: dynamic patterns, magnetic order and self-assembled swimmers

    NASA Astrophysics Data System (ADS)

    Snezhko, Alexey

    2010-03-01

    Ensembles of interacting particles subject to an external periodic forcing often develop nontrivial collective behavior and self-assembled dynamic patterns. We study emergent phenomena in magnetic granular ensembles suspended at a liquid-air and liquid-liquid interfaces and subjected to a transversal alternating magnetic field. Experiments reveal a new type of nontrivially ordered dynamic self-assembled structures (in particular, ``magnetic snakes'', ``asters'', ``clams'') emerging in such systems in a certain range of excitation parameters. These non-equilibrium dynamic structures emerge as a result of the competition between magnetic and hydrodynamic forces and have complex magnetic ordering. Transition between different self-assembled phases with parameters of external driving magnetic field is observed. I will show that above some frequency threshold magnetic snakes spontaneously break the symmetry of the self-induced surface flows (symmetry breaking instability) and turn into swimmers. Self-induced surface flows symmetry can be also broken in a controlled fashion by introduction of a large bead to a magnetic snake (bead-snake hybrid), that transforms it into a robust self-locomoting entity. Some features of the self-localized structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density and the Navier-Stokes equation for hydrodynamic flows.

  20. Magnetic cassette for radiographic film material

    SciTech Connect

    Dallas, D.

    1985-03-26

    A radiographic film cassette having a plurality of magnet components integral with the cassette holder for adhering the cassette to ferrous material in X-raying for defects in welds or fissures in shipyards, pipe lines, or the like. What is provided is a substantially flexible cassette envelope comprising first and second layers of radiographic intensifying screens with a sheet of radiographic film positioned therebetween. The cassette would be a cassette envelope constructed of waterproof fabric or other suitable material providing a light-free environment, and having the ability to flex around the curvature of the surface of a pipe or the like to be x-rayed. There is further provided a plurality of magnet components, preferably situated in each corner of the cassette envelope and flexibly attached thereto for overall adherence of the envelope to the surface of the pipe or the like to be x-rayed during the process.

  1. Magnetic order driven by orbital ordering in the semiconducting KFe1.5Se2

    NASA Astrophysics Data System (ADS)

    Jiang, Qing; Yao, Dao-Xin

    2016-04-01

    The two-orbital Hubbard model is studied numerically by using the Hartree-Fock approximation in both real space and momentum space, and the ground-state properties of the alkali metal iron selenide semiconducting KFe1.5Se2 are investigated. A rhombus-type Fe vacancy order with stripetype antiferromagnetic (AFM) order is found, as was observed in neutron scattering experiments [J. Zhao, et al., Phys. Rev. Lett. 109, 267003 (2012)]. Hopping parameters are obtained by fitting the experimentally observed stripe AFM phase in real space. These hopping parameters are then used to study the ground-state properties of the semiconductor in momentum space. It is found to be a strongly correlated system with a large on-site Coulomb repulsion U, similar to the AFM Mott insulator — the parent compound of copper oxide superconductors. We also find that the electronic occupation numbers and magnetizations in the d xz and d yz orbitals become different simultaneously when U > U c (˜3.4 eV), indicating orbital ordering. These results imply that the rotational symmetry between the two orbitals is broken by orbital ordering and thus drives the strong anisotropy of the magnetic coupling that has been observed by experiments and that the stripe-type AFM order in this compound may be caused by orbital ordering together with the observed large anisotropy.

  2. Metal-organic magnetic materials based on cobalt phthalocyanine and possibilities of their application in medicine

    NASA Astrophysics Data System (ADS)

    Harutyunyan, Avetik R.; Kuznetsov, Anatoly A.; Kuznetsov, Oleg A.; Kaliya, O. L.

    1999-04-01

    Cobalt phthalocyanines (CoPc), doped with sodium, exhibit ferromagnetic ordering at room temperature. Magnetic dilution or variation in dopant concentration leads to the formation of new magnetic materials. A proposed scheme of oncological disease treatment includes magnetic concentration of CoPc particles in the tumor zone and ascorbic acid injection into the organism for stimulation of oxidation reactions, which destroy the tumor.

  3. Magnetism in parent Fe-chalcogenides: quantum fluctuations select a plaquette order

    NASA Astrophysics Data System (ADS)

    Perkins, Natalia; Ducatman, Samuel; Chubukov, Andrey

    2013-03-01

    The analysis of magnetism in parent compounds of iron-based superconductors (FeSCs) is an integral part of the program to understand the origin of superconductivity in these materials. Here we analyze magnetic order in iron-chalcogenide Fe1+yTe - the parent compound of high-temperature superconductor Fe1+yTe1-xSex. Neutron scattering experiments show that magnetic order in this material contains components with momentum Q1 = (π / 2 , π / 2) and Q2 = (π / 2 , - π / 2) in Fe-only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works argued that spin order is a single- Q state (either Q1 or Q2). Such an order breaks rotational C4 symmetry and order spins into a double diagonal stripe. We show that quantum fluctuations actually select another order - a double Q plaquette state with equal weight of Q1 and Q2 components, which preserves C4 symmetry but breaks Z4 translational symmetry. We argue that the plaquette state is consistent with recent neutron scattering experiments on Fe1+yTe. supported by the grant NSF-DMR-0844115

  4. Study of the effect of magnetic ordering on order-disorder transitions in binary alloys

    NASA Astrophysics Data System (ADS)

    Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

    2014-06-01

    We set up a mean-field approximation in a random Ising model characterized by two order parameters: the local sublattice magnetization and a mean-field occupation variable which act as an order parameter for the order-disorder transition. In the effective model Hamiltonian the two order-parameters are coupled. We solve the coupled equations arising from this to describe the total phase diagram. The exchange energies for FeCo alloys have then been accurately obtained from first-principles based on the technique of orbital peeling and a Monte Carlo analysis using a coupled Metropolis-Kawasaki updating has been carried out. Our results reasonably successfully agree with earlier experimental data.

  5. Hysteretic behavior and magnetic ordering in CeRuSn

    NASA Astrophysics Data System (ADS)

    Mydosh, J. A.; Strydom, A. M.; Baenitz, M.; Chevalier, B.; Hermes, W.; Pöttgen, R.

    2011-02-01

    We report the thermodynamic and transport properties of the newly synthesized Ce-intermetallic compound CeRuSn. This ternary stannide possesses an unconventional structure with two Ce sites at room temperature which exhibit different valencies. Just below room temperature there are large thermal hysteretic effects in the magnetic susceptibility, in the specific heat, as well as in electronic and heat transport properties suggesting the formation of an incommensurate charge density wave modulation whose q vector changes as a function of temperature. Our measurements indicate that one site displays magnetic Ce3+ behavior while the other is a valence fluctuator. At 2.7 K antiferromagnetic long-range order occurs within one-half of the Ce sites, e.g., the magnetic entropy of the transition is (1)/(2)Rln2. Below TN a series of metamagnetic transitions takes place in rather small fields (~1-2 T), leaving a magnetically fluctuating background. Such behavior is unique among the many Ce-transition-metal compounds.

  6. Prominence material identified in magnetic cloud

    NASA Astrophysics Data System (ADS)

    Yao, Shuo; Marsch, E.; Tu, C.-Y.

    2010-03-01

    Coronal mass ejections (CMEs) often appear in coronagraph images as three-part structures composed of a leading bright front, a dark cavity and a bright core, which are believed to be associated with the sheath of compressed solar wind, the erupting magnetic flux rope and the cool and dense prominence plasma, respectively. However, a convincing identification of this three-part structure in the in-situ solar wind is extremely rare. Therefore, there still remains an open question as to what kind of signatures these three CME parts will reveal in the in situ data ([5]). Our work presents a clear identification of prominence material from in situ observations of the solar wind magnetic field and plasma parameters. The Helios 2 solar probe detected a magnetic cloud at 0.5 AU on 30 March 1976. In this event, we found a region with lower proton temperature and higher proton number density than outside, which is consistent with key features of a prominence as cold and dense solar material. During the same time we also found the occurrence of what possibly is He+, which is a special ion expected to occur only in prominence ejecta. Furthermore, the above observations were all made at a location related to the turning point of a bipolar structure of the interplanetary magnetic field, which is coincident with the notion that a solar prominence lies under the magnetic field lines of a bipolar region and is oriented along the neutral line. Furthermore, from our analysis of solar wind velocity distribution functions (VDFs) we can confirm by kinetic evidence that the plasma inside this special region is colder and more isotropic than outside. Above all, our observations circumstantially confirm the 3-part CME model as described in references [10] and [7].

  7. Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature

    PubMed Central

    Phillips, L. C.; Cherifi, R. O.; Ivanovskaya, V.; Zobelli, A.; Infante, I. C.; Jacquet, E.; Guiblin, N.; Ünal, A. A.; Kronast, F.; Dkhil, B.; Barthélémy, A.; Bibes, M.; Valencia, S.

    2015-01-01

    Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics. PMID:25969926

  8. Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature

    NASA Astrophysics Data System (ADS)

    Phillips, L. C.; Cherifi, R. O.; Ivanovskaya, V.; Zobelli, A.; Infante, I. C.; Jacquet, E.; Guiblin, N.; Ünal, A. A.; Kronast, F.; Dkhil, B.; Barthélémy, A.; Bibes, M.; Valencia, S.

    2015-05-01

    Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics.

  9. Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature.

    PubMed

    Phillips, L C; Cherifi, R O; Ivanovskaya, V; Zobelli, A; Infante, I C; Jacquet, E; Guiblin, N; Ünal, A A; Kronast, F; Dkhil, B; Barthélémy, A; Bibes, M; Valencia, S

    2015-01-01

    Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics. PMID:25969926

  10. Electric-field control of magnetic order above room temperature.

    PubMed

    Cherifi, R O; Ivanovskaya, V; Phillips, L C; Zobelli, A; Infante, I C; Jacquet, E; Garcia, V; Fusil, S; Briddon, P R; Guiblin, N; Mougin, A; Ünal, A A; Kronast, F; Valencia, S; Dkhil, B; Barthélémy, A; Bibes, M

    2014-04-01

    Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics. PMID:24464245

  11. Electric-field control of magnetic order above room temperature

    NASA Astrophysics Data System (ADS)

    Cherifi, R. O.; Ivanovskaya, V.; Phillips, L. C.; Zobelli, A.; Infante, I. C.; Jacquet, E.; Garcia, V.; Fusil, S.; Briddon, P. R.; Guiblin, N.; Mougin, A.; Ünal, A. A.; Kronast, F.; Valencia, S.; Dkhil, B.; Barthélémy, A.; Bibes, M.

    2014-04-01

    Controlling magnetism by means of electric fields is a key issue for the future development of low-power spintronics. Progress has been made in the electrical control of magnetic anisotropy, domain structure, spin polarization or critical temperatures. However, the ability to turn on and off robust ferromagnetism at room temperature and above has remained elusive. Here we use ferroelectricity in BaTiO3 crystals to tune the sharp metamagnetic transition temperature of epitaxially grown FeRh films and electrically drive a transition between antiferromagnetic and ferromagnetic order with only a few volts, just above room temperature. The detailed analysis of the data in the light of first-principles calculations indicate that the phenomenon is mediated by both strain and field effects from the BaTiO3. Our results correspond to a magnetoelectric coupling larger than previous reports by at least one order of magnitude and open new perspectives for the use of ferroelectrics in magnetic storage and spintronics.

  12. Magnetic branes in third order Lovelock-Born-Infeld gravity

    SciTech Connect

    Dehghani, M. H.; Bostani, N.; Hendi, S. H.

    2008-09-15

    Considering both the nonlinear invariant terms constructed by the electromagnetic field and the Riemann tensor in gravity action, we obtain a new class of (n+1)-dimensional magnetic brane solutions in third order Lovelock-Born-Infeld gravity. This class of solutions yields a spacetime with a longitudinal nonlinear magnetic field generated by a static source. These solutions have no curvature singularity and no horizons but have a conic geometry with a deficit angle {delta}. We find that, as the Born-Infeld parameter decreases, which is a measure of the increase of the nonlinearity of the electromagnetic field, the deficit angle increases. We generalize this class of solutions to the case of spinning magnetic solutions and find that, when one or more rotation parameters are nonzero, the brane has a net electric charge which is proportional to the magnitude of the rotation parameters. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes. We found that the conserved quantities do not depend on the Born-Infeld parameter, which is evident from the fact that the effects of the nonlinearity of the electromagnetic fields on the boundary at infinity are wiped away. We also find that the properties of our solution, such as deficit angle, are independent of Lovelock coefficients.

  13. Nature of magnetic ordering in Ni(OH)2 nanoplates

    NASA Astrophysics Data System (ADS)

    Rall, James; Seehra, Mohindar

    2009-03-01

    Nickel hydroxides are important for their potential applications in rechargeable batteries and as precursors for NiO and Ni catalysts. β--Ni(OH)2 has the CdI2 layered structure with Ni atoms forming a hexagonal unit cell. Here, we report on the magnetic ordering in 17 nm x 4 nm nanosheets of β--Ni(OH)2 . Measurements of the magnetization M as a function of temperature (2K to 300K) and magnetic field H up to ±65kOe are reported. M vs. T data in H =100 Oe for the ZFC case shows a peak in M at TN = 24 K characteristic of antiferromagnetic (AF) ordering; however for T > TN, the Curie-Weiss (χ = C/(T - θ)) fit yields θ = 26K characteristic of ferromagnetism. Following Takada (J. Phys. Soc. Jpn. 21, 2745, 1966), we measured M vs. H loops from T = 2K to 25K and observed a metamagnetic transition at Hc = 56 kOe at 2K, with Hc decreasing with increasing T. These results suggests strong ferromagnetic coupling among Ni within (001) sheets and a weaker antiferromagnetic coupling in the neighboring (001) sheets, and [001] as the easy axis. This model is used to determine the exchange constants consistent with the observed Curie-Weiss variation.

  14. Ordering and thermal excitations in dipolar coupled single domain magnet arrays (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Östman, Erik; Arnalds, Unnar; Kapaklis, Vassilios; Hjörvarsson, Björgvin

    2015-09-01

    For a small island of a magnetic material the magnetic state of the island is mainly determined by the exchange interaction and the shape anisotropy. Two or more islands placed in close proximity will interact through dipolar interactions. The state of a large system will thus be dictated by interactions at both these length scales. Enabling internal thermal fluctuations, e.g. by the choice of material, of the individual islands allows for the study of thermal ordering in extended nano-patterned magnetic arrays [1,2]. As a result nano-magnetic arrays represent an ideal playground for the study of physical model systems. Here we present three different studies all having used magneto-optical imaging techniques to observe, in real space, the order of the systems. The first study is done on a square lattice of circular islands. The remanent magnetic state of each island is a magnetic vortex structure and we can study the temperature dependence of the vortex nucleation and annihilation fields [3]. The second are long chains of dipolar coupled elongated islands where the magnetization direction in each island only can point in one of two possible directions. This creates a system which in many ways mimics the Ising model [4] and we can relate the correlation length to the temperature. The third one is a spin ice system where elongated islands are placed in a square lattice. Thermal excitations in such systems resemble magnetic monopoles [2] and we can investigate their properties as a function of temperature and lattice parameters. [1] V. Kapaklis et al., New J. Phys. 14, 035009 (2012) [2] V. Kapaklis et al., Nature Nanotech 9, 514(2014) [3] E. Östman et al.,New J. Phys. 16, 053002 (2014) [4] E. Östman et al.,Thermal ordering in mesoscopic Ising chains, In manuscript.

  15. Ising-like chain magnetism, Arrhenius magnetic relaxation, and case against 3D magnetic ordering in β-manganese phthalocyanine (C₃₂H₁₆MnN₈).

    PubMed

    Wang, Zhengjun; Seehra, Mohindar S

    2016-04-01

    Previous magnetic studies in the organic semiconductor β-manganese phthalocyanine (β-MnPc) have reported it to be a canted ferromagnet below T(C)  ≈  8.6 K. However, the recent result of the lack of a λ-type anomaly in the specific heat versus temperature data near the quoted T(C) has questioned the presence of long-range 3-dimensional (3D) magnetic ordering in this system. In this paper, detailed measurements and analysis of the temperature (2 K-300 K) and magnetic field (up to 90 kOe) dependence of the dc and ac magnetic susceptibilities in a powder sample of β-MnPc leads us to conclude that 3D long-range magnetic ordering is absent in this material. This is supported by the Arrott plots and the lack of a peak in the ac susceptibilities, χ' and χ″, near the quoted T(C). Instead, the system can be best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J/k(B)  =  2.6 K and the single ion anisotropy energy parameter |D|/k(B)  =  8.3 K. The absence of 3D long range order is consistent with the measured |D|/  >  J. PMID:26954989

  16. Ising-like chain magnetism, Arrhenius magnetic relaxation, and case against 3D magnetic ordering in β-manganese phthalocyanine (C32H16MnN8)

    NASA Astrophysics Data System (ADS)

    Wang, Zhengjun; Seehra, Mohindar S.

    2016-04-01

    Previous magnetic studies in the organic semiconductor β-manganese phthalocyanine (β-MnPc) have reported it to be a canted ferromagnet below T C  ≈  8.6 K. However, the recent result of the lack of a λ-type anomaly in the specific heat versus temperature data near the quoted T C has questioned the presence of long-range 3-dimensional (3D) magnetic ordering in this system. In this paper, detailed measurements and analysis of the temperature (2 K-300 K) and magnetic field (up to 90 kOe) dependence of the dc and ac magnetic susceptibilities in a powder sample of β-MnPc leads us to conclude that 3D long-range magnetic ordering is absent in this material. This is supported by the Arrott plots and the lack of a peak in the ac susceptibilities, χ‧ and χ″, near the quoted T C. Instead, the system can be best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J/k B  =  2.6 K and the single ion anisotropy energy parameter |D|/k B  =  8.3 K. The absence of 3D long range order is consistent with the measured \\mid D\\mid   >  J.

  17. Magnetic ordering in fullerene charge-transfer complexes

    NASA Astrophysics Data System (ADS)

    Sato, Tohru; Yamabe, Tokio; Tanaka, Kazuyoshi

    1997-07-01

    We have determined the ground states of the charge-transfer (CT) complexes in which the energy levels of the highest occupied molecular orbital (HOMO) of donors and the lowest unoccupied MO (LUMO) of acceptors are closely located, and examined some fullerene complexes consisting of C60, C70, tetrakis(dimethylamino)ethylene (TDAE), and 1,1',3,3'-tetramethyl-Δ2,2'-bi(imidazolidine) (TMBI). The observed magnetic properties of TDAE-C60, TMBI-C60, and TDAE-C70 can be accounted for by employing realistic parameters. The effective Hamiltonian including up to the fourth-order perturbation has also been derived in the fourfold degenerate model space. The effective Hamiltonian can plausibly reproduce the magnetic phase diagram obtained by the variational treatment of TDAE-C60. It has been shown that the third and the fourth processes contribute to the stabilization of the antiferromagnetic state.

  18. Electrodeposition of highly uniform magnetic nanoparticle arrays in ordered alumite

    NASA Astrophysics Data System (ADS)

    Sun, Ming; Zangari, Giovanni; Shamsuzzoha, Mohammad; Metzger, Robert M.

    2001-05-01

    We report the fabrication of nanometer scale ordered arrays of magnetic cylindrical nanoparticles with low aspect ratio (height/radius a=0.2-7) and ultrahigh uniformity. Anodization and electrochemical deposition are employed for template synthesis and metal particle growth, respectively. Particle uniformity is achieved by an electrodeposition scheme, utilizing pulse reverse voltage wave forms to control nucleation and growth of the particles. The resulting nanoparticles are polycrystalline and grains are randomly oriented. The magnetic properties of the array are dominated by particle shape and by interparticle magnetostatic interactions. A very clear transition of the anisotropy from perpendicular to in plane is observed at an aspect ratio a of about two. The arrays exhibit good thermal stability, demonstrating a great potential of these structures as future recording media in a patterned scheme. The pulse reverse electrodeposition technique shows great promise for the synthesis of nanostructures of various nature.

  19. Proximity-driven enhanced magnetic order at ferromagnetic-insulator-magnetic-topological-insulator interface

    SciTech Connect

    Li, Mingda; Zhu, Yimei; Chang, Cui -Zu; Kirby, B. J.; Jamer, Michelle E.; Cui, Wenping; Wu, Lijun; Wei, Peng; Heiman, Don; Li, Ju; Moodera, Jagadeesh S.; Katmis, Ferhat

    2015-08-17

    Magnetic exchange driven proximity effect at a magnetic-insulator–topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. In this study, we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb2–xVxTe3 hybrid heterostructure, where V doping is used to drive the TI (Sb2Te3) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.

  20. Proximity-driven enhanced magnetic order at ferromagnetic-insulator-magnetic-topological-insulator interface

    DOE PAGESBeta

    Li, Mingda; Zhu, Yimei; Chang, Cui -Zu; Kirby, B. J.; Jamer, Michelle E.; Cui, Wenping; Wu, Lijun; Wei, Peng; Heiman, Don; Li, Ju; et al

    2015-08-17

    Magnetic exchange driven proximity effect at a magnetic-insulator–topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. In this study, we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS/Sb2–xVxTe3 hybrid heterostructure, where V doping is used to drive the TI (Sb2Te3) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.

  1. Proximity-Driven Enhanced Magnetic Order at Ferromagnetic-Insulator-Magnetic-Topological-Insulator Interface

    NASA Astrophysics Data System (ADS)

    Li, Mingda; Chang, Cui-Zu; Kirby, Brian. J.; Jamer, Michelle E.; Cui, Wenping; Wu, Lijun; Wei, Peng; Zhu, Yimei; Heiman, Don; Li, Ju; Moodera, Jagadeesh S.

    2015-08-01

    Magnetic exchange driven proximity effect at a magnetic-insulator-topological-insulator (MI-TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI/magnetic-TI EuS /Sb2 -xVx Te3 hybrid heterostructure, where V doping is used to drive the TI (Sb2 Te3 ) magnetic. We observe an artificial antiferromagneticlike structure near the MI-TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping in a hybrid heterostructure provides insights into the engineering of magnetic ordering.

  2. Absence of Magnetic Order and Persistent Spin Dynamics in Tb2Ge2O7

    NASA Astrophysics Data System (ADS)

    Hallas, Alannah; Arevalo-Lopez, Angel; Wilson, Murray; Liu, Lian; Attfield, J. Paul; Uemura, Yasutomo; Wiebe, Chris; Luke, Graeme

    2015-03-01

    The terbium pyrochlores exhibit many unique magnetic properties, which has generated significant interest in this family of frustrated materials. A candidate spin liquid, Tb2Ti2O7 fails to magnetically order, despite strong antiferromagnetic correlations. The application of external pressure has been found to produce partial antiferromagnetic order in Tb2Ti2O7. Recently, we synthesized a new member of this family, Tb2Ge2O7. Due to the large ionic radii decrease from titanium to germanium, Tb2Ge2O7 can be considered a chemical pressure analog of Tb2Ti2O7. However, neutron scattering measurements revealed an absence of magnetic order in Tb2Ge2O7 down to 20 mK and dominant ferromagnetic correlations. Now, we have investigated the low temperature magnetism of Tb2Ge2O7 with muon spin rotation. Our zero field μSR measurements confirm an absence of static order in Tb2Ge2O7. We find a sharp increase in magnetic correlations below 10 K and persistent spin dynamics down to 25 mK. Our longitudinal field μSR measurements on Tb2Ge2O7 at 25 mK are consistent with a system of fluctuating moments, with a fluctuation rate of 11 MHz. This fluctuation rate is nearly temperature independent below 2.5 K.

  3. Imaging Magnetic Order and Frustration on Distinct Sublattices in Artificial Quasicrystals

    NASA Astrophysics Data System (ADS)

    Farmer, Barry; Balk, Andrew; Bhat, Vinayaka; Teipel, Eric; Smith, Nathan; Unguris, John; Hastings, Jeffrey Todd; de Long, Lance

    Scanning electron microscopy with polarization analysis (SEMPA) was used to acquire direct images of as-grown magnetization textures for Permalloy thin films patterned into Penrose P2 tilings (P2T). Simulations yield a low-energy manifold of textures composed of two distinct, perfectly ordered sublattices and two sublattices that remain frustrated. As-grown P2T samples exhibited large domains of the two ordered sublattices in the room-temperature SEMPA images. Higher resolution Monte Carlo simulations based on long-range dipolar interactions predict the two frustrated sublattices will order. These results indicate 3rd generation P2T will offer the first example of magnetic order in a quasicrystalline material. Research at University of Kentucky supported by U.S. Department of Energy Grant No. DE-FG02-97ER-45653, and U.S. National Science Foundation Grant No. DMR-1506979.

  4. SYNTHESIS AND CHARACTERIZATION OF ADVANCED MAGNETIC MATERIALS

    SciTech Connect

    Monica Sorescu

    2004-09-22

    The work described in this grant report was focused mainly on the properties of novel magnetic intermetallics. In the first project, we synthesized several 2:17 intermetallic compounds, namely Nd{sub 2}Fe{sub 15}Si{sub 2}, Nd{sub 2}Fe{sub 15}Al{sub 2}, Nd{sub 2}Fe{sub 15}SiAl and Nd{sub 2}Fe{sub 15}SiMn, as well as several 1:12 intermetallic compounds, such as NdFe{sub 10}Si{sub 2}, NdFe{sub 10}Al{sub 2}, NdFe{sub 10}SiAl and NdFe{sub 10}MnAl. In the second project, seven compositions of Nd{sub x}Fe{sub 100-x-y}B{sub y} ribbons were prepared by a melt spinning method with Nd and B content increasing from 7.3 and 3.6 to 11 and 6, respectively. The alloys were annealed under optimized conditions to obtain a composite material consisting of the hard magnetic Nd{sub 2}Fe{sub 14}B and soft magnetic {alpha}-Fe phases, typical of a spring magnet structure. In the third project, intermetallic compounds of the type Zr{sub 1}Cr{sub 1}Fe{sub 1}T{sub 0.8} with T = Al, Co and Fe were subjected to hydrogenation. In the fourth project, we performed three crucial experiments. In the first experiment, we subjected a mixture of Fe{sub 3}O{sub 4} and Fe (80-20 wt %) to mechanochemical activation by high-energy ball milling, for time periods ranging from 0.5 to 14 hours. In the second experiment, we ball-milled Fe{sub 3}O{sub 4}:Co{sup 2+} (x = 0.1) for time intervals between 2.5 and 17.5 hours. Finally, we exposed a mixture of Fe{sub 3}O{sub 4} and Co (80-20 wt %) to mechanochemical activation for time periods ranging from 0.5 to 10 hours. In all cases, the structural and magnetic properties of the systems involved were elucidated by X-ray diffraction (XRD), Moessbauer spectroscopy and hysteresis loop measurements. The four projects resulted in four papers, which were published in Intermetallics, IEEE Transactions on Magnetics, Journal of Materials Science Letters and Materials Chemistry and Physics. The contributions reveal for the first time in literature the effect of

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

    DOE PAGESBeta

    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]/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

  6. Magnetic field-induced switching of magnetic ordering in SrFeO3- δ

    NASA Astrophysics Data System (ADS)

    Mohan Radheep, D.; Shanmugapriya, K.; Palanivel, Balan; Murugan, Ramaswamy

    2016-08-01

    The oxygen-deficient strontium iron oxide SrFeO3- δ (SFO) exhibits richness in the phase diagram over a broad range of temperatures and for other external parameters. Room-temperature X-ray diffraction and Raman spectrum reveals that the structure of synthesized SFO system consists of two mixed phases, i.e., major orthorhombic and minor tetragonal phases. The low-temperature Raman and vibrating sample magnetometer measurements indicated a structural transition below 253 K. The magnetic property of the synthesized SFO for various external magnetic field (up to 5 T) reveals possible variation in oxygen stoichiometry. Also, the application of external H increases Neel transition temperature ( T N), suppresses the hysteresis width ( W H), and thus weakens the first-order nature of the transition. Our analysis revealed the vanishing of hysteresis and the first-order antiferromagnetic transition becomes a crossover above a critical magnetic field H CR ≈ 5 T. Possible switching of magnetic ordering and oxidation state observed in same system enhances interest in related compounds which may be used in magnetic sensors and other magnetic switching devices.

  7. Characteristics of anthropogenic magnetic materials in roadside dusts in Seoul, Korea using thermo-magnetic behaviors and electron microscope observations

    NASA Astrophysics Data System (ADS)

    Kim, W.; Doh, S.; Park, Y.

    2006-12-01

    It has been previously reported that magnetic concentration parameter (e.g., magnetic susceptibility) has a close affinity with heavy metal concentration in roadside dust of the Seoul metropolitan area. Magnetic concentration and magnetic particle size show systematic seasonal fluctuations (high and large during winter; low and small in summer) because of seasonal influx variation of anthropogenic magnetic materials. These observations suggest that magnetic parameters could be utilized as a proxy method of assessing heavy metal pollution in urban areas. In order to characterize anthropogenic magnetic materials and to find their potential sources, magnetic extracts from roadside dusts of Seoul metropolitan area were subject to SEM observation, elemental analysis (EDS), and thermo-magnetic experiments. Magnetic materials from vehicle emission and abraded brake lining were also observed for the comparison. The magnetic particles can be classified based on the morphology and elemental composition of the particles. Magnetic spherules are the most frequently observed type of particle throughout the study area. These particles are often associated with the elemental C and Al-Ca-Na-Si materials, and are believed to be the product of fossil fuel combustions in power plants, industries, and domestic heating systems. Aggregates of iron-oxides and Fe-C-S materials are probably originated from vehicle emission, while aggregates of pure Fe and Al-Ca-Fe-K-Mg-Si materials appear to be derived from abrasion of motor vehicle brake system. These aggregates are frequently observed in industrial sections of the city as well as areas of heavy traffic. Angular magnetic particles accompanied by silicates are only observed in park area and probably formed by natural process such as pedogenesis or weathering. Thermo-magnetic experiments indicate that the major magnetic phase in the studied samples is magnetite. Two distinctive behaviors observed are the presence of low Curie temperature

  8. Magnetic Resonance Studies of Energy Storage Materials

    NASA Astrophysics Data System (ADS)

    Vazquez Reina, Rafael

    In today's society there is high demand to have access to energy for portable devices in different forms. Capacitors with high performance in small package to achieve high charge/discharge rates, and batteries with their ability to store electricity and make energy mobile are part of this demand. The types of internal dielectric material strongly affect the characteristics of a capacitor, and its applications. In a battery, the choice of the electrolyte plays an important role in the Solid Electrolyte Interphase (SEI) formation, and the cathode material for high output voltage. Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR) spectroscopy are research techniques that exploit the magnetic properties of the electron and certain atomic nuclei to determine physical and chemical properties of the atoms or molecules in which they are contained. Both EPR and NMR spectroscopy technique can yield meaningful structural and dynamic information. Three different projects are discussed in this dissertation. First, High energy density capacitors where EPR measurements described herein provide an insight into structural and chemical differences in the dielectric material of a capacitor. Next, as the second project, Electrolyte solutions where an oxygen-17 NMR study has been employed to assess the degree of preferential solvation of Li+ ions in binary mixtures of EC (ethylene carbonate) and DMC (dimethyl carbonate) containing LiPF6 (lithium hexafluo-rophosphate) which may be ultimately related to the SEI formation mechanism. The third project was to study Bismuth fluoride as cathode material for rechargeable batteries. The objective was to study 19F and 7Li MAS NMR of some nanocomposite cathode materials as a conversion reaction occurring during lithiation and delithation of the BiF3/C nanocomposite.

  9. The superexchange interactions and magnetic ordering in low-dimentional ludwigite Ni5GeB2O10

    NASA Astrophysics Data System (ADS)

    Sofronova, S. N.; Bezmaternykh, L. N.; Eremin, E. V.; Nazarenko, I. I.; Volkov, N. V.; Kartashev, A. V.; Moshkina, E. M.

    2016-03-01

    The ludwigite Ni5Ge(BO5)2 belongs to a family of oxyborates which have low-dimensional subunits in the form of three-leg ladders unit structure. This material was studied by magnetic and thermodynamic measurements. Ni5Ge(BO5)2 does not show full long-range magnetic order, but one goes into a partial ordering or spin-glass state at 87 K. The superexchange interactions were calculated in the framework of a simple indirect coupling model. Different models of magnetic structure of Ni5Ge(BO5)2 and its unique magnetic behaviour was discussed.

  10. REACT: Alternatives to Critical Materials in Magnets

    SciTech Connect

    2012-01-01

    REACT Project: The 14 projects that comprise ARPA-E’s REACT Project, short for “Rare Earth Alternatives in Critical Technologies”, are developing cost-effective alternatives to rare earths, the naturally occurring minerals with unique magnetic properties that are used in electric vehicle (EV) motors and wind generators. The REACT projects will identify low-cost and abundant replacement materials for rare earths while encouraging existing technologies to use them more efficiently. These alternatives would facilitate the widespread use of EVs and wind power, drastically reducing the amount of greenhouse gases released into the atmosphere.

  11. Magnetic Order in the Mixed-Spin Triangular Lattice Antiferromagnet NaxMnO2

    NASA Astrophysics Data System (ADS)

    Chisnell, Robin; Parshall, Dan; Li, Xin; Larson, Amber; Suzuki, Takehito; Checkelsky, Joseph; Rodriguez, Efrain; Lynn, Jeffrey

    NaxTMO2 (TM = transition metal) materials consist of alternating layers of Na and TM ions with the TM ions arranged on a geometrically frustrated triangular lattice. Na can be easily and reversibly removed from these materials, making them of interest for application in rechargeable batteries and allowing for exploration of their rich phase diagrams as a function of Na concentration. Na ordering is an important factor in ground state selection, and is driven by electrostatic interactions in many NaxTMO2 systems. The TM = Mn series differs in that Na ordering is driven by a cooperative Jahn-Teller effect, due to the coexistence of Jahn-Teller active Mn3+ and inactive Mn4+ ions. This effect also results in an ordered arrangement of the Mn3+ and Mn4+ ions, and thus of spin-2 and spin-3/2 moments. For x = 5/8, we have recently shown the coexistence of charge and magnetic stripe orderings. Here, we present the results of neutron diffraction measurements performed on single crystal samples of NaxMnO2 and discuss the details of the magnetic structure in the magnetically ordered phase.

  12. Magnetic Compensation for Second-Order Doppler Shift in LITS

    NASA Technical Reports Server (NTRS)

    Burt, Eric; Tjoelker, Robert

    2008-01-01

    The uncertainty in the frequency of a linear-ion-trap frequency standard (LITS) can be reduced substantially by use of a very small magnetic inhomogeneity tailored to compensate for the residual second-order Doppler shift. An effect associated with the relativistic time dilatation, one cause of the second-order Doppler shift, is ion motion that is attributable to the trapping radio-frequency (RF)electromagnetic field used to trap ions. The second-order Doppler shift is reduced by using a multi-pole trap; however it is still the largest source of systematic frequency shift in the latest generation of LITSs, which are among the most stable clocks in the world. The present compensation scheme reduces the frequency instability of the affected LITS to about a tenth of its previous value. The basic principles of prior generation LITSs were discussed in several prior NASA Tech Briefs articles. Below are recapitulated only those items of basic information necessary to place the present development in context. A LITS includes a microwave local oscillator, the frequency of which is stabilized by comparison with the frequency of the ground state hyperfine transition of 199Hg+ ions. The comparison involves a combination of optical and microwave excitation and interrogation of the ions in a linear ion trap in the presence of a nominally uniform magnetic field. In the current version of the LITS, there are two connected traps (see figure): (1) a quadrupole trap wherein the optical excitation and measurement take place and (2) a 12-pole trap (denoted the resonance trap), wherein the microwave interrogation takes place. The ions are initially loaded into the quadrupole trap and are thereafter shuttled between the two traps. Shuttling ions into the resonance trap allows sensitive microwave interrogation to take place well away from loading interference. The axial magnetic field for the resonance trap is generated by an electric current in a finely wound wire coil surrounded by

  13. Novel diluted magnetic semiconductor materials based on zinc oxide

    NASA Astrophysics Data System (ADS)

    Chakraborti, Deepayan

    The primary aim of this work was to develop a ZnO based diluted magnetic semiconductor (DMS) materials system which displays ferromagnetism above room temperature and to understand the origin of long-range ferromagnetic ordering in these systems. Recent developments in the field of spintronics (spin based electronics) have led to an extensive search for materials in which semiconducting properties can be integrated with magnetic properties to realize the objective of successful fabrication of spin-based devices. For these devices we require a high efficiency of spin current injection at room temperature. Diluted magnetic semiconductors (DMS) can serve this role, but they should not only display room temperature ferromagnetism (RTFM) but also be capable of generating spin polarized carriers. Transition metal doped ZnO has proved to be a potential candidate as a DMS showing RTFM. The origin of ferromagnetic ordering in ZnO is still under debate. However, the presence of magnetic secondary phases, composition fluctuations and nanoclusters could also explain the observation of ferromagnetism in the DMS samples. This encouraged us to investigate Cu-doped(+ spin in the 2+ valence state) ZnO system as a probable candidate exhibiting RTFM because neither metallic Cu nor its oxides (Cu2O or CuO) are ferromagnetic. The role of defects and free carriers on the ferromagnetic ordering of Cu-doped ZnO thin films was studied to ascertain the origin of ferromagnetism in this system. A novel non-equilibrium Pulsed Laser Deposition technique has been used to grow high quality epitaxial thin films of Cu:ZnO and (Co,Cu):ZnO on c-plane Sapphire by domain matching epitxay. Both the systems showed ferromagnetic ordering above 300K but Cu ions showed a much stronger ferromagnetic ordering than Co, especially at low concentrations (1-2%) of Cu where we realized near 100% polarization. But, the incorporation of Cu resulted in a 2-order of magnitude rise in the resistivity from 10-1 to 101

  14. Magnetic order near 270 K in mineral and synthetic Mn2FeSbO6 ilmenite

    NASA Astrophysics Data System (ADS)

    Mathieu, R.; Ivanov, S. A.; Bazuev, G. V.; Hudl, M.; Lazor, P.; Solovyev, I. V.; Nordblad, P.

    2011-05-01

    The structural and magnetic properties of Mn2FeSbO6 single-crystalline mineral and ceramic samples synthesized under thermobaric treatment have been investigated, and compared to theoretical predictions based on first-principles electronic structure calculations. This ilmenite system displays a sharp magnetic transition just below the room temperature related to a ferrimagnetic ordering of the Mn2+ and Fe3+ cations, which makes Mn2FeSbO6 a promising candidate for designing functional magnetic materials.

  15. Magnetic Performance of a Nanocomposite Permanent Material

    NASA Astrophysics Data System (ADS)

    Liu, Min; Han, Guang-Bing; Gao, Ru-Wei

    2011-08-01

    We build a sandwiched structure model in which the intergranular phase (IP) is homogeneously distributed between soft and hard magnetic grains, and gives a continuously anisotropic expression of the coupling part under the assumption that the IP weakens the intergrain exchange-coupling interaction. Based on the idea that the hardening mechanism is of the pinning type, we calculate the effect of the IP's thickness d and its anisotropy constant K1(0) on the intrinsic coercivity of a nanocomposite permanent material. The calculated results indicate that the domain wall goes twice through irreversible domain wall displacement during the process of moving from soft to hard magnetic grains, and the intrinsic coercivity increases with increasing d, but decreases with increasing K1(0). When d and K1(0) take 2 nm and 0.7Kh, respectively, with Kh being the anisotropy constant in the inner part of the hard magnetic grain, the calculated intrinsic coercivity is in good agreement with the experimental data.

  16. Second order anisotropy contribution in perpendicular magnetic tunnel junctions

    PubMed Central

    Timopheev, A. A.; Sousa, R.; Chshiev, M.; Nguyen, H. T.; Dieny, B.

    2016-01-01

    Hard-axis magnetoresistance loops were measured on perpendicular magnetic tunnel junction pillars of diameter ranging from 50 to 150 nm. By fitting these loops to an analytical model, the effective anisotropy fields in both free and reference layers were derived and their variations in temperature range between 340 K and 5 K were determined. It is found that a second-order anisotropy term of the form −K2cos4θ must be added to the conventional uniaxial –K1cos2θ term to explain the experimental data. This higher order contribution exists both in the free and reference layers. At T = 300 K, the estimated −K2/K1 ratios are 0.1 and 0.24 for the free and reference layers, respectively. The ratio is more than doubled at low temperatures changing the ground state of the reference layer from “easy-axis” to “easy-cone” regime. The easy-cone regime has clear signatures in the shape of the hard-axis magnetoresistance loops. The existence of this higher order anisotropy was also confirmed by ferromagnetic resonance experiments on FeCoB/MgO sheet films. It is of interfacial nature and is believed to be due to spatial fluctuations at the nanoscale of the first order anisotropy parameter at the FeCoB/MgO interface. PMID:27246631

  17. Second order anisotropy contribution in perpendicular magnetic tunnel junctions.

    PubMed

    Timopheev, A A; Sousa, R; Chshiev, M; Nguyen, H T; Dieny, B

    2016-01-01

    Hard-axis magnetoresistance loops were measured on perpendicular magnetic tunnel junction pillars of diameter ranging from 50 to 150 nm. By fitting these loops to an analytical model, the effective anisotropy fields in both free and reference layers were derived and their variations in temperature range between 340 K and 5 K were determined. It is found that a second-order anisotropy term of the form -K2cos(4)θ must be added to the conventional uniaxial -K1cos(2)θ term to explain the experimental data. This higher order contribution exists both in the free and reference layers. At T = 300 K, the estimated -K2/K1 ratios are 0.1 and 0.24 for the free and reference layers, respectively. The ratio is more than doubled at low temperatures changing the ground state of the reference layer from "easy-axis" to "easy-cone" regime. The easy-cone regime has clear signatures in the shape of the hard-axis magnetoresistance loops. The existence of this higher order anisotropy was also confirmed by ferromagnetic resonance experiments on FeCoB/MgO sheet films. It is of interfacial nature and is believed to be due to spatial fluctuations at the nanoscale of the first order anisotropy parameter at the FeCoB/MgO interface. PMID:27246631

  18. Second order anisotropy contribution in perpendicular magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Timopheev, A. A.; Sousa, R.; Chshiev, M.; Nguyen, H. T.; Dieny, B.

    2016-06-01

    Hard-axis magnetoresistance loops were measured on perpendicular magnetic tunnel junction pillars of diameter ranging from 50 to 150 nm. By fitting these loops to an analytical model, the effective anisotropy fields in both free and reference layers were derived and their variations in temperature range between 340 K and 5 K were determined. It is found that a second-order anisotropy term of the form ‑K2cos4θ must be added to the conventional uniaxial –K1cos2θ term to explain the experimental data. This higher order contribution exists both in the free and reference layers. At T = 300 K, the estimated ‑K2/K1 ratios are 0.1 and 0.24 for the free and reference layers, respectively. The ratio is more than doubled at low temperatures changing the ground state of the reference layer from “easy-axis” to “easy-cone” regime. The easy-cone regime has clear signatures in the shape of the hard-axis magnetoresistance loops. The existence of this higher order anisotropy was also confirmed by ferromagnetic resonance experiments on FeCoB/MgO sheet films. It is of interfacial nature and is believed to be due to spatial fluctuations at the nanoscale of the first order anisotropy parameter at the FeCoB/MgO interface.

  19. 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.

  20. Magnetic filtration process, magnetic filtering material, and methods of forming magnetic filtering material

    SciTech Connect

    Taboada-Serrano, Patricia; Tsouris, Constantino; Contescu, Cristian I; McFarlane, Joanna

    2013-10-08

    The present invention provides magnetically responsive activated carbon, and a method of forming magnetically responsive activated carbon. The method of forming magnetically responsive activated carbon typically includes providing activated carbon in a solution containing ions of ferrite forming elements, wherein at least one of the ferrite forming elements has an oxidation state of +3 and at least a second of the ferrite forming elements has an oxidation state of +2, and increasing pH of the solution to precipitate particles of ferrite that bond to the activated carbon, wherein the activated carbon having the ferrite particles bonded thereto have a positive magnetic susceptibility. The present invention also provides a method of filtering waste water using magnetic activated carbon.

  1. Spatially resolved quantitative magnetic order measurement in spinel CuCr{sub 2}S{sub 4} nanocrystals

    SciTech Connect

    Negi, D. S.; Loukya, B.; Datta, R.; Ramasamy, K.; Gupta, A.

    2015-05-04

    We have utilized spatially resolved high resolution electron energy loss spectroscopy to quantify the relative percentage of ferromagnetic order in the core and the surface regions of CuCr{sub 2}S{sub 4} nanoparticles with nanocube and nanocluster morphology. The organic capping layer is found to play a significant role in restoring magnetic order at the surface. The technique is based on recording the fine features of the Cr L{sub 3} absorption edge and matching them with the theoretical spectra. The nanoscale probing technique we have developed is quite versatile and can be extended to understand magnetic ordering in a number of nanodimensional magnetic materials.

  2. Electric field control of the magnetic order parameter of magnetic pillars embedded in a ferroelectric matrix

    NASA Astrophysics Data System (ADS)

    Fitzsimmons, Michael; Wang, Q.; Chen, A.; Lookman, T.; Jia, Q. X.; Gilbert, D. A.; Borchers, J. A.; Holladay, B.; Sinha, S.

    Using polarized beam small angle neutron scattering (SANS) we quantitatively measured the influence of an electric field on correlation of magnetism in a ferroelectric/ferrimagnetic nanocomposite. The nanocomposite consists of ~12 nm wide pillars of CoFe2O4 (dark regions, inset figure left), a room temperature ferrimagnet, embedded in a ferroelectric, BaTiO3, matrix (light regions, inset figure right). We used a model-free method to extract the correlations of the magnetic structure from the SANS data (figure below). We found a 700 kV/cm electric field induced a change of magnetization of ~2% (scattering geometry, inset figure left). We explain our results using a simple representation for free energy that attributes coupling between electric polarization and magnetic order parameters to strain.

  3. Distinguishing magnetic particle size of iron oxide nanoparticles with first-order reversal curves

    SciTech Connect

    Kumari, Monika; Hirt, Ann M.; Widdrat, Marc; Faivre, Damien; Tompa, Éva; Pósfai, Mihály; Uebe, Rene; Schüler, Dirk

    2014-09-28

    Magnetic nanoparticles encompass a wide range of scientific study and technological applications. The success of using the nanoparticles in various applications demands control over size, dispersibility, and magnetics. Hence, the nanoparticles are often characterized by transmission electron microscopy (TEM), X-ray diffraction, and magnetic hysteresis loops. TEM analysis requires a thin layer of dispersed particles on the grid, which may often lead to particle aggregation thus making size analysis difficult. Magnetic hysteresis loops on the other hand provide information on the bulk property of the material without discriminating size, composition, and interaction effects. First order reversal curves (FORCs), described as an assembly of partial hysteresis loops originating from the major loop are efficient in identifying the domain size, composition, and interaction in a magnetic system. This study presents FORC diagrams on a variety of well-characterized biogenic and synthetic magnetite nanoparticles. It also introduces deconvoluted reversible and irreversible components from FORC as an important method for obtaining a semi-quantitative measure of the effective magnetic particle size. This is particularly important in a system with aggregation and interaction among the particles that often leads to either the differences between physical size and effective magnetic size. We also emphasize the extraction of secondary components by masking dominant coercivity fraction on FORC diagram to explore more detailed characterization of nanoparticle systems.

  4. Distinguishing magnetic particle size of iron oxide nanoparticles with first-order reversal curves

    NASA Astrophysics Data System (ADS)

    Kumari, Monika; Widdrat, Marc; Tompa, Éva; Uebe, Rene; Schüler, Dirk; Pósfai, Mihály; Faivre, Damien; Hirt, Ann M.

    2014-09-01

    Magnetic nanoparticles encompass a wide range of scientific study and technological applications. The success of using the nanoparticles in various applications demands control over size, dispersibility, and magnetics. Hence, the nanoparticles are often characterized by transmission electron microscopy (TEM), X-ray diffraction, and magnetic hysteresis loops. TEM analysis requires a thin layer of dispersed particles on the grid, which may often lead to particle aggregation thus making size analysis difficult. Magnetic hysteresis loops on the other hand provide information on the bulk property of the material without discriminating size, composition, and interaction effects. First order reversal curves (FORCs), described as an assembly of partial hysteresis loops originating from the major loop are efficient in identifying the domain size, composition, and interaction in a magnetic system. This study presents FORC diagrams on a variety of well-characterized biogenic and synthetic magnetite nanoparticles. It also introduces deconvoluted reversible and irreversible components from FORC as an important method for obtaining a semi-quantitative measure of the effective magnetic particle size. This is particularly important in a system with aggregation and interaction among the particles that often leads to either the differences between physical size and effective magnetic size. We also emphasize the extraction of secondary components by masking dominant coercivity fraction on FORC diagram to explore more detailed characterization of nanoparticle systems.

  5. Thickness-Dependent and Magnetic-Field-Driven Suppression of Antiferromagnetic Order in Thin V5S8 Single Crystals.

    PubMed

    Hardy, Will J; Yuan, Jiangtan; Guo, Hua; Zhou, Panpan; Lou, Jun; Natelson, Douglas

    2016-06-28

    With materials approaching the 2D limit yielding many exciting systems with intriguing physical properties and promising technological functionalities, understanding and engineering magnetic order in nanoscale, layered materials is generating keen interest. One such material is V5S8, a metal with an antiferromagnetic ground state below the Néel temperature TN ∼ 32 K and a prominent spin-flop signature in the magnetoresistance (MR) when H∥c ∼ 4.2 T. Here we study nanoscale-thickness single crystals of V5S8, focusing on temperatures close to TN and the evolution of material properties in response to systematic reduction in crystal thickness. Transport measurements just below TN reveal magnetic hysteresis that we ascribe to a metamagnetic transition, the first-order magnetic-field-driven breakdown of the ordered state. The reduction of crystal thickness to ∼10 nm coincides with systematic changes in the magnetic response: TN falls, implying that antiferromagnetism is suppressed; and while the spin-flop signature remains, the hysteresis disappears, implying that the metamagnetic transition becomes second order as the thickness approaches the 2D limit. This work demonstrates that single crystals of magnetic materials with nanometer thicknesses are promising systems for future studies of magnetism in reduced dimensionality and quantum phase transitions. PMID:27163511

  6. Noncollinear and noncoplanar magnetic order in the extended Hubbard model on anisotropic triangular lattice

    NASA Astrophysics Data System (ADS)

    Pasrija, Kanika; Kumar, Sanjeev

    2016-05-01

    Motivated by the importance of noncollinear and noncoplanar magnetic phases in determining various electrical properties in magnets, we investigate the magnetic phase diagram of the extended Hubbard model on an anisotropic triangular lattice. We map out the ground-state phase diagram within a mean-field scheme that treats collinear, noncollinear, and noncoplanar phases on equal footing. In addition to the standard ferromagnet and 120∘ antiferromagnet states, we find the four-sublattice flux, the 3Q noncoplanar, and the noncollinear charge-ordered states to be stable at specific values of filling fraction n . Inclusion of a nearest-neighbor Coulomb repulsion leads to intriguing spin-charge-ordered phases. The most notable of these are the collinear and noncollinear magnetic states at n =2 /3 , which occur together with a pinball-liquid-like charge order. Our results demonstrate that the elementary single-orbital extended Hubbard model on a triangular lattice hosts unconventional spin-charge ordered phases, which are similar to those reported in more complex and material-specific electronic Hamiltonians.

