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Sample records for magnetization reversal properties

  1. Dynamics of magnetization reversal

    NASA Astrophysics Data System (ADS)

    Safonov, Vladimir L.

    2000-03-01

    Advanced magnetic recording systems are designed for extremely high areal densities and data rate. These two aspects require both magnetization reversal at very short times (< 1 ns) and long term ( ~ 5-10 years) stability against thermal fluctuations. There are two basic physics problems associated with these requirements. The first is a characterization of thermal-dynamic reversal over very wide time range. The second is an understanding of the physics of the relaxation mechanisms. Both these subjects will be reviewed in this talk. Thermal dynamic reversal requires solution of the Landau-Lifshitz equation with fluctuations. We have solved this problem in terms of the ``random walk" dynamics of a nonlinear oscillator [1,2]. The expressions for the switching field versus pulse time are analytic and show good agreement with measurements on CrO_2. Our studies of fundamental relaxation mechanisms have involved a two step approach. First the results of computer simulations of magnetization reversal without phenomenological damping will be discussed. In this case coherent rotation of the magnetization excites spin waves during which an excess of Zeeman energy is transformed to anisotropy and exchange energies. However, for fine grains whose size is sufficiently small so that the grain magnetization is virtually uniform, non-linear spin waves cannot assist reversal [3]. A new analytic model of reversal that couples coherent rotation to impurity ions by an anisotropic exchange mechanism will be discussed. These impurity ions are assumed to relax at a very high rate to the lattice. [1] V.L.Safonov, JMMM 195, 523 (1999); J.Appl.Phys. 85, 4370 (1999). [2] V.L.Safonov, H.N.Bertram, MMM'99, CU-09. [3] V.L.Safonov, H.N.Bertram, J.Appl.Phys. 85, 5072 (1999); MMM'99, CD-11.

  2. Effect of reversible adsorption on the magnetic properties of iron garnet films

    SciTech Connect

    Zubov, V. E. Kudakov, A. D.; Levshin, N. L.; Vlasov, M. A.

    2013-05-15

    The reversible change in the domain structure and the magnetic domain width in bismuth-containing iron garnet films with an easy magnetization axis oriented normal to their surface during adsorption caused by hydrogen bonds is studied by a magnetooptical method. The dependence of the domain width on the vapor pressure of methyl alcohol or water in a cell with a sample is determined, and the time dependence of the domain width induced by the adsorption-desorption processes occurring between methyl alcohol molecules or water molecules on the film surface is studied. A model is proposed to explain the detected effects.

  3. Effects of strain-induced martensite and its reversion on the magnetic properties of AISI 201 austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Souza Filho, I. R.; Sandim, M. J. R.; Cohen, R.; Nagamine, L. C. C. M.; Hoffmann, J.; Bolmaro, R. E.; Sandim, H. R. Z.

    2016-12-01

    Strain-induced martensite (SIM) and its reversion in a cold-rolled AISI 201 austenitic stainless steel was studied by means of magnetic properties, light optical (LOM) and scanning electron (SEM) microscopy, electron backscatter diffraction (EBSD), texture measurements, and Vickers microhardness testing. According to Thermo-calc© predictions, the BCC phase (residual δ-ferrite and SIM) is expected to be stable until 600 °C. The current material was cold rolled up to 60% thickness reduction and submitted to both isothermal and stepwise annealing up to 800 °C. Magnetic measurements were taken during annealing (in situ) of the samples and also for their post mortem conditions. The Curie temperatures (Tc) of residual δ-ferrite and SIM have similar values between 550 and 600 °C. Besides Tc, the focused magnetic parameters were saturation magnetization (Ms), remanent magnetization (MR), and coercive field (Hc). SIM reversion was found to occur in the range of 600-700 °C in good agreement with Thermo-calc© predictions. The microstructures of the material, annealed at 600 and 700 °C for 1 h, were investigated via EBSD. Microtexture measurements for these samples revealed that the texture components were mainly those found for the 60% cold rolled material. This is an evidence that the SIM reversion occurred by an athermal mechanism.

  4. Structural and magnetic properties of nano nickel zinc ferrite synthesized by reverse micelle technique

    NASA Astrophysics Data System (ADS)

    Thakur, Sangeeta; Katyal, S. C.; Singh, M.

    2009-01-01

    Nanocrystalline nickel-zinc ferrites (Ni 0.58Zn 0.42Fe 2O 4) at different pH values (less than 9.6, 9.6, 10.96, and 11.40) for the alkali-precipitating reaction were synthesized by reverse micelle technique. X-ray diffraction reveals a well-defined nickel-zinc ferrite crystal phase at pH=9.6. Increase in pH value obstructs pure-phase formation and results in partial formation of α-Fe 2O 3. The magnetic behaviour of the samples was studied by superconducting quantum interference device. All the samples show superparamagnetic behaviour at room temperature (300 K) and negligible hysteresis at low temperature (5 K). The low value of saturation magnetization is explained on the basis of spin canting. The high-field irreversibility and shifting of the hysteresis loop detected in single-phase sample has been assigned to a spin-disordered phase, which has a spin-freezing temperature of approximately 42 K and other two samples have an antiferromagnetic phase (α-Fe 2O 3) coupled to the ferromagnetic phase.

  5. Magnetic reversals and mass extinctions

    NASA Technical Reports Server (NTRS)

    Raup, D. M.

    1985-01-01

    The results of a study of reversals of the earth's magnetic field over the past 165 Myr are presented. A stationary periodicity of 30 Myr emerges which predicts pulses of increased reversal activity centered at 10, 40, 70, . . . Myr before the present. The correlation between the reversal intensity and biological extinctions is examined, and a nontrivial discrepancy is found between the magnetic and extinction periodicity.

  6. Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping

    NASA Astrophysics Data System (ADS)

    Gerrits, Th.; van den Berg, H. A. M.; Hohlfeld, J.; Bär, L.; Rasing, Th.

    2002-08-01

    Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200ps, which is ten times faster than the natural damping time constant.

  7. Ancient Magnetic Reversals: Clues to the Geodynamo.

    ERIC Educational Resources Information Center

    Hoffman, Kenneth A.

    1988-01-01

    Discusses the question posed by some that the earth's magnetic field may reverse. States that rocks magnetized by ancient fields may offer clues to the underlying reversal mechanism in the earth's core. (TW)

  8. Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions - IV: the fine structure of self-reversed thermoremanent magnetization

    NASA Astrophysics Data System (ADS)

    Robinson, Peter; McEnroe, S. A.; Fabian, K.; Harrison, R. J.; Thomas, C. I.; Mukai, H.

    2014-03-01

    Magnetic experiments, a Monte Carlo simulation and transmission electron microscopy observations combine to confirm variable chemical phase separation during quench and annealing of metastable ferri-ilmenite compositions, caused by inhomogeneous Fe-Ti ordering and anti-ordering. Separation begins near interfaces between growing ordered and anti-ordered domains, the latter becoming progressively enriched in ilmenite component, moving the Ti-impoverished hematite component into Fe-enriched diffusion waves near the interfaces. Even when disordered regions are eliminated, Fe-enriched waves persist and enlarge on anti-phase boundaries between growing and shrinking ordered and anti-ordered domains. Magnetic results and conceptual models show that magnetic ordering with falling T initiates in the Fe-enriched wave crests. Although representing only a tiny fraction of material, identified at highest Ts on a field-cooling curve, they control the `pre-destiny' of progressive magnetization at lower T. They can provide a positive magnetic moment in a minority of ordered ferrimagnetic material, which, by exchange coupling, then creates a self-reversed negative moment in the remaining majority. Four Ts or T ranges are recognized on typical field-cooling curves: TPD is the T range of `pre-destination'; TC is the predominant Curie T where major positive magnetization increases sharply; TMAX is where magnetization reaches a positive maximum, beyond which it is outweighed by self-reversed magnetization and TZM is the T where total magnetization passes zero. Disposition of these Ts on cooling curves indicate the fine structure of self-reversed thermoremanent magnetization. These results confirm much earlier suspicions that the `x-phase' responsible for self-reversed magnetization resides in Fe-enriched phase boundaries.

  9. Magnetization reversal in europium sulfide nanocrystals

    NASA Astrophysics Data System (ADS)

    Redígolo, Marcela L.; Koktysh, Dmitry S.; Rosenthal, Sandra J.; Dickerson, James H.; Gai, Zheng; Gao, Lan; Shen, Jian

    2006-11-01

    The authors report the observation of the reversal in the magnetization hysteresis curve of europium sulfide nanocrystals. This phenomenon was investigated through the temperature-dependent magnetization of two classes of nanomaterials, nanocrystalline (2.0nm⩽dNCs⩽100nm) and quantum confined (dNCs⩽2.0nm), where dNCs is the diameter of the nanomaterial. The effect of the size of the nanomaterial on the magnetization is attributed to the competition between the magnetic properties of strained surface atoms and unstrained core atoms. Superconducting quantum interference device probed the magnetic response. Electron microscopy and X-ray diffraction spectroscopy revealed the crystallinity and monodispersivity of the nanomaterials.

  10. Magnetization Reversal in Europium Sulfide Nanocrystals

    NASA Astrophysics Data System (ADS)

    Dickerson, James; Redigolo, Marcela; Koktysh, Dmitry; Rosenthal, Sandra; Gai, Zheng; Gao, Lan; Shen, Jian

    2007-03-01

    We report the observation of the reversal in the magnetization hysteresis curve of europium sulfide nanocrystals. This phenomenon was investigated through the temperature-dependent magnetization of two classes of nanomaterials, nanocrystalline (2.0 nm <= dNCs <= 100 nm), and quantum-confined (dNCs <= 2.0 nm), where dNCs is the diameter of the nanomaterial. The effect of the size of the nanomaterial on the magnetization is attributed to the competition between the magnetic properties of strained surface atoms and unstrained core atoms. Superconducting quantum interference device (SQUID) probed the magnetic response. Electron microscopy and X-ray diffraction spectroscopy revealed the crystallinity and monodispersivity of the nanomaterials.

  11. Surfactant modified MgFe 2O 4 nanopowders by reverse micelle processing: Effect of water to surfactant ratio ( R) on the particle size and magnetic property

    NASA Astrophysics Data System (ADS)

    Chandradass, J.; Jadhav, Arvind H.; Kim, Hern

    2012-01-01

    Nanoparticles of surfactant modified MgFe2O4 have been synthesized by reverse micelle processing using tertiary system of heptane/Igepal CO 520/H2O. The effect of water to surfactant ratio on the particle size and magnetic property has been studied. X-ray diffraction analysis confirms that MgFe2O4 nanoparticles are crystalline in nature with cubic spinel structure. The average particle size increases with increase in water to surfactant ratio. The Fourier transform infrared (FTIR) analysis confirms that the surface of MgFe2O4 nanoparticles was coated with surfactants. The saturation magnetization ranged from 14.4 to 40.05 emu/g was measured by Superconducting Quantum Interference Device Magnetometry (SQUID).

  12. Magnetization reversal properties of Pr{sub 1-x}(Gd/Nd){sub x}MnO{sub 3} (x=0.3, 0.5, 0.7)

    SciTech Connect

    Biswas, Sanjay; Pal, Sudipta; Bose, Esa

    2015-06-24

    We report measurements of the temperature dependent magnetic properties of single phase orthorhombic perovskites system associated with space group Pbnm compounds Pr{sub 1-x}(Gd/Nd){sub x}MnO{sub 3} (x=0.3, 0.5, 0.7). Magnetic properties radically changes with the doping of Gd or Nd. A magnetization reversal is observed below the Neel temperature (T{sub N}), in DC magnetization measurements (at 50 Oe) in the doped compounds. The reversal of magnetization may be due to the antiparallel coupling between the two magnetic sublattices (|Pr+ Gd/ Nd | and Mn). The hysteresis plot taken at 50K indicates a ferrimagnetic characteristic and existence of spin canting of ions in the magnetic sublattices.

  13. Magnetic reversals from planetary dynamo waves.

    PubMed

    Sheyko, Andrey; Finlay, Christopher C; Jackson, Andrew

    2016-11-24

    A striking feature of many natural dynamos is their ability to undergo polarity reversals. The best documented example is Earth's magnetic field, which has reversed hundreds of times during its history. The origin of geomagnetic polarity reversals lies in a magnetohydrodynamic process that takes place in Earth's core, but the precise mechanism is debated. The majority of numerical geodynamo simulations that exhibit reversals operate in a regime in which the viscosity of the fluid remains important, and in which the dynamo mechanism primarily involves stretching and twisting of field lines by columnar convection. Here we present an example of another class of reversing-geodynamo model, which operates in a regime of comparatively low viscosity and high magnetic diffusivity. This class does not fit into the paradigm of reversal regimes that are dictated by the value of the local Rossby number (the ratio of advection to Coriolis force). Instead, stretching of the magnetic field by a strong shear in the east-west flow near the imaginary cylinder just touching the inner core and parallel to the axis of rotation is crucial to the reversal mechanism in our models, which involves a process akin to kinematic dynamo waves. Because our results are relevant in a regime of low viscosity and high magnetic diffusivity, and with geophysically appropriate boundary conditions, this form of dynamo wave may also be involved in geomagnetic reversals.

  14. Magnetization reversal in cobalt-phosphorus films

    NASA Astrophysics Data System (ADS)

    Hughes, Gordon F.

    1983-09-01

    A brief review is given of preparation, structure, and magnetization reversal in Co-P thin films for digital recording. From this, a magnetization reversal theory is developed which correctly predicts a number of observed facts about Co-P. Among these are &mA0.1 (conventional theory predicts 0.64 and 0.51, respectively), avalanche and cluster reversal mechanisms, transverse ripple, and sawtooth structure in recorded bits. Limitations to high bit and track density recording are discussed. It is suggested that lower Mr/Ms remanent squareness values may alleviate these density limiting mechanisms.

  15. Anomalous spontaneous reversal in magnetic heterostructures.

    PubMed

    Li, Zhi-Pan; Eisenmenger, Johannes; Miller, Casey W; Schuller, Ivan K

    2006-04-07

    We observe a thermally induced spontaneous magnetization reversal of epitaxial ferromagnet/antiferromagnet heterostructures under a constant applied magnetic field. Unlike any other magnetic system, the magnetization spontaneously reverses, aligning antiparallel to an applied field with decreasing temperature. We show that this unusual phenomenon is caused by the interfacial antiferromagnetic coupling overcoming the Zeeman energy of the ferromagnet. A significant temperature hysteresis exists, whose height and width can be tuned by the field applied during thermal cycling. The hysteresis originates from the intrinsic magnetic anisotropy in the system. The observation of this phenomenon leads to open questions in the general understanding of magnetic heterostructures. Moreover, this shows that in general heterogeneous nanostructured materials may exhibit unexpected phenomena absent in the bulk.

  16. A magnetic force microscopy study of the magnetic reversal of a single Fe nanowire.

    PubMed

    Wang, T; Wang, Y; Fu, Y; Hasegawa, T; Li, F S; Saito, H; Ishio, S

    2009-03-11

    The magnetization reversal properties of a single 60 nm diameter Fe nanowire were investigated with an in-field magnetic force microscope (MFM). MFM images were observed in a successively decreasing applied field, at various angles between the applied field and the nanowire axis. The results show that the magnetization undergoes a sharp reversal at various angles. When the applied field deviates from the nanowire axis, before complete magnetization reversal, a coherent rotation of magnetic moments inside the nanowire and a stable vortex state at the end of the nanowire are exhibited. The angle dependence of the switching field can be closely described by a curling model, despite the fact the magnetization reversal process is not identical to this model.

  17. Magnetization reversal of patterned disks with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Xiao, Zhuyun; Wang, Xiao; Cheng, X. M.; Liu, Yaohua; Te Velthuis, Suzanne; Rosenmann, Daniel; Divan, Ralu

    2013-03-01

    Magnetic vortex dynamics in magnetic disks have been extensively studied. However, spin dynamics in magnetic disks with perpendicular magnetic anisotropy (PMA) still remain to be fully understood. Magnetic configurations in disks with strong PMA are more complicated than magnetic vortices, resulting in novel spin dynamics with potential applications. In this work, we study the magnetization reversal of Co/Pd multilayered disks with PMA. Magnetic disks (3-8 microns in diameter) with the structure of [Co (0.3 nm)/Pd (0.5 nm)]5/Co(0.3nm) were patterned on Si substrates via direct laser writing lithography, electron beam evaporation, and lift-off methods. A Kerr microscope was used to image magnetization reversal processes at various bias fields. The imaging results revealed a nucleation dominated magnetization reversal process with the growth of dendritic domains. The coercivity of the disks is significantly bigger than that of thin films with the same structure. Quantitative analysis of the real time Kerr imaging results shed light on the magnetization reversal mechanism of the patterned disks with PMA. Work at Bryn Mawr is supported by NSF under Grant No. 1053854. Work at Argonne National Laboratory and use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  18. Magnetic stripes and skyrmions with helicity reversals

    PubMed Central

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-01-01

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion—a nano-sized bundle of noncoplanar spins—that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide–M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom—helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure. PMID:22615354

  19. Magnetic stripes and skyrmions with helicity reversals.

    PubMed

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-06-05

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion--a nano-sized bundle of noncoplanar spins--that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide-M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom--helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure.

  20. Magnetization reversal driven by a spin torque oscillator

    SciTech Connect

    Sbiaa, R.

    2014-09-01

    Magnetization reversal of a magnetic free layer under spin transfer torque (STT) effect from a magnetic hard layer with a fixed magnetization direction and an oscillating layer is investigated. By including STT from the oscillating layer with in-plane anisotropy and orthogonal polarizer, magnetization-time dependence of free layer is determined. The results show that the frequency and amplitude of oscillations can be varied by adjusting the current density and magnetic properties. For an optimal oscillation frequency (f{sub opt}), a reduction of the switching time (t{sub 0}) of the free layer is observed. Both f{sub opt} and t{sub 0} increase with the anisotropy field of the free layer.

  1. 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

  2. Incoherent magnetization reversal in 30-nm Ni particles

    NASA Astrophysics Data System (ADS)

    Ross, C. A.; Chantrell, R.; Hwang, M.; Farhoud, M.; Savas, T. A.; Hao, Y.; Smith, Henry I.; Ross, F. M.; Redjdal, M.; Humphrey, F. B.

    2000-12-01

    The magnetic properties of a 100-nm-period large-area array of regular, 30-nm polycrystalline nickel particles have been studied. The particles are found to reverse incoherently, and their hysteresis behavior has been compared with a computational model over a range of temperatures. Excellent agreement with the model is obtained, indicating that switching of the particles is dominated by the reversal of approximately 10-nm-diameter volumes within each particle. These switching volumes are identified with the columnar grains in the polycrystalline nickel, showing that the microstructure determines the magnetic behavior of the particles. This explains the anisotropy distribution and the onset of superparamagnetism in the sample. Incoherent reversal occurs even though the particles are only 1.5 times the exchange length in nickel, a size at which nearly uniform rotation is expected to occur if the particles were homogeneous.

  3. Reversals of the Earth's Magnetic Field

    NASA Astrophysics Data System (ADS)

    Champion, Duene E.

    J.A. Jacobs of Cambridge University has written a concise, authoritative, and up-todate text on reversals of the earth's magnetic field. Chapter 1 is a concise summary of the basic attributes of the geomagnetic field and its behavior in different time frames. It explains spherical harmonic analysis of the field and presents the history of acquisition of the data that best represent the recent field. Lastly, it includes a short summary of the origin and electrodynamics of the magnetic field, outlining the current theoretical basis for its generation.

  4. First order reversal curve studies of the magnetization reversal behavior in nanoscale magnetic materials

    NASA Astrophysics Data System (ADS)

    Davies, Joseph Edward

    2007-12-01

    This dissertation investigates the magnetic reversal processes in three types of fundamentally interesting and technologically important materials. In a FORC measurement, ˜100 partial hysteresis curves are used to map out magnetization reversal processes. A partial derivative of the FORC data yields a distribution, rho, which contains detailed information about the magnetization reversal processes. Throughout this thesis, the FORC method was developed into a rigorous experimental tool to address challenges in studying magnetization reversal. The materials studied are: Co/Pt multilayers, spring magnets, and La1-xSrxCoO3. Co/Pt multilayer thin films with perpendicular magnetic anisotropy show three distinct stages for reversal. Significant irreversible switching persists well beyond the apparent saturation field due to residual domains. These residual domains fell below the resolution limit of transmission x-ray microscopy measurements. In the conventional spring magnet Fe/epitaxial-SmCo, the reversal proceeds by reversible rotation of the Fe soft layer followed by irreversible switching of the SmCo hard layer. FORC studies of the Fe/epitaxial-SmCo spring magnets reveal rich features during partial SmCo layer demagnetization. Features at high fields track the amount of SmCo that has reversed while at low fields the change in interlayer coupling is observed. To directly measure the exchange field, a second order reversal curve (SORC) method is introduced. Comparison of the epitaxial Fe/SmCo is also made to FeNi/polycrystalline-FePt where the FeNi and FePt layers reverse in a continuous manner. La1-xSrxCoO3 shows a variation in magnetic behavior ranging from isolated ferromagnetic clusters to long range bulk ferromagnetic order with increased Sr doping. This manifests itself in an evolution in rho ranging from little feature at low doping to features tilting towards negative bias at high doping indicating an onset of long range FM order. With increasing temperature

  5. Inhomogeneous magnetization reversal on vicinal surfaces

    NASA Astrophysics Data System (ADS)

    Hyman, R. A.; Stiles, M. D.; Zangwill, A.

    1998-03-01

    We report numerical and analytic results for a model of magnetization reversal in single-crystal vicinal ultrathin films with in-plane magnetization. We model the vicinality by the inclusion of equally spaced infinitely long step edges separating flat terraces. Inhomogeneous magnetization reversal occurs because the intrinsic four-fold anisotropy of the terraces is augmented by uniaxial anisotropy localized at the step edges. The reversal process is a combination of domain nucleation at step edges, depinning due to domain wall interactions, and coherent rotation in the center of flat terraces. Hysteresis curves are calculated as a function of terrace length and exhibit two symmetrically shifted loops in qualitative agreement with experiments(R.K. Kawakami, Ernesto J.Escorcia-Aparicio, and Z.Q. Qui, Phys. Rev. Lett. 77, 2570 (1996), W. Weber, C.H. Back, A. Bischof, Ch. Wursch, R. Allenspach, Phys. Rev. Lett. 76, 1940 (1996)). In the limits of small and large miscut angle, simple analytic formula for the hysteretic jump fields are derived that agree well with our numerical work.

  6. Study of structure and magnetic properties of Ni-Zn ferrite nano-particles synthesized via co-precipitation and reverse micro-emulsion technique

    NASA Astrophysics Data System (ADS)

    Abdullah Dar, M.; Shah, Jyoti; Siddiqui, W. A.; Kotnala, R. K.

    2014-08-01

    Nano-crystalline Ni-Zn ferrites were synthesized by chemical co-precipitation and reverse micro-emulsion technique with an average crystallite size of 11 and 6 nm, respectively. The reverse micro-emulsion method has been found to be more appropriate for nano-ferrite synthesis as the produced particles are monodisperse and highly crystalline. Zero-field cooled and field cooled magnetization study under different magnetic fields and magnetic hysteresis loops at different temperatures have been performed. The non-saturated M-H loops, absence of hysteresis, and coercivity at room temperature are indicative of the presence of super paramagnetic and single-domain nano-particles for both the materials. In sample `a', the blocking temperature ( T B) has been observed to decrease from 255 to 120 K on increasing the magnetic field from 50 to 1,000 Oe, which can be attributed to the reduction of magneto crystalline anisotropy constant. The M S and coercivity were found to be higher for sample `a' as compared with sample `b' since surface effects are neglected on increasing the crystallite size.

  7. Magnetization reversal dynamics in antiferromagnetically coupled magnetic recording media

    NASA Astrophysics Data System (ADS)

    Schabes, Manfred

    2002-03-01

    Antiferromagnetically coupled (AFC) media have been shown to provide an important extension of longitudinal magnetic data storage at high bit densities.[1,2] In this work we report the results of micromagnetic calculations to examine the magnetization reversal mechanism in two-layer AFC media as a function of bottom layer thickness and interfacial exchange coupling. It is shown that the magnetization reversal in the top and bottom layers can proceed at rather different time scales, if the interfacial energy density is small or the bottom layer thickness is large. In this case the reversal of the bottom layer may involve spin wave like oscillations that require time periods for damping that are large compared to the reversal time of the top layer. Detailed solutions of the Landau-Lifshitz-Langevin[2] equations are discussed to study these novel oscillatory excitations in AFC media at a temperature of 350 K. [1] E.E. Fullerton et al., Appl. Phys. Lett., vol.77, (2000),3806. [2] M.E. Schabes et al., IEEE Trans. Mag. MAG-37, (2001), 1432.

  8. Lightweight Magnetic Cooler With a Reversible Circulator

    NASA Technical Reports Server (NTRS)

    Chen, Weibo; McCormick, John

    2011-01-01

    A design of a highly efficient and lightweight space magnetic cooler has been developed that can continuously provide remote/distributed cooling at temperatures in the range of 2 K with a heat sink at about 15 K. The innovative design uses a cryogenic circulator that enables the cooler to operate at a high cycle frequency to achieve a large cooling capacity. The ability to provide remote/distributed cooling not only allows flexible integration with a payload and spacecraft, but also reduces the mass of the magnetic shields needed. The active magnetic regenerative refrigerator (AMRR) system is shown in the figure. This design mainly consists of two identical magnetic regenerators surrounded by their superconducting magnets and a reversible circulator. Each regenerator also has a heat exchanger at its warm end to reject the magnetization heat to the heat sink, and the two regenerators share a cold-end heat exchanger to absorb heat from a cooling target. The circulator controls the flow direction, which cycles in concert with the magnetic fields, to facilitate heat transfer. Helium enters the hot end of the demagnetized column, is cooled by the refrigerant, and passes into the cold-end heat exchanger to absorb heat. The helium then enters the cold end of the magnetized column, absorbing heat from the refrigerant, and enters the hot-end heat exchanger to reject the magnetization heat. The efficient heat transfer in the AMRR allows the system to operate at a relatively short cycle period to achieve a large cooling power. The key mechanical components in the magnetic cooler are the reversible circulator and the magnetic regenerators. The circulator uses non-contacting, self-acting gas bearings and clearance seals to achieve long life and vibration- free operation. There are no valves or mechanical wear in this circulator, so the reliability is predicted to be very high. The magnetic regenerator employs a structured bed configuration. The core consists of a stack of thin

  9. Electric field assisted magnetization reversal in FePt films.

    NASA Astrophysics Data System (ADS)

    Lukashev, Pavel; Belashchenko, Kirill; Sabirianov, Renat

    2008-03-01

    We propose to use strain assisted reduction in anisotropy of FePt in order to make magnetization reversal easier in the writing of the magnetic storage devices. We performed first-principles calculations of the magnetocrystalline anisotropy of FePt under bi-axial stress using full-potential LAPW implemented in FLEUR code. Magnetocrystalline anisotropy decreases by 25% with application of 1.5% tensile biaxial strain. This is partially due to the reduction of the c/a ratio by about 1.5% (calculated Poisson ratio is 0.33) in the tetragonal cell and partially due to the increase in volume by about 1.5%. Biaxial strain can be obtained by placing piezoelectric film under FePt layer, and by applying electric field on the system. Modern ferroelectric systems can provide stress up to 2%. Besides, we propose using thin ferroelectric films with asymmetric interfaces, which provides a simple way to generate bias field in the polarization reversal and related properties. The existence of the polar interfaces results in a different average polarization in the film upon reversal. As a result, the strain in the film depends on the direction of polarization. This asymmetric strain can be used do modulate magnetic properties.

  10. Time-Reversal-Breaking Weyl Fermions in Magnetic Heusler Alloys

    NASA Astrophysics Data System (ADS)

    Wang, Zhijun; Vergniory, M. G.; Kushwaha, S.; Hirschberger, Max; Chulkov, E. V.; Ernst, A.; Ong, N. P.; Cava, Robert J.; Bernevig, B. Andrei

    2016-12-01

    Weyl fermions have recently been observed in several time-reversal-invariant semimetals and photonics materials with broken inversion symmetry. These systems are expected to have exotic transport properties such as the chiral anomaly. However, most discovered Weyl materials possess a substantial number of Weyl nodes close to the Fermi level that give rise to complicated transport properties. Here we predict, for the first time, a new family of Weyl systems defined by broken time-reversal symmetry, namely, Co-based magnetic Heusler materials X Co2Z (X =IVB or VB; Z =IVA or IIIA). To search for Weyl fermions in the centrosymmetric magnetic systems, we recall an easy and practical inversion invariant, which has been calculated to be -1 , guaranteeing the existence of an odd number of pairs of Weyl fermions. These materials exhibit, when alloyed, only two Weyl nodes at the Fermi level—the minimum number possible in a condensed matter system. The Weyl nodes are protected by the rotational symmetry along the magnetic axis and separated by a large distance (of order 2 π ) in the Brillouin zone. The corresponding Fermi arcs have been calculated as well. This discovery provides a realistic and promising platform for manipulating and studying the magnetic Weyl physics in experiments.

  11. Intercalation-driven reversible control of magnetism in bulk ferromagnets.

    PubMed

    Dasgupta, Subho; Das, Bijoy; Knapp, Michael; Brand, Richard A; Ehrenberg, Helmut; Kruk, Robert; Hahn, Horst

    2014-07-16

    An extension in magnetoelectric effects is proposed to include reversible chemistry-controlled magnetization variations. This ion-intercalation-driven magnetic control can be fully reversible and pertinent to bulk material volumes. The concept is demonstrated for ferromagnetic iron oxide where the intercalated lithium ions cause valence change and partial redistribution of Fe(3+) cations yielding a large and fully reversible change in magnetization at room temperature.

  12. Control of magnetization reversal in oriented strontium ferrite thin films

    SciTech Connect

    Roy, Debangsu Anil Kumar, P. S.

    2014-02-21

    Oriented Strontium Ferrite films with the c axis orientation were deposited with varying oxygen partial pressure on Al{sub 2}O{sub 3}(0001) substrate using Pulsed Laser Deposition technique. The angle dependent magnetic hysteresis, remanent coercivity, and temperature dependent coercivity had been employed to understand the magnetization reversal of these films. It was found that the Strontium Ferrite thin film grown at lower (higher) oxygen partial pressure shows Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of pinning and nucleation processes during magnetization reversal is used to explain the type of the magnetization reversal with different oxygen partial pressure during growth.

  13. Chondrule magnetic properties

    NASA Technical Reports Server (NTRS)

    Wasilewski, P. J.; Obryan, M. V.

    1994-01-01

    The topics discussed include the following: chondrule magnetic properties; chondrules from the same meteorite; and REM values (the ratio for remanence initially measured to saturation remanence in 1 Tesla field). The preliminary field estimates for chondrules magnetizing environments range from minimal to a least several mT. These estimates are based on REM values and the characteristics of the remanence initially measured (natural remanence) thermal demagnetization compared to the saturation remanence in 1 Tesla field demagnetization.

  14. Ultralow field magnetization reversal of two-body magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Fei; Lu, Jincheng; Lu, Xiaofeng; Tang, Rujun; Sun, Z. Z.

    2016-08-01

    Field induced magnetization reversal was investigated in a system of two magnetic nanoparticles with uniaxial anisotropies and magnetostatic interaction. By using the micromagnetic simulation, ultralow switching field strength was found when the separation distance between the two particles reaches a critical small value (on nanometer scale) in the perpendicular configuration where the anisotropic axes of the two particles are perpendicular to the separation line. The switching field increases sharply when the separation is away from the critical distance. The ultralow field switching phenomenon was missed in the parallel configuration where both the anisotropic axes are aligned along the separation line of the two particles. The micromagnetic results are consistent with the previous theoretical prediction [J. Appl. Phys. 109, 104303 (2011)] where dipolar interaction between two single-domain magnetic particles was considered. Our present simulations offered further proofs and possibilities for the low-power applications of information storage as the two-body magnetic nanoparticles might be implemented as a composite information bit.

  15. Magnetic properties of high-density patterned magnetic media

    NASA Astrophysics Data System (ADS)

    Gurovich, B. A.; Prikhodko, K. E.; Kuleshova, E. A.; Yu Yakubovsky, A.; Meilikhov, E. Z.; Mosthenko, М. G.

    2010-10-01

    Structures of patterned magnetic media (PMM) with a density of 100-155 Gb/in. 2 have been prepared using the original method of selective removal of atoms making use of irradiation by an accelerated ion beam for producing patterns of materials whose chemical and physical properties are different from those of the matrix. Magnetic hysteresis loops for cobalt PMM structures with Co bit sizes of 40×15, 30×15, and 15×15 nm 2 show linear increase of coercivity with bit anisotropy factor. Consecutive reversals of nanobit magnetizations in bit ensembles have been visualized by the MFM technique, which allows one to reconstruct corresponding magnetic hysteresis loops.

  16. Magnetotransport and magnetization reversal of electrodeposited multilayer nanowires

    NASA Astrophysics Data System (ADS)

    Tang, Xueti

    2007-12-01

    model for tCoNi >170 nm, where the anisotropic magnetoresistance (AMR) is not negligible. All the results obtained in this study have proven that electrodeposited multilayer nanowires exhibit unique magnetic properties and are advantageous for the study of CPP-GMR. The findings in magnetization reversal mechanism are believed to help better understand the complicated magnetic behavior of nanoscale multilayer systems and provide additional insights into theoretical modeling of such systems. The findings in CPP-GMR will help understand various spintronic phenomena and design new nanoscale magnetic sensors and high density data storage devices.

  17. Phenomenological Theory of the Processes of Magnetization Reversal of Permanent Magnets From Alloys of Types SmCo5 and Nd2Fe14B

    NASA Astrophysics Data System (ADS)

    Lileev, A. S.

    2017-01-01

    Amethod for simulating the hysteretic properties and the process of magnetization reversal of uniaxial highly anisotropic ferromagnets is developed with allowance for the presence of magnetostatic interaction between microvolumes of the material. It is based on the phenomenological approach to an elementary act of the process of magnetization reversal of these materials. Computer simulation is used to explain and illustrate the phenomenon of "thermal magnetization," the formation of "channels of reversal magnetization," the interrelation between the degree of crystal texture and the spin reorientation transfer, the coarsening of the domain structure in rapidly hardened powders, and the behavior of permanent magnets in a magnetic system in contact with a magnetically soft material.

  18. Micromagnetic calculation of magnetization reversal in magnetic rings

    NASA Astrophysics Data System (ADS)

    Lopez-Diaz, Luis

    2002-03-01

    The success of using patterned magnetic nanoelements in Magnetic Random Access Memories (MRAM) depends entirely on our ability to control accurately their switching fields. In a recent study1, we showed that micron-sized narrow rings present well defined stable states and nucleation-free switching between them. In the first part of the talk we review our experimental studies on ring magnets. Pre-patterned Si(100) substrates were used to grow free-standing epitaxial ring magnets of Cu(100)/Co(100)/Cu(100)/Si(100) with 1.8 mm outer diameter, 1.2 mm inner diameter and 34 nm thickness. The samples were magnetically characterised using specially adapted magneto-optic Kerr effect. The measurements show that a two step switching process occurs at high fields, indicating the existence of two different stable states. In addition to the vortex state, which occurs at intermediate fields, we have identified a second state which is also stable at remanence and undergoes a simple and well characterised nucleation free domain wall propagation switching process. Moreover, it is confirmed that the rings reverse by falling into vortex states with different circulation when the field is applied in opposite directions. This means a particular vortex state (clockwise or counter-clockwise) can be prepared using a uniform field only, which can be important for technological applications. In the second part of the talk we use micromagnetic simulations to further explore the potential performance of narrow rings as memory cells in MRAM devices in terms of scalability and switching speed. We introduce two artificial notches at the outer surface of the rings in order to control accurately the depinning fields for the domain walls. According to our simulations, well defined onion states1 and switching by domain wall motion can be achieved for ring diameters down 180 nm. In order to speed up the switching process, two different approaches are considered. In the first one, a field pulse is

  19. Magnetization reversal in TmCrO{sub 3}

    SciTech Connect

    Yoshii, Kenji

    2012-11-15

    Highlights: ► We observed two magnetization reversals in TmCrO{sub 3}. ► The reversal at 28 K is attributed to antiparallel coupling between Cr{sup 3+} and Tm{sup 3+}. ► The other reversal originates from spin reorientation. ► Magnetocaloric effect is observed at the spin reorientation temperature. ► Characteristic magnetization switching is demonstrated. -- Abstract: The perovskite chromite TmCrO{sub 3} shows magnetization reversal at two temperatures. The reversal at ∼28 K is attributed to the antiparallel coupling between Tm{sup 3+} and Cr{sup 3+} moments, while that at the lower temperature (∼6–7 K) is rooted in a rotation of the magnetic moments. Magnetocaloric measurements offer a relatively large entropy change (∼4–5 J kg{sup −1} K{sup −1}) at the lower temperature. The reversal at ∼28 K is accompanied by a sign change of an exchange-bias-like field. The absence of the training effect suggests that this behavior is rooted in unidirectional magnetic anisotropy. The existence of the two magnetization reversals offers the characteristic switching of magnetization. For example, the magnetization is flipped without changing the direction of the applied magnetic field.

  20. Full 180° magnetization reversal with electric fields.

    PubMed

    Wang, J J; Hu, J M; Ma, J; Zhang, J X; Chen, L Q; Nan, C W

    2014-12-16

    Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

  1. Full 180° Magnetization Reversal with Electric Fields

    PubMed Central

    Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

    2014-01-01

    Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

  2. Full 180° Magnetization Reversal with Electric Fields

    NASA Astrophysics Data System (ADS)

    Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

    2014-12-01

    Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

  3. Reversal of radial glow distribution in helicon plasma induced by reversed magnetic field

    NASA Astrophysics Data System (ADS)

    Y, Wang; G, Zhao; C, Niu; Z, W. Liu; J, T. Ouyang; Q, Chen

    2017-02-01

    In this work, the reversal of radial glow distribution induced by reversed magnetic field is reported. Based on the Boswell antenna which is symmetric and insensitive to the magnetic field direction, it seems such a phenomenon in theory appears impossible. However, according to the diagnostic of the helicon waves by magnetic probe, it is found that the direction of magnetic field significantly affects the propagation characteristic of helicon waves, i.e., the interchange of the helicon waves at the upper and the lower half of tube was caused by reversing the direction of magnetic field. It is suggested that the variation of helicon wave against the direction of magnetic field causes the reversed radial glow distribution. The appearance of the traveling wave does not only improve the discharge strength, but also determines the transition of the discharge mode.

  4. Tailoring the magnetization reversal of elliptical dots using exchange bias.

    SciTech Connect

    Sort, J.; Buchanan, K. S.; Pearson, J. E.; Hoffmann, A.; Menendez, E.; Salazar-Alvarez, G.; Baro, M. D.; Miron, M.; Rodamcq, B.; Dieny, B.; ICREA; Univ. Autonoma of Barcelona; Insti. Catala de Nanotecnologia; SPINTEC

    2008-01-01

    Exchange bias effects have been studied in elliptical dots composed of ferromagnetic Ni{sub 80}Fe{sub 20}-antiferromagnetic Ir{sub 20}Mn{sub 80} bilayers. The magnetization reversal mechanisms and magnetic configurations have been investigated by magneto-optic Kerr effect and magnetic force microscopy. Although the obtained bias fields in these dots are relatively small, the magnetization reversal is found to be influenced by the ferromagnetic-antiferromagnetic coupling. Namely, for some off-axis angles of measurement, the magnetization reversal mechanism of the Ni{sub 80}Fe{sub 20}-Ir{sub 20}Mn{sub 80} ellipses depends on whether exchange bias is induced along the minor or major axis of the ellipses. Hence, exchange bias is shown to be an effective means for tailoring the magnetization reversal of elliptical dots after sample fabrication.

  5. Magnetization reversal mechanism of a sintered Nd-Fe-B magnet with Dy segregation

    SciTech Connect

    Suzuki, Hiroyuki; Satsu, Yuichi; Komuro, Matahiro; Kohashi, Teruo; Motai, Kumi

    2011-04-01

    The magnetization reversal mechanism of a sintered Nd-Fe-B magnet with Dy segregation near grain boundaries (GB) was studied using spin polarized scanning electron spectroscopy and magnetization measurements. More fine magnetic domains near GB were found in the magnet with Dy segregation than in the magnet without treatment. Magnetic modifications near the GB had no effect on the magnetization development. The domain wall motion of a quasihard magnetic component in the magnet with Dy segregation was suppressed in comparison with those in the magnet without treatment; this could also be confirmed in the different behaviors of asymmetry components toward a magnetic field direction between both magnets. From analyzing the probability of rotating magnetization near the GB, the magnetization reversal of the magnet with Dy segregation was more difficult to produce than those of the magnet without treatment.

  6. Simple Mechanism for Reversals of Earth's Magnetic Field

    SciTech Connect

    Petrelis, Francois; Fauve, Stephan; Dormy, Emmanuel; Valet, Jean-Pierre

    2009-04-10

    We show that a model, recently used to describe all the dynamical regimes of the magnetic field generated by the dynamo effect in the von Karman sodium experiment, also provides a simple explanation of the reversals of Earth's magnetic field, despite strong differences between both systems. The validity of the model relies on the smallness of the magnetic Prandtl number.

  7. Electrical detection of microwave assisted magnetization reversal by spin pumping

    SciTech Connect

    Rao, Siddharth; Subhra Mukherjee, Sankha; Elyasi, Mehrdad; Singh Bhatia, Charanjit; Yang, Hyunsoo

    2014-03-24

    Microwave assisted magnetization reversal has been investigated in a bilayer system of Pt/ferromagnet by detecting a change in the polarity of the spin pumping signal. The reversal process is studied in two material systems, Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching behavior is indicated by a sharp transition in the spin pumping voltage. At a threshold value of the external field, the switching process changes from partial to full reversal with increasing microwave power. The proposed method provides a simple way to detect microwave assisted magnetization reversal.

  8. Reversible electric-field control of magnetization at oxide interfaces

    NASA Astrophysics Data System (ADS)

    Cuellar, F. A.; Liu, Y. H.; Salafranca, J.; Nemes, N.; Iborra, E.; Sanchez-Santolino, G.; Varela, M.; Hernandez, M. Garcia; Freeland, J. W.; Zhernenkov, M.; Fitzsimmons, M. R.; Okamoto, S.; Pennycook, S. J.; Bibes, M.; Barthélémy, A.; Te Velthuis, S. G. E.; Sefrioui, Z.; Leon, C.; Santamaria, J.

    2014-06-01

    Electric-field control of magnetism has remained a major challenge which would greatly impact data storage technology. Although progress in this direction has been recently achieved, reversible magnetization switching by an electric field requires the assistance of a bias magnetic field. Here we take advantage of the novel electronic phenomena emerging at interfaces between correlated oxides and demonstrate reversible, voltage-driven magnetization switching without magnetic field. Sandwiching a non-superconducting cuprate between two manganese oxide layers, we find a novel form of magnetoelectric coupling arising from the orbital reconstruction at the interface between interfacial Mn spins and localized states in the CuO2 planes. This results in a ferromagnetic coupling between the manganite layers that can be controlled by a voltage. Consequently, magnetic tunnel junctions can be electrically toggled between two magnetization states, and the corresponding spin-dependent resistance states, in the absence of a magnetic field.

  9. Equilibrium properties of hybrid field reversed configurations

    NASA Astrophysics Data System (ADS)

    Tuszewski, M.; Gupta, D.; Gupta, S.; Onofri, M.; Osin, D.; Deng, B. H.; Dettrick, S. A.; Hubbard, K.; Gota, H.

    2017-01-01

    Field Reversed Configurations (FRCs) heated by neutral beam injection may include a large fast ion pressure that significantly modifies the equilibrium. A new analysis is required to characterize such hybrid FRCs, as the simple relations used up to now prove inaccurate. The substantial contributions of fast ions to FRC radial pressure balance and diamagnetism are described. A simple model is offered to reconstruct more accurately the equilibrium parameters of elongated hybrid FRCs. Further modeling requires new measurements of either the magnetic field or the plasma pressure.

  10. Sun's Polar Magnetic Field Reversals in Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Pishkalo, M. I.; Leiko, U. M.

    It is known that polar magnetic field of the Sun changes its sign at the maximum of solar cycle. These changes were called as polar field reversals. We investigated dynamics of high-latitude solar magnetic fields separately in northern and southern hemispheres. Solar polar field strength measurements from the Wilcox Solar Observatory and low-resolution synoptic magnetic maps from the SOLIS project and from Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory were used. We analyzed total magnetic flux at near-polar zones, starting from 55, 60, 65, 70, 75, 80 and 85 degrees of latitude, and found time points when the total magnetic flux changed its sign. It was concluded that total magnetic flux changed its sign at first at lower latitudes and finally near the poles. Single polar magnetic field reversal was found in the southern hemisphere. The northern hemisphere was characterized by three-fold magnetic field reversal. Polar magnetic field reversals finished in northern and southern hemispheres by CR 2150 and CR 2162, respectively.

  11. A study on dynamic heat assisted magnetization reversal mechanisms under insufficient reversal field conditions

    SciTech Connect

    Chen, Y. J.; Yang, H. Z.; Leong, S. H.; Yu Ko, Hnin Yu; Wu, B. L.; Ng, V.; Asbahi, M.; Yang, J. K. W.

    2014-10-20

    We report an experimental study on the dynamic thermomagnetic (TM) reversal mechanisms at around Curie temperature (Tc) for isolated 60 nm pitch single-domain [Co/Pd] islands heated by a 1.5 μm spot size laser pulse under an applied magnetic reversal field (Hr). Magnetic force microscopy (MFM) observations with high resolution MFM tips clearly showed randomly trapped non-switched islands within the laser irradiated spot after dynamic TM reversal process with insufficient Hr strength. This observation provides direct experimental evidence by MFM of a large magnetization switching variation due to increased thermal fluctuation/agitation over magnetization energy at the elevated temperature of around Tc. The average percentage of non-switched islands/magnetization was further found to be inversely proportional to the applied reversal field Hr for incomplete magnetization reversal when Hr is less than 13% of the island coercivity (Hc), showing an increased switching field distribution (SFD) at elevated temperature of around Tc (where main contributions to SFD broadening are from Tc distribution and stronger thermal fluctuations). Our experimental study and results provide better understanding and insight on practical heat assisted magnetic recording (HAMR) process and recording performance, including HAMR writing magnetization dynamics induced SFD as well as associated DC saturation noise that limits areal density, as were previously observed and investigated by theoretical simulations.

  12. Magnetization reversal in melt-quenched NdFeB

    SciTech Connect

    Crew, D.C.; Lewis, L.H.; McCormick, P.G.; Street, R.; Panchanathan, V.

    1999-06-01

    Melt-quenched NdFeB is an important modern permanent magnet material. However there still remains doubt as to the magnetization reversal mechanism which controls coercivity in material prepared by this processing route. To investigate this problem a new technique based on measurements of reversible magnetization along recoil curves has been used. The technique identifies the presence of free domain walls during magnetic reversal. For this study samples of isotropic (MQI), hot pressed (MQII) and die upset (MQIII) melt-quenched NdFeB were examined. The results indicate that in MQI free domain walls are not present during reversal and the reversal mechanism is most likely incoherent rotation of some form. Free domain walls are also not present during reversal in the majority of grains of MQII, even though initial magnetization measurements indicate that the grain size is large enough to support them. In MQIII free domain walls are present during reversal. These results are attributed to the reduced domain wall nucleation field in MQIII compared with MQII and the increased dipolar interactions in MQIII.

  13. A moment equation description of magnetic reversals in the earth

    PubMed Central

    Robbins, K. A.

    1976-01-01

    Low order moments of the alpha dynamo equations in a geophysical regime are related to the dependent variables in a reversing disk dynamo. The link suggests that nonperiodic reversal is an intrinsic feature of the alpha dynamo equations provided the forcing is vigorous and the toroidal and poloidal magnetic fields are sufficiently out of phase. The nonuniformities in reversal frequency are then attributable to subcritical instability. PMID:16592371

  14. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Analytical model for reverse characteristics of 4H-SiC merged PN-Schottky (MPS) diodes

    NASA Astrophysics Data System (ADS)

    Song, Qing-Wen; Zhang, Yu-Ming; Zhang, Yi-Men; Lü, Hong-Liang; Chen, Feng-Ping; Zheng, Qing-Li

    2009-12-01

    A new analytical model for reverse characteristics of 4H-SiC merged PN-Schottky diodes (MPS or JBS) is developed. To accurately calculate the reverse characteristics of the 4H-SiC MPS diode, the relationship between the electric field at the Schottky contact and the reverse bias is analytically established by solving the cylindrical Poisson equation after the channel has pinched off. The reverse current density calculated from the Wentzel-Kramers-Brillouin (WKB) theory is verified by comparing it with the experimental result, showing that they are in good agreement with each other. Moreover, the effects of P-region spacing (S) and P-junction depth (Xj) on the characteristics of 4H-SiC MPS are analysed, and are particularly useful for optimizing the design of the high voltage MPS diodes.

  15. Microscopic reversal behavior of magnetically capped nanospheres

    SciTech Connect

    Guenther, C. M.; Pfau, B.; Eisebitt, S.; Hellwig, O.; Menzel, A.; Radu, F.; Makarov, D.; Albrecht, M.; Goncharov, A.; Schrefl, T.; Schlotter, W. F.; Rick, R.; Luening, J.

    2010-02-01

    The magnetic switching behavior of Co/Pd multilayer-capped nanospheres is investigated by x-ray spectro-holography. Images of the magnetic state of individual nanocaps are recorded as a function of externally applied magnetic field and the angle under which the field is applied, pertaining to magnetic data storage applications with patterned, tilted, and perpendicular storage media. Dispersed nanospheres with different coverage in the submonolayer regime are investigated simultaneously in a multiplexed experiment. In clustered nanosphere arrangements, we find that individual switching events are influenced by dipolar magnetostatic interactions. Micromagnetic simulations of the switching behavior complement the experimental observations, corroborating the influence of thermal activation processes and magnetostatic interactions in this system. Such magnetostatic interactions could lead to undesired cross-talk between bits in ultrahigh-density magnetic recording applications.

  16. Fast chirality reversal of the magnetic vortex by electric current

    SciTech Connect

    Lim, W. L. Liu, R. H.; Urazhdin, S.; Tyliszczak, T.; Erokhin, S. G.; Berkov, D.

    2014-12-01

    The possibility of high-density information encoding in magnetic materials by topologically stable inhomogeneous magnetization configurations such as domain walls, skyrmions, and vortices has motivated intense research into mechanisms enabling their control and detection. While the uniform magnetization states can be efficiently controlled by electric current using magnetic multilayer structures, this approach has proven much more difficult to implement for inhomogeneous states. Here, we report direct observation of fast reversal of magnetic vortex by electric current in a simple planar structure based on a bilayer of spin Hall material Pt with a single microscopic ferromagnetic disk contacted by asymmetric electrodes. The reversal is enabled by a combination of the chiral Oersted field and spin current generated by the nonuniform current distribution in Pt. Our results provide a route for the efficient control of inhomogeneous magnetization configurations by electric current.

  17. Magnetic reversals in a simple model of magnetohydrodynamics.

    PubMed

    Benzi, Roberto; Pinton, Jean-François

    2010-07-09

    We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constraints in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a nontrivial evolution--linked to the nature of the hydrodynamics turbulence.

  18. Modulated self-reversed magnetic hysteresis in iron oxides

    PubMed Central

    Ma, Ji; Chen, Kezheng

    2017-01-01

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe3+ cations due to their negative enough surface zeta potentials. These iron oxides@Fe3+ core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe3+ shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe3+ concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields. PMID:28220793

  19. Modulated self-reversed magnetic hysteresis in iron oxides.

    PubMed

    Ma, Ji; Chen, Kezheng

    2017-02-21

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe(3+) cations due to their negative enough surface zeta potentials. These iron oxides@Fe(3+) core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe(3+) shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe(3+) concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields.

  20. Modulated self-reversed magnetic hysteresis in iron oxides

    NASA Astrophysics Data System (ADS)

    Ma, Ji; Chen, Kezheng

    2017-02-01

    The steadfast rule of a ferromagnetic hysteresis loop claims its saturation positioned within the first and third quadrants, whereas its saturation positioned in the second and fourth quadrants (named as self-reversed magnetic hysteresis) is usually taken as an experimental artifact and is always intentionally ignored. In this report, a new insight in this unique hysteresis phenomenon and its modulation were discussed in depth. Different iron oxides (magnetite, maghemite and hematite) with varying dimensions were soaked in FeCl3 aqueous solution and absorbed Fe3+ cations due to their negative enough surface zeta potentials. These iron oxides@Fe3+ core-shell products exhibit well pronounced self-reversed magnetic hysteresis which concurrently have typical diamagnetic characteristics and essential ferromagnetic features. The presence of pre-magnetized Fe3+ shell and its negatively magnetic exchange coupling with post-magnetized iron-oxide core is the root cause for the observed phenomena. More strikingly, this self-reversed magnetic hysteresis can be readily modulated by changing the core size or by simply controlling Fe3+ concentration in aqueous solution. It is anticipated that this work will shed new light on the development of spintronics, magnetic recording and other magnetically-relevant fields.

  1. Probing the magnetization reversal of patterned cobalt and nickel-iron nanostructures

    NASA Astrophysics Data System (ADS)

    Uhlig, Willard Casey

    As the size of magnetic structures is decreased to the nanoscale, many physical properties such as magnetization reversal begin to change dramatically from those observed in bulk materials. An in-depth understanding of the magnetization reversal, which is of great scientific and technological importance is the focus of this dissertation. NiFe and Co nanostructures were fabricated and systematically studied as a function of size, shape, and temperature. The magnetic nanoelement arrays were fabricated using a bi-layer electron beam lithography process followed by electron beam evaporation and lift-off or by ion milling. The magnetization reversal of the samples was characterized using a variable temperature (2 K to 325 K), focused Magneto-optic Kerr effect measurement system that I constructed here at the University of Utah. Additional information about the magnetization states of the elements including inter-element coupling was obtained by micromagnetic simulations and through imaging by photoemission electron microscopy and magnetic force microscopy. It was found that the element shape and therefore the magnetostatic energy plays an important role in magnetization reversal. The temperature dependence of the switching field for many rectangular elements follows a linear behavior, which is predicted by the two-dimensional thermally activated nucleation theory. To better understand this nucleation process, long (60 mum) nanolines (where the magnetization must break into domains during reversal) ranging in width from 55 nm to 1 mum were studied as a function of width and thickness. The coercivity was found to have a universal dependence, inversely proportional to the width and proportional to both the saturation magnetization and the thickness of the element, which is consistent with the coherent rotation model prediction for smaller aspect ratio elements, but not expected for such long elements. An effective understanding of this behavior was found and is here

  2. Interplay between magnetic anisotropy and interlayer coupling in nanosecond magnetization reversal of spin-valve trilayers

    NASA Astrophysics Data System (ADS)

    Vogel, J.; Kuch, W.; Camarero, J.; Fukumoto, K.; Pennec, Y.; Pizzini, S.; Bonfim, M.; Petroff, F.; Fontaine, A.; Kirschner, J.

    2005-02-01

    The influence of magnetic anisotropy on nanosecond magnetization reversal in coupled FeNi/Cu/Co trilayers was studied using a photoelectron emission microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic samples the reversal of the soft FeNi layer is determined by domain-wall pinning that leads to the formation of small and irregular domains. In samples with uniaxial magnetic anisotropy, the domains are larger and the influence of local interlayer coupling dominates the domain structure and the reversal of the FeNi layer.

  3. Electrical control of large magnetization reversal in a helimagnet.

    PubMed

    Chai, Yi Sheng; Kwon, Sangil; Chun, Sae Hwan; Kim, Ingyu; Jeon, Byung-Gu; Kim, Kee Hoon; Lee, Soonchil

    2014-06-24

    Reversal of magnetization M by an electrical field E has been a long-sought phenomenon in materials science because of its potential for applications such as memory devices. However, the phenomenon has rarely been achieved and remains a considerable challenge. Here we report the large M reversal by E in a multiferroic Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22 crystal without any external magnetic field. Upon sweeping E through the range of ±2 MV m(-1), M varied quasi-linearly in the range of ±2 μB per f.u., resulting in the M reversal. Strong electrical modulation of M at zero magnetic field were observable up to ~\

  4. Study of the reduced magnetic field required for thermally assisted magnetization reversal

    NASA Astrophysics Data System (ADS)

    Firdausi, H. F. Y.; Utari; Purnama, B.

    2016-11-01

    The reduced magnetic field required for thermally magnetization reversal discussed in this paper. Study of thermally assisted magnetization reversal conduct by using micromagnetic simulation. The magnetic dot size of the simulation was 50 nm × 50 nm × 20 nm. The perpendicularly anisotropy constant was 2 × 106 erg/cm3. Initial condition was set single domain configuration. Then a sufficiently thermal pulse was used to get stochastic effect so that the magnetization along to the induce field direction for pico second duration. The results show that the reduced magnetic field mechanism seem to be temporary antiferromagnetic configuration before single domain configuration in alinging along to field direction. The same mechanims observed for modify of thickness dot particles. The require magnetic field of 145 Oe in thermally assisted magnetization reversal open a posibility for MRAM application.

  5. The topology of intrasector reversals of the interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Kahler, S. W.; Crooker, N. U.; Gosling, J. T.

    1996-11-01

    A technique has been developed recently to determine the polarities of interplanetary magnetic fields relative to their origins at the Sun by comparing energetic electron flow directions with local magnetic field directions. Here we use heat flux electrons from the Los Alamos National Laboratory (LANL) plasma detector on the ISEE 3 spacecraft to determine the field polarities. We examine periods within well-defined magnetic sectors when the field directions appear to be reversed from the normal spiral direction of the sector. About half of these intrasector field reversals (IFRs) are cases in which the polarities match those of the surrounding sectors, indicating that those fields have been folded back toward the Sun. The more interesting cases are those with polarity reversals. We find no clear cases of isolated reverse polarity fields, which suggests that islands of reverse polarity in the solar source dipole field probably do not exist. The IFRs with polarity reversals are strongly associated with periods of bidirectional electron flows, suggesting that those fields occur only in conjunction with closed fields. We propose that both those IFRs and the bidirectional flows are signatures of coronal mass ejections (CMEs). In that case, many interplanetary CMEs are larger and more complex than previously thought, consisting of both open and closed field components.

  6. Field orientation dependence of magnetization reversal in thin films with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Fallarino, Lorenzo; Hovorka, Ondrej; Berger, Andreas

    2016-08-01

    The magnetization reversal process of hexagonal-close-packed (hcp) (0001) oriented Co and C o90R u10 thin films with perpendicular magnetic anisotropy (PMA) has been studied as a function of temperature and applied magnetic field angle. Room temperature pure cobalt exhibits two characteristic reversal mechanisms. For angles near in-plane field orientation, the magnetization reversal proceeds via instability of the uniform magnetic state, whereas in the vicinity of the out-of-plane (OP) orientation, magnetization inversion takes place by means of domain nucleation. Temperature dependent measurements enable the modification of the magnetocrystalline anisotropy and reveal a gradual disappearance of the domain nucleation process during magnetization reversal for elevated temperatures. Ultimately, this suppression of the domain nucleation process leads to the exclusive occurrence of uniform state instability reversal for all field orientations at sufficiently high temperature. Comparative magnetic measurements of C o90R u10 alloy samples allow the identification and confirmation of the high temperature remanent magnetization state of cobalt as an OP stripe domain state despite the reduction of magnetocrystalline anisotropy. Detailed micromagnetic simulations supplement the experimental results and corroborate the physical understanding of the temperature dependent behavior. Moreover, they enable a comprehensive identification of the complex energy balance in magnetic films with PMA, for which three different magnetic phases occur for sufficiently high anisotropy values, whose coexistence point is tricritical in nature.

  7. Magnetization reversal and nanostructure refinement in magnetically annealed Nd2Fe14B/α-Fe-type nanocomposites

    NASA Astrophysics Data System (ADS)

    Cui, B. Z.; Yu, C. T.; Han, K.; Liu, J. P.; Garmestani, H.; Pechan, M. J.; Schneider-Muntau, H. J.

    2005-05-01

    Nanostructure refinement, magnetic anisotropy and hard magnetic property enhancement have been observed in melt-spun Nd2.4Pr5.6Dy1Fe84Mo1B6 nanocomposites annealed in an in-plane or out-of-plane field of 1.2T. The magnetic annealing results in an enhancement of an out-of-plane (110) crystal texture of α-Fe and an in-plane uniaxial magnetic anisotropy of the 2:14:1 phase. Magnetic annealing also introduces finer, less angular and more homogeneously distributed soft and hard nanograins. Field dependent torque measurement indicates a complex magnetization reversal mechanism in these nanocomposites. Compared with the sample annealed without a field, there is a noticeable improvement in the hard magnetic properties for the magnetically annealed samples. Especially, the energy product (BH )max was enhanced by 26.6% (from 94to119kJ/m3). The improvement in the magnetic properties is a result of the enhanced crystallographic texture, nanostructure refinement, and in-plane uniaxial magnetic anisotropy enhancement.

  8. Effect of reverse flotation on magnetic separation concentrates

    NASA Astrophysics Data System (ADS)

    Bada, S. O.; Afolabi, A. S.; Makhula, M. J.

    2012-08-01

    Reverse flotation studies on magnetite samples have revealed that the use of starch as a depressant of Fe-oxides has a hydrophilic effect on the surface of Fe-bearing silicates and significantly decreases Fe in the silica-rich stream when used in combination with an amine (Lilaflot D817M). In this study, the effect of reverse flotation on the optimization of products obtained from magnetic separation was investigated. Two different magnetic samples, zones 1 and 2, were milled to <75 μm and then subjected to low intensity magnetic separation (LIMS). The LIMS test conducted on the <75 μm shown an upgrade of 46.40wt% Fe, 28.40wt% SiO2 and 2.61wt% MnO for zone 1 and 47.60wt% Fe, 29.17wt% SiO2 and 0.50wt% MnO for zone 2. Further milling of the ore to <25 μm resulted in a higher magnetic-rich product after magnetic separation. Reverse flotation tests were conducted on the agitated magnetic concentrate feed, and the result shows a significant upgrade of Fe compared to that obtained from the non-agitated feed. Iron concentrations greater than 69%, and SiO2 concentrations less than 2% with overall magnetite recoveries greater than 67% and 71% were obtained for zones 1 and 2, respectively.

  9. Ferrimagnetism and magnetization reversal in Pr1- x Gd x MnO3

    NASA Astrophysics Data System (ADS)

    Biswas, Sanjay; Pal, Sudipta; Bose, Esa

    2014-10-01

    Temperature dependent magnetic properties of Pr1- x Gd x MnO3 ( x = 0.3, 0.5, 0.7) have been reported. All the samples belong to the family of orthorhombic perovskites structure with Pbnm space group. Below the Neel temperature T N ( 92 K), a magnetization reversal is observed in DC magnetization measurements (at 50 Oe), in all the samples. This may be due to the competition between two magnetic sublattices (Pr + Gd and Mn) coupled with a negative exchange interaction. In the temperature dependent magnetization data, the bifurcation between the zero field cooled and field cooled magnetization is attributed to the canted antiferromagnetism. Ferrimagnetic characteristic is observed in the field dependent magnetization curve below T N .

  10. Uniform magnetization reversal in dual main-phase (Ce,Nd)2Fe14B sintered magnets with inhomogeneous microstructure

    NASA Astrophysics Data System (ADS)

    Zhang, Le-le; Li, Zhu-bai; Zhang, Xue-feng; Ma, Qiang; Liu, Yan-li; Li, Yong-feng; Zhao, Qian

    2017-02-01

    The element distribution and the magnetic properties were investigated in (Ce,Nd)-Fe-B sintered magnets prepared by mixing Nd13.5Fe80B6.5 and Ce9Nd4.5Fe80B6.5 powders with different mass ratios. Two main phases exist, but element diffusion is evident, and the chemical composition of the main phase is widely different from that of the master alloy. The Ce element tends to be expelled from the Ce-rich Re2Fe14B phase. Compared with the Ce-rich main phase, the Nd-rich Re2Fe14B phase is more stable in structure. Although the microstructure is inhomogeneous and the magnetocrystalline anisotropy is variable, the magnetization reversal is uniform in these dual main-phase magnets, which should ascribe to the existence of the exchange coupling, and magnetization reversal undergoes the nucleation of the reversed domain in irreversible magnetization. It is expected to further improve the coercivity by optimizing the distribution of the Nd-rich main phase in preparing the resource-saving (Ce,Nd)2Fe14B sintered magnets.

  11. Paleomagnetic Study of a Reversal of the Earth's Magnetic Field.

    PubMed

    Dunn, J R; Fuller, M; Ito, H; Schmidt, V A

    1971-05-21

    A detailed record of a field reversal has been obtained from the natural remanent magnetization of the Tatoosh intrusion in Mount Rainier National Park, Washington. The reversal took place at 14.7 +/- 1 million years and is interpreted to be from reverse to normal. A decrease in the intensity of the field of about an order of magnitude occurs immediately before the reversal, while its orientation remains substantially unchanged. The onset of the reversal is marked by abrupt swinging of the virtual geomagnetic pole along an arc of a great circle. During the reversal the pole traces a path across the Pacific. In the last stage of the process recorded in the sections, the succession of virtual geomagnetic poles is very similar to those generated by secular variation in the recent past. Although the cooling rate of the intrusion is not sufficiently well known to permit a useful calculation of the duration of the reversal process, an estimate based on the length of the supposed secular variation cycles gives 1 to 4 x 103 years for the reversal of field direction and approximately 1 x 104 years for the time scale of the intensity changes.

  12. Magnetic reversals in basal Ediacaran cap carbonates: A critical review

    NASA Astrophysics Data System (ADS)

    Raub, T. D.; Evans, D. A.

    2006-05-01

    At least one paleomagnetic reversal has been reported from each of three "Snowball Earth" postglacial cap cabonate units: Walsh cap of Kimberley, northern Australia; Mirassol d'Oeste in Amazonia; and Hadash in Oman. Our data from Nuccaleena cap dolostone of South Australia add a fourth to that list. We critically review all four studies and note that: a) Strict stratigraphic control on position of reversals is only documented for Mirassol d'Oeste and Nuccaleena caps. The Walsh cap sites are not stratigraphically constrained, and the Hadash reversal stratigraphy is only apparent after site data are combined from sections separated by 10's to 100's of km. b) Although Walsh, Hadash, and Nuccaleena remanences pass regional fold tests, the folding events could be substantially younger than cap deposition. Dual-polarity remagnetizations are well-documented in other carbonates. Despite satisfactory rock-magnetic results from Mirassol d'Oeste, critical field stability tests on the age of magnetization are lacking. c) Indirect syn-sedimentary tests of magnetization are only documented and passed for Nuccaleena dolostone. Mean Nuccaleena magnetization directions are similar to those of the paraconformably underlying glacial Elatina Formation, which passes a synsedimentary fold test; and two postglacial reversal levels are correlatable across three sections and ~50 km of nearly continuous on-strike exposure. d) Reversals from Mirassol d'Oeste and Nuccaleena cap carbonates cannot correlate directly with each other if post-Snowball paleooceanographic carbon isotope trends or values are assumed to be globally synchronous. Allowing for complex ocean chemistry, the two units could be broadly coeval, but if both paleomagnetic signals are primary then they must be diachronous on polarity-zone timescales. e) Given the pattern of observed reversal profiles established with confidence for at least the Nuccaleena cap, we contend that only magnetostratigraphic studies of high spatial

  13. Bistability between equatorial and axial dipoles during magnetic field reversals.

    PubMed

    Gissinger, Christophe; Petitdemange, Ludovic; Schrinner, Martin; Dormy, Emmanuel

    2012-06-08

    Numerical simulations of the geodynamo in the presence of heterogeneous heating are presented. We study the dynamics and the structure of the magnetic field when the equatorial symmetry of the flow is broken. If the symmetry breaking is sufficiently strong, the m=0 axial dipolar field is replaced by a hemispherical magnetic field, dominated by an oscillating m=1 magnetic field. Moreover, for moderate symmetry breaking, a bistability between the axial and the equatorial dipole is observed. In this bistable regime, the axial magnetic field exhibits chaotic switches of its polarity, involving the equatorial dipole during the transition period. This new scenario for magnetic field reversals is discussed within the framework of Earth's dynamo.

  14. Investigation of the magnetization reversal mechanism of electrolessly deposited Co-B nanotubes

    NASA Astrophysics Data System (ADS)

    Richardson, David; Kingston, Samuel; Rhen, Fernando M. F.

    2016-05-01

    Co-B nanotubes were prepared via an electroless deposition method. The morphology, magnetic properties and the magnetization reversal mechanism of the nanotubes were investigated. Deposition was carried out in porous polycarbonate membranes leading to the formation of Co-B nanotubes with an average external diameter of 400 nm and lengths up to 6 μm. Electroless deposition resulted in the formation of alloys with composition Co70B30 and a specific magnetization of 65.6 J T-1kg-1, which is about 40 % of that of pure Co (161 J T-1kg-1). The transversal and vortex modes were identified as the mechanisms responsible for magnetization reversal in the nanotubes. A crossover between the two modes is observed at low angles and the results are in line with current models for switching mechanisms of nanotubes.

  15. Influence of time dependent longitudinal magnetic fields on the cooling process, exchange bias and magnetization reversal mechanism in FM core/AFM shell nanoparticles: a Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Yüksel, Yusuf; Akıncı, Ümit

    2016-12-01

    Using Monte Carlo simulations, we have investigated the dynamic phase transition properties of magnetic nanoparticles with ferromagnetic core coated by an antiferromagnetic shell structure. Effects of field amplitude and frequency on the thermal dependence of magnetizations, magnetization reversal mechanisms during hysteresis cycles, as well as on the exchange bias and coercive fields have been examined, and the feasibility of applying dynamic magnetic fields on the particle have been discussed for technological and biomedical purposes.

  16. Magnetization and microstructure dynamics in Fe/MnAs/GaAs(001): Fe magnetization reversal by a femtosecond laser pulse.

    PubMed

    Spezzani, C; Ferrari, E; Allaria, E; Vidal, F; Ciavardini, A; Delaunay, R; Capotondi, F; Pedersoli, E; Coreno, M; Svetina, C; Raimondi, L; Zangrando, M; Ivanov, R; Nikolov, I; Demidovich, A; Danailov, M B; Popescu, H; Eddrief, M; De Ninno, G; Kiskinova, M; Sacchi, M

    2014-12-12

    Thin film magnetization reversal without applying external fields is an attractive perspective for applications in sensors and devices. One way to accomplish it is by fine-tuning the microstructure of a magnetic substrate via temperature control, as in the case of a thin Fe layer deposited on a MnAs/GaAs(001) template. This work reports a time-resolved resonant scattering study exploring the magnetic and structural properties of the Fe/MnAs system, using a 100 fs optical laser pulse to trigger local temperature variations and a 100 fs x-ray free-electron laser pulse to probe the induced magnetic and structural dynamics. The experiment provides direct evidence that a single optical laser pulse can reverse the Fe magnetization locally. It reveals that the time scale of the magnetization reversal is slower than that of the MnAs structural transformations triggered by the optical pulse, which take place after a few picoseconds already.

  17. Voltage controlled core reversal of fixed magnetic skyrmions without a magnetic field

    PubMed Central

    Bhattacharya, Dhritiman; Al-Rashid, Md Mamun; Atulasimha, Jayasimha

    2016-01-01

    Using micromagnetic simulations we demonstrate core reversal of a fixed magnetic skyrmion by modulating the perpendicular magnetic anisotropy of a nanomagnet with an electric field. We can switch reversibly between two skyrmion states and two ferromagnetic states, i.e. skyrmion states with the magnetization of the core pointing down/up and periphery pointing up/down, and ferromagnetic states with magnetization pointing up/down, by sequential increase and decrease of the perpendicular magnetic anisotropy. The switching between these states is explained by the fact that the spin texture corresponding to each of these stable states minimizes the sum of the magnetic anisotropy, demagnetization, Dzyaloshinskii-Moriya interaction (DMI) and exchange energies. This could lead to the possibility of energy efficient nanomagnetic memory and logic devices implemented with fixed skyrmions without using a magnetic field and without moving skyrmions with a current. PMID:27506159

  18. Voltage controlled core reversal of fixed magnetic skyrmions without a magnetic field.

    PubMed

    Bhattacharya, Dhritiman; Al-Rashid, Md Mamun; Atulasimha, Jayasimha

    2016-08-10

    Using micromagnetic simulations we demonstrate core reversal of a fixed magnetic skyrmion by modulating the perpendicular magnetic anisotropy of a nanomagnet with an electric field. We can switch reversibly between two skyrmion states and two ferromagnetic states, i.e. skyrmion states with the magnetization of the core pointing down/up and periphery pointing up/down, and ferromagnetic states with magnetization pointing up/down, by sequential increase and decrease of the perpendicular magnetic anisotropy. The switching between these states is explained by the fact that the spin texture corresponding to each of these stable states minimizes the sum of the magnetic anisotropy, demagnetization, Dzyaloshinskii-Moriya interaction (DMI) and exchange energies. This could lead to the possibility of energy efficient nanomagnetic memory and logic devices implemented with fixed skyrmions without using a magnetic field and without moving skyrmions with a current.

  19. Voltage controlled core reversal of fixed magnetic skyrmions without a magnetic field

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Dhritiman; Al-Rashid, Md Mamun; Atulasimha, Jayasimha

    2016-08-01

    Using micromagnetic simulations we demonstrate core reversal of a fixed magnetic skyrmion by modulating the perpendicular magnetic anisotropy of a nanomagnet with an electric field. We can switch reversibly between two skyrmion states and two ferromagnetic states, i.e. skyrmion states with the magnetization of the core pointing down/up and periphery pointing up/down, and ferromagnetic states with magnetization pointing up/down, by sequential increase and decrease of the perpendicular magnetic anisotropy. The switching between these states is explained by the fact that the spin texture corresponding to each of these stable states minimizes the sum of the magnetic anisotropy, demagnetization, Dzyaloshinskii-Moriya interaction (DMI) and exchange energies. This could lead to the possibility of energy efficient nanomagnetic memory and logic devices implemented with fixed skyrmions without using a magnetic field and without moving skyrmions with a current.

  20. Reversing the polarity of a cochlear implant magnet after magnetic resonance imaging.

    PubMed

    Jeon, Ju Hyun; Bae, Mi Ran; Chang, Jae Won; Choi, Jae Young

    2012-08-01

    The number of patients with cochlear implant (CI) has been rapidly increasing in recent years, and these patients show a growing need of examination by magnetic resonance imaging (MRI). However, the use of MRI on patients with CI is restricted by the internal magnet of the CI. Many studies have investigated the safety of performing 1.5T MRI on patients with CI, which is now being practiced in a clinical setting. We experienced a case in which the polarity of the cochlear implant magnet was reversed after the patient was examined using 1.5T MRI. The external device was attached to the internal device oppositely. We could not find displacement of the internal device, magnet, or electrode upon radiological evaluation. We came up with two possible mechanisms by which the polarity of the magnet reversed. The first possibility was that the magnetic field of MRI reversed the polarity of the magnet. The second was that the internal magnet was physically realigned while interacting with the MRI. We believe the second hypothesis to be more reliable. A removable magnet and a loose magnet boundary of a CI device may have allowed for physical reorientation of the internal magnet. Therefore, in order to avoid these complications, first, the internal magnet must not be aligned anti-parallel with the magnetic polarity of MRI. In the Siemens MRI, the vector of the magnetic field is downward, so implant site should be placed in facing upwards to minimize demagnetization. In the GE Medical Systems MRI, the vector of the magnetic field is upward, so the implant site should be placed facing downwards. Second, wearing of a commercial mold which is fixed to the internal device before performing MRI can be helpful. In addition, any removable internal magnets in a CI device should be removed before MRI, especially in the trunk. However, to ultimately solve this problem, the pocket of the internal magnet should be redesigned for safety.

  1. Magnetic bistability and controllable reversal of asymmetric ferromagnetic nanorings.

    PubMed

    Zhu, F Q; Chern, G W; Tchernyshyov, O; Zhu, X C; Zhu, J G; Chien, C L

    2006-01-20

    Magnetization reversals through the formation of a vortex state and the rotation of an onion state are two processes with comparable probabilities for symmetric magnetic nanorings with a radius of about 50 nanometers. This magnetic bistability is the manifestation of the competition between the exchange energy and the magnetostatic energy in nanomagnets. The relative probability of the two processes in symmetric nanorings is dictated by the ring geometry and cannot be altered after fabrication. In this work, we report a novel type of nanorings--asymmetric nanorings. By tuning the asymmetry, we can control the fraction of the vortex formation process from about 40% to nearly 100% by utilizing the direction of the external magnetic field. The observed results have been accounted for by the dependence of the domain-wall energy on the local cross-section area for which we have provided theoretical calculations.

  2. Controlled Magnetic Reversal and Frustration in Artificial Quasicrystals

    NASA Astrophysics Data System (ADS)

    Bhat, Vinayak

    2014-03-01

    Recent studies of ferromagnetic (FM) antidot arrays have been restricted to simple periodic lattices (square, triangular, etc.). We have fabricated artificial FM quasicrystals (AFQ), which are aperiodic antidot lattices that are self-similar, retain definite rotational symmetry, and consist of a multiply-connected network of permalloy film segments. We focus on Penrose P2 tilings (P2T) constructed from film segments of two lengths (d1 = 810 nm -1618 nm, d2 = 500 nm - 1 μ m), width W ~ 100 nm, and thickness t = 25 nm. Static and dynamic magnetizations were studied using DC magnetometry, broadband (BB) FMR, and micromagnetic simulations (MS). Reproducible ``knee'' anomalies observed in the hysteretic, low-field DC magnetization M(H,T) signal a series of abrupt transitions between ordered magnetization textures, concluding in a smooth evolution into a saturated state. Numerous FMR mode signatures quantitatively reproduce in opposite DC field sweeps in the near-saturated regime, which suggests pinning of the magnetization parallel to the AD edges and confinement of domain walls at P2T vertices control segment polarization and reversal. Novel ``asymmetric'' modes, defined by their presence on only one side of the field origin in a given sweep, are observed only in the reversal regime, and accompany knee anomalies in M(H,T). MS agree with experimental DC hysteresis loops and FMR spectra, and indicate that systematic control of magnetic reversal and domain wall motion can be achieved via tiling design, offering a new paradigm of magnonic quasicrystals. AFQ also behave as novel artificial spin ice systems that exhibit non-stochastic switching due to their aperiodicity and inequivalent pattern vertices. MS indicate pinned Dirac monopoles and confined magnetic avalanches exist in AFQ. Research supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194.

  3. Transition states of magnetization reversal in ferromagnetic nanorings

    NASA Astrophysics Data System (ADS)

    Chaves-O'Flynn, Gabriel; Kent, Andrew; Stein, Daniel

    2008-03-01

    Thin ferromagnetic rings are of interest for fundamental studies of magnetization reversal, in part, because they are a rare example of a geometry for which an analytical solution for the rate of thermally induced switching has been determined [1]. The theoretical model predicts the transition state to be either a global magnetization rotation of constant azimuthal angle or a localized fluctuation, denoted the instanton saddle. Numerically we have confirmed that for a range of values of external magnetic field and ring size the instanton saddle is energetically favored [2]. The model takes the annular width to be small compared to the mean radius of the annulus; in which case the main contribution to the magnetization energy comes from the surface magnetostatic energy. We present numerical micromagnetic calculations of the activation energy for thermally induced magnetization reversal for the two different transition states for the case when the annular width is equal in magnitude to the mean radius of the ring. Results of the total and surface magnetostatic energies are compared for different ring sizes. [1] K. Martens, D.L. Stein, A.D. Kent, PRB 73, 054413 (2006) [2] G.D. Chaves-O'Flynn, K. Xiao, D.L. Stein, A. D. Kent, arXiv:0710.2546 (2007)

  4. Magnetic microparticle-polydimethylsiloxane composite for reversible microchannel bonding.

    PubMed

    Tsao, Chia-Wen; Lee, Yueh-Pu

    2016-01-01

    In this study, an iron oxide magnetic microparticles and poly(dimethylsiloxane) (MMPs-PDMS) composite material was employed to demonstrate a simple high-strength reversible magnetic bonding method. This paper presents the casting of opaque-view (where optical inspection through the microchannels was impossible) and clear-view (where optical inspection through the microchannel was possible) MMPs-PDMS. The influence of the microchannel geometries on the casting of the opaque-view casting was limited, which is similar to standard PDMS casting. Clear-view casting performance was highly associated with the microchannel geometries. The effects of the microchannel layout and the gap between the PDMS cover layer and the micromold substrate were thoroughly investigated. Compared with the native PDMS bonding strength of 31 kPa, the MMPs-PDMS magnetic bonding experiments showed that the thin PDMS film with an MMPs-PDMS layer effectively reduced the surface roughness and enhanced MMPs-PDMS reversible magnetic bonding strength. A thin PDMS film-coated opaque-view MMPs-PDMS device exhibited the greatest bonding strength of 110 kPa, and a clear-view MMPs-PDMS device with a thin PDMS film attained a magnetic bonding strength of 81 kPa.

  5. Magnetic microparticle-polydimethylsiloxane composite for reversible microchannel bonding

    PubMed Central

    Tsao, Chia-Wen; Lee, Yueh-Pu

    2016-01-01

    Abstract In this study, an iron oxide magnetic microparticles and poly(dimethylsiloxane) (MMPs-PDMS) composite material was employed to demonstrate a simple high-strength reversible magnetic bonding method. This paper presents the casting of opaque-view (where optical inspection through the microchannels was impossible) and clear-view (where optical inspection through the microchannel was possible) MMPs-PDMS. The influence of the microchannel geometries on the casting of the opaque-view casting was limited, which is similar to standard PDMS casting. Clear-view casting performance was highly associated with the microchannel geometries. The effects of the microchannel layout and the gap between the PDMS cover layer and the micromold substrate were thoroughly investigated. Compared with the native PDMS bonding strength of 31 kPa, the MMPs-PDMS magnetic bonding experiments showed that the thin PDMS film with an MMPs-PDMS layer effectively reduced the surface roughness and enhanced MMPs-PDMS reversible magnetic bonding strength. A thin PDMS film-coated opaque-view MMPs-PDMS device exhibited the greatest bonding strength of 110 kPa, and a clear-view MMPs-PDMS device with a thin PDMS film attained a magnetic bonding strength of 81 kPa. PMID:27877852

  6. SOLAR MAGNETIC FIELD REVERSALS AND THE ROLE OF DYNAMO FAMILIES

    SciTech Connect

    DeRosa, M. L.

    2012-09-20

    The variable magnetic field of the solar photosphere exhibits periodic reversals as a result of dynamo activity occurring within the solar interior. We decompose the surface field as observed by both the Wilcox Solar Observatory and the Michelson Doppler Imager into its harmonic constituents, and present the time evolution of the mode coefficients for the past three sunspot cycles. The interplay between the various modes is then interpreted from the perspective of general dynamo theory, where the coupling between the primary and secondary families of modes is found to correlate with large-scale polarity reversals for many examples of cyclic dynamos. Mean-field dynamos based on the solar parameter regime are then used to explore how such couplings may result in the various long-term trends in the surface magnetic field observed to occur in the solar case.

  7. The reversed internal magnet of cochlear implant after magnetic resonance imaging.

    PubMed

    Kong, Soo-Keun; Oh, Se-Joon; Lee, Il-Woo; Goh, Eui-Kyung

    2014-01-01

    Cochlear implants (CI) have now become a standard method of treating severe to profound hearing loss. Recently, the number of patients with CI has been rapidly increasing as the big benefits of CI become more widely known. Magnetic resonance imaging (MRI) has also become a routine diagnostic imaging modality, used in the diagnosis of common conditions, including stroke, back pain, and headache. We report our recent experience with a case in which internal magnet of the cochlear implant was reversed after 1.5-T lumbar spine MRI. This complication is managed successfully by reversing the orientation of the external magnet in the head coil.

  8. Magnetically induced enhancement of reversibly responding conductometric sensors

    SciTech Connect

    Baker, Caitlin; Laminack, William; Tune, Travis; Gole, James

    2014-04-28

    Small magnetic fields are found to greatly enhance the reversible room temperature conductometric responses of n and p- type porous silicon (PS) interfaces, treated with nanostructured island sites containing paramagnetic Co(II) and Fe(II). At concentrations sufficiently low so as to avoid cross talk between the nanostructured island sites, the response to NO concentrations demonstrates the significant effect which the Co(II) and Fe(II) have on the decorated extrinsic semiconductor majority charge carriers as they direct a dominant electron transduction process for reversible electron transduction and chemical sensing (Inverse Hard and Soft acid/base principle) in the absence of significant chemical bond formation. Co(II) and Fe(II) oxide sites enhance response and provide a means for small magnetic fields to interact with and enhance the sensor interface response. For p-type systems, the interaction is with small virtually constant thermal electron populations lying above the Fermi energy at 0 K. The electron removal rate increases with magnetic field strength. At the highest magnetic fields and NO analyte concentrations the available electron population is depleted, and the response to the analyte decreases at higher concentrations. At lower magnetic fields (<1000 G), the response faithfully follows concentration. For n-type systems, the magnetic field interaction increases resistance. This increase in response may be attributed to the interaction with donor levels ∼0.025 eV below the conduction band. A substantial enhancement of sensor response relative to that for the Co(II) and Fe(II) treated PS interfaces is observed, with the introduction of a small magnetic field greatly increasing an already enhanced conductometric response.