  7. A wireless and passive pressure sensor system based on the magnetic higher-order harmonic field

    NASA Astrophysics Data System (ADS)

    Tan, Ee Lim

    The goal of this work is to develop a magnetic-based passive and wireless pressure sensor for use in biomedical applications. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is composed of two magnetic elements: a magnetically-soft material acts as a sensing element, and a magnetically hard material acts as a biasing element. Both elements are embedded within a rigid sensor body and sealed with an elastomer pressure membrane. Upon excitation of an externally applied AC magnetic field, the sensing element is capable of producing higher-order magnetic signature that is able to be remotely detected with an external receiving coil. When exposed to environment with changing ambient pressure, the elastomer pressure membrane of pressure sensor is deflected depending on the surrounding pressure. The deflection of elastomer membrane changes the separation distance between the sensing and biasing elements. As a result, the higher-order harmonic signal emitted by the magnetically-soft sensing element is shifted, allowing detection of pressure change by determining the extent of the harmonic shifting. The passive and wireless nature of the sensor is enabled with an external excitation and receiving system consisting of an excitation coil and a receiving coil. These unique characteristics made the sensor suitable to be used for continuous and long-term pressure monitoring, particularly useful for biomedical applications which often require frequent surveillance. In this work, abdominal aortic aneurysm is selected as the disease model for evaluation the performance of pressure sensor and system. Animal model, with subcutaneous sensor implantation in mice, was conducted to demonstrate the efficacy and feasibility of pressure sensor in biological environment.

  8. Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers

    PubMed Central

    El Mel, Abdel-Aziz; Duvail, Jean-Luc; Gautron, Eric; Xu, Wei; Choi, Chang-Hwan; Angleraud, Benoit; Granier, Agnès

    2012-01-01

    Summary We report on the synthesis and magnetic characterization of ultralong (1 cm) arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes). Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications. PMID:23365798

  9. Magnetic properties of frictional volcanic materials

    NASA Astrophysics Data System (ADS)

    Kendrick, Jackie E.; Lavallée, Yan; Biggin, Andrew; Ferk, Annika; Leonhardt, Roman

    2015-04-01

    During dome-building volcanic eruptions, highly viscous magma extends through the upper conduit in a solid-like state. The outer margins of the magma column accommodate the majority of the strain, while the bulk of the magma is able to extrude, largely undeformed, to produce magma spines. Spine extrusion is often characterised by the emission of repetitive seismicity, produced in the upper <1 km by magma failure and slip at the conduit margins. The rheology of the magma controls the depth at which fracture can occur, while the frictional properties of the magma are important in controlling subsequent marginal slip processes. Upon extrusion, spines are coated by a carapace of volcanic fault rocks which provide insights into the deeper conduit processes. Frictional samples from magma spines at Mount St. Helens (USA), Soufriere Hills (Montserrat) and Mount Unzen (Japan) have been examined using structural, thermal and magnetic analyses to reveal a history of comminution, frictional heating, melting and cooling to form volcanic pseudotachylyte. Pseudotachylyte has rarely been noted in volcanic materials, and the recent observation of its syn-eruptive formation in dome-building volcanoes was unprecedented. The uniquely high thermal conditions of volcanic environments means that frictional melt remains at elevated temperatures for longer than usual, causing slow crystallisation, preventing the development of some signature "quench" characteristics. As such, rock-magnetic tests have proven to be some of the most useful tools in distinguishing pseudotachylytes from their andesite/ dacite hosts. In volcanic pseudotachylyte the mass normalised natural remanent magnetisation (NRM) when further normalised with the concentration dependent saturation remanence (Mrs) was found to be higher than the host rock. Remanence carriers are defined as low coercive materials across all samples, and while the remanence of the host rock displays similarities to an anhysteretic remanent

  10. Tuning order in the cuprate superconductors by a magnetic field

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir

    2002-03-01

    An innovative series of recent neutron scattering(B. Lake et al.), Science 291, 1759 (2001); B. Khyakovich et al., preprint; B. Lake et al., preprint. and STM(J. Hoffman et al.), Science, Feb 2002. experiments have shed new light on the nature of strong correlations in the cuprate superconductors. Some of these experiments use a magnetic field, applied perpendicular to the CuO2 layers, to tune the low temperature properties of the superconducting state. Their results support the idea that ground state correlations in the doped Mott insulator can be described using a framework of competing order parameters, and of proximity to quantum phase transitions associated with them. In our view, they also offer compelling evidence that the orders competing with superconductivity are spin and charge density waves. The predictions(E. Demler, S. Sachdev, and Y. Zhang, Phys. Rev. Lett. 87), 067202 (2001); S. Sachdev, cond- mat/0108238 A. Polkovnikov, S. Sachdev, M. Vojta, and E. Demler, cond- mat/0110329. of the theories of such quantum transitions will be reviewed and compared with the recent experimental results. In particular, we show that the quantum theory of a spin-density-wave ordering transition in a superconductor simultaneously describes a variety of observations with a single set of typical parameters: the field dependence of the elastic neutron scattering intensity, the absence of satellite Bragg peaks associated with the vortex lattice in existing neutron scattering experiments, and the spatial extent of the charge order in STM experiments.

  11. Recent advances in the microstructure design of materials for near room temperature magnetic cooling (invited)

    SciTech Connect

    Lyubina, Julia

    2011-04-01

    Successful operation of a magnetic cooling device depends crucially on the performance of active magnetic refrigerant material. Extensive research activity has been concentrated on optimizing the magnetic properties of these materials by chemical composition modification. Here, it is shown how the design of appropriate microstructure can be used to control the magnetic properties as well as mechanical stability of refrigerant materials experiencing a first-order magnetic phase transition. In particular, introducing porosity in LaFe{sub 13-x}Si{sub x} alloys provides long-term stability by sacrificing only a small fraction of the magnetocaloric effect and results in the desired reduction of the magnetic and thermal hysteresis by a factor of 5, as compared to bulk alloys. Reducing crystallite size down to the nanometer range is shown to substantially lower magnetic hysteresis. On the other hand, the magnetocaloric effect is weakened by about 40% and 60% in alloys with grain size of 70 and 44 nm, respectively.

  12. Recent advances in the microstructure design of materials for near room temperature magnetic cooling (invited)

    NASA Astrophysics Data System (ADS)

    Lyubina, Julia

    2011-04-01

    Successful operation of a magnetic cooling device depends crucially on the performance of active magnetic refrigerant material. Extensive research activity has been concentrated on optimizing the magnetic properties of these materials by chemical composition modification. Here, it is shown how the design of appropriate microstructure can be used to control the magnetic properties as well as mechanical stability of refrigerant materials experiencing a first-order magnetic phase transition. In particular, introducing porosity in LaFe13-xSix alloys provides long-term stability by sacrificing only a small fraction of the magnetocaloric effect and results in the desired reduction of the magnetic and thermal hysteresis by a factor of 5, as compared to bulk alloys. Reducing crystallite size down to the nanometer range is shown to substantially lower magnetic hysteresis. On the other hand, the magnetocaloric effect is weakened by about 40% and 60% in alloys with grain size of 70 and 44 nm, respectively.

  13. Exploring Possible Magnetic Properties of Ordered Manganese Monolayer on Wurtzite GaN

    NASA Astrophysics Data System (ADS)

    Smith, A. R.; Chinchore, A.; Wang, K.; Lin, W.; Chen, T.; Liu, Y.; Pak, J.

    2009-03-01

    For future spin-based device technologies, it is crucial to investigate magnetic material systems using techniques having high magnetic resolution. Spin-polarized scanning tunneling microscopy has proven to be extremely powerful for resolving magnetic structure down to even the atomic scale. Of great interest lately are transition-metal-on-semiconductor systems. We have recently discovered a well-ordered Mn monolayer having 3x3-R30^o structure, formed on wurtzite gallium nitride.[1] It is intriguing to explore the possibility of atomic-scale magnetic ordering in this system. For this purpose, we have designed a new SP-STM system combined with a highly flexible, epitaxial nitride growth facility. The new SP-STM has been designed for variable-low-temperature operation within an applied magnetic field of up to +/- 4.5 Tesla. Initial results with the new system are expected within the very near future. Work is supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No. 0730257). Equipment support from ONR is also acknowledged. [1] A. Chinchore et al., Appl. Phys. Lett. 93(18), 181908 (2008).

  14. Magnetic Order and Transitions in the Spin-web Compound Cu3TeO6

    NASA Astrophysics Data System (ADS)

    Månsson, Martin; Prša, Krunoslav; Sugiyama, Jun; Andreica, Daniel; Luetkens, Hubertus; Berger, Helmuth

    The spin-web compound Cu3TeO6, belongs to an intriguing group of materials where magnetism is governed by3d9 copper Cu2+ ions. This compound has been sparsely experimentally studied and we here present the first investigation of its local magnetic properties using muon-spin relaxation/rotation(μ+SR). Our results show a clear long-range 3D magnetic order below TN as indicated by clear zero-field (ZF) muon-precessions. At TN = 61.7K a very sharp transition is observed in the weak transverse-field (wTF) as well as ZF data. Contrary to suggestions by susceptibility measurements and inelastic neutron scattering, we find no evidence for either static or dynamic (on the time-scale of μ+SR) spin-correlations above TN.

  15. Magnetic properties of high Si steel with variable ordering obtained through thermomechanical processing

    NASA Astrophysics Data System (ADS)

    Ruiz, D.; Ros-Yañez, T.; Vandenberghe, R. E.; De Grave, E.; De Wulf, M.; Houbaert, Y.

    2003-05-01

    Alloys with a Si content of 4.2 and 5.4 wt % Si were produced to investigate the effect of increasing the Si on the materials processing and properties and to understand the effect of the order-disorder phenomenon on its magnetic properties. Different cooling rates after hot rolling were applied: Slow cooling from 780 °C to room temperature in 26 h, air cooling and water quench, followed by cold rolling until 0.5 to 0.7 mm thickness. Magnetic properties were measured after pickling and annealing at 950 °C for 2 h. 57Fe Mössbauer spectroscopy was used to study the effect of thermomechanical cycles on the ordering phenomena. It was noticed that the quenched samples have the highest values for the magnetic polarization, while slowly cooled samples have the lowest, for the power losses higher values are obtained for the quenched materials. The highest values for the polarization in the quenched samples were explained as a result of a higher B2 ordering.

  16. Soft ferrite materials for magnetic temperature transducers and applications

    NASA Astrophysics Data System (ADS)

    Miclea, C.; Tanasoiu, C.; Miclea, C. F.; Gheorghiu, A.; Tanasoiu, V.

    2005-04-01

    Soft ferrites in the CuZnTi system, having the formula Cu 1-xZn xTi yFe 2-yO 4, with 0.50⩽ x⩽0.60 and 0.00⩽ y⩽0.05 were investigated as a function of composition, sintering temperature and cooling speed, in order to obtain materials with controlled TC and very high change rate of permeability with temperature around their TC. The effect of Zn and Ti additions was a drastic change of the Curie temperature with about 10-12 °C for each atomic percent of Zn and Ti introduced into the spinel lattice while the cooling speed changed the behaviour of magnetic permeability with temperature around the Curie point. An application using such magnetic temperature sensors for a thermostat is presented.

  17. Analysis of tristable energy harvesting system having fractional order viscoelastic material

    SciTech Connect

    Oumbé Tékam, G. T.; Woafo, P.; Kitio Kwuimy, C. A.

    2015-01-15

    A particular attention is devoted to analyze the dynamics of a strongly nonlinear energy harvester having fractional order viscoelastic flexible material. The strong nonlinearity is obtained from the magnetic interaction between the end free of the flexible material and three equally spaced magnets. Periodic responses are computed using the KrylovBogoliubov averaging method, and the effects of fractional order damping on the output electric energy are analyzed. It is obtained that the harvested energy is enhanced for small order of the fractional derivative. Considering the order and strength of the fractional viscoelastic property as control parameter, the complexity of the system response is investigated through the Melnikov criteria for horseshoes chaos, which allows us to derive the mathematical expression of the boundary between intra-well motion and bifurcations appearance domain. We observe that the order and strength of the fractional viscoelastic property can be effectively used to control chaos in the system. The results are confirmed by the smooth and fractal shape of the basin of attraction as the order of derivative decreases. The bifurcation diagrams and the corresponding Lyapunov exponents are plotted to get insight into the nonlinear response of the system.

  18. Role of magnetic and orbital ordering at the metal-insulator transition in NdNiO{sub 3}

    SciTech Connect

    Scagnoli, V.; Staub, U.; Mulders, A. M.; Janousch, M.; Meijer, G. I.; Hammerl, G.; Tonnerre, J. M.; Stojic, N.

    2006-03-01

    Soft x-ray resonant scattering at the Ni L{sub 2,3} edges is used to test models of magnetic- and orbital-ordering below the metal-insulator transition in NdNiO{sub 3}. The large branching ratio of the L{sub 3} to L{sub 2} intensities of the (1/2 0 1/2) reflection and the observed azimuthal angle and polarization dependence originates from a noncollinear magnetic structure. The absence of an orbital signal and the noncollinear magnetic structure show that the nickelates are materials for which orbital ordering is absent at the metal-insulator transition.

  19. Magnetic ordering temperature of nanocrystalline Gd: enhancement of magnetic interactions via hydrogenation-induced “negative” pressure

    NASA Astrophysics Data System (ADS)

    Tereshina, E. A.; Khmelevskyi, S.; Politova, G.; Kaminskaya, T.; Drulis, H.; Tereshina, I. S.

    2016-03-01

    Gadolinium is a nearly ideal soft-magnetic material. However, one cannot take advantage of its properties at temperatures higher than the room temperature where Gd loses the ferromagnetic ordering. By using high-purity bulk samples with grains ~200 nm in size, we present proof-of-concept measurements of an increased Curie point (TC) and spontaneous magnetization in Gd due to hydrogenation. From first-principles we explain increase of TC in pure Gd due to the addition of hydrogen. We show that the interplay of the characteristic features in the electronic structure of the conduction band at the Fermi level in the high-temperature paramagnetic phase of Gd and “negative” pressure exerted by hydrogen are responsible for the observed effect.

  20. Magnetic ordering temperature of nanocrystalline Gd: enhancement of magnetic interactions via hydrogenation-induced “negative” pressure

    PubMed Central

    Tereshina, E. A.; Khmelevskyi, S.; Politova, G.; Kaminskaya, T.; Drulis, H.; Tereshina, I. S.

    2016-01-01

    Gadolinium is a nearly ideal soft-magnetic material. However, one cannot take advantage of its properties at temperatures higher than the room temperature where Gd loses the ferromagnetic ordering. By using high-purity bulk samples with grains ~200 nm in size, we present proof-of-concept measurements of an increased Curie point (TC) and spontaneous magnetization in Gd due to hydrogenation. From first-principles we explain increase of TC in pure Gd due to the addition of hydrogen. We show that the interplay of the characteristic features in the electronic structure of the conduction band at the Fermi level in the high-temperature paramagnetic phase of Gd and “negative” pressure exerted by hydrogen are responsible for the observed effect. PMID:26931775

  1. Magnetic ordering induced giant optical property change in tetragonal BiFeO3.

    PubMed

    Tong, Wen-Yi; Ding, Hang-Chen; Gong, Shi Jing; Wan, Xiangang; Duan, Chun-Gang

    2015-01-01

    Magnetic ordering could have significant influence on band structures, spin-dependent transport, and other important properties of materials. Its measurement, especially for the case of antiferromagnetic (AFM) ordering, however, is generally difficult to be achieved. Here we demonstrate the feasibility of magnetic ordering detection using a noncontact and nondestructive optical method. Taking the tetragonal BiFeO3 (BFO) as an example and combining density functional theory calculations with tight-binding models, we find that when BFO changes from C1-type to G-type AFM phase, the top of valance band shifts from the Z point to Γ point, which makes the original direct band gap become indirect. This can be explained by Slater-Koster parameters using the Harrison approach. The impact of magnetic ordering on band dispersion dramatically changes the optical properties. For the linear ones, the energy shift of the optical band gap could be as large as 0.4 eV. As for the nonlinear ones, the change is even larger. The second-harmonic generation coefficient d33 of G-AFM becomes more than 13 times smaller than that of C1-AFM case. Finally, we propose a practical way to distinguish the two AFM phases of BFO using the optical method, which is of great importance in next-generation information storage technologies. PMID:26648508

  2. Magnetic ordering induced giant optical property change in tetragonal BiFeO3

    PubMed Central

    Tong, Wen-Yi; Ding, Hang-Chen; Gong, Shi Jing; Wan, Xiangang; Duan, Chun-Gang

    2015-01-01

    Magnetic ordering could have significant influence on band structures, spin-dependent transport, and other important properties of materials. Its measurement, especially for the case of antiferromagnetic (AFM) ordering, however, is generally difficult to be achieved. Here we demonstrate the feasibility of magnetic ordering detection using a noncontact and nondestructive optical method. Taking the tetragonal BiFeO3 (BFO) as an example and combining density functional theory calculations with tight-binding models, we find that when BFO changes from C1-type to G-type AFM phase, the top of valance band shifts from the Z point to Γ point, which makes the original direct band gap become indirect. This can be explained by Slater-Koster parameters using the Harrison approach. The impact of magnetic ordering on band dispersion dramatically changes the optical properties. For the linear ones, the energy shift of the optical band gap could be as large as 0.4 eV. As for the nonlinear ones, the change is even larger. The second-harmonic generation coefficient d33 of G-AFM becomes more than 13 times smaller than that of C1-AFM case. Finally, we propose a practical way to distinguish the two AFM phases of BFO using the optical method, which is of great importance in next-generation information storage technologies. PMID:26648508

  3. Higher-Order Theory for Functionally Graded Materials

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob; Pindera, Marek-Jerzy; Arnold, Steven M.

    1999-01-01

    This paper presents the full generalization of the Cartesian coordinate-based higher-order theory for functionally graded materials developed by the authors during the past several years. This theory circumvents the problematic use of the standard micromechanical approach, based on the concept of a representative volume element, commonly employed in the analysis of functionally graded composites by explicitly coupling the local (microstructural) and global (macrostructural) responses. The theoretical framework is based on volumetric averaging of the various field quantities, together with imposition of boundary and interfacial conditions in an average sense between the subvolumes used to characterize the composite's functionally graded microstructure. The generalization outlined herein involves extension of the theoretical framework to enable the analysis of materials characterized by spatially variable microstructures in three directions. Specialization of the generalized theoretical framework to previously published versions of the higher-order theory for materials functionally graded in one and two directions is demonstrated. In the applications part of the paper we summarize the major findings obtained with the one-directional and two-directional versions of the higher-order theory. The results illustrate both the fundamental issues related to the influence of microstructure on microscopic and macroscopic quantities governing the response of composites and the technologically important applications. A major issue addressed herein is the applicability of the classical homogenization schemes in the analysis of functionally graded materials. The technologically important applications illustrate the utility of functionally graded microstructures in tailoring the response of structural components in a variety of applications involving uniform and gradient thermomechanical loading.

  4. Materials science: Magnetic nanoparticles line up

    NASA Astrophysics Data System (ADS)

    Faivre, Damien; Bennet, Mathieu

    2016-07-01

    Certain bacteria contain strings of magnetic nanoparticles and therefore align with magnetic fields. Inspired by these natural structures, researchers have now fabricated synthetic one-dimensional arrays of such particles.

  5. Nonlinear reduced order homogenization of materials including cohesive interfaces

    NASA Astrophysics Data System (ADS)

    Fritzen, Felix; Leuschner, Matthias

    2015-07-01

    The mechanical response of composite materials is strongly influenced by the nonlinear behavior of the interface between the constituents. In order to make reliable yet computationally efficient predictions for such materials, a reduced order model is developed. Conceptual ideas of the NTFA (Michel and Suquet, Int J Solids Struct 40:6937-6955, 2003, Comput Methods Appl Mech Eng 193:5477-5502, 2004) and of the pRBMOR (Fritzen, Hodapp and Leuschner Comput Methods Appl Mech Eng 260:143-154, 2013, Fritzen et al., Comput Methods Appl Mech Eng 278:186-217, 2014) are adopted. The key idea is to parameterize the displacement jumps on the cohesive interfaces by a reduced basis of global ansatz functions. Micromechanical considerations and the potential structure of the constitutive models lead to a variational formulation and reduced equilibrium conditions. The effect of the preanalysis phase on the accuracy is investigated using geometrically optimal training directions. The reduced model is tested for three-dimensional microstructures. Besides the effective stress response, the tension-compression asymmetry and the distribution of the separation of the interface are investigated. Memory savings on the order of are realized. The computing time is reduced considerably.

  6. Reinvestigation of long-range magnetic ordering in icosahedral Tb-Mg-Zn

    NASA Astrophysics Data System (ADS)

    Islam, Z.; Fisher, I. R.; Zarestky, J.; Canfield, P. C.; Stassis, C.; Goldman, A. I.

    1998-05-01

    We present results of a study of possible magnetic ordering in the icosahedral phase of Tb-Mg-Zn probed by bulk magnetization measurements and neutron diffraction. Measurements on both crushed single grains and cast polycrystalline samples of Tb-Mg-Zn were performed. Magnetization measurements on both samples reveal only a spin-glass-like transition at approximately 5.8 K. Neutron diffraction from the crushed single grains reveals only short-range magnetic ordering at low temperatures, with no evidence of the long-range magnetic ordering reported previously [Charrier, Ouladdiaf, and Schmitt, Phys. Rev. Lett. 78, 4637 (1997)]. Likewise, the cast polycrystalline samples exhibit primarily diffuse magnetic scattering at low temperature, but at least one relatively sharp diffraction peak was observed. Our results indicate that for single grain samples there is no long-range magnetic ordering and that, at best, the magnetic ordering in these quasicrystalline alloys is not very robust.

  7. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    DOE PAGESBeta

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; et al

    2016-01-28

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. We find Its zero-field magnetization produces distinctive magnetic self-interaction effects, includingmore » liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth’s magnetic field.« less

  8. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    NASA Astrophysics Data System (ADS)

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field.

  9. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates

    PubMed Central

    Shuai, M.; Klittnick, A.; Shen, Y.; Smith, G. P.; Tuchband, M. R.; Zhu, C.; Petschek, R. G.; Mertelj, A.; Lisjak, D.; Čopič, M.; Maclennan, J. E.; Glaser, M. A.; Clark, N. A.

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field. PMID:26817823

  10. Magnetic order of Au nanoparticle with clean surface

    NASA Astrophysics Data System (ADS)

    Sato, Ryuju; Ishikawa, Soichiro; Sato, Hiroyuki; Sato, Tetsuya

    2015-11-01

    Au nanoparticles, which are kept in vacuum after the preparation by gas evaporation method, show ferromagnetism even in 1.7 nm in diameter. The intrinsic magnetism is examined by detecting the disappearance of spontaneous magnetization in Au bulk prepared by heating the nanoparticles without exposure to the air. The temperature dependence of spontaneous magnetization is not monotonic and the increase in magnetization is observed after Au nanoparticles are exposed to the air. The magnetic behavior can be interpreted by the ferrimagnetic-like core-shell structure with shell thickness of 0.16±0.01 nm and magnetic moment of (1.5±0.1)×10-2 μB/Au atom, respectively.

  11. Spontaneous liquid crystal and ferromagnetic ordering of colloidal magnetic nanoplates.

    PubMed

    Shuai, M; Klittnick, A; Shen, Y; Smith, G P; Tuchband, M R; Zhu, C; Petschek, R G; Mertelj, A; Lisjak, D; Čopič, M; Maclennan, J E; Glaser, M A; Clark, N A

    2016-01-01

    Ferrofluids are familiar as colloidal suspensions of ferromagnetic nanoparticles in aqueous or organic solvents. The dispersed particles are randomly oriented but their moments become aligned if a magnetic field is applied, producing a variety of exotic and useful magnetomechanical effects. A longstanding interest and challenge has been to make such suspensions macroscopically ferromagnetic, that is having uniform magnetic alignment in the absence of a field. Here we report a fluid suspension of magnetic nanoplates that spontaneously aligns into an equilibrium nematic liquid crystal phase that is also macroscopically ferromagnetic. Its zero-field magnetization produces distinctive magnetic self-interaction effects, including liquid crystal textures of fluid block domains arranged in closed flux loops, and makes this phase highly sensitive, with it dramatically changing shape even in the Earth's magnetic field. PMID:26817823

  12. Third- and fifth-order optical nonlinearities in organic materials

    NASA Astrophysics Data System (ADS)

    Said, A. A.; Wamsley, C.; Hagan, D. J.; Van Stryland, E. W.; Reinhardt, Bruce A.; Roderer, Paul; Dillard, Ann G.

    1994-10-01

    We measure the nonlinear optical properties of solutions of a bisbenzethiozole-substituted thiophene compound (BBTDOT) and didecyloxy substituted polyphenyl (DDOS) using the Z-scan technique with 532 nm picosecond pulses. Both compounds exhibit two-photon absorption (2PA) and excited-state absorption (ESA) from the 2PA generated excited states. We measure the magnitude and sign of the real (refractive) and imaginary (2PA) parts of the third-order hyperpolarizability, and the excited-state absorptive and refractive cross sections. We observe third-order self-focusing in BBTDOT and self-defocusing in DDOS while both show excited-state defocusing. All these effects were previously observed and modeled in semiconductors giving insight into the nonlinearities occurring in these organic materials.

  13. Dynamic magnetic compaction of porous materials

    SciTech Connect

    1998-10-29

    IAP Research began development of the Dynamic Magnetic Compaction (DMC) process three years before the CRADA was established. IAP Research had experimentally demonstrated the feasibility of the process, and conducted a basic market survey. IAP identified and opened discussions with industrial partners and established the basic commercial cost structure. The purpose of this CRADA project was to predict and verify optimum pressure vs. time history for the compaction of porous copper and tungsten. LLNL modeled the rapid compaction of powdered material from an initial density of about 30% theoretical maximum to more than 90% theoretical maximum. The compaction simulations were benchmarked against existing data and new data was acquired by IAP Research. The modeling was used to perform parameter studies on the pressure loading time history, initial porosity and temperature. LLNL ran simulations using codes CALE or NITO and compared the simulations with published compaction data and equation of state (EOS) data. This project did not involve the development or modification of software code. CALE and NITO were existing software programs at LLNL. No modification of these programs occurred within the scope of the CRADA effort.

  14. First-order magnetization process as a tool of magnetic-anisotropy determination: Application to the uranium-based intermetallic U3C u4G e4

    NASA Astrophysics Data System (ADS)

    Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.; Skourski, Y.; Richter, M.; Havela, L.; Wosnitza, J.

    2016-02-01

    Uranium-based intermetallic compounds often display very strong magnetic anisotropies, the energy of which is usually not directly accessible by common experimental methods. Here, we report on static- and pulsed-field studies of U3C u4G e4 . This material orders ferromagnetically at TC=73 K with the easy magnetization direction along the a axis and a strong b c -plane anisotropy. The magnetization measured for fields along the hard b direction displays a first-order magnetization process that can be described well by use of a phenomenological theory yielding anisotropy constants up to the sixth order. This phenomenological description, working excellently for U3C u4G e4 , may also be applied for other uranium-based compounds.

  15. Magnetic compensation, field-dependent magnetization reversal, and complex magnetic ordering in Co2TiO4

    NASA Astrophysics Data System (ADS)

    Nayak, S.; Thota, S.; Joshi, D. C.; Krautz, M.; Waske, A.; Behler, A.; Eckert, J.; Sarkar, T.; Andersson, M. S.; Mathieu, R.; Narang, V.; Seehra, M. S.

    2015-12-01

    The complex nature of magnetic ordering in the spinel C o2Ti O4 is investigated by analyzing the temperature and magnetic field dependence of its magnetization (M ), specific heat (Cp), and ac magnetic susceptibilities χ' and χ″. X-ray diffraction of the sample synthesized by the solid-state reaction route confirmed the spinel structure whereas x-ray photoelectron spectroscopy shows its electronic structure to be C o2Ti O4=[C o2 +] [C o3 +T i3 +] O4 . From analysis of the temperature dependence of the dc paramagnetic susceptibility, the magnetic moments μ (A ) =3.87 μB and μ (B ) =5.19 μB on the A and B sites are determined with μ (B ) in turn yielding μ (T i3 +) =1.73 μB and μ (C o3 +) =4.89 μB . Analysis of the dc and ac susceptibilities combined with the weak anomalies observed in the Cp vs T data shows the existence of a quasi-long-range ferrimagnetic state below TN˜47.8 K and a compensation temperature Tcomp˜32 K , the latter characterized by sign reversal of magnetization with its magnitude depending on the applied magnetic field and the cooling protocol. Analysis of the temperature dependence of M (field cooled) and M (zero field cooled) data and the hysteresis loop parameters is interpreted in terms of large spin clusters. These results in C o2Ti O4 , significantly different from those reported recently in isostructural C o2Sn O4=[C o2 +] [C o2 +S n4 +] O4 , warrant further investigations of its magnetic structure using neutron diffraction.

  16. Inkjet printing of magnetic materials with aligned anisotropy

    NASA Astrophysics Data System (ADS)

    Song, Han; Spencer, Jeremy; Jander, Albrecht; Nielsen, Jeffrey; Stasiak, James; Kasperchik, Vladek; Dhagat, Pallavi

    2014-05-01

    3-D printing processes, which use drop-on-demand inkjet printheads, have great potential in designing and prototyping magnetic materials. Unlike conventional deposition and lithography, magnetic particles in the printing ink can be aligned by an external magnetic field to achieve both high permeability and low hysteresis losses, enabling prototyping and development of novel magnetic composite materials and components, e.g., for inductor and antennae applications. In this work, we report an inkjet printing technique with magnetic alignment capability. Magnetic films with and without particle alignment are printed, and their magnetic properties are compared. In the alignment-induced hard axis direction, an increase in high frequency permeability and a decrease in hysteresis losses are observed. Our results suggest that unique magnetic structures with arbitrary controllable anisotropy, not feasible otherwise, may be fabricated via inkjet printing.

  17. Neutron and X-Ray Diffraction Studies of Magnetic Order in Uranium-Based Heavy Fermion Superconductors

    NASA Astrophysics Data System (ADS)

    Lussier, Jean-Guy

    UPt_3, URu_2 Si_2, UNi_2 Al_3 and UPd_2 Al_3 form a special group among the uranium alloys because they exhibit heavy fermion character, magnetic order and superconductivity. This main interest in the study of this group of compounds resides in the simultaneous occurrence of magnetism and superconductivity at low temperature. Such a state could potentially involve an unconventional superconducting pairing mechanism, different from that contained in standard BCS theory. In this thesis, the magnetic states of three of these materials (URu_2Si _2, UNi_2Al _3 and UPd_2Al _3) is investigated with neutron and the relatively new resonant magnetic X-ray scattering techniques. The work presented here on URu_2Si _2 follows an earlier effort that demonstrated the applicabililty of the resonant X-ray technique to this weak magnetic system. Access to reciprocal space was extended in order to confirm the multipolar form of the resonant X-ray cross-section and to explore the limits of the technique compared to neutron scattering. The situation with the newly discovered UNi_2Al _3 and UPd_2Al _3 was different since their magnetic structure and phases needed first to be established. This task was achieved using two magnetic probes (neutron and X-ray scattering). Several magnetic order parameters in the normal and in the superconducting phase were also measured. The incommensurate magnetic order found in UNi_2Al_3 by neutron scattering constitutes the first observation of long range order in this compound. Other measurements on this compound provided some clues about the evolution of the magnetic structure in high magnetic fields.

  18. FOREWORD: Focus on Materials Analysis and Processing in Magnetic Fields Focus on Materials Analysis and Processing in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Sakka, Yoshio; Hirota, Noriyuki; Horii, Shigeru; Ando, Tsutomu

    2009-03-01

    Recently, interest in the applications of feeble (diamagnetic and paramagnetic) magnetic materials has grown, whereas the popularity of ferromagnetic materials remains steady and high. This trend is due to the progress of superconducting magnet technology, particularly liquid-helium-free superconducting magnets that can generate magnetic fields of 10 T and higher. As the magnetic energy is proportional to the square of the applied magnetic field, the magnetic energy of such 10 T magnets is in excess of 10 000 times that of conventional 0.1 T permanent magnets. Consequently, many interesting phenomena have been observed over the last decade, such as the Moses effect, magnetic levitation and the alignment of feeble magnetic materials. Researchers in this area are widely spread around the world, but their number in Japan is relatively high, which might explain the success of magnetic field science and technology in Japan. Processing in magnetic fields is a rapidly expanding research area with a wide range of promising applications in materials science. The 3rd International Workshop on Materials Analysis and Processing in Magnetic Fields (MAP3), which was held on 14-16 May 2008 at the University of Tokyo, Japan, focused on various topics including magnetic field effects on chemical, physical, biological, electrochemical, thermodynamic and hydrodynamic phenomena; magnetic field effects on the crystal growth and processing of materials; diamagnetic levitation, the magneto-Archimedes effect, spin chemistry, magnetic orientation, control of structure by magnetic fields, magnetic separation and purification, magnetic-field-induced phase transitions, properties of materials in high magnetic fields, the development of NMR and MRI, medical applications of magnetic fields, novel magnetic phenomena, physical property measurement by magnetic fields, and the generation of high magnetic fields. This focus issue compiles 13 key papers selected from the proceedings of MAP3. Other

  19. Development of a Thin Film Magnetic Moment Reference Material

    PubMed Central

    Pappas, D. P.; Halloran, S. T.; Owings, R. R.; da Silva, F. C. S.

    2008-01-01

    In this paper we present the development of a magnetic moment reference material for low moment magnetic samples. We first conducted an inter-laboratory comparison to determine the most useful sample dimensions and magnetic properties for common instruments such as vibrating sample magnetometers (VSM), SQUIDs, and alternating gradient field magnetometers. The samples were fabricated and then measured using a vibrating sample magnetometer. Their magnetic moments were calibrated by tracing back to the NIST YIG sphere, SRM 2853. PMID:27096108

  20. Development of a Thin Film Magnetic Moment Reference Material.

    PubMed

    Pappas, D P; Halloran, S T; Owings, R R; da Silva, F C S

    2008-01-01

    In this paper we present the development of a magnetic moment reference material for low moment magnetic samples. We first conducted an inter-laboratory comparison to determine the most useful sample dimensions and magnetic properties for common instruments such as vibrating sample magnetometers (VSM), SQUIDs, and alternating gradient field magnetometers. The samples were fabricated and then measured using a vibrating sample magnetometer. Their magnetic moments were calibrated by tracing back to the NIST YIG sphere, SRM 2853. PMID:27096108

  1. Magnetic properties modeling of soft magnetic composite materials using two-dimensional vector hybrid hysteresis model

    NASA Astrophysics Data System (ADS)

    Li, Dandan; Liu, Fugui; Li, Yongjian; Zhao, Zhigang; Zhang, Changgeng; Yang, Qingxin

    2014-05-01

    A 2-D vector hybrid hysteresis model for a soft magnetic composite (SMC) material is established, which is combined with classical Preisach model and Stoner-Wohlfarth (S-W) model. The rotational magnetic properties of SMC materials were studied using the vector model, and the computed results were compared with the experimental measurement. It is shown that the vector hybrid model can effectively simulate the rotational magnetic properties under low magnetization fields.

  2. High Field Pulse Magnets with New Materials

    NASA Astrophysics Data System (ADS)

    Li, L.; Lesch, B.; Cochran, V. G.; Eyssa, Y.; Tozer, S.; Mielke, C. H.; Rickel, D.; van Sciver, S. W.; Schneider-Muntau, H. J.

    2004-11-01

    High performance pulse magnets using the combination of CuNb conductor and Zylon fiber composite reinforcement with bore sizes of 24, 15 and 10 mm have been designed, manufactured and tested to destruction. The magnets successfully reached the peak fields of 64, 70 and 77.8 T respectively with no destruction. Failures occurred near the end flanges at the layer. The magnet design, manufacturing and testing, and the mode of the failure are described and analyzed.

  3. Spin-orbit correlated magnetic order in honeycomb α-RuCl3

    NASA Astrophysics Data System (ADS)

    Venkataraman, Vijay Shankar; Kim, Heung-Sik; Kee, Hae-Young

    2015-03-01

    There has been a lot of recent interest in the combined effects of spin-orbit coupling (SOC) and electronic correlations in transition metal compounds. RuCl3 with layered honeycomb structure was proposed as a candidate material, where SOC boosts the electronic interaction, leading to an insulating phase. However, the role of SOC is not clear in materials with 4d-orbitals, since SOC strength is weaker than 5d-orbital materials. Here we study electronic band structures of honeycomb RuCl3 using ab-initio and tight binding methods, and estimate its SOC strength. We find that SOC in RuCl3 is not strong enough to justify an effective jeff = 1 / 2 single band unlike in the iridates. However, when electronic interactions are introduced, a magnetic order develops, and upper- and lower-Hubbard bands are characterized by jeff = 1 / 2 and 3 / 2 , respectively. Within a mean field theory with multi-orbital bands, we find that a zig-zag magnetic order is a ground state. Experimental implications are also discussed.

  4. Plasmonic devices and sensors built from ordered nanoporous materials.

    SciTech Connect

    Jacobs, Benjamin W.; Kobayashi, Yoji; Houk, Ronald J. T.; Allendorf, Mark D.; Long, Jeffrey R.; Robertson, Ian M.; House, Stephen D.; Graham, Dennis D.; Talin, Albert Alec; Chang, Noel N.; El Gabaly Marquez, Farid

    2009-09-01

    The objective of this project is to lay the foundation for using ordered nanoporous materials known as metal-organic frameworks (MOFs) to create devices and sensors whose properties are determined by the dimensions of the MOF lattice. Our hypothesis is that because of the very short (tens of angstroms) distances between pores within the unit cell of these materials, enhanced electro-optical properties will be obtained when the nanopores are infiltrated to create nanoclusters of metals and other materials. Synthetic methods used to produce metal nanoparticles in disordered templates or in solution typically lead to a distribution of particle sizes. In addition, creation of the smallest clusters, with sizes of a few to tens of atoms, remains very challenging. Nanoporous metal-organic frameworks (MOFs) are a promising solution to these problems, since their long-range crystalline order creates completely uniform pore sizes with potential for both steric and chemical stabilization. We report results of synthetic efforts. First, we describe a systematic investigation of silver nanocluster formation within MOFs using three representative MOF templates. The as-synthesized clusters are spectroscopically consistent with dimensions {le} 1 nm, with a significant fraction existing as Ag{sub 3} clusters, as shown by electron paramagnetic resonance. Importantly, we show conclusively that very rapid TEM-induced MOF degradation leads to agglomeration and stable, easily imaged particles, explaining prior reports of particles larger than MOF pores. These results solve an important riddle concerning MOF-based templates and suggest that heterostructures composed of highly uniform arrays of nanoparticles within MOFs are feasible. Second, a preliminary study of methods to incorporate fulleride (K{sub 3}C{sub 60}) guest molecules within MOF pores that will impart electrical conductivity is described.

  5. Refrustration and competing orders in the prototypical Dy2Ti2O7 spin ice material

    NASA Astrophysics Data System (ADS)

    Henelius, P.; Lin, T.; Enjalran, M.; Hao, Z.; Rau, J. G.; Altosaar, J.; Flicker, F.; Yavors'kii, T.; Gingras, M. J. P.

    2016-01-01

    Spin ices, frustrated magnetic materials analogous to common water ice, have emerged over the past 15 years as exemplars of high frustration in three dimensions. Recent experimental developments aimed at interrogating anew the low-temperature properties of these systems, in particular whether the predicted transition to long-range order occurs, behoove researchers to scrutinize our current dipolar spin ice model description of these materials. In this work, we do so by combining extensive Monte Carlo simulations and mean-field theory calculations to analyze data from previous magnetization, diffuse neutron scattering, and specific-heat measurements on the paradigmatic Dy2Ti2O7 spin ice material. In this work, we also reconsider the possible importance of the nuclear specific heat Cnuc in Dy2Ti2O7 . We find that Cnuc is not entirely negligible below a temperature ˜0.5 K and must therefore be taken into account in a quantitative analysis of the calorimetric data of this compound below that temperature. We find that in this material, small effective spin-spin exchange interactions compete with the magnetostatic dipolar interaction responsible for the main spin ice phenomenology. This causes an unexpected "refrustration" of the long-range order that would be expected from the incompletely self-screened dipolar interaction and which positions the material at the boundary between two competing classical long-range-ordered ground states. This allows for the manifestation of new physical low-temperature phenomena in Dy2Ti2O7 , as exposed by recent specific-heat measurements. We show that among the four most likely causes for the observed upturn of the specific heat at low temperature [an exchange-induced transition to long-range order, quantum non-Ising (transverse) terms in the effective spin Hamiltonian, the nuclear hyperfine contribution, and random disorder], only the last appears to be reasonably able to explain the calorimetric data.

  6. Control over magnetic properties in bulk hybrid materials

    NASA Astrophysics Data System (ADS)

    Urban, Christian; Quesada, Adrian; Saerbeck, Thomas; Rubia, Miguel Angel De La; Garcia, Miguel Angel; Fernandez, Jose Francisco; Schuller, Ivan K.; UCSD Collaboration; Instituto de Ceramica, Madrid Collaboration; Institut Laue-Langevin, Grenoble Collaboration

    We present control of coercivity and remanent magnetization of a bulk ferromagnetic material embedded in bulk vanadium sesquioxide (V2O3) by using a standard bulk synthesis procedure. The method generalizes the use of structural phase transitions of one material to control structural and magnetic properties of another. A structural phase transition (SPT) in the V2O3 host material causes magnetic properties of Ni to change as function of temperature. The remanent magnetization and the coercivity are reversibly controlled by the SPT without additional external magnetic fields. The reversible tuning shown here opens the pathway for controlling the properties of a vast variety of magnetic hybrid bulk systems. This Work is supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS funded by the Department of Energy's Office of Basic Energy Science, DMR under grant DE FG02 87ER-45332.

  7. Application of broadband alternating current magnetic susceptibility to the characterization of magnetic nanoparticles in natural materials

    NASA Astrophysics Data System (ADS)

    Kodama, Kazuto

    2013-01-01

    A new method is proposed for characterizing magnetic particles by measuring low-field alternating current magnetic susceptibility at a number of frequency steps spanning four orders of magnitude, from 125 Hz to 512 kHz. This method was tested using natural samples with various grain size distributions, including basalt (Kilauea, Hawaii), loess and paleosol (Luochuan, China), tuff (Yucca Mountain, Nevada), granite (Minnesota Valley, Minnesota), and andesite (Sakurajima, Japan). The resulting frequency spectrum of magnetic susceptibility (FSMS) of the basalt, loess/paleosol, and tuff decreases with increasing frequency, but at different rates of decrease. The FSMS of the basalt is characterized by a monotonic decrease with increasing frequency over the entire range. The FSMS of the loess/paleosol and the tuff decreases more markedly than that of the basalt, which agrees with previous results showing that superparamagnetic particles are dominant in such material. Quantitative estimates using FSMSs allow reconstruction of characteristic grain size distributions and clearly identify differences in the distribution of superparamagnetic particles. The multidomain granite sample has no distinct frequency dependence, which is probably due to the smooth displacement of domain walls in the presence of the external field. In contrast, the FSMSs of the andesite samples exhibit maxima over a limited frequency range, between 16 and 128 kHz. This behavior, together with low-temperature measurements, can be accounted for by magnetic resonance of domain walls in the multidomain phenocrysts.

  8. Simulation of the inspection of planar non-magnetic materials with electro magnetic acoustic transducers

    NASA Astrophysics Data System (ADS)

    Prémel, Denis; Reboud, C.; Chatillon, S.; Reverdy, F.; Mahaut, S.

    2012-05-01

    For some specific applications in ultrasonic non destructive evaluation, EMATs (ElectroMagnetic Acoustic Transducers) are very useful for generating and receiving ultrasonic waves. EMAT works without any contact and liquid coupling. Various surface or bulk waves with any arbitrary polarities and orientations may be generated by changing the orientation of the magnets and the coils. Unfortunately, these types of probes show a poor sensitivity as receivers. CEA LIST has developed simulation tools, based on semi-analytical models dedicated to eddy current and ultrasonic testing, in order to predict signals obtained when inspecting planar structures. The first step of these developments concerns the inspection of conducting non-ferromagnetic materials. By combining eddy currents due to coils with the static magnetic field provided by magnets, the 3D Lorentz's force distribution is computed in the time domain and used as input for the semi-analytical ultrasonic models to compute the simulation of ultrasonic bulk waves and flaw interaction in the piece. This communication presents a specific configuration for our first experimental validation. The computation time is sufficiently low to perform parametric studies to improve the performances of the EMAT.

  9. Iron oxohydroxide-polyacrylic acid magnetic composite materials

    NASA Astrophysics Data System (ADS)

    Mata-Zamora, M. E.; Arriola, H.; Nava, N.; Saniger, J. M.

    1996-08-01

    Powdered nanometer-sized precipitates of Fe(II)Fe(III) 2O x(OH) y were obtained by reacting solutions of ferrous-ferric salts with a Fe(III)/Fe(II) ratio < 2, with an excess of ammonium hydroxide. These precipitates were then mixed at room temperature with a solution of polyacrylic acid (PAA) in order to obtain a composite material. The XRD analysis showed that the iron oxohydroxide precipitates, with an average size around 10 nm, were crystalline and had a spinel structure resembling to either magnetite or maghemite. The Mössbauer spectra of the iron oxohydroxide particles presented a major magnetic phase with the double Zeeman splitting characteristic of magnetite and a minor paramagnetic phase probably originated by the nanometer size of the particles. Its structure was found to correspond to a disordered spinel, as result of the analysis of the intrinsic magnetic field and its splitting parameters. The composite material PAA-Fe(II)Fe(III) 2O x(OH) y presented a diffractogram close to the original oxohydroxide, but its Mössbauer spectrum showed a major paramagnetic phase. This change was explained as a consequence of the chemical coordination of the nanometer sized iron oxohydroxides particles with the PAA carboxylate groups.

  10. Dynamic Magnetic Field Applications for Materials Processing

    NASA Technical Reports Server (NTRS)

    Mazuruk, K.; Grugel, Richard N.; Motakef, S.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    Magnetic fields, variable in time and space, can be used to control convection in electrically conducting melts. Flow induced by these fields has been found to be beneficial for crystal growth applications. It allows increased crystal growth rates, and improves homogeneity and quality. Particularly beneficial is the natural convection damping capability of alternating magnetic fields. One well-known example is the rotating magnetic field (RMF) configuration. RMF induces liquid motion consisting of a swirling basic flow and a meridional secondary flow. In addition to crystal growth applications, RMF can also be used for mixing non-homogeneous melts in continuous metal castings. These applied aspects have stimulated increasing research on RMF-induced fluid dynamics. A novel type of magnetic field configuration consisting of an axisymmetric magnetostatic wave, designated the traveling magnetic field (TMF), has been recently proposed. It induces a basic flow in the form of a single vortex. TMF may find use in crystal growth techniques such as the vertical Bridgman (VB), float zone (FZ), and the traveling heater method. In this review, both methods, RMF and TMF are presented. Our recent theoretical and experimental results include such topics as localized TMF, natural convection dumping using TMF in a vertical Bridgman configuration, the traveling heater method, and the Lorentz force induced by TMF as a function of frequency. Experimentally, alloy mixing results, with and without applied TMF, will be presented. Finally, advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, will be discussed.

  11. Magnetic reversal of an artificial square ice: dipolar correlation and charge ordering

    NASA Astrophysics Data System (ADS)

    Morgan, Jason; Stein, Aaron; Langridge, Sean; Marrows, Christopher

    2012-02-01

    Artificial spin ices are lithographically patterned arrays of single domain nanomagnets [1-4]. The elongated elements form a 2D system of interlinked vertices at which Ising-like dipole moments meet with incompatible interactions. They are directly analogous to 3D bulk spin ice materials [5]. We report on the magnetic reversal of an athermal artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal symmetry axis, investigated via magnetic force microscopy of the remanent states that result [1]. From an initial diagonally polarised state, sublattice independent reversal is observed via bulk-nucleated incrementally-pinned flipped moment chains along parallel channels of magnetic elements, as evident from analysis of vertex populations and dipolar correlation functions. Weak dipolar interactions between adjacent chains favour antialignment and give rise to weak charge ordering of ``monopole'' vertices during reversal. [4pt] [1] J. P. Morgan, A. Stein, S. Langridge & C.H. Marrows, New Journal of Physics (2011), 13, 105002.[0pt] [2] R. F. Wang et al., Nature (2006), 439, 303-306.[0pt] [3] E. Mengotti et al., Nature Physics (2011), 7, 68-74.[0pt] [4] J. P. Morgan et al., Nature Physics (2011), 7, 75-79.[0pt] [5] M. J. Harris et al., PRL (1997), 79, 2554-255

  12. Magnetic order near 270 K in mineral and synthetic Mn{sub 2}FeSbO{sub 6} ilmenite

    SciTech Connect

    Mathieu, R.; Hudl, M.; Nordblad, P.; Ivanov, S. A.; Bazuev, G. V.; Lazor, P.; Solovyev, I. V.

    2011-05-16

    The structural and magnetic properties of Mn{sub 2}FeSbO{sub 6} single-crystalline mineral and ceramic samples synthesized under thermobaric treatment have been investigated, and compared to theoretical predictions based on first-principles electronic structure calculations. This ilmenite system displays a sharp magnetic transition just below the room temperature related to a ferrimagnetic ordering of the Mn{sup 2+} and Fe{sup 3+} cations, which makes Mn{sub 2}FeSbO{sub 6} a promising candidate for designing functional magnetic materials.

  13. Magnetically Controlled Shape Memory Behaviour—Materials and Applications

    NASA Astrophysics Data System (ADS)

    Gandy, A. P.; Sheikh, A.; Neumann, K.; Neumann, K.-U.; Pooley, D.; Ziebeck, K. R. A.

    2008-06-01

    For most metals a microscopic change in shape occurs above the elastic limit by the irreversible creation and movement of dislocations. However a large number of metallic systems undergo structural, martensitic, phase transformations which are diffusionless, displacive first order transitions from a high-temperature phase to one of lower symmetry below a certain temperature TM. These transitions which have been studied for more than a century are of vital importance because of their key role in producing shape memory phenomena enabling the system to reverse large deformations in the martensitic phase by heating into the austenite phase. In addition to a change in shape (displacement) the effect can also produce a force or a combination of both. Materials having this unique property are increasing being used in medical applications—scoliosis correction, arterial clips, stents, orthodontic wire, orthopaedic implants etc. The structural phase transition essential for shape memory behaviour is usually activated by a change in temperature or applied stress. However for many applications such as for actuators the transformation is not sufficiently rapid. Poor energy conversion also limits the applicability of many shape memory alloys. In medicine a change of temperature or pressure is often inappropriate and new ferromagnetic materials are being considered in which the phenomena can be controlled by an applied magnetic field at constant temperature. In order to achieve this, it is important to optimise three fundamental parameters. These are the saturation magnetisation σs, the Curie temperature Tc and the martensitic temperature TM. Here, σs is important because the magnetic pressure driving the twin boundary motion is 2σsH. Furthermore the material must be in the martensitic state at the operating temperature which should be at or above room temperature. This may be achieved by alloying or controlling the stoichiometry. Recently new intermetallic compounds based

  14. Magnetic refrigeration apparatus with belt of ferro or paramagnetic material

    DOEpatents

    Barclay, John A.; Stewart, Walter F.; Henke, Michael D.; Kalash, Kenneth E.

    1987-01-01

    A magnetic refrigerator operating in the 12 to 77K range utilizes a belt which carries ferromagnetic or paramagnetic material and which is disposed in a loop which passes through the center of a solenoidal magnet to achieve cooling. The magnetic material carried by the belt, which can be blocks in frames of a linked belt, can be a mixture of substances with different Curie temperatures arranged such that the Curie temperatures progressively increase from one edge of the belt to the other. This magnetic refrigerator can be used to cool and liquefy hydrogen or other fluids.

  15. Magnetic refrigeration apparatus with belt of ferro or paramagnetic material

    DOEpatents

    Barclay, J.A.; Stewart, W.F.; Henke, M.D.; Kalash, K.E.

    1986-04-03

    A magnetic refrigerator operating in the 12 to 77 K range utilizes a belt which carries ferromagnetic or paramagnetic material and which is disposed in a loop which passes through the center of a solenoidal magnet to achieve cooling. The magnetic material carried by the belt, which can be blocks in frames of a linked belt, can be a mixture of substances with different Curie temperatures arranged such that the Curie temperatures progressively increase from one edge of the belt to the other. This magnetic refrigerator can be used to cool and liquefy hydrogen or other fluids.

  16. Anisotropy: Spin order and magnetization of single-crystalline Cu4(OH) 6FBr barlowite

    NASA Astrophysics Data System (ADS)

    Han, Tian-Heng; Isaacs, Eric D.; Schlueter, John A.; Singleton, John

    2016-06-01

    Despite decades-long fascination, the difficulty of maintaining high lattice symmetry in frustrated nonbipartite S =1/2 materials that can also be made into high-quality single crystals has been a persistent challenge. Here we report magnetization studies of a single-crystal sample of barlowite, Cu4(OH) 6 FBr , which has a geometrically perfect kagome motif. At T ≤4.2 K and 35 ≤μ0H ≤65 T, the interlayer spins are fully polarized, and the kagome-intrinsic magnetization is consistent with a Heisenberg model having J /kB=-180 K. Several field-driven anomalies are observed, having varied scalings with temperature. At an applied field, kagome disorder caused by the interlayer spins is smaller than that in herbertsmithite. At T ≤ 15 K, the bulk magnetic moment comes from the interlayer spins. An almost coplanar spin order suggests that the magnitude of in-plane Dzyaloshinskii-Moriya interaction is smaller than 0.006(6) J . On the other hand, the possibility of a spin-liquid state in the kagome lattice coexisting with ordered interlayer spins is left open.

  17. On the magnetic order of Gd5Ge3

    SciTech Connect

    Cadogan, J M; Ryan, D H; Mudryk, Ya.; Pecharsky, V K; Gschneidner, K A

    2014-05-07

    We have investigated the magnetic structure of Gd5Ge3 by neutron powder diffraction down to 3.6 K. This compound presents three events in the heat capacity which we show are related to fundamental changes in the magnetic order. The primary antiferromagnetic ordering occurs at 82(2) K and produces a magnetic cell that is tripled with respect to the underlying orthorhombic crystal cell. The propagation vector is k1=[00⅓] . At 74(2) K, the magnetic order becomes “anti-C” with a propagation vector k2 = [1 0 0]. A third change in the magnetic order occurs at 40(2) K, and the new magnetic structure is essentially the “anti-C” structure but with the addition of a tripled magnetic component corresponding to a propagation vector k3 = [⅓ 0 0] .

  18. Study of magnetic materials for biomedical and other applications

    NASA Astrophysics Data System (ADS)

    Ahmad, Shahid Nisar

    We have studied different aspects of magnetic materials in bulk, nanoparticles, and thinfilm form with emphasis on their use in biomedical and technological applications. In this work: (1) We have synthesized several new Gd based compounds and alloys and have optimized their magnetic properties for the self-controlled hyperthermia applications. The self-controlled hyperthermia is a new non-invasive technique to employ heat treatment to cure cancerous cells without overheating the normal cells. The need for developing such materials was dictated by the lack of existing magnetic materials with magnetic ordering temperatures in the temperature range of (40-45)°C, which is the critical operating temperature range for the hyperthermia applications. (2) We have produced gold coated Fe-Au nanoparticles which are biocompatible and can easily be functionalized through gold surface for various technological applications, besides hyperthermia applications. Contrary to the previous reports of time dependent degradation of magnetic properties of the Fe-Au nanoparticles, our gold coated nanoparticles are quite robust and their magnetic properties remain unchanged under the ambient conditions. We have made a comprehensive study of the Fe-Au nanoparticles, and have observed that superparamgnetic Fe-Au nanoparticles can be produced with variable Fe content up to 30 at.% and the particle size remains nearly uniform (˜ 5 nm). When subjected to annealing at elevated temperatures, the magnetic core in the Fe-Au nanoparticles undergoes various interesting changes and the blocking temperature and magnetization increase when nanoparticles are annealed at elevated temperatures. The observation of the Verwey transition at ˜ 125K in the magnetization versus temperature data for samples annealed at 450°C and above indicates the formation of Fe3O4. The absence of any oxide peaks in the as-formed sample and presence of oxide peaks in the samples annealed at 450°C and above in the x

  19. The Magnetic Ordering of Heavy Rare Earth Metals

    NASA Astrophysics Data System (ADS)

    Nordström, Lars

    1998-03-01

    The electronic and magnetic structures of the rare earth metals with hcp structure (Gd--Tm) are calculated by a full-potential LAPW method, which allows for non-collinear magnetism within the local approximation to spin-density functional theory. The 4f electrons are taken as localized, but their spin moment constrained as to fulfil Russel-Saunders coupling, polarizes the itinerant valence electrons. It is found that there are two competing magnetic structures; the ferromagnetic state, which dominates for the left-most elements (Gd and Tb), and a planar helical wave, which is found to have lowest energy for the last elements Er and Tm. In Ho the competition between the two leads to a compromise --- a helical cone. This trend is in accordance with the experimental situation. The mechanism behind the stabilization of the helical wave is confirmed to be an opening of a partial gap at the so-called ``webbing'' of the Fermi surface. This feature is found to exhibit nesting, a fact which is known both from earlier non-spin-polarized calculations and de Haas-van Alphen measurements. In contrast to prevailing models and earlier more primitive calculations, this nesting is found to exist for all elements, i.e. even for gadolinium. Instead, the magnitude of the spin splitting of the valence electrons due to the magnetic 4f states, is found to be an important quantity which has been missed out in the standard models for the magnetic structure of the rare earths.

  20. Magnetic Ordering in Sr3YCo4O10+x

    NASA Astrophysics Data System (ADS)

    Kishida, Takayoshi; Kapetanakis, Myron D.; Yan, Jiaqiang; Sales, Brian C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Chisholm, Matthew F.

    2016-01-01

    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has attracted considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations. Guided by theoretical results on Co-O distances projected on different planes, the atomic-scale images of several different orientations, especially of the fully oxygenated planes, allow the unambiguous extraction of the underlying structure. The calculated magnetic properties of the new structure are in excellent agreement with the experimental data.

  1. Magnetic Ordering in Sr3YCo4O10+x

    PubMed Central

    Kishida, Takayoshi; Kapetanakis, Myron D.; Yan, Jiaqiang; Sales, Brian C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Chisholm, Matthew F.

    2016-01-01

    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has attracted considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations. Guided by theoretical results on Co-O distances projected on different planes, the atomic-scale images of several different orientations, especially of the fully oxygenated planes, allow the unambiguous extraction of the underlying structure. The calculated magnetic properties of the new structure are in excellent agreement with the experimental data. PMID:26818899

  2. Magnetic Ordering in Sr3YCo4O10+x.

    PubMed

    Kishida, Takayoshi; Kapetanakis, Myron D; Yan, Jiaqiang; Sales, Brian C; Pantelides, Sokrates T; Pennycook, Stephen J; Chisholm, Matthew F

    2016-01-01

    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt's ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has attracted considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations. Guided by theoretical results on Co-O distances projected on different planes, the atomic-scale images of several different orientations, especially of the fully oxygenated planes, allow the unambiguous extraction of the underlying structure. The calculated magnetic properties of the new structure are in excellent agreement with the experimental data. PMID:26818899

  3. Magnetic ordering and crystal field effects in quasi-caged structure compound PrFe2Al8

    NASA Astrophysics Data System (ADS)

    Nair, Harikrishnan S.; Ghosh, Sarit K.; Ramesh Kumar, K.; Strydom, André M.

    2016-04-01

    The compound PrFe2Al8 possesses a three-dimensional network structure resulting from the packing of Al polyhedra centered at the transition metal element Fe and the rare earth Pr. Along the c-axis, Fe and Pr form chains which are separated from each other by the Al-network. In this paper, the magnetism and crystalline electric field effects in PrFe2Al8 are investigated through the analysis of magnetization and specific heat data. A magnetic phase transition in the Pr lattice is identified at TNPr ≈ 4 K in dc magnetization and ac susceptibility data. At 2 K, the magnetization isotherm presents a ferromagnetic saturation, however, failing to reach full spin-only ferromagnetic moment of Pr3+. Metamagnetic step-like low-field features are present in the magnetization curve at 2 K which is shown to shift upon field-cooling the material. Arrott plots centered around TPrN display "S"-like features suggestive of an inhomogeneous magnetic state. The magnetic entropy, Sm, estimated from specific heat outputs a value of R ln(2) at TN2 suggesting a doublet state for Pr3+. The magnetic specific heat is modeled by using a 9-level Schottky equation pertinent to the Pr3+ ion with J=4. Given the crystalline electric field situation of Pr3+, the inference of a doublet state from specific heat and consequent long-range magnetic order is an unexpected result.

  4. Magnetic Ordering in Sr3YCo4O10+x

    DOE PAGESBeta

    Kishida, Takayoshi; Kapetanakis, Myron D.; Yan, Jiaqiang; Sales, Brian C.; Pantelides, Sokrates T.; Pennycook, Stephen J.; Chisholm, Matthew F.

    2016-01-28

    Transition-metal oxides often exhibit complex magnetic behavior due to the strong interplay between atomic-structure, electronic and magnetic degrees of freedom. Cobaltates, especially, exhibit complex behavior because of cobalt’s ability to adopt various valence and spin state configurations. The case of the oxygen-deficient perovskite Sr3YCo4O10+x (SYCO) has gained considerable attention because of persisting uncertainties about its structure and the origin of the observed room temperature ferromagnetism. Here we report a combined investigation of SYCO using aberration-corrected scanning transmission electron microscopy and density functional theory calculations.

  5. Magnetic Materials Suitable for Fission Power Conversion in Space Missions

    NASA Technical Reports Server (NTRS)

    Bowman, Cheryl L.

    2012-01-01

    Terrestrial fission reactors use combinations of shielding and distance to protect power conversion components from elevated temperature and radiation. Space mission systems are necessarily compact and must minimize shielding and distance to enhance system level efficiencies. Technology development efforts to support fission power generation scenarios for future space missions include studying the radiation tolerance of component materials. The fundamental principles of material magnetism are reviewed and used to interpret existing material radiation effects data for expected fission power conversion components for target space missions. Suitable materials for the Fission Power System (FPS) Project are available and guidelines are presented for bounding the elevated temperature/radiation tolerance envelope for candidate magnetic materials.

  6. MSWI boiler fly ashes: magnetic separation for material recovery.

    PubMed

    De Boom, Aurore; Degrez, Marc; Hubaux, Paul; Lucion, Christian

    2011-07-01

    Nowadays, ferrous materials are usually recovered from Municipal Solid Waste Incineration (MSWI) bottom ash by magnetic separation. To our knowledge, such a physical technique has not been applied so far to other MSWI residues. This study focuses thus on the applicability of magnetic separation on boiler fly ashes (BFA). Different types of magnet are used to extract the magnetic particles. We investigate the magnetic particle composition, as well as their leaching behaviour (EN 12457-1 leaching test). The magnetic particles present higher Cr, Fe, Mn and Ni concentration than the non-magnetic (NM) fraction. Magnetic separation does not improve the leachability of the NM fraction. To approximate industrial conditions, magnetic separation is also applied to BFA mixed with water by using a pilot. BFA magnetic separation is economically evaluated. This study globally shows that it is possible to extract some magnetic particles from MSWI boiler fly ashes. However, the magnetic particles only represent from 23 to 120 g/kg of the BFA and, though they are enriched in Fe, are composed of similar elements to the raw ashes. The industrial application of magnetic separation would only be profitable if large amounts of ashes were treated (more than 15 kt/y), and the process should be ideally completed by other recovery methods or advanced treatments. PMID:21306886

  7. Eddy current characterization of magnetic treatment of materials

    NASA Technical Reports Server (NTRS)

    Chern, E. James

    1992-01-01

    Eddy current impedance measuring methods have been applied to study the effect that magnetically treated materials have on service life extension. Eddy current impedance measurements have been performed on Nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in a material's electromagnetic properties and does exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic-field processing effect on machine tool service life.

  8. Evidence for coexisting magnetic order in frustrated three-dimensional honeycomb iridates Li2IrO3

    NASA Astrophysics Data System (ADS)

    Breznay, Nicholas; Ruiz, Alejandro; Frano, Alex; Analytis, James

    The search for unconventional magnetism has found a fertile hunting ground in 5d iridium oxide (iridate) materials. The competition between coulomb, spin-orbit, and crystal field energy scales in honeycomb iridates leads to a quantum magnetic system with localized spin-1/2 moments communicating through spin-anisotropic Kitaev exchange interactions. Although early and ongoing work has focused on layered two-dimensional honeycomb compounds such as Na2IrO3 and a 4d analog, RuCl3, recently discovered polytypes of Li2IrO3 take on three-dimensional honeycomb structures. Bulk thermodynamic studies, as well as recent resonant x-ray diffraction and absorption spectroscopy experiments, have uncovered a rich phase diagram for these three-dimensional honeycomb iridates. Low temperature incommensurate and commensurate magnetic orders can be stabilized by tuning the applied magnetic field, displaying a delicate coexistence that signals highly frustrated magnetism.

  9. Magnetic materials selection for static inverter and converter transformers

    NASA Technical Reports Server (NTRS)

    Mclyman, C. W. T.

    1971-01-01

    Different magnetic alloys best suited for high-frequency and high-efficiency applications were comparatively investigated together with an investigation of each alloy's inherent characteristics. One of the characteristics in magnetic materials deterimental in transformer design is the residual flux density, which can be additive on turn-on and cause the transformer to saturate. Investigation of this problem led to the design of a transformer with a very low residual flux. Tests were performed to determine the dc and ac magnetic properties at 2400 Hz using square-wave excitation. These tests were performed on uncut cores, which were then cut for comparison of the gapped and ungapped magnetic properties. The optimum transformer was found to be that with the lowest residual flux and a small amount of air gap in the magnetic material. The data obtained from these tests are described, and the potential uses for the materials are discussed.

  10. Quantum Criticality and Unconventional Order in Magnetic and Dielectric Material

    NASA Astrophysics Data System (ADS)

    Rowley, S. E.; Smith, R.; Sutherland, M. L.; Alireza, P.; Saxena, S. S.; Lonzarich, G. G.

    2012-12-01

    We present an overview of unconventional phenomena arising close to ferromagnetic and ferroelectric quantum phase transitions. The applicability and potential breakdown of traditional field theories of quantum criticality and the emergence of a multiplicity of critical fields in particular will be discussed.

  11. Short- and long-range magnetic order in LaMnAsO

    NASA Astrophysics Data System (ADS)

    McGuire, Michael A.; Garlea, V. Ovidiu

    2016-02-01

    The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature TN=360 (1 ) K. Below TN the critical exponent describing the magnetic order parameter is β =0.33 -0.35 , consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to TSRO=650 (10 ) K. The magnetic susceptibility shows a weak anomaly at TSRO and no anomaly at TN. Analysis of the diffuse scattering data using a reverse Monte Carlo algorithm indicates that above TN nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. Comparison with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above TN is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.

  12. Short- and long-range magnetic order in LaMnAsO

    DOE PAGESBeta

    McGuire, Michael A.; Garlea, Vasile Ovidiu

    2016-02-02

    The magnetic properties of the layered oxypnictide LaMnAsO have been revisited using neutron scattering and magnetization measurements. The present measurements identify the Néel temperature TN = 360(1) K. Below TN the critical exponent describing the magnetic order parameter is β=0.33–0.35 , consistent with a three-dimensional Heisenberg model. Above this temperature, diffuse magnetic scattering indicative of short-range magnetic order is observed, and this scattering persists up to TSRO = 650(10) K. Morevoer, the magnetic susceptibility shows a weak anomaly at TSRO and no anomaly at TN. Analysis of the diffuse scattering data using a reverse Monte Carlo algorithm indicates that abovemore » TN nearly two-dimensional, short-range magnetic order is present with a correlation length of 9.3(3) Å within the Mn layers at 400 K. The inelastic scattering data reveal a spin gap of 3.5 meV in the long-range ordered state, and strong, low-energy (quasielastic) magnetic excitations emerging in the short-range ordered state. When we compared it with other related compounds correlates the distortion of the Mn coordination tetrahedra to the sign of the magnetic exchange along the layer-stacking direction, and suggests that short-range order above TN is a common feature in the magnetic behavior of layered Mn-based pnictides and oxypnictides.« less

  13. Observation of dimension dependent magnetic ordering in bismuth ferrite particulate and fiber nanostructures

    SciTech Connect

    Sakar, M.; Bharathkumar, S.; Balakumar, S.; Saravanan, P.

    2015-06-24

    Nanoparticles and nanofibers of bismuth ferrite were fabricated by sol-gel and electrospinning methods respectively. The structural and morphological analysis was carried out by XRD and FESEM techniques respectively. The magnetic measurements were carried out by SQUID magnetometer. The BFO nanofibers showed an enhanced magnetic property compared to nanoparticles. The observed magnetic properties were found to be associated with their magnetic ordering in the system where the antiferromagnetic/ferromagnetic core/shell like nature and ‘canted’ spin structure ordering was found to be the magnetic origin in the particulate and fiber nanostructures respectively.

  14. Thermo-magnetic materials for use in designing intelligent actuators

    SciTech Connect

    Ohtani, Yoshimutsu; Yoshimura, Fumikatsu; Hatakeyama, Iwao; Ishii, Yoshikazu

    1994-12-31

    The authors present the concept of an intelligent thermal actuator designed by using thermally sensitive magnetic materials. The use of the magnetic transition of FeRh alloy is very effective in increasing the actuator functions. These functions are freedom of direction, tuning temperature, and increasing both sensitivity and power. Two new types of actuator, a remote controlled optical driven thermo-magnetic motor and a temperature sensitive spring-less valve, are proposed and experimental results are shown.

  15. Experimental characterization of magnetic materials for the magnetic shielding of cryomodules in particle accelerators

    DOE PAGESBeta

    Sah, Sanjay; Myneni, Ganapati; Atulasimha, Jayasimha

    2015-10-26

    The magnetic properties of two important passive magnetic shielding materials (A4K and Amumetal) for accelerator applications, subjected to various processing and heat treatment conditions are studied comprehensively over a wide range of temperatures: from cryogenic to room temperature. Furthermore, we analyze the effect of processing on the extent of degradation of the magnetic properties of both materials and investigate the possibility of restoring these properties by re-annealing.

  16. Critical Magnetic Field Determination of Superconducting Materials

    SciTech Connect

    Canabal, A.; Tajima, T.; Dolgashev, V.A.; Tantawi, S.G.; Yamamoto, T.; /Tsukuba, Natl. Res. Lab. Metrol.

    2011-11-04

    Superconducting RF technology is becoming more and more important. With some recent cavity test results showing close to or even higher than the critical magnetic field of 170-180 mT that had been considered a limit, it is very important to develop a way to correctly measure the critical magnetic field (H{sup RF}{sub c}) of superconductors in the RF regime. Using a 11.4 GHz, 50-MW, <1 {mu}s, pulsed power source and a TE013-like mode copper cavity, we have been measuring critical magnetic fields of superconductors for accelerator cavity applications. This device can eliminate both thermal and field emission effects due to a short pulse and no electric field at the sample surface. A model of the system is presented in this paper along with a discussion of preliminary experimental data.

  17. Annual Conference on Magnetism and Magnetic Materials, 29th, Pittsburgh, PA, November 8-11, 1983, Proceedings

    SciTech Connect

    Hasegawa, R.; Koon, N.C.; Cooper, B.R.

    1984-03-15

    Various topics on magnetism and magnetic materials are addressed. The subjects considered include: spin glasses, amorphous magnetism, actinide and rare earth intermetallics, magnetic excitation, itinerant magnetism and magnetic structure, valence instabilities, Kondo effect, transport and Hall effects, mixed valence and Kondo compounds, superconductivity and magnetism, d and f electron magnetism and superconductivity, Fe-based microcrystalline and permanent magnetic alloys, hard and soft magnetic materials, and magnetooptics. Also discussed are: numerical methods for magnetic field computation, recording theory and experiments, recording heads and media, magnetic studies via hyperfine interactions, magnetic semiconductors, magnet insulators, transition metal systems, random fields, critical phenomena and magnetoelastic effects and resonance, surfaces and interfaces, magnetostatic waves and resonance, bubble materials and implantation, bubble devices and physics, magnetic separation, ferrofluids, magnetochemistry, new techniques and materials, and new applications.

  18. Spin frustration in one-dimensional magnetic materials

    NASA Astrophysics Data System (ADS)

    Borrás-Almenar, J. J.; Coronado, E.; Gallart, J. C.; Georges, R.; Gomez-García, Carlos J.

    1992-02-01

    Spin frustration is investigated in a classical-spin chain formed by antiferromagnetically coupled triangles sharing corners. This model considers two different magnetic sublattices which are coupled by three different Heisenberg exchange interactions. An exact expression of the zero-field magnetic susceptibility is derived and used in order to analyze the magnetic properties of the two-sublattice manganese chain MnMn(CDTA)·7H 2O.

  19. Magnetic patterning using ion irradiation for highly ordered CoPt alloys with perpendicular anisotropy

    SciTech Connect

    Abes, M.; Venuat, J.; Muller, D.; Carvalho, A.; Schmerber, G.; Beaurepaire, E.; Dinia, A.; Pierron-Bohnes, V.

    2004-12-15

    We used a combination of ion irradiation and e-beam lithography to magnetically pattern an ordered CoPt alloy with strong perpendicular magnetic anisotropy. Ion irradiation disorders the alloy and strongly reduces the magnetic anisotropy. Magnetic force microscopy showed a regular array of 1 {mu}m{sup 2} square dots with perpendicular anisotropy separated by 1 {mu}m large ranges with in-plane anisotropy. This is further confirmed by magnetic measurements, which showed that arrays protected by a 200 nm Pt layer present the same coercive field and the same perpendicular anisotropy as before irradiation. This is promising for applications in magnetic recording technologies.

  20. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    NASA Astrophysics Data System (ADS)

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-01

    Magnetic ordering temperatures in heavy rare earth metal dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to a pressure of 69 GPa and a temperature of 10 K. Previous studies using magnetic susceptibility measurements at high pressures were able to track magnetic ordering temperature only till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hcp phase and finally leveling off in the distorted face centered cubic phase of Dy. Our studies reaffirm that 4f-shell remains localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.

  1. Intrinsic magnetic order and inhomogeneous transport in Gd-implanted zinc oxide

    NASA Astrophysics Data System (ADS)

    Kennedy, John; Williams, Grant V. M.; Murmu, Peter P.; Ruck, Ben J.

    2013-12-01

    We report the results from magnetic, resistivity, and Hall effect measurements on a ferromagnetically ordered 5% Gd low energy implanted ZnO single crystal. Temperature-dependent magnetization measurements show that the Gd ions do not contribute to the magnetic order; hence, the magnetic order is intrinsic. The electronic transport in the Gd-implanted region is inhomogeneous, and there is a nonlinear Hall resistance. The nonlinear Hall resistance is likely to be a consequence of the inhomogeneous transport and not due to an anomalous Hall effect.

  2. Magnetic smart material application to adaptive x-ray optics

    NASA Astrophysics Data System (ADS)

    Ulmer, M. P.; Graham, Michael E.; Vaynman, Semyon; Cao, J.; Takacs, Peter Z.

    2010-09-01

    We discuss a technique of shape modification that can be applied to thin walled ({100-400 micron thickness) electroformed replicated optics or slumped glass optics to improve the near net shape of the mirror as well as the midfrequency ripple. The process involves sputter deposition of a magnetic smart material (MSM) film onto a permanently magnetic material. The MSM material exhibits strains about 400 times stronger than ordinary ferromagnetic materials. The deformation process involves a magnetic write head which traverses the surface, and under the guidance of active metrology feedback, locally magnetizes the surface to impart strain where needed. Designs and basic concepts as applied to space borne X-ray optics will be described.

  3. ADVANCED ELECTRIC AND MAGNETIC MATERIAL MODELS FOR FDTD ELECTROMAGNETIC CODES

    SciTech Connect

    Poole, B R; Nelson, S D; Langdon, S

    2005-05-05

    The modeling of dielectric and magnetic materials in the time domain is required for pulse power applications, pulsed induction accelerators, and advanced transmission lines. For example, most induction accelerator modules require the use of magnetic materials to provide adequate Volt-sec during the acceleration pulse. These models require hysteresis and saturation to simulate the saturation wavefront in a multipulse environment. In high voltage transmission line applications such as shock or soliton lines the dielectric is operating in a highly nonlinear regime, which require nonlinear models. Simple 1-D models are developed for fast parameterization of transmission line structures. In the case of nonlinear dielectrics, a simple analytic model describing the permittivity in terms of electric field is used in a 3-D finite difference time domain code (FDTD). In the case of magnetic materials, both rate independent and rate dependent Hodgdon magnetic material models have been implemented into 3-D FDTD codes and 1-D codes.

  4. Modulated magnetism in the ferromagnet PrPtAl: Clear experimental evidence of the `order by disorder' theory

    NASA Astrophysics Data System (ADS)

    Reid, J.-Ph.; O'Neill, Chris; Walker, Alex; Lithgow, Calum; Abdul-Jabbar, Gino; Yelland, Edward; Sokolov, Dmitry A.; Huxley, Andrew D.

    The ferromagnet PrPtAl is unlike any other. At the phase boundary between paramagnetism and ferromagnetism the fluctuations of the order parameter are so strong that energetically favourable phases of novel modulated magnetism emerge. In fact, it's the lack of order (the 'disorder') that is pivotal to promote a new 'order'. This mechanism is referred to as 'order by disorder' and is the centre of numerous theoretical studies. In this seminar, following an introduction on the topic of ferromagnetic materials, I will show how we can use both electrical and thermal conductivities to learn everything about these phases of modulated magnetism and to validate the predictions of the 'order by disorder' theory.

  5. Magnetization studies of first-order magnetostructural phase transition in polycrystalline FeRh thin films

    NASA Astrophysics Data System (ADS)

    Lu, Wei; Huang, Ping; Chen, Zhe; He, Chenchong; Wang, Yuxin; Yan, Biao

    2012-10-01

    The nucleation and growth of the transformed phase in the matrix of the original phase played an important role in the progress of magnetic transition. In spite of extensive investigations in B2 ordered FeRh alloy systems, until now few studies have been conducted for clarifying the nucleation and growth mechanism of the antiferromagnetic-ferromagnetic phase transition in FeRh alloys. In this work, B2 ordered polycrystalline FeRh thin films were fabricated on glass substrates by a sputtering technique and subsequent heat treatment. The as-deposited film shows a nonmagnetic property because of its face centred cubic structure. After annealing, the polycrystalline FeRh thin films show a clear first-order magnetostructural phase transition. The FeRh thin film shows an overall activation energy of about 228.6 kJ mol-1 for the entire first-order magnetostructural phase transition process. Results suggest that the first-order magnetostructural phase transition in ordered FeRh thin films follows the Johnson-Mehl-Avrami model with characteristic exponent n in the range 1-4, indicating that the phase transition process is a multi-step process characterized by different nucleation and growth mechanisms of the new ferromagnetic phase. The results obtained in this study will shed light on the underlying physics of the first-order magnetostructural phase transition of ordered FeRh alloys. The applicability of the concepts used in this study to the FeRh system shows universality and can be applied to other material systems where there is a first-order magnetostructural phase transition such as in manganites.

  6. Coexistence of Magnetic Order and Ferroelectricity at 2D Nanosheet Interfaces.

    PubMed

    Li, Bao-Wen; Osada, Minoru; Ebina, Yasuo; Ueda, Shigenori; Sasaki, Takayoshi

    2016-06-22

    Multiferroic materials, in which the electronic polarization can be switched by a magnetic field and vice versa, are of fundamental importance for new electronic technologies. However, there exist very few single-phase materials that exhibit such cross-coupling properties at room temperature, and heterostructures with a strong magnetoelectric coupling have only been made with complex techniques. Here, we present a rational design for multiferroic materials by use of a layer-by-layer engineering of 2D nanosheets. Our approach to new multiferroic materials is the artificial construction of high-quality superlattices by interleaving ferromagnetic Ti0.8Co0.2O2 nanosheets with dielectric perovskite-structured Ca2Nb3O10 nanosheets. Such an artificial structuring allows us to engineer the interlayer coupling, and the (Ti0.8Co0.2O2/Ca2Nb3O10/Ti0.8Co0.2O2) superlattices induce room-temperature ferroelectricity in the presence of the ferromagnetic order. Our technique provides a new route for tailoring artificial multiferroic materials in a highly controllable manner. PMID:27295544

  7. Magnetic relaxation dynamics driven by the first-order character of magnetocaloric La(Fe,Mn,Si)13.

    PubMed

    Lovell, Edmund; Bratko, Milan; Caplin, A David; Barcza, Alexander; Katter, Matthias; Ghivelder, Luis; Cohen, Lesley F

    2016-08-13

    Here, we study the temporal evolution of the magnetic field-driven paramagnetic to ferromagnetic transition in the La(Fe,Mn,Si)13 material family. Three compositions are chosen that show varying strengths of the first-order character of the transition, as determined by the relative magnitude of their magnetic hysteresis and temperature separation between the zero-field transition temperature Tc and the temperature Tcrit, where the transition becomes continuous. Systematic variations in the fixed field, isothermal rate of relaxation are observed as a function of temperature and as a function of the degree of first-order character. The relaxation rate is reduced in more weakly first-order compositions and is also reduced as the temperature is increased towards Tcrit At temperatures above Tcrit, the metastability of the transition vanishes along with its associated temporal dynamics.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'. PMID:27402929

  8. Digital lock-in detection of site-specific magnetism in magnetic materials

    DOEpatents

    Haskel, Daniel; Lang, Jonathan C.; Srajer, George

    2008-07-22

    The polarization and diffraction characteristics of x-rays incident upon a magnetic material are manipulated to provide a desired magnetic sensitivity in the material. The contrast in diffracted intensity of opposite helicities of circularly polarized x-rays is measured to permit separation of magnetic signals by element type and by atomic environment. This allows for the direct probing of magnetic signals from elements of the same species in nonequivalent atomic environments to better understand the behavior and characteristics of permanent magnetic materials. By using known crystallographic information together with manipulation of the polarization of x-rays having energies tuned near element-specific electronic excitations and by detecting and comparing the incident and diffracted photons at the same frequency, more accurate magnetic measurements can be made over shorter observation periods.

  9. Magnetic domain structure and thermal stabilization of laser treatment zones in soft magnetic materials

    NASA Astrophysics Data System (ADS)

    Pudov, V. I.; Dragoshanskii, Yu. N.

    2016-02-01

    A combined effect of laser treatment and introduced fine-grained weakly magnetic impurity Mg-P-B defects on the magnetic structure and physical properties of anisotropic electrotechnical materials has been investigated. Specific features of changes in the type and behavior of the magnetic domain structure under different types of deformation (laser irradiation, scratching, and introduction of interstitial defects) have been revealed. The physical basis and optimum conditions of increase in thermal stability of local laser treatment zones in soft magnetic alloys have been determined. The obtained results open the prospects of decreasing magnetic losses in soft magnetic alloys and producing magnetic materials with a high level of physical and mechanical properties that are more resistant to operating conditions.

  10. Pulse propagation, dispersion, and energy in magnetic materials.

    PubMed

    Scalora, Michael; D'Aguanno, Giuseppe; Mattiucci, Nadia; Akozbek, Neset; Bloemer, Mark J; Centini, Marco; Sibilia, Concita; Bertolotti, Mario

    2005-12-01

    We discuss pulse propagation effects in generic, electrically and magnetically dispersive media that may display large material discontinuities, such as a surface boundary. Using the known basic constitutive relations between the fields, and an explicit Taylor expansion to describe the dielectric susceptibility and magnetic permeability, we derive expressions for energy density and energy dissipation rates, and equations of motion for the coupled electric and magnetic fields. We then solve the equations of motion in the presence of a single interface, and find that in addition to the now-established negative refraction process an energy exchange occurs between the electric and magnetic fields as the pulse traverses the boundary. PMID:16486072

  11. Domain Collapse in Grooved Magnetic Garnet Material

    NASA Technical Reports Server (NTRS)

    Peredo, J.; Fedyunin, Y.; Patterson, G.

    1995-01-01

    Domain collapse fields in grooved garnet material were investigated by experimental observation and numerical simulation. The results indicate that the change in domain collapse field is largely due to magnetostatic effects produced by the groove edge. A simplified model based on the effective field produced at a groove edge, and local changes in the material thickness explain the observed trends very well.!.

  12. Electromagnetic valve for controlling the flow of molten, magnetic material

    DOEpatents

    Richter, T.

    1998-06-16

    An electromagnetic valve for controlling the flow of molten, magnetic material is provided, which comprises an induction coil for generating a magnetic field in response to an applied alternating electrical current, a housing, and a refractory composite nozzle. The nozzle is comprised of an inner sleeve composed of an erosion resistant refractory material (e.g., a zirconia ceramic) through which molten, magnetic metal flows, a refractory outer shell, and an intermediate compressible refractory material, e.g., unset, high alumina, thermosetting mortar. The compressible refractory material is sandwiched between the inner sleeve and outer shell, and absorbs differential expansion stresses that develop within the nozzle due to extreme thermal gradients. The sandwiched layer of compressible refractory material prevents destructive cracks from developing in the refractory outer shell. 5 figs.

  13. Electromagnetic valve for controlling the flow of molten, magnetic material

    DOEpatents

    Richter, Tomas

    1998-01-01

    An electromagnetic valve for controlling the flow of molten, magnetic material is provided, which comprises an induction coil for generating a magnetic field in response to an applied alternating electrical current, a housing, and a refractory composite nozzle. The nozzle is comprised of an inner sleeve composed of an erosion resistant refractory material (e.g., a zirconia ceramic) through which molten, magnetic metal flows, a refractory outer shell, and an intermediate compressible refractory material, e.g., unset, high alumina, thermosetting mortar. The compressible refractory material is sandwiched between the inner sleeve and outer shell, and absorbs differential expansion stresses that develop within the nozzle due to extreme thermal gradients. The sandwiched layer of compressible refractory material prevents destructive cracks from developing in the refractory outer shell.

  14. Straintronics-based magnetic tunneling junction: Dynamic and static behavior analysis and material investigation

    NASA Astrophysics Data System (ADS)

    Barangi, Mahmood; Mazumder, Pinaki

    2014-04-01

    We theoretically study the dynamic and static effects of mechanical stress on a straintronics device that includes a piezoelectric film combined with a magnetic tunneling junction. The inverse magnetostriction effect is studied in detail by realizing the varying magnetic susceptibility of the nanomagnet under stress. A dynamic model is developed based on the Landau-Lifshitz-Gilbert (LLG) equation, which provides a platform to simulate the magnetization vector's behavior, critical flipping voltage, and delay properties. Furthermore, by converting the LLG equation into a 2nd order damping differential equation, we develop a proximate approach. This approach predicts the dynamic behavior of the magnetization vector and its dependency on material properties and applied voltage across the device without using sophisticated numerical calculations of the LLG model. Different dynamic and static material properties are observed by simulating five common magnetostrictive materials, including a newly discovered alloy, Galfenol.

  15. Soft Magnetic Materials and Devices on Energy Applications

    NASA Astrophysics Data System (ADS)

    Xing, Xing

    The fast development of wireless communication system in recent years has been driving the development of the power devices from different aspects, especially the miniaturized volume and renewable power supply, and etc. In this work, we studied the high frequency magnetic properties of the soft magnetic material---FeCoB/Al2O3/FeCoB structures with varied Al2O3 thickness (2nm to 15nm), which would be applied in to the integrated inductors. Optimized Al2O3 thickness was found to achieve low coercive field and high permeability while maintaining high saturation field and low magnetic loss. Three types of on Si integrated solenoid inductors employing the FeCoB/Al2O3 multilayer structure were designed with the same area but different core configurations. A maximum inductance of 60 nH was achieved on a two-sided core inductor. The magnetic core was able to increase the inductance by a factor of 3.6 ˜6.7, compared with the air core structures. Vibration energy harvesting technologies have been utilized to serve as the renewable power supply for the wireless sensors. In this work, two generations of vibration energy harvesting devices based on high permeability magnetic material were designed and tested. The strong magnetic coupling between the magnetic material and the bias magnetic field leads to magnetic flux reversal and maximized flux change in the magnetic material during vibration. An output power of 74mW and a working bandwidth of 10Hz were obtained at an acceleration of 0.57g (g=9.8m/s2) for the 1st generation design, at 54Hz. An output voltage of 2.52 V and a power density of 20.84 mW/cm3 were demonstrated by the 2nd generation design at 42 Hz, with a half peak working bandwidth of 6 Hz.

  16. Magnetic Ordering-Induced Multiferroic Behavior in [CH3NH3][Co(HCOO)3] Metal-Organic Framework.

    PubMed

    Gómez-Aguirre, L Claudia; Pato-Doldán, Breogán; Mira, J; Castro-García, Socorro; Señarís-Rodríguez, María Antonia; Sánchez-Andújar, Manuel; Singleton, John; Zapf, Vivien S

    2016-02-01

    We present the first example of magnetic ordering-induced multiferroic behavior in a metal-organic framework magnet. This compound is [CH3NH3][Co(HCOO)3] with a perovskite-like structure. The A-site [CH3NH3](+) cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii-Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior. PMID:26717023

  17. Magnetic ordering-induced multiferroic behavior in [CH3NH3][Co(HCOO)3] metal-organic framework.

    DOE PAGESBeta

    Gomez-Aguirre, Lilian Claudia; Zapf, Vivien S.; Pato-Doldan, Breogan; Mira, Jorge; Castro-Garcia, Socorro; Senaris-Rodriguez, Maria Antonia; Sanchez-Andujara, Manuel; Singleton, John

    2015-12-30

    Here, we present the first example of magnetic ordering-induced multiferroic behavior in a metal–organic framework magnet. This compound is [CH3NH3][Co(HCOO)3] with a perovskite-like structure. The A-site [CH3NH3]+ cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii–Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangementmore » occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior.« less

  18. Design, Fabrication, and Implementation of a Wireless, Passive Implantable Pressure Sensor Based on Magnetic Higher-Order Harmonic Fields

    PubMed Central

    Tan, Ee Lim; DeRouin, Andrew J.; Pereles, Brandon D.; Ong, Keat Ghee

    2011-01-01

    A passive and wireless sensor was developed for monitoring pressure in vivo. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is an airtight chamber sealed with an elastic pressure membrane. A strip of magnetically-soft material is attached to the bottom of the chamber and a permanent magnet strip is embedded inside the membrane. Under the excitation of an externally applied AC magnetic field, the magnetically-soft strip produces a higher-order magnetic signature that can be remotely detected with an external receiving coil. As ambient pressure varies, the pressure membrane deflects, altering the separation distance between the magnetically-soft strip and the permanent magnet. This shifts the higher-order harmonic signal, allowing for detection of pressure change as a function of harmonic shifting. The wireless, passive nature of this sensor technology allows for continuous long-term pressure monitoring, particularly useful for biomedical applications such as monitoring pressure in aneurysm sac and sphincter of Oddi. In addition to demonstrating its pressure sensing capability, an animal model was used to investigate the efficacy and feasibility of the pressure sensor in a biological environment. PMID:25585564

  19. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review.

    PubMed

    Morón, Carlos; Cabrera, Carolina; Morón, Alberto; García, Alfonso; González, Mercedes

    2015-01-01

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a "simple" and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc. PMID:26569244

  20. Magnetic Sensors Based on Amorphous Ferromagnetic Materials: A Review

    PubMed Central

    Morón, Carlos; Cabrera, Carolina; Morón, Alberto; García, Alfonso; González, Mercedes

    2015-01-01

    Currently there are many types of sensors that are used in lots of applications. Among these, magnetic sensors are a good alternative for the detection and measurement of different phenomena because they are a “simple” and readily available technology. For the construction of such devices there are many magnetic materials available, although amorphous ferromagnetic materials are the most suitable. The existence in the market of these materials allows the production of different kinds of sensors, without requiring expensive manufacture investments for the magnetic cores. Furthermore, these are not fragile materials that require special care, favouring the construction of solid and reliable devices. Another important feature is that these sensors can be developed without electric contact between the measuring device and the sensor, making them especially fit for use in harsh environments. In this review we will look at the main types of developed magnetic sensors. This work presents the state of the art of magnetic sensors based on amorphous ferromagnetic materials used in modern technology: security devices, weapon detection, magnetic maps, car industry, credit cards, etc. PMID:26569244

  1. In-situ SAXS observation of magnetic field effects on block copolymer ordering and alignment

    NASA Astrophysics Data System (ADS)

    Osuji, Chinedum; Gopinadhan, Manesh; Majewksi, Pawel

    2012-02-01

    The use of external fields to direct block copolymer self-assembly is well documented. Magnetic fields offer particular promise due to their space-pervasive nature and the ability to produce arbitrary alignments over truly macroscopic length scales in appropriate systems. We present here the results of in-situ SAXS studies of side-chain liquid crystalline diblock copolymers ordering under high magnetic fields and ex-situ GISAXS data on thin films. Despite the coincidence of the block copolymer order-disorder transition (ODT) and the LC clearing temperature in these weakly segregated materials, there is no measurable effect of the field on the ODT of the system, up to 6 T. This is in line with rough estimates based simply on the magnitudes of the relevant energy scales - the free energy of field interaction and the enthalpy of the isotropic-LC transition. We show that the alignment of the system is critically limited by the viscosity of the mesophase such that alignment can only be advanced by residence in a small temperature window near TODT. This residence produces a weakly aligned system which thereafter transitions to a strongly aligned state on cooling even in the absence of the field.

  2. Ordering, thermal excitations and phase transitions in dipolar coupled mono-domain magnet arrays

    NASA Astrophysics Data System (ADS)

    Kapaklis, Vassilios

    2015-03-01

    Magnetism has provided a fertile test bed for physical models, such as the Heisenberg and Ising models. Most of these investigations have focused on solid materials and relate to their atomic properties such as the atomic magnetic moments and their interactions. Recently, advances in nanotechnology have enabled the controlled patterning of nano-sized magnetic particles, which can be arranged in extended lattices. Tailoring the geometry and the magnetic material of these lattices, the magnetic interactions and magnetization reversal energy barriers can be tuned. This enables interesting interaction schemes to be examined on adjustable length and energy scales. As a result such nano-magnetic systems represent an ideal playground for the study of physical model systems, being facilitated by direct magnetic imaging techniques. One particularly interesting case is that of systems exhibiting frustration, where competing interactions cannot be simultaneously satisfied. This results in a degeneracy of the ground state and intricate thermodynamic properties. An archetypical frustrated physical system is water ice. Similar physics can be mirrored in nano-magnetic arrays, by tuning the arrangement of neighboring magnetic islands, referred to as artificial spin ice. Thermal excitations in such systems resemble magnetic monopoles. In this presentation key concepts related to nano-magnetism and artificial spin ice will be introduced and discussed, along with recent experimental and theoretical developments.

  3. Charge orders, magnetism and pairings in the cuprate superconductors.

    PubMed

    Kloss, T; Montiel, X; de Carvalho, V S; Freire, H; Pépin, C

    2016-08-01

    We review the recent developments in the field of cuprate superconductors with special focus on the recently observed charge order in the underdoped compounds. We introduce new theoretical developments following the study of the antiferromagnetic quantum critical point in two dimensions, in which preemptive orders in both charge and superconducting (SC) sectors emerge, that are in turn related by an SU(2) symmetry. We consider the implications of this proliferation of orders in the underdoped region, and provide a study of the type of fluctuations which characterize the SU(2) symmetry. We identify an intermediate energy scale where the SC fluctuations are dominant and argue that they are unstable towards the formation of a resonant excitonic state at the pseudogap temperature T (*). We discuss the implications of this scenario for a few key experiments. PMID:27427401

  4. Charge orders, magnetism and pairings in the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Kloss, T.; Montiel, X.; de Carvalho, V. S.; Freire, H.; Pépin, C.

    2016-08-01

    We review the recent developments in the field of cuprate superconductors with special focus on the recently observed charge order in the underdoped compounds. We introduce new theoretical developments following the study of the antiferromagnetic quantum critical point in two dimensions, in which preemptive orders in both charge and superconducting (SC) sectors emerge, that are in turn related by an SU(2) symmetry. We consider the implications of this proliferation of orders in the underdoped region, and provide a study of the type of fluctuations which characterize the SU(2) symmetry. We identify an intermediate energy scale where the SC fluctuations are dominant and argue that they are unstable towards the formation of a resonant excitonic state at the pseudogap temperature T *. We discuss the implications of this scenario for a few key experiments.

  5. Thermal expansion of several materials for superconducting magnets. Final report

    SciTech Connect

    Clark, A.F.; Fujii, G.; Ranney, M.A.

    1981-09-01

    The thermal expansion of several materials used in the construction of high field superconducting magnets has been measured from 4 K to room temperature. The materials were a NbTi and two A15 multifilamentary conductors and several nonmetallic composites made from linen/phenolic, fiberglass/epoxy and superconducting wire/epoxy.

  6. Engineered materials for all-optical helicity-dependent magnetic switching.

    PubMed

    Mangin, S; Gottwald, M; Lambert, C-H; Steil, D; Uhlíř, V; Pang, L; Hehn, M; Alebrand, S; Cinchetti, M; Malinowski, G; Fainman, Y; Aeschlimann, M; Fullerton, E E

    2014-03-01

    The possibility of manipulating magnetic systems without applied magnetic fields have attracted growing attention over the past fifteen years. The low-power manipulation of the magnetization, preferably at ultrashort timescales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. Here we explore the optical manipulation of the magnetization in engineered magnetic materials. We demonstrate that all-optical helicity-dependent switching (AO-HDS) can be observed not only in selected rare earth-transition metal (RE-TM) alloy films but also in a much broader variety of materials, including RE-TM alloys, multilayers and heterostructures. We further show that RE-free Co-Ir-based synthetic ferrimagnetic heterostructures designed to mimic the magnetic properties of RE-TM alloys also exhibit AO-HDS. These results challenge present theories of AO-HDS and provide a pathway to engineering materials for future applications based on all-optical control of magnetic order. PMID:24531398

  7. In-situ microscopy of the first-order magnetic phase transition in FeRh thin films

    NASA Astrophysics Data System (ADS)

    Baldasseroni, Chloe

    Simple ferromagnetic (FM) and antiferromagnetic (AF) materials such as Fe and Cr become paramagnetic when heated above some critical temperature, in what is known as a second-order phase transition. Less usual magnetic transitions are found in the magnetic world, for example a first-order magnetic phase transition from AF to FM with increasing temperature. Equiatomic FeRh has been known to exhibit such a transition for over 50 years, with a transition temperature slightly above room temperature. Interest in this material has been renewed in the recent years due to its potential application for heat-assisted magnetic recording, as well as a test system for fundamental studies of the physics of magnetic phase transitions. Similarly to crystallization, this AF-FM transition is expected to proceed by nucleation of magnetic domains but the features of the first-order hysteretic transition have been difficult to study with macroscopic measurements and very few microscopic studies have been performed. In this work, FeRh thin films were synthesized by magnetron sputtering and structurally and magnetically characterized. A membrane-based heating device was designed to enable temperature-dependent microscopy measurements, providing a thermally uniform and well-controlled sample area. Synchrotron x-ray magnetic microscopy was used to study the temperature-driven AF-FM phase transition in epitaxial FeRh thin films in zero field. Using magnetic microscopy with x-ray magnetic circular dichroism, the different stages of nucleation, growth and coalescence of FM domains were observed across the transition and details of the nucleation were identified. The FM phase nucleates into single domain islands and the width of the transition of the individual nuclei upon heating is sharper than that of the macroscopic transition. Using magnetic microscopy with x-ray magnetic linear dichroism, the evolution of the AF phase was studied. Differences in the morphology of AF and FM phases were

  8. Multimaterial magnetically assisted 3D printing of composite materials

    NASA Astrophysics Data System (ADS)

    Kokkinis, Dimitri; Schaffner, Manuel; Studart, André R.

    2015-10-01

    3D printing has become commonplace for the manufacturing of objects with unusual geometries. Recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping. Here we show that a new dimension in this design space can be exploited through the control of the orientation of anisotropic particles used as building blocks during a direct ink-writing process. Particle orientation control is demonstrated by applying low magnetic fields on deposited inks pre-loaded with magnetized stiff platelets. Multimaterial dispensers and a two-component mixing unit provide additional control over the local composition of the printed material. The five-dimensional design space covered by the proposed multimaterial magnetically assisted 3D printing platform (MM-3D printing) opens the way towards the manufacturing of functional heterogeneous materials with exquisite microstructural features thus far only accessible by biological materials grown in nature.

  9. Multimaterial magnetically assisted 3D printing of composite materials

    PubMed Central

    Kokkinis, Dimitri; Schaffner, Manuel; Studart, André R.

    2015-01-01

    3D printing has become commonplace for the manufacturing of objects with unusual geometries. Recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping. Here we show that a new dimension in this design space can be exploited through the control of the orientation of anisotropic particles used as building blocks during a direct ink-writing process. Particle orientation control is demonstrated by applying low magnetic fields on deposited inks pre-loaded with magnetized stiff platelets. Multimaterial dispensers and a two-component mixing unit provide additional control over the local composition of the printed material. The five-dimensional design space covered by the proposed multimaterial magnetically assisted 3D printing platform (MM-3D printing) opens the way towards the manufacturing of functional heterogeneous materials with exquisite microstructural features thus far only accessible by biological materials grown in nature. PMID:26494528

  10. Multimaterial magnetically assisted 3D printing of composite materials.

    PubMed

    Kokkinis, Dimitri; Schaffner, Manuel; Studart, André R

    2015-01-01

    3D printing has become commonplace for the manufacturing of objects with unusual geometries. Recent developments that enabled printing of multiple materials indicate that the technology can potentially offer a much wider design space beyond unusual shaping. Here we show that a new dimension in this design space can be exploited through the control of the orientation of anisotropic particles used as building blocks during a direct ink-writing process. Particle orientation control is demonstrated by applying low magnetic fields on deposited inks pre-loaded with magnetized stiff platelets. Multimaterial dispensers and a two-component mixing unit provide additional control over the local composition of the printed material. The five-dimensional design space covered by the proposed multimaterial magnetically assisted 3D printing platform (MM-3D printing) opens the way towards the manufacturing of functional heterogeneous materials with exquisite microstructural features thus far only accessible by biological materials grown in nature. PMID:26494528

  11. Magnetic ordering and slow dynamics in a Ho-based bulk metallic glass with moderate random magnetic anisotropy

    SciTech Connect

    Luo, Q.; Schwarz, B.; Mattern, N.; Eckert, J.

    2011-06-01

    Results of magnetic measurements are presented for a Ho-based bulk metallic glass, which shows similarities and differences with conventional spin glasses (SGs), and significant differences with weak random magnetic anisotropy (RMA) systems. Both ac and dc magnetic measurements indicate a single transition from paramagnetic to speromagnetic or spin glasslike state around 5.6 K. The moderate RMA prevents the formation of long- (or quasilong)-range magnetic order and slows down the spin dynamics in the critical region. Further its isothermal remnant magnetization exhibits a small maximum, instead of a gradual increase with field in SGs. The roles of RMA in the magnetic structure and dynamics of disordered and frustrated systems are discussed by comparisons between the weak RMA system, the moderate or strong RMA system, and conventional SG.

  12. Magnetic order in α -RuCl3 : A honeycomb-lattice quantum magnet with strong spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Sears, J. A.; Songvilay, M.; Plumb, K. W.; Clancy, J. P.; Qiu, Y.; Zhao, Y.; Parshall, D.; Kim, Young-June

    2015-04-01

    We report magnetic and thermodynamic properties of single crystal α -RuCl3 , in which the Ru3+(4 d5) ion is in its low spin state and forms a honeycomb lattice. Two features are observed in both magnetic susceptibility and specific heat data; a sharp peak at 7 K and a broad hump near 10-15 K. In addition, we observe a metamagnetic transition between 5 and 10 T. Our neutron diffraction study of single crystal samples confirms that the low temperature peak in the specific heat is associated with a magnetic order with unit cell doubling along the honeycomb (100) direction, which is consistent with zigzag order, one of the types of magnetic order predicted within the framework of the Kitaev-Heisenberg model.