  9. Nucleation of Magnetization Reversal in Individual Nanosized Particles and Wires

    NASA Astrophysics Data System (ADS)

    Wernsdorfer, W.

    1997-03-01

    Low temperatures magnetization measurements of individual ferromagnetic particles and wires are presented. The detector was a Nb micro-bridge-DC-SQUID, elaborated using electron-beam lithography. We studied particles fabricated by electron beam lithography. They had an elliptic contour with axes between 50 and 1000 nm and a thickness between 5 and 50 nm and were made of Ni, Co, Fe (W. Wernsdorfer et al., J. Magn. Magn. Mat., 145, 33 (1995) and 151, 38 (1995), and Phys. Rev. B, 53, 3341 (1996).). Furthermore, we studied Ni and Co wires (cylinders) with diameters ranging from 40 nm to 100 nm and lengths up to 5000 nm (W. Wernsdorfer et al., Phys. Rev. Lett., 77, 1873 (1996)). They were produced by the technique of electrodeposition in nanoporous polycarbonate membranes (J. Meier, B. Doudin and J.-Ph. Ansermet, J. Appl. Phys, 79, 6010 (1996).). We studied nanoparticles and filled carbon nanotubes synthesized by arc-discharge, with dimensions between 10 and 500 nm. These particles are single crystalline and the surface roughness is about two atomic layers (C. Guerret-Pi=E9court, Y. Le Bouar, A. Loiseau and H. Pascard, Nature, 372, 761 (1994).). Finally, we studied single crystalline particles elaborated by colloidal self assemblies (M. P. Pileni et al., submitted.). The angular dependence of the magnetization reversal could be explained approximately by simple classical micromagnetic concepts: uniform rotation and curling. However, our measurement evidenced nucleation and propagation of domain walls except for the smallest particles of about 20 nm. The switching field distributions as a function of temperature and field sweeping rate and the probabilities of switching showed that the magnetization reversal was thermally activated. These measurements allowed us to estimate the "activation volume" which triggered the magnetization reversal. Our measurements showed for the first time that the magnetization reversal of a ferromagnetic nanoparticle of good quality can be

  10. Nonstochastic magnetic reversal in artificial quasicrystalline spin ice

    SciTech Connect

    Farmer, B.; Bhat, V. S.; Woods, J.; Teipel, E.; Smith, N.; De Long, L. E.; Sklenar, J.; Ketterson, J. B.; Hastings, J. T.

    2014-05-07

    We have measured the isothermal DC magnetization of Penrose P2 tilings (P2T) composed of wire segments of permalloy thin film. Micromagnetic simulations reproduce the coercive fields and “knee anomalies” observed in experimental data and show magnetic shape anisotropy constrains segments to be single-domain (Ising spins) at low fields, similar to artificial spin ice (ASI). Mirror symmetry controls the initial reversal of individual segments oriented parallel to the applied field, followed by complex switching of multiple adjacent segments (“avalanches”) of various orientations such that closed magnetization loops (“vortices”) are favored. Ferromagnetic P2T differ from previously studied ASI systems due to their aperiodic translational symmetry and numerous inequivalent pattern vertices, which drive nonstochastic switching of segment polarizations.

  11. Effect of horizontal magnetization reversal of the tips on magnetic force microscopy images.

    PubMed

    Alekseev, Alexander; Popkov, Anatoliy; Shubin, Andrey; Pudonin, Feodor; Djuzhev, Nikolay

    2014-01-01

    The effect of magnetization reversal of magnetic force microscope (MFM) tips based on low coercive thin-films on MFM images has been studied both experimentally and theoretically. By analyzing the MFM images obtained on structures with high magnetic stray fields we show that during the imaging process the magnetic state of the probe is modified anisotropically: the horizontal component of the magnetization follows the external field, whereas the vertical component of the magnetization stays almost constant. The observed complex magnetic behavior of the tip is explained theoretically based on the shape anisotropy of the tip. The obtained results are important for interpretation of MFM images of structures with high magnetic moment. Moreover, these results can be used for characterization of both laboratory-made and commercially available MFM tips.

  12. Magnetic properties of hybrid elastomers with magnetically hard fillers: rotation of particles

    NASA Astrophysics Data System (ADS)

    Stepanov, G. V.; Borin, D. Yu; Bakhtiiarov, A. V.; Storozhenko, P. A.

    2017-03-01

    Hybrid magnetic elastomers belonging to the family of magnetorheological elastomers contain magnetically hard components and are of the utmost interest for the development of semiactive and active damping devices as well as actuators and sensors. The processes of magnetizing of such elastomers are accompanied by structural rearrangements inside the material. When magnetized, the elastomer gains its own magnetic moment resulting in changes of its magneto-mechanical properties, which remain permanent, even in the absence of external magnetic fields. Influenced by the magnetic field, magnetized particles move inside the matrix forming chain-like structures. In addition, the magnetically hard particles can rotate to align their magnetic moments with the new direction of the external field. Such an elastomer cannot be demagnetized by the application of a reverse field.

  13. 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.

  14. Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets.

    PubMed

    Bizen, Teruhiko; Kinjo, Ryota; Hasegawa, Teruaki; Kagamihata, Akihiro; Kida, Yuichiro; Seike, Takamitsu; Watanabe, Takahiro; Hara, Toru; Itoga, Toshiro; Asano, Yoshihiro; Tanaka, Takashi

    2016-11-29

    We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

  15. Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

    NASA Astrophysics Data System (ADS)

    Bizen, Teruhiko; Kinjo, Ryota; Hasegawa, Teruaki; Kagamihata, Akihiro; Kida, Yuichiro; Seike, Takamitsu; Watanabe, Takahiro; Hara, Toru; Itoga, Toshiro; Asano, Yoshihiro; Tanaka, Takashi

    2016-11-01

    We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

  16. Radiation-induced magnetization reversal causing a large flux loss in undulator permanent magnets

    PubMed Central

    Bizen, Teruhiko; Kinjo, Ryota; Hasegawa, Teruaki; Kagamihata, Akihiro; Kida, Yuichiro; Seike, Takamitsu; Watanabe, Takahiro; Hara, Toru; Itoga, Toshiro; Asano, Yoshihiro; Tanaka, Takashi

    2016-01-01

    We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance. PMID:27897218

  17. Magnetic field reversals, polar wander, and core-mantle coupling

    SciTech Connect

    Courtillot, V.; Besse, J.

    1987-09-04

    True polar wander, the shifting of the entire mantle relative to the earth's spin axis, has been reanalyzed. Over the last 200 million years, true polar wander has been fast (approximately 5 centimeters per year) most of the time, except for a remarkable standstill from 170 to 110 million years ago. This standstill correlates with a decrease in the reversal frequency of the geomagnetic field and episodes of continental breakup. Conversely, true polar wander is high when reversal frequency increases. It is proposed that intermittent convection modulates the thickness of a thermal boundary layer at the base of the mantle and consequently the core-to-mantle heat flux. Emission of hot thermals from the boundary layer leads to increases in mantle convection and true polar wander. In conjunction, cold thermals released from a boundary layer at the top of the liquid core eventually lead to reversals. Changes in the locations of subduction zones may also affect true polar wander. Exceptional volcanism and mass extinctions at the Cretaceous-Tertiary and Permo-Triassic boundaries may be related to thermals released after two unusually long periods with no magnetic reversals. These environmental catastrophes may therefore be a consequence of thermal and chemical coupling in the earth's multilayer heat engine rather than have an extraterrestrial cause.

  18. Supershot performance with reverse magnetic shear in TFTR

    SciTech Connect

    Batha, S.H.; Levinton, F.M.; Zarnstorff, M.C.; Schmidt, G.L.

    1995-08-01

    Discharges with large regions of reversed magnetic shear and good energy and particle confinement have been produced in the Tokamak Fusion Test Reactor. These plasmas were created by heating the plasma during a rapid plasma current increase. The stability of these discharges is dependent on the shape of the q profile, in particular the value and location of the minimum value of q. Control of the q profile by optimizing the plasma startup, prelude start time, the neutral-beam directionality during the prelude heating phase, and the plasma current ramp rate is demonstrated. High-performance discharges, created by injecting more than 18 to 25 MW of neutral beam power into a plasma with reverse shear, are also described.

  19. Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle

    PubMed Central

    Bleve, Valentina; Schäfer, Christian; Franchi, Paola; Silvi, Serena; Mezzina, Elisabetta; Credi, Alberto; Lucarini, Marco

    2015-01-01

    Invited for this months cover are the groups of Professors Marco Lucarini and Alberto Credi at the University of Bologna. The cover picture shows coupled and uncoupled states of a [2]rotaxane incorporating stable nitroxide radical units in both the ring and dumbbell components. Interaction between nitroxide radicals could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon deprotonation of the rotaxane NH2+ centers that effects a quantitative displacement of a dibenzocrown macroring to a 4,4’-bipyridinium recognition site. The complete base- and acid-induced switching cycle of the EPR pattern was repeated several times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. For more details, see the Communication on p. 18 ff. PMID:25870780

  20. Tokamak equilibria with toroidal current reversal: properties and computational issues

    SciTech Connect

    Rodrigues, Paulo; Bizarro, Joao P. S.

    2006-11-30

    Several properties of axisymmetric plasma equilibria with toroidal-current reversal (TCR) are discussed using some unifying concepts from catastrophe theory. Namely, those of structural stability of functions near critical points, singularity unfolding by small perturbations, and model parameter-space division by bifurcation sets are found to be of particular usefulness. Magnetic configurations displaying, simultaneously, TCR and nested flux surfaces are thence shown to be necessarily degenerate and structurally unstable, meaning that they are easily transformed into non-nested ones by small perturbations in the model parameter set. This should lead to a new paradigm when discussing TCR equilibria, as most of present knowledge relies mainly on the properties of nested solutions, which is expected to favor the study of the broader class of non-nested configurations that recently attracted a considerable discussion in the fusion community. In addition, it is also shown how TCR imposes some constraints on plasma profiles, and how these may be dealt with computationally while keeping the ability to manipulate the shape of the inner island system.

  1. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys.

    PubMed

    Bruno, N M; Wang, S; Karaman, I; Chumlyakov, Y I

    2017-01-16

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg(-1) K(-1) or 22 J kg (-1) K(-1), and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed.

  2. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Bruno, N. M.; Wang, S.; Karaman, I.; Chumlyakov, Y. I.

    2017-01-01

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg‑1 K‑1 or 22 J kg ‑1 K‑1, and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed.

  3. Reversible Martensitic Transformation under Low Magnetic Fields in Magnetic Shape Memory Alloys

    PubMed Central

    Bruno, N. M.; Wang, S.; Karaman, I.; Chumlyakov, Y. I.

    2017-01-01

    Magnetic field-induced, reversible martensitic transformations in NiCoMnIn meta-magnetic shape memory alloys were studied under constant and varying mechanical loads to understand the role of coupled magneto-mechanical loading on the transformation characteristics and the magnetic field levels required for reversible phase transformations. The samples with two distinct microstructures were tested along the [001] austenite crystallographic direction using a custom designed magneto-thermo-mechanical characterization device while carefully controlling their thermodynamic states through isothermal constant stress and stress-varying magnetic field ramping. Measurements revealed that these meta-magnetic shape memory alloys were capable of generating entropy changes of 14 J kg−1 K−1 or 22 J kg −1 K−1, and corresponding magnetocaloric cooling with reversible shape changes as high as 5.6% under only 1.3 T, or 3 T applied magnetic fields, respectively. Thus, we demonstrate that this alloy is suitable as an active component in near room temperature devices, such as magnetocaloric regenerators, and that the field levels generated by permanent magnets can be sufficient to completely transform the alloy between its martensitic and austenitic states if the loading sequence developed, herein, is employed. PMID:28091551

  4. Asymmetric magnetization reversal process in Co nanohill arrays

    SciTech Connect

    Rosa, W. O.; Martinez, L.; Jaafar, M.; Asenjo, A.; Vazquez, M.

    2009-11-15

    Co thin films deposited by sputtering onto nanostructured polymer [poly(methyl methacrylate)] were prepared following replica-antireplica process based on porous alumina membrane. In addition, different capping layers were deposited onto Co nanohills. Morphological and compositional analysis was performed by atomic force microscopy and x-ray photoemission spectroscopy techniques to obtain information about the surface characteristics. The observed asymmetry in the magnetization reversal process at low temperatures is ascribed to the exchange bias generated by the ferromagnetic-antiferromagnetic interface promoted by the presence of Co oxide detected in all the samples. Especially relevant is the case of the Cr capping, where an enhanced magnetic anisotropy in the Co/Cr interface is deduced.

  5. Polarity reversals and tilt of the Earth's magnetic dipole

    NASA Technical Reports Server (NTRS)

    Dolginov, A. Z.

    1993-01-01

    There is evidence that the terrestrial magnetic field is connected with the Earth's mantle: (1) there are magnetic anomalies that do not take part in the westward drift of the main field, but are fixed with respect to the mantle; (2) the geomagnetic pole position flips in a particular way by preferred meridional paths during a reversal; and (3) magnetic polarity reversals are correlated with the activations of geological processes. These facts may be explained if we take into account that a significant horizontal temperature gradient can exist in the top levels of the liquid core because of the different thermoconductivity of the different areas of the core-mantle boundary. These temperature inhomogeneities can penetrate the core because fluxes along the core boundary (the thermal wind) can be strongly suppressed by a small redistribution of the chemical composition in the top of the core. The nonparallel gradients of the temperature, density, and composition on the top of the core create a curled electric field that produces a current and a magnetic field. This seed-field can be amplified by motions in the core. The resulting field does not forget the seed-field distribution and in this way the field on the Earth surface (that can be created only in regions with high conductivity, i.e. in the core) is connected with the core-mantle boundary. Contrary to the usual approach to the dynamo problem, we will take into account that the seed field of thermoelectric origin is acting not only at some initial moment of time but permanently.

  6. Computational micromagnetic investigation of magnetization reversal in Nd-Fe-B nanocomposite magnets

    NASA Astrophysics Data System (ADS)

    David, S.; Kevorkian, B.; Toussaint, J. C.; Givord, D.

    1998-06-01

    As a complement to the experimental analysis of magnetization reversal in a two-phase system, a numerical micromagnetic three-dimensional calculation is developed and tested. It is applied to a set of 64 nanometer-scale hard (Nd2Fe14B) and soft (Fe3B) cubic grains. Calculations reproduce qualitatively the experimentally observed processes and allow the relation between the structure and the coercivity mechanism in nanocomposite hard magnetic materials to be better understood.

  7. Micromagnetic model of noncollective magnetization reversal in ultrathin magnetic dots with in-plane uniaxial anisotropy

    NASA Astrophysics Data System (ADS)

    Fruchart, O.; Kevorkian, B.; Toussaint, J. C.

    2001-05-01

    In most magnetic systems the magnetization reversal is nonuniform, and is initiated in a so-called ``nucleation volume,'' whose dimensions are by far smaller than the total system volume. For simplicity reasons magnetization reversal theories are usually based on the assumption that coherent rotation occurs in this ``nucleation volume.'' In this approach, self-dipolar fields and exchange forces are obviously not well described, because in reality the nucleation volume is coupled with the rest of the system. In the case of ultrathin dots with in-plane uniaxial anisotropy, we could take into account dipolar fields and the exchange stiffness explicitly. The approximations used to derive analytical equations were suggested by experimental results on real dots. The model yields the nonuniform micromagnetic configuration of nucleation volumes. It predicts nucleation and reversal field values, as well as the field dependence of the energy barrier to be overcome to reverse the dot at finite temperature. The (negative) reversal field is found to increase with the dot thickness T and the volume magnetization Ms, and to decrease with the material anisotropy K. In the low-thickness limit, the reversal field Hr approaches the Stoner-Wohlfarth reversal field Ha with a law close to 1-\\|Hr/Ha\\|~M7/2sA- 3/4K-1T3/2, where A is the exchange constant. The relevance of the approximations used is discussed and demonstrated by the good agreement found for all predictions between experiment and/or numerical calculations on the one hand and the model on the other hand.

  8. Recording-media-related morphology and magnetic properties of crystalline CoPt{sub 3} and CoPt{sub 3}-Au core-shell nanoparticles synthesized via reverse microemulsion

    SciTech Connect

    Bahmanrokh, Ghazaleh Hashim, Mansor; Matori, Khamirul Amin; Kanagesan, Samikannu; Sabbaghizadeh, Rahim; Ezzad Shafie, Mohd Shamsul; Navasery, Manizheh; Soltani, Nayereh; Vaziri, Parisa

    2014-09-07

    A comparative experimental study of the magnetic properties of CoPt{sub 3} and CoPt{sub 3}/Au nanoparticles as well as a detailed study of the structural properties of the samples by X-ray diffraction, Transmission electron microscopy, and vibrating sample magnetometer is presented in this work. In addition, the effect of particle size on the structure and magnetic properties of nanoparticles prepared by microemulsion is studied. The correlation between particle size, crystallinity, and magnetization was studied as well. CoPt nanoparticles have been studied intensively over the last decade because of their increased magnetic anisotropy in the ordered phase that can be interesting for high density magnetic recording. A significant high coercivity for as-prepared CoPt{sub 3} and CoPt{sub 3}-Au nanoparticles was obtained at room temperature and enhanced after annealing. The focused aim of our study is to obtain high coercivity at room temperature that follows the Curie-Weiss law. This indicates an interacting system in which the nanoparticles behave like single domain ferromagnetic materials in the particle size range of 8 to 35 nm. In addition, the interaction increases by cooling the samples to low temperature around 15 K. Temperature dependence 1/M graph was obtained to investigate the behavior of nanoparticles at low temperature and shows the best fit with Curie-Weis mode.

  9. A general perspective on the magnetization reversal in cylindrical soft magnetic nanowires with dominant shape anisotropy

    NASA Astrophysics Data System (ADS)

    Kuncser, A.; Antohe, S.; Kuncser, V.

    2017-02-01

    Peculiarities of the magnetization reversal process in cylindrical Ni-Cu soft magnetic nanowires with dominant shape anisotropy are analyzed via both static and time dependent micromagnetic simulations. A reversible process involving a coherent-like spin rotation is always observed for magnetic fields applied perpendicularly to the easy axis whereas nucleation of domain walls is introduced for fields applied along the easy axis. Simple criteria for making distinction between a Stoner-Wohlfarth type rotation and a nucleation mechanism in systems with uniaxial magnetic anisotropy are discussed. Superposed reversal mechanisms can be in action for magnetic fields applied at arbitrary angles with respect to the easy axis within the condition of an enough strong axial component required by the nucleation. The dynamics of the domain wall, involving two different stages (nucleation and propagation), is discussed with respect to initial computing conditions and orientations of the magnetic field. A nucleation time of about 3 ns and corkscrew domain walls propagating with a constant velocity of about 150 m/s are obtained in case of Ni-Cu alloy (Ni rich side) NWs with diameters of 40 nm and high aspect ratio.

  10. Control of magnetization reversal by combining shape and magnetocrystalline anisotropy in epitaxial Fe planar nanowires.

    PubMed

    Paz, E; Cebollada, F; Palomares, F J; García-Sánchez, F; González, J M

    2010-06-25

    This work presents an analysis of the in-plane magnetization reversal mechanisms of Fe nanowires, with widths from 100 nm to 1 microm, fabricated in epitaxial Au(001)/Fe(001)/MgO(001) thin films by means of focused ion and electron beam lithographies, with either positive or negative resist. The experimental results show that the switching mechanisms and hysteresis are almost exclusively functions of the dimensions of the wires and of the Fe intrinsic properties, with minor influence of the specific fabrication route employed upon optimization of nanostructure parameters in terms of crystallinity and morphology, and well defined and reproducible geometry. The reversal processes evolve from wall pinning at low angles between the applied field and the axis of the wires to basically uniform magnetization rotation at high angles. This behaviour can be described in terms of single spin configurations, thus ruling out the formation of multidomain structures even at high angles. The ability to achieve these high quality and well controlled nanowires allowed us to develop an analytical model, based on uniform magnetization configurations considering just the intrinsic Fe properties and the shape and dimensions of the wires. This simple approach provides a very good qualitative and quantitative agreement with the experimental results, thus evidencing the relatively small role of other extrinsic factors in the magnetization processes.

  11. Microwave-assisted magnetization reversal in a Co/Pd multilayer with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Nozaki, Yukio; Narita, Naoyuki; Tanaka, Terumitsu; Matsuyama, Kimihide

    2009-08-01

    Microwave-assisted magnetization reversal in a rectangle of a Co/Pd multilayer with a perpendicular magnetic anisotropy is examined using vector network analyzer ferromagnetic resonance (FMR) spectroscopy. A microwave field is applied along the in-plane direction of the rectangle together with a negative dc easy-axis field smaller than the coercive field. Broadening or splitting of the peak profile in the FMR spectrum suggesting the formation of multidomain structure appears after the microwave field is applied. The dominance of microwave-assisted nucleation of magnetization is supported by the frequency dependence of the probability with which the multidomain structure appears.

  12. A Rare Complication of Cochlear Implantation After Magnetic Resonance Imaging: Reversion of the Magnet.

    PubMed

    Öztürk, Erkan; Doruk, Can; Orhan, Kadir Serkan; Çelik, Mehmet; Polat, Beldan; Güldiken, Yahya

    2017-03-21

    Cochlear implants are mechanical devices used for patients with severe sensory-neural hearing loss, which has an inner magnet. It is proven that 1.5 Tesla magnetic resonance imaging (MRI) scanners are safe to use in patients with cochlear implant. In our patient, the authors aim to introduce a rare complication caused after a 1.5 Tesla MRI scanning and the management of this situation; the reversion of the magnet of the implant without displacement and significance of surgery in management.

  13. Inhomogeneities in spin states and magnetization reversal of geometrically identical elongated Co rings

    NASA Astrophysics Data System (ADS)

    Gao, X. S.; Adeyeye, A. O.; Goolaup, S.; Singh, N.; Jung, W.; Castaño, F. J.; Ross, C. A.

    2007-05-01

    The magnetic configurations and magnetic reversal processes in arrays of geometrically identical rounded rectangular Co rings have been investigated. Magnetic imaging reveals a range of configurations, including diagonal onion, horseshoe onion, and vortex states. Reversal from the onion to the vortex state can occur via different routes involving domain wall motion within the rings, and the mechanism depends on the applied field orientation.

  14. Magnetization Reversal Study of Geometrically Frustrated, Quasiperiodic Antidot Arrays

    NASA Astrophysics Data System (ADS)

    Woods, Justin; Bhat, Vinayak; Farmer, Barry; de Long, Lance; Hastings, Todd; Sklenar, Joseph; Ketterson, John

    2013-03-01

    We have used electron beam lithography to pattern quasiperiodic AD arrays in permalloy films of thickness 25 nm. Two five-fold rotationally symmetric Penrose tilings were fabricated with AD kites and darts having long (d1) and short edges (d2) equal to 1620 nm or 810 nm, and 1000 nm or 500 nm, respectively, with fixed Py line width of 100 nm. Two eight-fold Ammann tilings were patterned with square and rhomboid AD of edge lengths of 1000 nm or 2000 nm, resp. Magnetization reversal was studied at various angles between the in-plane, applied DC magnetic field H and the quasiperiodic array. We observed very reproducible hysteresis curves with low-field anomalies not present in our previous studies of periodic, square arrays of square-, circular- and diamond-shaped AD; e.g., for the Penrose tilings, we observed four reproducible knee anomalies (both for 81 H >-71 Oe). Micromagnetic simulations exhibit systematic evolution of domain walls (DW) in the hysteretic regime due to DW pinning by edges of the quasicrystalline pattern, which correlates DW evolution with observed features in magnetic hysteresis. Research at Kentucky is supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194.

  15. Study on the coherence degree of magnetization reversal in Permalloy single-domain nano-ellipses

    NASA Astrophysics Data System (ADS)

    Júnior, D. S. Vieira; Leonel, S. A.; Toscano, D.; Sato, F.; Coura, P. Z.; Dias, R. A.

    2017-03-01

    Numerical simulations have been performed to study the magnetization reversal in Permalloy nano-ellipses, under combined in-plane magnetic fields along the longitudinal and the transverse directions. We have considered nano-ellipses with two different aspect ratios and five thicknesses: 220×80×t nm3 and 70×50×t nm3, where t ranging from 5 to 25 nm in steps of 5 nm. We found that the mechanism of magnetization reversal is not only dependent on the parameters of the magnetic field pulse but also related to the ellipse dimensions. It is known that the reversal time is related to the mechanism behind the magnetization reversal. In particular, ultrafast magnetization reversals occur by coherent rotation, when applying a field oriented mainly perpendicular to the initial magnetization. In order to evaluate the degree of coherence of the magnetization reversal we have introduced a quantity called "coherence index". Besides complementing the previous studies by including the effect of the thickness on the magnetization reversal, our results indicate that it is possible to obtain magnetization reversals with high degree of coherence in small nano-ellipses by adjusting the geometric factors of the ellipse and the parameters of the magnetic field pulse simultaneously.

  16. Reversible control of magnetization of Fe3O4 by a solid-state film lithium battery

    NASA Astrophysics Data System (ADS)

    Wei, Guodong; Wei, Lin; Wang, Dong; Chen, Yanxue; Tian, Yufeng; Yan, Shishen; Mei, Liangmo; Jiao, Jun

    2017-02-01

    The LiCoO2/LISICON/Fe3O4 structured solid-state film lithium battery is designed to realize a reversible control of the magnetization in Fe3O4 film. LISICON (Li1.5Al0.5Ge1.5P3O12) is selected to serve as the solid-state electrolyte owing to its excellent Li ion transport property at room temperature. A reversible and non-volatile control of the saturation magnetization of Fe3O4 film between the charged and discharged states was obtained, and the modulation ratio can reach as high as 10%. The redox of Fe ions, caused by the intercalation/deintercalation of lithium ion in Fe3O4 film, is responsible for the observed magnetic variation. The battery consisting entirely of solid films provides a promising strategy to control the magnetic properties electrically, which will be a very hopeful candidate for many practical applications.

  17. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

    PubMed Central

    Staruch, Margo; Gopman, Daniel B.; Iunin, Yury L.; Shull, Robert D.; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-01-01

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices. PMID:27869152

  18. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature.

    PubMed

    Staruch, Margo; Gopman, Daniel B; Iunin, Yury L; Shull, Robert D; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-11-21

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

  19. Reversible strain control of magnetic anisotropy in magnetoelectric heterostructures at room temperature

    NASA Astrophysics Data System (ADS)

    Staruch, Margo; Gopman, Daniel B.; Iunin, Yury L.; Shull, Robert D.; Cheng, Shu Fan; Bussmann, Konrad; Finkel, Peter

    2016-11-01

    The ability to tune both magnetic and electric properties in magnetoelectric (ME) composite heterostructures is crucial for multiple transduction applications including energy harvesting or magnetic field sensing, or other transduction devices. While large ME coupling achieved through interfacial strain-induced rotation of magnetic anisotropy in magnetostrictive/piezoelectric multiferroic heterostructures has been demonstrated, there are presently certain restrictions for achieving a full control of magnetism in an extensive operational dynamic range, limiting practical realization of this effect. Here, we demonstrate the possibility of generating substantial reversible anisotropy changes through induced interfacial strains driven by applied electric fields in magnetostrictive thin films deposited on (0 1 1)-oriented domain-engineered ternary relaxor ferroelectric single crystals with extended temperature and voltage ranges as compared to binary relaxors. We show, through a combination of angular magnetization and magneto-optical domain imaging measurements, that a 90° in-plane rotation of the magnetic anisotropy and propagation of magnetic domains with low applied electric fields under zero electric field bias are realized. To our knowledge, the present value attained for converse magnetoelectric coupling coefficient is the highest achieved in the linear piezoelectric regime and expected to be stable for a wide temperature range, thus representing a step towards practical ME transduction devices.

  20. Magnetic Reversal of an Artificial Square Ice: Dipolar Correlation and Charge Ordering

    SciTech Connect

    Stein A.; Morgan J.P.; Langridge S.; Marrows C.H.

    2011-10-13

    Magnetic reversal of an artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal axis is investigated via magnetic force microscopy of the remanent states that result. Sublattice independent reversal is observed via correlated incrementally pinned flip cascades along parallel dipolar chains, 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 the reversal process.

  1. The magnetic properties of the hollow cylindrical ideal remanence magnet

    NASA Astrophysics Data System (ADS)

    Bjørk, R.

    2016-10-01

    We consider the magnetic properties of the hollow cylindrical ideal remanence magnet. This magnet is the cylindrical permanent magnet that generates a uniform field in the cylinder bore, using the least amount of magnetic energy to do so. The remanence distribution of this magnet is derived and the generated field is compared to that of a Halbach cylinder of equal dimensions. The ideal remanence magnet is shown in most cases to generate a significantly lower field than the equivalent Halbach cylinder, although the field is generated with higher efficiency. The most efficient Halbach cylinder is shown to generate a field exactly twice as large as the equivalent ideal remanence magnet.

  2. Magnetic domain wall gratings for magnetization reversal tuning and confined dynamic mode localization

    PubMed Central

    Trützschler, Julia; Sentosun, Kadir; Mozooni, Babak; Mattheis, Roland; McCord, Jeffrey

    2016-01-01

    High density magnetic domain wall gratings are imprinted in ferromagnetic-antiferromagnetic thin films by local ion irradiation by which alternating head-to-tail-to-head-to-tail and head-to-head-to-tail-to-tail spatially overlapping domain wall networks are formed. Unique magnetic domain processes result from the interaction of anchored domain walls. Non-linear magnetization response is introduced by the laterally distributed magnetic anisotropy phases. The locally varying magnetic charge distribution gives rise to localized and guided magnetization spin-wave modes directly constrained by the narrow domain wall cores. The exchange coupled multiphase material structure leads to unprecedented static and locally modified dynamic magnetic material properties. PMID:27487941

  3. Magnetic reversal dynamics of a quantum system on a picosecond timescale.

    PubMed

    Klenov, Nikolay V; Kuznetsov, Alexey V; Soloviev, Igor I; Bakurskiy, Sergey V; Tikhonova, Olga V

    2015-01-01

    We present our approach for a consistent, fully quantum mechanical description of the magnetization reversal process in natural and artificial atomic systems by means of short magnetic pulses. In terms of the simplest model of a two-level system with a magnetic moment, we analyze the possibility of a fast magnetization reversal on the picosecond timescale induced by oscillating or short unipolar magnetic pulses. We demonstrate the possibility of selective magnetization reversal of a superconducting flux qubit using a single flux quantum-based pulse and suggest a promising, rapid Λ-scheme for resonant implementation of this process. In addition, the magnetization reversal treatment is fulfilled within the framework of the macroscopic theory of the magnetic moment, which allows for the comparison and explanation of the quantum and classical behavior.

  4. Properties of asymmetric magnetic reconnection

    SciTech Connect

    Birn, J.; Borovsky, J. E.; Hesse, M.

    2008-03-15

    Properties of magnetic reconnection are investigated in two-dimensional, resistive magnetohydrodynamic (MHD) simulations of current sheets separating plasmas with different magnetic field strengths and densities. Specific emphasis is on the influence of the external parameters on the reconnection rate. The effect of the dissipation in the resistive MHD model is separated from this influence by evaluating resistivity dependence together with the dependence on the background parameters. Two scenarios are considered, which may be distinguished as driven and nondriven reconnection. In either scenario, the maximum reconnection rate (electric field) is found to depend on appropriate hybrid expressions based on a magnetic field strength and an Alfven speed derived from the characteristic values in the two inflow regions. The scaling compares favorably with an analytic formula derived recently by Cassak and Shay [Phys. Plasmas 14, 102114 (2007)] applied to the regime of fast reconnection. An investigation of the energy flow and conversion in the vicinity of the reconnection site revealed a significant role of enthalpy flux generation, in addition to the expected conversion of Poynting flux to kinetic energy flux. This enthalpy flux generation results from Ohmic heating as well as adiabatic, that is, compressional heating. The latter is found more important when the magnetic field strengths in the two inflow regions are comparable in magnitude.

  5. First order reversal curves (FORC) analysis of individual magnetic nanostructures using micro-Hall magnetometry

    NASA Astrophysics Data System (ADS)

    Pohlit, Merlin; Eibisch, Paul; Akbari, Maryam; Porrati, Fabrizio; Huth, Michael; Müller, Jens

    2016-11-01

    Alongside the development of artificially created magnetic nanostructures, micro-Hall magnetometry has proven to be a versatile tool to obtain high-resolution hysteresis loop data and access dynamical properties. Here we explore the application of First Order Reversal Curves (FORC)—a technique well-established in the field of paleomagnetism for studying grain-size and interaction effects in magnetic rocks—to individual and dipolar-coupled arrays of magnetic nanostructures using micro-Hall sensors. A proof-of-principle experiment performed on a macroscopic piece of a floppy disk as a reference sample well known in the literature demonstrates that the FORC diagrams obtained by magnetic stray field measurements using home-built magnetometers are in good agreement with magnetization data obtained by a commercial vibrating sample magnetometer. We discuss in detail the FORC diagrams and their interpretation of three different representative magnetic systems, prepared by the direct-write Focused Electron Beam Induced Deposition (FEBID) technique: (1) an isolated Co-nanoisland showing a simple square-shaped hysteresis loop, (2) a more complex CoFe-alloy nanoisland exhibiting a wasp-waist-type hysteresis, and (3) a cluster of interacting Co-nanoislands. Our findings reveal that the combination of FORC and micro-Hall magnetometry is a promising tool to investigate complex magnetization reversal processes within individual or small ensembles of nanomagnets grown by FEBID or other fabrication methods. The method provides sub-μm spatial resolution and bridges the gap of FORC analysis, commonly used for studying macroscopic samples and rather large arrays, to studies of small ensembles of interacting nanoparticles with the high moment sensitivity inherent to micro-Hall magnetometry.

  6. First order reversal curves (FORC) analysis of individual magnetic nanostructures using micro-Hall magnetometry.

    PubMed

    Pohlit, Merlin; Eibisch, Paul; Akbari, Maryam; Porrati, Fabrizio; Huth, Michael; Müller, Jens

    2016-11-01

    Alongside the development of artificially created magnetic nanostructures, micro-Hall magnetometry has proven to be a versatile tool to obtain high-resolution hysteresis loop data and access dynamical properties. Here we explore the application of First Order Reversal Curves (FORC)-a technique well-established in the field of paleomagnetism for studying grain-size and interaction effects in magnetic rocks-to individual and dipolar-coupled arrays of magnetic nanostructures using micro-Hall sensors. A proof-of-principle experiment performed on a macroscopic piece of a floppy disk as a reference sample well known in the literature demonstrates that the FORC diagrams obtained by magnetic stray field measurements using home-built magnetometers are in good agreement with magnetization data obtained by a commercial vibrating sample magnetometer. We discuss in detail the FORC diagrams and their interpretation of three different representative magnetic systems, prepared by the direct-write Focused Electron Beam Induced Deposition (FEBID) technique: (1) an isolated Co-nanoisland showing a simple square-shaped hysteresis loop, (2) a more complex CoFe-alloy nanoisland exhibiting a wasp-waist-type hysteresis, and (3) a cluster of interacting Co-nanoislands. Our findings reveal that the combination of FORC and micro-Hall magnetometry is a promising tool to investigate complex magnetization reversal processes within individual or small ensembles of nanomagnets grown by FEBID or other fabrication methods. The method provides sub-μm spatial resolution and bridges the gap of FORC analysis, commonly used for studying macroscopic samples and rather large arrays, to studies of small ensembles of interacting nanoparticles with the high moment sensitivity inherent to micro-Hall magnetometry.

  7. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    SciTech Connect

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-18

    Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (-8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

  8. Large reversible magnetocaloric effect in a Ni-Co-Mn-In magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Huang, L.; Cong, D. Y.; Ma, L.; Nie, Z. H.; Wang, Z. L.; Suo, H. L.; Ren, Y.; Wang, Y. D.

    2016-01-01

    Reversibility of the magnetocaloric effect in materials with first-order magnetostructural transformation is of vital significance for practical magnetic refrigeration applications. Here, we report a large reversible magnetocaloric effect in a Ni49.8Co1.2Mn33.5In15.5 magnetic shape memory alloy. A large reversible magnetic entropy change of 14.6 J/(kg K) and a broad operating temperature window of 18 K under 5 T were simultaneously achieved, correlated with the low thermal hysteresis (˜8 K) and large magnetic-field-induced shift of transformation temperatures (4.9 K/T) that lead to a narrow magnetic hysteresis (1.1 T) and small average magnetic hysteresis loss (48.4 J/kg under 5 T) as well. Furthermore, a large reversible effective refrigeration capacity (76.6 J/kg under 5 T) was obtained, as a result of the large reversible magnetic entropy change, broad operating temperature window, and small magnetic hysteresis loss. The large reversible magnetic entropy change and large reversible effective refrigeration capacity are important for improving the magnetocaloric performance, and the small magnetic hysteresis loss is beneficial to reducing energy dissipation during magnetic field cycle in potential applications.

  9. Effects of surface topography on magnetization reversal of magnetic thin films.

    PubMed

    Girgis, E; Pogossian, S P; Benkhedar, M L

    2006-04-01

    The influence of the created surface roughness on the coercivity of magnetic thin films has been investigated. The magnetic thin films (CoFe and alternatively NiFe) are sputtered on top of smooth substrates that were previously covered with an array of considerably rougher lines with one of these materials Pt, Cu, CoFe, and NiFe. The lines have been patterned using optical lithography into arrays that are deposited with different thicknesses varying between 5 nm-15 nm. The lines have been designed to have a very rough edge and seated in two different angles relative to the wafer edge (zero and 45 degrees). Magneto-optic Kerr effect (MOKE) measurements showed two distinct switching fields in the hysteresis loops that are due to magnetic domain wall trapping created by the surface roughness. The magnetization reversal showed a strong dependence on the height, the orientation angle, and the material's type of the created surface roughness (the lines).

  10. Numerical Studies of Magnetization Reversal in Thin Annular Nanorings

    NASA Astrophysics Data System (ADS)

    Chaves-O'Flynn, Gabriel; Kent, Andrew; Stein, Daniel; Bedau, Daniel

    2009-03-01

    The rate of thermally activated magnetization reversal in thin ferromagnetic nanorings has been found analytically in a 1D model in which the demagnetization energy is approximated by a local surface term [1]. Numerical micromagnetic calculations confirm all aspects of the analytic model for narrow thin rings, such as permalloy rings of 200 nm mean radius, 40 nm width and 2 nm thickness [2]. However, the model breaks down in for extremely wide rings, when the ring width approaches its mean diameter. Here we present numerical micromagnetic results for the transition states between the clockwise and counterclockwise state in this limit. We describe how the two transition configurations of narrow rings cease to be saddles of the energy functional. Also, a new low energy metastable state is found to exist for a narrow range of fields. We discuss the results of applying the String Method [3] to determine the transition states and energy barriers between the lowest magnetization configurations of rings. [1] K. Martens, D.L. Stein, and A.D. Kent, PRB 73, 054413 (2006) [2] G. D. Chaves-O'Flynn, D.L. Stein, and A.D. Kent, arXiv:0811.0440 (2008) [3] W. E, W. Ren, E. Vanden-Eijnden, J. Chem. Phys 126, 164103 (2007)

  11. Reversible assembly of magnetized particles: Application to water-borne pathogen enumeration

    NASA Astrophysics Data System (ADS)

    Ramadan, Qasem

    2009-12-01

    Reversible assembly of magnetized particles and cells has been proposed and implemented. The approach is based on magnetized particles or magnetically labeled cell immobilization in an array of individual particle/cell for optical counting. The device has been tested for few types of magnetic particles and one water-borne pathogen: Giardia Lamblia. An individual particle immobilization efficiency of 92% was achieved.

  12. Magnetic interaction reversal in watermelon nanostructured Cr-doped Fe nanoclusters

    SciTech Connect

    Kaur, Maninder; Dai, Qilin; Bowden, Mark; Engelhard, Mark; Wu, Yaqiao; Tang, Jinke; Qiang, You

    2013-01-01

    Cr-doped core-shell Fe/Fe-oxide nanoclusters (NCs) were synthesized at varied atomic percentages of Cr from 0 at. % to 8 at. %. The low concentrations of Cr (<10 at. %) were selected in order to inhibit the complete conversion of the Fe-oxide shell to Cr2O3 and the Fe core to FeCr alloy. The magnetic interaction in Fe/Fe-oxide NCs (rv25 nm) can be controlled by antiferromagnetic Cr-dopant. We report the origin of r-FeCr phase at very low Cr concentration (2 at. %) unlike in previous studies, and the interaction reversal from dipolar to exchange interaction in watermelon-like Cr-doped core-shell NCs. The giant magnetoresistance (GMR) effect,1,2 where an antiferromagnetic (AFM) exchange coupling exists between two ferromagnetic (FM) layers separated by a certain type of magnetic or non-magnetic spacer,3 has significant potential for application in the magnetic recording industry. Soon after the discovery of the GMR, the magnetic properties of multilayer systems (FeCr) became a subject of intensive study. The application of bulk iron-chromium (Fe-Cr) alloys has been of great interest, as these alloys exhibit favorable prop- erties including corrosion resistance, high strength, hardness, low oxidation rate, and strength retention at elevated temper- ature. However, the structural and magnetic properties of Cr-doped Fe nanoclusters (NCs) have not been investigated in-depth. Of all NCs, Fe-based clusters have unique magnetic properties as well as favorable catalytic characteristics in reactivity, selectivity, and durability.4 The incorporation of dopant of varied type and concentration in Fe can modify its chemical ordering, thereby optimizing its electrical, optical, and magnetic properties and opening up many new applications. The substitution of an Fe atom (1.24 A°) by a Cr atom (1.25 A° ) can easily modify the magnetic properties, since (i) the curie temperature (Tc ) of Fe is 1043 K, while Cr is an itinerant AFM with a bulk Neel temperature TN =311 K, and (ii) Fe

  13. Modeling Magnetic Properties in EZTB

    NASA Technical Reports Server (NTRS)

    Lee, Seungwon; vonAllmen, Paul

    2007-01-01

    A software module that calculates magnetic properties of a semiconducting material has been written for incorporation into, and execution within, the Easy (Modular) Tight-Binding (EZTB) software infrastructure. [EZTB is designed to model the electronic structures of semiconductor devices ranging from bulk semiconductors, to quantum wells, quantum wires, and quantum dots. EZTB implements an empirical tight-binding mathematical model of the underlying physics.] This module can model the effect of a magnetic field applied along any direction and does not require any adjustment of model parameters. The module has thus far been applied to study the performances of silicon-based quantum computers in the presence of magnetic fields and of miscut angles in quantum wells. The module is expected to assist experimentalists in fabricating a spin qubit in a Si/SiGe quantum dot. This software can be executed in almost any Unix operating system, utilizes parallel computing, can be run as a Web-portal application program. The module has been validated by comparison of its predictions with experimental data available in the literature.