  13. Competing magnetic double-Q phases and superconductivity-induced reentrance of C2 magnetic stripe order in iron pnictides

    NASA Astrophysics Data System (ADS)

    Gastiasoro, Maria N.; Andersen, Brian M.

    2015-10-01

    We perform a microscopic theoretical study of the generic properties of competing magnetic phases in iron pnictides. As a function of electron filling and temperature, the magnetic stripe (single-Q ) order forms a dome, but competing noncollinear and nonuniform double-Q phases exist at the foot of the dome, in agreement with recent experiments. We compute and compare the electronic properties of the different magnetic phases, investigate the role of competing superconductivity, and show how disorder may stabilize double-Q order. Superconductivity is shown to compete more strongly with double-Q magnetic phases, which can lead to reentrance of the C2 (single-Q ) order, in agreement with recent thermal expansion measurements on K-doped Ba-122 crystals.

  14. Novel Magnetic Materials for Sensing and Cooling Applications

    NASA Astrophysics Data System (ADS)

    Chaturvedi, Anurag

    2011-12-01

    The overall goals of the present PhD research are to explore the giant magnetoimpedance (GMI) and giant magnetocaloric (GMC) effects in functional magnetic materials and provide guidance on the optimization of the material properties for use in advanced magnetic sensor and refrigeration applications. GMI has attracted growing interest due to its promising applications in high-performance magnetic sensors. Research in this field is focused on the development of new materials with properties appropriate for practical GMI sensor applications. In this project, we have successfully set up a new magneto-impedance measurement system in the Functional Materials Laboratory at USF. We have established, for the first time, the correlation between sample surface, magnetic softness, critical length, and GMI in Co-based amorphous ribbon materials, which provide a good handle on selecting the suitable operating frequency range of magnetic materials for GMI-based field sensor applications. The impact of field-induced magnetic anisotropy on the GMI effect in Co-based nanocrystalline ribbon materials has also been investigated, providing an important understanding of the correlation between the microstructure, magnetic anisotropy, and GMI in these materials. We have shown that coating a thin layer of magnetic metal on the surface of a magnetic ribbon can reduce stray fields due to surface irregularities and enhance the magnetic flux paths closure of the bilayer structure, both of which, in effect, increase the GMI and its field sensitivity. This finding provides a new way for tailoring GMI in surface-modified soft ferromagnetic ribbons for use in highly sensitive magnetic sensors. We have also introduced the new concepts of incorporating GMI technology with superparamagnetic nanoparticles for biosensing applications and with carbon nanotubes for gas and chemical sensing applications. GMC forms the basis for developing advanced magnetic refrigeration technology and research in this

  15. Higher-Order Theory for Functionally Graded Materials

    NASA Technical Reports Server (NTRS)

    Aboudi, J.; Pindera, M. J.; Arnold, Steven M.

    2001-01-01

    Functionally graded materials (FGM's) are a new generation of engineered materials wherein the microstructural details are spatially varied through nonuniform distribution of the reinforcement phase(s). Engineers accomplish this by using reinforcements with different properties, sizes, and shapes, as well as by interchanging the roles of the reinforcement and matrix phases in a continuous manner (ref. 1). The result is a microstructure that produces continuously or discretely changing thermal and mechanical properties at the macroscopic or continuum scale. This new concept of engineering the material's microstructure marks the beginning of a revolution both in the materials science and mechanics of materials areas since it allows one, for the first time, to fully integrate the material and structural considerations into the final design of structural components. Functionally graded materials are ideal candidates for applications involving severe thermal gradients, ranging from thermal structures in advanced aircraft and aerospace engines to computer circuit boards. Owing to the many variables that control the design of functionally graded microstructures, full exploitation of the FGM's potential requires the development of appropriate modeling strategies for their response to combined thermomechanical loads. Previously, most computational strategies for the response of FGM's did not explicitly couple the material's heterogeneous microstructure with the structural global analysis. Rather, local effective or macroscopic properties at a given point within the FGM were first obtained through homogenization based on a chosen micromechanics scheme and then subsequently used in a global thermomechanical analysis.

  16. 76 FR 75950 - Hazardous Materials: Emergency Restriction/Prohibition Order

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-05

    ... constitutes an imminent hazard to the safe transportation of hazardous materials. For more detailed... transportation or transport hazardous materials in commerce within the United States and are therefore ``persons... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF...

  17. Opportunities and challenges of 2D magnetic van der Waals materials: magnetic graphene?

    NASA Astrophysics Data System (ADS)

    Park, Je-Geun

    2016-08-01

    There has been a huge increase of interests in two-dimensional van der Waals materials over the past ten years or so with the conspicuous absence of one particular class of materials: magnetic van der Waals systems. In this Viewpoint, we point it out and illustrate how we might be able to benefit from exploring these so-far neglected materials.

  18. Magnetic materials selection for static inverter and converter transformers

    NASA Technical Reports Server (NTRS)

    Mclyman, W. T.

    1973-01-01

    A program to study magnetic materials is described for use in spacecraft transformers used in static inverters, converters, and transformer-rectifier supplies. Different magnetic alloys best suited for high-frequency and high-efficiency applications were comparatively investigated together with an investigation of each alloy's inherent characteristics. The materials evaluated were the magnetic alloys: (1) 50% Ni, 50% Fe; (2) 79% Ni, 17% Fe, 4% Mo; (3) 48% Ni, 52% Fe; (4) 78% Ni, 17% Fe, 5% Mo; and (5) 3% Si, 97% Fe. Investigations led to the design of a transformer with a very low residual flux. Tests were performed to determine the dc and ac magnetic properties at 2400 Hz using square-wave excitation. These tests were performed on uncut cores, which were then cut for comparison of the gapped and ungapped magnetic properties. When the data of many transformers in many configurations were compiled the optimum transformer was found to be that with the lowest residual flux and a small amount of air gap in the magnetic material. The data obtained from these tests are described, and the potential uses for the materials are discussed.

  19. Reinvestigation of long-range magnetic ordering in icosahedral Tb-Mg-Zn

    SciTech Connect

    Islam, Z.; Fisher, I.R.; Zarestky, J.; Canfield, P.C.; Stassis, C.; Goldman, A.I.

    1998-05-01

    We present results of a study of possible magnetic ordering in the icosahedral phase of Tb-Mg-Zn probed by bulk magnetization measurements and neutron diffraction. Measurements on both crushed single grains and cast polycrystalline samples of Tb-Mg-Zn were performed. Magnetization measurements on both samples reveal only a spin-glass-like transition at approximately 5.8K. Neutron diffraction from the crushed single grains reveals only short-range magnetic ordering at low temperatures, with no evidence of the long-range magnetic ordering reported previously [Charrier, Ouladdiaf, and Schmitt, Phys. Rev. Lett. {bold 78}, 4637 (1997)]. Likewise, the cast polycrystalline samples exhibit primarily diffuse magnetic scattering at low temperature, but at least one relatively sharp diffraction peak was observed. Our results indicate that for single grain samples there is no long-range magnetic ordering and that, at best, the magnetic ordering in these quasicrystalline alloys is not very robust. {copyright} {ital 1998} {ital The American Physical Society}

  20. Development of a boundary magnetic charge method for computing magnetic fields in a system containing saturated magnetic materials

    NASA Astrophysics Data System (ADS)

    Murata, H.; Ishigami, M.; Shimoyama, H.

    2016-01-01

    In previous research, we developed a three-dimensional (3D) boundary magnetic charge method (BMCM) for high-accuracy field calculations in a static magnetic field, even when there exist great differences between the magnitudes of permeability between neighboring magnetic materials. This method, however, cannot be applied to a system that contains saturated magnetic materials. In the present study, therefore, we have developed a novel method that addresses this issue. According to this new method, we divide the region containing the magnetic material into small-volume elements and divide the boundaries between neighboring small-volume elements into small-surface elements, assigning each element an appropriate initial value of permeability. The magnetic field inside and outside of the magnetic material is calculated using this permeability. The value of the permeability of each element is iteratively updated using μ-H data. The updated value of the permeability after the i-th iteration, μi, is compared with that of the previous value, μi-1. If the difference between the two values is within a preset range, the iteration process is judged to have converged and the value of μi is regarded as the final converged value of the permeability. The magnetic field at an arbitrary point in space and/or inside the body of the magnetic material is calculated from the converged permeability of each element. As a result, we have succeeded in developing a novel BMCM for the calculation of a static magnetic field with high accuracy in a system containing saturated magnetic materials.

  1. Kinetic arrest of the first order austenite to martensite phase transition in Ni50Mn34In16 : dc magnetization studies

    NASA Astrophysics Data System (ADS)

    Sharma, V. K.; Chattopadhyay, M. K.; Roy, S. B.

    2007-10-01

    We report results of dc magnetization studies focusing particularly on the austenite-martensite phase transition in Ni50Mn34In16 . We show that the nature of this phase transition depends significantly on the temperature (T) and magnetic field (H) history of the sample. In the presence of high magnetic field, this austenite to martensite first order phase transition is kinetically arrested. The low-temperature and high-field magnetic state shows a typical nonergodic glasslike dynamical response. Comparisons are made with similar phenomena observed recently in various classes of magnetic materials including CMR manganites.

  2. Magnetic, thermodynamic and transport properties at the first and second order magnetic phase transitions in Dy5Si3 compound

    NASA Astrophysics Data System (ADS)

    Falkowski, M.; Kowalczyk, A.; Toliński, T.

    2013-04-01

    We present extended studies including the dc and ac magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistivity measurements for the Dy5Si3 compound with the hexagonal Mn5Si3-type structure. The results indicate that this compound orders antiferromagnetically below TN=137 K. The magnetic properties of Dy5Si3 are mainly governed by the presence of the magnetic moments of Dy3+ ions. In the paramagnetic range, the magnetic susceptibility follows the Curie-Weiss law with μeff=10.57 μB/Dy, which is very close to the theoretical value of 10.6 μB. From the magnetometric, specific heat and transport data it has been found that below 50 K this compound reveals a non-collinear magnetic order, associated with a phase transition, probably of the first order type. On the basis of the thermodynamic approach, we report the magnetocaloric properties in the whole temperature range but concentrate mainly on the region around 50 K. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change ΔSM as well as the adiabatic temperature change ΔTad using the specific heat data. In spite of the only moderate ΔSM values a significant relative cooling power has been observed.

  3. Nonporous magnetic materials as enzyme supports: studies with immobilized chymotrypsin.

    PubMed

    Munro, P A; Dunnill, P; Lilly, M D

    1977-01-01

    Chymotrypsin has been immobilized to several nonporous magnetic materials. Nickel particles were considered to be most suitable as immobilized enzyme supports. Chymotrypsin immobilized to nonporous magnetic supports was not fouled significantly by either whole milk or clarified yeast homogenate. AE-cellulose-chymotrypsin was rapidly fouled by both these materials and chymotrypsin immobilized to acrylic-based ion exchangers was slowly fouled. Immobilized enzyme activity was found to be inversely proportional to particle diameter for nonporous rock magnetic particles. Immobilization by adsorption and then glutaraldehyde crosslinking was used to produce controlled amounts of chymotrypsin on the particles. Esterolytic activity increased with enzyme loading but caseinolytic activity did not increase. Chymotrypsin is inhibited by metal ions from the magnetic supports. It is partially protected by use of a preliminary protein coating and may be reactivated by incubation with EDTA or BSA. PMID:14743

  4. Multipolar phases and magnetically hidden order: review of the heavy-fermion compound Ce1-x La x B6.

    PubMed

    Cameron, Alistair S; Friemel, Gerd; Inosov, Dmytro S

    2016-06-01

    Cerium hexaboride is a cubic f-electron heavy-fermion compound that displays a rich array of low-temperature magnetic ordering phenomena which have been the subject of investigation for more than 50 years. Its complex behaviour is the result of competing interactions, with both itinerant and local electrons playing important roles. Investigating this material has proven to be a substantial challenge, in particular because of the appearance of a 'magnetically hidden order' phase, which remained elusive to neutron-scattering investigations for many years. It was not until the development of modern x-ray scattering techniques that the long suspected multipolar origin of this phase was confirmed. Doping with non-magnetic lanthanum dilutes the magnetic cerium sublattice and reduces the f-electron count, bringing about substantial changes to the ground state with the emergence of new phases and quantum critical phenomena. To this day, Ce1-x La x B6 and its related compounds remain a subject of intense interest. Despite the substantial progress in understanding their behaviour, they continue to reveal new and unexplained physical phenomena. Here we present a review of the accumulated body of knowledge on this family of materials in order to provide a firm standpoint for future investigations. PMID:27177075

  5. Complex magnetic ordering in CeFe1.76 studied by neutron diffraction

    SciTech Connect

    Jayasekara, Wageesha T; Tian, W; Hodovanets, Halyna; Canfield, Paul C; Bud'ko, Serguei L; Kreyssig, Andreas; Goldman, Alan I

    2014-10-01

    Neutron diffraction measurements on a single crystal of CeGe1.76 reveal a complex series of magnetic transitions at low temperature. At TN≈7 K, there is a transition from a paramagnetic state at higher temperature to an incommensurate magnetic structure characterized by a magnetic propagation vector (0 0 τ) with τ≈1/4 and the magnetic moment along the a axis of the orthorhombic unit cell. Below TLI≈5 K, the magnetic structure locks in to a commensurate structure with τ=1/4 and the magnetic moment remains along the a axis. Below T≈4 K, we find additional half-integer and integer indexed magnetic Bragg peaks consistent with a second commensurately ordered antiferromagnetic state.

  6. NMR investigation of field-induced magnetic order in barium manganese oxide

    NASA Astrophysics Data System (ADS)

    Suh, Steve

    As early as 1956, Matsubara and Matsuda found an exact correspondence between a lattice gas model and a quantum antiferromagnet model[1]. They paved the way for the language of integer spin boson particles to be used interchangeably with quantum magnetic insulator systems in a general manner. For example, an analogy of density of bosons is found in magnetization, and analogy of chemical potential is found in external field. Just as there exist corresponding parameters between these two seemingly unrelated systems, quantum magnets can also exhibit consequences of Boson particle systems. In particular, spin-ordering transition in quantum magnets can be interpreted as Bose-Einstein condensate (BEC) transition in Boson particle framework. Direct observation of BEC in Boson particles has been realized in 4He's superfluid transition and in dilute atomic gas clouds cooled to very low temperatures[2]. In this thesis, we try to realize and analyze BEC transition through field-induced spin-ordering transition in the S = 1 antiferromagnetic dimer system, Ba3Mn2O8. We perform NMR measurements with 135,137Ba nucleus as a local probe. Although S = 1 spin properties of Ba 3Mn2O8 come from electronic spins on Mn atoms, hyperfine coupling between Mn electronic spins and Ba nuclear spins allow us to infer Mn electrons' spin information. Since there are 2 inequivalent Ba sites, Ba(1) and Ba(2), in Ba3Mn2O8, we essentially have two probes that provide a detailed picture of structure and nature of magnetism in this material. There are many antiferromagnetic BEC candidates, but there is a significant advantage of studying Ba3Mn 2O8. Unlike the other popular antiferromagnetic BEC candidates such as TlCuCl3[3] or BaCuSi2O6[4], we find no evidence of lattice deformation in Ba3Mn2O8 . This allows us an unprecedented clean look at magnetic properties. Aside from the aforementioned simple technical advantage, there are new physics that we can learn from Ba3Mn2O 8. The geometric frustration of

  7. Magnetic ordering of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6

    NASA Astrophysics Data System (ADS)

    Asai, Shinichiro; Soda, Minoru; Kasatani, Kazuhiro; Ono, Toshio; Avdeev, Maxim; Masuda, Takatsugu

    2016-01-01

    We investigate the magnetic order of the buckled honeycomb lattice antiferromagnet Ba2NiTeO6 and its related antiferromagnet Ba3NiTa2O9 by neutron diffraction measurements. We observe magnetic Bragg peaks below the transition temperatures, and identify propagation vectors for these oxides. A combination of representation analysis and Rietveld refinement leads to a collinear magnetic order for Ba2NiTeO6 and a 120∘ structure for Ba3NiTa2O9 . We find that the spin model of the bilayer triangular lattice is equivalent to that of the two-dimensional buckled honeycomb lattice having magnetic frustration. We discuss the magnetic interactions and single-ion anisotropy of Ni+2 ions for Ba2NiTeO6 in order to clarify the origin of the collinear magnetic structures. Our calculation suggests that the collinear magnetic order of Ba2NiTeO6 is induced by the magnetic frustration and easy-axis anisotropy.

  8. Model for temperature-dependent magnetization of nanocrystalline materials

    SciTech Connect

    Bian, Q.; Niewczas, M.

    2015-01-07

    A magnetization model of nanocrystalline materials incorporating intragrain anisotropies, intergrain interactions, and texture effects has been extended to include the thermal fluctuations. The method relies on the stochastic Landau–Lifshitz–Gilbert theory of magnetization dynamics and permits to study the magnetic properties of nanocrystalline materials at arbitrary temperature below the Currie temperature. The model has been used to determine the intergrain exchange constant and grain boundary anisotropy constant of nanocrystalline Ni at 100 K and 298 K. It is found that the thermal fluctuations suppress the strength of the intergrain exchange coupling and also reduce the grain boundary anisotropy. In comparison with its value at 2 K, the interparticle exchange constant decreases by 16% and 42% and the grain boundary anisotropy constant decreases by 28% and 40% at 100 K and 298 K, respectively. An application of the model to study the grain size-dependent magnetization indicates that when the thermal activation energy is comparable to the free energy of grains, the decrease in the grain size leads to the decrease in the magnetic permeability and saturation magnetization. The mechanism by which the grain size influences the magnetic properties of nc–Ni is discussed.

  9. Model for temperature-dependent magnetization of nanocrystalline materials

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2015-01-01

    A magnetization model of nanocrystalline materials incorporating intragrain anisotropies, intergrain interactions, and texture effects has been extended to include the thermal fluctuations. The method relies on the stochastic Landau-Lifshitz-Gilbert theory of magnetization dynamics and permits to study the magnetic properties of nanocrystalline materials at arbitrary temperature below the Currie temperature. The model has been used to determine the intergrain exchange constant and grain boundary anisotropy constant of nanocrystalline Ni at 100 K and 298 K. It is found that the thermal fluctuations suppress the strength of the intergrain exchange coupling and also reduce the grain boundary anisotropy. In comparison with its value at 2 K, the interparticle exchange constant decreases by 16% and 42% and the grain boundary anisotropy constant decreases by 28% and 40% at 100 K and 298 K, respectively. An application of the model to study the grain size-dependent magnetization indicates that when the thermal activation energy is comparable to the free energy of grains, the decrease in the grain size leads to the decrease in the magnetic permeability and saturation magnetization. The mechanism by which the grain size influences the magnetic properties of nc-Ni is discussed.

  10. Materials for efficient high-flux magnetic bearing actuators

    NASA Technical Reports Server (NTRS)

    Williams, M. E.; Trumper, D. L.

    1994-01-01

    Magnetic bearings have demonstrated the capability for achieving positioning accuracies at the nanometer level in precision motion control stages. This makes possible the positioning of a wafer in six degrees of freedom with the precision necessary for photolithography. To control the position of an object at the nanometer level, a model of the magnetic bearing actuator force-current-airgap relationship must be accurately obtained. Additionally, to reduce thermal effects the design of the actuator should be optimized to achieve maximum power efficiency and flux density. Optimization of the actuator is accomplished by proper pole face sizing and utilizing a magnetic core material which can be magnetized to the highest flux density with low magnetic loss properties. This paper describes the construction of a magnetic bearing calibration fixture designed for experimental measurement of the actuator force characteristics. The results of a material study that review the force properties of nickel-steel, silicon-steel, and cobalt-vanadium-iron, as they apply to magnetic bearing applications are also presented.

  11. Volume magnetization for system-level testing of magnetic materials within small satellites

    NASA Astrophysics Data System (ADS)

    Gerhardt, David T.; Palo, Scott E.

    2016-10-01

    Passive Magnetic Attitude Control (PMAC) is a popular among small satellites due to its low resource cost and simplicity of installation. However, predicting the performance of these systems can be a challenge, chiefly due to the difficulty of measurement and simulation of hysteresis materials. We present a low-cost method of magnetic measurement allowing for characterization of both hard and soft magnetic materials. A Helmholtz cage uniformly magnetizes a 30 cm×30 cm×30 cm test volume. The addition of a thin sense coil allows this system to characterize individual hysteresis rod performance when in close proximity to other hard and/or soft magnetic materials. This test setup is applied to hard and soft magnetic materials used aboard the Colorado Student Space Weather Experiment (CSSWE), a 3U CubeSat for space weather investigation which used a PMAC system. The measured hard magnet dipole of 0.80±0.017 A m2 is in good agreement with the dynamics-based satellite dipole moment fits. Five hysteresis rods from the same set as the CSSWE flight rods are tested; significant differences in dampening abilities are found. In addition, a limitation of the widely-used Flatley model is described. The interaction of two hysteresis rods in a variety of relative geometries are tested; perpendicular rods are found to have no significant interaction while parallel rods could have their dampening ability reduced by half, depending on the rod separation distance. Finally, the performance of the hysteresis rods are measured in their flight configuration, with hard and soft magnetic material dispersed as it is on CSSWE itself. For the CSSWE PMAC system design, interactions between rods have a greater affect than the magnetic flux density offset due to the onboard bar magnet.

  12. Orientational and magnetic ordering of buckyballs in TDAE-C60

    SciTech Connect

    Mihailovic, D.; Arcon, D.; Venturini, P.; Blinc, R.; Omerzu, A.; Cevc, P.

    1995-04-01

    Spin ordering in the low-temperature magnetic phase is directly linked to the orientational ordering of C60 molecules in organically doped fullerene derivatives. Electron spin resonance and alternating current susceptometry measurements on tetrakis (dimethylamino) ethylene-C60 (TDAE-C60) (Curie temperature T(sub c) = 16 kelvin) show a direct coupling between spin and merohedral degrees of freedom. This coupling was experimentally demonstrated by showing that ordering the spins in the magnetic phase imprints a merohedral order on the solid or, conversely, that merohedrally ordering the C60 molecules influences the spin order at low temperature. The merohedral disorder gives rise to a distribution of pi-electron exchange interactions between spins on neighboring C60 molecules, suggesting a microscopic origin for the observed spin-glass behavior of the magnetic state. 18 refs.

  13. Macroscopic modeling of anisotropic magnetostriction and magnetization in soft ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Mbengue, Serigne Saliou; Buiron, Nicolas; Lanfranchi, Vincent

    2016-04-01

    Magnetic and magnetoelastic properties of soft ferromagnetic materials, used as laminated sheets, are sensitive to manufacturing processes such as rolling, cutting and coating. One of the effects of these processes is to induce an anisotropic behavior of materials. Therefore, an anhysteretic magnetostriction and magnetization calculation taking into account the anisotropy effect at macroscopic scale is presented. This model is based on the expression and then the minimization of the total energy in order to determine magnetization and magnetostriction at equilibrium. The total energy to minimize depends on energy terms identified from measurements of the magnetization and magnetostriction at a scale large enough to neglect the heterogeneity due to grains. Therefore, this approach attempts to reproduce ferromagnetic polycrystal behavior at macroscopic without knowing texture (Orientation Density Function) nor grain properties.

  14. Remanence enhancement based on L10 ordering in Fe-Pt permanent magnets

    NASA Astrophysics Data System (ADS)

    Tanaka, Y.; Hisatsune, K.

    2003-03-01

    This study investigated the relationship between the hard magnetic properties and microstructure of bulk FePt magnets, which can potentially be used in dental prostheses. A high level of remanence was obtained in a Fe-39.5 mol %Pt alloy aged at 873 K, in which minute FePt ordered domains of about 10 nm in size were uniformly created. The change in the maximum energy product of this alloy was in good agreement with the level of remanence: they both decreased with increasing aging time, and the size of the ordered domains gradually grew. The remanence ratio of as-quenched Fe-40 mol %Pt magnet has been estimated at 0.69, despite the morphological isotropy of the magnet. Remanence enhancement occurred in an FePt single phase without the presence of the magnetically soft disordered phase, since the spring back phenomenon was not observed in the recoil curve measurements, and the entire area was covered with minute FePt ordered domains. The hard magnetic properties were enhanced at the optimum ordered domain size of about 10 nm. This study found that the ordered domains behaved as a single magnetic domain particle and improved remanence through intergranular exchange interaction.

  15. Design for a 1 MHz soft magnetic material hysteresisgraph (abstract)

    NASA Astrophysics Data System (ADS)

    Dennison, Eric

    1993-05-01

    Until recently, high frequency (1 MHz) testing of magnetically soft materials has been typically limited to measurement of core loss and peak or inductive ac permeability. A high frequency hysteresisgraph allows direct examination of the hysteresis loop and calculation of values for magnetic parameters such as coercivity (Hc), peak permeability (μp), remanence (Br), core loss (Pc,Pcv,Pcm), bias drive field strength (Hbias), maximum H drive (Hmax) and maximum or saturation induction (Bmax). This paper describes the methods used to construct and calibrate a commercial high frequency magnetic hysteresisgraph which is capable of recording the primary current and secondary voltage waveforms of magnetic cores driven at up to 1 MHz. A system accuracy of 2% (for B and H parameter values) and 5% (for core loss) was achieved through careful control and calibration of signal phase shifts within the circuitry. System calibration, magnetic field calculations, and use of FFT post-processing of the acquired waveforms are discussed. The ability to accurately record the hysteresis loop of a material at 1 MHz allows high frequency core materials to be characterized not only by core loss and permeability, but by their hysteresis loop shape, coercivity, and remanence, both under pure ac and dc biased ac drive conditions. Changes in material characteristics due to dc biasing, temperature variations, defects, or mechanical stresses can be readily observed and described in terms of changes to the hysteresis curve shape.

  16. Mechanically induced magnetic diffusion in cylindrical magnetoelastic materials

    NASA Astrophysics Data System (ADS)

    Scheidler, Justin J.; Dapino, Marcelo J.

    2016-01-01

    This paper considers the radial dependence of magnetic diffusion in cylindrical magnetoelastic materials that results from the simultaneous application of a constant surface magnetic field and a dynamic mechanical input. Mechanically induced magnetic diffusion is particularly pronounced in materials that exhibit a strong magnetoelastic coupling, such as magnetostrictive materials and ferromagnetic shape memory alloys. Analytical time- and frequency-domain solutions of the PDE governing the radial diffusion of magnetic field are derived. The solutions are non-dimensionalized by deriving a skin depth and cut-off frequency for mechanically induced diffusion, which are about 2.08 and 4.34 times those for field-induced diffusion, respectively. It is shown that the effects of mechanically induced diffusion can be incorporated in linear constitutive models through the use of a complex-valued, frequency-dependent magnetoelastic coupling coefficient and Young's modulus. The solutions show that for forcing frequencies f up to about the cut-off frequency, the magnitude of the steady-state, dynamic field increases in proportion to f. As forcing frequency increases above that range, the magnitude overshoots its high frequency limit, peaks, then decreases to its high frequency limit, at which point the dynamic magnetic flux becomes zero and continued increases in forcing frequency have no effect. Together, the derived frequency responses, skin depth, and cut-off frequency can be used to design magnetoelastic systems and determine if lamination of the magnetoelastic material is necessary

  17. Effect of size, composition, and morphology on magnetic performance: First-order reversal curves evaluation of iron oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Hirt, Ann M.; Sotiriou, Georgios A.; Kidambi, Piran R.; Teleki, Alexandra

    2014-01-01

    Superparamagnetic nanoparticles are employed in a broad range of applications that demand detailed magnetic characterization for superior performance, e.g., in drug delivery or cancer treatment. Magnetic hysteresis measurements provide information on saturation magnetization and coercive force for bulk material but can be equivocal for particles having a broad size distribution. Here, first-order reversal curves (FORCs) are used to evaluate the effective magnetic particle size and interaction between equally sized magnetic iron oxide (Fe2O3) nanoparticles with three different morphologies: (i) pure Fe2O3, (ii) Janus-like, and (iii) core/shell Fe2O3/SiO2 synthesized using flame technology. By characterizing the distribution in coercive force and interaction field from the FORC diagrams, we find that the presence of SiO2 in the core/shell structures significantly reduces the average coercive force in comparison to the Janus-like Fe2O3/SiO2 and pure Fe2O3 particles. This is attributed to the reduction in the dipolar interaction between particles, which in turn reduces the effective magnetic particle size. Hence, FORC analysis allows for a finer distinction between equally sized Fe2O3 particles with similar magnetic hysteresis curves that can significantly influence the final nanoparticle performance.

  18. Magnetic susceptibility and magnetic resonance measurements of the moisture content and hydration condition of a magnetic mixture material

    SciTech Connect

    Tsukada, K. Kusaka, T.; Saari, M. M.; Takagi, R.; Sakai, K.; Kiwa, T.; Bito, Y.

    2014-05-07

    We developed a magnetic measurement method to measure the moisture content and hydration condition of mortar as a magnetic mixture material. Mortar is a mixture of Portland cement, sand, and water, and these materials exhibit different magnetic properties. The magnetization–magnetic field curves of these components and of mortars with different moisture contents were measured, using a specially developed high-temperature-superconductor superconducting quantum interference device. Using the differences in magnetic characteristics, the moisture content of mortar was measured at the ferromagnetic saturation region over 250 mT. A correlation between magnetic susceptibility and moisture content was successfully established. After Portland cement and water are mixed, hydration begins. At the early stage of the hydration/gel, magnetization strength increased over time. To investigate the magnetization change, we measured the distribution between bound and free water in the mortar in the early stage by magnetic resonance imaging (MRI). The MRI results suggest that the amount of free water in mortar correlates with the change in magnetic susceptibility.

  19. 78 FR 34156 - Hazardous Materials: Emergency Recall Order

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-06

    ... filled, refilled, or used for the transportation of hazardous materials. Effective Immediately, Lite... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION... United States Department of Transportation (DOT) pursuant to 49 U.S.C. 5121(d) and 49 CFR 109.17(c);...

  20. Thermal expansion of several materials for superconducting magnets

    SciTech Connect

    Clark, A.F.; Fujii, G.; Ranney, M.A.

    1981-09-01

    The thermal expansion of several materials used in the consruction of high field superconducting magnets has been measured from 4 K to room temperature. The materials were a NbTi and two A15 multifilamentary conductors and several nonmetallic composites made from linen/phenolic, fiberglass/epoxy and superconducitng wire/epoxy. The conductor expansions are typical of metals and the composite expansions are highy anisotropic. Both graphic and tabular values are provided by a computer fitting of the experimental data. The importnce of thermal expansion differences in critical current measurement apparatus and superconducting magnet design are discussed. 12 refs.

  1. 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.

  2. Magnetic cluster expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys

    NASA Astrophysics Data System (ADS)

    Lavrentiev, M. Yu.; Wróbel, J. S.; Nguyen-Manh, D.; Dudarev, S. L.; Ganchenkova, M. G.

    2016-07-01

    A Magnetic Cluster Expansion model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed, using DFT data spanning binary and ternary alloy configurations. Using this Magnetic Cluster Expansion model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low-temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rather than iron atoms. Replacement of Ni by Cr in ordered alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations. In random alloys, both magnetization and the Curie temperature decrease abruptly with increasing chromium content, in agreement with experiment.

  3. Hydrogenated arsenenes as planar magnet and Dirac material

    SciTech Connect

    Zhang, Shengli; Cai, Bo; Zeng, Haibo E-mail: zeng.haibo@njust.edu.cn; Hu, Yonghong; Hu, Ziyu E-mail: zeng.haibo@njust.edu.cn

    2015-07-13

    Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.

  4. Continuation of tailored composite structures of ordered staple thermoplastic material

    NASA Technical Reports Server (NTRS)

    Santare, Michael H.; Pipes, R. Byron

    1992-01-01

    The search for the cost effective composite structure has motivated the investigation of several approaches to develop composite structure from innovative material forms. Among the promising approaches is the conversion of a planar sheet to components of complex curvature through sheet forming or stretch forming. In both cases, the potential for material stretch in the fiber direction appears to offer a clear advantage in formability over continuous fiber systems. A framework was established which allows the simulation of the anisotropic mechanisms of deformation of long discontinuous fiber laminates wherein the matrix phase is a viscous fluid. Predictions for the effective viscosities of a hyper-anisotropic medium consisting of collimated, discontinuous fibers suspended in viscous matrix were extended to capture the characteristics of typical polymers including non-Newtonian behavior and temperature dependence. In addition, the influence of fiber misorientation was also modeled by compliance averaging to determine ensemble properties for a given orientation distribution. A design tool is presented for predicting the effect of material heterogeneity on the performance of curved composite beams such as those used in aircraft fuselage structures. Material heterogeneity can be induced during manufacturing processes such as sheet forming and stretch forming of thermoplastic composites. This heterogeneity can be introduced in the form of fiber realignment and spreading during the manufacturing process causing radial and tangential gradients in material properties. Two analysis procedures are used to solve the beam problems. The first method uses separate two-dimensional elasticity solutions for the stresses in the flange and web sections of the beam. The separate solutions are coupled by requiring that forces and displacements match section boundaries. The second method uses an approximate Rayleigh-Ritz technique to find the solutions for more complex beams. Analyses

  5. Dynamic origin of first and second order phase transitions in magnetization reversal of elliptical nanodots.

    SciTech Connect

    Montoncello, F.; Giovannini, L.; Nizzoli, F.; Vavassori, P.; Grimsditch, M.; Materials Science Division; Univ. di Ferrara; CNISM; CNR-INFM; CIC nanoGUNE Res. Ctr.

    2008-06-01

    We study the magnetization reversal in elliptical nanodots with the external field applied exactly along the minor (hard) axis. By varying the magnitude of the applied field, several first and second order transitions take place and the system proceeds through magnetic configurations characterized by different symmetry properties. The dynamical matrix method is used to calculate the spin excitations as function of the applied field. This model system allows us to investigate the relationship between the singularities of the magnetization, the presence of soft spin excitations, and the symmetry properties of the static and dynamic magnetization fields. Rules that govern the transitions are formulated.

  6. Microfluidic separation of magnetic nanoparticles on an ordered array of magnetized micropillars

    NASA Astrophysics Data System (ADS)

    Orlandi, G.; Kuzhir, P.; Izmaylov, Y.; Alves Marins, J.; Ezzaier, H.; Robert, L.; Doutre, F.; Noblin, X.; Lomenech, C.; Bossis, G.; Meunier, A.; Sandoz, G.; Zubarev, A.

    2016-06-01

    Microfluidic separation of magnetic particles is based on their capture by magnetized microcollectors while the suspending fluid flows past the microcollectors inside a microchannel. Separation of nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bioanalysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregation that amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increases nanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficient capture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickel micropillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as 6-10 kA/m, and experiments were carried out at flow rates ranging between 0.3 and 30 μ L /min . Nanoparticle capture is shown to be mostly governed by the Mason number Ma, while the dipolar coupling parameter α does not exhibit a clear effect in the studied range, 1.4 < α < 4.5. The capture efficiency Λ shows a strongly decreasing Mason number behavior, Λ ∝M a-1.78 within the range 32 ≤ Ma ≤ 3250. We have proposed a simple theoretical model which considers destructible nanoparticle chains and gives the scaling behavior, Λ ∝M a-1.7 , close to the experimental findings.

  7. Complex incommensurate helicoidal magnetic ordering of EuNiGe3.

    PubMed

    Ryan, D H; Cadogan, J M; Rejali, Rasa; Boyer, C D

    2016-07-01

    (151)Eu Mössbauer spectroscopy and neutron powder diffraction are combined to show that the tetragonal (I4mm #107) compound EuNiGe3 orders magnetically below [Formula: see text] K and adopts a complex incommensurate helicoidal magnetic structure at 3.6 K, with a propagation vector [Formula: see text] and a Eu moment of 7.1(2) [Formula: see text]. On warming through 6 K an incommensurate sinusoidal modulation develops and dominates the magnetic order by 12 K. PMID:27173847

  8. Complex incommensurate helicoidal magnetic ordering of EuNiGe3

    NASA Astrophysics Data System (ADS)

    Ryan, D. H.; Cadogan, J. M.; Rejali, Rasa; Boyer, C. D.

    2016-07-01

    151Eu Mössbauer spectroscopy and neutron powder diffraction are combined to show that the tetragonal (I4mm #107) compound EuNiGe3 orders magnetically below {{T}\\text{N}}∼ 14 K and adopts a complex incommensurate helicoidal magnetic structure at 3.6 K, with a propagation vector \\mathbf{k}=≤ft[0.255(1),~0.054(14),~0\\right] and a Eu moment of 7.1(2) {μ\\text{B}} . On warming through 6 K an incommensurate sinusoidal modulation develops and dominates the magnetic order by 12 K.

  9. Magnetic Ordering in BaFe_{11.9} In_{0.1} O_{19} Hexaferrite

    NASA Astrophysics Data System (ADS)

    Trukhanov, S. V.; Trukhanov, A. V.; Turchenko, V. O.; Kostishin, V. G.; Panina, L. V.; Kazakevich, I. S.; Balagurov, A. M.

    2016-07-01

    The crystal and magnetic structure by powder neutron diffractometry as well as the magnetic properties by vibration sample magnetometry for the BaFe_{11.9} In_{0.1} O_{19} polycrystalline sample have been performed in a wide temperature range from 10 up to 730 K and in magnetic field up to 14 T. The atomic coordinates and lattice parameters have been Rietveld refined. The Invar effect has been observed in the low-temperature range below 150 K. It was explained by the thermal oscillation anharmonicity of atoms. The increase of the microstress value with decreasing temperature has been defined from Rietveld refinement. It is established that the ferrimagnet-paramagnet phase transition is a standard second-order one. From the macroscopic magnetization measurement, the Curie temperature and ordered magnetic moment per nominal iron ion are obtained. From the microscopic diffraction measurement, the magnetic moments at different atomic position and total magnetic moment per iron ion have been defined at different temperatures. The most likely reasons and the mechanism of magnetic ordering are discussed.

  10. Persistence of magnetic order in a highly excited Cu2+ state in CuO

    NASA Astrophysics Data System (ADS)

    Staub, U.; de Souza, R. A.; Beaud, P.; Möhr-Vorobeva, E.; Ingold, G.; Caviezel, A.; Scagnoli, V.; Delley, B.; Turner, J. J.; Krupin, O.; Lee, W.-S.; Chuang, Y.-D.; Patthey, L.; Moore, R. G.; Lu, D.; Yi, M.; Kirchmann, P. S.; Trigo, M.; Denes, P.; Doering, D.; Hussain, Z.; Shen, Z. X.; Prabhakaran, D.; Boothroyd, A. T.; Johnson, S. L.

    2014-06-01

    We use ultrafast resonant x-ray diffraction to study the magnetic order in CuO under conditions of high electronic excitation. By measuring changes in the spectral shape of the Cu2+ magnetic (1/2 0 -1/2) reflection we investigate how an intense optical pump pulse perturbs the electronic and magnetic states. We observe an energy shift in the magnetic resonance at short times after the pump pulse. This shift is compared with expectations from band structure calculations at different electronic temperatures. This spectral line shift indicates that although the electrons are heated to effective electron temperatures far above TN on a time scale faster than the experimental resolution, magnetic order persists in this highly excited state for several hundred femtoseconds.

  11. Observation of Pr magnetic order in PrBa2Cu3O7

    NASA Astrophysics Data System (ADS)

    Skanthakumar, S.; Lynn, J. W.; Rosov, N.; Cao, G.; Crow, J. E.

    1997-02-01

    Neutron-diffraction experiments have been carried out to investigate the magnetic order in PrBa2Cu3O7. Our neutron data indicate that the Cu spins order above 300 K. This ordering is not significantly affected at low temperatures, where new magnetic Bragg peaks develop below 17 K that must be associated with the antiferromagnetic ordering of Pr spins, with an ordered moment of 0.79(5)μB. This rules out the possibility recently proposed by Nehrke and Pieper [Phys. Rev. Lett. 76, 1936 (1996)] that the new magnetic Bragg peaks arise from a spin reorientation of the Cu spins and that the Pr carries essentially no moment.

  12. Magnetic field dependent ordering in ferrofluids at SiO2 interfaces.

    PubMed

    Vorobiev, A; Major, J; Dosch, H; Gordeev, G; Orlova, D

    2004-12-31

    We report pronounced smecticlike ordering in a ferrofluid adjacent to a SiO2 wall. In the presence of small magnetic fields perpendicular to the interface, ordered layers of magnetite nanoparticles form that can extend up to 30 layers. We also show that short ranged ordered structures emerge when the magnetic field direction is parallel to the interface; however, the layering is strongly perturbed. These results have been obtained by in situ neutron reflectometry which gives a detailed microscopic picture of these ordering phenomena. They also reveal the formation of a wetting double-layer which forms the magnetic template for the observed ordering sheets. The implications of these findings are discussed. PMID:15698017

  13. On the magnetic order of Gd{sub 5}Ge{sub 3}

    SciTech Connect

    Cadogan, J. M.; Ryan, D. H.; Mudryk, Ya.; Pecharsky, V. K.; Gschneidner, K. A.

    2014-05-07

    We have investigated the magnetic structure of Gd{sub 5}Ge{sub 3} by neutron powder diffraction down to 3.6 K. This compound presents three events in the heat capacity which we show are related to fundamental changes in the magnetic order. The primary antiferromagnetic ordering occurs at 82(2) K and produces a magnetic cell that is tripled with respect to the underlying orthorhombic crystal cell. The propagation vector is k{sub 1}=[0 0 1/3 ]. At 74(2) K, the magnetic order becomes “anti-C” with a propagation vector k{sub 2} = [1 0 0]. A third change in the magnetic order occurs at 40(2) K, and the new magnetic structure is essentially the “anti-C” structure but with the addition of a tripled magnetic component corresponding to a propagation vector k{sub 3} = [1/3  0 0].

  14. New type of incommensurate magnetic ordering in Mn{sub 3}TeO{sub 6}

    SciTech Connect

    Ivanov, S.A.; Nordblad, P.; Mathieu, R.; Tellgren, R.; Ritter, C.; Golubko, N.V.; Politova, E.D.; Weil, M.

    2011-11-15

    Highlights: {yields} Mn{sub 3}TeO{sub 6} has a corundum related structure and orders magnetically below 23 K. {yields} The magnetic structure consists of several types of Mn-chains. {yields} The unique Mn site is split into two magnetically different orbits. {yields} One orbit forms a perfect helix with the spiral axis along the c-axis. {yields} The other orbit has a sine wave character along the c-axis. -- Abstract: The complex metal oxide Mn{sub 3}TeO{sub 6} exhibits a corundum related structure and has been prepared both in forms of single crystals by chemical transport reactions and of polycrystalline powders by a solid state reaction route. The crystal structure and magnetic properties have been investigated using a combination of X-ray and neutron powder diffraction, electron microscopy, calorimetric and magnetic measurements. At room temperature this compound adopts a trigonal structure, space group R3{sup -bar} with a = 8.8679(1) A, c = 10.6727(2) A. A long-range magnetically ordered state is identified below 23 K. An unexpected feature of this magnetic structure is several types of Mn-chains. Under the action of the incommensurate magnetic propagation vector k = [0, 0, 0.4302(1)] the unique Mn site is split into two magnetically different orbits. One orbit forms a perfect helix with the spiral axis along the c-axis while the other orbit has a sine wave character along the c-axis.

  15. Applied magnetism: A supply-driven materials challenge

    DOE PAGESBeta

    Rios, Orlando; McCall, Scott K.

    2016-05-27

    Permanent magnets are important in many green energy technologies including wind turbine generators and hybrid-electric vehicle motors. For these applications, volume and weight are important factors driving the overall design, and therefore a high energy density, or energy product, is an important figure of merit. This quantity defines the magnetic energy contained in a given volume of material, and so higher energy density magnets enable smaller, lighter applications. Currently, the most powerful magnets suitable for commercial purposes contain rare earth elements (REE), usually neodymium and dysprosium in the neodymium-iron-boride class of magnets. However, for select applications, often requiring high temperatures,more » samarium cobalt is the alloy of choice. These magnets have energy densities several times greater than their nearest non-REE-based competitor, which for some applications is the defining factor in creating a viable device. The global supply of these REE is overwhelmingly produced in China, which in 2015 mined more than ten times as much as the next largest producer (Australia). Such market domination effectively creates a single source of supply, leaving industries which rely on REE consumption susceptible to price shocks and supply disruptions of these critical materials. Furthermore, this supply sensitivity may act as a drag on the adaptation rate of green energy technologies, particularly for large-scale users.« less

  16. Thermal stability of MnBi magnetic materials

    SciTech Connect

    Cui, Jinfang; Choi, J. P.; Li, G.; Polikarpov, E.; Darsell, J.; Overman, N.; Olszta, M.; Schreiber, D.; Bowden, M.; Droubay, T.; Kramer, Matthew J.; Zarkevich, Nikolay A.; Wang, L L.; Johnson, Duane D.; Marinescu, M.; Takeuchi, I.; Huang, Q. Z.; Wu, H.; Reeve, H.; Vuong, N. V.; Liu, J P.

    2014-01-27

    MnBi has attracted much attention in recent years due to its potential as a rare-earth-free permanent magnet material. It is unique because its coercivity increases with increasing temperature, which makes it a good hard phase material for exchange coupling nanocomposite magnets. MnBi phase is difficult to obtain, partly because the reaction between Mn and Bi is peritectic, and partly because Mn reacts readily with oxygen. MnO formation is irreversible and harmful to magnet performance. In this paper, we report our efforts toward developing MnBi permanent magnets. To date, high purity MnBi (>90%) can be routinely produced in large quantities. The produced powder exhibits 74:6 emu g1 saturation magnetization at room temperature with 9 T applied field. After proper alignment, the maximum energy product (BH) max of the powder reached 11.9 MGOe, and that of the sintered bulk magnet reached 7.8 MGOe at room temperature. A comprehensive study of thermal stability shows that MnBi powder is stable up to 473 K in air.

  17. Fluorescent and Magnetic Mesoporous Hybrid Material: A Chemical and Biological Nanosensor for Hg2+ Ions

    PubMed Central

    Suresh, Moorthy; Anand, Chokkalingam; Frith, Jessica E.; Dhawale, Dattatray S.; Subramaniam, Vishnu P.; Strounina, Ekaterina; Sathish, Clastinrusselraj I.; Yamaura, Kazunari; Cooper-White, Justin J.; Vinu, Ajayan

    2016-01-01

    We introduce “sense, track and separate” approach for the removal of Hg2+ ion from aqueous media using highly ordered and magnetic mesoporous ferrosilicate nanocages functionalised with rhodamine fluorophore derivative. These functionalised materials offer both fluorescent and magnetic properties in a single system which help not only to selectively sense the Hg2+ ions with a high precision but also adsorb and separate a significant amount of Hg2+ ion in aqueous media. We demonstrate that the magnetic affinity of these materials, generated from the ultrafine γ-Fe2O3 nanoparticles present inside the nanochannels of the support, can efficiently be used as a fluorescent tag to sense the Hg2+ ions present in NIH3T3 fibroblasts live cells and to track the movement of the cells by external magnetic field monitored using confocal fluorescence microscopy. This simple approach of introducing multiple functions in the magnetic mesoporous materials raise the prospect of creating new advanced functional materials by fusing organic, inorganic and biomolecules to create advanced hybrid nanoporous materials which have a potential use not only for sensing and the separation of toxic metal ions but also for cell tracking in bio-separation and the drug delivery. PMID:26911660

  18. Fluorescent and Magnetic Mesoporous Hybrid Material: A Chemical and Biological Nanosensor for Hg2+ Ions

    NASA Astrophysics Data System (ADS)

    Suresh, Moorthy; Anand, Chokkalingam; Frith, Jessica E.; Dhawale, Dattatray S.; Subramaniam, Vishnu P.; Strounina, Ekaterina; Sathish, Clastinrusselraj I.; Yamaura, Kazunari; Cooper-White, Justin J.; Vinu, Ajayan

    2016-02-01

    We introduce “sense, track and separate” approach for the removal of Hg2+ ion from aqueous media using highly ordered and magnetic mesoporous ferrosilicate nanocages functionalised with rhodamine fluorophore derivative. These functionalised materials offer both fluorescent and magnetic properties in a single system which help not only to selectively sense the Hg2+ ions with a high precision but also adsorb and separate a significant amount of Hg2+ ion in aqueous media. We demonstrate that the magnetic affinity of these materials, generated from the ultrafine γ-Fe2O3 nanoparticles present inside the nanochannels of the support, can efficiently be used as a fluorescent tag to sense the Hg2+ ions present in NIH3T3 fibroblasts live cells and to track the movement of the cells by external magnetic field monitored using confocal fluorescence microscopy. This simple approach of introducing multiple functions in the magnetic mesoporous materials raise the prospect of creating new advanced functional materials by fusing organic, inorganic and biomolecules to create advanced hybrid nanoporous materials which have a potential use not only for sensing and the separation of toxic metal ions but also for cell tracking in bio-separation and the drug delivery.

  19. Imaging Spatially Varying Magnetic Order in Proximity Induced Magnetic Topological Insulator

    NASA Astrophysics Data System (ADS)

    Rosenberg, Aaron J.; Katmis, Ferhat; Wang, Yihua H.; Kirtley, John R.; Moodera, Jagadeesh S.; Moler, Kathryn A.

    Broken time-reversal symmetry on the surface states of a three dimensional topological insulator, such as Bi2Se3, results in quantized anomalous Hall conductance and is predicted to exhibit topological magneto-electric effects. We plan investigate how Dirac fermions interact with magnetism by imaging the magnetization of a topological insulator (Bi2Se3) sandwiched between two ferromagnetic insulator layers (EuS) with a scanning SQUID microscope. Cooling in an in-plane field leads to a magnetization that varies spatially on a micron scale, with 6-fold rotational symmetry. Understanding the origin of this magnetism may shed light on the exchange interaction and electronic properties of topological insulators.

  20. Structural and magnetic characterization of actinide materials

    SciTech Connect

    Cort, B.; Allen, T.H.; Lawson, A.C.

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The authors have successfully used neutron scattering techniques to investigate physicochemical properties of elements, compounds, and alloys of the light actinides. The focus of this work is to extend the fundamental research capability and to address questions of practical importance to stockpile integrity and long-term storage of nuclear material. Specific subject areas are developing neutron diffraction techniques for smaller actinide samples; modeling of inelastic scattering data for actinide metal hydrides; characterizing actinide oxide structures; and investigating aging effects in actinides. These studies utilize neutron scattering supported by equilibrium studies, kinetics, and x-ray diffraction. Major accomplishments include (1) development of encapsulation techniques for small actinide samples and neutron diffraction studies of AmD{sub 2.4} and PuO{sub 2.3}; (2) refinement of lattice dynamics model to elucidate hydrogen-hydrogen and hydrogen-metal interactions in rare-earth and actinide hydrides; (3) kinetic studies with PuO{sub 2} indicating that the recombination reaction is faster than radiolytic decomposition of adsorbed water but a chemical reaction produces H{sub 2}; (4) PVT studies of the reaction between PuO{sub 2} and water demonstrate that PuO{sub 2+x} and H{sub 2} form and that PuO{sub 2} is not the thermodynamically stable form of the oxide in air; and (5) model calculations of helium in growth in aged plutonium predicting bubble formation only at grain boundaries at room temperature. The work performed in this project has application to fundamental properties of actinides, aging, and long-term storage of plutonium.

  1. Exchange bias and room-temperature magnetic order in molecular layers

    NASA Astrophysics Data System (ADS)

    Gruber, Manuel; Ibrahim, Fatima; Boukari, Samy; Isshiki, Hironari; Joly, Loïc; Peter, Moritz; Studniarek, Michał; da Costa, Victor; Jabbar, Hashim; Davesne, Vincent; Halisdemir, Ufuk; Chen, Jinjie; Arabski, Jacek; Otero, Edwige; Choueikani, Fadi; Chen, Kai; Ohresser, Philippe; Wulfhekel, Wulf; Scheurer, Fabrice; Weber, Wolfgang; Alouani, Mebarek; Beaurepaire, Eric; Bowen, Martin

    2015-10-01

    Molecular semiconductors may exhibit antiferromagnetic correlations well below room temperature. Although inorganic antiferromagnetic layers may exchange bias single-molecule magnets, the reciprocal effect of an antiferromagnetic molecular layer magnetically pinning an inorganic ferromagnetic layer through exchange bias has so far not been observed. We report on the magnetic interplay, extending beyond the interface, between a cobalt ferromagnetic layer and a paramagnetic organic manganese phthalocyanine (MnPc) layer. These ferromagnetic/organic interfaces are called spinterfaces because spin polarization arises on them. The robust magnetism of the Co/MnPc spinterface stabilizes antiferromagnetic ordering at room temperature within subsequent MnPc monolayers away from the interface. The inferred magnetic coupling strength is much larger than that found in similar bulk, thin or ultrathin systems. In addition, at lower temperature, the antiferromagnetic MnPc layer induces an exchange bias on the Co film, which is magnetically pinned. These findings create new routes towards designing organic spintronic devices.

  2. A model of magnetic order in hexagonal HoMnO3.

    PubMed

    Condran, S G; Plumer, M L

    2010-04-28

    Symmetry arguments are used to develop a spin Hamiltonian for the description of the complex magnetic ordering in HoMnO(3). Using a novel application of the Landau-Lifshitz-Gilbert dynamic torque equations to this model of the frustrated Mn ions on an AB stacked triangular antiferromagnetic, it is shown that the four principal spin configurations observed in this compound are stabilized. Ho-Mn coupling is found to be a consequence of an unusual trigonal anisotropy term which is responsible for simultaneous Mn spin reorientation and the onset of Ho magnetic order. On the basis of these microscopic considerations, a mean-field Landau-type free energy is derived which reproduces the succession of observed temperature-driven magnetic phase transitions at zero field, including re-entrant behavior. In addition, our analysis suggests that the basal-plane magnetic order should be slightly incommensurate with the lattice. PMID:21386404

  3. Magnetic ordering and non-Fermi-liquid behavior in the multichannel Kondo-lattice model

    NASA Astrophysics Data System (ADS)

    Irkhin, Valentin Yu.

    2016-05-01

    Scaling equations for the Kondo lattice in the paramagnetic and magnetically ordered phases are derived to next-leading order with account of spin dynamics. The results are applied to describe various mechanisms of the non-Fermi-liquid (NFL) behavior in the multichannel Kondo-lattice model where a fixed point occurs in the weak-coupling region. The corresponding temperature dependences of electronic and magnetic properties are discussed. The model describes naturally formation of a magnetic state with soft boson mode and small moment value. An important role of Van Hove singularities in the magnon spectral function is demonstrated. The results are rather sensitive to the type of magnetic ordering and space dimensionality, the conditions for NFL behavior being more favorable in the antiferromagnetic and 2D cases.

  4. Evidence of L10 chemical order in CoPt nanoclusters: Direct observation and magnetic signature

    NASA Astrophysics Data System (ADS)

    Tournus, Florent; Tamion, Alexandre; Blanc, Nils; Hannour, Abdelkrim; Bardotti, Laurent; Prével, Brigitte; Ohresser, Philippe; Bonet, Edgar; Epicier, Thierry; Dupuis, Véronique

    2008-04-01

    We report the synthesis and characterization of well-defined CoPt clusters with a mean diameter of 3 nm, produced in ultrahigh vacuum conditions following a physical route. Samples made of diluted layers of CoPt clusters embedded in amorphous carbon have been studied by transmission electron microscopy. High-resolution observations have revealed the appearance of L10 chemical order upon annealing, even for clusters with a 2 nm diameter, without cluster coalescence. The magnetic properties of both chemically disordered and ordered CoPt clusters embedded in amorphous carbon have then been measured by x-ray magnetic circular dichroism and superconducting quantum interference device magnetometry. Despite a striking change of the Co magnetic moment, the magnetic anisotropy of chemically ordered nanoparticles increases, with respect to the chemically disordered A1 phase, in much lower proportions than what is observed for the bulk.

  5. Nonmagnetic ions enhance magnetic order in the ludwigite Co5Sn(O2BO3)2

    NASA Astrophysics Data System (ADS)

    Medrano, Cynthia P. Contreras; Freitas, D. C.; Sanchez, D. R.; Pinheiro, C. B.; Eslava, G. G.; Ghivelder, L.; Continentino, M. A.

    2015-02-01

    The ludwigite Co5Sn(O2BO3)2 was studied using x-ray diffraction, Mössbauer spectroscopy, and magnetic and thermodynamic measurements. This material belongs to a family of oxyborates which presents low-dimensional subunits in the form of three-leg ladders in its structure. The subunits confer to these materials a strong anisotropy in their exchange interactions that provide to the ludwigites several interesting magnetic properties, from partial ordering to spin-glass states. Despite being doped by nonmagnetic ions, Co5Sn(O2BO3)2 has long-range magnetic order below 82 K which is, surprisingly, the highest critical temperature found so far in the ludwigites. This record can be explained by the absence of double-exchange interactions, usually present in the ludwigites and that gives rise to strong competition. In this paper we study the magnetic and structural properties of Co5Sn(O2BO3)2 and compare our results with those obtained in other cobalt ludwigites.

  6. Magnetic structures of actinide materials by pulsed neutron diffraction

    SciTech Connect

    Lawson, A.C.; Goldstone, J.A.; Huber, J.G.; Giorgi, A.L.; Conant, J.W.; Severing, A.; Cort, B.; Robinson, R.A.

    1990-01-01

    We describe some attempts to observe magnetic structure in various actinide (5f-electron) materials. Our experimental technique is neutron powder diffraction as practiced at a spallation (pulsed) neutron source. We will discuss our investigations of {alpha}-Pu, {delta}-Pu, {alpha}-UD{sub 3} and {beta}-UD{sub 3}. {beta}-UD{sub 3} is a simple ferromagnet: surprisingly, the moments on the two non-equivalent uranium atoms are the same within experimental error. {alpha}-UD{sub 3}, {alpha}-Pu and {delta}-Pu are non-magnetic, within the limits of our observations. Our work with pulsed neutron diffraction shows that it is a useful technique for research on magnetic materials.

  7. Disorder-promoted C4-symmetric magnetic order in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Hoyer, Mareike; Fernandes, Rafael M.; Levchenko, Alex; Schmalian, Jörg

    2016-04-01

    In most iron-based superconductors, the transition to the magnetically ordered state is closely linked to a lowering of structural symmetry from tetragonal (C4) to orthorhombic (C2). However, recently, a regime of C4-symmetric magnetic order has been reported in certain hole-doped iron-based superconductors. This novel magnetic ground state can be understood as a double-Q spin density wave characterized by two order parameters M1 and M2 related to each of the two Q vectors. Depending on the relative orientations of the order parameters, either a noncollinear spin-vortex crystal or a nonuniform charge-spin density wave could form. Experimentally, Mössbauer spectroscopy, neutron scattering, and muon spin rotation established the latter as the magnetic configuration of some of these optimally hole-doped iron-based superconductors. Theoretically, low-energy itinerant models do support a transition from single-Q to double-Q magnetic order, but with nearly degenerate spin-vortex crystal and charge-spin density wave states. In fact, extensions of these low-energy models including additional electronic interactions tip the balance in favor of the spin-vortex crystal, in apparent contradiction with the recent experimental findings. In this paper we revisit the phase diagram of magnetic ground states of low-energy multiband models in the presence of weak disorder. We show that impurity scattering not only promotes the transition from C2 to C4-magnetic order, but it also favors the charge-spin density wave over the spin-vortex crystal phase. Additionally, in the single-Q phase, our analysis of the nematic coupling constant in the presence of disorder supports the experimental finding that the splitting between the structural and stripe-magnetic transition is enhanced by disorder.

  8. Hexagonal phase stabilization and magnetic orders of multiferroic L u1 -xS cxFe O3

    NASA Astrophysics Data System (ADS)

    Lin, L.; Zhang, H. M.; Liu, M. F.; Shen, Shoudong; Zhou, S.; Li, D.; Wang, X.; Yan, Z. B.; Zhang, Z. D.; Zhao, Jun; Dong, Shuai; Liu, J.-M.

    2016-02-01

    Hexagonal LuFe O3 has drawn a lot of research attention due to its contentious room-temperature multiferroicity. Due to the instability of hexagonal phase in the bulk form, most experimental studies focused on LuFe O3 thin films which can be stabilized by strain using proper substrates. Here we report on the hexagonal phase stabilization, magnetism, and magnetoelectric coupling of bulk LuFe O3 by partial Sc substitution of Lu. First, our first-principles calculations show that the hexagonal structure can be stabilized by partial Sc substitution, while the multiferroic properties, including the noncollinear magnetic order and geometric ferroelectricity, remain robustly unaffected. Therefore, L u1 -xS cxFe O3 can act as a platform to check the multiferroicity of LuFe O3 and related materials in the bulk form. Second, the magnetic characterizations on bulk L u1 -xS cxFe O3 demonstrate a magnetic anomaly (probable antiferromagnetic ordering) above room temperature, ˜425-445 K, followed by magnetic transitions in low temperatures (˜167-172 K). In addition, a magnetoelectric response is observed in the low-temperature region. Our study provides useful information on the multiferroic physics of hexagonal R Fe O3 and related systems.

  9. Emergence of long-range order in sheets of magnetic dimers

    PubMed Central

    Haravifard, S.; Banerjee, A.; van Wezel, J.; Silevitch, D. M.; dos Santos, A. M.; Lang, J. C.; Kermarrec, E.; Srajer, G.; Gaulin, B. D.; Molaison, J. J.; Dabkowska, H. A.; Rosenbaum, T. F.

    2014-01-01

    Quantum spins placed on the corners of a square lattice can dimerize and form singlets, which then can be transformed into a magnetic state as the interactions between dimers increase beyond threshold. This is a strictly 2D transition in theory, but real-world materials often need the third dimension to stabilize long-range order. We use high pressures to convert sheets of Cu2+ spin 1/2 dimers from local singlets to global antiferromagnet in the model system SrCu2(BO3)2. Single-crystal neutron diffraction measurements at pressures above 5 GPa provide a direct signature of the antiferromagnetic ordered state, whereas high-resolution neutron powder and X-ray diffraction at commensurate pressures reveal a tilting of the Cu spins out of the plane with a critical exponent characteristic of 3D transitions. The addition of anisotropic, interplane, spin–orbit terms in the venerable Shastry–Sutherland Hamiltonian accounts for the influence of the third dimension. PMID:25246541

  10. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice

    PubMed Central

    Xie, Y.-L.; Du, Z.-Z.; Yan, Z.-B.; Liu, J.-M.

    2015-01-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented. PMID:26511870

  11. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice

    NASA Astrophysics Data System (ADS)

    Xie, Y.-L.; Du, Z.-Z.; Yan, Z.-B.; Liu, J.-M.

    2015-10-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented.

  12. Magnetic-charge ordering and phase transitions in monopole-conserved square spin ice.

    PubMed

    Xie, Y-L; Du, Z-Z; Yan, Z-B; Liu, J-M

    2015-01-01

    Magnetic-charge ordering and corresponding magnetic/monopole phase transitions in spin ices are the emergent topics of condensed matter physics. In this work, we investigate a series of magnetic-charge (monopole) phase transitions in artificial square spin ice model using the conserved monopole density algorithm. It is revealed that the dynamics of low monopole density lattices is controlled by the effective Coulomb interaction and the Dirac string tension, leading to the monopole dimerization which is quite different from the dynamics of three-dimensional pyrochlore spin ice. The condensation of the monopole dimers into monopole crystals with staggered magnetic-charge order can be predicted clearly. For the high monopole density cases, the lattice undergoes two consecutive phase transitions from high-temperature paramagnetic/charge-disordered phase into staggered charge-ordered phase before eventually toward the long-range magnetically-ordered phase as the ground state which is of staggered charge order too. A phase diagram over the whole temperature-monopole density space, which exhibits a series of emergent spin and monopole ordered states, is presented. PMID:26511870

  13. Fragile magnetic order in the honeycomb lattice Iridate Na2IrO3 revealed by magnetic impurity doping

    NASA Astrophysics Data System (ADS)

    Mehlawat, Kavita; Sharma, G.; Singh, Yogesh

    2015-10-01

    We report the structure, magnetic, and thermal property measurements on single-crystalline and polycrystalline samples of the Ru-substituted honeycomb lattice iridate Na2Ir1 -xRuxO3 (x =0 ,0.05 ,0.1 ,0.15 ,0.2 ,0.3 ,0.5 ) . The evolution of magnetism in Na2Ir1 -xRuxO3 has been studied using dc and ac magnetic susceptibilities and heat-capacity measurements. The parent compound Na2IrO3 is a spin-orbit-driven Mott insulator with magnetic order of reduced moments below TN=15 K . In the Ru-substituted samples the antiferromagnetic long-range state is replaced by a spin-glass-like state even for the smallest substitution suggesting that the magnetic order in Na2IrO3 is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na2IrO3 . Additionally, all samples show insulating electrical transport.

  14. Photoinduced melting of magnetic order in the correlated electron insulator NdNiO3

    NASA Astrophysics Data System (ADS)

    Caviglia, A. D.; Först, M.; Scherwitzl, R.; Khanna, V.; Bromberger, H.; Mankowsky, R.; Singla, R.; Chuang, Y.-D.; Lee, W. S.; Krupin, O.; Schlotter, W. F.; Turner, J. J.; Dakovski, G. L.; Minitti, M. P.; Robinson, J.; Scagnoli, V.; Wilkins, S. B.; Cavill, S. A.; Gibert, M.; Gariglio, S.; Zubko, P.; Triscone, J.-M.; Hill, J. P.; Dhesi, S. S.; Cavalleri, A.

    2013-12-01

    Using ultrafast resonant soft x-ray diffraction, we demonstrate photoinduced melting of antiferromagnetic order in the correlated electron insulator NdNiO3. Time-dependent analysis of the resonant diffraction spectra allows us to follow the temporal evolution of the charge imbalance between adjacent Ni sites. A direct correlation between the melting of magnetic order and charge rebalancing is found. Furthermore, we demonstrate that the magnetic ordering on the Ni and Nd sites, which are locked together in equilibrium, become decoupled during this nonthermal process.

  15. Effects of the fractional order and magnetic field on the blood flow in cylindrical domains

    NASA Astrophysics Data System (ADS)

    Ali Shah, Nehad; Vieru, Dumitru; Fetecau, Constantin

    2016-07-01

    In this paper, based on the magnetohydrodynamics approach, the blood flow along with magnetic particles through a circular cylinder is studied. The fluid is acted by an oscillating pressure gradient and an external magnetic field. The study is based on a mathematical model with Caputo fractional derivatives. The model of ordinary fluid, corresponding to time-derivatives of integer order, is obtained as a particular case. Closed forms of the fluid velocity and magnetic particles velocity are obtained by means of the Laplace and finite Hankel transforms. Effects of the order of Caputo's time-fractional derivatives and of the external magnetic field on flow parameters of both blood and magnetic particles are studied. Numerical simulations and graphical illustrations are used in order to study the influence of the fractional parameter α, Reynolds number and Hartmann number on the fluid and particles velocity. The results highlights that, models with fractional derivatives bring significant differences compared to the ordinary model. This fact can be an important advantage for some practical problems. It also results that the blood velocity, as well as that of magnetic particles, is reduced under influence of the exterior magnetic field.

  16. Robust Charge and Magnetic Orders under Electric Field and Current in the Multiferroic LuFe2O4

    SciTech Connect

    Wen, J.; Xu, G.; Gu, G..D.; Shapiro, S.M.

    2010-04-01

    We performed elastic neutron-scattering measurements on the charge and magnetically ordered multiferroic material LuFe{sub 2}O{sub 4}. An external electric field along the [001] direction with strength up to 20 kV/cm applied at low temperature (-100 K) does not affect either the charge or magnetic structure. At higher temperatures (-360 K), before the transition to three-dimensional charge-ordered state, the resistivity of the sample is low, and an electric current was applied instead. A reduction in the charge and magnetic peak intensities occurs when the sample is cooled under a constant electric current. However, after calibrating the real sample temperature using its own resistance-temperature curve, we show that the actual sample temperature is higher than the thermometer readings, and the 'intensity reduction' is entirely due to internal sample heating by the applied current. Our results suggest that the charge and magnetic orders in LuFe{sub 2}O{sub 4} are unaffected by the application of external electric field and current, and previously observed electric-field and current effects can be naturally explained by internal sample heating.

  17. Interplay of magnetic order and defect modulation in mononlayer FeSe

    NASA Astrophysics Data System (ADS)

    Lu, Junqiang; Zhang, Pengfei; Wu, Jian

    We investigate the role of the defects (vacancy and anti-site) at the Fe-site on the magnetic order in monolayer FeSe. Experimental STM studies of defect states reveal that two type dumbbell-like dimers are formed at the surface of monolayer FeSe. We perform first-principles calculations of the magnetic structure of FeSe monolayer in the presence of defects in order to identify the origin of the STM observations. We consider various distribution of the defects and compare the checkerboard and collinear antiferromagnetic orders. Our results show that a single defect can give a dimer in STM image. A preliminary analysis show that both dimers are centered at the defects with their bright ends positioned on two adjacent Se atoms. We show that the two magnetic orders give rise to two distinct dimers types, in agreement with experiments. This work was supported by the NSF EPSCOR (Grant 1010094).

  18. Sc2NiMnO6: A Double-Perovskite with a Magnetodielectric Response Driven by Multiple Magnetic Orders.

    PubMed

    Yi, Wei; Princep, Andrew J; Guo, Yanfeng; Johnson, Roger D; Khalyavin, Dmitry; Manuel, Pascal; Senyshyn, Anatoliy; Presniakov, Igor A; Sobolev, Alexey V; Matsushita, Yoshitaka; Tanaka, Masahiko; Belik, Alexei A; Boothroyd, Andrew T

    2015-08-17

    Perovskite materials provide a large variety of interesting physical properties and applications. Here, we report on unique properties of a fully ordered magnetodielectric double-perovskite, Sc2NiMnO6 (space group P21/n, a = 4.99860 Å, b = 5.35281 Å, c = 7.34496 Å, and β = 90.7915°), exhibiting sequential magnetic transitions at T1 = 35 K and T2 = 17 K. The transition at T1 corresponds to a single-k antiferromagnetic phase with propagation vector k1 = (1/2, 0, 1/2), while the second transition at T2 corresponds to a 2-k magnetic structure with propagation vectors k1 = (1/2, 0, 1/2) and k2 = (0, 1/2, 1/2). Symmetry analysis suggests that the two ordering wave vectors are independent, and calculations imply that k1 is associated with the Mn sublattice and k2 with the Ni sublattice, suggesting that Mn-Ni coupling is very small or absent. A magnetodielectric anomaly at T2 likely arises from an antiferroelectric ordering that results from the exchange-striction between the two magnetic sublattices belonging to k1 and k2. The behavior of Sc2NiMnO6 demonstrates 3d double-perovskites with small A-site cations as a promising avenue in which to search for magnetoelectric materials. PMID:26241691

  19. Fabrication and integration of permanent magnet materials into MEMS transducers

    NASA Astrophysics Data System (ADS)

    Wang, Naigang

    Microscale permanent magnets (PM) are a key building block for magnetically based microelectromechanical systems (MEMS), such as sensors, actuators, and energy converters. However, the inability to concurrently achieve good magnetic properties and an integrated magnet fabrication process hinders the development of magnetic MEMS. To address this need, this dissertation develops methods for wafer-level microfabrication of thick (10--500+ microm), high-performance, permanent magnets using low-temperature (<180 °C) process steps. These methods and materials are then used to demonstrate fully batch-fabricated magnetic MEMS transducers. Two methods to fabricate micromagnets are developed: electroplating of Co-rich Co-Pt magnets into photoresist-defined molds and micro-packing of rare-earth magnetic powders to form wax-bonded magnets embedded in silicon. Patterned micromagnets with excellent magnetic properties and process-flow compatibility are demonstrated. Electroplated Co-Pt micromagnets with thickness up to 10 microm exhibit out-of-plane anisotropy with coercivities and energy products of 330 kA/m and 69 kJ/m3, respectively. Wax-bonded Nd-Fe-B micromagnets (500 x 500 x 320 microm3) exhibit a coercivity of 737 kA/m and a maximum energy product of 17 kJ/m3 with isotopic behavior. The wax-bonded powder magnets are then integrated into MEMS fabrication processes to batch-fabricate various electrodynamic transducer prototypes. A cantilever-type microtransducer achieves a 2.7 microm vertical deflection at a driving current of 5.5 mArms at 100 Hz. A piston-type transducer with elastomeric membrane obtains a 2.2 microm vertical displacement at a driving current of 670 mArms at 200 Hz. These devices demonstrate the integrability of wax-bonded Nd-Fe-B powder magnets into microscale electromechanical transducers. Electromechanical lumped element models are then developed for the piston-type electrodynamic actuators. The models enable prediction of the device performance as an

  20. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    SciTech Connect

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-03

    Magnetic ordering temperatures in heavy rare earth metal Dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to extreme conditions of pressure to 69 GPa and temperature to 10 K. Previous studies using magnetic susceptibility measurements at high pressures were only able to track magnetic ordering temperature till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This is followed by a rapid increase in the magnetic ordering temperatures in the double hexagonal close packed phase and finally leveling off in the distorted face centered cubic phase of Dy. Lastly, our studies reaffirm that 4f-shell remain localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.

  1. Magnetic ordering temperatures in rare earth metal dysprosium under ultrahigh pressures

    DOE PAGESBeta

    Samudrala, Gopi K.; Tsoi, Georgiy M.; Weir, Samuel T.; Vohra, Yogesh K.

    2014-04-03

    Magnetic ordering temperatures in heavy rare earth metal Dysprosium (Dy) have been studied using an ultrasensitive electrical transport measurement technique in a designer diamond anvil cell to extreme conditions of pressure to 69 GPa and temperature to 10 K. Previous studies using magnetic susceptibility measurements at high pressures were only able to track magnetic ordering temperature till 7 GPa in the hexagonal close packed (hcp) phase of Dy. Our studies indicate that the magnetic ordering temperature shows an abrupt drop of 80 K at the hcp-Sm phase transition followed by a gradual decrease that continues till 17 GPa. This ismore » followed by a rapid increase in the magnetic ordering temperatures in the double hexagonal close packed phase and finally leveling off in the distorted face centered cubic phase of Dy. Lastly, our studies reaffirm that 4f-shell remain localized in Dy and there is no loss of magnetic moment or 4f-shell delocalization for pressures up to 69 GPa.« less

  2. Investigation of the optical properties of ordered semiconductor materials

    NASA Astrophysics Data System (ADS)

    McCrae, Jack E., Jr.

    1997-11-01

    Optical Studies have been conducted upon CdGeAs2 and ZnGeP2, two of the most promising semiconductors being developed for mid-infrared non-linear optics applications. These experiments included photoluminescence (PL) studies of both compounds as well as photoreflectance (PR) measurements upon CdGeAs2. In addition, Hall effect measurements were carried out upon CdGeAs2, to aid in interpretation of the optical data. PL was measured as a function of laser power, sample temperature, and crystal orientation for CdGeAs2. One broad weak peak near 0.38 eV, and another somewhat narrower and often far brighter peak near 0.57 eV were found by low temperature (4 K) PL measurements. Strongly polarized PL was observed with the E field of the PL parallel to the material's c-axis. A polarization ratio as high as 6:1 was observed. PL on ZnGeP2 in the mid-IR revealed a previously unreported PL peak near 0.35 eV. PR measurements on CdCeAs2 allowed the estimation of the bandgap as a function of temperature. The low temperature bandgap proved to be lower than that reported for electroreflectance measurements on other samples of this compound. Hall effect measurements on CdGeAs2 reveals the dominant acceptor level lies about 120 meV above the valence band.

  3. Science and technology of reduced-dimensional magnetic materials

    SciTech Connect

    Heffner, R.H.; Bishop, A.R.; Hundley, M.F.; Jia, Q.; Neumeier, J.J.; Trugman, S.A.; Thompson, J.D.; Wu, X.D.; Zhang, J.

    1998-12-31

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work involved the synthesis of single crystal and thin film samples of magnetoresistive manganites (LaMnO{sub 3} doped with Ca and Sr) and the characterization of their electronic transport properties to understand the underlying physical mechanisms responsible for the colossal magnetoresistance (CMR) of these materials. The experimental program was supplemented by a modeling effort that sought to develop microscopic mathematical models of the observed phenomena. The authors succeeded in finding an important relation between the magnetization and resistivity in these materials, which helps to explain the importance of lattice distortions accompanied by clusters of ferromagnetic spins (called spin-lattice polarons) in the CMR phenomena. In addition, they developed rudimentary tunnel junctions of CMR-insulator-CMR multilayers that will lead to possible applications of these materials as magnetic sensors.

  4. Magnetic Separation for Nuclear Material Detection and Surveillance

    SciTech Connect

    Worl, L.A.; Devlin, D.; Hill, D.; Padilla, D.; Prenger, F.C.

    1998-08-01

    A high performance superconducting magnet is being developed for particle retrieval from field collected samples. Results show that maximum separation effectiveness is obtained when the matrix fiber diameter approaches the diameter of the particles to be captured. Experimentally, the authors obtained a single particle capture limit with 0.8{micro}m PuO{sub 2} particles with dodecane as a carrier fluid. The development of new matrix materials is being pursued through the controlled corrosion of stainless steel wool, or the deposition of nickel dendrites on the existing stainless steel matrix material. They have also derived a model from a continuity equation that uses empirically determined capture cross section values. This enables the prediction of high gradient magnetic separator performance for a variety of materials and applications. The model can be used to optimize the capture cross section and thus increase the capture efficiency.

  5. Model of the magnetization of nanocrystalline materials at low temperatures

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2014-07-01

    A theoretical model incorporating the material texture has been developed to simulate the magnetic properties of nanocrystalline materials at low temperatures where the effect of thermal energy on magnetization is neglected. The method is based on Landau-Lifshitz-Gilbert (LLG) theory and it describes the magnetization dynamics of individual grains in the effective field. The modified LLG equation incorporates the intrinsic fields from the intragrain magnetocrystalline and grain boundary anisotropies and the interacting fields from intergrain dipolar and exchange couplings between the neighbouring grains. The model is applied to study magnetic properties of textured nanocrystalline Ni samples at 2K and is capable to reproduce closely the hysteresis loop behaviour at different orientations of applied magnetic field. Nanocrystalline Ni shows the grain boundary anisotropy constant K 1 s = - 6.0 × 104 J / m 3 and the intergrain exchange coupling denoted by the effective exchange constant Ap = 2.16 × 10-11 J/m. Analytical expressions to estimate the intergrain exchange energy density and the effective exchange constant have been formulated.

  6. Magnon-phonon interconversion in a dynamically reconfigurable magnetic material

    NASA Astrophysics Data System (ADS)

    Guerreiro, Sergio C.; Rezende, Sergio M.

    2015-12-01

    The ferrimagnetic insulator yttrium iron garnet (YIG) is an important material in the field of magnon spintronics, mainly because of its low magnetic losses. YIG also has very low acoustic losses, and for this reason the conversion of a state of magnetic excitation (magnons) into a state of lattice vibration (phonons), or vice versa, broadens its possible applications in spintronics. Since the magnetic parameters can be varied by some external action, the magnon-phonon interconversion can be tuned to perform a desired function. We present a quantum theory of the interaction between magnons and phonons in a ferromagnetic material subject to a dynamic variation of the applied magnetic field. It is shown that when the field gradient at the magnetoelastic crossover region is much smaller than a critical value, an initial elastic excitation can be completely converted into a magnetic excitation, or vice versa. This occurs with conservation of linear momentum and spin angular momentum, implying that phonons created by the conversion of magnons have spin angular momentum and carry spin current. It is shown further that if the system is initially in a quantum coherent state, its coherence properties are maintained regardless of the time dependence of the field.

  7. Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds

    NASA Astrophysics Data System (ADS)

    Steil, Daniel; Schmitt, Oliver; Fetzer, Roman; Kubota, Takahide; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Rodan, Steven; Blum, Christian G. F.; Balke, Benjamin; Wurmehl, Sabine; Aeschlimann, Martin; Cinchetti, Mirko

    2015-04-01

    Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demagnetization studies can, thus, help to understand the impact of stoichiometry and order on ultrafast spin dynamics. Here, we present a comparative study of the structural ordering and magnetization dynamics for thin films and bulk single crystals of the family of Heusler alloys with composition Co2Fe1 - xMnxSi. The local ordering is studied by 59Co nuclear magnetic resonance (NMR) spectroscopy, while the time-resolved magneto-optical Kerr effect gives access to the ultrafast magnetization dynamics. In the NMR studies we find significant differences between bulk single crystals and thin films, both regarding local ordering and stoichiometry. The ultrafast magnetization dynamics, on the other hand, turns out to be mostly unaffected by the observed structural differences, especially on the time scale of some hundreds of femtoseconds. These results confirm hole-mediated spin-flip processes as the main mechanism for ultrafast demagnetization and the robustness of this demagnetization channel against defect states in the minority band gap as well as against the energetic position of the band gap with respect to the Fermi energy. The very small differences observed in the magnetization dynamics on the picosecond time-scale, on the other hand, can be explained by considering the

  8. Magnetism of ordered and disordered Ni2MnAl full Heusler compounds

    NASA Astrophysics Data System (ADS)

    Simon, E.; Vida, J. Gy.; Khmelevskyi, S.; Szunyogh, L.

    2015-08-01

    Based on ab initio calculations and Monte Carlo simulations, we present a systematic study of the magnetic ground state and finite temperature magnetism of ordered and disordered Ni2MnAl full Heusler compounds. By increasing the degree of the long-range chemical disorder between the Mn and Al sublattices, the magnetic order progressively changes from the ferromagnetic state in the ordered L 21 phase toward a fully compensated antiferromagnetic state in the disordered B 2 phase and we also conclude that the Ni atoms exhibit induced moments. We determine the Mn-Mn interactions by using the magnetic force theorem and find dominating, but rather weak ferromagnetic couplings in the ordered L 21 phase. We used a recently proposed renormalization technique to include the weak Ni moments into the spin model, which indeed remarkably increased the nearest-neighbor Mn-Mn interaction. In accordance with the total energy calculations, in the disordered compounds, strong antiferromagnetic site-antisite Mn-Mn interactions appear. Determining the spin-spin correlation functions from Monte Carlo simulations, we conclude that above the transition temperature, short-range antiferromagnetic correlations prevail between the Mn atoms. In view of the potential application of disordered Ni2MnAl as a room temperature antiferromagnet, we calculate the magnetic anisotropy energies of tetragonally distorted samples in the B 2 phase and find that they are smaller by two orders in magnitude than in the frustrated antiferromagnet IrMn3.

  9. 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.

  10. [Application of magnetic materials in analysis on Chinese herb medicines].

    PubMed

    Xu, Li-Wei; Wang, Jiu-Rong; Han, Xue-Feng

    2012-12-01

    China is the cradle of Chinese herb medicines,with rich plant resources. However, traditional processing methods have many disadvantages, such as high comsumption of organic solvent, long extraction time and high loss of effective constituents. For the purpose of rational use of Chinese herb medicines and accurate analysis on their constituents,the sample pre-treatment method with magnetic nanoparticles as the carrier brought new opportunities in recent years. after consulting literatures,the essay summarizes traditional extraction methods of Chinese herb medicines, characteristics of magnetic materials and their application in the analysis on Chinese herb medicines. PMID:23477130

  11. Magnetic order, magnetic correlations, and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7

    NASA Astrophysics Data System (ADS)

    Dalmas de Réotier, P.; Yaouanc, A.; Chapuis, Y.; Curnoe, S. H.; Grenier, B.; Ressouche, E.; Marin, C.; Lago, J.; Baines, C.; Giblin, S. R.

    2012-09-01

    Er2Ti2O7 is believed to be a realization of an XY antiferromagnet on a frustrated lattice of corner-sharing regular tetrahedra. It is presented as an example of the order-by-disorder mechanism in which fluctuations lift the degeneracy of the ground state, leading to an ordered state. Here we report detailed measurements of the low-temperature magnetic properties of Er2Ti2O7, which displays a second-order phase transition at TN≃1.2 K with coexisting short- and long-range orders. Magnetic susceptibility studies show that there is no spin-glass-like irreversible effect. Heat capacity measurements reveal that the paramagnetic critical exponent is typical of a 3-dimensional XY magnet while the low-temperature specific heat sets an upper limit on the possible spin-gap value and provides an estimate for the spin-wave velocity. Muon spin relaxation measurements show the presence of spin dynamics in the nanosecond time scale down to 21 mK. This time range is intermediate between the shorter time characterizing the spin dynamics in Tb2Sn2O7, which also displays long- and short-range magnetic order, and the time scale typical of conventional magnets. Hence the ground state is characterized by exotic spin dynamics. We determine the parameters of a symmetry-dictated Hamiltonian restricted to the spins in a tetrahedron, by fitting the paramagnetic diffuse neutron scattering intensity for two reciprocal lattice planes. These data are recorded in a temperature region where the assumption that the correlations are limited to nearest neighbors is fair.

  12. Orientational order and translational dynamics of magnetic particle assemblies in liquid crystals.

    PubMed

    Peroukidis, Stavros D; Klapp, Sabine H L

    2016-08-10

    Implementing extensive molecular dynamics simulations we explore the organization of magnetic particle assemblies (clusters) in a uniaxial liquid crystalline matrix comprised of rodlike particles. The magnetic particles are modelled as soft dipolar spheres with diameter significantly smaller than the width of the rods. Depending on the dipolar strength coupling the magnetic particles arrange into head-to-tail configurations forming various types of clusters including rings (closed loops) and chains. In turn, the liquid crystalline matrix induces long range orientational ordering to these structures and promotes their diffusion along the director of the phase. Different translational dynamics are exhibited as the liquid crystalline matrix transforms either from isotropic to nematic or from nematic to smectic state. This is caused due to different collective motion of the magnetic particles into various clusters in the anisotropic environments. Our results offer a physical insight for understanding both the structure and dynamics of magnetic particle assemblies in liquid crystalline matrices. PMID:27460190

  13. Magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles confined within ordered mesoporous carbons as efficient microwave absorbers.

    PubMed

    Wang, Jiacheng; Zhou, Hu; Zhuang, Jiandong; Liu, Qian

    2015-02-01

    A series of magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles have been successfully introduced into the mesochannels of ordered mesoporous carbons by the combination of the impregnation of iron salt precursors and then in situ hydrolysis, pyrolysis and reduction processes. The magnetic nanoparticles are uniformly dispersed and confined within the mesopores of mesoporous carbons. Although the as-prepared magnetic mesoporous carbon composites have high contents of magnetic components, they still possess very high specific surface areas and pore volumes. The magnetic hysteresis loops measurements indicate that the magnetic constituents are poorly-crystalline nanoparticles and their saturation magnetization is evidently smaller than bulky magnetic materials. The confinement of magnetic nanoparticles within the mesopores of mesoporous carbons results in the decrease of the complex permittivity and the increase of the complex permeability of the magnetic nanocomposites. The maximum reflection loss (RL) values of -32 dB at 11.3 GHz and a broad absorption band (over 2 GHz) with RL values <-10 dB are obtained for 10-Fe3O4-CMK-3 and 10-γ-Fe2O3-CMK-3 composites in a frequency range of 8.2-12.4 GHz (X-band), showing their great potentials in microwave absorption. This research opens a new method and idea for developing novel magnetic mesoporous carbon composites as high-performance microwave absorbing materials. PMID:25562071

  14. Nanogranular soft magnetic material and on-package integrated inductors

    NASA Astrophysics Data System (ADS)

    Li, Liangliang

    2007-12-01

    Integrated inductors used in electronic circuits are mainly spiral-shaped aluminum devices fabricated on Si chip. They have several disadvantages---large silicon area consumption, high DC resistance and high cost. An attractive approach to address these issues is directly integrating inductors into package substrates, which provide plenty of usage area, low resistance and low cost. The goals of this dissertation are designing and fabricating magnetic and air-core inductors with characteristic low resistance and high quality factor on package substrates. The research work includes three parts which are summarized below. First, the CoFeHfO nanogranular magnetic material developed on Si wafers and package substrates by pulsed DC reactive sputtering were investigated. On Si wafers, the optimized CoFeHfO film has soft magnetic properties. On printed circuit board (PCB) substrates, these magnetic properties degrade due to the rough surface. Surface planarization such as chemical-mechanical polishing can be applied on PCB substrates to reduce the surface roughness and hence improve these properties. Second, on-package inductors with small resistances and high quality factors were designed, fabricated, measured and analyzed. Air-core and magnetic inductors (20 design variations) were built on 8-inch PCB substrates. The DC resistances of these inductors are less than 12 mO, one of the lowest values ever reported. The maximum quality factors can be as large as ˜80 at around 1 GHz for the air-core inductors and ˜25 at 200 MHz for the magnetic inductors. Third, inductor simulation was carried out to study the effects of magnetic materials on the properties of inductors using the Ansoft HFSS software package. The measurement data for the permeability spectra of the CoFeHfO film and the tensor nature of the permeability were taken into account in the simulation. The simulation results matched the experimental data for the inductances, resistances and quality factors. This

  15. Novel microwave magnetic and magnetoelectric composite materials and devices

    NASA Astrophysics Data System (ADS)

    Pettiford, Carl I.

    Bulk microwave magnetic materials and devices have been widely used in different RF/microwave devices such as inductors, filters, circulars, isolators, and phase shifters. With the even increasing level of integration of RFIC and MMIC, there is an urgent need for new microwave magnetic thin film materials and new integrated RF/microwave magnetic devices. In this thesis, we have addressed these needs in three different areas: (1) exchange biased ferromagnetic/anti-ferromagnetic multilayer thin films with enhanced anisotropy fields, (2) magneto-electric heterostructures and devices, and (3) metamaterial multilayers for FMR enhancement, tunability, and plane wave absorption. Metallic soft magnetic thin films have been demonstrated to have high saturation magnetization, large permeability and relatively high self-biased ferromagnetic resonance (FMR) frequencies, showing great promise for applications in integrated RF and microwave magnetic devices. One problem for these metallic magnetic films is however their relatively low anisotropy fields that are typically in the range of 10˜30 Oe, which severely limit their application frequency range. In this work, we investigated the exchange coupled ferromagnetic/anti-ferromagnetic/ferromagnetic CoFe/PtMn/CoFe multilayer films. These CoFe/PtMn/CoFe multilayer films showed a significantly enhanced anisotropy field of 160 Oe, which was 5˜10 times of that of the FeCo films. In addition, a narrow FMR linewidth of 45 Oe at X-band was achieved in the CoFe/PtMn/CoFe trilayer. The exchange coupling in the ferromagnetic/anti-ferromagnetic/ferromagnetic trilayers leads to a significantly enhanced anisotropy field that is crucial for the application of metallic magnetic films in integrated magnetic RF/microwave devices. The magnetoelectric coupling of novel YIG/PZT, FeCoB/PZT and FeGaB/PZT multiferroic heterostructures were investigated at DC and at microwave frequencies. An electrostatically tunable band-reject filter device was

  16. Superconductivity and Magnetism in Organic Materials Studied with μSR

    NASA Astrophysics Data System (ADS)

    Pratt, Francis

    2016-09-01

    A review is given of the current status and recent progress in the use of μSR for the study of superconductivity and magnetism in organic materials. For organic superconductors, important factors are discussed that influence the observed μSR line widths and their field and temperature dependences in the superconducting state. The accumulated μSR results give direct information about the scaling relationship between superfluid stiffness and transition temperature that provides a strong constraint for theories of organic superconductors. For organic magnetism, μSR offers a sensitive probe for detecting various weak magnetic phenomena ranging from spin-density-wave transitions through spin dynamics and 3D ordering of Heisenberg chain systems to field induced magnetism of quantum spin liquids. Finally, experiments are described that focus on two current issues in organic spintronics: direct measurement of the spin coherence length and the identification of the relative importance of different mechanisms of spin decoherence.

  17. Nuclear magnetic resonance of laser-polarized noble gases in molecules, materials and organisms

    SciTech Connect

    Goodson, Boyd M.

    1999-12-01

    Conventional nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are fundamentally challenged by the insensitivity that stems from the ordinarily low spin polarization achievable in even the strongest NMR magnets. However, by transferring angular momentum from laser light to electronic and nuclear spins, optical pumping methods can increase the nuclear spin polarization of noble gases by several orders of magnitude, thereby greatly enhancing their NMR sensitivity. This dissertation is primarily concerned with the principles and practice of optically pumped nuclear magnetic resonance (OPNMR). The enormous sensitivity enhancement afforded by optical pumping noble gases can be exploited to permit a variety of novel NMR experiments across many disciplines. Many such experiments are reviewed, including the void-space imaging of organisms and materials, NMR and MRI of living tissues, probing structure and dynamics of molecules in solution and on surfaces, and zero-field NMR and MRI.

  18. Studies of a magnetically focused electrostatic mirror. I. Experimental test of the first order properties

    PubMed

    Crewe; Ruan; Korda; Tsai

    2000-02-01

    When a uniform magnetic field is superimposed on a uniform electrostatic field, the combination can act as a magnetically focused mirror. This mirror is predicted to have aberrations of opposite sign to those of a magnetic lens and may therefore be useful as a corrector. We have built an electron optical system to test these ideas. The results are presented in two papers. This first paper describes the general design and the results of the measurements of the first order properties. The second paper (Tsai, F., J. Microsc. 197 (2000) 118-135) will describe the measurements of the aberration properties. PMID:10652005

  19. Ultra-low field nuclear magnetic resonance and magnetic resonance imaging to discriminate and identify materials

    DOEpatents

    Kraus, Robert H.; Matlashov, Andrei N.; Espy, Michelle A.; Volegov, Petr L.

    2010-03-30

    An ultra-low magnetic field NMR system can non-invasively examine containers. Database matching techniques can then identify hazardous materials within the containers. Ultra-low field NMR systems are ideal for this purpose because they do not require large powerful magnets and because they can examine materials enclosed in conductive shells such as lead shells. The NMR examination technique can be combined with ultra-low field NMR imaging, where an NMR image is obtained and analyzed to identify target volumes. Spatial sensitivity encoding can also be used to identify target volumes. After the target volumes are identified the NMR measurement technique can be used to identify their contents.

  20. The triathlon of magnetic actuation: Rolling, propelling, swimming with a single magnetic material

    PubMed Central

    Vach, Peter J.; Faivre, Damien

    2015-01-01

    Magnetic actuation of microscopic devices in a liquid environment has been achieved in various ways, which can be grouped into rolling, propelling and swimming. Previous actuators were designed with a focus on one particular type of magnetic actuation. We have shown earlier that efficient magnetic propellers can be selected from randomly shaped magnetic nanostructures synthesized in solution. Here we show that these synthesized nanostructures can be used for all three types of magnetic actuation. Whereas it might not be surprising that single structures can roll in addition to propelling, swimming is unexpectedly also observed using the same material. In this case, however, the magnetically guided self-assembly of several individual particles into chain-like structures is necessary to obtain swimmers, since individual rigid nanostructures cannot swim. Interestingly, the direction of the swimming motion is not necessarily parallel to the long axis of the chain-like assembly, a finding that had been theoretically expected but experimentally not observed so far. Our findings show that the range of structures that can be effectively actuated by external magnetic fields is much broader than assumed until now. This could open up new opportunities for the design of magnetically actuated devices. PMID:25791721

  1. Analysis of ringing due to magnetic core materials used in pulsed nuclear magnetic resonance applications

    NASA Astrophysics Data System (ADS)

    Prabhu Gaunkar, Neelam; Nlebedim, Cajetan; Hadimani, Ravi; Bulu, Irfan; Song, Yi-Qiao; Mina, Mani; Jiles, David

    Oil-field well logging instruments employ pulsed nuclear magnetic resonance (NMR) techniques and use inductive sensors to detect and evaluate the presence of particular fluids in geological formations. Acting as both signal transmitters and receivers most inductive sensors employ magnetic cores to enhance the quality and amplitude of signals recorded during field measurements. It is observed that the magnetic core also responds to the applied input signal thereby generating a signal (`ringing') that interferes with the measurement of the signals from the target formations. This causes significant noise and receiver dead time and it is beneficial to eliminate/suppress the signals received from the magnetic core. In this work a detailed analysis of the magnetic core response and in particular loading of the sensor due to the presence of the magnetic core is presented. Pulsed NMR measurements over a frequency band of 100 kHz to 1MHz are used to determine the amplitude and linewidth of the signals acquired from different magnetic core materials. A lower signal amplitude and a higher linewidth are vital since these would correspond to minimal contributions from the magnetic core to the inductive sensor response and thus leading to minimized receiver dead time.

  2. On magnetic ordering in heavily sodium substituted hole doped lanthanum manganites

    NASA Astrophysics Data System (ADS)

    Sethulakshmi, N.; Unnimaya, A. N.; Al-Omari, I. A.; Al-Harthi, Salim; Sagar, S.; Thomas, Senoy; Srinivasan, G.; Anantharaman, M. R.

    2015-10-01

    Mixed valence manganite system with monovalent sodium substituted lanthanum manganites form the basis of the present work. Lanthanum manganites belonging to the series La1-xNaxMnO3 with x=0.5-0.9 were synthesized using modified citrate gel method. Variation of lattice parameters and unit cell volume with Na concentration were analyzed and the magnetization measurements indicated ferromagnetic ordering in all samples at room temperature. Low temperature magnetization behavior indicated that all samples exhibit antiferromagnetism along with ferromagnetism and it has also been observed that antiferromagnetic ordering dominates ferromagnetic ordering as concentration is increased. Evidence for such a magnetic inhomogeneity in these samples has been confirmed from the variation in Mn3+/Mn4+ ion ratio from X-ray Photoelectron Spectroscopy and from the absorption peak studies using Ferromagnetic Resonance Spectroscopy.

  3. A High-Order Finite-Volume Algorithm for Fokker-Planck Collisions in Magnetized Plasmas

    SciTech Connect

    Xiong, Z; Cohen, R H; Rognlien, T D; Xu, X Q

    2007-04-18

    A high-order finite volume algorithm is developed for the Fokker-Planck Operator (FPO) describing Coulomb collisions in strongly magnetized plasmas. The algorithm is based on a general fourth-order reconstruction scheme for an unstructured grid in the velocity space spanned by parallel velocity and magnetic moment. The method provides density conservation and high-order-accurate evaluation of the FPO independent of the choice of the velocity coordinates. As an example, a linearized FPO in constant-of-motion coordinates, i.e. the total energy and the magnetic moment, is developed using the present algorithm combined with a cut-cell merging procedure. Numerical tests include the Spitzer thermalization problem and the return to isotropy for distributions initialized with velocity space loss cones. Utilization of the method for a nonlinear FPO is straightforward but requires evaluation of the Rosenbluth potentials.

  4. CeRu2Al10: Anomalous Magnetic Ordering and Its Field Stability

    NASA Astrophysics Data System (ADS)

    Strydom, A. M.

    2010-04-01

    The intermetallic compound CeRu2Al10 orders in a new crystal structure type that is cage-like on account of its peculiar atomic arrangement and large interatomic distances—especially concerning the environment of the rare-earth element Ce. In previous work we showed that anomalous thermal, electronic, and magnetic properties of this compound coalesce into a phase transition at T *=27 K, which is exceptionally high for a cerium intermetallic compound. T * has been characterized through various temperature-dependent properties which suggest a multi-parameter nature of the ordering at T *. Here we report on continued investigations into this compound and focus in particular on the response to applied magnetic fields. Whereas transport properties in the ordered region are receptive to magnetic fields, the transition itself turns out to be more robust and is insensitive to static fields up to 14 T.

  5. Non-equilibrium magnetic colloidal dispersions at liquid-air interfaces: dynamic patterns, magnetic order and self-assembled swimmers.

    SciTech Connect

    Snezhko, A.

    2011-04-20

    Colloidal dispersions of interacting particles subjected to an external periodic forcing often develop nontrivial self-assembled patterns and complex collective behavior. A fundamental issue is how collective ordering in such non-equilibrium systems arises from the dynamics of discrete interacting components. In addition, from a practical viewpoint, by working in regimes far from equilibrium new self-organized structures which are generally not available through equilibrium thermodynamics can be created. In this review spontaneous self-assembly phenomena in magnetic colloidal dispersions suspended at liquid-air interfaces and driven out of equilibrium by an alternating magnetic field are presented. Experiments reveal a new type of nontrivially ordered self-assembled structures emerging in such systems in a certain range of excitation parameters. These dynamic structures emerge as a result of the competition between magnetic and hydrodynamic forces and have complex unconventional magnetic ordering. Nontrivial self-induced hydrodynamic fields accompany each out-of-equilibrium pattern. Spontaneous symmetry breaking of the self-induced surface flows leading to a formation of self-propelled microstructures has been discovered. Some features of the self-localized structures can be understood in the framework of the amplitude equation (Ginzburg-Landau type equation) for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density and the Navier-Stokes equation for hydrodynamic flows. To understand the fundamental microscopic mechanisms governing self-assembly processes in magnetic colloidal dispersions at liquid-air interfaces a first-principle model for a non-equilibrium self-assembly is presented. The latter model allows us to capture in detail the entire process of out-of-equilibrium self-assembly in the system and reproduces most of the observed phenomenology.

  6. In situ study of atomic-vacancy ordering in stoichiometric titanium monoxide by the magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Valeeva, A. A.; Nazarova, S. Z.; Rempel, A. A.

    2015-02-01

    An in situ temperature study of a variation in the degree of long-range order in stoichiometric titanium monoxide has been performed by the magnetic susceptibility method. The measurements have been performed on annealed and quenched titanium monoxide in the temperature range from 300 to 1200 K. It has been found that the degree of long-range order depends on the regime and temperature of annealing of the initial samples. The degree of long-range order in the process of measurement of the magnetic susceptibility varies from 0.21 to 1.00; the larger the degree of long-range order, the smaller the magnetic susceptibility. Furthermore, the long-range order parameter decreases with an increase in the temperature above 1200 K and vanishes sharply at the order-disorder transition temperature. According to the results of this work, the critical long-range order parameter is 0.21 and the temperature of the nonequilibrium disorder-order transition is about 1073 K.

  7. Advances in core loss calculations for magnetic materials

    NASA Technical Reports Server (NTRS)

    Triner, J. E.

    1982-01-01

    A new analytical technique which predicts the basic magnetic properties under various operating conditions encountered in state-of-the-art dc-ac/dc converters is discussed. Using a new flux-controlled core excitation circuit, magnetic core characteristics were developed for constant values of ramp flux (square wave voltage excitation) and frequency. From this empirical data, a mathematical loss characteristics equation is developed to analytically predict the specific core loss of several magnetic materials under various waveform excitation conditions. In addition, these characteristics show the circuit designer for the first time the direct functional relatonships between induction level and specific core loss as a function of the two key dc-dc converter operating parameters of input voltage and duty cycle.

  8. Magnetic coercivity and ferromagnetic species in lunar materials

    NASA Technical Reports Server (NTRS)

    Wasilewski, P.

    1972-01-01

    Lunar samples have reduced coercive force, high values of R sub H (ratio of remanent coercive force to coercive force), and constriction in their magnetic hysteresis loops due to the presence of superparamagnetic and multidomain iron grains. The high R sub H values are also attributable to the magnetic shape effects of the iron grains. Spheres, cubes, and needles, as well as more irregular metal grains were observed. The coercive force values are quite meaningless unless the size and shape distributions are determined. The R sub H and the ratio of saturation remanence to saturation magnetization values can be considered characteristic of the size and shape modes of the ferromagnetic grains in a natural sample, and a classification of natural materials based on their hysteresis characteristics is presented with special reference to lunar samples.

  9. Pressure dependence of the magnetic order in CrAs: a neutron diffraction investigation

    DOE PAGESBeta

    Keller, L.; White, J. S.; Babkevich, P.; Susner, Michael A.; Sims, Zachary C; Safa-Sefat, Athena; Ronnow, H. M.; Ruegg, Ch.