  14. Irreversible magnetization reversal in some Co-based alloy thin films

    NASA Astrophysics Data System (ADS)

    Admon, U.; Dariel, M. P.; Grunbaum, E.; Lodder, J. C.

    1989-07-01

    Irreversible magnetization reversal occurs either by coherent or incoherent spin rotation or by wall displacement. In electrodeposited Co-W, Co-Fe, and Co-P 300-500-Å films, vibrating sample magnetometer hysteresis loop analyses indicate that magnetization reversal takes place by wall displacement. The formation and movement of domain walls has been put in evidence by Lorentz electron microscopy.

  15. Strain-assisted current-induced magnetization reversal in magnetic tunnel junctions: A micromagnetic study with phase-field microelasticity

    SciTech Connect

    Huang, H. B.; Hu, J. M.; Yang, T. N.; Chen, L. Q.; Ma, X. Q.

    2014-09-22

    Effect of substrate misfit strain on current-induced in-plane magnetization reversal in CoFeB-MgO based magnetic tunnel junctions is investigated by combining micromagnetic simulations with phase-field microelasticity theory. It is found that the critical current density for in-plane magnetization reversal decreases dramatically with an increasing substrate strain, since the effective elastic field can drag the magnetization to one of the four in-plane diagonal directions. A potential strain-assisted multilevel bit spin transfer magnetization switching device using substrate misfit strain is also proposed.

  16. Magnetic Properties of Magnetic Nanoparticles for Efficient Hyperthermia

    PubMed Central

    Obaidat, Ihab M.; Issa, Bashar; Haik, Yousef

    2015-01-01

    Localized magnetic hyperthermia using magnetic nanoparticles (MNPs) under the application of small magnetic fields is a promising tool for treating small or deep-seated tumors. For this method to be applicable, the amount of MNPs used should be minimized. Hence, it is essential to enhance the power dissipation or heating efficiency of MNPs. Several factors influence the heating efficiency of MNPs, such as the amplitude and frequency of the applied magnetic field and the structural and magnetic properties of MNPs. We discuss some of the physics principles for effective heating of MNPs focusing on the role of surface anisotropy, interface exchange anisotropy and dipolar interactions. Basic magnetic properties of MNPs such as their superparamagnetic behavior, are briefly reviewed. The influence of temperature on anisotropy and magnetization of MNPs is discussed. Recent development in self-regulated hyperthermia is briefly discussed. Some physical and practical limitations of using MNPs in magnetic hyperthermia are also briefly discussed. PMID:28347000

  17. Magnetic polarity stratigraphy of the Permian and Carboniferous: The extension of the magnetic reversal record into the Paleozoic

    SciTech Connect

    Opdyke, N.D. )

    1991-03-01

    Magnetic polarity stratigraphy has revolutionized stratigraphic studies in Jurassic to Pleistocene sediments. These studies have been greatly facilitated by the reversal record that is recorded in rocks of the ocean floor. For times prior to the Jurassic, the reversal history of the magnetic field must be determined and eventually related through the type section concept. The magnetic reversal history of the late Paleozoic is dominated by the Permo-Carboniferous reversed superchron (PCRS), which extends from the late Permian to the Carboniferous (Westphalian). Recent studies by the author and his students in Middle Carboniferous sediments of eastern Canada, Pennsylvania, Arizona, and Nevada reveal that the magnetic field has reversed frequently in late Mississippian and early Pennsylvanian times (Meramecian through late Morrowan). The polarity of the magnetic field over this interval is approximately 50% normal and 50% reversed. The frequency of reversal appears to be about one reversal per m.y. The possibility, therefore, exists that this pattern may be used for continental and intercontinental correlation. Attempts are currently underway to correlate this magnetic stratigraphy to fossiliferous marine sections. The base of the PCRS is probably of Atokan age.

  18. Magnetization reversal mechanism of Nd-Fe-B films with perpendicular magnetic anisotropy

    SciTech Connect

    Liu Xiaoxi; Ishida, Go; Morisako, Akimitsu

    2011-04-01

    The microstructure and magnetic properties of Nd-Fe-B films with thicknesses from 100 nm to 3 nm have been investigated. All the films show excellent perpendicular magnetic anisotropy with a squareness ratio of 1 in the perpendicular direction and almost zero coercivity in the in-plane direction. Of particular interest is that the initial magnetization curves sensitively depended on the film thickness. Films thicker than 15 nm show steep initial magnetization curve. Although the films have coercivities larger than 21 kOe, the films can be fully magnetized from the thermally demagnetized state with a field as small as 5 kOe. With the decrease of film thickness to 5 nm, the initial magnetization curve becomes flat. The evolution of initial magnetization curves with film thickness can be understood by the microstructure of the films. Films with thickness of 15 nm show close-packed grains without any intergranular phases. Such microstructures lead to steep initial magnetization curves. On the other hand, when the film thickness decreased to 3 nm, the film thickness became nonuniform. Such microstructure leads to flat initial magnetization curves.

  19. Synthesis and magnetic properties of a novel ferrite organogel

    NASA Astrophysics Data System (ADS)

    Li, Sichu; John, Vijay T.; Irvin, Glen C.; Rachakonda, Suguna H.; McPherson, Gary L.; O'Connor, Charles J.

    1999-04-01

    A novel magnetic organogel that can be considered a precursor example of a magnetoresponsive gel is reported. The gel is formed by the bridging of ferrite containing anionic bis(2-ethlhexyl) sodium sulfosuccinate reverse micelles with 2,6-dihydroxynaphthalene (2,6-DHN). The addition of 2,6-DHN leads to a room temperature quotes "freezing in" of the liquid solution to a clear organogel. Ferrite particles in the size range 10-15 nm are doped into the gel network and are thus suspended in the optically clear gel media. The magnetic properties of the gel were measured using a superconducting quantum interference device magnetometer. The results reveal that the gel exhibits superparamagnetic behavior with a blocking temperature of 6 K (at an applied field of 1000 G), and a coercivity of 850 G at 2 K. The ferrites introduced into the gel serve the function of magnetic "seeds" via which magnetic properties are acquired by the gel.

  20. Tailoring the magnetization reversal of elliptical dots using exchange bias (invited)

    NASA Astrophysics Data System (ADS)

    Sort, J.; Buchanan, K. S.; Pearson, J. E.; Hoffmann, A.; Menéndez, E.; Salazar-Alvarez, G.; Baró, M. D.; Miron, M.; Rodmacq, B.; Dieny, B.; Nogués, J.

    2008-04-01

    Exchange bias effects have been studied in elliptical dots composed of ferromagnetic Ni80Fe20-antiferromagnetic Ir20Mn80 bilayers. The magnetization reversal mechanisms and magnetic configurations have been investigated by magneto-optic Kerr effect and magnetic force microscopy. Although the obtained bias fields in these dots are relatively small, the magnetization reversal is found to be influenced by the ferromagnetic-antiferromagnetic coupling. Namely, for some off-axis angles of measurement, the magnetization reversal mechanism of the Ni80Fe20-Ir20Mn80 ellipses depends on whether exchange bias is induced along the minor or major axis of the ellipses. Hence, exchange bias is shown to be an effective means for tailoring the magnetization reversal of elliptical dots after sample fabrication.

  1. Magnetization reversal and microstructure in polycrystalline Fe50Pd50 dot arrays by self-assembling of polystyrene nanospheres

    PubMed Central

    Tiberto, Paola; Celegato, Federica; Barrera, Gabriele; Coisson, Marco; Vinai, Franco; Rizzi, Paola

    2016-01-01

    Abstract Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe50Pd50 thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L10 phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity. PMID:27877896

  2. Magnetization reversal and magnetic anisotropy in patterned Co/Pd multilayer thin films

    SciTech Connect

    Smith, Darren; Parekh, Vishal; E, Chunsheng; Litvinov, Dmitri; Zhang Shishan; Donner, Wolfgang; Lee, T. Randall; Khizroev, Sakhrat

    2008-01-15

    (Co/Pd){sub N} multilayers exhibit high vertical magnetic anisotropy and have been extensively explored as recording medium candidates for high density magnetic recording applications. In this work (Co/Pd){sub N} multilayers are deposited by magnetron sputtering and patterned into large periodic arrays of 200 nm islands to enable controlled domain wall injection for quantitative comparison of magnetic anisotropy energies. Magnetic properties are correlated with x-ray photoelectron spectroscopy data, an approach commonly used to probe the binding energies and valence band positions. Confirming theoretical predictions, it is demonstrated that the degree of d-shell hybridization at Co/Pd interfaces directly correlated with the magnitude of magnetic anisotropy.

  3. Electric-field control of magnetic domain wall motion and local magnetization reversal

    PubMed Central

    Lahtinen, Tuomas H. E.; Franke, Kévin J. A.; van Dijken, Sebastiaan

    2012-01-01

    Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics. PMID:22355770

  4. Electric-Field-Induced Magnetization Reversal in a Ferromagnet-Multiferroic Heterostructure

    DTIC Science & Technology

    2011-11-14

    system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a...system. The effect is reversible and mediated by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a...by an interfacial magnetic coupling dictated by the multiferroic. Such electric-field control of a magnetoelectric device demonstrates an avenue for

  5. Asymmetric kinetics of magnetization reversal of thin exchange-coupled ferromagnetic films

    NASA Astrophysics Data System (ADS)

    Uspenskaya, L. S.

    2010-11-01

    This paper reports on the results of the investigation of the kinetics of magnetization reversal in FeNi-FeMn ferromagnet-antiferromagnet thin hybrid films grown by magnetron sputtering on silicon substrates in the presence of in-plane magnetic field, which provided unidirectional in-plane magnetic anisotropy in the ferromagnetic layer and a single-domain structure of the ferromagnet in the absence of an external magnetic field. The constructed hysteresis loops and magnetization loci have made it possible to reveal the specific features of the magnetization reversal process of an exchange-coupled ferromagnet, to establish new types of asymmetry, and to obtain new proofs for the existence of a spin spring at the ferromagnet-antiferromagnet interface. The visualization of the magnetization reversal process has allowed one to establish a one-to-one correspondence between the macrocharacteristics of the material and the real processes occurring in ferromagnet-antiferromagnet hybrid structures.

  6. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy.

    PubMed

    Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

    2014-10-01

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

  7. A detailed study of magnetization reversal in individual Ni nanowires

    SciTech Connect

    Vilanova Vidal, Enrique; Ivanov, Yurii P.; Mohammed, Hanan; Kosel, Jürgen

    2015-01-19

    Magnetic nanowires have emerged as essential components for a broad range of applications. In many cases, a key property of these components is the switching field, which is studied as a function of the angle between the field and the nanowire. We found remarkable differences of up to 100% between the switching fields of different nanowires from the same fabrication batch. Our experimental results and micromagnetic simulations indicate that the nanowires exhibit a single domain behavior and that the switching mechanism includes vortex domain wall motion across the nanowire. The differences between the switching fields are attributed to different cross-sections of the nanowires, as found by electron microscopy. While a circular cross-section yields the smallest switching field values, any deviation from this shape results in an increase of the switching field. The shape of the nanowires' cross-sections is thus a critical parameter that has not been previously taken into account.

  8. Nanoscale imaging of magnetization reversal driven by spin-orbit torque

    NASA Astrophysics Data System (ADS)

    Gilbert, Ian; Chen, P. J.; Gopman, Daniel B.; Balk, Andrew L.; Pierce, Daniel T.; Stiles, Mark D.; Unguris, John

    2016-09-01

    We use scanning electron microscopy with polarization analysis to image deterministic, spin-orbit torque-driven magnetization reversal of in-plane magnetized CoFeB rectangles in zero applied magnetic field. The spin-orbit torque is generated by running a current through heavy metal microstrips, either Pt or Ta, upon which the CoFeB rectangles are deposited. We image the CoFeB magnetization before and after a current pulse to see the effect of spin-orbit torque on the magnetic nanostructure. The observed changes in magnetic structure can be complex, deviating significantly from a simple macrospin approximation, especially in larger elements. Overall, however, the directions of the magnetization reversal in the Pt and Ta devices are opposite, consistent with the opposite signs of the spin Hall angles of these materials. Our results elucidate the effects of current density, geometry, and magnetic domain structure on magnetization switching driven by spin-orbit torque.

  9. Nanoscale imaging of magnetization reversal driven by spin-orbit torque

    PubMed Central

    Chen, P.J.; Gopman, Daniel B.; Balk, Andrew L.; Pierce, Daniel T.; Stiles, Mark D.; Unguris, John

    2016-01-01

    We use scanning electron microscopy with polarization analysis to image deterministic, spin-orbit torque-driven magnetization reversal of in-plane magnetized CoFeB rectangles in zero applied magnetic field. The spin-orbit torque is generated by running a current through heavy metal microstrips, either Pt or Ta, upon which the CoFeB rectangles are deposited. We image the CoFeB magnetization before and after a current pulse to see the effect of spin-orbit torque on the magnetic nanostructure. The observed changes in magnetic structure can be complex, deviating significantly from a simple macrospin approximation, especially in larger elements. Overall, however, the directions of the magnetization reversal in the Pt and Ta devices are opposite, consistent with the opposite signs of the spin Hall angles of these materials. Our results elucidate the effects of current density, geometry, and magnetic domain structure on magnetization switching driven by spin-orbit torque. PMID:27957557

  10. Dynamic origin of segment magnetization reversal in thin-film Penrose tilings

    NASA Astrophysics Data System (ADS)

    Montoncello, F.; Giovannini, L.; Farmer, B.; De Long, L.

    2017-02-01

    We investigate the low-frequency spin wave dynamics involved in the magnetization reversal of a Penrose P2 tiling using the dynamical matrix method. This system consists of a two-dimensional, connected wire network of elongated thin-film segments, whose complete reversal occurs as a cascade of successive local segment reversals. Using soft mode theory, we interpret the reversal of an individual segment as a first order magnetic transition, in which magnetization curve of the system suffers a small discontinuity. Near this discontinuity a specific mode of the spin wave spectrum goes soft (i.e., its frequency goes to zero), triggering a local instability of the magnetization. We show that this mode is localized, and is at the origin of the local reversal. We discuss the correlation of the mode spatial profile with the ;reversal mechanism;, which is the passage of a domain wall through the segment. This process differs from reversal in periodic square or honeycomb artificial spin ices, where a cascade of reversing segments (e.g., ;Dirac string;) follows an extended (though irregular) path across the sample; here the spatial distribution of successive segment reversals is discontinuous, but strictly associated with the area where a soft mode is localized. The migration of the localization area across the P2 tiling (during reversal in decreasing applied fields) depends on changes in the internal effective field map. We discuss these results in the context of spin wave localization due to the unique topology of the P2 tiling.

  11. Reverse osmosis membrane of high urea rejection properties. [water purification

    NASA Technical Reports Server (NTRS)

    Johnson, C. C.; Wydeven, T. J. (Inventor)

    1980-01-01

    Polymeric membranes suitable for use in reverse osmosis water purification because of their high urea and salt rejection properties are prepared by generating a plasma of an unsaturated hydrocarbon monomer and nitrogen gas from an electrical source. A polymeric membrane is formed by depositing a polymer of the unsaturated monomer from the plasma onto a substrate, so that nitrogen from the nitrogen gas is incorporated within the polymer in a chemically combined form.

  12. Time-resolved imaging of pulse-induced magnetization reversal with a microwave assist field

    PubMed Central

    Rao, Siddharth; Rhensius, Jan; Bisig, Andre; Mawass, Mohamad-Assaad; Weigand, Markus; Kläui, Mathias; Bhatia, Charanjit S.; Yang, Hyunsoo

    2015-01-01

    The reversal of the magnetization under the influence of a field pulse has been previously predicted to be an incoherent process with several competing phenomena such as domain wall relaxation, spin wave-mediated instability regions, and vortex-core mediated reversal dynamics. However, there has been no study on the direct observation of the switching process with the aid of a microwave signal input. We report a time-resolved imaging study of magnetization reversal in patterned magnetic structures under the influence of a field pulse with microwave assistance. The microwave frequency is varied to demonstrate the effect of resonant microwave-assisted switching. We observe that the switching process is dominated by spin wave dynamics generated as a result of magnetic instabilities in the structures, and identify the frequencies that are most dominant in magnetization reversal. PMID:26023723

  13. Electric-field-driven magnetization reversal in square-shaped nanomagnet-based multiferroic heterostructure

    SciTech Connect

    Peng, Ren-Ci; Nan, Ce-Wen E-mail: cwnan@tsinghua.edu.cn; Wang, J. J. E-mail: cwnan@tsinghua.edu.cn; Chen, Long-Qing; Hu, Jia-Mian

    2015-04-06

    Based on phase field modeling and thermodynamic analysis, purely electric-field-driven magnetization reversal was shown to be possible in a multiferroic heterostructure of a square-shaped amorphous Co{sub 40}Fe{sub 40}B{sub 20} nanomagnet on top of a ferroelectric layer through electrostrain. The reversal is made possible by engineering the mutual interactions among the built-in uniaxial magnetic anisotropy, the geometry-dependent magnetic configuration anisotropy, and the magnetoelastic anisotropy. Particularly, the incorporation of the built-in uniaxial anisotropy made it possible to reverse magnetization with one single unipolar electrostrain pulse, which is simpler than previous designs involving the use of bipolar electrostrains and may alleviate ferroelectric fatigue. Critical conditions for triggering the magnetization reversal are identified.

  14. First-principles determination of magnetic properties

    NASA Astrophysics Data System (ADS)

    Wu, Ruqian; Yang, Zongxian; Hong, Jisang

    2003-02-01

    First-principles density functional theory calculations have achieved great success in the exciting field of low-dimension magnetism, in explaining new phenomena observed in experiments as well as in predicting novel properties and materials. As known, spin-orbit coupling (SOC) plays an extremely important role in various magnetic properties such as magnetic anisotropy, magnetostriction, magneto-optical effects and spin-dynamics. Using the full potential linearized augmented plane wave approach, we have carried out extensive investigations for the effects of SOC in various materials. Results of selected examples, such as structure and magnetic properties of Ni/Cu(001), magnetism and magnetic anisotropy in magnetic Co/Cu(001) thin films, wires and clusters, magnetostriction in FeGa alloys and magneto-optical effects in Fe/Cr superlattices, are discussed.

  15. Resonance and Chaotic Trajectories in Magnetic Field Reversed Configuration

    SciTech Connect

    A.S. Landsman; S.A. Cohen; M. Edelman; G.M. Zaslavsky

    2005-04-13

    The nonlinear dynamics of a single ion in a field-reversed configuration (FRC) were investigated. FRC is a toroidal fusion device which uses a specific type of magnetic field to confine ions. As a result of angular invariance, the full three-dimensional Hamiltonian system can be expressed as two coupled, highly nonlinear oscillators. Due to the high nonlinearity in the equations of motion, the behavior of the system is extremely complex, showing different regimes, depending on the values of the conserved canonical angular momentum and the geometry of the fusion vessel. Perturbation theory and averaging were used to derive the unperturbed Hamiltonian and frequencies of the two degrees of freedom. The derived equations were then used to find resonances and compare to Poincar{copyright} surface-of-section plots. A regime was found where the nonlinear resonances were clearly separated by KAM [Kolmogorov-Arnold-Mosher] curves. The structure of the observed island chains was explained. The condition for the destruction of KAM curves and the onset of strong chaos was derived, using Chirikov island overlap criterion, and shown qualitatively to depend both on the canonical angular momentum and geometry of the device. After a brief discussion of the adiabatic regime the paper goes on to explore the degenerate regime that sets in at higher values of angular momenta. In this regime, the unperturbed Hamiltonian can be approximated as two uncoupled linear oscillators. In this case, the system is near-integrable, except in cases of a universal resonance, which results in large island structures, due to the smallness of nonlinear terms, which bound the resonance. The linear force constants, dominant in this regime, were derived and the geometry for a large one-to-one resonance identified. The above analysis showed good agreement with numerical simulations and was able to explain characteristic features of the dynamics.

  16. Influence of internal geometry on magnetization reversal in asymmetric permalloy rings

    NASA Astrophysics Data System (ADS)

    Gopman, D. B.; Kabanov, Y. P.; Cui, J.; Lynch, C. S.; Shull, R. D.

    2016-08-01

    We report the magnetization reversal behavior of microstructured Ni80Fe20 rings using magneto-optic indicator film imaging and magnetometry. While the reversal behavior of rings with a symmetric (circular) interior hole agrees with micromagnetic simulations of an onion → vortex → onion transition, we experimentally demonstrate that rings possessing an elliptical hole with an aspect ratio of 2 exhibit complex reversal behavior comprising incoherent domain propagation in the rings. Magneto optic images reveal metastable magnetic configurations that illustrate this incoherent behavior. These results have important implications for understanding the reversal behavior of asymmetric ferromagnetic rings.

  17. Simulating magnetic nanotubes using a chain of ellipsoid-rings model with a magnetization reversal process by fanning rotation.

    PubMed

    Wang, Jieqiong; Yang, Sen; Gong, Junfeng; Xu, Minwei; Adil, Murtaza; Wang, Yu; Zhang, Yin; Song, Xiaoping; Zeng, Hao

    2015-04-21

    Recently, magnetic nanotubes have attracted great attention owing to the advantages of tubular geometry. Of all the physical properties of magnetic nanotubes, the magnetic behavior plays a pivotal role in potential applications, particularly in biotechnology. Modeling magnetic nanotubes provides an effective way to determine the geometry dependent magnetic properties. In the present article, we model the nanotube as a chain of ellipsoid-rings; thus the magnetic behavior of nanotubes is simulated by the fanning rotation of magnetic moments. Based on this model, we further discuss the influence of tubular geometric parameters on the magnetic properties. The calculated magnetic properties of Fe, Co, Ni, Fe3O4 and CoFe2O4 nanotubes are all consistent with their experimental data. Consequently, our model provides an easy and general approach to magnetic nanotubes.

  18. Optical Writing of Magnetic Properties by Remanent Photostriction.

    PubMed

    Iurchuk, V; Schick, D; Bran, J; Colson, D; Forget, A; Halley, D; Koc, A; Reinhardt, M; Kwamen, C; Morley, N A; Bargheer, M; Viret, M; Gumeniuk, R; Schmerber, G; Doudin, B; Kundys, B

    2016-09-02

    We present an optically induced remanent photostriction in BiFeO_{3}, resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO_{3}/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO_{3}. Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

  19. Optical Writing of Magnetic Properties by Remanent Photostriction

    NASA Astrophysics Data System (ADS)

    Iurchuk, V.; Schick, D.; Bran, J.; Colson, D.; Forget, A.; Halley, D.; Koc, A.; Reinhardt, M.; Kwamen, C.; Morley, N. A.; Bargheer, M.; Viret, M.; Gumeniuk, R.; Schmerber, G.; Doudin, B.; Kundys, B.

    2016-09-01

    We present an optically induced remanent photostriction in BiFeO3 , resulting from the photovoltaic effect, which is used to modify the ferromagnetism of Ni film in a hybrid BiFeO3/Ni structure. The 75% change in coercivity in the Ni film is achieved via optical and nonvolatile control. This photoferromagnetic effect can be reversed by static or ac electric depolarization of BiFeO3 . Hence, the strain dependent changes in magnetic properties are written optically, and erased electrically. Light-mediated straintronics is therefore a possible approach for low-power multistate control of magnetic elements relevant for memory and spintronic applications.

  20. Magnetic Properties of Tcnq Complexes

    NASA Astrophysics Data System (ADS)

    Qureshi, Saleem

    Available from UMI in association with The British Library. Requires signed TDF. This work can be divided up into three complementary steps. The first part of the work involved synthesis of a large number of TCNQ complexes, in particular complex salts, which are known to have promising electrical properties due to reduction in the on-site Coloumbic repulsion between the electrons. The cations used for the complexes are C12BPE (dodecyl bi pyridyl ethelenium), C10BPE, C8BPE, C6BPE, GTPP (geronyl triphenyl phosphonium), BI (butyl imidazolium), DMI (dimethyl imidazolium) and TB (toluidine blue). The second part of the project was to characterize these materials using different techniques to try to build up a knowledge of the materials. Particular interest was involved in the study of magnetic behaviour and in the later parts of the work some electrical measurements were made to try to determine the band gap, mobility and temperature dependence of conductivity. Considering the quasi-one-dimensional nature of the TCNQ salts, a theoretical model was devised based on the solution of one dimensional Heisenberg spin Hamiltonian. A computer program was developed that allowed for a numerical solution of a chain of spins in which number of spins could be varied. The Hamiltonian could be solved for up to 12 spins, the maximum allowable by the ICL 2900 computer at Crips computer centre of the University of Nottingham. The program allowed the user to input the coupling energy and alternation parameter between adjacent spins. The results from this program were used to explain magnetic behaviour of the TCNQ complexes prepared during this work.

  1. Possibility of checking the magnetic properties of ultrathin electrical steel strip during production

    SciTech Connect

    Korzunin, G.S.; Alekseev, V.A.; Rimshev, F.F.

    1995-12-01

    The possibility of making a final check of the magnetic properties of ultrathin electrical steel strip during production at the Ashina Metallurgical Works by using existing texturometers, which have proven themselves well in checking the uniformity of the properties of thick steel, or by direct measurement of the principal operating characteristics of steel (the energy loss due to magnetic reversal and the value of the magnetic induction). We consider how the degree of perfection of the crystallographic texture are related to the magnetic properties of thin strip and how the results of measurements of those properties are affected by the inevitable tension of the strip during production.

  2. Magnetic properties of carbon nanoparticles

    NASA Astrophysics Data System (ADS)

    Lähderanta, E.; Lashkul, A. V.; Lisunov, K. G.; Zherebtsov, D. A.; Galimov, D. M.; Titkov, A. N.

    2012-08-01

    Magnetization M (T, B) of powder and glassy samples containing carbon nanoparticles is investigated in the interval of temperatures T between ~ 3 - 300 K and magnetic fields B up to 5 T. Low-field magnetization, M (T), exhibits a strong magnetic irreversibility, which is suppressed above the field of ~ 1 T. The dependence of M (B) saturates at high temperatures above B ~ 2 T, magnetic hysteresis is observed already at 300 K. The values of the saturation magnetization, the coercivity field and the maximum blocking temperature are obtained. Analysis of the experimental data gives evidence for concentration of the magnetization close to the surface of the particles, which is consistent with the origin of magnetism in nanocarbon presumably due to intrinsic disorder and surface defects.

  3. Magnetization reversal assisted by half antivortex states in nanostructured circular cobalt disks

    SciTech Connect

    Lara, A.; Aliev, F. G.; Dobrovolskiy, O. V.; Prieto, J. L.; Huth, M.

    2014-11-03

    The half antivortex, a fundamental topological structure which determines magnetization reversal of submicron magnetic devices with domain walls, has been suggested also to play a crucial role in spin torque induced vortex core reversal in circular disks. Here, we report on magnetization reversal in circular disks with nanoholes through consecutive metastable states with half antivortices. In-plane anisotropic magnetoresistance and broadband susceptibility measurements accompanied by micromagnetic simulations reveal that cobalt (Co) disks with two and three linearly arranged nanoholes directed at 45° and 135° with respect to the external magnetic field show reproducible step-like changes in the anisotropic magnetoresistance and magnetic permeability due to transitions between different intermediate states mediated by vortices and half antivortices confined to the dot nanoholes and edges, respectively. Our findings are relevant for the development of multi-hole based spintronic and magnetic memory devices.

  4. Aspect-ratio dependence of magnetization reversal in cylindrical ferromagnetic nanowires

    NASA Astrophysics Data System (ADS)

    Sultan, Musaab S.; Atkinson, Del

    2016-05-01

    The magnetization reversal behavior in isolated cylindrical and square cross-section Ni81Fe19 nanowires was systematically studied as a function of nanowire cross-section dimensions from 10 up to 200 nm using micromagnetic simulations. This approach provides access to the switching field, remanence ratio and most significantly the magnetization structures during reversal, which allows the evolution of magnetization processes to be studied with scaling of the cross-sectional dimensions. The dimensional trends in reversal behavior for both square and circular cross-section were comparable throughout the range of dimensions studied. The thinnest nanowires showed simple square switching and 100% remanence. With increasing diameter the switching field reduces and above 40 nm the reversal behavior shows an increasing rotational component prior to sharp switching of the magnetization. The magnitude of the reversible component increases with increasing dimensions up to 150 nm, above which the magnetization reversal process is more complicated and the hysteresis loops are no longer bistable. The micromagnetic structures evolve from simple uniform parallel single domain states in the thinnest wires through the formation of vortex-like end states in thicker wires to complex multidomain structures during the reversal of the thickest wires. In the later cases the reversal is not simple curling-like behavior, although the angular switching field dependence was comparable with curling.

  5. Electron thermal transport within magnetic islands in the reversed-field pinch

    SciTech Connect

    Stephens, H. D.; Reusch, J. A.; Den Hartog, D. J.; Hegna, C. C.

    2010-05-15

    Tearing mode induced magnetic islands have a significant impact on the thermal characteristics of magnetically confined plasmas such as those in the reversed-field pinch (RFP). New Thomson scattering diagnostic capability on the Madison Symmetric Torus (MST) RFP has enabled measurement of the thermal transport characteristics of islands. Electron temperature (T{sub e}) profiles can now be acquired at 25 kHz, sufficient to measure the effect of an island on the profile as the island rotates by the measurement point. In standard MST plasmas with a spectrum of unstable tearing modes, remnant islands are present in the core between sawtoothlike reconnection events. Associated with these island remnants is flattening of the T{sub e} profile inside the island separatricies. This flattening is characteristic of rapid parallel heat conduction along helical magnetic field lines. In striking contrast, a temperature gradient within an m=1, n=5 island is observed in these same plasmas just after a sawtooth event when the m=1, n=5 mode may briefly come into resonance near the magnetic axis. This suggests local heating and relatively good confinement within the island. Local power balance calculations suggest reduced thermal transport within this island relative to the confinement properties of standard MST discharges between reconnection events. The magnetic field and island structure is modeled with three-dimensional nonlinear resistive magnetohydrodynamic simulations (DEBS code) with Lundquist numbers matching those in MST during standard discharges. During improved confinement plasmas with reduced tearing mode activity, temperature fluctuations correlated with magnetic signals are small with characteristic fluctuation amplitudes of order T-tilde{sub e}/T{sub e}approx2%.

  6. Magnetization Reversal Process of Single Crystal α-Fe Containing a Nonmagnetic Particle

    SciTech Connect

    Li, Yi; Xu, Ben; Hu, Shenyang Y.; Li, Yulan; Li, Qiu-Lin; Liu, Wei

    2015-09-25

    The magnetization reversal process and hysteresis loops in a single crystal α-iron with nonmagnetic particles are simulated in this work based on the Landau-Lifshitz–Gilbert equation. The evolutions of the magnetic domain morphology are studied, and our analyses show that the magnetization reversal process is affected by the interaction between the moving domain wall and the existing nonmagnetic particles. This interaction strongly depends on the size of the particles, and it is found that particles with a particular size contribute the most to magnetic hardening.

  7. Direct Observation of the Controlled Magnetization Reversal Processes in Py/Al/Py Assymmetric Ring Stacks

    SciTech Connect

    Huang, L.; Schofield, M.A.; Zhu, Y.

    2009-07-27

    Electron holographic experiments were performed to study the magnetization reversal process of patterned Py/Al/Py (20nm/20nm/10nm) asymmetric ring stacks. By changing the in-plane field applied perpendicular to the ring's symmetric axis, we directly observed the vortex-based magnetization reversal process through controlled domain wall motion and annihilation. The two magnetic layers were found to switch at different critical fields, leading to the existence of various distinct domain state combinations. Quantitative agreement was obtained between measured phase shifts and those derived from micromagnetic calculations, which allows us to resolve the layer-by-layer magnetic behavior as a function of applied external field.

  8. The Liverpool Geomagnetic Polarity Reversal : New evidences for a complex magnetic field behavior during reversals.

    NASA Astrophysics Data System (ADS)

    Camps, P.; Perrin, M.; Hoffman, K. A.; Singer, B. S.

    2009-04-01

    We carried out a detailed and continuous paleomagnetic re-sampling of the reversed-to-normal Eocene -36 Ma- geomagnetic transition recorded in the Liverpool (NSW, Australia) volcanic range [Hoffman, 1986]. Our main objective was to obtain a precise description of the variation in the paleofield vector (direction and absolute intensity) as the geomagnetic field reverses. With more than 30 transitional directions documented, the Liverpool reversal is, along with the Miocene record -16.2 Ma- of the Steens Mountain (Oregon, USA) [Mankinen et al., 1985] and the Matuyama-Brunhes -780 Ka- record of Hawaii [Coe et al, 2004], among the best example of a transition record from a volcanic sequence. The Liverpool polarity reversal shows a complex path of the Virtual Geomagnetic poles between the initial (reverse) and final (normal) polarities. Two loops in the trajectory of VGPs before the actual polarity switch are documented [Hoffman, 1986]. Such swings preceding the reversal seems to be a common characteristic of reversal since similar features are described on the Steens Mountain [Jarboe et al., 2007] and a long period of instability, estimated to 18 ka, is now well established prior to the Matuyama-Brunhes reversal [Singer et al., 2005]. In the present study, we found an additional swing through the reversed polarity yielding a complex R-T-R-T-R-T-R-T-N path for VGPs to achieve the reversal process. During the sampling campaign, we did not find evidence for significant hiatus in the eruptive activity such as soil horizons or sediments. We do not believe either that some part of the volcanic sequence be duplicate by the presence of tectonic faults. Hence, we think that the three excursions and the actual reversal belong to a single phenomenon. In order to strengthen this conclusion, precise Ar/ Ar will be performed. Twelve flows (5 of transitional and 7 of reversed polarity, respectively) all located in the lower half part of the Liverpool record, yielded paleointensity

  9. Magnetization-reversal processes in an ultrathin Co/Au film

    NASA Astrophysics Data System (ADS)

    Ferré, J.; Grolier, V.; Meyer, P.; Lemerle, S.; Maziewski, A.; Stefanowicz, E.; Tarasenko, S. V.; Tarasenko, V. V.; Kisielewski, M.; Renard, D.

    1997-06-01

    Magnetization-reversal processes in a ferromagnetic cobalt film structure (Au/Co/Au), with perpendicular anisotropy, were investigated by magneto-optical magnetometry and microscopy. In the considered ultrathin Co film, the magnetization reversal between the two Ising-spin equilibrium states is dominated by the domain-wall motion mechanism. We focused our studies on processes initiated from a given demagnetized state. Starting from a magnetically saturated state generated under a large field HS, applied perpendicular to the film, this demagnetized state is created through magnetic aftereffects in a field Hd antiparallel but smaller than HS and applied during a selected time. Direct (RD) and indirect (RI) magnetization processes are then studied from this state for application of the field parallel and antiparallel to Hd, respectively. The dynamics of the magnetization reversal is much faster for the RI process since it is initiated from a quasihomogeneous 'Swiss cheese' domain state with small nonreversed regions. The magnetic accommodation phenomenon is studied, and a domain-shape memory effect evidenced. A theoretical analysis of the dynamics of magnetization processes is proposed, starting from the model of a patchy inhomogeneous media with a realistic distribution of local coercivities. The pertinent parameters for calculations are deduced from our experimental data using appropriate analytical expressions of the magnetic relaxation time and domain-wall velocity under a field. Computer simulations using these parameters reproduce well the time evolution of the magnetic domain pattern and different magnetization curves both for RD and RI magnetization processes.

  10. Angular dependence of exchange bias and magnetization reversal controlled by electric-field-induced competing anisotropies

    NASA Astrophysics Data System (ADS)

    Zhao, Yonggang; Chen, Aitian; Li, Peisen; Zhang, Xu; Peng, Renci; Huang, Haoliang; Zou, Lvkuan; Zheng, Xiaoli; Zhang, Sen; Miao, Peixian; Lu, Yalin; Cai, Jian; Nan, Ce-Wen

    Combination of exchange-biased systems and FE materials gives a new avenue to study angular dependence of exchange bias and achieve reversible electric-field-controlled magnetization reversal. We study the angular dependence of electric-field-controlled exchange bias and magnetization reversal in CoFeB/IrMn/Pb(Mg1/3Nb2/3)0.7 Ti0.3O3. It is demonstrated that the ratio of the exchange-coupled unidirectional anisotropy and the uniaxial anisotropy of the FM layer, as well as their relative orientation can be dramatically and continuously tuned via electric fields. Simulations confirm that the electric-field-controlled exchange bias originates from the competition between the uniaxial anisotropy induced by the piezostrain and the exchange-coupled unidirectional anisotropy. Moreover, electric-field-controlled magnetization reversal was realized at zero magnetic field.

  11. Transport and magnetic properties in topological materials

    NASA Astrophysics Data System (ADS)

    Liang, Tian

    The notion of topology has been the central topic of the condensed matter physics in recent years, ranging from 2D quantum hall (QH) and quantum spin hall (QSH) states, 3D topological insulators (TIs), topological crystalline insulators (TCIs), 3D Dirac/Weyl semimetals, and topological superconductors (TSCs) etc. The key notion of the topological materials is the bulk edge correspondence, i.e., in order to preserve the symmetry of the whole system (bulk+edge), edge states must exist to counter-compensate the broken symmetry of the bulk. Combined with the fact that the bulk is topologically protected, the edge states are robust due to the bulk edge correspondence. This leads to interesting phenomena of chiral edge states in 2D QH, helical edge states in 2D QSH, "parity anomaly'' (time reversal anomaly) in 3D TI, helical edge states in the mirror plane of TCI, chiral anomaly in Dirac/Weyl semimetals, Majorana fermions in the TSCs. Transport and magnetic properties of topological materials are investigated to yield intriguing phenomena. For 3D TI Bi1.1Sb0.9Te 2S, anomalous Hall effect (AHE) is observed, and for TCI Pb1-x SnxSe, Seebeck/Nernst measurements reveal the anomalous sign change of Nernst signals as well as the massive Dirac fermions. Ferroelectricity and pressure measurements show that TCI Pb1-xSnxTe undergoes quantum phase transition (QPT) from trivial insulator through Weyl semimetal to anomalous insulator. Dirac semimetals Cd3As2, Na 3Bi show interesting results such as the ultrahigh mobility 10 7cm2V-1s-1 protected from backscattering at zero magnetic field, as well as anomalous Nernst effect (ANE) for Cd3As2, and the negative longitudinal magnetoresistance (MR) due to chiral anomaly for Na3Bi. In-plane and out-of-plane AHE are observed for semimetal ZrTe5 by in-situ double-axes rotation measurements. For interacting system Eu2Ir2O7, full angle torque magnetometry measurements reveal the existence of orthogonal magnetization breaking the symmetry of

  12. Depth-resolved magnetization reversal in nanoporous perpendicular anisotropy multilayers

    NASA Astrophysics Data System (ADS)

    Kirby, B. J.; Rahman, M. T.; Dumas, R. K.; Davies, J. E.; Lai, C. H.; Liu, Kai

    2013-01-01

    We have used polarized neutron reflectometry to study the field-dependent magnetizations of Co/Pt mulitlayers patterned via deposition onto nanoporous alumina hosts with varying pore aspect ratio. Despite the porosity and lack of long-range order, robust spin-dependent reflectivities are observed, allowing us to distinguish the magnetization of the surface multilayer from that of material in the pores. We find that as the pores become wider and shallower, the surface Co/Pt multilayers have progressively smaller high field magnetization and exhibit softer magnetic reversal—consistent with increased magnetic disorder and a reduction of the perpendicular anisotropy near the pore rims. These results reveal complexities of magnetic order in nanoporous heterostructures, and help pave the way for depth-resolved studies of complex magnetic heterostructures grown on prepatterned substrates.

  13. Origin of Magnetic Properties in Amorphous Metals.

    DTIC Science & Technology

    1979-12-01

    Magnetic Properties of Fe-Ni-B Amorphous Alloys," F. E. Luborsky, J. L. Walter, and H. H. Liebermann , IEEE Trans. on Magnetics MAG-15, 909 (1979). Also GE...Report 78CRD132. 2. "Formation and Magnetic Properties of Fe-B-Si Amorphous Alloys," F. E. Luborsky, J. J. Becker, J. L. Walter, and H. H. Liebermann ...Amorphous Alloys," F. E. Luborsky and H. H. Liebermann , J. Appl. Phys., to appear. Also GE Report 79CRD177. 4. "The Effect of Temperature on Magnetic

  14. Magnetization reversal in epitaxial highly anisotropic CoFe2O4 hetero-structures

    NASA Astrophysics Data System (ADS)

    Lisfi, A.; Pokharel, S.; Morgan, W.; Salamanca-Riba, L.; Wuttig, M.

    2015-05-01

    Magnetization reversal in epitaxial cobalt ferrite films grown on (110) MgO substrate has been investigated through angular studies of hysteresis loop and DCD remanence curve. The angular dependences of the coercivity and the switching field of these films strongly deviate from those typically known for coherent and incoherent rotation modes. However, the best fit for these angular curves suggests that domain wall nucleation is the appropriate mode for the magnetization reversal in these hetero-structures.

  15. Magnetic Properties of Antiferromagnetic Iron Oxyhydroxides

    NASA Astrophysics Data System (ADS)

    Guyodo, Y. J.; Till, J. L.; Lagroix, F.; Bonville, P.; Penn, R. L.; Sainctavit, P.; Carvallo, C.; ona-Nguema, G.; Morin, G.

    2013-12-01

    Weakly magnetic iron oxyhydroxides such as ferrihydrite, lepidocrocite or goethite are commonly found in diverse geological and environmental setting, including ground waters and streams, sediments, soils, or acid mine drainage. These minerals take part in multiple biological and abiological processes, and can evolve to more magnetic phases such as hematite, maghemite, or magnetite. Therefore, they represent key minerals with regard to paleoclimate, paleoenvironmental, and paleomagnetic studies. At this meeting, we will present low temperature magnetic properties acquired on fully characterized synthetic samples. The complex nature of the magnetism of these minerals is revealed by comparing magnetic data with other types of characterizations such as high-resolution transmission electron microscopy or synchrotron X-ray magnetic circular dichroism (XMCD), or by studying the early-stages of solid-state alteration (under oxidizing or reducing atmosphere). In particular, we will present recent results about the presence of ferri-magnetic nano-clusters in lepidocrocite, and about uncompensated magnetic moments in goethite nanoparticles.