    2015-01-29

    The suppression of magnetic order with pressure concomitant with the appearance of pressure-induced superconductivity was recently discovered in CrAs. Here we present a neutron diffraction study of the pressure evolution of the helimagnetic ground-state towards and in the vicinity of the superconducting phase. Neutron diffraction on polycrystalline CrAs was employed from zero pressure to 0.65 GPa and at various temperatures. The helimagnetic long-range order is sustained under pressure and the magnetic propagation vector does not show any considerable change. The average ordered magnetic moment is reduced from 1.73(2) μB at ambient pressure to 0.4(1) μB close to the critical pressuremore » Pc ≈ 0.7 GPa, at which magnetic order is completely suppressed. The width of the magnetic Bragg peaks strongly depends on temperature and pressure, showing a maximum in the region of the onset of superconductivity. In conclusion, we interpret this as associated with competing ground-states in the vicinity of the superconducting phase.« less

  10. Pressure dependence of the magnetic order in CrAs: a neutron diffraction investigation

    SciTech Connect

    Keller, L.; White, J. S.; Babkevich, P.; Susner, Michael A.; Sims, Zachary C; Safa-Sefat, Athena; Ronnow, H. M.; Ruegg, Ch.

    2015-01-29

    The suppression of magnetic order with pressure concomitant with the appearance of pressure-induced superconductivity was recently discovered in CrAs. Here we present a neutron diffraction study of the pressure evolution of the helimagnetic ground-state towards and in the vicinity of the superconducting phase. Neutron diffraction on polycrystalline CrAs was employed from zero pressure to 0.65 GPa and at various temperatures. The helimagnetic long-range order is sustained under pressure and the magnetic propagation vector does not show any considerable change. The average ordered magnetic moment is reduced from 1.73(2) μB at ambient pressure to 0.4(1) μB close to the critical pressure Pc ≈ 0.7 GPa, at which magnetic order is completely suppressed. The width of the magnetic Bragg peaks strongly depends on temperature and pressure, showing a maximum in the region of the onset of superconductivity. In conclusion, we interpret this as associated with competing ground-states in the vicinity of the superconducting phase.

  11. Mixed Convection Peristaltic Flow of Third Order Nanofluid with an Induced Magnetic Field

    PubMed Central

    Noreen, Saima

    2013-01-01

    This research is concerned with the peristaltic flow of third order nanofluid in an asymmetric channel. The governing equations of third order nanofluid are modelled in wave frame of reference. Effect of induced magnetic field is considered. Long wavelength and low Reynolds number situation is tackled. Numerical solutions of the governing problem are computed and analyzed. The effects of Brownian motion and thermophoretic diffusion of nano particles are particularly emphasized. Physical quantities such as velocity, pressure rise, temperature, induced magnetic field and concentration distributions are discussed. PMID:24260130

  12. Ageneral approach to first order phase transitions and the anomalous behavior of coexisting phases in the magnetic case.

    SciTech Connect

    Gama, S.; de Campos, A.; Coelho, A. A.; Alves, C. S.; Ren, Y.; Garcia, F.; Brown, D. E.; da Silva, L. M.; Magnus, A.; Carvalho, G.; Gandra, G. C.; dos Santos, A. O.; Cardoso, L. P.; von Ranke, P. J.; X-Ray Science Division; Univ. Federal de Sao Paulo; Unv. Estadual de Champinas; Univ. Estadual de Maringa Lab. Nacional de Luz Sincrotron; Northern Univ.; Univ. de Estado do Rio de Janerio

    2009-01-01

    First order phase transitions for materials with exotic properties are usually believed to happen at fixed values of the intensive parameters (such as pressure, temperature, etc.) characterizing their properties. It is also considered that the extensive properties of the phases (such as entropy, volume, etc.) have discontinuities at the transition point, but that for each phase the intensive parameters remain constant during the transition. These features are a hallmark for systems described by two thermodynamic degrees of freedom. In this work it is shown that first order phase transitions must be understood in the broader framework of thermodynamic systems described by three or more degrees of freedom. This means that the transitions occur along intervals of the intensive parameters, that the properties of the phases coexisting during the transition may show peculiar behaviors characteristic of each system, and that a generalized Clausius-Clapeyron equation must be obeyed. These features for the magnetic case are confirmed, and it is shown that experimental calorimetric data agree well with the magnetic Clausius-Clapeyron equation for MnAs. An estimate for the point in the temperature-field plane where the first order magnetic transition turns to a second order one is obtained (the critical parameters) for MnAs and Gd{sub 5}Ge{sub 2}Si{sub 2} compounds. Anomalous behavior of the volumes of the coexisting phases during the magnetic first order transition is measured, and it is shown that the anomalies for the individual phases are hidden in the behavior of the global properties as the volume.

  13. Observation of low-temperature magnetic ordering in mixed-phase Sr-Ca-Cu-O superconductors substituted by iron

    NASA Astrophysics Data System (ADS)

    Sklyarova, A.; Shinoda, S.; Nagumo, T.; Chizhik, V. I.; Matveev, V. V.; Suematsu, H.

    2016-08-01

    The series of unsubstituted Sr2CaCu2O6 and iron-substituted Sr2CaCu2‑x Fe x O6 (x=0.1,x=0.05) materials were produced by a high-pressure synthesis route and characterized using X-ray diffraction and SQUID magnetometry. The change of contained phase ratio was found at different substituent concentrations in the samples synthesized under the same conditions: unexpected growth of 0201 and CuO phase with decrease of iron content was observed. Synthesis temperature-dependence of obtained phase fractions was found for the samples with x=0.05. The superconductivity transition was found for all obtained samples and the highest critical temperature was around 103 K. From the SQUID measurements distortions of the magnetic susceptibility curves were found; these were explained by the magnetic ordering arising at low temperatures. This magnetic ordering was associated with the magnetic moment appearing in iron-doped 0201 phase.

  14. Electrochromic & magnetic properties of electrode materials for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Zheng-Fei, Guo; Kun, Pan; Xue-Jin, Wang

    2016-01-01

    Progress in electrochromic lithium ion batteries (LIBs) is reviewed, highlighting advances and possible research directions. Methods for using the LIB electrode materials’ magnetic properties are also described, using several examples. Li4Ti5O12 (LTO) film is discussed as an electrochromic material and insertion compound. The opto-electrical properties of the LTO film have been characterized by electrical measurements and UV-Vis spectra. A prototype bi-functional electrochromic LIB, incorporating LTO as both electrochromic layer and anode, has also been characterized by charge- discharge measurements and UV-Vis transmittance. The results show that the bi-functional electrochromic LIB prototype works well. Magnetic measurement has proven to be a powerful tool to evaluate the quality of electrode materials. We introduce briefly the magnetism of solids in general, and then discuss the magnetic characteristics of layered oxides, spinel oxides, olivine phosphate LiFePO4, and Nasicon-type Li3Fe2(PO4)3. We also discuss what kind of impurities can be detected, which will guide us to fabricate high quality films and high performance devices. Project supported by the National High Technology Research and Development Program of China (Grant No. 2015AA034201) and the Chinese Universities Scientific Fund (Grant No. 2015LX002).

  15. Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film

    PubMed Central

    Zhao, Hongyang; Kimura, Hideo; Cheng, Zhenxiang; Osada, Minoru; Wang, Jianli; Wang, Xiaolin; Dou, Shixue; Liu, Yan; Yu, Jianding; Matsumoto, Takao; Tohei, Tetsuya; Shibata, Naoya; Ikuhara, Yuichi

    2014-01-01

    Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of ~1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature. PMID:24918357

  16. Probing soil and aquifer material porosity with nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Hinedi, Z. R.; Kabala, Z. J.; Skaggs, T. H.; Borchardt, D. B.; Lee, R. W. K.; Chang, A. C.

    1993-12-01

    Nuclear magnetic resonance relaxation measurements were used to identify different characteristic porosity domains in soil and aquifer materials. The porosity distribution can be inferred from these measurements by a regularization method applicable to any nuclear magnetic resonance (NMR) relaxation, or by an analytic method applicable only to multiexponential relaxations (D. Orazio et al., 1989). The porosity distribution obtained from NMR relaxation measurements strongly depends on the pore shape factor. For the Borden aquifer material, both the regularized and the analytic pore size distribution obtained from NMR relaxation measurements are consistent with those obtained by Ball et al. (1990) using Hg porosimetry and N2 adsorption. For the Eustis and the Webster soils, the measured porosity domains are qualitatively consistent with those expected based on their respective composition. Our findings suggest that due to the long time required to saturate fine pores, NMR measurements of porosity distribution that are collected at short saturation times are biased toward larger pore sizes.

  17. Fabrication and characterization of ultra-uniform magnetic nanoparticle arrays in ordered aluminum oxide templates

    NASA Astrophysics Data System (ADS)

    Sun, Ming

    2001-07-01

    Anodization of aluminum in acid solutions can generate unique morphologies of the resulting amorphous alumina films, consisting of long and columnar nanopores with approximately hexagonal ordering (alumite). Alumite has attracted broad attention, both on a fundamental and applied level, for more than half a century. In particular, the possibility of synthesizing nano-structures for magnetic recording technology makes this classic self-assembly process even more attractive. Previous studies have shown that the pore size and pore distance could be easily tuned by controlling anodization conditions. Recently, excellent hexagonal ordering of these nanopores has been achieved by multi-step anodization. Although the maximum ordered area could be increased to 100 mum 2 by further extending the anodization time and using a multi-step anodization, the defects and grain structure in the Al metal surface hamper the achievement of longer-range order. Alumite structures are an almost ideal template for the synthesis of magnetic nanoparticle arrays, which have possible applications in advanced magnetic recording technology and as model systems for the study of well-defined and uniform magnetic nanoparticles. Electroplating can allow a systematic study of how best to make such arrays controlled. Various voltage and current waveforms were employed to control the nucleation, growth, and consequently the magnetic properties of the magnetic metal array in ordered alumite. At first, Fe nanowires were deposited in disordered pores, then Co nanowires were deposited in ordered pores by AC sinusoidal waveform electrodeposition. The average length and diameter of these nanowires can be controlled, but a wide distribution of nanowire lengths is observed. Successively, particle uniformity was achieved by a novel electrodeposition scheme, utilizing pulse-reverse voltage waveforms (pulse-reverse electrodeposition) to control nucleation and growth of the particles. The resulting nanoparticles

  18. Pulsed field magnetometer for nondestructive monitoring of encapsulated magnetic materials

    NASA Astrophysics Data System (ADS)

    Rothwarf, F.; Simizu, S.; Huang, M. Q.; Schaefer, R. J.

    1993-05-01

    A study was recently undertaken to consolidate Sm2Fe17N3-x-based materials by hot isostatic pressing (HIPing). For HIPing, pressed green samples were placed at the center of evacuated, closely fitting, nonmagnetic, thin-walled, stainless-steel cans. The use of nonmagnetic, high-resistivity containers for the samples offered a unique opportunity to evaluate the magnetic properties of the samples after HIPing, without removing them from the HIP cans, by using a pulsed field magnetometer (PFM). The high electrical resistivity of the samples and their containers permits the slowly varying magnetic field (˜5 ms rise time, 45 ms pulse length) to penetrate a sample fully with no phase lags. Thus, the magnetization of a sample is essentially in equilibrium with the applied, time-varying magnetic field. With this method, a given set of encapsulated samples could be subjected to successively higher temperature heat treatments to determine their effects on the magnetic properties. The PFM allowed the rapid acquisition, storage, and processing of digital data by computer. The design of the PFM system, demagnetization corrections, procedures used, and some results are presented.

  19. Magnetization studies of the nuclear spin ordered phases of solid 3He in silver sinters

    NASA Astrophysics Data System (ADS)

    Schuberth, E. A.; Kath, M.; Tassini, L.; Millan-Chacartegui, C.

    2005-08-01

    Solid 3He, in the bcc lattice between 34 and 100 bar, exhibits two nuclear magnetic ordered phases in the sub-mK temperature range, the so called U2D2 low (magnetic) field phase and the “high field phase” above 0.4 T. To determine the exact spin structure of these phases we started a project of neutron scattering from the ordered solid in collaboration with the Hahn-Meitner Institute, Berlin, and other European and US groups. For this experiment it is crucial to grow a single crystal within the sinter needed for cooling the solid to temperatures of the order of 500 μK (or even twenty times lower in the case of the hcp lattice which is formed above 100 bar) and to keep it there long enough to measure a magnetic neutron reflection. We studied the growth of crystals in Ag sinters of different pore size and with different growth speeds to find an optimal way to obtain single crystalline samples. As a first diagnostic step we performed pulsed NMR measurements in the ordered phases of solid 3He in a sinter of 2700 Å particle size down to temperatures of 450 μK at various molar volumes. We could keep the samples in the ordered state for as long as 140 h. The second method we used was SQUID magnetometry. For the low field phase TN was indicated by a drop of the intensity, both in the NMR signal and in the dc magnetization, whereas in the high field phase an increase of about 30% was observed below the ordering temperature. For the fabrication of the sinters a packing fraction of 50% and subsequent annealing proved to be very favorable to obtain cold ordered solid. Furthermore, we find that a paramagnetic surface contribution from a few monolayers of 3He exists down to 500 μK in addition to the bulk magnetization.

  20. Tunning the magnetic ordering in EuTiO3 through doping

    NASA Astrophysics Data System (ADS)

    Gui, Zhigang; Janotti, Anderson

    EuTiO3 (ETO) is a complex oxide that displays strong spin-lattice coupling, large magnetoelectric effects, and undergoes a series of structural and magnetic phase transitions when subjected to pressure or epitaxial strain. ETO adopts a cubic structure and is paramagnetic at high temperatures, while at very low temperatures it transforms to an antiferrodistortive tetragonal structure with a G-type antiferromagnetic (AFM) ordering. Several approaches have been presented to tune the magnetic ordering from the G-type antiferromagnetism to the F-type ferromagnetism, often relying on external pressure or epitaxial strain. Doping through substitution of trivalent species on the europium sites or creation of oxygen vacancies have also been proposed to lead to ferromagnetism. However, the fundamental mechanism by which excess electrons from impurities or defects lead to ferromagnetic ordering is unclear. In this study, we explore the effects of doping on the magnetic ordering in EuTiO3 through first-principles calculations. We show how itinerant carriers in the Ti- d-derived conduction-band states interact with europium f states, inducing an alignment of the large moments on the europium ions. The effects of doping of different types of magnetic ordering are considered, a

  1. Solution Processing of Ordered Thin Film Nanowire Composites by Magnetic Field Alignment

    NASA Astrophysics Data System (ADS)

    Singer, Jonathan; Pelligra, Candice; Huang, Su; Osuji, Chinedum

    2014-03-01

    Vertically aligned nanowire forests are a desirable geometry for many applications, including as electrodes, heterojunctions, and high surface energy interfaces. Most conventional aligned nanowire structures, however, are generated by methods that require (i) high temperatures, (ii) a specific substrate, or (iii) high cost lithographic techniques. We seek to utilize the magnetic alignment of cobalt-doped zinc oxide nanowires to enable the solution processing of thin films of aligned nanowires on a generalized substrate at a fraction of the cost of other methods. By functionalization of the nanowires with various surface modifications, they can be dispersed in several solvent systems and aligned by a 6 T field. Further, by including polymer in the wire solution, we can both control the areal density and also incorporate additional functionalities to the final composite device. As an example, the use of a conjugated polymer (such as poly(3-hexylthiophene-2,5-diyl) (P3HT)) allows for the final structures to act as inorganic-organic ordered heterojunction solar cells. While final device quality depends on the simultaneous optimization of several key processing parameters, the process does not rely on top-down fabrication or costly materials. Supported by ONR YIP Award N000141210657.

  2. Magnetic core test stand for energy loss and permeability measurements at a high constant magnetization rate and test results for nanocrystalline and ferrite materials.

    PubMed

    Burdt, Russell; Curry, Randy D

    2008-09-01

    A test stand was developed to measure the energy losses and unsaturated permeability of toroidal magnetic cores, relevant to applications of magnetic switching requiring a constant magnetization rate of the order of 1-10 T/micros. These applications in pulsed power include linear induction accelerators, pulse transformers, and discharge switches. The test stand consists of a coaxial transmission line pulse charged up to 100 kV that is discharged into a magnetic core load. Suitable diagnostics measure the voltage across and the current through a winding on the magnetic core load, from which the energy losses and unsaturated permeability are calculated. The development of the test stand is discussed, and test results for ferrite CN20 and the nanocrystalline material Finemet FT-1HS are compared to demonstrate the unique properties of a nanocrystalline material. The experimental data are compared with published data in a similar parameter space to demonstrate the efficacy of the experimental methods. PMID:19044442

  3. Nanoindentation and nanoscratching of hard coating materials for magnetic disks

    SciTech Connect

    Tsui, T.Y.; Pharr, G.M.; Oliver, W.C.; Chung, Y.W.; Cutiongco, E.C.; Bhatia, C.S.; White, R.L.; Rhodes, R.L.; Gorbatkin, S.M.

    1994-12-31

    Nanoindentation and nanoscratching experiments have been performed to assess the mechanical and tribological behavior of three thin film materials with potential application as wear resistant coatings for magnetic disk storage: (1) hydrogenated-carbon (CHx); (2) nitrogenated-carbon (CNx); and (3) boron suboxide (BOx). The hardness and elastic modulus were measured using nanoindentation. Ultra-low load nanoscratching tests were performed to assess the relative scratch resistance of the films and measure their friction coefficients. The mechanical and tribological performance of the three materials are discussed and compared.

  4. Hard magnets based on layered cobalt hydroxide: The importance of dipolar interaction for long-range magnetic ordering

    SciTech Connect

    Kurmoo, M.

    1999-11-01

    The synthesis of 4 cobalt hydroxides, the characterization by electron microscopy, XRD, TGA, IR, UV-vis, and XANES, and their magnetic properties are reported. They belong to a family of layered compounds having a triangular magnetic lattice. The basal spacing is 22.8, 16.2, 25.0, and 11.5 {angstrom} for the carboxylate, dicarboxylate, sulfate, and cyanide, respectively. From the powder X-ray and crystal electron diffraction data, the compounds are inferred to adopt the structure of the monoclinic form of Xn{sub 5}(OH){sub 8}X{sub 2}{sm{underscore}bullet}solvent. XANES confirms that only divalent cobalt is present in the compounds and visible adsorption spectra display bands originating from both octahedral and tetrahedral coordinated Co{sup II} and none from Co{sup III}. The magnetic data show that all the compounds behave as two sublattice ferrimagnets which are characterized by a minimum in the temperature dependence of the moments and long-range ordering observed by spontaneous magnetization in small dc applied field, out-of-phase components in the ac magnetization and hysteresis loop. The saturation magnetization, approaching 3 {mu}{sub B} at 2 K in field of 5 T, is in good agreement with the proposed structure consisting of three Co{sup II} in octahedral coordination in one sublattice and two Co{sup II} in tetrahedral coordination for the other. The Curie temperature attains 58 K and coercive field approaches 12,000 Oe at 2 K. The long-range ordering is driven by dipolar interaction between layers which have large effective moment resulting from short-range intralayer interactions. Interestingly, the Curie temperatures are independent of the chemical and physical nature of the anions, as expected for the proposed dipolar mechanism. The large coercive fields result from the synergy of crystalline shape and single ion anisotropies and to the alignment of the moments perpendicular to the layers.

  5. Alternative material study for heat assisted magnetic recording transducer application

    SciTech Connect

    Xu, B. X. Cen, Z. H.; Hu, J. F.; Tsai, J. W. H.

    2015-05-07

    In heat assisted magnetic recording (HAMR), optical near field transducer (NFT) is a key component. Au is currently used as NFT material because of its strong surface plasmon effect. Due to the soft property of Au material, reliability of Au NFT becomes a key issue for realizing HAMR production. In this paper, the possibility of alternative materials, including transition metal nitrides (TMNs) and transparent conducting oxides (TCOs) to replace Au is studied. The results show that all of the listed TMN and TCO materials can meet the mechanical requirements at room temperature in terms of hardness and thermal expansion. An optical model, which includes optical waveguide, NFT and FePt media, is used to simulate NFT performances. The results indicate that the resonant wavelengths for NFT with TCO materials are longer than 1500 nm, which is not suitable for HAMR application. TMN materials are suitable for NFT application at wavelength band of around 800 nm. But the NFT efficiency is very low. ZrN is the best material among TMN materials and the efficiency of ZrN NFT is only 13% of the Au NFT's efficiency. Reducing refractive index (n) and increasing extinction coefficient (k) will both lead to efficiency increase. Increasing k contributes more in the efficiency increase, while reducing n has a relatively low NFT absorption. For materials with the same figure of merit, the NFT with larger k material has higher efficiency. Doping materials to increase the material conduction electron density and growing film with larger size grain may be the way to increase k and reduce n.

  6. Alternative material study for heat assisted magnetic recording transducer application

    NASA Astrophysics Data System (ADS)

    Xu, B. X.; Cen, Z. H.; Hu, J. F.; Tsai, J. W. H.

    2015-05-01

    In heat assisted magnetic recording (HAMR), optical near field transducer (NFT) is a key component. Au is currently used as NFT material because of its strong surface plasmon effect. Due to the soft property of Au material, reliability of Au NFT becomes a key issue for realizing HAMR production. In this paper, the possibility of alternative materials, including transition metal nitrides (TMNs) and transparent conducting oxides (TCOs) to replace Au is studied. The results show that all of the listed TMN and TCO materials can meet the mechanical requirements at room temperature in terms of hardness and thermal expansion. An optical model, which includes optical waveguide, NFT and FePt media, is used to simulate NFT performances. The results indicate that the resonant wavelengths for NFT with TCO materials are longer than 1500 nm, which is not suitable for HAMR application. TMN materials are suitable for NFT application at wavelength band of around 800 nm. But the NFT efficiency is very low. ZrN is the best material among TMN materials and the efficiency of ZrN NFT is only 13% of the Au NFT's efficiency. Reducing refractive index (n) and increasing extinction coefficient (k) will both lead to efficiency increase. Increasing k contributes more in the efficiency increase, while reducing n has a relatively low NFT absorption. For materials with the same figure of merit, the NFT with larger k material has higher efficiency. Doping materials to increase the material conduction electron density and growing film with larger size grain may be the way to increase k and reduce n.

  7. Simultaneous occurrence of multiferroism and short-range magnetic order in DyFeO3

    DOE PAGESBeta

    Wang, Jinchen; Liu, Juanjuan; Sheng, Jieming; Luo, Wei; Ye, Feng; Zhao, Zhiying; Sun, Xuefeng; Danilkin, Sergey A.; Deng, Guochu; Bao, Wei

    2016-04-06

    In this paper, we present a combined neutron scattering and magnetization study on the multiferroic DyFeO3, which shows a very strong magnetoelectric effect. Applying magnetic field along the c axis, the weak ferromagnetic order of the Fe ions is quickly recovered from a spin reorientation transition, and the long-range antiferromagnetic order of Dy becomes a short-range one. We found that the short-range order concurs with the multiferroic phase and is responsible for its sizable hysteresis. In conclusion, our H-T phase diagram suggests that the strong magnetoelectric effect in DyFeO3 has to be understood with not only the weak ferromagnetism ofmore » Fe but also the short-range antiferromagnetic order of Dy.« less

  8. 2D and 3D ordered arrays of Co magnetic nanowires

    NASA Astrophysics Data System (ADS)

    Garcia, J.; Prida, V. M.; Vega, V.; Rosa, W. O.; Caballero-Flores, R.; Iglesias, L.; Hernando, B.

    2015-06-01

    Cobalt nanowire arrays spatially distributed in 2D and 3D arrangements have been performed by pulsed electrodeposition into the pores of planar and cylindrical nanoporous anodic alumina membranes, respectively. Morphological characterization points out the good filling factor reached by electroplated Co nanowires in both kinds of alumina membranes exhibiting hexagonally self-ordered porous structures. Co nanowires grown in both kinds of alumina templates exhibit the same crystalline phases. DC magnetometry and First Order Reversal Curve (FORC) analysis were carried out in order to determine the overall magnetic behavior for both nanowire array geometries. It is found that when the Co nanowires of two kinds of arrays are perpendicularly magnetized, both hysteresis loops are identical, suggesting that neither the intrinsic magnetic behavior of the nanowires nor the collective one depend on the arrays geometry. FORC analysis performed along the radial direction of the Co nanowire arrays embedded in the cylindrical alumina template reveals that the contribution of each nanowire to the magnetization reversal process involves its specific orientation with respect to the applied field direction. Furthermore, the comparison between the magnetic properties for both kinds of Co nanowire arrays allows discussing about the effect of the cylindrical geometry of the template on the magnetostatic interaction among nanowires.

  9. Electric Field Effect on the Magnetic Order in Multiferroic LuMnO3

    NASA Astrophysics Data System (ADS)

    Duan, Chunruo; Yang, Junjie; Harriger, Leland; Louca, Despina

    LuMnO3 belongs to the family of hexagonal multiferroics in which ferroelectric and magnetic orders coexist and compete. The Mn3+ ions reside on a triangular lattice that is geometrically frustrated but undergoes a Neel transition at TN ~90 K. Neutron experiments under electric field were carried out on a single crystal of LuMnO3 at SPINS to investigate the coupling of the electric field to the magnetic order. The elastic and inelastic scattering around the commensurate (101) magnetic peak and the Mn trimerization induced (100) peak with and without electric field were investigated. When applying an E-field of 13.3 kV/cm along the (001) direction on an unpoled sample, an increase in (101) peak as well as a shift of the inelastic excitation near (100) to higher ΔE have been observed. Once the sample is polarized, these effects exist without the field. On the other hand, an E-field along (110) direction shows almost no effect. The spin arrangement of the magnetic order is within the ab-plane, thus the Dzyaloshinskii-Moriya interaction explains why a polarization perpendicular to the magnetic moment gives a larger effect. The implication will be discussed.

  10. Solid state nuclear magnetic resonance investigations of advanced energy materials

    NASA Astrophysics Data System (ADS)

    Bennett, George D.

    In order to better understand the physical electrochemical changes that take place in lithium ion batteries and asymmetric hybrid supercapacitors solid state nuclear magnetic resonance (NMR) spectroscopy has been useful to probe and identify changes on the atomic and molecular level. NMR is used to characterize the local environment and investigate the dynamical properties of materials used in electrochemical storage devices (ESD). NMR investigations was used to better understand the chemical composition of the solid electrolyte interphase which form on the negative and positive electrodes of lithium batteries as well as identify the breakdown products that occur in the operation of the asymmetric hybrid supercapacitors. The use of nano-structured particles in the development of new materials causes changes in the electrical, structural and other material properties. NMR was used to investigate the affects of fluorinated and non fluorinated single wall nanotubes (SWNT). In this thesis three experiments were performed using solid state NMR samples to better characterize them. The electrochemical reactions of a lithium ion battery determine its operational profile. Numerous means have been employed to enhance battery cycle life and operating temperature range. One primary means is the choice and makeup of the electrolyte. This study focuses on the characteristics of the solid electrolyte interphase (SEI) that is formed on the electrodes surface during the charge discharge cycle. The electrolyte in this study was altered with several additives in order to determine the influence of the additives on SEI formation as well as the intercalation and de-intercalation of lithium ions in the electrodes. 7Li NMR studies where used to characterize the SEI and its composition. Solid state NMR studies of the carbon enriched acetonitrile electrolyte in a nonaqueous asymmetric hybrid supercapacitor were performed. Magic angle spinning (MAS) coupled with cross polarization NMR

  11. Low-temperature magnetic ordering and structural distortions in vanadium sesquioxide V2O3

    NASA Astrophysics Data System (ADS)

    Grieger, Daniel; Fabrizio, Michele

    2015-08-01

    Vanadium sesquioxide (V2O3 ) is an antiferromagnetic insulator below TN≈155 K . The magnetic order does not consist of only antiferromagnetic nearest-neighbor bonds, possibly excluding the interplane vanadium pairs, as one would infer from the bipartite character of the hexagonal basal plane in the high-temperature corundum structure. In fact, a magnetic structure with one ferromagnetic bond and two antiferromagnetic ones in the honeycomb plane is known experimentally to be realized, accompanied by a monoclinic distortion that makes the ferromagnetic bond inequivalent from the other two. We show here that the magnetic ordering, the accompanying monoclinic structural distortion, the magnetic anisotropy, and also the recently discovered high-pressure nonmagnetic monoclinic phase, can all be accurately described by conventional electronic structure calculations within GGA and GGA+U . Remarkably, our calculations yield that the corundum phase would be unstable to a monoclinic distortion even without magnetic ordering, thus suggesting that magnetism and lattice distortion are independent phenomena, though they reinforce each other. By means of GGA+U , we find a metal-to-insulator transition at a critical Uc. Both metal at U ≤Uc and insulator above Uc have the same magnetic order as that actually observed below TN, but different monoclinic distortions. Reassuringly, the distortion on the insulating side agrees with the experimental one. Our results are in line with DMFT calculations for the paramagnetic phase [A. I. Poteryaev et al., Phys. Rev. B 76, 085127 (2007)], 10.1103/PhysRevB.76.085127, which predict that the insulating character is driven by a correlation-enhanced crystal-field splitting between egπ and a1 g orbitals that pushes the latter above the chemical potential. We find that the a1 g orbital, although almost empty in the insulating phase, is actually responsible for the unusual magnetic order as it leads to magnetic frustration whose effect is similar

  12. Manifestation of axion electrodynamics through magnetic ordering on edges of a topological insulator

    PubMed Central

    Lee, Yea-Lee; Park, Hee Chul; Ihm, Jisoon; Son, Young-Woo

    2015-01-01

    Because topological surface states of a single-crystal topological insulator can exist on all surfaces with different crystal orientations enclosing the crystal, mutual interactions among those states contiguous to each other through edges can lead to unique phenomena inconceivable in normal insulators. Here we show, based on a first-principles approach, that the difference in the work function between adjacent surfaces with different crystal-face orientations generates a built-in electric field around facet edges of a prototypical topological insulator such as Bi2Se3. Owing to the topological magnetoelectric coupling for a given broken time-reversal symmetry in the crystal, the electric field, in turn, forces effective magnetic dipoles to accumulate along the edges, realizing the facet-edge magnetic ordering. We demonstrate that the predicted magnetic ordering is in fact a manifestation of the axion electrodynamics in real solids. PMID:26324891

  13. Quantum melting of magnetic order in an organic dimer Mott-insulating system

    NASA Astrophysics Data System (ADS)

    Naka, Makoto; Ishihara, Sumio

    2016-05-01

    Quantum entanglement effects between the electronic spin and charge degrees of freedom are examined in an organic molecular solid, termed a dimer Mott-insulating system, in which molecular dimers are arranged in a crystal as fundamental units. A low energy effective model includes an antisymmetric exchange interaction, as one of the dominant magnetic interactions. This interaction favors a 90 deg spin configuration, and competes with the Heisenberg-type exchange interaction. Stabilities of the magnetic ordered phases are examined by using the spin-wave theory, as well as the Schwinger-boson theory. It is found that the spin-charge interaction promotes an instability of the long-range magnetic ordered state around a parameter region where two spin-spiral phases are merged. Implication for the quantum spin liquid state observed in κ -(BEDT-TTF)2Cu2 (CN) 3 is discussed.

  14. Manifestation of axion electrodynamics through magnetic ordering on edges of a topological insulator.

    PubMed

    Lee, Yea-Lee; Park, Hee Chul; Ihm, Jisoon; Son, Young-Woo

    2015-09-15

    Because topological surface states of a single-crystal topological insulator can exist on all surfaces with different crystal orientations enclosing the crystal, mutual interactions among those states contiguous to each other through edges can lead to unique phenomena inconceivable in normal insulators. Here we show, based on a first-principles approach, that the difference in the work function between adjacent surfaces with different crystal-face orientations generates a built-in electric field around facet edges of a prototypical topological insulator such as Bi2Se3. Owing to the topological magnetoelectric coupling for a given broken time-reversal symmetry in the crystal, the electric field, in turn, forces effective magnetic dipoles to accumulate along the edges, realizing the facet-edge magnetic ordering. We demonstrate that the predicted magnetic ordering is in fact a manifestation of the axion electrodynamics in real solids. PMID:26324891

  15. Field Evolution of Coexisting Superconducting and Magnetic Orders in CeCoIn5

    NASA Astrophysics Data System (ADS)

    Koutroulakis, G.; Stewart, M. D., Jr.; Mitrović, V. F.; Horvatić, M.; Berthier, C.; Lapertot, G.; Flouquet, J.

    2010-02-01

    We present nuclear magnetic resonance (NMR) measurements on the three distinct In sites of CeCoIn5 with a magnetic field applied in the [100] direction. We identify the microscopic nature of the long range magnetic order (LRO) stabilized at low temperatures in fields above 10.2 T while still in the superconducting (SC) state. We infer that the ordered moment is oriented along the c^ axis and map its field evolution. The study of the field dependence of the NMR shift for the different In sites indicates that the LRO likely coexists with a modulated SC phase, possibly that predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. Furthermore, we discern a field region dominated by strong spin fluctuations where static LRO is absent and propose a revised phase diagram.

  16. Long-range magnetic order in models for rare-earth quasicrystals

    NASA Astrophysics Data System (ADS)

    Thiem, Stefanie; Chalker, J. T.

    2015-12-01

    We take a two-step theoretical approach to study magnetism of rare-earth quasicrystals by considering Ising spins on quasiperiodic tilings, coupled via Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First, we compute RKKY interactions from a tight-binding Hamiltonian defined on the two-dimensional quasiperiodic tilings. We find that the magnetic interactions are frustrated and strongly dependent on the local environment. This results in the formation of clusters with strong bonds at certain patterns of the tilings that repeat quasiperiodically. Second, we examine the statistical mechanics of Ising spins with these RKKY interactions, using extensive Monte Carlo simulations. Although models that have frustrated interactions and lack translational invariance might be expected to display spin-glass behavior, we show that the spin system has a phase transition to low-temperature states with long-range quasiperiodic magnetic order. Additionally, we find that in some of the systems spin clusters can fluctuate much below the ordering temperature.

  17. Critical entropies for magnetic ordering in bosonic mixtures on a lattice

    SciTech Connect

    Capogrosso-Sansone, B.; Soeyler, S. G.; Prokof'ev, N. V.; Svistunov, B. V.

    2010-05-15

    We perform a numeric study (Worm algorithm Monte Carlo simulations) of ultracold two-component bosons in two- and three-dimensional optical lattices. At strong enough interactions and low enough temperatures the system features magnetic ordering. We compute critical temperatures and entropies for the disappearance of the Ising antiferromagnetic and the xy-ferromagnetic order and find that the largest possible entropies per particle are {approx} 0.5k{sub B}. We also estimate (optimistically) the experimental hold times required to reach equilibrium magnetic states to be on a scale of seconds. Low critical entropies and long hold times render the experimental observations of magnetic phases challenging and call for increased control over heating sources.

  18. Synthesis and characterization of low-dimensional molecular magnetic materials

    NASA Astrophysics Data System (ADS)

    Liu, Chen

    This dissertation presents experimental results from the synthesis and structural, magnetic characterization of representative low-dimensional molecule-based magnetic materials. Most of the materials reported in this dissertation, both coordination polymers and cuprate, are obtained as the result of synthesizing and characterizing spin ladder systems; except the material studied in Chapter 2, ferricenyl(III)trisferrocenyl(II)borate, which is not related to the spin ladder project. The interest in spin ladder systems is due to the discovery of high-temperature superconductivity in doped cuprates possessing ladder-like structures, and it is hoped that investigation of the magnetic behavior of ladder-like structures will help us understand the mechanism of high-temperature superconductivity. Chapter 1 reviews fundamental knowledge of molecular magnetism, general synthetic strategies for low-dimensional coordination polymers, and a brief introduction to the current status of research on spin ladder systems. Chapter 2 presents a modified synthetic procedure of a previously known monomeric complex, ferricenyl(III)trisferrocenyl(II)borate, 1. Its magnetic properties were characterized and previous results have been disproved. Chapter 3 investigates the magnetism of [CuCl2(CH3CN)] 2, 2, a cuprate whose structure consists of isolated noninterpenetrating ladders formed by the stacking of Cu(II) dimers. This material presents an unexpected ferromagnetic interaction both within the dimeric units and between the dimers, and this behavior has been rationalized based on the effect of its terminal nonbridging ligands. In Chapter 4, the synthesis and magnetism of two ladder-like coordination polymers, [Co(NO3)2(4,4'-bipyridine) 1.5(MeCN)]n, 3, and Ni2(2,6-pyridinedicarboxylic acid)2(H2O)4(pyrazine), 4, are reported. Compound 3 possesses a covalent one-dimensional ladder structure in which Co(II) ions are bridged through bipyridine molecules. Compared to the materials discussed in

  19. Relationship between Magnetocrystalline Anisotropy and Orbital Magnetic Moment in L10-Type Ordered and Disordered Alloys

    NASA Astrophysics Data System (ADS)

    Kota, Yohei; Sakuma, Akimasa

    2012-08-01

    The magnetocrystalline anisotropy energy and orbital magnetic moment in L10-type transition metal alloys such as FePt, FePd, FeNi, CoPt, CoPd, and MnAl are evaluated while continuously varying the degree of order. The electronic structure with spin--orbit interaction is calculated by employing the tight-binding linear muffin-tin orbital method based on the local spin-density approximation. To control the degree of order, we consider a substitutional disorder and then adopt the coherent potential approximation. The magnetocrystalline anisotropy energy Δ E is roughly proportional to the power of the long-range order parameter S, i.e., Δ E \\propto Sn (n ˜ 1.6{--}2.4). We also discuss the relationship between the magnetocrystalline anisotropy energy and the orbital magnetic moment. In the same compositional system with different degrees of order, the difference between the orbital magnetic moment in the magnetic easy axis and that in the hard one is proportional to Δ E. However, the coefficient corresponding to the effective spin--orbit coupling is inconsistent with the intrinsic one in some cases.

  20. Magnetic ordering of Ce in the heavy-fermion compound Ce3Al

    NASA Astrophysics Data System (ADS)

    Li, W.-H.; Peng, J. C.; Lin, Y.-C.; Lee, K. C.; Lynn, J. W.; Chen, Y. Y.

    1998-06-01

    Neutron diffraction and specific heat measurements have been performed to study the magnetic ordering of the Ce ions in the heavy-fermion compound Ce3Al. Detailed crystal structure analysis, determined using high resolution neutron diffraction patterns and Rietveld method, shows that the Ce ions may be grouped into two types: one in the Ce-Al chain, the other in the Ce-Ce chain. The specific-heat data reveal an anomaly at T≈2.2 K, but the calculated magnetic entropy is much smaller than the expected R ln 2 if all Ce spins ordered. Low temperature neutron diffraction measurements confirm that the transition at 2.2 K is magnetic and is associated with the ordering of the Ce spins. The magnetic unit cell is double the nuclear one along the a and c axes, and contains 48 Ce ions. Only the Ce ions in the Ce-Al chains participate in the ordering at 2.2 K, and they are coupled antiferromagnetically.

  1. Magnetic ordering in Ho{sub 2}Fe{sub 2}Si{sub 2}C

    SciTech Connect

    Susilo, R. A. Cadogan, J. M.; Cobas, R.; Hutchison, W. D.; Campbell, S. J.; Avdeev, M.

    2015-05-07

    We have used neutron diffraction and {sup 57}Fe Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho{sub 2}Fe{sub 2}Si{sub 2}C. We have established that Ho{sub 2}Fe{sub 2}Si{sub 2}C orders antiferromagnetically below T{sub N} = 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k=[0 0 1/2 ]. {sup 57}Fe Mössbauer spectra collected below T{sub N} show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the {sup 57}Fe spectra below T{sub N}, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice.

  2. Observations of charge-ordered and magnetic domains in LuFe2O4 using transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Maruyama, T.; Murakami, Y.; Shindo, D.; Abe, N.; Arima, T.

    2012-08-01

    Both charge-ordered and magnetic domains produced in LuFe2O4, which have attracted significant attention due to the interplay of electronic and magnetic degrees of freedom, have been studied using transmission electron microscopy techniques. Dark-field images, obtained using a weak satellite reflection, revealed the nanometer-scale charge-ordered domains, which were observed over a wide temperature range below TCO (critical temperature of charge ordering; ˜310 K). Electron holography demonstrated an aspect of the long-range magnetic order wherein the magnetic flux lines were completely parallel to the c axis of LuFe2O4, in a specimen cooled to 17 K under an applied magnetic field. In contrast, there was no appreciable magnetic signal observed in a specimen cooled in a negligible magnetic field. These observations provide useful information for further understanding of the complex magnetic phase transitions in this compound.

  3. Nanoscale Magnetic Materials for Energy-Efficient Spin Based Transistors

    NASA Astrophysics Data System (ADS)

    Incorvia, Jean Anne Currivan

    In this dissertation, I study the physical behavior of nanoscale magnetic materials and build spin-based transistors that encode information in magnetic domain walls. It can be argued that energy dissipation is the most serious problem in modern electronics, and one that has been resistant to a breakthrough. Wasted heat during computing both wastes energy and hinders further technology scaling. This is an opportunity for physicists and engineers to come up with creative solutions for more energy-efficient computing. I present the device we have designed, called domain wall logic (DW-Logic). Information is stored in the position of a magnetic domain wall in a ferromagnetic wire and read out using a magnetic tunnel junction. This hybrid design uses electrical current as the input and output, keeping the device compatible with charge- based transistors. I build an iterative model to predict both the micromagnetic and circuit behavior of DW- Logic, showing a single device can operate as a universal gate. The model shows we can build complex circuits including an 18-gate Full Adder, and allows us to predict the device switching energy compared to complementary metal-oxide semiconductor (CMOS) transistors. Comparing ?15 nm feature nodes, I find DW-Logic made with perpendicular magnetic anisotropy materials, and utilizing both spin torque transfer and the Spin Hall effect, could operate with 1000x reduced switching energy compared to CMOS. I fabricate DW-Logic device prototypes and show in experiment they can act as AND and NAND gates. I demonstrate that one device can drive two subsequent devices, showing gain, which is a necessary requirement for fanout. I also build a clocked ring oscillator circuit to demonstrate successful bit propagation in a DW-Logic circuit and show that properly scaled devices can have improved operation. Through building the devices, I develop a novel fabrication method for patterning sub-25 nm magnetic wires with very low (˜ 2 nm) average edge

  4. Magnetic order and crystal structure study of YNi{sub 4}Si-type NdNi{sub 4}Si

    SciTech Connect

    Yao, Jinlei; Isnard, O.; Morozkin, A.V.; Ivanova, T.I.; Koshkid'ko, Yu.S.; Bogdanov, A.E.; Nikitin, S.A.; Suski, W.

    2015-02-15

    Magnetic measurements and neutron powder diffraction investigation of the magnetic structure of the orthorhombic YNi{sub 4}Si-type (space group Cmmm) NdNi{sub 4}Si compound are presented. The magnetocaloric effect of NdNi{sub 4}Si is calculated in terms of the isothermal magnetic entropy change and it reaches the maximum value of –3.3 J/kg K for a field change of 50 kOe near T{sub C}=12 K. Below ∼12 K, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group in a zero magnetic field. At 1.5 K, the neodymium atoms have the magnetic moment of 2.37(5) μ{sub B}. The orthorhombic crystal structure and its thermal evolution are discussed in comparison with the CaCu{sub 5}-type compound. - Graphical abstract: The NdNi{sub 4}Si supplement the series of the orthorhombic derivative of the CaCu{sub 5}-type, namely the YNi{sub 4}Si-type, RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho). Below ∼12 K in a zero applied magnetic field, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group. Compared to the CaCu{sub 5}-type NdNi{sub 4}Si compound, the YNi{sub 4}Si-type counterpart has the relatively high ferromagnetic ordering temperature (9.2 K vs. 12 K), the small magnetocaloric effect (–7.3 J/kg K vs. –3.3 J/kg K for ∆H=50 kOe), and the large magnetic anisotropy at low temperatures. In contrast with CaCu{sub 5}-type NdNi{sub 4}Si, YNi{sub 4}Si-type NdNi{sub 4}Si shows distinct hysteresis loop at 2 K.We suggest that orthorhombic distortion may be used as a prospective route for optimization of permanent magnetic properties in the family of CaCu{sub 5}-type rare earth materials. - Highlights: • Below ∼12 K the YNi{sub 4}Si-type NdNi{sub 4}Si shows a ferromagnetic ordering. • MCE of NdNi{sub 4}Si reaches value of –3.3 J/kg K in 0–50 kOe near Curie point. • NdNi{sub 4}Si exhibits b-axis ferromagnetic order with the Cmm′m magnetic space

  5. A model-based method for the characterisation of stress in magnetic materials using eddy current non-destructive evaluation

    NASA Astrophysics Data System (ADS)

    Dahia, Abla; Berthelot, Eric; Le Bihan and, Yann; Daniel, Laurent

    2015-03-01

    A precise knowledge of the distribution of internal stresses in materials is key to the prediction of magnetic and mechanical performance and lifetime of many industrial devices. This is the reason why many efforts have been made to develop and enhance the techniques for the non-destructive evaluation of stress. In the case of magnetic materials, the use of eddy current (EC) techniques is a promising pathway to stress evaluation. The principle is based on the significant changes in magnetic permeability of magnetic materials subjected to mechanical stress. These modifications of magnetic permeability affect in turn the signal obtained from an EC probe inspecting the material. From this principle, a numerical tool is proposed in this paper to predict the EC signal obtained from a material subjected to stress. This numerical tool is a combination of a 3D finite element approach with a magneto-mechanical constitutive law describing the effect of stress on the magnetic permeability. The model provides the variations of impedance of an EC probe as a function of stress. An experimental setup in which a magnetic material subjected to a tension stress is inspected using EC techniques is tailored in order to validate the model. A very good agreement is found between experimental and modelling results. For the Iron-Cobalt alloy tested in this study, it is shown that a uniaxial tensile stress can be detected with an error lower than 3 MPa in the range from 0 to 100 MPa.

  6. Apparatus for magnetic separation of paramagnetic and diamagnetic material

    DOEpatents

    Doctor, R.D.

    1988-10-18

    The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadrupole magnet. The open gradient magnetic field further segregates the paramagnetic particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin. 5 figs.

  7. Apparatus for magnetic separation of paramagnetic and diamagnetic material

    DOEpatents

    Doctor, R.D.

    1986-07-24

    The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadrupole magnet. The open gradient magnetic field further segregates the paramagnetic-particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin. 5 figs.

  8. Apparatus for magnetic separation of paramagnetic and diamagnetic material

    DOEpatents

    Doctor, Richard D.

    1988-01-01

    The present invention relates to methods and apparatus for segregating paramagnetic from diamagnetic particles in particulate material and, in particular, to the open gradient magnetic separation of ash producing components and pyritic sulfur from coal. The apparatus includes a vertical cylinder and a rotatable vertical screw positioned within the cylinder, the screw having a helical blade angled downwardly and outwardly from the axis. Rotation of the vertical screw causes denser particles, which in the case of coal include pyritic sulfur and ash, which are paramagnetic, to migrate to the outside of the screw, and less dense particles, such as the low sulfur organic portion of the coal, which are diamagnetic, to migrate towards the center of the screw. A vibration mechanism attached to the screw causes the screw to vibrate during rotation, agitating and thereby accommodating further segregation of the particles. An open gradient magnetic field is applied circumferentially along the entire length of the screw by a superconducting quadropole magnet. The open gradient magnetic field further segregates the paramagnetic particles from the diamagnetic particles. The paramagnetic particles may then be directed from the cylinder into a first storage bin, and the diamagnetic particles, which are suitable for relatively clean combustion, may be directed into a second storage bin.

  9. Multifunctional Upconversion-Magnetic Hybrid Nanostructured Materials: Synthesis and Bioapplications

    PubMed Central

    Li, Xiaomin; Zhao, Dongyuan; Zhang, Fan

    2013-01-01

    The combination of nanotechnology and biology has developed into an emerging research area: nano-biotechnology. Upconversion nanoparticles (UCNPs) have attracted a great deal of attention in bioapplications due to their high chemical stability, low toxicity, and high signal-to-noise ratio. Magnetic nanoparticles (MNPs) are also well-established nanomaterials that offer controlled size, ability to be manipulated externally, and enhancement of contrast in magnetic resonance imaging (MRI). As a result, these nanoparticles could have many applications in biology and medicine, including protein purification, drug delivery, and medical imaging. Because of the potential benefits of multimodal functionality in biomedical applications, researchers would like to design and fabricate multifunctional upconversion-magnetic hybrid nanostructured materials. The hybrid nanostructures, which combine UCNPs with MNPs, exhibit upconversion fluorescence alongside superparamagnetism property. Such structures could provide a platform for enhanced bioimaging and controlled drug delivery. We expect that the combination of unique structural characteristics and integrated functions of multifunctional upconversion-magnetic nanoparticles will attract increasing research interest and could lead to new opportunities in nano-bioapplications. PMID:23650477

  10. Novel hybrid materials of magnetic nanoparticles and cellulose fibers.

    PubMed

    Small, Aaron C; Johnston, James H

    2009-03-01

    In this study, magnetic cellulose fibers have been prepared by coating bleached Kraft fibers (Pinus radiata) with magnetite nanoparticles. In doing so, the inherent properties of the fiber (such as tensile strength and flexibility) have been preserved, but imparted to it are the magnetic properties of the coating. The surface coating approach used differs from other methods in the literature in which the lumen loading or in situ approach is taken. After successive washings and sonication, the particles remained bonded to the surface of the fiber, and the fibers could be formed into a paper sheet. The chemical and physical characterization of these materials were carried out using scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and SQUID magnetometry. SEM shows the surface of the fibers to be completely encapsulated by the ferrite nanoparticles. This is also confirmed by EDS. XRD line broadening analysis shows the average particle sizes of the nanoparticles range from 12-26 nm. Magnetically responsive cellulose fibers such as those synthesized in this study, will allow the investigation of new concepts in papermaking and packaging, security paper, and information storage. Potential applications are in electromagnetic shielding, magnetographic printing and magnetic filtering. PMID:19062033

  11. Anisotropic Thermal Properties of Nanostructured Magnetic, Carbon and Hybrid Magnetic - Carbon Materials

    NASA Astrophysics Data System (ADS)

    Ramirez, Sylvester

    In this dissertation research we investigated thermal properties of three groups of nanostructured materials: (i) magnetic; (ii) reduced graphene oxide films; and (iii) hybrid magnetic -- graphite -- graphene composites. The thermal measurements were conducted using the transient "hot disk" and "laser flash" techniques. The rare-earth free nanostructured SrFe12O19 permanent magnets were produced by the current activated pressure assisted densification technique. The thermal conductivity of the nanostructured bulk magnets was found to range from 3.8 to 5.6 W/mK for the in-plane and 2.36 W/mk to 2.65 W/mK for the cross-plane directions, respectively. The heat conduction was dominated by phonons near the room temperature. The anisotropy of heat conduction was explained by the brick-like alignment of crystalline grains with the longer grain size in-plane direction. The thermal conductivity scales up with the average grain size and mass density of the material revealing weak temperature dependence. Using the nanostructured ferromagnetic Fe3O4 composites as an example system, we incorporated graphene and graphite fillers into magnetic material without changing their morphology. It was demonstrated that addition of 5 wt. % of equal mixture of graphene and graphite flakes to the composite results in a factor of x2.6 enhancement of the thermal conductivity without significant degradation of the saturation magnetization. We investigated thermal conductivity of free-standing reduced graphene oxide films subjected to a high-temperature treatment of up to 1000°C. It was found that the high-temperature annealing dramatically increased the in-plane thermal conductivity, K, of the films from ˜3 W/mK to ˜61 W/mK at room temperature. The cross-plane thermal conductivity, K⊥, revealed an interesting opposite trend of decreasing to a very small value of ˜0.09 W/mK in the reduced graphene oxide films annealed at 1000°C. The obtained films demonstrated an exceptionally strong

  12. Magnetic ordering of nickel hydroxide layers 30 Å apart obtained by intercalating dodecyl sulfate

    NASA Astrophysics Data System (ADS)

    Seehra, M. S.; Singh, V.