  16. 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.

  17. Uniaxial anisotropy and temperature driven magnetization reversal of Fe deposited on a MnAs/GaAs(001) magnetic template

    NASA Astrophysics Data System (ADS)

    Sacchi, Maurizio; Marangolo, Massimiliano; Spezzani, Carlo; Coelho, Leticia; Breitwieser, Romain; Milano, Julian; Etgens, Victor H.

    2008-04-01

    We investigated the magnetic behavior of a 5nm thick Fe layer deposited on a ferromagnetic MnAs/GaAs(001) template by using resonant magnetic scattering of polarized soft x rays. The Fe film displays in-plane uniaxial anisotropy and its magnetization can be modified and reversed by fine-tuning the substrate temperature around ambient because of the self-organization of the coexisting ferromagnetic and paramagnetic phases of the template.

  18. Development of Field-Reversed Configuration Plasma Gun Formation Techniques for Magnetized Target Fusion

    NASA Astrophysics Data System (ADS)

    Lynn, Alan; Gilmore, Mark; Wynkoop, Tyler; Intrator, Thomas; Weber, Thomas

    2012-10-01

    Magnetized Target Fusion (MTF) is an innovative approach for a relatively fast and cheap path to the production of fusion energy that utilizes magnetic confinement to assist in the compression of a hot plasma to thermonuclear conditions by an external driver. Los Alamos National Laboratory (LANL) is currently pursing demonstration of the MTF concept via compression of an FRC (field-reversed configuration) plasma by a metal liner z-pinch in conjunction with the Air Force Research Laboratory in Albuquerque, NM. A key physics issue for the FRC as an MTF target lies in the initial pre-ionization (PI) stage. The PI formation process determines the amount of magnetic flux that can be trapped to form the FRC. This trapped flux plays an important role in the FRC's final equilibrium, transport, and stability properties. It also provides the route to greatest potential gains in FRC lifetime, which is essential to provide enough time to translate and compress the FRC effectively. In conjunction with LANL we plan to test and characterize a new system to improve the initial PI plasma formation. This system will use an array of plasma guns to form the initial plasma. Initial characterization of the plasma gun behavior will be presented.

  19. Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

    SciTech Connect

    Zhou, Hengan; Fan, Xiaolong Wang, Fenglong; Jiang, Changjun; Rao, Jinwei; Zhao, Xiaobing; Xue, Desheng; Gui, Y. S.; Hu, C.-M.

    2014-03-10

    In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg{sub 1∕3}Nb{sub 2∕3})O{sub 3}-PbTiO{sub 3} substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

  20. Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

    NASA Astrophysics Data System (ADS)

    Sugihara, A.; Suzuki, K. Z.; Miyazaki, T.; Mizukami, S.

    2015-05-01

    We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5-130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

  1. Magnetic Flux Emergence into the Solar Corona. I. Its Role for the Reversal of Global Coronal Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Zhang, M.; Low, B. C.

    2001-11-01

    Some physical insights into how the corona reverses its global magnetic field are described in this paper based on a set of elementary hydromagnetic calculations. We assume that a fresh magnetic field of opposite polarity has emerged into a corona containing a preexisting magnetic field. The inevitable magnetic reconnection that takes place between the two magnetic flux systems may result in an expulsion of magnetic flux to infinity. Our calculations suggest the following physical story of the coronal reversal process: When the emerged flux exceeds the preexisting flux by a critical amount, the corona will reverse its polarity. Before this critical ratio is attained, the field with the emerged flux may have enough energy to let only one or two bipolar parts of the multipolar field open up. This opening-up process, taking place as a coronal mass ejection (CME), may take some of the preexisting flux out of the corona and thus increase the emerged-to-preexisting flux ratio and bring the corona closer to the critical value for its global magnetic reversal. Our calculations also indicate that it is possible that the position where the field opens up may be different from that where the new flux emerges. This may help explain the difference in the latitude distribution of active regions and CMEs during a solar cycle as observed by Hundhausen.

  2. Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis

    SciTech Connect

    Zhang, C.; Yamanouchi, M. Ikeda, S.; Sato, H.; Fukami, S.; Matsukura, F.; Ohno, H.

    2014-05-07

    We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.

  3. Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy.

    PubMed

    Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

    2014-08-07

    Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results.

  4. Antiphase domains and reverse thermoremanent magnetism in ilmenite-hematite minerals

    USGS Publications Warehouse

    Lawson, C.A.; Nord, G.L.; Dowty, Eric; Hargraves, R.B.

    1981-01-01

    Examination of synthetic ilmenite-hematite samples by transmission electron microscopy has for the first time revealed the presence of well-defined antiphase domains and antiphase domain boundaries in this mineral system. Samples quenched from 1300??C have a high density of domain boundaries, whereas samples quenched from 900??C have a much lower density. Only the high-temperature samples acquire reverse thermoremanent magnetism when cooled in an applied magnetic field. The presence of a high density of domain boundaries seems to be a necessary condition for the acquisition of reverse thermoremanent magnetism.

  5. Reversals of the solar magnetic dipole in the light of observational data and simple dynamo models

    NASA Astrophysics Data System (ADS)

    Pipin, V. V.; Moss, D.; Sokoloff, D.; Hoeksema, J. T.

    2014-07-01

    Context. Observations show that the photospheric solar magnetic dipole usually does not vanish during the reversal of the solar magnetic field, which occurs in each solar cycle. In contrast, mean-field solar dynamo models predict that the dipole field does become zero. In a recent paper it was suggested that this contradiction could be explained as a large-scale manifestation of small-scale magnetic fluctuations of the surface poloidal field. Aims: Our aim is to confront this interpretation with the available observational data. Methods: Here we compare this interpretation with Wilcox Solar Observatory (WSO) photospheric magnetic field data in order to determine the amplitude of magnetic fluctuations required to explain the phenomenon and to compare the results with predictions from a simple dynamo model which takes these fluctuations into account. Results: We demonstrate that the WSO data concerning the magnetic dipole reversals are very similar to the predictions from our very simple solar dynamo model, which includes both mean magnetic field and fluctuations. The ratio between the rms value of the magnetic fluctuations and the mean field is estimated to be about 2, in reasonable agreement with estimates from sunspot data. The reversal epoch, during which the fluctuating contribution to the dipole is larger than that from the mean field, is about 4 months. The memory time of the fluctuations is about 2 months. Observations demonstrate that the rms of the magnetic fluctuations is strongly modulated by the phase of the solar cycle. This gives additional support to the concept that the solar magnetic field is generated by a single dynamo mechanism rather than also by independent small-scale dynamo action. A suggestion of a weak nonaxisymmetric magnetic field of a fluctuating nature arises from the analysis, with a lifetime of about 1 year. Conclusions: The behaviour of the magnetic dipole during the reversal epoch gives valuable information about details of solar

  6. Impact of low level praseodymium substitution on the magnetic properties of YCrO3 orthochromites

    NASA Astrophysics Data System (ADS)

    Kumar, Surendra; Coondoo, Indrani; Rao, Ashok; Lu, Bo-Han; Kuo, Yung-Kang; Kholkin, Andrei L.; Panwar, Neeraj

    2017-04-01

    Praseodymium (Pr) modified yttrium orthochromites (YCrO3 with Pr =0% and 5% at Y-sites) have been investigated with the aim of exploring the impact of low level Pr substitution on the magnetic properties including magnetization reversal, spin reorientation, and exchange bias of YCrO3 compound. The samples exhibit a distorted orthorhombic structure with Pnma space group. A negative magnetization (or magnetization reversal) was observed under zero-field cooled (ZFC) mode for the pristine YCrO3 sample, whereas such a feature disappeared with a 5% Pr substitution. In addition, the Pr-doped samples exhibited a spin reorientation behaviour which was absent in the pristine sample. Most interestingly, the ZFC magnetic hysteresis loops revealed a left and upward shift, resembling a negative exchange bias effect. These results indicate the effectiveness of low level doping in tailoring the magnetic properties of orthochromites.

  7. Investigation of spin torque driven magnetization reversal in elliptical elements

    NASA Astrophysics Data System (ADS)

    Montgomery, Angelique; Mewes, Claudia K. A.; Mewes, Tim

    2011-03-01

    Spin transfer torque [1, 2] can be utilized to switch the magnetization in small ferromagnetic elements, which can be used to implement a magnetic random access memory. One crucial parameter for spin torque switching is the critical current required to achieve switching. To investigate spin transfer torque we simulate the magnetization dynamics using our Matlab based micromagnetic code (M3) , which uses a fast Fourier transform method to evaluate the longrange magnetostatic field, exchange interaction is implemented using 6, 12 or 26 neighbor methods and also includes adiabatic and non-adiabatic spin torque terms. We have performed simulations using different mesh sizes to examine the influence of the cell size on the micromagnetic results. We have investigated the influence of the current density and pinned layer orientation on the magnetization dynamics and in particular on the switching time. This work was supported by REU supplement #1023069 for NSF DMR #0804243.

  8. Magnetic properties of nanosize iron clusters

    SciTech Connect

    Venturini, E.L.; Wilcoxon, J.P.; Newcomer, P.P.

    1993-12-31

    Isolated, monodisperse {alpha}-Fe clusters between 1.4 and 15 nm in diameter were prepared inside inverse micelles using an oil-continuous, nonaqueous system. The magnetic properties of these clusters were studied in a SQUID magnetometer as a function of cluster size, temperature and applied magnetic field. The blocking temperature, coercive field and remanent moment of 12.5 nm Fe clusters in inverse micelles are significantly lower than those reported for clusters of similar {alpha}-Fe core size but with a surface oxide. The novel synthesis technique may yield metallic clusters with essentially intrinsic magnetic properties.

  9. Temperature- and magnetic-field-induced magnetization reversal in perovskite YFe0.5Cr0.5O3

    NASA Astrophysics Data System (ADS)

    Mao, Jinhua; Sui, Yu; Zhang, Xingquan; Su, Yantao; Wang, Xianjie; Liu, Zhiguo; Wang, Yi; Zhu, Ruibin; Wang, Yang; Liu, Wanfa; Tang, Jinke

    2011-05-01

    Perovskite YFe0.5Cr0.5O3 exhibits magnetization reversal at low applied fields due to the competition between the single ion magnetic anisotropy and the antisymmetric Dzyaloshinsky-Moriya interaction. Below a compensation temperature (Tcomp), a tunable bipolar switching of magnetization is demonstrated by changing the magnitude of the field while keeping it in the same direction. The present compound also displays both normal and inverse magnetocaloric effects above and below 260 K, respectively. These phenomena coexisting in a single magnetic system can be tuned in a predictable manner and have potential applications in electromagnetic devices.

  10. Preparation and characterization of supported magnetic nanoparticles prepared by reverse micelles

    PubMed Central

    Han, Luyang; Biskupek, Johannes; Kaiser, Ute; Ziemann, Paul

    2010-01-01

    Summary Monatomic (Fe, Co) and bimetallic (FePt and CoPt) nanoparticles were prepared by exploiting the self-organization of precursor loaded reverse micelles. Achievements and limitations of the preparation approach are critically discussed. We show that self-assembled metallic nanoparticles can be prepared with diameters d = 2–12 nm and interparticle distances D = 20–140 nm on various substrates. Structural, electronic and magnetic properties of the particle arrays were characterized by several techniques to give a comprehensive view of the high quality of the method. For Co nanoparticles, it is demonstrated that magnetostatic interactions can be neglected for distances which are at least 6 times larger than the particle diameter. Focus is placed on FePt alloy nanoparticles which show a huge magnetic anisotropy in the L10 phase, however, this is still less by a factor of 3–4 when compared to the anisotropy of the bulk counterpart. A similar observation was also found for CoPt nanoparticles (NPs). These results are related to imperfect crystal structures as revealed by HRTEM as well as to compositional distributions of the prepared particles. Interestingly, the results demonstrate that the averaged effective magnetic anisotropy of FePt nanoparticles does not strongly depend on size. Consequently, magnetization stability should scale linearly with the volume of the NPs and give rise to a critical value for stability at ambient temperature. Indeed, for diameters above 6 nm such stability is observed for the current FePt and CoPt NPs. Finally, the long-term conservation of nanoparticles by Au photoseeding is presented. PMID:21977392

  11. Sudden motility reversal indicates sensing of magnetic field gradients in Magnetospirillum magneticum AMB-1 strain

    PubMed Central

    González, Lina M; Ruder, Warren C; Mitchell, Aaron P; Messner, William C; LeDuc, Philip R

    2015-01-01

    Many motile unicellular organisms have evolved specialized behaviors for detecting and responding to environmental cues such as chemical gradients (chemotaxis) and oxygen gradients (aerotaxis). Magnetotaxis is found in magnetotactic bacteria and it is defined as the passive alignment of these cells to the geomagnetic field along with active swimming. Herein we show that Magnetospirillum magneticum (AMB-1) show a unique set of responses that indicates they sense and respond not only to the direction of magnetic fields by aligning and swimming, but also to changes in the magnetic field or magnetic field gradients. We present data showing that AMB-1 cells exhibit sudden motility reversals when we impose them to local magnetic field gradients. Our system employs permalloy (Ni80Fe20) islands to curve and diverge the magnetic field lines emanating from our custom-designed Helmholtz coils in the vicinity of the islands (creating a drop in the field across the islands). The three distinct movements we have observed as they approach the permalloy islands are: unidirectional, single reverse and double reverse. Our findings indicate that these reverse movements occur in response to magnetic field gradients. In addition, using a permanent magnet we found further evidence that supports this claim. Motile AMB-1 cells swim away from the north and south poles of a permanent magnet when the magnet is positioned less than ∼30 mm from the droplet of cells. All together, these results indicate previously unknown response capabilities arising from the magnetic sensing systems of AMB-1 cells. These responses could enable them to cope with magnetic disturbances that could in turn potentially inhibit their efficient search for nutrients. PMID:25478682

  12. Sign reversal of magnetization and exchange bias in Ni(Cr1-xAlx)2O4 (x=0-0.50)

    NASA Astrophysics Data System (ADS)

    Barman, Junmoni; Ravi, S.

    2017-03-01

    Ni(Cr1-xAlx)2O4 (x=0-0.50) samples were prepared in single phase form by using sol-gel method and their structural and magnetic properties were studied. Al substitution transforms the crystal structure of NiCr2O4 from tetragonal cell with space group I41/amd to cubic cell of Fd 3 barm space group. Magnetization measurements by varying the temperature and magnetic field were carried out to investigate the interesting magnetization reversal and exchange bias behaviors. Magnetization reversal is observed for x=0.10 sample with a magnetic compensation temperature of 40 K and it is explained by considering different temperature dependences of magnetic moments of the two sublattices. Shifting of magnetic hysteresis loops towards the negative magnetic field axis and hence the presence of negative exchange bias field is observed for x=0.15 sample. The x=0.10 sample exhibits the tunable positive and negative exchange bias field. Exchange bias in these samples is explained considering the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic spins. However, the sign reversal of exchange bias field is due to the change in domination of one ferrimagnetic sublattice over the other with variation in temperature. Both normal and inverse magnetocaloric effects are observed for x=0.10 sample.

  13. Plasmonic enhancement of ultrafast all-optical magnetization reversal

    NASA Astrophysics Data System (ADS)

    Kochergin, Vladimir; Neely, Lauren N.; Allin, Leigh J.; Kochergin, Eugene V.; Wang, Kang L.

    2011-10-01

    Ultrafast all optical magnetization switching in GdFeCo layers on the basis of Inverse Faraday Effect (IFE) was demonstrated recently and suggested as a possible path toward next generation magnetic data storage medium with much faster writing time. However, to date, the demonstrations of ultrafast all-optical magnetization switching were performed with powerful femtosecond lasers, hardly useful for practical applications in data storage and data processing. Here we show that utilization of IFE enhancement in plasmonic nanostructures enables fast all-optical magnetization switching with smaller/cheaper laser sources with longer pulse durations. Our modeling results predict significant enhancement of IFE around all major types of plasmonic nanostructures for a circularly polarized incident light. Unlike the IFE in uniform bulk materials, nonzero value of IFE is predicted in plasmonic nanostructures even with a linearly polarized excitation. Experimentally, all-optical magnetization switching at 20 times lower laser fluence and roughly 100 times lower value of laser fluence/pulse duration ratio is demonstrated in plasmonic samples to verify the model predictions. The path to achieve higher levels of enhancement experimentally is discussed.

  14. Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

    PubMed Central

    Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

    2015-01-01

    We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638

  15. Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

    NASA Astrophysics Data System (ADS)

    Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

    2015-12-01

    We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.

  16. Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

    SciTech Connect

    Skomski, Ralph; Manchanda, Priyanka; Takeuchi, Ichiro; Cui, Jun

    2014-06-11

    The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

  17. Geometry Dependence of Magnetization Reversal in Nanocomposite Alloys

    SciTech Connect

    Skomski, R; Manchanda, P; Takeuchi, I; Cui, J

    2014-05-31

    The geometrical optimization of aligned hard-soft permanent-magnet nanocomposites is investigated by model calculations. Considered criteria are the shapes of the soft and c-axis-aligned hard phases, the packing fraction of the soft phase, and magnetostatic interactions. Taking into account that the energy product is enhanced via the volume fraction of the soft phase, subject to maintaining coercivity, we find that the best structures are soft-magnetic cubes as well as long rods with a square cross section. Comparing embedded soft cubes with embedded soft spheres of the same size, our nucleation-field analysis shows that the volume fraction of the soft phase is enhanced by 91%, with a coercivity reduction of only 25%. Magnetostatic interactions often but not always deteriorate the permanent-magnet performance, as exemplified by the example of MnBi:FeCo bilayers and multilayers.

  18. Thermally activated magnetization reversal in monatomic magnetic chains on surfaces studied by classical atomistic spin-dynamics simulations.

    PubMed

    Bauer, David S G; Mavropoulos, Phivos; Lounis, Samir; Blügel, Stefan

    2011-10-05

    We analyse the spontaneous magnetization reversal of supported monatomic chains of finite length due to thermal fluctuations via atomistic spin-dynamics simulations. Our approach is based on the integration of the Landau-Lifshitz equation of motion of a classical spin Hamiltonian in the presence of stochastic forces. The associated magnetization lifetime is found to obey an Arrhenius law with an activation barrier equal to the domain wall energy in the chain. For chains longer than one domain wall width, the reversal is initiated by nucleation of a reversed magnetization domain primarily at the chain edge followed by a subsequent propagation of the domain wall to the other edge in a random-walk fashion. This results in a linear dependence of the lifetime on the chain length, if the magnetization correlation length is not exceeded. We studied chains of uniaxial and triaxial anisotropy and found that a triaxial anisotropy leads to a reduction of the magnetization lifetime due to a higher reversal attempt rate, even though the activation barrier is not changed.

  19. Onset of a Propagating Self-Sustained Spin Reversal Front in a Magnetic System

    NASA Astrophysics Data System (ADS)

    Kent, Andrew D.

    2014-03-01

    The energy released in a magnetic material by reversing spins as they relax toward equilibrium can lead to a dynamical magnetic instability in which all the spins in a sample rapidly reverse in a run-away process known as magnetic deflagration. A well-defined front separating reversed and un-reversed spins develops that propagates at a constant speed. This process is akin to a chemical reaction in which a flammable substance ignites and the resulting exothermic reaction leads via thermal conduction to increases in the temperature of an adjacent unburned substance that ignites it. In a magnetic system the reaction is the reversal of spins that releases Zeeman energy and the magnetic anisotropy barrier is the reaction's activation energy. An interesting aspect of magnetic systems is that these key energies-the activation energy and the energy released-can be independently controlled by applied magnetic fields enabling systematic studies of these magnetic instabilities. We have studied the instability that leads to the ignition of magnetic deflagration in a thermally driven Mn12-Ac molecular magnet single crystal. Each Mn12-ac molecule is a uniaxial nanomagnet with spin 10 and energy barrier of 60 K. We use a longitudinal field (a field parallel to the easy axis) to set the energy released and a transverse field to control the activation energy. A heat pulse is applied to one end of the crystal to initiate the process. We study the crossover between slow magnetic relaxation and rapid, self-sustained magnetic deflagration as a function of these fields at low temperature (0.5 K). An array of Hall sensors adjacent to a single crystal is used to detect and measure the speed of the spin-reversal front. I will describe a simple model we developed based on a reaction-diffusion process that describes our experimental findings. I will also discuss prospects for observing spin-fronts driven by magnetic dipole interactions between molecules that can be sonic, i.e. travel near

  20. Magnetization reversal mechanism in perpendicular exchange-coupled Fe/L10-FePt bilayers

    NASA Astrophysics Data System (ADS)

    Varvaro, G.; Albertini, F.; Agostinelli, E.; Casoli, F.; Fiorani, D.; Laureti, S.; Lupo, P.; Ranzieri, P.; Astinchap, B.; Testa, A. M.

    2012-07-01

    The magnetization reversal mechanism in perpendicular soft/hard Fe/FePt exchange-coupled bilayers has been investigated as a function of the soft layer thickness (tFe = 2, 3.5, 5 nm) combining magnetization loops at variable angle, magnetic domain analysis by magnetic force microscopy and numerical micromagnetic simulations. The analytical model proposed in the literature can properly account for some features of the reversal mechanism, such as positive nucleation fields and the reduction of the perpendicular coercive field and remanence by increasing the soft layer thickness, but cannot satisfactorily describe the magnetization process of real systems. We showed that for a thickness of the soft layer exceeding the FePt exchange length (˜2 nm), numerical micromagnetic calculations are needed to reproduce experimental observations. Indeed, just above the coercive field, the magnetization reversal does not proceed in single step switching, as predicted by the analytical model, but according to a more complex process: evolution of nucleated magnetic domains whose magnetization is approximately along the surface normal in the hard layer and slightly out of the film plane in the soft layer, followed by rotation of Fe moments along the field direction.

  1. Magnetic turbulent electron transport in a reversed field pinch

    SciTech Connect

    Schoenberg, K.; Moses, R.

    1990-01-01

    A model of magnetic turbulent electron transport is presented. The model, based on the thermal conduction theory of Rechester and Rosenbluth, entails a Boltzmann description of electron dynamics in the long mean-free-path limit and quantitatively describes the salient features of superthermal electron measurements in the RFP edge plasma. Included are predictions of the mean superthermal electron energy, current density, and power flux asymmetry. A discussion of the transport model, the assumptions implicit in the model, and the relevance of this work to more general issue of magnetic turbulent transport in toroidal systems is presented. 32 refs., 3 figs.

  2. Tailoring Magnetic Properties in Bulk Nanostructured Solids

    NASA Astrophysics Data System (ADS)

    Morales, Jason Rolando

    Important magnetic properties and behaviors such as coercivity, remanence, susceptibility, energy product, and exchange coupling can be tailored by controlling the grain size, composition, and density of bulk magnetic materials. At nanometric length scales the grain size plays an increasingly important role since magnetic domain behavior and grain boundary concentration determine bulk magnetic behavior. This has spurred a significant amount of work devoted to developing magnetic materials with nanometric features (thickness, grain/crystallite size, inclusions or shells) in 0D (powder), 1D (wires), and 2D (thin films) materials. Large 3D nanocrystalline materials are more suitable for many applications such as permanent magnets, magneto-optical Faraday isolators etc. Yet there are relatively few successful demonstrations of 3D magnetic materials with nanoscale influenced properties available in the literature. Making dense 3D bulk materials with magnetic nanocrystalline microstructures is a challenge because many traditional densification techniques (HIP, pressureless sintering, etc.) move the microstructure out of the "nano" regime during densification. This dissertation shows that the Current Activated Pressure Assisted Densification (CAPAD) method, also known as spark plasma sintering, can be used to create dense, bulk, magnetic, nanocrystalline solids with varied compositions suited to fit many applications. The results of my research will first show important implications for the use of CAPAD for the production of exchange-coupled nanocomposite magnets. Decreases in grain size were shown to have a significant role in increasing the magnitude of exchange bias. Second, preferentially ordered bulk magnetic materials were produced with highly anisotropic material properties. The ordered microstructure resulted in changing magnetic property magnitudes (ex. change in coercivity by almost 10x) depending on the relative orientation (0° vs. 90°) of an externally

  3. Tuning the Magnetic Properties of Nanoparticles

    PubMed Central

    Kolhatkar, Arati G.; Jamison, Andrew C.; Litvinov, Dmitri; Willson, Richard C.; Lee, T. Randall

    2013-01-01

    The tremendous interest in magnetic nanoparticles (MNPs) is reflected in published research that ranges from novel methods of synthesis of unique nanoparticle shapes and composite structures to a large number of MNP characterization techniques, and finally to their use in many biomedical and nanotechnology-based applications. The knowledge gained from this vast body of research can be made more useful if we organize the associated results to correlate key magnetic properties with the parameters that influence them. Tuning these properties of MNPs will allow us to tailor nanoparticles for specific applications, thus increasing their effectiveness. The complex magnetic behavior exhibited by MNPs is governed by many factors; these factors can either improve or adversely affect the desired magnetic properties. In this report, we have outlined a matrix of parameters that can be varied to tune the magnetic properties of nanoparticles. For practical utility, this review focuses on the effect of size, shape, composition, and shell-core structure on saturation magnetization, coercivity, blocking temperature, and relaxation time. PMID:23912237

  4. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Improved anti-Stokes energy transfer between rare earth ions in Er(0.5)Yb(9.5): FOV oxyfluoride vitroceramics explains the strong color reversal

    NASA Astrophysics Data System (ADS)

    Chen, Xiao-Bo; Wang, Ce; Gregory, Salamo J.; Naruhito, Sawanobori; Kang, Dong-Guo; Masaaki, Ohtsuka; Yang, Guo-Jian; Peng, Fang-Lin

    2009-12-01

    The widely used energy transfer theory is a foundation of luminescence, in which the rates of Stokes and anti-Stokes processes have the same calculation formula. An improvement on the anti-Stokes energy transfer to explain the fluorescence intensity reversal between the red and green fluorescence of Er(0.5)Yb(9.5):FOV is reported in the present article. The range of the intensity reversal σ was measured to be 877. Dynamic processes for 16 levels were simulated. A coefficient, the improvement factor of the intensity ratio of Stokes to anti-Stokes processes in quantum Raman theory compared to classical Raman theory, is introduced to successfully describe the anti-Stokes energy transfer. A new method to calculate the distance between the rare earth ions, which is critical for the energy transfer calculation, is proposed. The validity of these important improvements is also proved by experiment.

  5. Direct real-space observation of nearly stochastic behavior in magnetization reversal process on a nanoscale

    SciTech Connect

    Im, M.-Y.; Kim, D.-H.; Lee, K.-D.; Fischer, P.; Shin, S.-C.

    2007-06-01

    We report a non-deterministic nature in the magnetization reversal of nanograins of CoCrPt alloy film. Magnetization reversal process of CoCrPt alloy film is investigated using high resolution soft X-ray microscopy which provides real space images with a spatial resolution of 15 nm. Domain nucleation sites mostly appear stochastically distributed within repeated hysteretic cycles, where the correlation increases as the strength of the applied magnetic field increases in the descending and ascending branches of the major hysteresis loop. In addition, domain configuration is mostly asymmetric with inversion of an applied magnetic field in the hysteretic cycle. Nanomagnetic simulation considering thermal fluctuations of the magnetic moments of the grains explains the nearly stochastic nature of the domain nucleation behavior observed in CoCrPt alloy film. With the bit size in high-density magnetic recording media approaching nanometer length scale, one of the fundamental and crucial issues is whether the domain nucleation during magnetization reversal process exhibits a deterministic behavior. Repeatability of local domain nucleation and deterministic switching behavior are basic and essential factors for achieving high performance in high-density magnetic recording [1-3]. Most experimental studies on this issue reported so far have been mainly performed by indirect probes through macroscopic hysteresis loop and Barkhausen pattern measurements, which provide the ensemble-average magnetization. Thus, they are inadequate to gain insight into the domain-nucleation behavior on a nanometer length scale during the magnetization reversal process [4-6]. Very recently, coherent X-ray speckle metrology, where the speckle pattern observed in reciprocal space acts as a fingerprint of the domain configurations, was adopted to investigate stochastic behavior in the magnetization reversal of a Co/Pt multilayer film [7,8]. However, no direct observation on the stochastic behavior of

  6. Magnetic Properties of Electrically Contacted Fe4 Molecular Magnets

    NASA Astrophysics Data System (ADS)

    Burgess, Jacob; Malavolti, Luigi; Lanzilotto, Valeria; Mannini, Matteo; Totti, Frederico; Ninova, Silviya; Yan, Shichao; Choi, Deung-Jang; Rolf-Pissarczyk, Steffen; Cornia, Andrea; Sessoli, Roberta; Loth, Sebastian

    2015-03-01

    Single molecule magnets (SMMs) are often large and fragile molecules. This poses challenges for the construction of SMM based spintronics. Device geometries with two electronic leads contacting a molecule may be explored via scanning tunneling microscopy (STM). The Fe4 molecule stands out as a robust, thermally evaporable SMM, making it ideal for such an experiment. Here we present the first STM investigations of individual Fe4 molecules thermally evaporated onto a monolayer of Cu2N on a Cu (100) crystal. Using inelastic electron tunneling spectroscopy (IETS), spin excitations in single Fe4 molecules can be detected at meV energies. Analysis using a Spin Hamiltonian allows extraction of magnetic properties of individual Fe4 molecules, and investigation of the influence of the electronic leads. The tip and sample induce small changes in the magnetic properties of Fe4 molecules, making Fe4 a promising candidate for the development of spintronics devices based on SMMs.

  7. Electric-field control of magnetization reversal in a Y-type hexaferrite

    NASA Astrophysics Data System (ADS)

    Yang, Y. T.; Wang, L. Y.; Shen, L. J.; Zhou, W. P.; Song, Y. Q.; Lv, L. Y.; Wang, D. H.; Cao, Q. Q.; Du, Y. W.; Zhang, Y. J.; Yang, J. H.

    2014-01-01

    We report on the giant magnetoelectric effect in Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22 (x=0.08). Large electric field tuning of magnetism is observed near room-temperature. Electrically controlled magnetization reversal is observed at 315 K. The sign of the magnetization exhibits an on-off behavior with the electric field. The scanning probe microscopy results show direct and powerful evidence of electric control of magnetism at room temperature.

  8. Using injection molding and reversible bonding for easy fabrication of magnetic cell trapping and sorting devices

    NASA Astrophysics Data System (ADS)

    Royet, David; Hériveaux, Yoann; Marchalot, Julien; Scorretti, Riccardo; Dias, André; Dempsey, Nora M.; Bonfim, Marlio; Simonet, Pascal; Frénéa-Robin, Marie

    2017-04-01

    Magnetism and microfluidics are two key elements for the development of inexpensive and reliable tools dedicated to high-throughput biological analysis and providing a large panel of applications in domains ranging from fundamental biology to medical diagnostics. In this work, we introduce a simple protocol, relying on injection molding and reversible bonding for fabrication of magnetic cell trapping and sorting devices using only standard soft-lithography equipment. Magnetic strips or grids made of Polydimethylsiloxane (PDMS) doped with hard (NdFeB) or soft (carbonyl iron) magnetic powders were integrated at the bottom of whole PDMS chips. Preliminary results show the effective deviation/trapping of magnetic beads or magnetically-labeled bacteria as the sample flows through the microchannel, proving the potential of this rapid prototyping approach for easy fabrication of magnetic cell sorters.

  9. Origin of the asymmetric magnetization reversal behavior in exchange-biased systems: competing anisotropies.

    PubMed

    Camarero, Julio; Sort, Jordi; Hoffmann, Axel; García-Martín, Jose Miguel; Dieny, Bernard; Miranda, Rodolfo; Nogués, Josep

    2005-07-29

    The magnetization reversal in exchange-biased ferromagnetic-antiferromagnetic (FM-AFM) bilayers is investigated. Different reversal pathways on each branch of the hysteresis loop, i.e., asymmetry, are obtained both experimentally and theoretically when the magnetic field is applied at certain angles from the anisotropy direction. The range of angles and the magnitude of this asymmetry are determined by the ratio between the FM anisotropy and the interfacial FM-AFM exchange anisotropy. The occurrence of asymmetry is linked with the appearance of irreversibility, i.e., finite coercivity, as well as with the maximum of exchange bias, increasing for larger anisotropy ratios. Our results indicate that asymmetric hysteresis loops are intrinsic to exchange-biased systems and the competition between anisotropies determines the asymmetric behavior of the magnetization reversal.

  10. Non-resonant fishbone instabilities of qmin ≳ 1 in tokamak plasmas with weakly reversed magnetic shear

    NASA Astrophysics Data System (ADS)

    Wang, Xian-Qu; Zhang, Rui-Bin; Qin, Liang; Wang, Xiao-Gang

    2014-09-01

    In this study, we theoretically explore properties of non-resonant fishbone (NRF) instabilities with a safety factor profile slightly above unity (qmin ≳ 1) in tokamak plasmas with reversed magnetic shear configuration. From the dispersion relation of the NRF mode, it is found that the growth rate of the mode in general reversed shear scenarios with qmin ≳ 1 depends on fast ion beta βh in a power law of {\\sim} \\beta_{h}^{2/3} , different from that of ˜βh in a conventional positive magnetic shear configuration. Meanwhile, due to the slow ion precession and small continuum damping in ITER-like tokamaks with reversed shear, the mode has a lower trigger threshold than those with monotonously positive magnetic shear. In addition, the ion diamagnetic drift has been found to destabilize the fast ion-driven NRF mode. Other effects such as the shape of the q-profile, characterized by values of qmin and q(0), neutral beam energy, magnetohydrodynamic potential energy and the fraction of fast ions on the instability threshold are also discussed. Nonlinear behavior of the mode is further analyzed using a modified model.

  11. Using Polar Coronal Hole Area Measurements to Determine the Solar Polar Magnetic Field Reversal in Solar Cycle 24

    NASA Technical Reports Server (NTRS)

    Karna, N.; Webber, S.A. Hess; Pesnell, W.D.

    2014-01-01

    An analysis of solar polar coronal hole (PCH) areas since the launch of the Solar Dynamics Observatory (SDO) shows how the polar regions have evolved during Solar Cycle 24. We present PCH areas from mid-2010 through 2013 using data from the Atmospheric Imager Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) instruments onboard SDO. Our analysis shows that both the northern and southern PCH areas have decreased significantly in size since 2010. Linear fits to the areas derived from the magnetic-field properties indicate that, although the northern hemisphere went through polar-field reversal and reached solar-maximum conditions in mid-2012, the southern hemisphere had not reached solar-maximum conditions in the polar regions by the end of 2013. Our results show that solar-maximum conditions in each hemisphere, as measured by the area of the polar coronal holes and polar magnetic field, will be offset in time.

  12. Magnetic properties of magnetoactive spin clusters

    SciTech Connect

    Khamzin, A. M.; Nigmatullin, R. R.

    2010-01-15

    A simple model is proposed for describing magnetic properties of magnetoactive nanoclusters, which permits exact analytic solution. Exact expressions are obtained for thermodynamic characteristics of the model, which hold in the entire range of temperatures, magnetic fields, and interaction parameters. It is found that in the case of easy-axis anisotropy, the field dependence of magnetization of a nanocluster consisting of N particles with a spin of 1/2 has [N/2] fractional plateaus ([ Horizontal-Ellipsis ] is the integer part) corresponding to polarized phases with ruptures singlet pairs. A nonmonotonic behavior observed for the magnetic susceptibility of an easy-plane cluster is typical of gap magnets. The spin gap between the ground state and excited states is proportional to the anisotropy parameter.

  13. Magnetic properties of one-dimensional Au-Co chains on the copper(110) surface

    NASA Astrophysics Data System (ADS)

    Kolesnikov, S. V.; Tsysar, K. M.; Saletsky, A. M.

    2015-08-01

    Magnetic properties of cobalt atoms in Au-Co chains on the Cu(110) surface (such as the magnetic moment, magnetic anisotropy energy, and exchange energy) have been calculated in the framework of the density functional theory. It has been found, at zero temperature, an infinitely long Au-Co chain is in the ferromagnetic state. The magnetostatic and magnetodynamic properties of finite-length Au-Co chains at a nonzero temperature have been investigated within the Heisenberg model using the kinetic Monte Carlo method. The dependences of the Curie temperature and magnetization reversal time on the chain length have been obtained, as well as the dependences of the coercivity of the chain on the temperature, chain length, and magnetization reversal rate.

  14. Synthesis, magnetic and microstructural properties of Alnico magnets with additives

    NASA Astrophysics Data System (ADS)

    Ahmad, Zubair; Liu, Zhongwu; ul Haq, A.

    2017-04-01

    The phase formation, crystal structure, crystallographic texture, microstructure and magnetic properties of Alnico-8 alloys with varying Co and Nb content have been investigated and presented. Alnico-8 alloys were fabricated by induction melting and casting techniques. Magnetic properties in the alloys were induced by optimized thermomagnetic treatment and subsequent aging. The 37.9Fe-32Co-14Ni-7.5Al-3.1Cu-5.5Ti alloy exhibits coercivity of 110 kA/m, remanence of 0.66 T and energy product of 31.2 kJ/m3. The addition of 35 wt% Co in conjunction with 1.5 wt% Nb to 37.9Fe-14Ni-7.5Al-3.1Cu-5.5Ti alloys led to increase the magnetic properties, especially coercivity. The enhancement of the coercivity is attributed to ideal shape anisotropy and optimum mass fraction of ferromagnetic Fe-Co rich particles, which are 25-30 nm in diameter and 300-350 nm in length. The 33.4Fe-35Co-14Ni-7.5Al-5.5Ti-3.1Cu-1.5 Nb alloy yields the optimum magnetic properties of coercivity of 141.4 kA/m, remanence of 0.83 T and energy product of 42.4 kJ/m3. The good magnetic properties in the studied alloys are attributed to the nanostructured microstructure comprising textured Fe-Co-Nb rich α1 phase and Al-Ni-Cu rich α2 phase.

  15. Magnetization reversal in ferromagnetic spirals via domain wall motion

    NASA Astrophysics Data System (ADS)

    Schumm, Ryan D.; Kunz, Andrew

    2016-11-01

    Domain wall dynamics have been investigated in a variety of ferromagnetic nanostructures for potential applications in logic, sensing, and recording. We present a combination of analytic and simulated results describing the reliable field driven motion of a domain wall through the arms of a ferromagnetic spiral nanowire. The spiral geometry is capable of taking advantage of the benefits of both straight and circular wires. Measurements of the in-plane components of the spirals' magnetization can be used to determine the angular location of the domain wall, impacting the magnetoresistive applications dependent on the domain wall location. The spirals' magnetization components are found to depend on the spiral parameters: the initial radius and spacing between spiral arms, along with the domain wall location. The magnetization is independent of the parameters of the rotating field used to move the domain wall, and therefore the model is valid for current induced domain wall motion as well. The speed of the domain wall is found to depend on the frequency of the rotating driving field, and the domain wall speeds can be reliably varied over several orders of magnitude. We further demonstrate a technique capable of injecting multiple domain walls and show the reliable and unidirectional motion of domain walls through the arms of the spiral.

  16. Effect of Zr Addition on the Magnetization Reversal Behavior for α-Fe/Pr2Fe14B Nanocomposite Alloys

    NASA Astrophysics Data System (ADS)

    Pan, Minxiang; Zhang, Pengyue; Ge, Hongliang; Hong, Zhanglian; Wu, Qiong; Jiao, Zhiwei; Yang, Hangfu

    2011-09-01

    The microstructure and magnetic properties of the Zr-doped α-Fe/Pr2Fe14B nanocomposite magnets prepared by melt-spinning method have been studied by X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The magnetization reversal behavior during the recoil processes of nanocomposite alloys has been investigated by analyzing the hysteresis curves and recoil loops of demagnetization curves. An enhanced magnetic properties has been obtained by the addition of 1 at. % Zr in α-Fe/Pr2Fe14B alloys, where the coercivity Hc increases from 470.7 to 793.2 kA/m, the maximum energy product (BH)max from 66.8 to 90.8 kJ/m3, the remanence ratio Mr/Ms from 0.74 to 0.77. The recoil loop results show that the maximum value of the integrated recoil loop area for 1 at. % Zr doped sample is quietly low of 1.87×10-3, only 1/2 for the Zr-free and 1/3 for 5 at. % Zr doped samples respectively. This result indicates that the 1 at. % Zr doped sample has a lower energy loss, resulting from a low recoverable portion of the magnetization remaining as long as the applied reversal field is below the coercivity Hc. This study provides a promising guideline for the future fabrication of low-energy-loss nanocomposite magnets for electric machines and generators.

  17. Effect of temperature on magnetization reversal characteristics of ferromagnetic 3 d metal layers within exchange-coupled FeMn-based structures

    NASA Astrophysics Data System (ADS)

    Vas'kovskiy, V. O.; Adanakova, O. A.; Gorkovenko, A. N.; Lepalovskij, V. N.; Svalov, A. V.; Stepanova, E. A.

    2015-12-01

    Multilayer films Fe20Ni80/FeMn/FM (with FM = Ni, Fe11Ni89, Fe20Ni80, Co30Ni70, Fe, Co) have been prepared and their structure has been estimated. Their hysteretic properties and interlayer coupling parameters have been studied in a temperature range of 5-350 K. Regularities of the magnetization reversal of ferromagnetic layers under magnetic exchange-bias conditions have been interpreted.

  18. Internal magnetic field measurement on C-2 field-reversed configuration plasmas.

    PubMed

    Gota, H; Thompson, M C; Knapp, K; Van Drie, A D; Deng, B H; Mendoza, R; Guo, H Y; Tuszewski, M

    2012-10-01

    A long-lived field-reversed configuration (FRC) plasma has been produced in the C-2 device by dynamically colliding and merging two oppositely directed, highly supersonic compact toroids (CTs). The reversed-field structure of the translated CTs and final merged-FRC state have been directly verified by probing the internal magnetic field structure using a multi-channel magnetic probe array near the midplane of the C-2 confinement chamber. Each of the two translated CTs exhibits significant toroidal fields (B(t)) with opposite helicity, and a relatively large B(t) remains inside the separatrix after merging.

  19. Magnetization reversal phenomena in (Cr0.70Ti0.30)5S6

    NASA Astrophysics Data System (ADS)

    Hashimoto, Satoshi; Matsuda, Yuji; Sato, Tetsuya; Anzai, Shuichiro

    2005-12-01

    Magnetization reversal phenomena (MRP) along magnetic order-order transitions have recently been reported on impurity-doped magnetic systems. Because imperfect long-range magnetic order exists in these systems, it is expected that a systematic investigation of MRP will give physical information on thermomagnetic processes of magnetic systems in the range from the micro- to nanoscales. As a typical order-order transition (a state doubly modulated by helical and canting orders to a collinear ferrimagnetic state) has been known to occur on Cr5S6 at a transition temperature Tt, we investigate the magnetizations of (Cr0.70Ti0.30)5S6 on heating and cooling runs in various magnetic fields. At 20Oe, the field-cooled magnetization just below the Curie temperature has a positive sign; the sign turns negative below the compensation temperature TCM (first step) and finally returns to positive below Tt (second step). The first-step MRP observed in this system is explained by the potential barriers resulting from anisotropy energy when the preferred direction of collinear ferrimagnetic moment reverses. The proposed mechanism for second-step MRP is the pinning effect caused by the impurity atoms (Ti) in the helical long-range-order chains. Comparing other examples of MRPs, we discuss the roles of local impurity centers in the thermomagnetic process in magnetic order-order transitions.

  20. Magnetic and microstructural properties of nanocrystalline exchange coupled PrFeB permanent magnets

    NASA Astrophysics Data System (ADS)

    Goll, D.; Seeger, M.; Kronmüller, H.

    1998-05-01

    Nanocrystalline exchange coupled Pr 2Fe 14B single-phase and Pr 2Fe 14B+α-Fe two-phase magnets with grain sizes of about 20 nm were produced using the melt-spinning procedure. In the stoichiometric Pr 2Fe 14B composition a significantly enhanced remanence of JR=0.95 T was achieved in comparison with conventional Pr-rich and therefore decoupled isotropic PrFeB magnets ( JR⩽0.5 JS=0.78 T). In the composite magnets with overstoichiometric Fe a further enhancement of the remanence is possible. Values up to JR=1.42 T and ( BH) max=180.7 kJ/m 3 were obtained. As there exists no spin reorientation in PrFeB magnets, our attention was not only directed to the magnetic behaviour at room temperature but also to the magnetic properties in the whole ferromagnetic temperature range. The microstructural parameters Neff, αK and αex describing the influence of the non-ideal microstructure and the effect of the exchange coupling on the coercive field were determined within the framework of the nucleation model from the temperature dependence of the coercive field. Furthermore, reversibility measurements of the demagnetization curves in the second quadrant give important information about the magnetization processes in exchange coupled magnets. Moreover, we have investigated the law of approach to ferromagnetic saturation of the single-phase magnet in comparison with the decoupled one. The magnetic results are correlated with TEM investigations of the real microstructure.

  1. Magnetic properties of nanocrystalline transition metals

    NASA Astrophysics Data System (ADS)

    Aus, Martin J.

    1999-09-01

    In the past decade, considerable attention has been devoted to the nanoprocessing of magnetic materials to enhance specific magnetic properties. For nanocrystalline materials in which the grain size approaches the dimensions of the domain wall thickness of conventional materials, considerable changes in magnetic behaviour are expected. In the present work, various electrodeposited ferromagnetic nanocrystalline pure metals and alloys were characterized by using a vibrating sample magnetometer. The systems investigated include pure Ni and Co as well as alloys of Ni-P, Ni-Fe and Co-Fe. These studies explored the effect of gram size on coercivity, indicating that the crystallographic texture is more significant than gram size. In addition, these studies reported, for the first time, that saturation magnetization of pore-free electroplated bulk nanocrystalline transition metals and their alloys is relatively little affected by grain size. In contrast, previously reported results for ultra-fine particles and nanomaterials produced from compacted powders showed a strong decrease in saturation magnetization with decreasing grain size. The difference in results for pore-free electrodeposits and ultrafine particles/compacted powders has been attributed to antiferromagnetic surface oxide layers, which is a direct result of large internal porosity in the latter group of materials. Further magnetic studies were completed on nanocrystalline electrodeposits produced by magnetoelectrohydrolysis. The effects of applied magnetic field strength and substrate orientation on saturation magnetization and coercivity of Ni-Fe and Co were explored. The results have shown that both nanoprocessing and electroplating in a magnetic field can improve soft magnetic properties by lowering the coercivity. Thermomagnetic studies examined saturation magnetization as a function of temperature, Curie temperature and coercivity changes during annealing. The Curie temperatures of electrodeposited

  2. Magnetization reversal by electric-field decoupling of magnetic and ferroelectric domain walls in multiferroic-based heterostructures.

    PubMed

    Skumryev, V; Laukhin, V; Fina, I; Martí, X; Sánchez, F; Gospodinov, M; Fontcuberta, J

    2011-02-04

    We demonstrate that the magnetization of a ferromagnet in contact with an antiferromagnetic multiferroic (LuMnO(3)) can be speedily reversed by electric-field pulsing, and the sign of the magnetic exchange bias can switch and recover isothermally. As LuMnO(3) is not ferroelastic, our data conclusively show that this switching is not mediated by strain effects but is a unique electric-field driven decoupling of the ferroelectric and antiferromagnetic domain walls. Their distinct dynamics are essential for the observed magnetic switching.

  3. Magnetization reversal processes in hot-extruded τ-MnAl-C

    NASA Astrophysics Data System (ADS)

    Thielsch, J.; Bittner, F.; Woodcock, T. G.

    2017-03-01

    The magnetic domain structure of hot-extruded bulk τ-Mn53Al45C2 was studied by Kerr microscopy under application of a magnetic field in-situ. The microstructure consists of recrystallized, fine-grained regions and large non-recrystallized grains which contain a high density of twins. Within these large polytwinned grains, a clear pinning interaction of magnetic domain walls at twin boundaries was observed but with a rather small pinning force. The smaller, recrystallized grains show a higher resistance to magnetization reversal. The critical single domain particle size of this material was estimated at 773 nm and the fine, recrystallized grains are in the range of this size. Demagnetizing the sample following saturation using a 3 T field pulse revealed that individual fine grains reverse independently from their neighbours.

  4. Graphene as a reversible spin manipulator of molecular magnets.

    PubMed

    Bhandary, Sumanta; Ghosh, Saurabh; Herper, Heike; Wende, Heiko; Eriksson, Olle; Sanyal, Biplab

    2011-12-16

    One of the primary objectives in molecular nanospintronics is to manipulate the spin states of organic molecules with a d-electron center, by suitable external means. In this Letter, we demonstrate by first principles density functional calculations, as well as second order perturbation theory, that a strain induced change of the spin state, from S=1→S=2, takes place for an iron porphyrin (FeP) molecule deposited at a divacancy site in a graphene lattice. The process is reversible in the sense that the application of tensile or compressive strains in the graphene lattice can stabilize FeP in different spin states, each with a unique saturation moment and easy axis orientation. The effect is brought about by a change in Fe-N bond length in FeP, which influences the molecular level diagram as well as the interaction between the C atoms of the graphene layer and the molecular orbitals of FeP.

  5. Linear and nonlinear magnetic properties of ferrofluids

    NASA Astrophysics Data System (ADS)

    Szalai, I.; Nagy, S.; Dietrich, S.

    2015-10-01

    Within a high-magnetic-field approximation, employing Ruelle's algebraic perturbation theory, a field-dependent free-energy expression is proposed which allows one to determine the magnetic properties of ferrofluids modeled as dipolar hard-sphere systems. We compare the ensuing magnetization curves, following from this free energy, with those obtained by Ivanov and Kuznetsova [Phys. Rev. E 64, 041405 (2001), 10.1103/PhysRevE.64.041405] as well as with new corresponding Monte Carlo simulation data. Based on the power-series expansion of the magnetization, a closed expression for the magnetization is also proposed, which is a high-density extension of the corresponding equation of Ivanov and Kuznetsova. From both magnetization equations the zero-field susceptibility expression due to Tani et al. [Mol. Phys. 48, 863 (1983), 10.1080/00268978300100621] can be obtained, which is in good agreement with our MC simulation results. From the closed expression for the magnetization the second-order nonlinear magnetic susceptibility is also derived, which shows fair agreement with the corresponding MC simulation data.

  6. Magnetic properties and energy-mapping analysis.

    PubMed

    Xiang, Hongjun; Lee, Changhoon; Koo, Hyun-Joo; Gong, Xingao; Whangbo, Myung-Hwan

    2013-01-28

    The magnetic energy levels of a given magnetic solid are closely packed in energy because the interactions between magnetic ions are weak. Thus, in describing its magnetic properties, one needs to generate its magnetic energy spectrum by employing an appropriate spin Hamiltonian. In this review article we discuss how to determine and specify a necessary spin Hamiltonian in terms of first principles electronic structure calculations on the basis of energy-mapping analysis and briefly survey important concepts and phenomena that one encounters in reading the current literature on magnetic solids. Our discussion is given on a qualitative level from the perspective of magnetic energy levels and electronic structures. The spin Hamiltonian appropriate for a magnetic system should be based on its spin lattice, i.e., the repeat pattern of its strong magnetic bonds (strong spin exchange paths), which requires one to evaluate its Heisenberg spin exchanges on the basis of energy-mapping analysis. Other weaker energy terms such as Dzyaloshinskii-Moriya (DM) spin exchange and magnetocrystalline anisotropy energies, which a spin Hamiltonian must include in certain cases, can also be evaluated by performing energy-mapping analysis. We show that the spin orientation of a transition-metal magnetic ion can be easily explained by considering its split d-block levels as unperturbed states with the spin-orbit coupling (SOC) as perturbation, that the DM exchange between adjacent spin sites can become comparable in strength to the Heisenberg spin exchange when the two spin sites are not chemically equivalent, and that the DM interaction between rare-earth and transition-metal cations is governed largely by the magnetic orbitals of the rare-earth cation.

  7. The relationship between microstructure and magnetic properties in high-energy permanent magnets characterized by polytwinned structures

    NASA Astrophysics Data System (ADS)

    This report summarizes the results of a study of the relationship between microstructure and magnetic properties in a unique genre of ferromagnetic material characterized by a polysynthetically twinned structure which arises during solid state transformation. These results stem from the work over a period of approximately 27 months of a nominal 3 year grant period. The report also contains a proposal to extend the research project for an additional 3 years. The polytwinned structures produce an inhomogeneous magnetic medium in which the easy axis of magnetization varies quasi-periodically giving rise to special domain configurations which are expected to markedly influence the mechanism of magnetization reversal and hysteresis behavior of these materials in bulk or thin films. The extraordinary permanent magnet properties exhibited by the well-known Co-Pt alloys as well as the Fe-Pt and Fe-Pd systems near the equiatomic composition derive from the formation of a polytwinned microstructure.

  8. Reversals.

    ERIC Educational Resources Information Center

    National Center on Educational Media and Materials for the Handicapped, Columbus, OH.

    Selected from the National Instructional Materials Information System (NIMIS)--a computer based on-line interactive retrieval system on special education materials--the bibliography covers nine materials for remediating reversals in handicapped students at the early childhood and elementary levels. Entries are presented in order of NIMIS accession…

  9. Cryogenic properties of dispersion strengthened copper for high magnetic fields

    SciTech Connect

    Toplosky, V. J.; Han, K.; Walsh, R. P.; Swenson, C. A.

    2014-01-27

    Cold deformed copper matrix composite conductors, developed for use in the 100 tesla multi-shot pulsed magnet at the National High Magnetic Field Laboratory (NHMFL), have been characterized. The conductors are alumina strengthened copper which is fabricated by cold drawing that introduces high dislocation densities and high internal stresses. Both alumina particles and high density of dislocations provide us with high tensile strength and fatigue endurance. The conductors also have high electrical conductivities because alumina has limited solubility in Cu and dislocations have little scattering effect on conduction electrons. Such a combination of high strength and high conductivity makes it an excellent candidate over other resistive magnet materials. Thus, characterization is carried out by tensile testing and fully reversible fatigue testing. In tensile tests, the material exceeds the design criteria parameters. In the fatigue tests, both the load and displacement were measured and used to control the amplitude of the tests to simulate the various loading conditions in the pulsed magnet which is operated at 77 K in a non-destructive mode. In order to properly simulate the pulsed magnet operation, strain-controlled tests were more suitable than load controlled tests. For the dispersion strengthened coppers, the strengthening mechanism of the aluminum oxide provided better tensile and fatigue properties over convention copper.

  10. 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.

  11. Magnetic Properties of 3D Printed Toroids

    NASA Astrophysics Data System (ADS)

    Bollig, Lindsey; Otto, Austin; Hilpisch, Peter; Mowry, Greg; Nelson-Cheeseman, Brittany; Renewable Energy; Alternatives Lab (REAL) Team

    Transformers are ubiquitous in electronics today. Although toroidal geometries perform most efficiently, transformers are traditionally made with rectangular cross-sections due to the lower manufacturing costs. Additive manufacturing techniques (3D printing) can easily achieve toroidal geometries by building up a part through a series of 2D layers. To get strong magnetic properties in a 3D printed transformer, a composite filament is used containing Fe dispersed in a polymer matrix. How the resulting 3D printed toroid responds to a magnetic field depends on two structural factors of the printed 2D layers: fill factor (planar density) and fill pattern. In this work, we investigate how the fill factor and fill pattern affect the magnetic properties of 3D printed toroids. The magnetic properties of the printed toroids are measured by a custom circuit that produces a hysteresis loop for each toroid. Toroids with various fill factors and fill patterns are compared to determine how these two factors can affect the magnetic field the toroid can produce. These 3D printed toroids can be used for numerous applications in order to increase the efficiency of transformers by making it possible for manufacturers to make a toroidal geometry.

  12. On the Structural and Dynamical Properties of DOPC Reverse Micelles.

    PubMed

    Abel, Stéphane; Galamba, Nuno; Karakas, Esra; Marchi, Massimo; Thompson, Ward H; Laage, Damien

    2016-10-04

    The structure and dynamics of phospholipid reverse micelles are studied by molecular dynamics. We report all-atom unconstrained simulations of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC) reverse micelles in benzene of increasing sizes, with water-to-surfactant number ratios ranging from W0 = 1 to 16. The aggregation number, i.e., the number of DOPC molecules per reverse micelle, is determined to fit experimental light-scattering measurements of the reverse micelle diameter. The simulated reverse micelles are found to be approximately spherical. Larger reverse micelles (W0 > 4) exhibit a layered structure with a water core and the hydration structure of DOPC phosphate head groups is similar to that found in phospholipid membranes. In contrast, the structure of smaller reverse micelles (W0 ≤ 4) cannot be described as a series of concentric layers successively containing water, surfactant head groups, and surfactant tails, and the head groups are only partly hydrated and frequently present in the core. The dynamics of water molecules within the phospholipid reverse micelles slow down as the reverse micelle size decreases, in agreement with prior studies on AOT and Igepal reverse micelles. However, the average water reorientation dynamics in DOPC reverse micelles is found to be much slower than in AOT and Igepal reverse micelles with the same W0 ratio. This is explained by the smaller water pool and by the stronger interactions between water and the charged head groups, as confirmed by the red-shift of the computed infrared line shape with decreasing W0.

  13. Properties of magnetically attractive experimental resin composites.

    PubMed

    Hirano, S; Yasukawa, H; Nomoto, R; Moriyama, K; Hirasawa, T

    1996-12-01

    SUS444 stainless steel filled chemically cured resin composites that can attract magnet were fabricated. The filler was treated with various concentrations of silane. The experimental composite was easy to handle and showed a good shelf life. The maximal properties obtained are as follows; The attraction force to a magnetic attachment was 1/3-1/4 lower than the commercially available magnet-keeper system for dental magnetic attachment. Flexural strength and Knoop hardness of the composite were 76MPa (7.7 kgf/mm2) and 64 KHN. These values were lower than the commercially available chemically cured composite used as a reference. Eluted metal from the composite in 1% lactic acid solution for 7 days showed 0.7 mg/cm2, but in 0.9% NaCl solution for 7 days, it could not be detected.

  14. On Polar Magnetic Field Reversal and Surface Flux Transport During Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Hoeksema, J. Todd; Liu, Yang; Zhao, Junwei

    2015-01-01

    As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33-2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in 2013 October; the northern and southern polar fields (mean above 60° latitude) reversed in 2012 November and 2014 March, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR tilt, higher total AR flux, or slower mid-latitude near-surface meridional flow, while exceptions occur during low magnetic activity. In particular, the AR flux and the mid-latitude poleward flow speed exhibit a clear anti-correlation. We discuss how these features can be explained in a surface flux transport process that includes a field-dependent converging flow toward the ARs, a characteristic that may contribute to solar cycle variability.

  15. ON POLAR MAGNETIC FIELD REVERSAL AND SURFACE FLUX TRANSPORT DURING SOLAR CYCLE 24

    SciTech Connect

    Sun, Xudong; Todd Hoeksema, J.; Liu, Yang; Zhao, Junwei

    2015-01-10

    As each solar cycle progresses, remnant magnetic flux from active regions (ARs) migrates poleward to cancel the old-cycle polar field. We describe this polarity reversal process during Cycle 24 using four years (2010.33-2014.33) of line-of-sight magnetic field measurements from the Helioseismic and Magnetic Imager. The total flux associated with ARs reached maximum in the north in 2011, more than two years earlier than the south; the maximum is significantly weaker than Cycle 23. The process of polar field reversal is relatively slow, north-south asymmetric, and episodic. We estimate that the global axial dipole changed sign in 2013 October; the northern and southern polar fields (mean above 60° latitude) reversed in 2012 November and 2014 March, respectively, about 16 months apart. Notably, the poleward surges of flux in each hemisphere alternated in polarity, giving rise to multiple reversals in the north. We show that the surges of the trailing sunspot polarity tend to correspond to normal mean AR tilt, higher total AR flux, or slower mid-latitude near-surface meridional flow, while exceptions occur during low magnetic activity. In particular, the AR flux and the mid-latitude poleward flow speed exhibit a clear anti-correlation. We discuss how these features can be explained in a surface flux transport process that includes a field-dependent converging flow toward the ARs, a characteristic that may contribute to solar cycle variability.

  16. Magnetic dipole discharges. I. Basic properties

    SciTech Connect

    Stenzel, R. L.; Urrutia, J. M.; Teodorescu-Soare, C. T.; Ionita, C.; Schrittwieser, R.

    2013-08-15

    A simple discharge is described which uses a permanent magnet as a cold cathode and the metallic chamber wall as an anode. The magnet's equator is biased strongly negative, which produces secondary electrons due to the impact of energetic ions. The emitted electrons are highly confined by the strong dipolar magnetic field and the negative potential in the equatorial plane of the magnet. The emitted electrons ionize near the sheath and produce further electrons, which drift across field lines to the anode while the nearly unmagnetized ions are accelerated back to the magnet. A steady state discharge is maintained at neutral pressures above 10{sup −3} mbar. This is the principle of magnetron discharges, which commonly use cylindrical and planar cathodes rather than magnetic dipoles as cathodes. The discharge properties have been investigated in steady state and pulsed mode. Different magnets and geometries have been employed. The role of a background plasma has been investigated. Various types of instabilities have been observed such as sheath oscillations, current-driven turbulence, relaxation instabilities due to ionization, and high frequency oscillations created by sputtering impulses, which are described in more detail in companion papers. The discharge has also been operated in reactive gases and shown to be useful for sputtering applications.

  17. An Enhanced Nonlinear Critical Gradient for Electron Turbulent Transport due to Reversed Magnetic Shear

    SciTech Connect

    Peterson, J. L.; Hammet, G. W.; Mikkelsen, D. R.; Yuh, H. Y.; Candy, J.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B.

    2011-05-11

    The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.

  18. Numerical analysis of thermally assisted spin-transfer torque magnetization reversal in synthetic ferrimagnetic free layers

    SciTech Connect

    Shen, J.; Shi, M.; Tanaka, T. Matsuyama, K.

    2015-05-07

    The spin transfer torque magnetization reversal of synthetic ferrimagnetic free layers under pulsed temperature rise was numerically studied by solving the Landau–Lifshitz–Gilbert equation, taking into account the stochastic random fields, the temperature dependence of magnetic parameters, and the spin torque terms. The anti-parallel magnetization configuration was retained at the elevated temperature, due to interlayer dipole coupling. A significant thermal assistance effect, resulting in a 40% reduction in the switching current, was demonstrated during a nanosecond pulsed temperature rise up to 77% of the Curie temperature.

  19. A superconducting reversible rectifier that controls the motion of magnetic flux quanta.

    PubMed

    Villegas, J E; Savel'ev, Sergey; Nori, Franco; Gonzalez, E M; Anguita, J V; García, R; Vicent, J L

    2003-11-14

    We fabricated a device that controls the motion of flux quanta in a niobium superconducting film grown on an array of nanoscale triangular pinning potentials. The controllable rectification of the vortex motion is due to the asymmetry of the fabricated magnetic pinning centers. The reversal in the direction of the vortex flow is explained by the interaction between the vortices trapped on the magnetic nanostructures and the interstitial vortices. The applied magnetic field and input current strength can tune both the polarity and magnitude of the rectified vortex flow. Our ratchet system is explained and modeled theoretically, taking the interactions between particles into consideration.

  20. Ultra-fast magnetic vortex core reversal by a local field pulse

    SciTech Connect

    Rückriem, R.; Albrecht, M.; Schrefl, T.

    2014-02-03

    Magnetic vortex core reversal of a 20-nm-thick permalloy disk with a diameter of 100 nm was studied by micromagnetic simulations. By applying a global out-of-plane magnetic field pulse, it turned out that the final core polarity is very sensitive to pulse width and amplitude, which makes it hard to control. The reason for this phenomenon is the excitation of radial spin waves, which dominate the reversal process. The excitation of spin waves can be strongly suppressed by applying a local field pulse within a small area at the core center. With this approach, ultra-short reversal times of about 15 ps were achieved, which are ten times faster compared to a global pulse.

  1. Magnetic properties on the surface of FeAl stripes induced by nanosecond pulsed laser irradiation

    NASA Astrophysics Data System (ADS)

    Kaiju, H.; Yoshida, Y.; Watanabe, S.; Kondo, K.; Ishibashi, A.; Yoshimi, K.

    2014-05-01

    We demonstrate the formation of magnetic nanostripes on the surface of Fe52Al48 induced by nanosecond pulsed laser irradiation and investigate their magnetic properties. The magnetic stripe consists of a disordered A2 phase of Fe-Al alloys with Al-oxide along the [110] direction on the (111)-oriented plane. According to the focused magneto-optical Kerr effect measurement, the coercive force of the magnetic stripe obeys the 1/cos θ law, where θ is the field rotation angle estimated from the stripe direction. Also, the jump field can be observed in the magnetic hysteresis loop. These results indicate that the magnetization reversal in the magnetic stripe originates from the domain pinning, showing that the magnetization rotates incoherently.

  2. Magnetization reversal process at atomic scale in systems with itinerant electrons.

    PubMed

    Uzdin, V M; Vega, A

    2012-05-02

    The magnetic response of itinerant electrons systems to an external magnetic field is investigated on the basis of a microscopic Hamiltonian from which the spin-polarized electronic structure is determined. The magnetic moment and grand thermodynamic potential of the d-electronic subsystem on a particular atomic site in the presence of the external field are calculated as a function of the moment's orientation for fixed electron configuration of its local environment. Self-consistent magnetic solutions strongly depend on the d-electron number, determined by the position of the d level relative to the Fermi energy. For parameters corresponding to α-Fe, two branches of self-consistent solutions with high and low magnetic moments are found. For parameters corresponding to bulk Cr, a Fe impurity in the Cr matrix and a Cr impurity in the Fe matrix, there are only low-spin solutions. The theory is also applied for describing magnetization reversal processes in exchange spring magnets. A slab of Fe was considered as a soft magnetic layer. The influence of the hard magnet is modeled by the inclusion of an external magnetic field applied to the interface Fe layers. The dependence of the hysteresis loop on the thickness of the Fe slab and on the value of the interface field is investigated.

  3. Field-free magnetization reversal by spin-Hall effect and exchange bias.

    PubMed

    van den Brink, A; Vermijs, G; Solignac, A; Koo, J; Kohlhepp, J T; Swagten, H J M; Koopmans, B

    2016-03-04

    As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin-orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface.

  4. Field-free magnetization reversal by spin-Hall effect and exchange bias

    NASA Astrophysics Data System (ADS)

    van den Brink, A.; Vermijs, G.; Solignac, A.; Koo, J.; Kohlhepp, J. T.; Swagten, H. J. M.; Koopmans, B.

    2016-03-01

    As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin-orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface.

  5. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature.

    PubMed

    Gao, Ya; Hu, Jia-Mian; Nelson, C T; Yang, T N; Shen, Y; Chen, L Q; Ramesh, R; Nan, C W

    2016-03-31

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  6. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    NASA Astrophysics Data System (ADS)

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-03-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface.

  7. Dynamic in situ observation of voltage-driven repeatable magnetization reversal at room temperature

    PubMed Central

    Gao, Ya; Hu, Jia-Mian; Nelson, C. T.; Yang, T. N.; Shen, Y.; Chen, L. Q.; Ramesh, R.; Nan, C. W.

    2016-01-01

    Purely voltage-driven, repeatable magnetization reversal provides a tantalizing potential for the development of spintronic devices with a minimum amount of power consumption. Substantial progress has been made in this subject especially on magnetic/ferroelectric heterostructures. Here, we report the in situ observation of such phenomenon in a NiFe thin film grown directly on a rhombohedral Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PMN-PT) ferroelectric crystal. Under a cyclic voltage applied perpendicular to the PMN-PT without a magnetic field, the local magnetization of NiFe can be repetitively reversed through an out-of-plane excursion and then back into the plane. Using phase field simulations we interpret magnetization reversal as a synergistic effect of the metastable ferroelastic switching in the PMN-PT and an electrically rotatable local exchange bias field arising from the heterogeneously distributed NiO clusters at the interface. PMID:27029464

  8. Influence of shape, size and internal structure on magnetic properties of core-edge nanodots with perpendicular anisotropy

    SciTech Connect

    Milińska, E. Wawro, A.

    2014-11-21

    The properties of perpendicularly magnetized isolated nanodots different in shape, size, and internal structure are simulated by micromagnetic calculations. Investigated dots are magnetically uniform, or they are composed of a core and an edge characterized by different anisotropy—stronger or weaker than that of the core. Based on calculated hysteresis loops, we discuss in details the magnetization reversal processes, stability of magnetic structures, and spin configurations in the dots.

  9. Reversible Control of Interfacial Magnetism through Ionic-Liquid-Assisted Polarization Switching

    DOE PAGES

    Herklotz, Andreas; Guo, Er-Jia; Wong, Anthony T.; ...

    2017-02-06

    The ability to control magnetism of materials via electric field enables a myriad of technological innovations in information storage, sensing, and computing. In this paper, we use ionic-liquid-assisted ferroelectric switching to demonstrate reversible modulation of interfacial magnetism in a multiferroic heterostructure composed of ferromagnetic (FM) La0.8Sr0.2MnO3 and ferroelectric (FE) PbZr0.2Ti0.8O3. It is shown that ionic liquids can be used to persistently and reversibly switch a large area of a FE film. Finally, this is a prerequisite for polarized neutron reflectometry (PNR) studies that are conducted to directly probe magnetoelectric coupling of the FE polarization to the interfacial magnetization.

  10. Magnetization reversal of uncompensated Fe moments in exchangebiased Ni/FeF2 bilayers

    SciTech Connect

    Arenholz, Elke; Liu, Kai; Li, Zhipan; Schuller, Ivan K.

    2006-01-01

    The magnetization reversal of uncompensated Fe moments in exchange biased Ni/FeF{sub 2} bilayers was determined using soft x-ray magnetic circular and linear dichroism. The hysteresis loops resulting from the Fe moments are almost identical to those of the ferromagnetic Ni layer. However, a vertical loop shift indicates that some Fe moments are pinned in the antiferromagnetically ordered FeF{sub 2}. The pinned moments are oriented antiparallel to small cooling fields leading to negative exchange bias, but parallel to large cooling fields resulting in positive exchange bias. No indication for the formation of a parallel antiferromagnetic domain wall in the FeF{sub 2} layer upon magnetization reversal in the Ni layer was found.

  11. Reversible Control of Interfacial Magnetism through Ionic-Liquid-Assisted Polarization Switching.

    PubMed

    Herklotz, Andreas; Guo, Er-Jia; Wong, Anthony T; Meyer, Tricia L; Dai, Sheng; Ward, T Zac; Lee, Ho Nyung; Fitzsimmons, Michael R

    2017-03-08

    The ability to control magnetism of materials via electric field enables a myriad of technological innovations in information storage, sensing, and computing. We use ionic-liquid-assisted ferroelectric switching to demonstrate reversible modulation of interfacial magnetism in a multiferroic heterostructure composed of ferromagnetic (FM) La0.8Sr0.2MnO3 and ferroelectric (FE) PbZr0.2Ti0.8O3. It is shown that ionic liquids can be used to persistently and reversibly switch a large area of a FE film. This is a prerequisite for polarized neutron reflectometry (PNR) studies that are conducted to directly probe magnetoelectric coupling of the FE polarization to the interfacial magnetization.

  12. Magnetic properties of heterotrophic bacteria (abstract)

    NASA Astrophysics Data System (ADS)

    Verkhovceva, Nadezda V.; Glebova, Irina N.; Romanuk, Anatoly V.

    1994-05-01

    The magnetic properties (magnetic susceptibility and saturation magnetization) of six species of heterotrophic bacteria were studied: alcaligenes faecalis 81, arthrobacter globiformis BKM 685, bacillus cereus 8, leptothrix pseudo-ochracea D-405, proteus vulgaris 14, and seliberia stellata. It has been shown that the magnetic properties of bacteria depend on (1) the peculiarity of the micro-organism (species-specific and connected with cultivation conditions); (2) the source of the iron in the media. Most of the bacteria are diamagnetic in media with a minimum of iron (χ∞=-7.2-0.3×10-6 sm3/g). The spore forming species (bacillus cereus) has increased diamagnetism. Usually the bacteria are paramagnetic in iron-containing media because they concentrate into Fe compounds. The paramagnetism of the iron-concentrating species (anthrobacter globiformis -χpar=2.4×10-6, leptothrix pseudo-ochtracea χpar=11.0×10-6 and seliberia stellata χpar=3.2×10-6 sm3/g) depends, in general, on magnetically ordered compounds. Iron compounds not accumulated by proteus vulgaris and these species are always diamagnetic .

  13. Observations of improved confinement in field reversed configurations sustained by antisymmetric rotating magnetic fields

    SciTech Connect

    Guo, H.Y.; Hoffman, A.L.; Steinhauer, L.C.

    2005-06-15

    Rotating magnetic fields (RMF) have been employed to both form and sustain currents in field reversed configurations (FRC). A major concern about this method has been the fear of opening up magnetic field lines with even small ratios of vacuum RMF B{sub {omega}} to external confinement field B{sub e}. A recently proposed innovation was to use an antisymmetric arrangement of RMF, but vacuum calculations with full RMF penetration showed that very low values of B{sub {omega}}/B{sub e} would still be required to provide field-line closure. Recent comparisons of symmetric and antisymmetric RMF drive on the translation, confinement, and sustainment (TCS) facility [A. L. Hoffman, H. Y. Guo, J. T. Slough et al., Fusion Sci. Technol. 41, 92 (2002)] have shown strong improvements in the basic confinement properties of the FRCs when using antisymmetric drive, even with ratios of B{sub {omega}}/B{sub e} as high as 0.3. This is due to normal standard operation with only partial penetration of the RMF beyond the FRC separatrix. The uniform transverse RMF in vacuum is shielded by the conducting plasma, resulting in a mostly azimuthal field near the FRC separatrix with a very small radial component. Simple numerical calculations using analytical solutions for the partially penetrated antisymmetric RMF, superimposed on Grad-Shafranov solutions for the poloidal FRC fields, show good field-line closure for the TCS experimental conditions. The antisymmetric arrangement also leads to more efficient current drive and improved stabilization of rotational modes.

  14. Magnetic properties of maraging steel in relation to deformation and structural phase transformations

    SciTech Connect

    Ahmed, M.; Ali, A.; Hashmi, F.; Khan, A.Q. ); Hasnain, S.K. . Dept. of Physics)

    1994-03-01

    Magnetic properties in annealed and cold rolled conditions have been investigated for maraging steel grade 18%Ni-2,400. The austenite content, coercive field, saturation magnetization and remanence were determined after aging for 1 h in the temperature range from 400 to 800 C. The results show that the degree of deformation imparted to martensite influences both the amount of reverted austenite and the magnetic properties obtained following aging. Transmission electron microscopy was carried out in order to investigate the structural changes taking place during reversion of austenite.

  15. Magnetization reversal in a preferred oriented (111) L1(0) FePt grown on a soft magnetic metallic glass for tilted magnetic recording.

    PubMed

    Wang, Yaocen; Sharma, Parmanand; Makino, Akihiro

    2012-02-22

    L1(0) FePt is an important material for the fabrication of high density perpendicular recording media, but the ultrahigh coercivity of L1(0) FePt restricts its use. Tilting of the magnetic easy axis and the introduction of a soft magnetic underlayer can solve this problem. However, high temperature processing and the requirement of epitaxial growth conditions for obtaining an L1(0) FePt phase are the main hurdles to be overcome. Here, we introduce a bilayered magnetic structure ((111) L1(0) FePt/glassy Fe(71)Nb(4)Hf(3)Y(2)B(20)/SiO(2)/Si) in which the magnetic easy axis of L1(0) FePt is tilted by ~36° from the film plane and epitaxial growth conditions are not required. The soft magnetic underlayer not only promotes the growth of L1(0) FePt with the preferred orientation but also provides an easy cost-effective micro/nanopatterning of recording bits. A detailed magnetic characterization of the bilayered structure in which the thickness of (111) L1(0) FePt with the soft magnetic Fe(71)Nb(4)Hf(3)Y(2)B(20) glassy underlayer varied from 5 to 60 nm is carried out in an effort to understand the magnetization switching mechanism. The magnetization switching behavior is almost the same for bilayered structures in which FePt layer thickness is >10 nm (greater than the domain wall thickness of FePt). For FePt film ~10 nm thick, magnetization reversal takes place in a very narrow field range. Magnetization reversal first takes place in the soft magnetic underlayer. On further increase in the reverse magnetic field, the domain wall in the soft magnetic layer compresses at the interface of the hard and soft layers. Once the domain wall energy becomes sufficiently large to overcome the nucleation energy of the domain wall in L1(0) FePt, the magnetization of the whole bilayer is reversed. This process takes place quickly because the domain walls in the hard layer do not need to move, and the formation of a narrower domain wall may not be favorable energetically. Our results

  16. Magnetic properties of friction stir processed composite

    SciTech Connect

    Das, Shamiparna; Martinez, Nelson Y.; Das, Santanu; Mishra, Rajiv S.; Grant, Glenn J.; Jana, Saumyadeep; Polikarpov, Evgueni

    2016-03-29

    There are many existing inspection systems each with their own advantages and drawbacks. These usually comprise of semi-remote sensors which frequently causes difficulty in reaching complex areas of a component. This study proposes to overcome that difficulty by developing embedded functional composites. Through this route, embedding can be achieved in virtually any component part and can be periodically interrogated by a reading device. The “reinforcement rich” processed areas can then be utilized to record properties like strain, temperature, stress state etc. depending on the reinforcement material. In this work, friction stir processing (FSP) was utilized to fabricate a magnetostrictive composite by embedding galfenol particles into a nonmagnetic aluminum (Al) matrix. It targets to develop a composite that produces strain in a varying magnetic field. Reinforcements were observed to be distributed uniformly in the matrix. Magnetization curves were studied using a vibrating sample magnetometer (VSM). A simple and cheap setup was developed to measure the magnetostrictive strain of the composites. Important factors affecting the magnetic properties were identified and ways to improve the magnetic properties discussed.

  17. Statistical properties of reversals and chrons in numerical dynamos and implications for the geodynamo

    NASA Astrophysics Data System (ADS)

    Lhuillier, Florian; Hulot, Gauthier; Gallet, Yves

    2013-07-01

    We analyse a series of very long runs (equivalent to up to 50 Myr) produced by chemically-driven dynamos. All runs assume homogeneous boundary conditions, an electrically conducting inner-core (except for one run) and only differ by the choice of the Rayleigh number Ra★. Introducing dynamo-based definitions of reversals, chrons and related concepts, such as "failed reversals" and "segments" (bounded by reversals or failed reversals), we investigate the distributions of chron and segment lengths, those of reversal and failed reversal durations, the way dipole field behaves through reversals and failed reversals, and the possible links between the axial dipole intensity and chron or segment lengths. We show that chron and segment lengths are very well described in terms of a Poisson process (with no occurrence of superchrons), while distributions of reversal and failed reversal durations are better fitted by log-normal distributions. We found that reversal rates generally increase in proportion to Rm-Rmc,Rm being the magnetic Reynolds number and Rmc a critical value. In contrast, reversal and failed reversal durations appear to be mainly controlled by the core's magnetic diffusion timescale. More generally, we show that much of the reversing behaviour of these dynamos can be understood by examining their signature in a (g10,g11,h11) phase-space plot. This reveals that the run with an insulating inner-core is very different and has only two distinct modes of opposite polarity, which we argue is the reason it displays less reversals and failed reversals, and has a clear tendency to produce an intensity "overshoot" and some systematic pattern in the dipole pole behaviour through reversals and failed reversals. This contrasts with conducting inner-core runs, which display an additional central unstable mode, the importance of which increases with Rm, and which is responsible for the more complex reversing behaviour of these dynamos. Available paleomagnetic data suggest

  18. Magnetic properties of ZnO nanoparticles.

    PubMed

    Garcia, M A; Merino, J M; Fernández Pinel, E; Quesada, A; de la Venta, J; Ruíz González, M L; Castro, G R; Crespo, P; Llopis, J; González-Calbet, J M; Hernando, A

    2007-06-01

    We experimentally show that it is possible to induce room-temperature ferromagnetic-like behavior in ZnO nanoparticles without doping with magnetic impurities but simply inducing an alteration of their electronic configuration. Capping ZnO nanoparticles ( approximately 10 nm size) with different organic molecules produces an alteration of their electronic configuration that depends on the particular molecule, as evidenced by photoluminescence and X-ray absorption spectroscopies and altering their magnetic properties that varies from diamagnetic to ferromagnetic-like behavior.

  19. Structure and Magnetic Properties of Lanthanide Nanocrystals

    SciTech Connect

    Dickerson, James Henry

    2014-06-01

    We have had considerable success on this project, particularly in the understanding of the relationship between nanostructure and magnetic properties in lanthanide nanocrystals. We also have successfully facilitated the doctoral degrees of Dr. Suseela Somarajan, in the Department of Physics and Astronomy, and Dr. Melissa Harrison, in the Materials Science Program. The following passages summarize the various accomplishments that were featured in 9 publications that were generated based on support from this grant. We thank the Department of Energy for their generous support of our research efforts in this area of materials science, magnetism, and electron microscopy.

  20. Effect of the morphology on the mechanisms of the magnetization reversal of multilayered thin Co/Pd films

    NASA Astrophysics Data System (ADS)

    Kasiuk, J. V.; Maksimenko, A. A.; Fedotova, J. A.; Marszałek, M.; Lazaruk, S. K.; Kupreeva, O. V.

    2016-11-01

    A comparative study of the magnetization curves of continuous and porous multilayered Pd10 nm /[Co0.3 nm ]/Pd0.55 nm ]15/Pd2 nm films deposited on an anodized TiO2 template was performed by magnetometry. Based on the comparison of the dependences of coercive field H C on angle θ between the easy-magnetization axis and the direction of external magnetic field H with theoretical dependences HC(θ) for the magnetization reversal by domain walls motion (according to the Kondorski model) and the rotation of magnetic moments (by the Stoner-Wohlfarth model), the differences in the mechanisms of magnetization reversal for two mentioned types of the films were revealed. The correlation between the difference in the morphologies of the continuous and porous films and revealed change in the mechanisms of the magnetization reversal, as well as the changes in values of H C and calculated constants of the magnetic anisotropy, is discussed.

  1. Magnetic Properties of Some Gadolinium, Erbium, Dysprosium, Manganese Substituted Samarium-2 Cobalt-17 Intermetallic Compounds.

    DTIC Science & Technology

    1979-08-01

    that excellent temperature compensation could be achieved in these compounds in the teinper~ture (cont’d) ~‘ DD I ? ) 1Q3 L°’TI°M °’ INOV BI...following prop— erties: energy products in excess of 30 MGOe, low reversible tem- perature coefficients of magnetization , c~, and linear demagnetiza...Sm2(Co,Fe) i7 compounds significantly enhances their coercivities and energy products. Thus, we have been investigating the magnetic properties of these

  2. First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems

    NASA Astrophysics Data System (ADS)

    Ruta, Sergiu; Hovorka, Ondrej; Huang, Pin-Wei; Wang, Kangkang; Ju, Ganping; Chantrell, Roy

    2017-03-01

    The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach.

  3. First order reversal curves and intrinsic parameter determination for magnetic materials; limitations of hysteron-based approaches in correlated systems

    PubMed Central

    Ruta, Sergiu; Hovorka, Ondrej; Huang, Pin-Wei; Wang, Kangkang; Ju, Ganping; Chantrell, Roy

    2017-01-01

    The generic problem of extracting information on intrinsic particle properties from the whole class of interacting magnetic fine particle systems is a long standing and difficult inverse problem. As an example, the Switching Field Distribution (SFD) is an important quantity in the characterization of magnetic systems, and its determination in many technological applications, such as recording media, is especially challenging. Techniques such as the first order reversal curve (FORC) methods, were developed to extract the SFD from macroscopic measurements. However, all methods rely on separating the contributions to the measurements of the intrinsic SFD and the extrinsic effects of magnetostatic and exchange interactions. We investigate the underlying physics of the FORC method by applying it to the output predictions of a kinetic Monte-Carlo model with known input parameters. We show that the FORC method is valid only in cases of weak spatial correlation of the magnetisation and suggest a more general approach. PMID:28338056

  4. Magnetic and structural properties of ferrihydrite/hematite nanocomposites

    NASA Astrophysics Data System (ADS)

    Pariona, N.; Camacho-Aguilar, K. I.; Ramos-González, R.; Martinez, Arturo I.; Herrera-Trejo, M.; Baggio-Saitovitch, E.

    2016-05-01

    A rich variety of ferrihydrite/hematite nanocomposites (NCs) with specific size, composition and properties were obtained in transformation reactions of 2-line ferrihydrite. Transmission electron microscopy (TEM) observations showed that the NCs consist of clusters of strongly aggregated nanoparticles (NPs) similarly to a "plum pudding", where hematite NPs "raisins" are surrounded by ferrihydrite "pudding". Magnetic measurements of the NCs correlate very well with TEM results; i.e., higher coercive fields correspond to greater hematite crystallite size. First order reversal curve (FORC) measurements were used for the characterization of the magnetic components of the NCs. FORC diagrams revealed that the NCs prepared at short times are composed by single domains with low coercivity, and NCs prepared at times larger than 60 min exhibited elongated distribution along the Hc axis. It suggested that these samples consist of mixtures of different kinds of hematite particles, ones with low coercivity and others with coercivity greater than 600 Oe. For NCs prepared at times larger than 60 min, Mossbauer spectroscopy revealed the presence of two sextets, which one was assigned to fine hematite particles and other to hematite particles with hyperfine parameters near to bulk hematite. The correlation of the structural and magnetic properties of the ferrihydrite/hematite NCs revealed important characteristics of these materials which have not been reported elsewhere.