    2013-09-01

    The nature of magnetic ordering in quasi-2D layered hydroxide of Ni (LH-Ni-DS) with hexagonal structure and synthesized by intercalating dodecyl sulfate (DS) ligand, (C12H25OSO3)-, between the layers using a hydrothermal technique is investigated. The observation of (00l) peaks up to l = 8 in x-ray diffraction on the sample yields an interlayer spacing c ≃ 30.5 Å and a crystallite size ≃ 16 nm. Assignment of the lines observed in the FTIR spectra to the various groups of the DS ligand confirms the intercalation. From the analysis of detailed investigations of the temperature dependence of the magnetization M at different magnetic fields, ac susceptibilities at frequencies from 0.1 to 1 kHz, and electron magnetic resonance spectra at 9.28 GHz, it is concluded that LH-Ni-DS orders ferromagnetically at TC ≃ 23 K. This TC is about 45% higher than TC ≃ 16 K reported for LH-Ni-Ac with c ≃ 8.6 Å obtained by intercalating an acetate ligand between the layers. The roles of the interlayer dipolar interaction, magnetic anisotropy and exchange interactions in determining TC in LH-Ni-L systems for several ligands L yielding different c-axes are discussed.

  13. Magnetic flux structure and formfactor of SANS in a superconductor with multicomponent order parameter

    NASA Astrophysics Data System (ADS)

    Zeltser, A. S.; Pashkevich, Yu. G.; Filippov, A. E.

    1999-09-01

    Possible observable consequences of a recently described scenario of vortex generation in superconductors with multicomponent order parameter are discussed. According to this scenario the vortices appear inside domain boundaries separating the phases with different realizations of the equilibrium order parameter. It is shown that, as a rule, solitary vortex has an anisotropic distribution of the current and magnetic field even in absence of anisotropy in gradient terms. The lattice formed by such vortices has symmetry lower than hexagonal or tetragonal ones. It is simulated with the help of brownian dynamics. Ordered structure manifests itself in the correlation function for magnetic field density and, as a result, in the positions, intensity and formfactor of the peaks of small angle neutron scattering (SANS).

  14. Ethylenediaminium di(4-nitrophenolate): a third order NLO material for optical limiting applications.

    PubMed

    Thangaraj, M; Ravi, G; Sabari Girisun, T C; Vinitha, G; Loganathan, A

    2015-03-01

    Single crystals of ethylenediaminium di(4-nitrophenolate) [EDA4NP] were grown by slow evaporation solution growth technique using ethanol as solvent at constant temperature. It crystallizes in monoclinic centrosymmetric space group C2/c with cell dimension a=11.326Ǻ, b=7.264Ǻ, c=20.036Ǻ; β=93.55°. Fourier Transform Infra Red (FT-IR) spectrum was recorded to identify various functional groups present in EDA4NP. Nuclear Magnetic Resonance (NMR) spectral studies were performed to confirm the functional groups. Thermogravimetric analysis and differential thermal analysis showed that the compound melts at 142.9°C. The material possesses a wide optical transparency window in the visible and near IR region (500-1200nm). The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of EDA4NP were estimated to be n2=5.46×10(-8)cm(2)W(-1), β=0.65×10(-3)cmW(-1) and χ((3))=2.96×10(-6)esu respectively. The limiting behavior observed with the sample is attributed mainly to nonlinear refraction. PMID:25498811

  15. Predicting the Future of Permanent-Magnet Materials

    SciTech Connect

    Skomski, R; Manchanda, P; Kumar, P; Balamurugan, B; Kashyap, A; Sellmyer, DJ

    2013-07-01

    There are two main thrusts towards new permanent-magnet materials: improving extrinsic properties by nanostructuring and intrinsic properties by atomic structuring. Theory-both numerical and analytical-plays an important role in this ambitious research. Our analysis of aligned hard-soft nanostructures shows that soft-in-hard geometries are better than hard-in-soft geometries and that embedded soft spheres are better than sandwiched soft layers. Concerning the choice of the hard phase, both a high magnetization and a high anisotropy are necessary. As an example of first-principle research, we consider interatomic Mn exchange in MnAl and find strongly ferromagnetic intralayer exchange, in spite of the small Mn-Mn distances.

  16. Ordered ferrimagnetic form of ferrihydrite reveals links among structure, composition, and magnetism

    PubMed Central

    Michel, F. Marc; Barrón, Vidal; Torrent, José; Morales, María P.; Serna, Carlos J.; Boily, Jean-François; Liu, Qingsong; Ambrosini, Andrea; Cismasu, A. Cristina; Brown, Gordon E.

    2010-01-01

    The natural nanomineral ferrihydrite is an important component of many environmental and soil systems and has been implicated as the inorganic core of ferritin in biological systems. Knowledge of its basic structure, composition, and extent of structural disorder is essential for understanding its reactivity, stability, and magnetic behavior, as well as changes in these properties during aging. Here we investigate compositional, structural, and magnetic changes that occur upon aging of “2-line” ferrihydrite in the presence of adsorbed citrate at elevated temperature. Whereas aging under these conditions ultimately results in the formation of hematite, analysis of the atomic pair distribution function and complementary physicochemical and magnetic data indicate formation of an intermediate ferrihydrite phase of larger particle size with few defects, more structural relaxation and electron spin ordering, and pronounced ferrimagnetism relative to its disordered ferrihydrite precursor. Our results represent an important conceptual advance in understanding the nature of structural disorder in ferrihydrite and its relation to the magnetic structure and also serve to validate a controversial, recently proposed structural model for this phase. In addition, the pathway we identify for forming ferrimagnetic ferrihydrite potentially explains the magnetic enhancement that typically precedes formation of hematite in aerobic soil and weathering environments. Such magnetic enhancement has been attributed to the formation of poorly understood, nano-sized ferrimagnets from a ferrihydrite precursor. Whereas elevated temperatures drive the transformation on timescales feasible for laboratory studies, our results also suggest that ferrimagnetic ferrihydrite could form naturally at ambient temperature given sufficient time. PMID:20133643

  17. Ordered ferrimagnetic form of ferrihydrite reveals links among structure, composition, and magnetism

    SciTech Connect

    Michel, F. Marc; Barrón, Vidal; Torrent, José; Morales, María P.; Serna, Carlos J.; Boily, Jean-François; Liu, Qingsong; Ambrosini, Andrea; Cismasu, A. Cristina; Brown, Jr., Gordon E.

    2010-11-19

    The natural nanomineral ferrihydrite is an important component of many environmental and soil systems and has been implicated as the inorganic core of ferritin in biological systems. Knowledge of its basic structure, composition, and extent of structural disorder is essential for understanding its reactivity, stability, and magnetic behavior, as well as changes in these properties during aging. Here we investigate compositional, structural, and magnetic changes that occur upon aging of '2-line' ferrihydrite in the presence of adsorbed citrate at elevated temperature. Whereas aging under these conditions ultimately results in the formation of hematite, analysis of the atomic pair distribution function and complementary physicochemical and magnetic data indicate formation of an intermediate ferrihydrite phase of larger particle size with few defects, more structural relaxation and electron spin ordering, and pronounced ferrimagnetism relative to its disordered ferrihydrite precursor. Our results represent an important conceptual advance in understanding the nature of structural disorder in ferrihydrite and its relation to the magnetic structure and also serve to validate a controversial, recently proposed structural model for this phase. In addition, the pathway we identify for forming ferrimagnetic ferrihydrite potentially explains the magnetic enhancement that typically precedes formation of hematite in aerobic soil and weathering environments. Such magnetic enhancement has been attributed to the formation of poorly understood, nano-sized ferrimagnets from a ferrihydrite precursor. Whereas elevated temperatures drive the transformation on timescales feasible for laboratory studies, our results also suggest that ferrimagnetic ferrihydrite could form naturally at ambient temperature given sufficient time.

  18. Emergence of magnetic order in ultra-thin pyrochlore iridate films

    NASA Astrophysics Data System (ADS)

    Cheema, Suraj; Serrao, Claudy; Mundy, Julia; Patankar, Shreyas; Birgeneau, Robert; Orenstein, Joseph; Salahuddin, Sayeef; Ramesh, Ramamoorthy

    We report on thickness-dependent magnetotransport in (111) - oriented Pb2Ir2O7-x (Pb227) epitaxial thin films. For thicknesses greater than 4 nm, the magnetoresistance (MR) of metallic Pb227 is positive, linear and non-saturated up to 14 T. Meanwhile at 4 nm, the conduction turns nonmetallic and the MR becomes negative and asymmetric upon field-cooling; such traits are reminiscent of all-in-all-out (AIAO) magnetic order in the insulating pyrochlore iridates. Hysteretic low-field MR dips and trained-untrained resistivity bifurcations suggest the presence of magnetic conducting domain walls within the chiral AIAO spin structure. Beyond just AIAO order, angular-dependent MR indicates a magnetic phase space hosting 2-in-2-out (2I2O) spin ice order. Such anomalous magnetotransport calls for re-evaluation of the pyrochlore iridate phase diagram, as epitaxially strained Pb227 exhibits traits reminiscent of both the insulating magnetic and metallic spin-liquid members. Furthermore, these results open avenues for realizing topological phase predictions in (111) - oriented pyrochlore slabs of kagome-triangular iridate heterostructures. This work is supported by the Office of Basic Energy Sciences of the US Department of Energy under Contract No. DE-AC02-05CH11231.

  19. Imposed, ordered dust structures and other plasma features in a strongly magnetized plasma

    NASA Astrophysics Data System (ADS)

    Thomas, Edward; Leblanc, Spencer; Lynch, Brian; Konopka, Uwe; Merlino, Robert; Rosenberg, Marlene

    2015-11-01

    The Magnetized Dusty Plasma Experiment (MDPX) device has been in operation for just over one year. In that time, the MDPX device has been operating using a uniform magnetic field configuration up to 3.0 Tesla and has successfully produced plasmas and dusty plasmas at high magnetic fields. In these experimental studies, we have made observations of a new type of imposed, ordered structure in a dusty plasma at magnetic fields above 1 T. These dusty plasma structures are shown to scale inversely with neutral pressure and are shown to reflect the spatial structure of a wire mesh placed in the plasma. Additionally, recent measurements have been made that give insights into the effective potential that establishes the ordered structures in the plasma. In this presentation, we report on details of the imposed, ordered dusty plasma structure as well as filamentary features that also appear in the plasma and modify the confinement of the dusty plasma. This work is supported with funding from the NSF and Department of Energy.

  20. Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    McClure, Adam Marc

    Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe1-xGax and Fe1-x Znx. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe1-xGax samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe1-xGax. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy.

  1. Magnetic order and spin excitations in the Kitaev-Heisenberg model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Vladimirov, A. A.; Ihle, D.; Plakida, N. M.

    2016-06-01

    We consider the quasi-two-dimensional pseudo-spin-1/2 Kitaev-Heisenberg model proposed for A2IrO3 (A = Li, Na) compounds. The spin-wave excitation spectrum, the sublattice magnetization, and the transition temperatures are calculated in the random phase approximation for four different ordered phases observed in the parameter space of the model: antiferromagnetic, stripe, ferromagnetic, and zigzag phases. The Néel temperature and temperature dependence of the sublattice magnetization are compared with the experimental data on Na2IrO3.

  2. Observations of imposed ordered structures in a dusty plasma at high magnetic field

    NASA Astrophysics Data System (ADS)

    Thomas, Edward; Lynch, Brian; Konopka, Uwe; Merlino, Robert L.; Rosenberg, Marlene

    2015-03-01

    Dusty plasmas have been studied in argon, rf glow discharge plasmas at magnetic fields up to 2 T, where the electrons and ions are strongly magnetized. In this experiment, plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper, electrically floating electrode supports a semi-transparent, titanium mesh. We report on the formation of an ordered dusty plasma, where the dust particles form a spatial structure that is aligned to the mesh. We discuss possible mechanisms that may lead to the formation of the "dust grid" and point out potential implications and applications of these observations.

  3. Observations of imposed ordered structures in a dusty plasma at high magnetic field

    SciTech Connect

    Thomas, Edward Lynch, Brian; Konopka, Uwe; Merlino, Robert L.; Rosenberg, Marlene

    2015-03-15

    Dusty plasmas have been studied in argon, rf glow discharge plasmas at magnetic fields up to 2 T, where the electrons and ions are strongly magnetized. In this experiment, plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper, electrically floating electrode supports a semi-transparent, titanium mesh. We report on the formation of an ordered dusty plasma, where the dust particles form a spatial structure that is aligned to the mesh. We discuss possible mechanisms that may lead to the formation of the “dust grid” and point out potential implications and applications of these observations.

  4. Testing spin-flip scattering as a possible mechanism of ultrafast demagnetization in ordered magnetic alloys

    NASA Astrophysics Data System (ADS)

    Günther, Stefan; Spezzani, Carlo; Ciprian, Roberta; Grazioli, Cesare; Ressel, Barbara; Coreno, Marcello; Poletto, Luca; Miotti, Paolo; Sacchi, Maurizio; Panaccione, Giancarlo; Uhlíř, Vojtěch; Fullerton, Eric E.; De Ninno, Giovanni; Back, Christian H.

    2014-11-01

    We use element-resolved IR-pump/extreme ultraviolet-probe experiments to disentangle the ultrafast interplay of the magnetic sublattices of an ordered crystalline magnetic alloy. As a paradigmatic example, we investigate the case of the FeRh alloy, which shows a delayed response for the different components. Furthermore, a detailed time-resolved magneto-optic study shows that the data can be analyzed by only assuming Elliot-Yafet-like scattering, as the underlying mechanism for ultrafast demagnetization, resulting in an unexpected nonmonotonic dependence of the spin-flip rate, as a function of quenching.

  5. Nuclear magnetic and quadrupole resonance studies of the stripes materials

    NASA Astrophysics Data System (ADS)

    Grafe, H.-J.

    2012-11-01

    Nuclear Magnetic and Quadrupole Resonance (NMR/NQR) is a powerful tool to probe electronic inhomogeneities in correlated electron systems. Its local character allows for probing different environments due to spin density modulations or inhomogeneous doping distributions emerging from the correlations in these systems. In fact, NMR/NQR is not only sensitive to magnetic properties through interaction of the nuclear spin, but also allows to probe the symmetry of the charge distribution and its homogeneity, as well as structural modulations, through sensitivity to the electric field gradient (EFG). We review the results of NMR and NQR in the cuprates from intrinsic spatial variations of the hole concentration in the normal state to stripe order at low temperatures, thereby keeping in mind the influence of doping induced disorder and inhomogeneities. Finally, we briefly discuss NQR evidence for local electronic inhomogeneities in the recently discovered iron pnictides, suggesting that electronic inhomogeneities are a common feature of correlated electron systems.

  6. Extensions of guiding center motion to higher order. [for plasma in static magnetic field

    NASA Technical Reports Server (NTRS)

    Northrop, T. G.; Rome, J. A.

    1978-01-01

    In a static magnetic field, some well-known guiding-center equations maintain their form when extended to next order in gyroradius. In these cases, it is only necessary to include the next order term in the magnetic moment series. The differential equation for guiding-center motion which describes both the parallel and perpendicular velocities correctly through first order in gyroradius is given. The question of how to define the guiding center position through second order arises and is discussed, and second order drifts are derived for one usual definition. The toroidal canonical angular momentum, P-phi, of the guiding center in an axisymmetric field is shown to be conserved using the guiding center velocity correct through first order. When second-order motion is included, P-phi is no longer a constant. The above extensions of guiding-center theory help to resolve the different tokamak orbits obtained either by using the guiding-center equations of motion or by using conservation of P-phi.

  7. Magnetic preferential orientation of metal oxide superconducting materials

    DOEpatents

    Capone, Donald W.; Dunlap, Bobby D.; Veal, Boyd W.

    1990-01-01

    A superconductor comprised of a polycrystalline metal oxide such as YBa.sub.2 Cu.sub.3 O.sub.7-X (where 0material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state.

  8. Magnetic preferential orientation of metal oxide superconducting materials

    DOEpatents

    Capone, D.W.; Dunlap, B.D.; Veal, B.W.

    1990-07-17

    A superconductor comprised of a polycrystalline metal oxide such as YBa[sub 2]Cu[sub 3]O[sub 7[minus]X] (where 0 < X < 0.5) exhibits superconducting properties and is capable of conducting very large current densities. By aligning the two-dimensional Cu-O layers which carry the current in the superconducting state in the a- and b-directions, i.e., within the basal plane, a high degree of crystalline axes alignment is provided between adjacent grains permitting the conduction of high current densities. The highly anisotropic diamagnetic susceptibility of the polycrystalline metal oxide material permits the use of an applied magnetic field to orient the individual crystals when in the superconducting state to substantially increase current transport between adjacent grains. In another embodiment, the anisotropic paramagnetic susceptibility of rare-earth ions substituted into the oxide material is made use of as an applied magnetic field orients the particles in a preferential direction. This latter operation can be performed with the material in the normal (non-superconducting) state. 4 figs.

  9. Analysis of ringing effects due to magnetic core materials in pulsed nuclear magnetic resonance circuits

    SciTech Connect

    Prabhu Gaunkar, N. Bouda, N. R. Y.; Nlebedim, I. C.; Hadimani, R. L.; Mina, M.; Jiles, D. C.; Bulu, I.; Ganesan, K.; Song, Y. Q.

    2015-05-07

    This work presents investigations and detailed analysis of ringing in a non-resonant pulsed nuclear magnetic resonance (NMR) circuit. Ringing is a commonly observed phenomenon in high power switching circuits. The oscillations described as ringing impede measurements in pulsed NMR systems. It is therefore desirable that those oscillations decay fast. It is often assumed that one of the causes behind ringing is the role of the magnetic core used in the antenna (acting as an inductive load). We will demonstrate that an LRC subcircuit is also set-up due to the inductive load and needs to be considered due to its parasitic effects. It is observed that the parasitics associated with the inductive load become important at certain frequencies. The output response can be related to the response of an under-damped circuit and to the magnetic core material. This research work demonstrates and discusses ways of controlling ringing by considering interrelationships between different contributing factors.

  10. Use of High Magnetic Field to Control Microstructural Evolution in Metallic and Magnetic Materials

    SciTech Connect

    Ludtka, G.M.; Mackiewicz- Ludtka, G.; Wilgen, J.B.; Kisner, R.A.

    2010-06-27

    The Amendment 1, referred to as Phase 2, to the original CRADA NFE-06-00414 added tasks 3 through 7 to the original statement of work that had two main tasks that were successfully accomplished in Phase 1 of this project. In this Phase 2 CRADA extension, extensive research and development activities were conducted using high magnetic field processing effects for the purpose of manipulating microstructure in the SAE 5160 steel to refine grain size isothermally and to develop nanocrystalline spacing pearlite during continuous cooling, and to enhance the formability/forgability of the non-ferrous precipitation hardening magnesium alloy AZ90 by applying a high magnetic field during deformation processing to investigate potential magnetoplasticity in this material. Significant experimental issues (especially non-isothermal conditions evolving upon insertion of an isothermal sample in the high magnetic field) were encountered in the isothermal phase transformation reversal experiments (Task 4) that later were determined to be due to various condensed matter physics phenomenon such as the magnetocaloric (MCE) effect that occurs in the vicinity of a materials Curie temperature. Similarly the experimental deformation rig had components for monitoring deformation/strain (Task 3) that were susceptible to the high magnetic field of the ORNL Thermomagnetic Processing facility 9-T superconducting magnet that caused electronic components to fail or record erroneous (very noisy) signals. Limited experiments on developing nanocrystalline spacing pearlite were not sufficient to elucidate the impact of high magnetic field processing on the final pearlite spacing since significant statistical evaluation of many pearlite colonies would need to be done to be conclusive. Since extensive effort was devoted to resolving issues for Tasks 3 and 7, only results for these focused activities are included in this final CRADA report along with those for Task 7 (described in the Objectives Section

  11. Three-dimensional magnetic resonance microscopy of materials.

    PubMed

    Botto, R E; Cody, G D; Dieckman, S L; French, D C; Gopalsami, N; Rizo, P

    1996-07-01

    Several aspects of magnetic resonance microscopy are examined employing three-dimensional (3D) back-projection reconstruction techniques in combination with either simple Bloch-decay methods or MREV-8 multiple-pulse line narrowing techniques in the presence of static field gradients. Applications to the areas of ceramic processing, catalyst porosity measurements and the characterization of polymeric materials are presented. The focus of the discussion centers on issues of sensitivity and resolution using this approach compared with other methods. Advantages and limitations of 3D microscopy over more commonly employed slice selection protocols are discussed, as well as potential remedies to some of the inherent limitations of the technique. PMID:8902960

  12. Interactions between magnetic resonance imaging and dental material

    PubMed Central

    Mathew, Chalakuzhiyl Abraham; Maller, Sudhakara; Maheshwaran

    2013-01-01

    Magnetic resonance imaging (MRI) has become a common and important life-saving diagnostic tool in recent times, for diseases of the head and neck region. Dentists should be aware of the interactions of various restorative dental materials and different technical factors put to use by an MRI scanning machine. Specific knowledge about these impacts, at the dentist level and at the level of the personnel at the MRI centers can save valuable time for the patient and prevent errors in MRI images. Artifacts from metal restorations are a major hindrance at such times, as they result in disappearance or distortion of the image and loss of important information. PMID:23946562

  13. Magnetism, structure and chemical order in small CoPd clusters: A first-principles study

    NASA Astrophysics Data System (ADS)

    Mokkath, Junais Habeeb

    2014-01-01

    The structural, electronic and magnetic properties of small ComPdn(N=m+n=8,m=0-N) nanoalloy clusters are studied in the framework of a generalized-gradient approximation to density-functional theory. The optimized cluster structures have a clear tendency to maximize the number of nearest-neighbor CoCo pairs. The magnetic order is found to be ferromagnetic-like (FM) for all the ground-state structures. Antiferromagnetic-like spin arrangements were found in some low-lying isomers. The average magnetic moment per atom μ increases approximately linearly with Co content. A remarkable enhancement of the local Co moments is observed as a result of Pd doping. This is a consequence of the increase in the number of Co d holes, due to CoPd charge transfer, combined with the reduced local coordination. The influence of spin-orbit interactions on the cluster properties is also discussed.

  14. Magnetostatic interaction in soft magnetic bilayer ribbons unambiguously identified by first-order reversal curve analysis

    NASA Astrophysics Data System (ADS)

    Rivas, M.; Martínez-García, J. C.; Škorvánek, I.; Marcin, J.; Švec, P.; Gorria, P.

    2015-09-01

    Monolithic amorphous Fe73.5Nb3Si13.5B9Cu1/Fe74.5Nb3Si13.5B9 bilayer ribbons were obtained by double-nozzle melt-spinning and subsequently annealed to produce a composite with a tailored nano/micro-crystalline structure. The overall magnetic behavior is characterized by butterfly-shaped high field hysteresis loops and positively biased low field ones. The main questions we wish to address here are whether the global magnetic behavior of the bilayer can be separated into the individual contributions of each layer and the magneto-coupling between them can be well understood. For that purpose, we performed first-order reversal curve analysis, which enabled us to distinctly identify two phases, of ultra-soft and semi-soft magnetic natures, whose mutual predominant interaction is the magnetostatic coupling.

  15. Need for development of higher strength cryogenic structural materials for fusion magnet

    NASA Astrophysics Data System (ADS)

    Nishimura, Arata

    2014-01-01

    A prototype fusion reactor is targeted as a beyond ITER project which is so called DEMO. Several conceptual designs have been carried out. Recently, in order to recognize practical aspects on maintenance of the prototype reactor, the replacement procedure of in-vessel components was focused and "sector process" was proposed. The process is that the reactor consists of sectors and all sectors will be drowned and replaced in a short time. The slim coil which generated higher magnetic field is required to realize the sector process. From the point of coil design, the occupancy of the structural material on the cross section of the coil increases with an increase of magnetic field. To realize the slim coil, the cryogenic structural material with higher yield strength and the proper toughness is desired.

  16. Phase stability, ordering, and magnetism of single-phase fcc Fe-Au alloys

    NASA Astrophysics Data System (ADS)

    An, Joonhee M.; Barabash, Sergey V.; Belashchenko, Kirill D.

    2013-03-01

    Motivated by experimental evidence of L10 ordering in single-phase fcc Fe-Au nanoparticles, we study the structural thermodynamics of Fe-Au alloys. First, separate cluster expansions for fcc and bcc lattices are constructed for fully optimized ferromagnetic structures using density functional theory calculations. The optimized structures were assigned to fcc or bcc lattice by a structural filter. Although the lowest formation enthalpy at 50% Au is reached in the bcc lattice, the fcc lattice is preferred for the random alloy. Dynamical stability of specific orderings strongly depends on the magnetic configuration. To analyze the ordering tendencies of the fcc alloy, we restrict uniform lattice relaxations and separate the contributions of chemical interaction and local relaxations. By using the effective tetrahedron model (Ruban et al., Phys. Rev. B 67, 214302 (2003)) and explicit calculations for ordered and special quasi-random structures, we find that the local relaxation energies depend weakly on the magnetization. Although the L10 ordering is the ground state at 50% Au on the ideal lattice, local relaxations make it unfavorable compared to the random alloy. Moderate compression due to the size effect tends to slightly stabilize the L10 ordering.

  17. In situ observation of ferromagnetic order breaking in MnAs/GaAs(001) and magnetocrystalline anisotropy of α -MnAs by electron magnetic chiral dichroism

    NASA Astrophysics Data System (ADS)

    Fu, X.; Warot-Fonrose, B.; Arras, R.; Seine, G.; Demaille, D.; Eddrief, M.; Etgens, V.; Serin, V.

    2016-03-01

    We report an in situ observation of temperature-dependent phase transition in MnAs thin film by transmission electron microscopy (TEM) techniques. Following the identification of the crystallographic transition, from hexagonal α -MnAs to quasihexagonal β -MnAs, the orbital-to-spin moment ratio is measured and a breaking of the ferromagnetic order locally observed, thanks to the electron magnetic chiral dichroism (EMCD) technique. To achieve quantitative information, applying the sum rules to the dichroic signal of magnetic anisotropic materials is accurately discussed. Finally, the orbital-to-spin moment ratio of α -MnAs along the easy, hard, and intermediate magnetic axes is estimated by EMCD and compared to implemented density functional theory (DFT) calculations. The influence of the magnetocrystalline anisotropy is locally demonstrated. This work in particular illustrates the feasibility of the EMCD technique for in situ experiments, and proves its potential to explore the anisotropy of magnetic materials.

  18. Cryogenic Considerations for Superconducting Magnet Design for the Material Plasma Exposure eXperiment

    SciTech Connect

    Duckworth, Robert C; Demko, Dr. Jonathan A; Lumsdaine, Arnold; Caughman, John B; Goulding, Richard Howell; McGinnis, William Dean; Bjorholm, Thomas P; Rapp, Juergen

    2015-01-01

    In order to determine long term performance of plasma facing components such as diverters and first walls for fusion devices, next generation plasma generators are needed. A Material Plasma Exposure eXperiment (MPEX) has been proposed to address this need through the generation of plasmas in front of the target with electron temperatures of 1-15 eV and electron densities of 1020 to 1021 m-3. Heat fluxes on target diverters could reach 20 MW/m2. In order generate this plasma, a unique radio frequency helicon source and heating of electrons and ions through Electron Bernstein Wave (EBW) and Ion Cyclotron Resonance Heating (ICRH) has been proposed. MPEX requires a series of magnets with non-uniform central fields up to 2 T over a 5m length in the heating and transport region and 1 T uniform central field over a 1-m length on a diameter of 1.3 m. Given the field requirements, superconducting magnets are under consideration for MPEX. In order to determine the best construction method for the magnets, the cryogenic refrigeration has been analyzed with respect to cooldown and operational performance criteria for open-cycle and closed-cycle systems, capital and operating costs of these system, and maturity of supporting technology such as cryocoolers. These systems will be compared within the context of commercially available magnet constructions to determine the most economical method for MPEX operation. The current state of the MPEX magnet design including details on possible superconducting magnet configurations will be presented.

  19. Magnetism at grain boundary interfacesin the colossal permittivity dielectric material; In+Nb Co-Doped Rutile

    NASA Astrophysics Data System (ADS)

    Berlie, Adam; Terry, Ian; Cottrell, Stephen; Hu, Wanbiao; Liu, Yun

    With the emphasis in recent years on understanding novel materials with potential technological applications this work seeks to understand magnetic ordering within the colossal-permittivity material, In+Nb co-doped rutile (TiO2). Evidence for a spin-freezing transition was reported from a step like feature in the dielectic data below 50 K but this was largly glossed over. Within this work we show that below 300 K there is a slowing down of magnetic fluctuations associated with the electronic magnetism due to the defect-dipoles created by the co-doping, but the muon spectroscopy results are strongly suggestive of the behaviour being localised to the edges/interfaces of particles/grains. The TC is strongly dependent on the doping level of the samples that presents novel way to control the magnetism and ultimately magneto-electric coupling within a dielectric material.

  20. Magnetically shaped cell aggregates: from granular to contractile materials.

    PubMed

    Frasca, G; Du, V; Bacri, J-C; Gazeau, F; Gay, C; Wilhelm, C

    2014-07-28

    In recent decades, significant advances have been made in the description and modelling of tissue morphogenesis. By contrast, the initial steps leading to the formation of a tissue structure, through cell-cell adhesion, have so far been described only for small numbers of interacting cells. Here, through the use of remote magnetic forces, we succeeded at creating cell aggregates of half million cells, instantaneously and for several cell types, not only those known to form spheroids. This magnetic compaction gives access to the cell elasticity, found in the range of 800 Pa. The magnetic force can be removed at any time, allowing the cell mass to evolve spontaneously thereafter. The dynamics of contraction of these cell aggregates just after their formation (or, in contrast, their spreading for non-interacting monocyte cells) provides direct information on cell-cell interactions and allows retrieving the adhesion energy, in between 0.05 and 2 mJ m(-2), depending on the cell type tested, and in the case of cohesive aggregates. Thus, we show, by probing a large number of cell types, that cell aggregates behave like complex materials, undergoing a transition from a wet granular to contractile network, and that this transition is controlled by cell-cell interactions. PMID:24710948

  1. Strong cooperative coupling of pressure-induced magnetic order and nematicity in FeSe.

    PubMed

    Kothapalli, K; Böhmer, A E; Jayasekara, W T; Ueland, B G; Das, P; Sapkota, A; Taufour, V; Xiao, Y; Alp, E; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I

    2016-01-01

    A hallmark of the iron-based superconductors is the strong coupling between magnetic, structural and electronic degrees of freedom. However, a universal picture of the normal state properties of these compounds has been confounded by recent investigations of FeSe where the nematic (structural) and magnetic transitions appear to be decoupled. Here, using synchrotron-based high-energy x-ray diffraction and time-domain Mössbauer spectroscopy, we show that nematicity and magnetism in FeSe under applied pressure are indeed strongly coupled. Distinct structural and magnetic transitions are observed for pressures between 1.0 and 1.7 GPa and merge into a single first-order transition for pressures ≳1.7 GPa, reminiscent of what has been found for the evolution of these transitions in the prototypical system Ba(Fe1-xCox)2As2. Our results are consistent with a spin-driven mechanism for nematic order in FeSe and provide an important step towards a universal description of the normal state properties of the iron-based superconductors. PMID:27582003

  2. Spacetimes with longitudinal and angular magnetic fields in third order Lovelock gravity

    SciTech Connect

    Dehghani, M. H.; Bostani, N.

    2007-04-15

    We obtain two new classes of magnetic solutions in third order Lovelock gravity. The first class of solutions yields an (n+1)-dimensional spacetime with a longitudinal magnetic field generated by a static source. We generalize this class of solutions to the case of spinning magnetic strings with one or more rotation parameters. These solutions have no curvature singularity and no horizons, but have a conic geometry. For the spinning string, when one or more rotation parameters are nonzero, the string has a net electric charge which is proportional to the magnitude of the rotation parameters, while the static string has no net electric charge. The second class of solutions yields a spacetime with an angular magnetic field. These solutions have no curvature singularity, no horizon, and no conical singularity. Although the second class of solutions may be made electrically charged by a boost transformation, the transformed solutions do not present new spacetimes. Finally, we use the counterterm method in third order Lovelock gravity and compute the conserved quantities of these spacetimes.

  3. Spin state ordering of strongly correlating LaCoO3 induced at ultrahigh magnetic fields

    NASA Astrophysics Data System (ADS)

    Ikeda, Akihiko; Nomura, Toshihiro; Matsuda, Yasuhiro H.; Matsuo, Akira; Kindo, Koichi; Sato, Keisuke

    2016-06-01

    Magnetization measurements of LaCoO3 have been carried out up to 133 T, generated with a destructive pulse magnet at a wide temperature range from 2 to 120 K. A novel magnetic transition was found at B >100 T and T >T*=32 ±5 K, which is characterized by its transition field increasing with increasing temperature. At T orders of the spin states and possibly other degrees of freedom such as orbitals. An inherent strong correlation of spin states among cobalt sites should have triggered the emergence of the ordered phases in LaCoO3 at high magnetic fields.

  4. Magnetic ordering and quantum anomalous Hall phase of Cr-doped topological insulators: First principles studies

    NASA Astrophysics Data System (ADS)

    Kim, Jeongwoo; Jhi, Seung-Hoon; Wu, Ruqian

    Realization of transverse electric currents without external magnetic fields, so called the quantum anomalous Hall effect (QAHE), is achieved in Cr-doped topological insulating (Bi,Sb)2Te3 compounds. However, detailed mechanism of QAHE and magnetic ordering in topological insulators (TIs) is still unclear with several models in controversy. We study the origin of QAHE in magnetic impurity-doped TIs using first-principles calculations. We investigate a possibility of the quantum anomalous Hall phase in conventional three-dimensional topological insulators, such as Bi2Se3, Bi2Te3, and Sb2Te3. We find that Sb2Te3 is the most suitable compound for realizing QAHE, because it maintains insulating phase and relatively strong ferromagnetic ordering in a wide range of Cr doping while Bi2Se3 and Bi2Te3 become metallic even by a small amount of Cr doping. Contrary to previous predictions, the kinetic exchange is responsible for the magnetic phase of Cr-doped TIs and it induces spin-polarized valence and conduction bands in Sb2Te3. We also discuss the role of Bi doping in topological surfaces states of Cr-doped Sb2Te3, which leads to QAHE in (Bi,Sb)2Te3. Work was supported as part of the SHINES, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. SC0012670.

  5. Three-dimensional charge density wave order in YBCO at high magnetic field

    NASA Astrophysics Data System (ADS)

    Lee, Wei-Sheng

    Charge density wave (CDW) correlations have been shown to universally exist in cuprate superconductors. However, their nature at high magnetic fields, e . g . inferred from nuclear magnetic resonance, Hall coefficient, and sound velocity measurements, is distinct from that measured by x-ray scattering at zero and low fields. In this talk, I will discuss our recent experiment which combines a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below ~150 K, is essentially two dimensional, a three-dimensionally ordered CDW emerges at magnetic fields beyond 15 Tesla and at temperatures below the zero-field superconducting transition temperature. While the two CDW arrange differently along the c-axis, they share the same incommensurate periodicity in the CuO2plane. Our observations imply that the two forms of CDW and high-temperature superconductivity are intimately linked.

  6. Magnetic behavior of Eu(3)Ni(4)Ga(4): antiferromagnetic order and large magnetoresistance.

    PubMed

    Anupam; Geibel, C; Hossain, Z

    2012-08-15

    The results of the magnetic susceptibility, isothermal magnetization, heat capacity, electrical resistivity and magnetoresistance measurements on polycrystalline Eu(3)Ni(4)Ga(4) are presented. Eu(3)Ni(4)Ga(4) forms in Na(3)Pt(4)Ge(4)-type cubic crystal structure (space group [Formula: see text]). The temperature dependence of the magnetic susceptibility of Eu(3)Ni(4)Ga(4) confirms the divalent state (Eu(2+)) of Eu ions with an effective magnetic moment μ(eff) = 7.98 μ(B). At low fields, e.g. at 0.01 T, a magnetic phase transition to an antiferromagnetically ordered state occurs at T(N) = 10.9 K, which is further confirmed by the temperature dependence of the heat capacity and electrical resistivity. The field dependence of isothermal magnetization at 2 K reveals the presence of two field induced metamagnetic transitions at H(c1) and H(c2) = 0.55 and 1.2 T, respectively and a polarized phase above H(PO) = 1.7 T. The reduced jump in the heat capacity at the transition temperature, ΔC|(T(N)) = 13.48 J/mol-Eu K would indicate an amplitude modulated (AM) antiferromagnetic structure. An interesting feature is that a large negative magnetoresistance, MR = [ρ(H) - ρ(0)]/ρ(0), is observed in the vicinity of magnetic transition even up to 2T(N). Similar large magnetoresistance has been observed in the paramagnetic state in some Gd and Eu based alloys and has been attributed to the magneto-polaronic effect. PMID:22785157

  7. Magnetic order in the two-dimensional compass-Heisenberg model

    NASA Astrophysics Data System (ADS)

    Vladimirov, Artem A.; Ihle, Dieter; Plakida, Nikolay M.

    2015-06-01

    A Green-function theory for the dynamic spin susceptibility in the square-lattice spin-1/2 antiferromagnetic compass-Heisenberg model employing a generalized mean-field approximation is presented. The theory describes magnetic long-range order (LRO) and short-range order (SRO) at arbitrary temperatures. The magnetization, Néel temperature TN, specific heat, and uniform static spin susceptibility χ are calculated self-consistently. As the main result, we obtain LRO at finite temperatures in two dimensions, where the dependence of TN on the compass-model interaction is studied. We find that TN is close to the experimental value for Ba2IrO4. The effects of SRO are discussed in relation to the temperature dependence of χ.

  8. Electron motion in solenoidal magnetic fields using a first order symplectic integration algorithm

    SciTech Connect

    Fraser, J.S.

    1984-05-07

    The use of nonsymplectic procedures in particle tracing codes for relativistic electrons leads to errors that can be reduced only at the expense of using very small integration steps. More accurate results are obtained with symplectic transformations for position and momentum. A first-order symplectic integration procedure requires an iterative calculation of the new position coordinates using the old momenta, but the process usually converges in three or four steps. A first-order symplectic algorithm has been coded for cylindrical as well as Cartesian coordinates using the relativistic equations of motion with Hamiltonian variables. The procedure is applied to the steering of a beam of 80-keV electrons by a weak transverse magnetic field superposed on a strong magnetic field in the axial direction. The steering motion is shown to be parallel to the transverse field rather than perpendicular as would be the case without the strong axial field.

  9. Magnetic order in the filled skutterudites RPt4Ge12 (R = Nd, Eu)

    NASA Astrophysics Data System (ADS)

    Nicklas, M.; Gumeniuk, R.; Schnelle, W.; Rosner, H.; Leithe-Jasper, A.; Steglich, F.; Grin, Yu

    2011-01-01

    Rare-earth metal filled skutterudites RPt4Ge12 with R=La-Nd, and Eu exhibit a variety of different ground states, e.g., conventional and unconventional superconductivity in LaPt4Ge12 and PrPt4Ge12, respectively, and intermediate valence behavior in CePt4Ge12. In this work we investigate the magnetic state of NdPt4Ge12 and EuPt4Ge12 by specific heat, dc-susceptibility and magnetization. NdPt4Ge12 shows two magnetic phase transitions at TN1 = 0.67 K and TN2 = 0.58 K, while EuPt4Ge12 displays a complex magnetic phase diagram below the magnetic ordering temperature of 1.78 K. The specific heat indicates that in NdPt4Ge12 the crystalline electric field (CEF) ground state of the Nd3+ is a quartet and that, as expected, in EuPt4Ge12 the Eu2+ state is fully degenerate.

  10. Polymeric variable optical attenuators based on magnetic sensitive stimuli materials

    NASA Astrophysics Data System (ADS)

    de Pedro, S.; Cadarso, V. J.; Ackermann, T. N.; Muñoz-Berbel, X.; Plaza, J. A.; Brugger, J.; Büttgenbach, S.; Llobera, A.

    2014-12-01

    Magnetically-actuable, polymer-based variable optical attenuators (VOA) are presented in this paper. The design comprises a cantilever which also plays the role of a waveguide and the input/output alignment elements for simple alignment, yet still rendering an efficient coupling. Magnetic properties have been conferred to these micro-opto-electromechanical systems (MOEMS) by implementing two different strategies: in the first case, a magnetic sensitive stimuli material (M-SSM) is obtained by a combination of polydimethylsiloxane (PDMS) and ferrofluid (FF) in ratios between 14.9 wt % and 29.9 wt %. An M-SSM strip under the waveguide-cantilever, defined with soft lithography (SLT), provides the required actuation capability. In the second case, specific volumes of FF are dispensed at the end of the cantilever tip (outside the waveguide) by means of inkjet printing (IJP), obtaining the required magnetic response while holding the optical transparency of the waveguide-cantilever. In the absence of a magnetic field, the waveguide-cantilever is aligned with the output fiber optics and thus the intrinsic optical losses can be obtained. Numerical simulations, validated experimentally, have shown that, for any cantilever length, the VOAs defined by IJP present lower intrinsic optical losses than their SLT counterparts. Under an applied magnetic field (Bapp), both VOA configurations experience a misalignment between the waveguide-cantilever and the output fiber optics. Thus, the proposed VOAs modulate the output power as a function of the cantilever displacement, which is proportional to Bapp. The experimental results for the three different waveguide-cantilever lengths and six different FF concentrations (three per technology) show maximum deflections of 220 µm at 29.9 wt % of FF for VOASLT and 250 µm at 22.3 wt % FF for VOAIJP, at 0.57 kG for both. These deflections provide maximum actuation losses of 16.1 dB and 18.9 dB for the VOASLT and VOAIJP

  11. Magnetic Order and Dimensional Crossover in Optical Lattices with Repulsive Interaction

    NASA Astrophysics Data System (ADS)

    Xu, Jie

    One of the most interesting and challenging problems in physics is understanding strongly correlated many-body systems, where strong interactions can yield many remarkable phenomena such as superfluidity in 4He, high-temperature superconductivity, etc. In order to attack these problems, we often need to reduce the complexity of the systems to simple models in hopes of getting better insights into the properties of the systems. The Hubbard model, the focus of this dissertation, is one of the most famous examples of such model, which describes a tunneling of electrons between nearest neighbor sites of a lattice with on-site interactions. This simple model is an important concept in condensed matter physics and provides rich understandings of electronic and magnetic properties of materials. Despite its simplicity, there is no general analytical solution to the Hubbard model beyond 1D. The discovery of ultracold atoms and optical lattices opens up the possibility of emulating the Hubbard model in experiments. Optical lattices provide an ideal realization of the Hubbard model where relevant parameters can be tuned systematically. It makes theoretical studies of the Hubbard model increasingly attractive since a direct comparison between theoretical calculations and experimental results becomes more and more possible. In this dissertation, the ground-state properties of the repulsive Hubbard model for weak to intermediate interaction strengths in two, three dimensions and their dimensional crossover are studied within the mean field theory. We show that the system exhibits unidirectional spin-density wave (SDW) order with antiferromagnetic correlations and a long wavelength modulation. The modulating wave is along the [0011-direction at low interaction strength U/t and along the [1111-direction at higher U/t. The evolution of the wavelength of the SDW is determined as a function of U/t, the density, and t⊥/t. With an analysis of the pairing of spins based on nesting and

  12. Charge Order in LuFe2O4: Antiferroelectric Ground State and Coupling to Magnetism

    SciTech Connect

    Angst, Manuel; Hermann, Raphael P.; Christianson, Andrew D; Lumsden, Mark D; Lee, C; Whangbo, M.-H.; Kim, J.-W.; Ryan, P J; Nagler, Stephen E; Tian, Wei; Jin, Rongying; Sales, Brian C; Mandrus, David

    2008-11-01

    X-ray scattering by multiferroic LuFe2O4 is reported. Below 320 K, superstructure reflections indicate an incommensurate charge order with propagation close to 1 3 1 3 3 2 . The corresponding charge configuration, also found by electronic structure calculations as most stable, contains polar Fe=O double layers with antiferroelectric stacking. Diffuse scattering at 360 K, with 1 3 1 3 0 propagation, indicates ferroelectric short-range correlations between neighboring double layers. The temperature dependence of the incommensuration indicates that charge order and magnetism are coupled.

  13. Magnetic order tuned by Cu substitution in Fe1.1–zCuzTe

    DOE PAGESBeta

    Wen, Jinsheng; Xu, Zhijun; Xu, Guangyong; Lumsden, M. D.; Valdivia, P. N.; Bourret-Courchesne, E.; Gu, Genda; Lee, Dung-Hai; Tranquada, J. M.; Birgeneau, R. J.

    2012-07-02

    We study the effects of Cu substitution in Fe₁.₁Te, the nonsuperconducting parent compound of the iron-based superconductor, Fe₁₊yTe₁₋xSex, utilizing neutron scattering techniques. It is found that the structural and magnetic transitions, which occur at ~60 K without Cu, are monotonically depressed with increasing Cu content. By 10% Cu for Fe, the structural transition is hardly detectable, and the system becomes a spin glass below 22 K, with a slightly incommensurate ordering wave vector of (0.5–δ, 0, 0.5) with δ being the incommensurability of 0.02, and correlation length of 12 Å along the a axis and 9 Å along the cmore » axis. With 4% Cu, both transition temperatures are at 41 K, though short-range incommensurate order at (0.42, 0, 0.5) is present at 60 K. With further cooling, the incommensurability decreases linearly with temperature down to 37 K, below which there is a first-order transition to a long-range almost-commensurate antiferromagnetic structure. A spin anisotropy gap of 4.5 meV is also observed in this compound. Our results show that the weakly magnetic Cu has a large effect on the magnetic correlations; it is suggested that this is caused by the frustration of the exchange interactions between the coupled Fe spins.« less

  14. Leading-order hadronic contributions to the lepton anomalous magnetic moments from the lattice

    NASA Astrophysics Data System (ADS)

    Burger, Florian; Feng, Xu; Jansen, Karl; Petschlies, Marcus; Pientka, Grit; Renner, Dru B.

    2016-04-01

    The hadronic leading-order (hlo) contribution to the lepton anomalous magnetic moments alhlo of the Standard Model leptons still accounts for the dominant source of the uncertainty of the Standard Model estimates. We present the results of an investigation of the hadronic leading order anomalous magnetic moments of the electron, muon and tau lepton from first principles in twisted mass lattice QCD. With lattice data for multiple pion masses in the range 230MeV ≲ mPS ≲ 490 MeV, multiple lattice volumes and three lattice spacings we perform the extrapolation to the continuum and to the physical pion mass and check for all systematic uncertainties in the lattice calculation. As a result we calculate alhlo for the three Standard Model leptons with controlled statistical and systematic error in agreement with phenomenological determinations using dispersion relations and experimental data. In addition, we also give a first estimate of the hadronic leading order anomalous magnetic moments from simulations directly at the physical value of the pion mass.

  15. Nitriding-induced texture, ordering and coercivity enhancement in FePtAgB nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    Crisan, O.; Vasiliu, F.; Palade, P.; Mercioniu, I.

    2016-03-01

    FePt system attracts currently a great deal of interest for applications as future RE free permanent magnets. Among the key issues to be solved one may count the decreasing of the ordering temperature and improvement of magnetic behavior. For that purpose we have studied the effect of a nitriding post-synthesis procedure on the FePtAgB melt spun ribbons, aimed at refining the microstructure and enhancing the magnetic performances. Deep structural characterization by transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy and X-ray diffraction allowed us to observe the morphology and to correctly assign and identify the nature of the main granular phases observed. Nitriding procedure is shown to strongly enhance the (001) texturing and the degree of ordering of the L10 FePt phase, as well as largely increase of coercivity, compared to the as-cast state. These changes are interpreted in terms of Ag segregation towards intergranular region associated to N diffusion and creation of vacancies that favor consistently the process of ordering the FePt grains into the L10 tetragonal phase.

  16. Combined first-order reversal curve and x-ray microscopy investigation of magnetization reversal mechanisms in hexagonal antidot lattices

    NASA Astrophysics Data System (ADS)

    Gräfe, Joachim; Weigand, Markus; Stahl, Claudia; Träger, Nick; Kopp, Michael; Schütz, Gisela; Goering, Eberhard J.; Haering, Felix; Ziemann, Paul; Wiedwald, Ulf

    2016-01-01

    The magnetization reversal in nanoscaled antidot lattices is widely investigated to understand the tunability of the magnetic anisotropy and the coercive field through nanostructuring of thin films. By investigating highly ordered focused ion beam milled antidot lattices with a combination of first-order reversal curves and magnetic x-ray microscopy, we fully elucidate the magnetization reversal along the distinct orientations of a hexagonal antidot lattice. This combination proves especially powerful as all partial steps of this complex magnetization reversal can be identified and subsequently imaged. Through this approach we discovered several additional steps that were neglected in previous studies. Furthermore, by imaging the microscopic magnetization state during each reversal step, we were able to link the coercive and interaction fields determined by the first-order reversal curve method to true microscopic magnetization configurations and determine their origin.

  17. Tenth-order QED contribution to lepton anomalous magnetic moment: Fourth-order vertices containing sixth-order vacuum-polarization subdiagrams

    SciTech Connect

    Aoyama, Tatsumi; Hayakawa, Masashi; Kinoshita, Toichiro; Nio, Makiko

    2011-03-01

    This paper reports the tenth-order contributions to the g-2 of the electron a{sub e} and those of the muon a{sub {mu}} from the gauge-invariant Set II(c), which consists of 36 Feynman diagrams, and Set II(d), which consists of 180 Feynman diagrams. Both sets are obtained by insertion of sixth-order vacuum-polarization diagrams in the fourth-order anomalous magnetic moment. The mass-independent contributions from Set II(c) and Set II(d) are -0.116 489 (32)({alpha}/{pi}){sup 5} and -0.243 00 (29)({alpha}/{pi}){sup 5}, respectively. The leading contributions to a{sub {mu}}, which involve electron loops only, are -3.888 27 (90)({alpha}/{pi}){sup 5} and 0.4972 (65)({alpha}/{pi}){sup 5} for Set II(c) and Set II(d), respectively. The total contributions of the electron, muon, and tau-lepton loops to a{sub e} are -0.116 874 (32)({alpha}/{pi}){sup 5} for the Set II(c), and -0.243 10 (29)({alpha}/{pi}){sup 5} for the Set II(d), respectively. The contributions of the electron, muon, and tau-lepton loop to a{sub {mu}} are -5.5594 (11)({alpha}/{pi}){sup 5} for the Set II(c) and 0.2465 (65)({alpha}/{pi}){sup 5} for the Set II(d), respectively.

  18. Second-order-like cluster-monomer transition within magnetic fluids and its impact upon the magnetic susceptibility

    PubMed Central

    2012-01-01

    The low-field (below 5 Oe) ac and dc magnetic response of a magnetic fluid [MF] sample in the range of 305 to 360 K and 410 to 455 K was experimentally and theoretically investigated. We found a systematic deviation of Curie's law, which predicts a linear temperature dependence of inverse initial susceptibility in the range of our investigation. This finding, as we hypothesized, is due to the onset of a second-order-like cluster-to-monomer transition with a critical exponent which is equal to 0.50. The susceptibility data were well fitted by a modified Langevin function, in which cluster dissociation into monomers, at the critical temperature [T*], was included. In the ac experiments, we found that T* was reducing from 381.8 to 380.4 K as the frequency of the applied field increases from 123 to 173 Hz. In addition, our ac experiments confirm that only monomers respond for the magnetic behavior of the MF sample above T*. Furthermore, our Monte Carlo simulation and analytical results support the hypothesis of a thermal-assisted dissociation of chain-like structures. PACS: 75.75.-C; 75.30.Kz; 75.30.Cr. PMID:22390618

  19. Mechanical and Thermal Characteristics of Insulation Materials for the KSTAR Magnet System at Cryogenic Temperature

    NASA Astrophysics Data System (ADS)

    Chung, Wooho; Lim, Bungsu; Kim, Myungkyu; Park, Hyunki; Kim, Keeman; Chu, Yong; Lee, Sangil

    2004-06-01

    The KSTAR(Korea Superconducting Tokamak Advanced Research) superconducting magnet is electrically insulated by the composite material of epoxy resin and glass fiber (2.5 kV/mm) and Kapton (8 kV/mm). The insulation composite material of epoxy resin and glass fiber is prepared using a VPI (Vacuum Pressure Impregnation) process. The superconducting magnet is under mechanical stress caused by the large temperature difference between the operation temperature of the magnet and room temperature. The large electro-magnetic force during the operation of the magnet is also exerted on the magnet. Therefore, the characteristics of the insulation material at cryogenic temperatures are very important and the tensile stress and thermal expansion coefficient for the insulation materials of the KSTAR superconducting magnet are measured. This paper presents results on mechanical properties of the insulation material for KSTAR magnets, such as density, ultimate tensile stress and thermal contraction between room temperature and cryogenic temperatures.