  5. Properties of Magnetic Reconnection as a function of magnetic shear

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Daughton, W. S.; Karimabadi, H.; Li, H.; Gary, S. P.; Guo, F.

    2013-12-01

    Observations of reconnection events at the Earth's magnetopause and in the solar wind show that reconnection occurs for a large range in magnetic shear angles extending to the very low shear limit 1. Here we report a fully kinetic study of the influence of the magnetic shear on details of reconnection such as its structure and rate. In previous work, we found that the electron diffusion region bifurcates into two or more distinct layers in regimes with weak magnetic shear2, a new feature that may be observable by NASA's up-coming Magnetospheric Multiscale mission. In this work, we have systematically extended the study to lower shear cases and found a new regime, where the reconnection electric field becomes much smaller and the properties of the reconnection changes significantly. We will discuss the role of various physics mechanisms in determining the observed scaling of the reconnection rate, including the dispersive properties of the waves in the system, the dissipation mechanisms and the tearing instability. 1 J. T. Goslings and T. D. Phan. APJL 763, L39, 2013 2 Yi-Hsin Liu et al. Phys. Rev. Lett. 110 , 265004, 2013

  6. Magnetic properties of artificially synthesized ferritins

    NASA Astrophysics Data System (ADS)

    Kim, B. J.; Lee, H. I.; Cho, S.-B.; Yoon, S.; Suh, B. J.; Jang, Z. H.; St. Pierre, T. G.; Kim, S.-W.; Kim, K.-S.

    2005-05-01

    Human ferritin homopolymers with H or L subunits (rHF and rLF) were genetically engineered in E coli. Apoferritins were then reconstituted with 2000 Fe atoms. A big difference was observed in the rates of iron uptake, whereas the mean core size was similar in rHF and rLF. Magnetization of the recombinant human ferritins were measured as functions of temperature and field. The blocking temperature TB(H) at low fields is considerably higher in rLF than in rHF. From the fit of M(H ) data to a modified Langevin function: M(H )=M0L(μpH/kBT)+χaH, the effective magnetic moment μp is found to be much larger in rLF than in rHF. Experimental data demonstrate that the magnetic properties, in particular, the uncompensated spins of ferritin core are related to the biomineralization process in ferritins.

  7. The effect of underlayers on the reversal of perpendicularly magnetized multilayer thin films for magnetic micro- and nanoparticles

    NASA Astrophysics Data System (ADS)

    Vemulkar, T.; Mansell, R.; Petit, D. C. M. C.; Cowburn, R. P.; Lesniak, M. S.

    2017-01-01

    Perpendicularly magnetized microparticles offer the ability to locally apply high torques on soft matter under an applied magnetic field. These particles are engineered to have a zero remanence magnetic configuration via synthetic antiferromagnetic coupling using a Ru coupling interlayer. The flexibility offered by the top down thin film fabrication process in a CoFeB/Pt perpendicular thin film is demonstrated by using the Pt interlayer thicknesses in a Pt/Ru/Pt antiferromagnetic coupling multilayer to tune the applied magnetic field value of the easy axis spin-flip transition to saturation and hence the field value at which the magnetic particles are magnetically activated via a distinct transition to saturation. The importance of a Ta buffer layer on the magnetic behavior of the stack is shown. While Au capping layers are desirable for biotechnology applications, we demonstrate that they can drastically change the nucleation and propagation of domains in the film, thereby altering the reversal behavior of the thin film. The effect of Au underlayers on a multilayer thin film composed of repeated motifs of a synthetic antiferromagnetic building block is also investigated.

  8. Magnetic properties and microstructure of bulk Nd-Fe-B magnets solidified in magnetic field

    NASA Astrophysics Data System (ADS)

    Wang, C.; Lai, Y. S.; Hsieh, C. C.; Chang, W. C.; Chang, H. W.; Sun, A. C.

    2011-04-01

    The Nd-Fe-B bulk magnets with a slab shape of 0.9 × 4 × 15 mm3 were prepared by injection casting into a copper mold. The effects of applying a magnetic field during the casting process on the magnetic properties and microstructure of Nd9.5Fe71.5Ti2.5Zr0.5Cr1B14.5C0.5 alloy have been studied. The results show that the sample cast with magnetic field has a stronger (00L) texture of Nd2Fe14B phase with the c-axis perpendicular to the slab plane than the sample cast without magnetic field. The intensity of the texture weakens from surface to inner region of the bulk magnets. Applying a magnetic field during the casting process is helpful to refine the grain size effectively. As a result, the magnetic properties are improved from Br = 5.8 kG, iHc = 6.5 kOe, and (BH)max = 5.9 MGOe for thesample cast without magnetic field to Br = 6.1 kG, iHc = 10.3 kOe, and (BH)max = 7.3 MGOe for the sample cast with a 3.7 kOe magnetic field.

  9. Magnetic properties and coercivity mechanism of isotropic HDDR NdFeB bonded magnets with Co and Dy addition

    NASA Astrophysics Data System (ADS)

    Chen, W.; Gao, R. W.; Zhu, M. G.; Pan, W.; Li, W.; Li, X. M.; Han, G. B.; Feng, W. C.; Wang, B.

    2003-04-01

    Isotropic NdDyFeCoB bonded magnets with high coercivity of 1.59 MA/m and low temperature coefficient of remanence of -0.056%/ K (in the temperature range 298-428 K) were prepared successfully by controlling the HDDR process and adjusting the compositions. The influence of Co and Dy additions on the magnetic properties and the magnetization reversal process in magnet was investigated. The high coercivity in (Nd 0.8Dy 0.2) 13(Fe 0.875Co 0.125) 81B 6 HDDR magnet can be attributed to its unique microstructure and the enhancement of anisotropy field of 2:14:1 phase by substitution of Nd by Dy.

  10. Magnetic and dielectric properties of lunar samples

    NASA Technical Reports Server (NTRS)

    Strangway, D. W.; Pearce, G. W.; Olhoeft, G. R.

    1977-01-01

    Dielectric properties of lunar soil and rock samples showed a systematic character when careful precautions were taken to ensure there was no moisture present during measurement. The dielectric constant (K) above 100,000 Hz was directly dependent on density according to the formula K = (1.93 + or - 0.17) to the rho power where rho is the density in g/cc. The dielectric loss tangent was only slightly dependent on density and had values less than 0.005 for typical soils and 0.005 to 0.03 for typical rocks. The loss tangent appeared to be directly related to the metallic ilmenite content. It was shown that magnetic properties of lunar samples can be used to study the distribution of metallic and ferrous iron which shows systematic variations from soil type to soil type. Other magnetic characteristics can be used to determine the distribution of grain sizes.

  11. Magnetic properties and large magnetocaloric effect in Laves phase metallic compound

    NASA Astrophysics Data System (ADS)

    Gao, Tian; Qi, Ningning; Zhang, Yufeng; Zhou, Tao

    2014-12-01

    We investigated the magnetic properties and magnetocaloric effect of C15 Laves phase TbMn1.6Fe0.4 by magnetization and heat capacity measurements. A sharp second-order magnetic Tb-Tb ordering transition at Curie temperature TC ~ 120 K and a short-range Fe-Fe ordering transition at ~230 K are observed. Around TC, the compound shows a large magnetocaloric effect with no obvious thermal and magnetic hysteresis loss. The maximum value of magnetic entropy change reaches 8.72 J kg-1 K-1 for a magnetic field change ΔH = 7 T over a wide temperature range. The obtained relative cooling power reaches 184, 560, and 803 J kg-1 for ΔH = 2, 5 and 7 T, respectively. Large reversible magnetocaloric effect and the wide operating temperature range indicate that TbMn1.6Fe0.4 could be a promising candidate for magnetic refrigeration.

  12. Swingback in magnetization reversal in MnAs-GaAs coaxial nanowire heterostructures.

    PubMed

    Takagaki, Y; Herfort, J; Hilse, M; Geelhaar, L; Riechert, H

    2011-03-30

    The reversal processes of magnetization in epitaxial MnAs nanotubes prepared by an overgrowth on the sidewall of GaAs nanowires having a diameter of 26 nm are investigated. While the magnetic hard axis is aligned in the direction of the nanowire axis, we apply an external magnetic field perpendicular to the axis to examine the flipping characteristics of magnetic moments. We determine the contributions from the substrate by a direct measurement in order to extract the magnetization of the core-shell heterostructures. The abrupt change in the thus-obtained magnetization due to a flip when the field is varied exhibits an overshoot at about 0.4 kOe for samples with a thickness of the ferromagnetic shell (40-50 nm) larger than the diameter of the core. Moreover, the peak value exceeds the value when the field is swept in the opposite direction. The magnetic hysteresis loop consequently involves line crossings. We speculate that the spin textures of domain walls in such thick hollow cylinders and their movement at the magnetization flip are affected by the geometry and magnetostatic interactions of various origins, giving rise to the anomalous behaviour.

  13. Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Gopman, D. B.; Dennis, C. L.; Chen, P. J.; Iunin, Y. L.; Finkel, P.; Staruch, M.; Shull, R. D.

    2016-06-01

    Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices.

  14. Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy

    PubMed Central

    Gopman, D. B.; Dennis, C. L.; Chen, P. J.; Iunin, Y. L.; Finkel, P.; Staruch, M.; Shull, R. D.

    2016-01-01

    Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices. PMID:27297638

  15. Strain-assisted magnetization reversal in Co/Ni multilayers with perpendicular magnetic anisotropy.

    PubMed

    Gopman, D B; Dennis, C L; Chen, P J; Iunin, Y L; Finkel, P; Staruch, M; Shull, R D

    2016-06-14

    Multifunctional materials composed of ultrathin magnetic films with perpendicular magnetic anisotropy combined with ferroelectric substrates represent a new approach toward low power, fast, high density spintronics. Here we demonstrate Co/Ni multilayered films with tunable saturation magnetization and perpendicular anisotropy grown directly on ferroelectric PZT [Pb(Zr0.52Ti0.48)O3] substrate plates. Electric fields up to ±2 MV/m expand the PZT by 0.1% and generate at least 0.02% in-plane compression in the Co/Ni multilayered film. Modifying the strain with a voltage can reduce the coercive field by over 30%. We also demonstrate that alternating in-plane tensile and compressive strains (less than 0.01%) can be used to propagate magnetic domain walls. This ability to manipulate high anisotropy magnetic thin films could prove useful for lowering the switching energy for magnetic elements in future voltage-controlled spintronic devices.

  16. Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers

    NASA Astrophysics Data System (ADS)

    Sbiaa, R.; Ranjbar, M.; Åkerman, J.

    2015-05-01

    Domain structures and magnetization reversal of (Co/Pd) and (CoFeB/Pd) multilayers with 7 and 14 repeats were investigated. The Co-based multilayers show much larger coercivities, a better squareness, and a sharper magnetization switching than CoFeB-based multilayers. From magnetic force microscopy observations, both structures show strong reduction in domains size as the number of repeats increases but the magnetic domains for Co-based multilayers are more than one order of magnitude larger than for CoFeB-based multilayers. By imaging domains at different times, breaks in the (CoFeB/Pd) multilayer stripes were observed within only few hours, while no change could be seen for (Co/Pd) multilayers. Although CoFeB single layers are suitable for magnetoresistive devices due to their large spin polarization and low damping constants, their lamination with Pd suffers mainly from thermal instability.

  17. Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers

    SciTech Connect

    Sbiaa, R.; Ranjbar, M.; Åkerman, J.

    2015-05-07

    Domain structures and magnetization reversal of (Co/Pd) and (CoFeB/Pd) multilayers with 7 and 14 repeats were investigated. The Co-based multilayers show much larger coercivities, a better squareness, and a sharper magnetization switching than CoFeB-based multilayers. From magnetic force microscopy observations, both structures show strong reduction in domains size as the number of repeats increases but the magnetic domains for Co-based multilayers are more than one order of magnitude larger than for CoFeB-based multilayers. By imaging domains at different times, breaks in the (CoFeB/Pd) multilayer stripes were observed within only few hours, while no change could be seen for (Co/Pd) multilayers. Although CoFeB single layers are suitable for magnetoresistive devices due to their large spin polarization and low damping constants, their lamination with Pd suffers mainly from thermal instability.

  18. Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma

    DOEpatents

    Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang

    2007-02-20

    A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

  19. Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma

    DOEpatents

    Rostoker, Norman; Binderbauer, Michl; Qerushi, Artan; Tahsiri, Hooshang

    2006-02-07

    A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

  20. Formation of a field reversed configuration for magnetic and electrostatic confinement of plasma

    DOEpatents

    Rostoker, Norman; Binderbauer, Michl

    2003-12-16

    A system and method for containing plasma and forming a Field Reversed Configuration (FRC) magnetic topology are described in which plasma ions are contained magnetically in stable, non-adiabatic orbits in the FRC. Further, the electrons are contained electrostatically in a deep energy well, created by tuning an externally applied magnetic field. The simultaneous electrostatic confinement of electrons and magnetic confinement of ions avoids anomalous transport and facilitates classical containment of both electrons and ions. In this configuration, ions and electrons may have adequate density and temperature so that upon collisions they are fused together by nuclear force, thus releasing fusion energy. Moreover, the fusion fuel plasmas that can be used with the present confinement system and method are not limited to neutronic fuels only, but also advantageously include advanced fuels.

  1. Magnetohydrodynamic Effects in Propagating Relativistic Ejecta: Reverse Shock and Magnetic Acceleration

    NASA Technical Reports Server (NTRS)

    Mizuno, Y.; Nishikawa, K.I.; Zhang, B.; Giacomazzo, B.; Hardee, P.E.; Nagataki, S.; Hartmann, D.H.

    2008-01-01

    We solve the Riemann problem for the deceleration of arbitrarily magnetized relativistic ejecta injected into a static unmagnetized medium. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization s (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when s exceeds a critical value, sc, defined by the balance between the magnetic pressure in the ejecta and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value. This acceleration mechanism is due to the strong magnetic pressure in the ejecta.

  2. Calculations of alpha particle loss for reversed magnetic shear in the Tokamak Fusion Test Reactor

    SciTech Connect

    Redi, M.H.; White, R.B.; Batha, S.H.; Levinton, F.M.; McCune, D.C.

    1997-03-01

    Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma predict both total alpha losses and ripple diffusion losses to be greater than those from a comparable non-reversed magnetic shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. A simple ripple loss model, benchmarked against the guiding center code, is found to work satisfactorily in transport analysis modelling of reversed and monotonic shear scenarios. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. The 40% alpha particle loss predictions for TFTR suggest that reduction of toroidal field ripple will be a critical issue in the design of a reversed shear fusion reactor.

  3. Spin-polarized transport and magnetization reversal behavior of transition metal and half-metallic chromium dioxide thin films and multilayers

    NASA Astrophysics Data System (ADS)

    Anguelouch, Alexandre

    In recent years the interest in the properties of sub-micron ferromagnetic systems has been growing due to both their fundamental significance and practical applications in the fields of magnetic random access memory and magnetic sensing. In the thesis we have studied the magnetization reversal and spin-dependent transport behavior in transition-metal ferromagnets and half-metallic chromium dioxide films and heterostructures. In the case of transition-metal ferromagnets we have investigated the contribution that thermal fluctuations make toward the reversal process of sub-micron patterned elements. We establish that the fluctuations are significant and as a result, that the switching is a stochastic process. Our conclusion is that the Neel-Arrhenius theory of thermally activated magnetic transitions adequately describes the observed behavior. Further, we have demonstrated that domain structure can have a drastic effect on critical "astroid" curves of transition metal micron- and sub-micron-size ferromagnetic films. For these studies, we used magnetic tunnel junctions (MTJs) as a tool for characterization, and we believe that this technique provides a useful method for investigation of the magnetic properties of patterned media. Half-metals are a class of ferromagnets with 100% spin polarization. These materials show great promise for use in magnetoelectronic applications, such as MTJ-based memory and as magnetic sensors. We have perfected a fabrication technique for obtaining single-crystal epitaxial CrO2 films with nearly complete spin polarization. We have analyzed the thickness dependence of electron transport and magnetic properties of CrO2, and have established that the magnetic, transport and structural properties in these films are closely interrelated. We also report the results of our attempts to fabricate CrO2-based MTJs.

  4. Bistability properties of magnetic micro-nanowires

    NASA Astrophysics Data System (ADS)

    Baranov, S. A.; Yaltychenko, O. V.; Kanarovskii, E. Yu.

    2016-12-01

    A mathematical model that describes the process of the reversal magnetization of an amorphous microwire with the help of a large Barkhausen jump is proposed. The model has been estimated with regard to the optimization of the signal-tonoise ratio. Using nonlinear model, we studied the physical factors that cause the fluctuations of the start field. Based on the results of numerical experiments, the new data on the behavior of the start field under different conditions of a switching in a bistable ferromagnetic, including the conditions of high-frequency swapping, have been obtained and compared to the existing data. The results obtained do not contradict the existing physical concepts concerning a domain wall motion and are more general and realistic in a comparison with the previous model.

  5. Magnetic vortex core reversal by excitation with short bursts of an alternating field.

    PubMed

    Van Waeyenberge, B; Puzic, A; Stoll, H; Chou, K W; Tyliszczak, T; Hertel, R; Fähnle, M; Brückl, H; Rott, K; Reiss, G; Neudecker, I; Weiss, D; Back, C H; Schütz, G

    2006-11-23

    The vortex state, characterized by a curling magnetization, is one of the equilibrium configurations of soft magnetic materials and occurs in thin ferromagnetic square and disk-shaped elements of micrometre size and below. The interplay between the magnetostatic and the exchange energy favours an in-plane, closed flux domain structure. This curling magnetization turns out of the plane at the centre of the vortex structure, in an area with a radius of about 10 nanometres--the vortex core. The vortex state has a specific excitation mode: the in-plane gyration of the vortex structure about its equilibrium position. The sense of gyration is determined by the vortex core polarization. Here we report on the controlled manipulation of the vortex core polarization by excitation with small bursts of an alternating magnetic field. The vortex motion was imaged by time-resolved scanning transmission X-ray microscopy. We demonstrate that the sense of gyration of the vortex structure can be reversed by applying short bursts of the sinusoidal excitation field with amplitude of about 1.5 mT. This reversal unambiguously indicates a switching of the out-of-plane core polarization. The observed switching mechanism, which can be understood in the framework of micromagnetic theory, gives insights into basic magnetization dynamics and their possible application in data storage.

  6. Scaling of magnetic reversal avalanches in connected structures of artificial kagome ice

    NASA Astrophysics Data System (ADS)

    Cumings, John; Daunheimer, Stephen; Drisko, Jasper; Chern, Gia-Wei; Moessner, Roderich; Tchernyshyov, Oleg

    2015-03-01

    We will present results on magnetic avalanches observed by Lorentz-force transmission electron microscopy during the magnetic reversal of magnetic lattices. The lattices are fabricated from permalloy (Ni80Fe20) in the geometry known as artificial kagome ice. The avalanches show power law behavior in the probability of reaching a given size scale, with the power law persisting right up to a cutoff for the size of the sample. Such behavior occurs in the vicinity of critical transitions, and we will present an analysis of the evidence for such critical behavior in our system. We will make connections with the model of directed percolation, where the magnetic reversal may be considered as an infiltration of magnetic charges of opposites signs from the two opposite ends of the lattice. The possible realization of a system of directed percolation in two dimensions (one spatial, plus one field-directed time dimension), could open up new avenues for research with artificial spin ices. Supported by NSF CAREER Award DMR-1056974.

  7. Reversal of lattice, electronic structure, and magnetism in epitaxial SrCoOx thin films

    NASA Astrophysics Data System (ADS)

    Jeen, H.; Choi, W. S.; Lee, J. H.; Cooper, V. R.; Lee, H. N.; Seo, S. S. A.; Rabe, K. M.

    2014-03-01

    SrCoOx (x = 2.5 - 3.0, SCO) is an ideal material to study the role of oxygen content for electronic structure and magnetism, since SCO has two distinct topotactic phases: the antiferromagnetic insulating brownmillerite SrCoO2.5 and the ferromagnetic metallic perovskite SrCoO3. In this presentation, we report direct observation of a reversible lattice and electronic structure evolution in SrCoOx epitaxial thin films as well as different magnetic and electronic ground states between the topotactic phases.[2] By magnetization measurements, optical absorption, and transport measurements drastically different electronic and magnetic ground states are found in the epitaxially grown SrCoO2.5 and SrCoO3 thin films by pulsed laser epitaxy. First-principles calculations confirm substantial, which originate from the modification in the Co valence states and crystallographic structures. By real-time spectroscopic ellipsometry, the two electronically and magnetically different phases can be reversibly changed by changing the ambient pressure at greatly reduced temperatures. Our finding provides an important pathway to understanding the novel oxygen-content-dependent phase transition uniquely found in multivalent transition metal oxides. The work was supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division.

  8. Ultralow field magnetization reversal of two-body Stoner particles system

    NASA Astrophysics Data System (ADS)

    Li, Fei; Lu, Xiaofeng; Tang, Rujun; Sun, Z. Z.

    Magnetic mechanism of nanoparticles has attracted explosive attention in the development of modern information industry. On the base of Landau-Lifshitz-Gilbert equation, we studied the magnetization reversal in a system of two Stoner particles with uniaxial anisotropies and static magnetic interaction. Using micromagnetic simulation, two typical geometrical configurations of perpendicular(PERP) and parallel(PARA) configuration where the diameter of each particle is 20nm are considered. We found that when the separation between two particles has 23nm in PERP configuration ultralow switching field strength, 17mT can be realized, which satisfies the zero-field condition in our previous works[J. Appl. Phys. 109, 104303(2011)] according to the chosen parameters of cobalt material. For other separation values the switching field are multiple of lowest field. However, in PARA configuration the switching field changes with the separation faintly. This two-body system considered in our work might be implement as a composite information bit and our results offer further possibilities for its applications in information storage and/or fast magnetic response. Ultralow field magnetization reversal of two-body Stoner particles system.

  9. The effects of thermally reversible agents on PVC stability properties

    NASA Astrophysics Data System (ADS)

    Wang, J.; Yao, J.; Xiong, X. H.; Jia, C. X.; Ren, R.; Chen, P.; Liu, X. M.

    2016-07-01

    One kind of thermally reversible cross-linking agents for improving PVC thermally stability was synthesized. The chemical structure and thermally reversible characteristics of cross-linking agents were investigated by FTIR and DSC analysis, respectively. FTIR results confirmed that the cyclopentadienyl barium mercaptides ((CPD-C2H4S)2Ba) were successfully synthesized. DSC results showed it has thermally reversible characteristics and the depolymerization temperature was between 170 °C and 205 °C. The effects of cross-linking reaction time on gel content of Poly(vinyl chloride) compounds was evaluated. The gel content value arrived at 42% after being cross-linked for 25 min at 180 C. The static thermally stability measurement proved that the thermally stability of PVC compounds was improved.

  10. Tracking a large pseudostreamer to pinpoint the southern polar magnetic field reversal

    NASA Astrophysics Data System (ADS)

    Rachmeler, Laurel; Guennou, Chloé; Seaton, Daniel B.; Gibson, Sarah; Auchère, Frédéric

    2016-05-01

    The reversal of the solar polar magnetic field is notoriously hard to pin down due to the extreme viewing angle of the pole. In Cycle 24, the southern polar field reversal can be pinpointed with high accuracy due to a large-scale pseudostreamer that formed over the pole and persisted for approximately a year. We tracked the size and shape of this structure with multiple observations and analysis techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP data, and 3D tomographic reconstructions. We find that the heliospheric field reversed polarity in February 2014, whereas in the photosphere the last vestiges of the previous polar field polarity remained until March 2015.

  11. Physical and magnetic properties of magnetic nanoparticle arrays

    NASA Astrophysics Data System (ADS)

    Mohtasebzadeh, Abdul Rahman

    Using Scanning Electron Microscope (SEM) , Atomic Force Microscope (AFM) and Vibrating Sample Magnetometer (VSM) I studied magnetic-field directed selfassembly of magnetic nanoparticles into patterned arrays on the surface of perpendicular magnetic recording media. A controllable machine was used to coat super paramagnetic nano particles onto the surface of perpendicular recording media for different time intervals. Self assembled nano particles on the surface of the media, were transferred to a polymer layer to observe physical properties. Results from imaging shows that the average width and height of arrays is increasing as a function of time. Width of arrays with assembly time varies from 100nm at 5 minutes to 500nm at 120 minutes. Similarly, height changes from 13nm at 5 minutes to 37nm at 120 minutes. Therefore the pattern aspect ratio changes from 8:1 at 5 minutes to 14:1 at 120 minutes. For large widths compared with pattern spacing, array interaction appears as a slope change in VSM hysteresis loops. The hypothesis is that the difference in slope as a function of time for two cases; patterns oriented parallel and perpendicular to the external field is caused by array interaction; in other words wider patterns interact with each other more than narrower patterns.

  12. Dual origin of defect magnetism in graphene and its reversible switching by molecular doping.

    PubMed

    Nair, R R; Tsai, I-L; Sepioni, M; Lehtinen, O; Keinonen, J; Krasheninnikov, A V; Castro Neto, A H; Katsnelson, M I; Geim, A K; Grigorieva, I V

    2013-01-01

    Control of magnetism by applied voltage is desirable for spintronics applications. Finding a suitable material remains an elusive goal, with only a few candidates found so far. Graphene is one of them and attracts interest because of its weak spin-orbit interaction, the ability to control electronic properties by the electric field effect and the possibility to introduce paramagnetic centres such as vacancies and adatoms. Here we show that the magnetism of adatoms in graphene is itinerant and can be controlled by doping, so that magnetic moments are switched on and off. The much-discussed vacancy magnetism is found to have a dual origin, with two approximately equal contributions; one from itinerant magnetism and the other from dangling bonds. Our work suggests that graphene's spin transport can be controlled by the field effect, similar to its electronic and optical properties, and that spin diffusion can be significantly enhanced above a certain carrier density.

  13. Magnetization Reversal in an Fe Film with an Array of Elliptical Holes on a Square Lattice

    DTIC Science & Technology

    2006-01-01

    UNCLASSIFIED NSN 7540-01-280-5500 I. Guedes , M. Grimsditch, V. Metlushko, R. Camley, B. Ilic, P. Neuzil, R. Kumar University of Colorado - Colorado...description of the phenomenon. Magnetization reversal in an Fe film with an array of elliptical holes on a square lattice I. Guedes * and M. Grimsditch...applied field is along the long and short axes of the ellipses. I. GUEDES et al. PHYSICAL REVIEW B 67, 024428 ~2003! 024428-2 have quite different

  14. Micromagnetic study of exchange interaction effect on magnetization reversal mode of CoFeAl

    NASA Astrophysics Data System (ADS)

    Azizah, Umi Muflihatun Nurul; Trihandaru, Suryasatriya; Wibowo, Nur Aji

    2016-02-01

    A magnetization switching dynamics of perpendicular magnetic anisotropy material CoFeAl has been simulated. This simulation was conducted using Landau-Lifshift Gilbert equation. The used magnetic parameters are magnetic anisotropy 2.3 × 106 erg/cm3, magnetic saturation 10 kG, medium Gilbert damping 0.3 and various exchange constants in a range of (1.5 - 4.0) × 10-7 erg/cm. CoFeAl is modeled as a parallel-pipe with the dimension is 50 × 50 × 20 nm3. As a result, this simulation predicts that the chosen materials exhibit good thermal stability which is greatly affected by exchange energy. Magnetization reversal mechanism is dominated by domain wall propagation process. Moreover, the simultaneous distribution of thermal with external magnetic field on the materials reduces the writing field which reaches the minimum value when exchange constant is 3.5 × 10-7 erg/cm.

  15. Direct imaging of the magnetization reversal in microwires using all-MOKE microscopy

    NASA Astrophysics Data System (ADS)

    Stupakiewicz, A.; Chizhik, A.; Tekielak, M.; Zhukov, A.; Gonzalez, J.; Maziewski, A.

    2014-10-01

    We report a method of imaging of the magnetization reversal process using analysis of real-time images of magnetic domain structures in cylindrically shaped microwires. This method uses wide-field polarizing optical microscopy and is based on the magneto-optical Kerr effect (MOKE). The aperture diaphragm in MOKE microscope was used to control the incident angles of the light rays that reached the non-planar surface of the microwire and also determined the MOKE geometries. The movement of the non-central position of the hole in this diaphragm leads to a change in the orientation of the plane of incidence of the light along the perpendicular or the parallel direction to the axial direction of the wire. The visualization of the surface magnetic domain structures is obtained using polar and longitudinal MOKE geometries. The hysteresis loops were obtained by plotting the averaged image contrast as a function of the external magnetic field. The separation of the all-magnetization components is performed using different MOKE geometries in a microscope. We demonstrate the use of vector magnetometry to analyze the orientation of the magnetization in a cylindrically shaped microwire under the influence of an external magnetic field.

  16. Formation of field-reversed ion rings in a magnetized background plasma

    SciTech Connect

    Omelchenko, Y.A.; Sudan, R.N.

    1995-07-01

    In typical field-reversed ion ring experiments, an intense annular ion beam is injected across a magnetic cusp into neutral gas immersed in a solenoidal magnetic field. In anticipation of a new experimental thrust to create strong field-reversed ion rings the beam evolution is investigated in a preformed background plasma on a time scale greater than an ion cyclotron period, using a new two and a half-dimensional (21/2-D) hybrid, particle-in-cell (PIC) code FIRE, in which the beam and background ions are treated as macro-particles and the electrons as a massless fluid. It is shown that under appropriate conditions axial beam bunching occurs in the downstream applied field and a compact field-reversed ring is formed. It is observed that the ring is reflected in a ramped magnetic field. Upon reflection its axial velocity is very much less than that expected from a single particle model due to the transfer of the mean axial momentum to the background ions. This increases the time available to apply a pulsed mirror for trapping the ring experimentally. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  17. Grain Texture, Nd Content and Processing Condition Effects on Magnetic Properties of NdFeB Composite Magnets

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoya; Hu, Lianxi; Li, Yuping; Deng, Taiqing

    2013-07-01

    The effects of grain texture, Nd content, processing conditions on magnetic properties and behavior of NdFeB nanocomposite magnet were investigated. The results demonstrate that mechanically activated disproportionation and desorption-recombination combined with plastic deformation process (M-HDDR & D) is an effective way to produce anisotropic NdFeB-type magnet. Magnetic anisotropy significantly enhances the magnetic properties of Nd16Fe76B8 nanocomposite magnet, with the intrinsic coercivity (Hci), magnetic induction (Br), and the energy product (BH)max achieving 0.88 T, 676.8 kA/m, and 135.2 kJ/m3, respectively. Decrease in Nd content improves the remanence but deteriorates the coercivity of NdFeB ternary composites. A low annealing temperature or short annealing time leads to an incomplete recombination, while a high temperature or long annealing time may result in grain overgrowth, and the optimum processing condition is found to be 780°C × 30 min. Pinning mechanism dominates in the magnetic hardening mechanism of Nd16Fe76B8 composites prepared by both complete and incomplete recombination process, and particularly reversal nucleation process is also responsible for the latter case.

  18. Integral physicochemical properties of reverse micelles of sodium bis(2-ethylhexyl) sulfosuccinate (AOT)

    NASA Astrophysics Data System (ADS)

    Fedyaeva, O. A.; Shubenkova, E. G.; Poshelyuzhnaya, E. G.; Lutaeva, I. A.

    2016-08-01

    The effect the degree of hydration has on optical and electrophysical properties of water/AOT/ n-hexane system is studied. It is found that AOT reverse micelles form aggregates whose dimensions grow along with the degree of hydration and temperature. Aggregation enhances their electrical conductivity and shifts the UV spectrum of AOT reverse emulsions to the red region. Four states of water are found in the structure of AOT reverse micelles.

  19. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmasa)

    NASA Astrophysics Data System (ADS)

    Lu, Z. X.; Wang, W. X.; Diamond, P. H.; Tynan, G.; Ethier, S.; Gao, C.; Rice, J.

    2015-05-01

    Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear ( s ̂ ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s ̂ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s ̂ discharges and that the value of s ̂ c r i t is consistent with the experimental results ŝ c r i t e x p ≈ 0.2 ˜ 0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s ̂ and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s ̂ .

  20. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

    SciTech Connect

    Lu, Z. X.; Tynan, G.; Wang, W. X.; Ethier, S.; Diamond, P. H.; Gao, C.; Rice, J.

    2015-05-15

    Intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. This work focuses on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (s{sup ^}) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak s{sup ^}. Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak s{sup ^} discharges and that the value of s{sup ^}{sub crit} is consistent with the experimental results s{sup ^}{sub crit}{sup exp}≈0.2∼0.3 [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. The consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak s{sup ^} and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive s{sup ^}.

  1. Intrinsic torque reversals induced by magnetic shear effects on the turbulence spectrum in tokamak plasmas

    SciTech Connect

    Lu, Z. X.; Wang, W. X.; Diamond, P. H.; Tynan, G.; Ethier, S.; Gao, C.; Rice, J.

    2015-05-04

    We report that intrinsic torque, which can be generated by turbulent stresses, can induce toroidal rotation in a tokamak plasma at rest without direct momentum injection. Reversals in intrinsic torque have been inferred from the observation of toroidal velocity changes in recent lower hybrid current drive (LHCD) experiments. Here we focus on understanding the cause of LHCD-induced intrinsic torque reversal using gyrokinetic simulations and theoretical analyses. A new mechanism for the intrinsic torque reversal linked to magnetic shear (sˆ) effects on the turbulence spectrum is identified. This reversal is a consequence of the ballooning structure at weak sˆ . Based on realistic profiles from the Alcator C-Mod LHCD experiments, simulations demonstrate that the intrinsic torque reverses for weak sˆ discharges and that the value of sˆ crit is consistent with the experimental results sˆ expcrit [Rice et al., Phys. Rev. Lett. 111, 125003 (2013)]. In conclusion, the consideration of this intrinsic torque feature in our work is important for the understanding of rotation profile generation at weak and its consequent impact on macro-instability stabilization and micro-turbulence reduction, which is crucial for ITER. It is also relevant to internal transport barrier formation at negative or weakly positive sˆ .

  2. The magnetization reversal in CoFe2O4/CoFe2 granular systems

    NASA Astrophysics Data System (ADS)

    Jin, J.; Sun, X.; Wang, M.; Ding, Z. L.; Ma, Y. Q.

    2016-12-01

    The temperature-dependent field cooling (FC) and zero-field cooling (ZFC) magnetizations, i.e., M FC and M ZFC, measured under different magnetic fields from 500 Oe to 20 kOe have been investigated on two exchange-spring CoFe2O4/CoFe2 composites with different relative content of CoFe2. Two samples exhibit different magnetization reversal behaviors. With decreasing temperature, a progressive freezing of the moments in two composites occurs at a field-dependent irreversible temperature T irr. For the sample with less CoFe2, the curves of - d( M FC - M ZFC)/ dT versus temperature T exhibit a broad peak at an intermediate temperature T 2 below T irr , and the moments are suggested not to fully freeze till the lowest measuring temperature 10 K. However, for the - d( M FC - M ZFC)/ dT curves of the sample with more CoFe2, besides a broad peat at an intermediate temperature T 2, a rapid rise around the low temperature T 1 15 K is observed, below which the moments are suggested to fully freeze. Increase of magnetic field from 2 kOe leads to the shift of T 2 and T irr towards a lower temperature, and the shift of T 2 is attributable to the moment reversal of CoFe2O4.

  3. Magnetic and structural studies on CoFe2O4 nanoparticles synthesized by co-precipitation, normal micelles and reverse micelles methods

    NASA Astrophysics Data System (ADS)

    Sharifi, Ibrahim; Shokrollahi, H.; Doroodmand, Mohammad Mahdi; Safi, R.

    2012-05-01

    Cobalt ferrite nanoparticles were synthesized by the chemical co-precipitation, normal micelles and reverse micelles methods of iron and cobalt chlorides. X-ray diffraction analysis, Fourier Transform Infrared (FTIR) and Vibrating Sample Magnetometer were carried out at room temperature to study the structural and magnetic properties. X-ray patterns revealed the production of a broad single cubic phase with the average particle sizes of ∼12 nm, 5 nm and 8 nm for co-precipitation, normal micelles and reverse micelles methods, respectively. The FTIR measurements between 400 and 4000 cm-1 confirmed the intrinsic cation vibrations of spinel structure for each one of the three methods. Moreover, the average particle sizes were lower than the single domain size (128 nm) and higher than the super-paramagnetic size (2-3 nm) at room temperature. The results revealed that the magnetic properties depend on the particle size and cation distribution, whereas the role of particle size is more significant.

  4. Magnetic properties of nano-composite particles

    NASA Astrophysics Data System (ADS)

    Xu, Xia

    Chemical synthesis routes for hollow spherical BaFe12O 19, hollow mesoporous spherical BaFe12O19, worm-shape BaFe12O19 and FeCo particles were developed. These structured particles have great potentials for the applications including magnetic recording medium, catalyst support, and energy storage. Magnetically exchange coupled hard/soft SrFe12O19/FeCo and MnBi/FeCo composites were synthesized through a newly proposed process of magnetic self-assembly. These exchange coupled composites can be potentially used as rare-earth free permanent magnets. Hollow spherical BaFe12O19 particles (shell thickness ˜5 nm) were synthesized from eth-ylene glycol assisted spray pyrolysis. Hollow mesoporous spherical BaFe12O19 particles (shell thickness ˜100 nm) were synthesized from ethanol assisted spray pyrolysis, followed by alkaline ethylene glycol etching at 185 °C. An alpha-Fe2O3 and BaCO3 nanoparticle mixture was synthesized with reverse microemulsion, followed by annealing at 900 °C for 2 hours to get worm-shape BaFe 12O19 particles, which consisted of 3-7 stacked hexagonal plates. FeCo nanoparticles were synthesized by reducing FeCl2 and CoCl2 in diphenyl ether with n-butyllithium at 200 °C in an inert gas environment. The surfactant of oleic acid was used in the synthesis to make particles well dispersed in nonpolar solvents (such as hexane). SrFe12O19/FeCo core/shell particles were prepared through a magnetic self-assembly process. The as-synthesized soft FeCo nanoparticles were magnetically attracted by hard SrFe12O19 parti-cles, forming a SrFe12O19/FeCo core/shell structure. The magnetic self-assembly mechanism was confirmed by applying alternating-current demagnetization to the core/shell particles, which re-sulted in a separation of SrFe 12O19 and FeCo particles. MnBi/FeCo composites were synthesized, and the exchange coupling between MnBi and FeCo phases was demonstrated by smooth magnetic hysteresis loop of MnBi/FeCo composites. The thermal stability of Mn

  5. A measurement setup for acquiring the local magnetic properties of plastically deformed soft magnetic materials

    SciTech Connect

    Bi Shasha; Sutor, Alexander; Lerch, Reinhard; Xiao Yunshi

    2011-04-01

    This paper introduces a new measurement setup for extraction of the local magnetic properties. With the help of finite element method simulations, modifications are made on the previous double-C-yoke method. Small dimension measuring coils are applied in the stray field produced by the magnetic circuit to evaluate the local magnetic properties of the specified part of the specimen. Through the measurements with the plastically deformed materials at different temperatures, it indicates that the magnetic properties of soft magnetic materials are quite sensitive to plastic straining. After high-temperature thermal treatment on the plastically deformed specimen, the local magnetic properties exhibit an obvious recovery.

  6. Hygroscopic properties of magnetic recording tape

    NASA Technical Reports Server (NTRS)

    Cuddihy, E. F.

    1976-01-01

    Relative humidity has been recognized as an important environmental factor in many head-tape interface phenomena such as headwear, friction, staining, and tape shed. Accordingly, the relative humidity is usually specified in many applications of tape use, especially when tape recorders are enclosed in hermetically sealed cases. Normally, the relative humidity is believed regulated by humidification of the fill gas to the specification relative humidity. This study demonstrates that the internal relative humidity in a sealed case is completely controlled by the time-dpendence of the hygroscopic properties of the pack of magnetic recording tape. Differences are found in the hygroscopic properties of the same brand of tape, which apparently result from aging, and which may have an effect on the long-term humidity-regulating behavior in a sealed case, and on the occurrence of head-tape interface phenomena from the long-term use of the tape. Results are presented on the basic hygroscopic properties of magnetic tape, its humidity-regulating behavior in a sealed case, and a theoretical commentary on the relative humidity dependence of head-wear by tape, is included.

  7. Observation of in plane magnetization reversal using polarization dependent magneto-optic Kerr effect

    NASA Astrophysics Data System (ADS)

    Ohldag, H.; Weber, N. B.; Hillebrecht, F. U.; Kisker, E.

    2002-02-01

    We present an experimental setup for in plane two axis magnetometry using the polarization dependent magneto-optic Kerr effect (MOKE). A conventional setup to measure longitudinal MOKE with crossed polarizers is extended by a Faraday cell to compensate for the rotation of the polarization vector caused by a magnetized sample. The shape of the hysteresis loops measured on thin FeNi alloy films depends strongly on the angle between the optical axis of the analyzer and the plane of incidence. We derive expressions for the compensation angle which allow for extraction of vectorial magnetic information from loops detected with oblique polarization. For a small deviation from pure s or p polarization the transverse magnetization is found to be proportional to the difference between the loop obtained with oblique polarization and the one obtained with pure s or p polarization. Thus the complete in plane reversal process split up into longitudinal and transverse components can be observed.

  8. 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.

  9. Origin of the Reversible Thermochromic Properties of Polydiacetylenes Revealed by Ultrafast Spectroscopy.

    PubMed

    Baek, Junwoo; Joung, Joonyoung F; Lee, Songyi; Rhee, Hanju; Kim, Myung Hwa; Park, Sungnam; Yoon, Juyoung

    2016-01-21

    Polydiacetylenes (PDAs) with thermochromic properties undergo colorimetric transitions when the external temperature is varied. This capability has the potential to enable these materials to be used as temperature sensors. These thermochromic properties of PDAs stem from their temperature-dependent optical properties. In this work, we studied the temperature-dependent optical properties of Bis-PDA-Ph, which exhibits reversible thermochromic properties, and PCDA-PDA, which exhibits irreversible thermochromic properties, by UV-visible absorption and femtosecond transient absorption spectroscopy. Our results indicate that the electronic relaxation of PDAs occurs via an intermediate state in cases where the material exhibits reversible thermochromic properties, whereas the excited PDAs relax directly back to the ground state when irreversible thermochromic properties are observed. The existence of this intermediate state in the electronic relaxation of PDAs thus plays an important role in determining their thermochromic properties. These results are very important for both understanding and strategically modulating the thermochromic properties of PDAs.