  20. Materials, Strands, and Cables for Superconducting Accelerator Magnets. Final Report

    SciTech Connect

    Sumption, Mike D.; Collings, Edward W.

    2014-09-19

    This report focuses on Materials, Strands and Cables for High Energy Physics Particle accelerators. In the materials area, work has included studies of basic reactions, diffusion, transformations, and phase assemblage of Nb3Sn. These materials science aspects have been married to results, in the form of flux pinning, Bc2, Birr, and transport Jc, with an emphasis on obtaining the needed Jc for HEP needs. Attention has also been paid to the “intermediate-temperature superconductor”, magnesium diboride emphasis being placed on (i) irreversibility field enhancement, (ii) critical current density and flux pinning, and (iii) connectivity. We also report on studies of Bi-2212. The second area of the program has been in the area of “Strands” in which, aside from the materials aspect of the conductor, its physical properties and their influence on performance have been studied. Much of this work has been in the area of magnetization estimation and flux jump calculation and control. One of the areas of this work was strand instabilities in high-performance Nb3Sn conductors due to combined fields and currents. Additionally, we investigated quench and thermal propagation in YBCO coated conductors at low temperatures and high fields. The last section, “Cables”, focussed on interstrand contact resistance, ICR, it origins, control, and implications. Following on from earlier work in NbTi, the present work in Nb3Sn has aimed to make ICR intermediate between the two extremes of too little contact (no current sharing) and too much (large and unacceptable magnetization and associated beam de-focussing). Interstrand contact and current sharing measurements are being made on YBCO based Roebel cables using transport current methods. Finally, quench was investigated for YBCO cables and the magnets wound from them, presently with a focus on 50 T solenoids for muon collider applications.

  1. Direct observation of Cr magnetic order in CoCrTa and CoCrPt thin films

    SciTech Connect

    Kemner, K.M.; Idzerda, Y.U.; Harris, V.G.; Chakarian, V.; Elam, W.T.; Kao, C.; Johnson, E.; Feng, Y.C.; Laughlin, D.E.; Chen, C.; Lee, K.; Lodder, J.C.

    1997-01-01

    Magnetic circular dichroism measurements of room temperature, sputter deposited Co{sub 86}Cr{sub 12}Ta{sub 2} and Co{sub 86}Cr{sub 12}Pt{sub 2} films were performed to investigate the local magnetic ordering of the Co and Cr atoms. The results demonstrate that the Cr has a net magnetic moment and that a small fraction of the Cr is magnetically oriented opposite to the Co moment. {copyright} {ital 1997 American Institute of Physics.}

  2. Applications of high dielectric materials in high field magnetic resonance

    NASA Astrophysics Data System (ADS)

    Haines, Kristina Noel

    At high magnetic fields, radiation losses, wavelength effects, self-resonance, and the high resistance of components all contribute to losses in conventional RF MRI coil designs. The hypothesis tested here is that these problems can be combated by the use of high permittivity ceramic materials at high fields. High permittivity ceramic dielectric resonators create strong uniform magnetic fields in compact structures at high frequencies and can potentially solve some of the challenges of high field coil design. In this study NMR probes were constructed for operation at 600 MHz (14.1 Tesla) and 900 MHz (21.1 Tesla) using inductively fed CaTiO3 (relative permittivity of 156-166) cylindrical hollow bore dielectric resonators. The designs showed the electric field is largely confined to the dielectric itself, with near zero values in the hollow bore, which accommodates the sample. The 600 MHz probe has an unmatched Q value greater than 2000. Experimental and simulation mapping of the RF field show good agreement, with the ceramic resonator giving a pulse width approximately 25% less than a loop gap resonator of similar inner dimensions. High resolution images, with voxel dimensions less than 50 microm3, have been acquired from fixed zebrafish samples, showing excellent delineation of several fine structures. The 900 MHz probe has an unmatched Q value of 940 and shows Q performance five times better than Alderman-Grant and loop-gap resonators of similar dimensions. High resolution images were acquired of an excised mouse spinal cord (25 microm 3) and an excised rat soleus muscle (20 microm3). The spatial distribution of electromagnetic fields within the human body can be tailored using external dielectric materials. Here, a new material is introduced with high dielectric constant and low background MRI signal. The material is based upon metal titanates, which can be made into geometrically formable suspensions in de-ionized water. The suspension's material properties are

  3. Phase ordering and its effect on magnetic and structural properties of FeRh ultrathin films

    NASA Astrophysics Data System (ADS)

    Yap, Q. J.; Qiu, J. J.; Luo, P.; Ying, J. F.; Han, G. C.; Laughlin, D. E.; Zhu, J.-G.; Kanbe, T.; Shige, T.

    2014-07-01

    Applications using FeRh for controllable exchange coupling of two magnetic layers with in-plane and out-of-plane anisotropies require ultrathin (˜10 nm) films with pure antiferromagnetic (AF) FeRh α″ phase at room temperature (RT). However, it is also well known that the antiferromagnetic-ferromagnetic (AF-FM) transition of FeRh is sensitive to composition and deteriorates at low thicknesses. Hence, in this work, we study the composition-dependent phase ordering of co-sputtered FeRh thin films at ultrathin thicknesses of ˜10 nm. As the ultrathin films get richer in Rh, the appearance of α″ phase is typically characterized magnetically by a sudden drop in RT moment, and structurally by a slight decrease in degree of B2 chemical ordering with a sharp decrease in c-axis lattice constant. These observations are consistent with the FeRh phase diagram where FeRh abruptly enters the AF α″ phase once it becomes slightly disordered. Dependences of magnetic transition parameters on composition were also described. Moreover, higher sputtering powers possibly allow the formation of purer α″ phase with less γ-face centered cubic phase impurities. Consequently, a composition optimized 10 nm film shows a relatively low residual moment (13.5 emu/cc), thus suggesting good AF phase formation. In addition, correlation of the magnetic transition parameters with the crystal structural parameters reveal that the maximum rate of AF-FM transition (Rmax,h) and the corresponding total change in magnetization (ΔMh) interestingly shows linear dependence on the c-axis lattice constant, but would depart from this linearity under certain conditions, i.e., when grain sizes were large, crystallinity was improved and Fe content was high.

  4. Suppression of Ultracold Neutron Depolarization on Material Surfaces with Magnetic Holding Fields

    NASA Astrophysics Data System (ADS)

    Rios, Raymond

    2009-10-01

    Experiments involving polarized Ultracold Neutrons (UCN) for high precision measurements require the use of high Fermi potential materials with a low spin flip probability per bounce. Previous studies show that the spin flip probability for materials vary on the order of 10-3 to 10-6. In this study, the depolarization of UCN was measured within 1-m long, 2 3/4" diameter bare copper, electropolished copper, diamond-like carbon-coated copper, and stainless steel guide tubes as a function of the magnetic holding field. The UCN were trapped between a 6 Tesla solenoidal magnet and a copper plate. A series of Helmholtz coils produced a magnetic holding field over the length of the test guide at 10, 100, or 250 Gauss. The surface depolarization was observed to be suppressed at higher holding fields. These measurements will aid in the determination of an upper limit on depolarization of UCN in the UCNA beta asymmetry measurement at LANL and in understanding the mechanisms for depolarization in non-magnetic guides.

  5. Atomistic modelling of iron with magnetic analytic Bond-Order Potentials

    NASA Astrophysics Data System (ADS)

    Ford, Michael E.

    The development of interatomic potentials for magnetic transition metals, and particularly for iron, is difficult, yet it is also necessary for large-scale atomistic simulations of industrially important iron and steel alloys. The magnetism of iron is especially important as it is responsible for many of the element's unique physical properties -- its bcc ground state structure, its high-temperature phase transitions, and the mobility of its self-interstitial atom (SIA) defects. Yet an accurate description of itinerant magnetism within a real-space formalism is particularly challenging and existing interatomic potentials based on the Embedded Atom Method are suited only for studies of near-equilibrium ferritic iron, due to their restricted functional forms. For this work, the magnetic analytic Bond-Order Potential (BOP) method has been implemented in full to test the convergence properties in both collinear and non-collinear magnetic iron. The known problems with negative densities of states (DOS) are addressed by assessing various possible definitions for the bandwidth and by including the damping factors adapted from the Kernel Polynomial Method. A 9-moment approximation is found to be sufficient to reproduce the major structural energy differences observed in Density Functional Theory (DFT) and Tight Binding (TB) reference calculations, as well as the volume dependence of the atomic magnetic moments. The Bain path connecting bcc and fcc structures and the formation energy of mono- and divacancies are also described well at this level of approximation. Other quantities such as the high-spin/low-spin transition in fcc iron, the bcc elastic constants and the SIA formation energies converge more slowly towards the TB reference data. The theory of non-collinear magnetism within analytic BOP is extended as required for a practical implementation. The spin-rotational behaviour of the energy is shown to converge more slowly than the collinear bulk energy differences

  6. Use of magnetic carbon composites from renewable resource materials for oil spill clean up and recovery

    DOEpatents

    Viswanathan, Tito

    2015-10-27

    A method of separating a liquid hydrocarbon material from a body of water, includes: (a) mixing magnetic carbon-metal nanocomposites with a liquid hydrocarbon material dispersed in a body of water to allow the magnetic carbon-metal nanocomposites each to be adhered by the liquid hydrocarbon material to form a mixture; (b) applying a magnetic force to the mixture to attract the magnetic carbon-metal nanocomposites each adhered by the liquid hydrocarbon material; and (c) removing the body of water from the magnetic carbon-metal nanocomposites each adhered by the liquid hydrocarbon material while maintaining the applied magnetic force. The magnetic carbon-metal nanocomposites is formed by subjecting one or more metal lignosulfonates or metal salts to microwave radiation, in presence of lignin/derivatives either in presence of alkali or a microwave absorbing material, for a period of time effective to allow the carbon-metal nanocomposites to be formed.

  7. FEASIBILITY OF MAGNETIC PARTICLE FILMS FOR CURIE TEMPERATURE-CONTROLLED PROCESSING OF COMPOSITE MATERIALS

    EPA Science Inventory

    The feasibility of using magnetic particulate susceptor materials for induction heating during bonding of polymer matrix composite materials is investigated. If properly designed, these systems should rapidly heat to the particulate material Curie temperature and dwell at that te...

  8. Hot accretion flow with ordered magnetic field, outflow, and saturated conduction

    NASA Astrophysics Data System (ADS)

    Faghei, Kazem

    2013-05-01

    The importance of thermal conduction on hot accretion flow is confirmed by observations of hot gas that surrounds Sgr A∗ and a few other nearby galactic nuclei. On the other hand, the existence of outflow in accretion flows is confirmed by observations and magnetohydrodynamic (MHD) simulations. In this research, we study the influence of both thermal conduction and outflow on hot accretion flows with ordered magnetic field. Since the inner regions of hot accretion flows are, in many cases, collisionless with an electron mean free path due to Coulomb collision larger than the radius, we use a saturated form of thermal conduction, as is appropriate for weakly collisional systems. We also consider the influence of outflow on accretion flow as a sink for mass, and the radial and the angular momentum, and energy taken away from or deposited into the inflow by outflow. The magnetic field is assumed to have a toroidal component and a vertical component as well as a stochastic component. We use a radially self-similar method to solve the integrated equations that govern the behavior of such accretion flows. The solutions show that with an ordered magnetic field, both the surface density and the sound speed decrease, while the radial and angular velocities increase. We found that a hot accretion flow with thermal conduction rotates more quickly and accretes more slowly than that without thermal conduction. Moreover, thermal conduction reduces the influences of the ordered magnetic field on the angular velocities and the sound speed. The study of this model with the magnitude of outflow parameters implies that the gas temperature decreases due to mass, angular momentum, and energy loss. This property of outflow decreases for high thermal conduction.

  9. Magnetic behavior of Joule-heated magnetic core-shell nanowires with positive magnetostrictive core material

    NASA Astrophysics Data System (ADS)

    Dumitru, Ioan; Astefanoaei, Iordana; Cimpoesu, Dorin; Stancu, Alexandru

    2015-10-01

    Temperature field is an important parameter to be known and controlled in the magnetization process of the core-shell nanowires. The paper analyzes the temperature dependence of hysteretic process in a core-shell nanowire subjected to a dc Joule heating process. An electrical current that passes through the wire induces a temperature and a thermal stress field in the system. Spatial and temporal evolution of the temperature in system was analyzed using a model based on time-dependent heat conduction equation. The stresses determined by thermal gradients and different expansion characteristics of core and shell materials were computed. The temperature and stress depend on the size parameters of the system, dc Joule current and the initial temperature of the system. The magnetic behavior of the nanowire was analyzed using the Micromag application. The magnetic state of the core is influenced by the temperature field induced by a dc current applied to the system. For core materials with positive magnetostriction coefficient the coercive field increases at the increase of dc current intensity passed through the system.

  10. Strong correlations between vacancy and magnetic ordering in superconducting K0.8Fe2 -ySe2

    NASA Astrophysics Data System (ADS)

    Yang, J.; Duan, C.; Huang, Q.; Brown, C.; Neuefeind, J.; Louca, Despina

    2016-07-01

    The coexistence of magnetic and nonmagnetic phases in the superconducting potassium iron selenide, KxFe2 -ySe2 , has been intensely debated. With superconductivity proposed to appear in a stoichiometric, nonmagnetic phase with I4/mmm crystal symmetry, the proposed nonsuperconducting phase is magnetic and has a lower symmetry, I4/m. The latter consists of Fe vacancies that go through a disordered-to-ordered transition in which the partially filled Fe sites create a supercell upon ordering. We show, using neutron scattering on the optimally doped composition, K0.8Fe2 -ySe2 , that the absence of magnetism does not signal the presence of superconductivity. Moreover, the degree of vacancy order is coupled to the strength of the magnetic order. Superconductivity coincides with the presence of the magnetic order parameter, albeit the latter is significantly weaker than previously reported, contradicting the current understanding of this ˜30 K superconductor.

  11. Exploring high temperature magnetic order in CeTi1-xScxGe

    NASA Astrophysics Data System (ADS)

    Sereni, J. G.; Pedrazzini, P.; Gómez Berisso, M.; Chacoma, A.; Encina, S.; Gruner, T.; Caroca-Canales, N.; Geibel, C.

    2015-03-01

    We studied the magnetic, transport, and thermodynamic properties of the alloy CeTi1-xScxGe in order to shed some light into the origin of the exceptionally large antiferromagnetic (AFM) ordering temperature TN = 47 K in pure CeScGe. We observed a complex magnetic phase diagram, which present an interesting dichotomy: Despite strong changes in the nature of the ordered state, from ferromagnetic (FM) for x <= 0.55 to AFM for x > 0.55, the ordering temperature increases smoothly and continuously from TC = 7 K at x = 0.25 to TN = 47 K at x = 1. Within the AFM regime we observe a metamagnetic transition at a critical field increasing from H = 0 at x ≈ 0.55 to μ0 * H ≈ 6 Tesla at x = 1. Furthermore a second transition appears at TL <= TN for x >= 0.65. In contrast to observations in CeRh2Si2 or CeRh3B2, we found no evidence for a strong hybridization of the 4f electrons at large Sc contents. Therefore the exceptionally large TN of CeScGe could be attributed to the unusually strong RKKY interaction in this type of compounds.

  12. Structure determination of CoPt nanoparticles: Chemical ordering and its effect on magnetic properties

    NASA Astrophysics Data System (ADS)

    Blanc, Nils; Bardotti, Laurent; Hillenkamp, Matthias; Tamion, Alexandre; Tournus, Florent; Tuaillon-Combes, Juliette; Dupuis, Veronique; Bonet, Edgar; Tolentino, Helio; Ramos, Aline; de Santis, Maurizio; Ohresser, Philippe; Epicier, Thierry

    2009-03-01

    Due to the huge magnetocrystalline anisotropy of bulk CoPt crystallized in the L10 phase, CoPt nanoparticles have been widely studied during the last decade. In order to determine the intrinsic magnetic properties of CoPt clusters, we synthesize benchmark samples: 3 nm diameter CoPt clusters, pre-formed in the gas phase, are embedded in an amorphous carbon matrix under UHV conditions. The transition from the chemically disordered A1 to the ordered L10 phase is then obtained by annealing. Chemical ordering has clearly been evidenced by different techniques (HRTEM, GIXRD). In the case of nanoparticles, this phase transition goes with a magnetic anisotropy increase much lower than for the bulk. Besides, XMCD measurements have revealed a μL/μS increase for Co and Pt atoms and a strong μS enhancement for Co upon L10 ordering. F. Tournus et al. Phys. Rev. B 77, 144411 (2008) Thanks are due to the CLYM (Centre Lyonnais de Microscope) for the access to the tranmission electron microscope

  13. Cryogenic considerations for superconducting magnet design for the material plasma exposure experiment

    NASA Astrophysics Data System (ADS)

    Duckworth, R. C.; Demko, J. A.; Lumsdaine, A.; Rapp, J.; Bjorholm, T.; Goulding, R. H.; Caughman, J. B. O.; McGinnis, W. D.

    2015-12-01

    In order to determine long term performance of plasma facing components such as diverters and first walls for fusion devices, next generation plasma generators are needed. A Material Plasma Exposure eXperiment (MPEX) has been proposed to address this need through the generation of plasmas in front of the target with electron temperatures of 1-15 eV and electron densities of 1020 to 1021 m-3. Heat fluxes on target diverters could reach 20 MW/m2. To generate this plasma, a unique radio frequency helicon source and heating of electrons and ions through Electron Bernstein Wave (EBW) and Ion Cyclotron Resonance Heating (ICRH) has been proposed. MPEX requires a series of magnets with non-uniform central fields up to 2 T over a 5-m length in the heating and transport region and 1 T uniform central field over a 1-m length on a diameter of 1.3 m. Given the field requirements, superconducting magnets are under consideration for MPEX. In order to determine the best construction method for the magnets, the cryogenic refrigeration has been analyzed with respect to cooldown and operational performance criteria for open-cycle and closed-cycle systems, capital and operating costs of these system, and maturity of supporting technology such as cryocoolers. These systems will be compared within the context of commercially available magnet constructions to determine the most economical method for MPEX operation. The current state of the MPEX magnet design including details on possible superconducting magnet configurations is presented.

  14. Ferromagnetic ordering in CeIr2B2: Transport, magnetization, specific heat, and NMR studies

    NASA Astrophysics Data System (ADS)

    Prasad, A.; Anand, V. K.; Paramanik, U. B.; Hossain, Z.; Sarkar, R.; Oeschler, N.; Baenitz, M.; Geibel, C.

    2012-07-01

    We present a complete characterization of the ferromagnetic system CeIr2B2 using powder x-ray diffraction (XRD), magnetic susceptibility χ(T), isothermal magnetization M(H), specific heat C(T), electrical resistivity ρ(T,H), and thermoelectric power S(T) measurements. Furthermore, 11B NMR study was performed to probe the magnetism on a microscopic scale. Rietveld refinement of powder XRD data confirms that CeIr2B2 crystallizes in CaRh2B2-type orthorhombic structure (space group fddd). The χ(T), C(T), and ρ(T) data confirm bulk ferromagnetic ordering with Tc=5.1 K. Ce ions in CeIr2B2 are in a stable trivalent state. Our low-temperature C(T) data measured down to 0.4 K yield a Sommerfeld coefficient γ = 73(4) mJ/mol K2, which is much smaller than the previously reported value of γ = 180 mJ/mol K2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2, γ = 6(1) mJ/mol K2, which implies the density of states at the Fermi level D(EF)=2.54 states/(eV f.u.) for both spin directions. The renormalization factor for quasiparticle density of states and hence for quasiparticle mass due to 4f correlations in CeIr2B2 is ≈12. The Kondo temperature TK˜4 K is estimated from the jump in specific heat of CeIr2B2 at Tc. Both C(T) and ρ(T) data exhibit a gapped-magnon behavior in the magnetically ordered state with an energy gap Eg˜3.5 K. The ρ data as a function of magnetic field H indicate a large negative magnetoresistance (MR) which is highest for T=5 K. While at 5 K the negative MR keeps on increasing up to 10 T, at 2 K an upturn is observed near H=3.5 T. On the other hand, the thermoelectric power data have small absolute values (S˜7μV/K), indicating a weak Kondo interaction. A shoulder in S(T) at about 30 K, followed by a minimum at ˜10 K, is attributed to crystal electric field effects and the onset of magnetic ordering. 11B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.

  15. Stimuli-responsive hybrid materials: breathing in magnetic layered double hydroxides induced by a thermoresponsive molecule

    DOE PAGESBeta

    Abellán, Gonzalo; Jordá, Jose Luis; Atienzar, Pedro; Varela, María; Jaafar, Miriam; Gómez-Herrero, Julio; Zamora, Félix; Ribera, Antonio; García, Hermenegildo; Coronado, Eugenio

    2014-12-04

    In this study, a hybrid magnetic multilayer material of micrometric size, with highly crystalline hexagonal crystals consisting of CoAl–LDH ferromagnetic layers intercalated with thermoresponsive 4-(4 anilinophenylazo)benzenesulfonate (AO5) molecules diluted (ratio 9 : 1) with a flexible sodium dodecylsulphate (SDS) surfactant has been obtained. The resulting material exhibits thermochromism attributable to the isomerization between the azo (prevalent at room temperature) and the hydrazone (favoured at higher temperatures) tautomers, leading to a thermomechanical response. In fact, these crystals exhibited thermally induced motion triggering remarkable changes in the crystal morphology and volume. In situ variable temperature XRD of these thin hybrids shows thatmore » the reversible change into the two tautomers is reflected in a shift of the position of the diffraction peaks at high temperatures towards lower interlayer spacing for the hydrazone form, as well as a broadening of the peaks reflecting lower crystallinity and ordering due to non-uniform spacing between the layers. These structural variations between room temperature (basal spacing (BS) = 25.91 Å) and 100 °C (BS = 25.05 Å) are also reflected in the magnetic properties of the layered double hydroxide (LDH) due to the variation of the magnetic coupling between the layers. Finally and in conclusion, our study constitutes one of the few examples showing fully reversible thermo-responsive breathing in a 2D hybrid material. In addition, the magnetic response of the hybrid can be modulated due to the thermotropism of the organic component that, by influencing the distance and in-plane correlation of the inorganic LDH, modulates the magnetism of the CoAl–LDH sheets in a certain range.« less

  16. Stimuli-responsive hybrid materials: breathing in magnetic layered double hydroxides induced by a thermoresponsive molecule

    SciTech Connect

    Abellán, Gonzalo; Jordá, Jose Luis; Atienzar, Pedro; Varela, María; Jaafar, Miriam; Gómez-Herrero, Julio; Zamora, Félix; Ribera, Antonio; García, Hermenegildo; Coronado, Eugenio

    2014-12-04

    In this study, a hybrid magnetic multilayer material of micrometric size, with highly crystalline hexagonal crystals consisting of CoAl–LDH ferromagnetic layers intercalated with thermoresponsive 4-(4 anilinophenylazo)benzenesulfonate (AO5) molecules diluted (ratio 9 : 1) with a flexible sodium dodecylsulphate (SDS) surfactant has been obtained. The resulting material exhibits thermochromism attributable to the isomerization between the azo (prevalent at room temperature) and the hydrazone (favoured at higher temperatures) tautomers, leading to a thermomechanical response. In fact, these crystals exhibited thermally induced motion triggering remarkable changes in the crystal morphology and volume. In situ variable temperature XRD of these thin hybrids shows that the reversible change into the two tautomers is reflected in a shift of the position of the diffraction peaks at high temperatures towards lower interlayer spacing for the hydrazone form, as well as a broadening of the peaks reflecting lower crystallinity and ordering due to non-uniform spacing between the layers. These structural variations between room temperature (basal spacing (BS) = 25.91 Å) and 100 °C (BS = 25.05 Å) are also reflected in the magnetic properties of the layered double hydroxide (LDH) due to the variation of the magnetic coupling between the layers. Finally and in conclusion, our study constitutes one of the few examples showing fully reversible thermo-responsive breathing in a 2D hybrid material. In addition, the magnetic response of the hybrid can be modulated due to the thermotropism of the organic component that, by influencing the distance and in-plane correlation of the inorganic LDH, modulates the magnetism of the CoAl–LDH sheets in a certain range.

  17. Helical states with ordered magnetic topology in the Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Bonfiglio, D.; Cappello, S.; Gobbin, M.; Spizzo, G.

    2008-11-01

    The reversed field pinch (RFP) configuration for magnetic confinement has shown to develop helical configurations characterized by good magnetic surfaces both in experiments and visco-resistive 3D MHD numerical computations [1]. In the RFX-mod experiment, quasi-single helicity (QSH) states with ordered magnetic topology have been found to develop both spontaneously during high current discharges [2] and in a stimulated way through the periodic oscillation of the toroidal flux (so-called OPCD technique) [3]. In both cases, the expulsion of the separatrix of the dominant mode has proved to be the key for significant chaos healing [4], as expected by theory [5]. In this work, we present results of visco-resistive 3D MHD numerical modeling aiming at clarifying the mechanism and the conditions for separatrix expulsion and chaos healing in spontaneous and stimulated cases. The effect is investigated by reconstruction of the magnetic topology through field line tracing algorithms and by study of test particle dynamics. [1] S. Cappello, Plasma Phys. Control. Fusion 46, B313 (2004) & references therein. [2] M. Valisa et al., invited oral, EPS Conf. on Plasma Physics (2008). [3] D. Terranova et al., Phys. Rev. Lett. 99, 095001 (2007). [4] R. Lorenzini et al., Phys. Rev. Lett. 101, 025005 (2008). [5] D. F. Escande, R. Paccagnella et al., Phys. Rev. Lett. 85, 3169 (2000).

  18. Size-tuned Highly-ordered Magnetic Nanodot Arrays via ALD-Assisted Block Copolymer Nanolithography

    NASA Astrophysics Data System (ADS)

    Polisetty, Srinivas; Lin, Chun-Hao; Gladfelter, Wayne L.; Hillmyer, Marc H.; Leighton, Chris

    2014-03-01

    Block copolymer nanolithography of large-area well-ordered magnetic nanostructures is now possible via a variety of approaches and holds considerable appeal for fundamental science and for bit patterned recording media. Here, we demonstrate a non-lift-off damascene-type approach combined with low temperature atomic layer deposition (ALD) of a conformal ZnO layer to provide size-controlled magnetic nanodots. Perpendicularly-aligned nonporous templates were achieved by solvent annealing polystyrene- b-polylactide (PS-PLA) films. Low temperature ALD was then used to conformally coat the template with a ZnO layer of variable thickness to systematically reduce the pore diameter. Our damascene-type non-lift-off process was then used to synthesize Ni80Fe20 dot arrays from such templates, achieving tunable dot diameters (6-30 nm) and controlled dot height (by Ar milling time). Magnetic measurements were used as a probe of island volume, good agreement being obtained between simple calculations, imaging, and blocking temperature measurements. The results demonstrate a simple route to size control from a fixed polymer template, enabling detailed studies of separation-dependent inter-dot magnetic interactions for example. This work was supported primarily by the NSF through the University of Minnesota MRSEC under Award Number DMR-0819885.

  19. Convergence of an analytic bond-order potential for collinear magnetism in Fe

    NASA Astrophysics Data System (ADS)

    Ford, Michael E.; Drautz, Ralf; Hammerschmidt, Thomas; Pettifor, D. G.

    2014-04-01

    Analytic bond-order potentials (BOPs) for magnetic transition metals are applied for pure iron as described by an orthogonal d-valent tight-binding (TB) model. Explicit analytic equations for the gradients of the binding energy with respect to the Hamiltonian on-site levels are presented, and are then used to minimize the energy with respect to the magnetic moments, which is equivalent to a TB self-consistency scheme. These gradients are also used to calculate the exact forces, consistent with the energy, necessary for efficient relaxations and molecular dynamics. The Jackson kernel is used to remove unphysical negative densities of states, and approximations for the asymptotic recursion coefficients are examined. BOP, TB and density functional theory results are compared for a range of bulk and defect magnetic structures. The BOP energies and magnetic moments for bulk structures are shown to converge with increasing numbers of moments, with nine moments sufficient for a quantitative comparison of structural energy differences. The formation energies of simple defects such as the monovacancies and divacancies also converge rapidly. Other physical quantities, such as the position of the high-spin to low-spin transition in ferromagnetic fcc (face centred cubic) iron, surface peaks in the local density of states, the elastic constants and the formation energies of the self-interstitial atom defects, require higher moments for convergence.

  20. Atomic-Scale Imaging and Control of Interface Magnetic States in Vacancy Ordered Cobaltite Thin Films

    NASA Astrophysics Data System (ADS)

    Borisevich, Albina; Kim, Young-Min; Biegalski, Michael; He, Jun; Christen, Hans; Pantelides, Sokrates; Pennycook, Stephen

    2012-02-01

    Magnetic properties of complex oxide thin films are strongly affected by strain, chemical composition, and octahedral tilt of the substrate. Here, we study lanthanum/strontium cobaltite (La0.5Sr0.5CoO3-x, LSCO) thin films via quantitative aberration-corrected scanning transmission electron microscopy and Electron Energy Loss Spectroscopy (EELS) to explore the coupling between magnetic properties, ionic behavior, and oxygen octahedral tilts. LSCO films were grown by PLD in identical conditions on two different substrates, LSAT (cubic) and NGO (orthorhombic). These substrates have nearly identical lattice parameters, but different octahedral tilts. The film on NGO appears to be La0.5Sr0.5CoO2.5, while the film on LSAT is less oxygen deficient. Comparison of measured lattice parameters with the first-principles calculations allows us to determine oxygen content in the film. In La0.5Sr0.5CoO2.5/NGO films, EELS reveals different valence states of Co at the interface depending on termination, resulting in different magnetic states. Therefore changes in octahedral tilts can induce changes in oxygen stoichiometry and interface magnetic states of the vacancy ordered structures.

  1. Magnetic and Non-Magnetic Nanoparticles from a Group of Uniform Materials Based on Organic Salts

    PubMed Central

    Tesfai, Aaron; El-Zahab, Bilal; Kelley, Algernon T.; Li, Min; Garno, Jayne C.; Baker, Gary A.; Warner, Isiah M.

    2009-01-01

    The size and uniformity of magnetic nanoparticles developed from a Group of Uniform Materials Based on Organic Salts (GUMBOS) were controlled using an in situ ion exchange, water-in-oil (w/o) microemulsion preparation. Most of these nanoGUMBOS are in fact ionic liquids (i.e., melting points less than 100 °C), while others have melting points above the conventional 100 °C demarcation. Simple variations in the reagent concentrations following a w/o approach allowed us to smoothly and predictably vary nanoparticle dimensions across a significant size regime with excellent uniformity. Average sizes of GUMBOS ranging from 14 to 198 nm were achieved by manipulation of the reagent concentration for example. Controllable formation of this new breed of nanoparticles is important for numerous potential applications and will open up interesting new opportunities in drug delivery, magnetic resonance imaging, and protein separations, among other areas. PMID:19780529

  2. Atomic and magnetic order in the shape memory alloy Mn2NiGa

    NASA Astrophysics Data System (ADS)

    Brown, P. J.; Kanomata, T.; Neumann, K.; Neumann, K. U.; Ouladdiaf, B.; Sheikh, A.; Ziebeck, K. R. A.

    2010-12-01

    Magnetization and high resolution neutron powder diffraction measurements on the magnetic shape memory alloy Mn2NiGa have confirmed that it is ferromagnetic with a Curie temperature above 500 K. The compound undergoes a broad structural phase transformation ΔT ~ 90 K with a mean transition temperature TM ~ 270 K. The high temperature parent phase is cubic (a = 5.937 Å) and has a modified L 21 structure. At 500 K the ordered magnetic moment essentially all on the 4a site is 1.35 μB/Mn. The low temperature martensite has space group I4/mmm and is related to the cubic phase through a Bain transformation atet = (acub + bcub)/2, btet = (acub - bcub) and ctet = ccub in which the change in cell volume is < 2.6%. In this structure at 5 K the ordered moment of ≈2.3 μB is again found to be confined to the sites with full Mn occupation and is aligned parallel to c. Neutron diffraction patterns obtained at 5 K suggested the presence of a weak incommensurate antiferromagnetic phase characterized by either a (\\frac 13 0 \\frac 13) or (0 0 \\frac 13) propagation vector.

  3. Magnetically aligned phospholipid bilayers with positive ordering: a new model membrane system.

    PubMed

    Prosser, R S; Hwang, J S; Vold, R R

    1998-05-01

    A stable smectic phospholipid bilayer phase aligned with the director parallel to the magnetic field can be generated by the addition of certain trivalent paramagnetic lanthanide ions to a bicellar solution of dimyristoylphosphatidylcholine (DMPC) and dihexanoylphosphatidylcholine (DHPC) in water. Suitable lanthanide ions are those with positive anisotropy of their magnetic susceptibility, namely Eu3+, Er3+, Tm3+, and Yb3+. For samples doped with Tm3+, this phase extends over a wide range of Tm3+ concentrations (6-40 mM) and temperatures (35-90 degrees C) and appears to undergo a transition from a fluid nematic discotic to a fluid, but highly ordered, smectic phase at a temperature that depends on the thulium concentration. As a membrane mimetic, these new, positively ordered phospholipid phases have high potential for structural studies using a variety of techniques such as magnetic resonance (EMR and NMR), small-angle x-ray and neutron diffraction, as well as optical and infrared spectroscopy. PMID:9591667

  4. Hydrogen-mediated long-range magnetic ordering in Pd-rich alloy film

    SciTech Connect

    Lin, Wen-Chin Tsai, Cheng-Jui; Huang, Han-Yuan; Mudinepalli, Venkata Ramana; Chiu, Hsiang-Chih; Wang, Bo-Yao

    2015-01-05

    The effect of hydrogenation on a 14 nm Co{sub 14}Pd{sub 86}/Al{sub 2}O{sub 3}(0001) thin film was investigated on the basis of the magnetooptical Kerr effect. After exposure to H{sub 2} gas, the squareness of the hysteresis loop showed a large transition from approximately 10% to 100% and the saturation Kerr signal was reduced to nearly 30% of the pristine value. The reversibility of the transition was verified and the response time was within 2–3 s. These observations indicate that the hydride formation transformed the short-range coupled and disordered magnetic state of the Co{sub 14}Pd{sub 86} film to a long-range-ordered ferromagnetic state and induced appreciable decrease in the magnetic moment. The enhanced long-range-ordering and the reduction of the magnetic moment were attributed to the change of electronic structure in Co{sub 14}Pd{sub 86} with hydrogen uptake.

  5. Magnetic Order in TbCo2Zn20 and TbFe2Zn20

    SciTech Connect

    Tian, W.; Christianson, Andrew D; Zarestky, J. L.; Jia, S.; Bud'ko, S. L.; Canfield, P. C.; Piccoli, P. M. B.; Schultz, A. J.

    2010-01-01

    We report neutron di raction studies of TbCo2Zn20 and TbFe2Zn20, two isostructural compounds which exhibit dramatically di erent magnetic behavior. In the case of TbCo2Zn20, magnetic Bragg peaks corresponding to antiferromagnetic order are observed below TN 2.5 K with a propagation vector of (0.5 0.5 0.5). On the other hand, TbFe2Zn20 undergoes a ferromagnetic transition at temperatures as high as 66 K which shows a high sensitivity to sample-to-sample variations. Two samples of TbFe2Zn20 with the same nominal compositions but with substantially di erent mag- netic ordering temperatures (Tc 51 and 66 K) were measured by single crystal neutron di raction. Structural re nements of the neutron di raction data nd no direct signature of atomic site disorder between the two TbFe2Zn20 samples except for subtle di erences in the anisotropic thermal param- eters. The di erences in the anisotropic thermal parameters between the two samples is likely due to very small amounts of disorder. This provides further evidence for the extreme sensitivity of the magnetic properties of TbFe2Zn20 to small sample variations, even small amounts of disorder.

  6. Correlation Between Domain Behavior and Magnetic Properties of Materials

    SciTech Connect

    Jeffrey Scott Leib

    2003-05-31

    Correlation between length scales in the field of magnetism has long been a topic of intensive study. The long-term desire is simple: to determine one theory that completely describes the magnetic behavior of matter from an individual atomic particle all the way up to large masses of material. One key piece to this puzzle is connecting the behavior of a material's domains on the nanometer scale with the magnetic properties of an entire large sample or device on the centimeter scale. In the first case study involving the FeSiAl thin films, contrast and spacing of domain patterns are clearly related to microstructure and stress. Case study 2 most clearly demonstrates localized, incoherent domain wall motion switching with field applied along an easy axis for a square hysteresis loop. In case study 3, axis-specific images of the complex Gd-Si-Ge material clearly show the influence of uniaxial anisotropy. Case study 4, the only study with the sole intent of creating domain structures for imaging, also demonstrated in fairly simple terms the effects of increasing stress on domain patterns. In case study 5, it was proven that the width of magnetoresistance loops could be quantitatively predicted using only MFM. When all of the case studies are considered together, a dominating factor seems to be that of anisotropy, both magneticrostaylline and stress induced. Any quantitative bulk measurements heavily reliant on K coefficients, such as the saturation fields for the FeSiAl films, H{sub c} in cases 1, 3, and 5, and the uniaxial character of the Gd{sub 5}(Si{sub 2}Ge{sub 2}), transferred to and from the domain scale quite well. In-situ measurements of domain rotation and switching, could also be strongly correlated with bulk magnetic properties, including coercivity, M{sub s}, and hysteresis loop shape. In most cases, the qualitative nature of the domain structures, when properly considered, matched quite well to what might have been expected from theory and calculation

  7. Effect of rare earth dopants on the magnetic ordering of frustrated h-YMnO3

    NASA Astrophysics Data System (ADS)

    Sharma, Neetika; Das, A.; Prajapat, C. L.; Singh, M. R.

    2016-12-01

    In this report the combined effects of chemical pressure and R-Mn interaction on the structural and magnetic properties of frustrated h-YMnO3 have been investigated. Towards this, neutron powder diffraction and magnetization measurements were carried out on isostructural compounds Y1-xRxMnO3(R=Yb, Er, Tb, Ho; x≤0.2) with hexagonal structure (P63cm space group). The dopants are evenly distributed between the two Yttrium sites. The unit cell volume shows a linear increase with average A-site ionic radii, . The average apical a and planar p bond lengths are found to increase with . The tilting angle of the MnO5 polyhedron decreases linearly with increase in , whereas the buckling angle remains constant. No significant change in TN (within 10 K) is observed on doping. The temperature variation of the volume indicates an anomalous reduction in volume at TN which is found to be correlated with the square of the antiferromagnetic Mn moment. A spin reorientation behavior (evident from a change in the irreducible representation (IR) Γ3 to Γ4) is observed on decreasing from 1.019 Å (Y) to 1.012 Å (Yb) similar to that reported in external pressure studies on YMnO3. Additional interaction between the doped R and Mn influences the magnetic structure in the case of Ho and Tb doped samples. With Ho doping at Y site, the magnetic structure is described by IR Γ3 alone for 5 K≤T<35 K and a mixture of Γ3 and Γ4 for T≥35 K. However, in Tb doped sample, the magnetic structure is better described by Γ4Tb,Mn IR with additional moment on Tb. The frustration parameter, f reduces from 6 to 1 in the doped samples. A combination of chemical pressure effect and magnetic coupling between the magnetic R ion and Mn moments thus describes the magnetic structures and relieves the frustration effects inherent to the quasi-two dimensional Mn moment ordering.

  8. Soft Magnetic Materials in High-Frequency, High-Power Conversion Applications

    NASA Astrophysics Data System (ADS)

    Leary, Alex M.; Ohodnicki, Paul R.; McHenry, Michael E.

    2012-07-01

    Advanced soft magnetic materials are needed to match high-power density and switching frequencies made possible by advances in wide band-gap semiconductors. Magnetics capable of operating at higher operating frequencies have the potential to greatly reduce the size of megawatt level power electronics. In this article, we examine the role of soft magnetic materials in high-frequency power applications and we discuss current material's limitations and highlight emerging trends in soft magnetic material design for high-frequency and power applications using the materials paradigm of synthesis → structure → property → performance relationships.

  9. Soft Magnetic Materials in High-Frequency, High-Power Conversion Applications

    SciTech Connect

    Leary, AM; Ohodnicki, PR; McHenry, ME

    2012-07-04

    Advanced soft magnetic materials are needed to match high-power density and switching frequencies made possible by advances in wide band-gap semiconductors. Magnetics capable of operating at higher operating frequencies have the potential to greatly reduce the size of megawatt level power electronics. In this article, we examine the role of soft magnetic materials in high-frequency power applications and we discuss current material's limitations and highlight emerging trends in soft magnetic material design for high-frequency and power applications using the materials paradigm of synthesis -> structure -> property -> performance relationships.

  10. Magnetic ordering in digital alloys of group-IV semiconductors with 3d-transition metals

    SciTech Connect

    Otrokov, M. M.; Tugushev, V. V.; Ernst, A.; Ostanin, S. A.; Kuznetsov, V. M.; Chulkov, E. V.

    2011-04-15

    The ab initio investigation of the magnetic ordering in digital alloys consisting of monolayers of 3d-transition metals Ti, V, Cr, Mn, Fe, Co, and Ni introduced into the Si, Ge, and Si{sub 0.5}Ge{sub 0.5} semiconductor hosts is reported. The calculations of the parameters of the exchange interactions and total-energy calculations indicate that the ferromagnetic order appears only in the manganese monolayers, whereas the antiferromagnetic order is more probable in V, Cr, and Fe monolayers, and Ti, Co, and Ni monolayers are nonmagnetic. The stability of the ferromagnetic phase in digital alloys containing manganese monolayers has been analyzed using the calculations of magnon spectra.

  11. Method and apparatus for separating materials magnetically. [Patent application; iron pyrite from coal

    DOEpatents

    Hise, E.C. Jr.; Holman, A.S.; Friedlaender, F.J.

    1980-11-06

    Magnetic and nonmagnetic materials are separated by passing stream thereof past coaxial current-carrying coils which produce a magnetic field wherein intensity varies sharply with distance radially of the axis of the coils.

  12. Composite Materials with Magnetically Aligned Carbon Nanoparticles Having Enhanced Electrical Properties and Methods of Preparation

    NASA Technical Reports Server (NTRS)

    Hong, Haiping (Inventor); Peterson, G.P. (Bud) (Inventor); Salem, David R. (Inventor)

    2016-01-01

    Magnetically aligned carbon nanoparticle composites have enhanced electrical properties. The composites comprise carbon nanoparticles, a host material, magnetically sensitive nanoparticles and a surfactant. In addition to enhanced electrical properties, the composites can have enhanced mechanical and thermal properties.

  13. Intra-layer Cation Ordering in a Brownmillerite Super- Structure: Synthesis, Crystal and Magnetic Structures of Ca2FeCoO5

    SciTech Connect

    Ramezanipour, Farshid; Greedan, John; Grosvenor, Andrew; Britten, James; Cranswick, Lachlan M.D.; Garlea, Vasile O

    2010-01-01

    The synthesis, crystal and magnetic structures and the bulk magnetic properties of Ca2FeCoO5, a brownmillerite type oxide, are presented. The crystal structure, solved and refined from single crystal x-ray and powder neutron diffraction data, is described in Pbcm with cell parameters, a = 5.3652(3) , b = 11.0995(5) , c = 14.7982(7) . Thus, one axis, b in this setting, is doubled in comparison with the standard brownmillerite structure description giving rise to two sets of octahedral and tetrahedral sites. Aided by the strong scattering contrast between Fe and Co for neutrons, a nearly perfect cation site ordering, unique to this compound, is observed in the tetrahedral layers (which may be implicated in the b-axis doubling). A lesser degree of cation site ordering occurs in the octahedral sites. As well, this material shows an unique arrangement of tetrahedral chains, and a new space group for the brownmillerite family. The magnetic structure is G-type antiferromagnetic, with preferred orientation of magnetic moments parallel to the c-axis between 3.8K to 100K. A spin re-orientation occurs in the range of 100K to 225K, above which and up to 510K the orientation of magnetic moments switches to along the a-axis. This spin re-orientation has not been seen for any brownmillerite material before. The neutron diffraction data indicate different site specific ordering temperatures at about 450(5)K and 520(5)K. The refined ordered moments at 3.8K are somewhat smaller than expected for Fe3+ and Co3+(high spin) but are similar to those found in Sr2FeCoO5. There is evidence for spin canting from isothermal magnetization data that shows well pronounced hysteresis and remnant magnetization at 5K and 200K.

  14. Innovative uses of X-ray FEL and the pulsed magnets: High magnetic field X-ray scattering studies on quantum materials

    NASA Astrophysics Data System (ADS)

    Jang, H.; Nojiri, H.; Gerber, S.; Lee, W.-S.; Zhu, D.; Lee, J.-S.; Kao, C.-C.

    X-ray scattering under high magnetic fields provides unique opportunities for solving many scientific puzzles in quantum materials, such as strongly correlated electron systems. Incorporating high magnetic field capability presents serious challenges at an x-ray facility, including the limitation on the maximum magnetic field even with a DC magnet (up to ~20 Tesla), expensive cost in development, radiation damage, and limited flexibility in the experimental configuration. These challenges are especially important when studying the symmetry broken state induced by the high magnetic field are necessary, for example, exploring intertwined orders between charge density wave (CDW) and high Tc superconductivity. Moreover, a gap in magnetic field strengths has led to many discrepancies and puzzling issues for understanding strongly correlated systems - is a CDW competing or more intimately intertwined with high-temperature superconductivity. To bridge this gap and resolve these experimental discrepancies, one needs an innovative experimental approach. Here, we will present a new approach to x-ray scattering under high magnetic field up to 28 Teals by taking advantage of brilliant x-ray free electron laser (FEL). The FEL generates sufficiently high photon flux for single shot x-ray scattering experiment. In this talk, we will also present the first demonstration about the field induced CDW order in YBCO Ortho-VIII with 28 Tesla, which show the totally unexpected three-dimensional behavior.

  15. Magnetic ordering and spin-reorientation transitions in TbCo{sub 3}B{sub 2}

    SciTech Connect

    Dubman, Moshe; Caspi, El'ad N.; Ettedgui, Hanania; Keller, Lukas; Melamud, Mordechai; Shaked, Hagai

    2005-07-01

    The magnetic structure of the compound TbCo{sub 3}B{sub 2} has been studied in the temperature range 1.5 K{<=}T{<=}300 K by means of neutron powder diffraction, magnetization, magnetic ac susceptibility, and heat capacity measurements. The compound is of hexagonal symmetry and is paramagnetic at 300 K, undergoes a magnetic Co-Co ordering transition at {approx}170 K, and a second magnetic Tb-Tb ordering transition at {approx}30 K. The latter induces a spin-reorientation transition, in which the magnetic axis rotates from the c axis toward the basal plane. Below this transition a symmetry decrease ({gamma} magnetostriction) sets in, leading to an orthorhombic distortion of the crystal lattice. The crystal and magnetic structures and interactions and their evolution with temperature are discussed using a microscopic physical model.

  16. Assessment of creep damage of ferromagnetic material using magnetic inspection

    SciTech Connect

    Chen, Z.J.; Govindaraju, M.R.; Jiles, D.C.; Biner, S.B. Iowa State Univ., Ames, IA . Center for NDE); Sablik, M.J. )

    1994-11-01

    Results of inspection creep damage by magnetic hysteresis measurements on Cr-Mo steel are presented. It is shown that structure sensitive parameters such as coercivity, remanence and hysteresis loss are sensitive to the creep damage. Previous metallographic studies have shown that creep changes the microstructure of the material by introducing voids, dislocations, and grain boundary cavities. As cavities develop, dislocations and voids move out to the grain boundaries; therefore the total pinning sources for domain wall motion are reduced. This, together with the introduction of a demagnetization field due to the cavities, results in the decrease of both coercivity and remanence. Numerical computations with a modified Jiles-Atherton model are presented which are consistent with the proposed mechanisms.

  17. Synthetic magnetic fluxes and topological order in one-dimensional spin systems

    NASA Astrophysics Data System (ADS)

    Graß, Tobias; Muschik, Christine; Celi, Alessio; Chhajlany, Ravindra W.; Lewenstein, Maciej

    2015-06-01

    Engineering topological quantum order has become a major field of physics. Many advances have been made by synthesizing gauge fields in cold atomic systems. Here we carry over these developments to other platforms which are extremely well suited for quantum engineering, namely, trapped ions and nano-trapped atoms. Since these systems are typically one-dimensional, the action of artificial magnetic fields has so far received little attention. However, exploiting the long-range nature of interactions, loops with nonvanishing magnetic fluxes become possible even in one-dimensional settings. This gives rise to intriguing phenomena, such as fractal energy spectra, flat bands with localized edge states, and topological many-body states. We elaborate on a simple scheme for generating the required artificial fluxes by periodically driving an XY spin chain. Concrete estimates demonstrating the experimental feasibility for trapped ions and atoms in wave guides are given.

  18. Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

    NASA Astrophysics Data System (ADS)

    Raut, Suyog A.; Kanhe, Nilesh S.; Bhoraskar, S. V.; Das, A. K.; Mathe, V. L.

    2014-10-01

    Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125-1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.

  19. Bose-Einstein condensation and the magnetically ordered state of TlCuCl3

    NASA Astrophysics Data System (ADS)

    Jensen, Jens; Smith, Henrik

    2009-12-01

    The dimerized S=(1)/(2) spins of the Cu2+ ions in TlCuCl3 are ordered antiferromagnetically in the presence of a field larger than about 54 kOe in the zero-temperature limit. Within the mean-field approximation all thermal effects are frozen out below 6 K. Nevertheless, experiments show significant changes in the critical field and the magnetization below this temperature, which reflect the presence of low-energetic dimer-spin excitations. We calculate the dimer-spin correlation functions within a self-consistent random-phase approximation, using as input the effective exchange-coupling parameters obtained from the measured excitation spectra. The calculated critical field and magnetization curves exhibit the main features of those measured experimentally but differ in important respects from the predictions of simplified boson models.

  20. Magnetic ordering-induced multiferroic behavior in [CH3NH3][Co(HCOO)3] metal-organic framework.

    SciTech Connect

    Gomez-Aguirre, Lilian Claudia; Zapf, Vivien S.; Pato-Doldan, Breogan; Mira, Jorge; Castro-Garcia, Socorro; Senaris-Rodriguez, Maria Antonia; Sanchez-Andujara, Manuel; Singleton, John

    2015-12-30

    Here, we present the first example of magnetic ordering-induced multiferroic behavior in a metal–organic framework magnet. This compound is [CH3NH3][Co(HCOO)3] with a perovskite-like structure. The A-site [CH3NH3]+ cation strongly distorts the framework, allowing anisotropic magnetic and electric behavior and coupling between them to occur. This material is a spin canted antiferromagnet below 15.9 K with a weak ferromagnetic component attributable to Dzyaloshinskii–Moriya (DM) interactions and experiences a discontinuous hysteretic magnetic-field-induced switching along [010] and a more continuous hysteresis along [101]. Coupling between the magnetic and electric order is resolved when the field is applied along this [101]: a spin rearrangement occurs at a critical magnetic field in the ac plane that induces a change in the electric polarization along [101] and [10-1]. The electric polarization exhibits an unusual memory effect, as it remembers the direction of the previous two magnetic-field pulses applied. The data are consistent with an inverse-DM mechanism for multiferroic behavior.