  10. Interfacial exchange coupling and magnetization reversal in perpendicular [Co/Ni]N/TbCo composite structures.

    PubMed

    Tang, M H; Zhang, Zongzhi; Tian, S Y; Wang, J; Ma, B; Jin, Q Y

    2015-06-15

    Interfacial exchange coupling and magnetization reversal characteristics in the perpendicular heterostructures consisting of an amorphous ferrimagnetic (FI) TbxCo(100-x) alloy layer exchange-coupled with a ferromagnetic (FM) [Co/Ni]N multilayer have been investigated. As compared with pure TbxCo(100-x) alloy, the magnetization compensation composition of the heterostructures shift to a higher Tb content, implying Co/Ni also serves to compensate the Tb moment in TbCo layer. The net magnetization switching field Hc⊥ and interlayer interfacial coupling field Hex, are not only sensitive to the magnetization and thickness of the switched TbxCo(100-x) or [Co/Ni]N layer, but also to the perpendicular magnetic anisotropy strength of the pinning layer. By tuning the layer structure we achieve simultaneously both large Hc⊥ = 1.31 T and Hex = 2.19 T. These results, in addition to the fundamental interest, are important to understanding of the interfacial coupling interaction in the FM/FI heterostructures, which could offer the guiding of potential applications in heat-assisted magnetic recording or all-optical switching recording technique.

  11. Magnetic properties of iron minerals produced by natural iron- and manganese-reducing groundwater bacteria

    NASA Astrophysics Data System (ADS)

    Abrajevitch, Alexandra; Kondratyeva, Lubov M.; Golubeva, Evgeniya M.; Kodama, Kazuto; Hori, Rie S.

    2016-08-01

    Understanding the contribution of biogenic magnetic particles into sedimentary assemblages is a current challenge in palaeomagnetism. It has been demonstrated recently that magnetic particles produced through biologically controlled mineralization processes, such as magnetosomes from magnetotactic bacteria, contribute to the recording of natural remanent magnetization in marine and lacustrian sediments. Contributions from other, biologically induced, mineralization types, which are known from multiple laboratory experiments to include magnetic minerals, remain largely unknown. Here, we report magnetic properties of iron minerals formed by a community of iron- and manganese-reducing bacteria isolated from a natural groundwater deposit during a 2 yr long incubation experiment. The main iron phases of the biomineralized mass are lepidocrocite, goethite and magnetite, each of which has environmental significance. Unlike the majority of the previous studies that reported superparamagnetic grain size, and thus no remanence carrying capacity of biologically induced magnetite, hysteresis and first-order reversal curves measurements in our study have not detected significant superparamagnetic contribution. The biomineralized mass, instead, contains a mixture of single-domain to pseudo-single-domain and multidomain magnetite particles that are capable of carrying a stable chemical remanent magnetization. Isothermal remanent magnetization acquisition parameters and first-order reversal curves signatures of the biomineralized samples deviate from previously proposed criteria for the distinction of extracellular (biologically induced) magnetic particles in mixtures. Given its potential significance as a carrier of natural remanent magnetization, environmental requirements, distribution in nature and the efficiency in the geomagnetic field recording by biologically induced mineralization need comprehensive investigation.

  12. Magnetic properties of arrays of electrodeposited nanowires

    NASA Astrophysics Data System (ADS)

    Ross, C. A.; Hwang, M.; Shima, M.; Smith, Henry I.; Farhoud, M.; Savas, T. A.; Schwarzacher, W.; Parrochon, J.; Escoffier, W.; Bertram, H. Neal; Humphrey, F. B.; Redjdal, M.

    2002-08-01

    The fabrication and magnetic properties of arrays of short nanowires are reviewed. The arrays consist of electrodeposited ferromagnetic cylinders with aspect ratios of up to 3 and diameters of 57-180 nm. Their hysteresis loops are characterized and their remanent states are related to the predictions of a three-dimensional micromagnetic model, which shows a transition from a single-domain 'flower' state to a lower-remanence 'vortex' state with increasing diameter. The shapes of the array hysteresis loops are governed by interactions between the particles. The switching fields of small Ni cylinders can be described using a dynamic micromagnetic model.

  13. The effects of 10 to >160 GPa shock on the magnetic properties of basalt and diabase

    NASA Astrophysics Data System (ADS)

    Bezaeva, N. S.; Swanson-Hysell, N. L.; Tikoo, S. M.; Badyukov, D. D.; Kars, M.; Egli, R.; Chareev, D. A.; Fairchild, L. M.; Khakhalova, E.; Strauss, B. E.; Lindquist, A. K.

    2016-11-01

    Hypervelocity impacts within the solar system affect both the magnetic remanence and bulk magnetic properties of planetary materials. Spherical shock experiments are a novel way to simulate shock events that enable materials to reach high shock pressures with a variable pressure profile across a single sample (ranging between ˜10 and >160 GPa). Here we present spherical shock experiments on basaltic lava flow and diabase dike samples from the Osler Volcanic Group whose ferromagnetic mineralogy is dominated by pseudo-single-domain (titano)magnetite. Our experiments reveal shock-induced changes in rock magnetic properties including a significant increase in remanent coercivity. Electron and magnetic force microscopy support the interpretation that this coercivity increase is the result of grain fracturing and associated domain wall pinning in multidomain grains. We introduce a method to discriminate between mechanical and thermal effects of shock on magnetic properties. Our approach involves conducting vacuum-heating experiments on untreated specimens and comparing the hysteresis properties of heated and shocked specimens. First-order reversal curve (FORC) experiments on untreated, heated, and shocked specimens demonstrate that shock and heating effects are fundamentally different for these samples: shock has a magnetic hardening effect that does not alter the intrinsic shape of FORC distributions, while heating alters the magnetic mineralogy as evident from significant changes in the shape of FORC contours. These experiments contextualize paleomagnetic and rock magnetic data of naturally shocked materials from terrestrial and extraterrestrial impact craters.

  14. The symmetry properties of planetary magnetic fields

    SciTech Connect

    Raedler, K.H. ); Ness, N.F. )

    1990-03-01

    This paper provides a comparative study of the geometrical structures of the magnetic fields of Earth, Jupiter, Saturn, and Uranus, starting from the traditional multipolar representations of these fields. For Earth, Jupiter, and Saturn the centered dipole, quadrupole, and octupole contributions are included, while at Uranus, only the dipole and quadrupole contributoins are considered. The magnetic fields are analyzed by decomposing them into those parts which have simple symmetry properties with respect to the rotation axis and the equatorial plane. It is found that there are a number of common features of the magnetic fields of Earth and Jupiter. Compared to Earth and Jupiter, the Saturnian field exhibits not only a high degree of symmetry about the rotation axis, by now rather well known, but also a high degree of antisymmetry about the equatorial plane. The Uranian field shows strong deviations from both such symmetries. Nevertheless, there remain features common to all four planets. The implications of these results for dynamo models are discussed. With a vgiew to Cowling's theorem the symmetry of the fields is investigated with respect to not only the rotation axis but also to other axes intersecting the plaentary center. Surprisingly, the high degree of asymmetry of the Uranian field that is observed with respect to the rotation axis reduces considerably to being compare to that for Earth or Jupiter when the appropriate axis is employed.

  15. Reverse shock emission driven by post-merger millisecond magnetar winds: Effects of the magnetization parameter

    NASA Astrophysics Data System (ADS)

    Liu, L. D.; Wang, L. J.; Dai, Z. G.

    2016-08-01

    The study of short-duration gamma-ray bursts provides growing evidence that a good fraction of double neutron star mergers lead to the formation of stable millisecond magnetars. The launch of Poynting flux by the millisecond magnetars could leave distinct electromagnetic signatures that reveal the energy dissipation processes in the magnetar wind. In previous studies, we assume that the magnetar wind becomes completely lepton-dominated so that electrons/positrons in the magnetar wind are accelerated by a diffusive shock. However, theoretical modeling of pulsar wind nebulae shows that in many cases the magnetic field energy in the pulsar wind may be strong enough to suppress diffusive shock acceleration. In this paper, we investigate the reverse shock emission and the forward shock emission with an arbitrary magnetization parameter σ of a magnetar wind. We find that the reverse shock emission strongly depends on σ, and in particular that σ ~ 0.3 leads to the strongest reverse shock emission. Future observations would be helpful to diagnose the composition of the magnetar wind.

  16. Simulations of magnetic reversal in continuously distorted artificial spin ice lattices

    NASA Astrophysics Data System (ADS)

    Farmer, Barry; Bhat, Vinayak; Woods, Justin; Hastings, J. Todd; de Long, Lance

    2014-03-01

    Artificial spin ice (ASI) systems consist of lithographically patterned ferromagnetic segments that behave as Ising spins. The honeycomb lattice is an ASI analogue of the Kagomé spin ice lattice found in bulk pyrochlore crystals. We have developed a method to continuously distort the honeycomb lattice such that the pattern vertex spacings follow a Fibonacci chain sequence. The distortions break the rotational symmetry of the honeycomb lattice and alter the segment orientations and lengths such that all vertices retain three-fold coordination, but are no longer equivalent. We have performed micromagnetic simulations (OOMMF) of magnetization reversal for many samples having different strengths of distortion, and found the kinetics of magnetic reversal to be dramatically slowed, and avalanches (sequential switching of neighboring segments) shortened by only small deviations from perfect honeycomb symmetry. The coercivity increases as the distortion is strengthened, which is consistent with the retarded reversal. Research supported by U.S. DoE Grant DE-FG02-97ER45653 and NSF Grant EPS-0814194.

  17. Stable, polymer-directed and SPION-nucleated magnetic amphiphilic block copolymer nanoprecipitates with readily reversible assembly in magnetic fields

    NASA Astrophysics Data System (ADS)

    Giardiello, Marco; Hatton, Fiona L.; Slater, Rebecca A.; Chambon, Pierre; North, Jocelyn; Peacock, Anita K.; He, Tao; McDonald, Tom O.; Owen, Andrew; Rannard, Steve P.

    2016-03-01

    The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications.The formation of inorganic-organic magnetic nanocomposites using reactive chemistry often leads to a loss of super-paramagnetisim when conducted in the presence of iron oxide nanoparticles. We present here a low energy and chemically-mild process of co-nanoprecipitation using SPIONs and homopolymers or amphiphilic block copolymers, of varying architecture and hydrophilic/hydrophobic balance, which efficiently generates near monodisperse SPION-containing polymer nanoparticles with complete retention of magnetism, and highly reversible aggregation and redispersion behaviour. When linear and branched block copolymers with inherent water-solubility are used, a SPION-directed nanoprecipitation mechanism appears to dominate the nanoparticle formation presenting new opportunities for tailoring and scaling highly functional systems for a range of applications. Electronic supplementary information (ESI) available: Additional experimental details, NMR spectra, GPC chromatograms, kinetics experiments, graphs of nanopreciptate aggregation and cycling studies and SPION characterisation. See DOI: 10.1039/c6nr00788k

  18. Monte Carlo simulation for thermal assisted reversal process of micro-magnetic torus ring with bistable closure domain structure

    NASA Astrophysics Data System (ADS)

    Terashima, Kenichi; Suzuki, Kenji; Yamaguchi, Katsuhiko

    2016-04-01

    Monte Carlo simulations were performed for temperature dependences of closure domain parameter for a magnetic micro-torus ring cluster under magnetic field on limited temperature regions. Simulation results show that magnetic field on tiny limited temperature region can reverse magnetic closure domain structures when the magnetic field is applied at a threshold temperature corresponding to intensity of applied magnetic field. This is one of thermally assisted switching phenomena through a self-organization process. The results show the way to find non-wasteful pairs between intensity of magnetic field and temperature region for reversing closure domain structure by temperature dependence of the fluctuation of closure domain parameter. Monte Carlo method for this simulation is very valuable to optimize the design of thermally assisted switching devices.

  19. Bromelain Reversibly Inhibits Invasive Properties of Glioma Cells

    PubMed Central

    Tysnes, Berit B; Maurer, H Rainer; Porwol, Torsten; Probst, Beatrice; Bjerkvig, Rolf; Hoover, Frank

    2001-01-01

    Abstract Bromelain is an aqueous extract from pineapple stem that contains proteinases and exhibits pleiotropic therapeutic effects, i.e., antiedematous, antiinflammatory, antimetastatic, antithrombotic, and fibrinolytic activities. In this study, we tested bromelain's effects on glioma cells to assess whether bromelain could be a potential contributor to new antiinvasive strategies for gliomas. Several complementary assays demonstrated that bromelain significantly and reversibly reduced glioma cell adhesion, migration, and invasion without affecting cell viability, even after treatment periods extending over several months. Immunohistochemistry and immunoblotting experiments demonstrated that α3 and β1 integrin subunits and hyaluronan receptor CD44 protein levels were reduced within 24 hours of bromelain treatment. These effects were not reflected at the RNA level because RNA profiling did not show any significant effects on gene expression. Interestingly, metabolic labelling with 35-S methionine demonstrated that de novo protein synthesis was greatly attenuated by bromelain, in a reversible manner. By using a trans-activating signaling assay, we found that CRE-mediated signaling processes were suppressed. These results indicate that bromelain exerts its antiinvasive effects by proteolysis, signaling cascades, and translational attenuation. PMID:11774029

  20. Polarity Reversal of the Solar Photospheric Magnetic Field During Activity Cycle 24

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Hoeksema, Jon Todd; Liu, Yang; Zhao, Junwei

    2014-06-01

    The large-scale solar magnetic field reverses its polarity during the maximum phase of each activity cycle. As observed on the photosphere, active region (AR) magnetic flux migrates poleward in narrow, sheared streams resulted from large-scale flows and diffusion. A small net flux of the trailing sunspot polarity eventually aggregates at high latitudes, manifesting the poloidal field of the next cycle. We characterize this process for the ongoing cycle 24 based on four years' line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI). The axial dipole component reversed sign in early 2012, but the poleward flux migration was grossly out of phase in the two hemispheres. As a proxy, the northern polar field (taken as mean above 70 degrees latitude) switched from negative to positive in late 2012, whereas the southern remained positive as of March 2014. Three factors that are in line with the surface flux transport model may have contributed. First, AR emergence started and peaked earlier in the north. Second, several ARs with small or inverse tilt angles (w.r.t. the Joy's law) emerged in the south in late 2010. Third, meridional flow speed inferred from helioseismology varied greatly prior to 2013; slower streams (compared to a three-year mean at the same latitude) appeared earlier in the north. We correlate HMI with the long-running Wilcox Solar Observatory (WSO) dataset, and compare the current cycle with the previous three.

  1. Magnetic colloid by PLA: Optical, magnetic and thermal transport properties

    NASA Astrophysics Data System (ADS)

    Pandey, B. K.; Shahi, A. K.; Gopal, Ram

    2015-08-01

    Ferrofluids of cobalt and cobalt oxide nanoparticles (NPs) have been successfully synthesized using liquid phase-pulse laser ablation (LP-PLA) in ethanol and double distilled water, respectively. The mechanism of laser ablation in liquid media and formation process for Co target in double distilled water (DDW) and ethanol are speculated based on the reactions between laser generated highly nascent cobalt species and vaporized solvent media in a confined high temperature and pressure at the plume-surrounding liquid interface region. Optical absorption, emission, vibrational and rotational properties have been investigated using UV-vis absorption, photoluminescence (PL) and Fourier transform-infra red (FT-IR) spectroscopy, respectively. In this study optical band gap of cobalt oxide ferrofluids has been engineered using different pulse energy of Nd:YAG laser in the range of (2.80-3.60 eV). Vibrating sample magnetometer (VSM) is employed to determine the magnetic properties of ferrofluids of cobalt and cobalt oxide NPs while their thermal conductivities are examined using rotating disc method. Ferrofluids have gained enormous curiosity due to many technological applications, i.e. drug delivery, coolant and heating purposes.

  2. Effects Of Hydrothermal Alteration On Magnetic Properties And Magnetic Signatures - Implications For Predictive Magnetic Exploration Models

    NASA Astrophysics Data System (ADS)

    Clark, D.

    2012-12-01

    Magnetics is the most widely used geophysical method in hard rock exploration and magnetic surveys are an integral part of exploration programs for many types of mineral deposit, including porphyry Cu, intrusive-related gold, volcanic-hosted epithermal Au, IOCG, VMS, and Ni sulfide deposits. However, the magnetic signatures of ore deposits and their associated mineralized systems are extremely variable and exploration that is based simply on searching for signatures that resemble those of known deposits and systems is rarely successful. Predictive magnetic exploration models are based upon well-established geological models, combined with magnetic property measurements and geological information from well-studied deposits, and guided by magnetic petrological understanding of the processes that create, destroy and modify magnetic minerals in rocks. These models are designed to guide exploration by predicting magnetic signatures that are appropriate to specific geological settings, taking into account factors such as tectonic province; protolith composition; post-formation tilting/faulting/ burial/ exhumation and partial erosion; and metamorphism. Patterns of zoned hydrothermal alteration are important indicators of potentially mineralized systems and, if properly interpreted, can provided vectors to ore. Magnetic signatures associated with these patterns at a range of scales can provide valuable information on prospectivity and can guide drilling, provided they are correctly interpreted in geological terms. This presentation reviews effects of the important types of hydrothermal alteration on magnetic properties within mineralized systems, with particular reference to porphyry copper and IOCG deposits. For example, an unmodified gold-rich porphyry copper system, emplaced into mafic-intermediate volcanic host rocks (such as Bajo de la Alumbrera, Argentina) exhibits an inner potassic zone that is strongly mineralized and magnetite-rich, which is surrounded by an outer

  3. Reversible electrically-driven magnetic domain wall rotation in multiferroic heterostructures to manipulate suspended on-chip magnetic particles

    NASA Astrophysics Data System (ADS)

    Nowakowski, Mark; Sohn, Hyunmin; Liang, Cheng-Yen; Hockel, Joshua; Wetzlar, Kyle; Keller, Scott; McLellan, Brenda; Marcus, Matthew; Doran, Andrew; Young, Anthony; Kläui, Mathias; Carman, Gregory; Bokor, Jeffrey; Candler, Robert

    2015-03-01

    We experimentally demonstrate reversible electrically-driven, strain-mediated domain wall (DW) rotation in Ni rings fabricated on piezoelectric [Pb(Mg1/3Nb2/3) O3]0.66-[PbTiO3]0.34 (PMN-PT) substrates. An electric field applied across the PMN-PT substrate induces a strain in the Ni rings producing DW rotation around the ring toward the dominant PMN-PT strain axis by inverse magnetostriction. We observe DWs reversibly cycled between their initial and rotated state as a function of the applied electric field with x-ray magnetic circular dichroism photo-emission electron microscopy. The DW rotation is analytically predicted using a fully coupled micromagnetic/elastodyanmic multi-physics simulation to verify that the experimental behavior is caused by the electrically-generated strain in this multiferroic system. Finally, this DW rotation is used to capture and manipulate magnetic particles in a fluidic environment to demonstrate a proof-of-concept energy-efficient pathway for multiferroic-based lab-on-a-chip applications. Supported by TANMS (NSF 11-537), E3S, US Dept of Energy (DE-AC02-05CH11231), EU, and DFG.

  4. A Study of Magnetic Properties of Magnetotactic Bacteria

    PubMed Central

    Wajnberg, E.; de Souza, L. H. Salvo; de Barros, Henrique G. P. Lins; Esquivel, Darci M. S.

    1986-01-01

    The first direct measurements of magnetic properties of magnetotactic bacteria from natural samples are presented. Measurements were made at 4.2 K, using a Superconducting Quantum Interfering Device (SQUID) magnetometer. From the magnetization results an anisotropy is obtained that is typical of magnetized ferro- or ferri-magnetic materials. The average magnetic moment of the bacteria determined from the results is in good agreement with the estimated moment from electron microscopy. ImagesFIGURE 2 PMID:19431685

  5. Time-Reversal Symmetry Breaking and Consequent Physical Responses Induced by All-In-All-Out Type Magnetic Order on the Pyrochlore Lattice

    NASA Astrophysics Data System (ADS)

    Arima, Taka-Hisa

    2014-03-01

    Pyrochlore-type 5d transition-metal oxide compounds Cd2Os2O7 and R2Ir2O7 (R =rare earth) undergo a metal-insulator transition accompanied by a magnetic transition. Recently, the magnetic structures of Cd2Os2O7 and Eu2Ir2O7 were investigated by means of resonant x-ray magnetic scattering. The x-ray data indicated the all-in/all-out type magnetic order. The all-in/all-out order breaks the time-reversal symmetry, while the spontaneous magnetization is essentially absent. The magnetic order can be viewed as ferroic magnetic octupolar order. The magnetic order is expected to provide several unique physical properties like quadratic magnetization. linear magneto-capacitance, linear magneto-resistance, linear magneto-mechanical coupling and so on. The symmetry breaking results in two non-equivalent domains, ``all-in/all-out'' and ``all-out/all-in.'' Interestingly, some theoretical works predict that a peculiar metallic state would appear on the domain wall. The observation and control of the domain distribution are essential for studying verious exotic physical responses. We have developed an x-ray technique for domain imaging and started studying the effects of external stimuli on the domain distribution. This work was performed in collaboration with S. Tardif, S. Takeshita, H. Ohsumi, D. Uematsu, H. Sagayama, J. J. Ishikawa, S. Nakatsuji, J. Yamaura, and Z. Hiroi.

  6. Study of grain interactions in perpendicular magnetic recording media using first order reversal curve diagrams

    NASA Astrophysics Data System (ADS)

    Papusoi, C.; Srinivasan, K.; Acharya, R.

    2011-10-01

    It is demonstrated that, for perpendicular magnetic recording (PMR) media, first order reversal curve analysis can independently measure the grain coercive field distribution (or switching field distribution) and the strength of grain interactions, i.e., the demagnetization (mean-field) factor and the dispersion of grain interaction fields around the mean-field. The coercive field distribution is used to determine the intrinsic anisotropy field distribution of PMR media. The temperature dependence of the demagnetization factor shows that the strength of inter-granular exchange coupling is increasing with increasing medium thickness and it is decreasing with increasing temperature.

  7. Transient loss of plasma from a theta pinch having an initially reversed magnetic field

    SciTech Connect

    Heidrich, J. E.

    1981-01-01

    The results of an experimental study of the transient loss of plasma from a 25-cm-long theta pinch initially containing a reversed trapped magnetic field are presented. The plasma, amenable to MHD analyses, was a doubly ionized helium plasma characterized by an ion density N/sub i/ = 2 x 10/sup 16/ cm/sup -3/ and an ion temperature T/sub i/ = 15 eV at midcoil and by N/sub i/ = 0.5 x 10/sup 16/ cm/sup -3/ and T/sub i/ = 6 eV at a position 2.5 cm beyond the end of the theta coil.

  8. Novel mechanism of photoinduced reversible phase transitions in molecule-based magnets.

    PubMed

    Kawamoto, T; Asai, Y; Abe, S

    2001-01-08

    A novel microscopic mechanism of bidirectional structural changes is proposed for the photoinduced magnetic phase transition in Co-Fe Prussian blue analogs on the basis of ab initio quantum chemical cluster calculations. It is shown that the local potential energies of various spin states of Co are sensitive to the number of nearest neighbor Fe vacancies. As a result, the forward and backward structural changes are most readily initiated by excitation of different local regions by different photons. This mechanism suggests an effective strategy to realize photoinduced reversible phase transitions in a general system consisting of two local components.

  9. Magnetic Properties of the Chelyabinsk meteorite

    NASA Astrophysics Data System (ADS)

    Bezaeva, N. S.; Badyukov, D. D.; Nazarov, M. A.; Rochette, P.; Feinberg, J. M.

    2013-12-01

    The Chelyabinsk meteorite (the fall of February 15, 2013; Russia) is a LL5 ordinary chondrite. Numerous (thousands) stones fell as a shower to the south and the south-west of the city of Chelyabinsk. The stones consist of two intermixed lithologies, with the majority (2/3) being a light lithology with a typical chondritic texture and shock stage S4 (~30 GPa). The second lithology (1/3) is an impact melt breccia (IMB) consisting of blackened chondrite fragments embedded in a fine-grained matrix. We investigated the magnetic properties of the meteorite stones collected immediately after the fall by the expedition of the Vernadsky Institute, Moscow. The low-field magnetic susceptibility (χ0) of 174 fragments (135 chondritic and 39 IMB) weighing >3 g was measured. Each sample was measured three times in mutually perpendicular directions to average anisotropy. Also hysteresis loops (saturation magnetization Ms, coercivity Bc) and back-field remanence demagnetization curves (coercivity of remanence Bcr) in the temperature range from 10K to 700°C and other characteristics of some pieces (NRM, SIRM with their thermal and alternating field demagnetization spectra) were acquired. The mean logχ0 is 4.57×0.09 (s.d.) for the light lithology and 4.65×0.09 (s.d.) (×10-9 m3/kg) for the IMB, indicating that IMB is slightly richer in metal than the light chondritic lithology. According to [1], Chelyabinsk is three times more magnetic than the average LL5 fall, but similar to other metal-rich LL5 (e.g., Paragould, Aldsworth, Bawku, Richmond), as well as L/LL chondrites (e.g., Glanerbrug, Knyahinya, Qidong). The estimation of metal content from the Ms value gives 3.7 wt.% for the light fragments and 4.1 wt.% for IMB whereas the estimation from χ0 yields overestimated contents, e.g., 6.9 wt.% for the light lithology. Thermomagnetic curves Ms(T) up to 800°C identify the main magnetic carriers at room temperature (T0) and above as taenite and kamacite (no tetrataenite found), in

  10. Brunhes-Matuyama Magnetic Polarity Reversal Tracing using Chinese loess10Be

    NASA Astrophysics Data System (ADS)

    Zhou, W.; Beck, W.; Kong, X.; An, Z.; Qiang, X.; Wu, Z.; Xian, F.; Ao, H.

    2014-12-01

    The geomagnetic polarity reversal is generally considered to occur synchronously around the world, and is commonly used as a time marker. However, in the case of the most recent reversal, the Brunhes-Matuyama (B-M) reversal (~780 ka), comparison of paleomagnetic studies in Chinese loess-paleosol sequences versus marine sediments revealed a marked discrepancy in timing of this event (Tauxe et al., 1996; Zhou and Shackleton, 1999), leading to the debate on uncertainties of paleoclimatic correlation between the Chinese loess-paleosol sequences and marine sediments (Wang et al., 2006; Liu et al., 2008; Jin and Liu, 2011). Based on this issue, here we propose to use the cosmogenic 10Be to address this conundrum. 10Be is a long-lived radionuclide produced in the atmosphere by cosmic ray spallation reactions and carried to the ground attached to aerosols. Its atmospheric production rate is inversely proportional to the geomagnetic field intensity (Masarik and Beer, 1999). This allows us to reconstruct past geomagnetic field intensity variations using 10Be concentrations recorded in different sedimentary archives. We carried out the 10Be studies in Luochuan and Xifeng sections in Chinese Loess Plateau, both loess profiles show that 10Be production rate was at a maximum-an indication of the dipole field reversal-at ca. 780 ± 3 ka BP., in paleosol unit S7corresponding to MIS 19. These results have proven that the timing of B-M reversal recorded in Chinese loess is synchronous with that seen in marine records (Tauxe et al., 1996) and reaffirmed the conventional paleoclimatic correlation of loess-paleosol sequences with marine isotope stages and the standard loess timescale as correct. However, it is ~25 ka younger than the age (depth) of the magnetic polarity reversal recorded in these same Chinese loess-paleosol sequences, demonstrating that loess magnetic overprinting has occurred. 1.Jin, C.S.,et al., 2011,PALAEOGEOGR PALAEOCL, 299, 309-3172.Liu, Q.S., et al., 2008, EARTH

  11. Microstructure and Magnetic Properties of Electrodeposited Cobalt Film

    SciTech Connect

    Bhuiyan, Md S; Taylor, B. J.; Paranthaman, Mariappan Parans; Thompson, James R; Sinclair, J.

    2008-01-01

    Cobalt films were electrodeposited onto both iron and copper substrates from an aqueous solution containing a mixture of cobalt sulfate, boric acid, sodium citrate, and vanadyl sulfate. The structural, intermetallic diffusion and magnetic properties of the electrodeposited films were studied. Cobalt electrodeposition was carried out in a passively divided cell aided by addition of vanadyl sulfate to keep the counter electrode clean. The divided electrolytic cell with very negative current densities cause the electrodeposited Co to adopt a face-centered cubic (fcc) structure, which is more magnetically reversible than the hexagonally close-packed (hcp) structured Co. The coercive field is also significantly less in the fcc-electrodeposited cobalt than in the hcp. SEM images show dense, uniform Co films without any cracks or porosity. Beside the deposition current, thickness of the film was also found to affect the crystal orientation particularly on iron substrates. Diffusion of cobalt film into the iron substrate was studied under reduced environment and a fast process was observed.

  12. Magnetic and magnetoelastic properties of amorphous ribbons

    SciTech Connect

    Chiriac, H.; Ciobotaru, I.; Mohorianu, S.

    1994-03-01

    A phenomenological model for the magnetic and magnetoelastic behavior of the field-annealed magnetostrictive ribbon is proposed. The basic hypothesis is that the magnetic domain coupling energy due to the inhomogeneity inherent to amorphous state is dependent on the reduced magnetization. The model takes into account the anisotropy energy, Zeeman energy, magnetoelastic energy and magnetic domain coupling energy. The magnetization, engineering magnetostriction and Young`s modulus are derived as continuous functions of the applied magnetic field and stress.

  13. Analysis of antimycin A by reversed-phase liquid chromatography/nuclear magnetic-resonance spectrometry

    USGS Publications Warehouse

    Ha, Steven T.K.; Wilkins, Charles L.; Abidi, Sharon L.

    1989-01-01

    A mixture of closely related streptomyces fermentation products, antimycin A, Is separated, and the components are identified by using reversed-phase high-performance liquid chromatography with directly linked 400-MHz proton nuclear magnetic resonance detection. Analyses of mixtures of three amino acids, alanine, glycine, and valine, are used to determine optimal measurement conditions. Sensitivity increases of as much as a factor of 3 are achieved, at the expense of some loss in chromatographic resolution, by use of an 80-μL NMR cell, Instead of a smaller 14-μL cell. Analysis of the antimycin A mixture, using the optimal analytical high performance liquid chromatography/nuclear magnetic resonance conditions, reveals it to consist of at least 10 closely related components.

  14. Anomalous Beam-Ion Loss in TFTR Reversed Magnetic Shear Plasmas

    SciTech Connect

    Ruskov, E.; Bell, M.; Budny, R.V.; McCune, D.C.; Medley, S.S.; Redi, M.H.; Scott, S.; Synakowski, E.J.; von Goeler, S.; White, R.B.; Zweben, S.J.

    1999-02-01

    Anomalous beam-ion loss has been observed in an experiment with short tritium beam pulses injected into deuterium-beam-heated Tokamak Fusion Test Reactor plasmas (P{sub NBI}=15 thinspthinspMW) with reversed magnetic shear (RS). Comparisons of the measured total 14thinspthinspMeV neutron emission, the neutron flux along eight radial locations, and the perpendicular plasma stored energy with predictions from an extensive set of TRANSP simulations suggest that about 40{percent} beam power is lost on a time scale much shorter than the tritium beam pulse length {Delta}t=70 thinspthinspms. In contrast with recent results [K. Tobita {ital et al.,} Nucl.thinspthinspFusion {bold 37}, 1583 (1997)] from RS experiments at JT-60U, we were not able to show conclusively that magnetic field ripple is responsible for this anomaly. {copyright} {ital 1999} {ital The American Physical Society}

  15. Anomalous Beam-Ion Loss in TFTR Reversed Magnetic Shear Plasmas

    NASA Astrophysics Data System (ADS)

    Ruskov, E.; Bell, M.; Budny, R. V.; McCune, D. C.; Medley, S. S.; Redi, M. H.; Scott, S.; Synakowski, E. J.; von Goeler, S.; White, R. B.; Zweben, S. J.

    1999-02-01

    Anomalous beam-ion loss has been observed in an experiment with short tritium beam pulses injected into deuterium-beam-heated Tokamak Fusion Test Reactor plasmas ( PNBI = 15 MW) with reversed magnetic shear (RS). Comparisons of the measured total 14 MeV neutron emission, the neutron flux along eight radial locations, and the perpendicular plasma stored energy with predictions from an extensive set of TRANSP simulations suggest that about 40% beam power is lost on a time scale much shorter than the tritium beam pulse length Δt = 70 ms. In contrast with recent results [K. Tobita et al., Nucl. Fusion 37, 1583 (1997)] from RS experiments at JT-60U, we were not able to show conclusively that magnetic field ripple is responsible for this anomaly.

  16. Magnetic diagnostic suite of the C-2 field-reversed configuration experiment confinement vessela)

    NASA Astrophysics Data System (ADS)

    Thompson, M. C.; Douglass, J. D.; Feng, P.; Knapp, K.; Luo, Y.; Mendoza, R.; Patel, V.; Tuszewski, M.; Van Drie, A. D.

    2012-10-01

    Magnetic measurements are a fundamental part of determining the size and shape of field-reversed configuration (FRC) plasmas in the C-2 device. The magnetic probe suite consists of 44 in-vessel and ex-vessel probes constructed using various technologies: ultra-high vacuum compatible mineral-insulated cable, nested triple axis coils hand-wound on ceramic bobbins, and commercial chip inductors mounted on printed circuit boards. Together, these probes measure the three-dimensional excluded flux profile of the FRC, which approximates the shape of the separatrix between the confined plasma volume and the scrape-off layer. High accuracy is achieved by using the extensive probe measurements to compensate for non-ideal effects such as flux leakage through the vacuum vessel and bulk motion of the FRC towards the wall. A subset of the probes is also used as a set of Mirnov arrays that provide sensitive detection of perturbations and oscillations of the FRC.

  17. Improvement of the magnetic configuration in the reversed field pinch through successive bifurcationsa)

    NASA Astrophysics Data System (ADS)

    Lorenzini, R.; Agostini, M.; Alfier, A.; Antoni, V.; Apolloni, L.; Auriemma, F.; Barana, O.; Baruzzo, M.; Bettini, P.; Bonfiglio, D.; Bolzonella, T.; Bonomo, F.; Brombin, M.; Buffa, A.; Canton, A.; Cappello, S.; Carraro, L.; Cavazzana, R.; Chitarin, G.; Dal Bello, S.; De Lorenzi, A.; De Masi, G.; Escande, D. F.; Fassina, A.; Franz, P.; Gaio, E.; Gazza, E.; Giudicotti, L.; Gnesotto, F.; Gobbin, M.; Grando, L.; Guo, S. C.; Innocente, P.; Luchetta, A.; Manduchi, G.; Marchiori, G.; Marcuzzi, D.; Marrelli, L.; Martin, P.; Martini, S.; Martines, E.; Milani, F.; Moresco, M.; Novello, L.; Ortolani, S.; Paccagnella, R.; Pasqualotto, R.; Peruzzo, S.; Piovan, R.; Piovesan, P.; Piron, L.; Pizzimenti, A.; Pomaro, N.; Predebon, I.; Puiatti, M. E.; Rostagni, G.; Sattin, F.; Scarin, P.; Serianni, G.; Sonato, P.; Spada, E.; Soppelsa, A.; Spagnolo, S.; Spizzo, G.; Spolaore, M.; Taliercio, C.; Terranova, D.; Toigo, V.; Valisa, M.; Veltri, P.; Vianello, N.; Zaccaria, P.; Zaniol, B.; Zanotto, L.; Zilli, E.; Zuin, M.

    2009-05-01

    The reversed field pinch (RFP) is a magnetic configuration alternative to the tokamak that can be considered for a second generation of reactors. In this paper new remarkable results obtained in the RFP experiment RFX-mod are presented, showing that an internal transport barrier delimitates a large fraction of the plasma volume in a RFP when the current is raised to ˜1.5 MA. The formation of this transport barrier is related to a profound, spontaneous modification of the magnetic topology. Due to the occurrence of a saddle node bifurcation the plasma enters in the single helical axis state, which is theoretically known to be more resilient to chaos. This bifurcation is driven by the amplitude of the helical perturbation which dominates the mode spectrum.

  18. Hot magnetized nuclear matter: Thermodynamic and saturation properties

    NASA Astrophysics Data System (ADS)

    Rezaei, Z.; Bordbar, G. H.

    2017-03-01

    We have used a realistic nuclear potential, AV_{18}, and a many-body technique, the lowest-order constraint variational (LOCV) approach, to calculate the properties of hot magnetized nuclear matter. By investigating the free energy, spin polarization parameter, and symmetry energy, we have studied the temperature and magnetic field dependence of the saturation properties of magnetized nuclear matter. In addition, we have calculated the equation of state of magnetized nuclear matter at different temperatures and magnetic fields. It was found that the flashing temperature of nuclear matter decreases by increasing the magnetic field. In addition, we have studied the effect of the magnetic field on liquid gas phase transition of nuclear matter. The liquid gas coexistence curves, the order parameter of the liquid gas phase transition, and the properties of critical point at different magnetic fields have been calculated.

  19. Reversible “triple-Q” elastic field structures in a chiral magnet

    PubMed Central

    Hu, Yangfan; Wang, Biao

    2016-01-01

    The analytical solution of the periodic elastic fields in chiral magnets caused by presence of periodically distributed eigenstrains is obtained. For the skyrmion phase, both the periodic displacement field and the stress field are composed of three “triple-Q” structures with different wave numbers. The periodic displacement field, obtained by combining the three “triple-Q” displacement structures, is found to have the same lattice vectors with the magnetic skyrmion lattice. We find that for increasing external magnetic field, one type of “triple-Q” displacement structure and stress structure undergo a “configurational reversal”, where the initial and the final field configuration share similar pattern but with opposite direction of all the field vectors. The solution obtained is of fundamental significance for understanding the emergent mechanical properties of skyrmions in chiral magnets. PMID:27457629

  20. Loess 10Be evidence for an asynchronous Brunhes-Matuyama magnetic polarity reversal

    NASA Astrophysics Data System (ADS)

    Zhou, Weijian; Beck, J. Warren; Kong, Xianghui; An, Zhisheng; Qiang, Xiaoke; Wu, Zhenkun; Xian, Feng; Ao, Hong

    2015-04-01

    In Chinese loess the Brunhes-Matuyama (B-M) geomagnetic reversal appears to occur about 25 ka prior to the established axial dipole reversal age found in many marine sediments, i.e., in Chinese loess this magnetic reversal boundary is found in glacial loess unit L8 which is thought to be correlated with Marine Isotope Stage 20 (MIS 20), in marine sediment records, however, this boundary is commonly found in interglacial period of MIS 19 (Tauxe et al., 1996; Zhou and Shackleton, 1999), leading to the debate on uncertainties of paleoclimatic correlation between the Chinese loess-paleosol sequences and marine sediments (Wang et al., 2006; Liu et al., 2008; Jin and Liu, 2011). Based on this issue, here we propose to use the cosmogenic 10Be to address this conundrum. 10Be is a long-lived radionuclide produced in the atmosphere by cosmic ray spallation reactions and carried to the ground attached to aerosols. Its atmospheric production rate is inversely proportional to the geomagnetic field intensity (Masarik and Beer, 1999). This allows us to reconstruct past geomagnetic field intensity variations using 10Be concentrations recorded in different sedimentary archives. We carried out both the 10Be studies and paleogeomagnetic measurements in Luochuan and Xifeng sections in Chinese Loess Plateau. Both loess profiles show that 10Be production rate was at a maximum-an indication of the dipole field reversal-at ca. 780 ± 3 ka BP., in paleosol unit S7 corresponding to MIS 19, proving that the timing of B-M reversal recorded in Chinese loess is synchronous with that seen in marine records (Tauxe et al., 1996). These results reaffirmed the conventional paleoclimatic correlation of loess-paleosol sequences with marine isotope stages and the standard loess timescale as correct. However, it is ~25 ka younger than the age (depth) of the paleogeomagnetic measurements which show that the B-M boundary is in L8 in these two Chinese loess-paleosol sequences, demonstrating that loess

  1. Magnetic entrapment for fast, simple and reversible electrode modification with carbon nanotubes: application to dopamine detection.

    PubMed

    Baldrich, Eva; Gómez, Rodrigo; Gabriel, Gemma; Muñoz, Francesc Xavier

    2011-01-15

    Carbon nanotubes (CNT) have been exploited for an important number of electroanalytical and sensing purposes. Specifically, CNT incorporation to an electrode surface coating increases its roughness and area, provides electrocatalytic activity towards a variety of molecules, and improves electron transfer. This modification is generally based on the irreversible deposition of CNT on surface. Nevertheless, CNT are highly porous materials that might promote molecule non-specific adsorption and/or electrodeposition, which could induce sample-to-sample cross-contamination and affect measurement specificity and reproducibility. This drawback has been often circumvented by combining CNT with charged polymers able to repel molecules of opposed charge. We demonstrate that single-walled CNT (SWCNT) have a strong tendency to non-specifically adsorb onto the surface of protein-coated magnetic particles (MP). Magnetic capture of those MP generates CNT coentrapment and allows extremely fast, simple and reversible production of SWCNT electrodes. We have exploited this phenomenon for the production of modified screen-printed electrodes (MP/CNT-SPE), which have been characterized by Scanning Electron Microscopy. The surface has been additionally optimized by evaluating the electrochemical performance of SPE modified with different amounts and proportions of MP and CNT. The modified devices have then been used for dopamine detection. MP/CNT-SPE generated improved assay sensitivity, lower limit of detection, and up to 500% higher current signals than bare electrodes. Magnetic entrapment is proposed as a promising strategy for the fast, simple and reversible generation of nanostructured electrodes of enhanced performance within a few minutes and electrode re-utilisation by simple magnet removal and surface washing.

  2. Influence of domain structure induced coupling on magnetization reversal of Co/Pt/Co film with perpendicular anisotropy

    NASA Astrophysics Data System (ADS)

    Matczak, Michał; Schäfer, Rudolf; Urbaniak, Maciej; Kuświk, Piotr; Szymański, Bogdan; Schmidt, Marek; Aleksiejew, Jacek; Stobiecki, Feliks

    2017-01-01

    A magnetic multilayer of substrate/Pt-15 nm/Co-0.8 nm/Pt-wedge 0-7 nm/Co-0.6 nm/Pt-2 nm structure is characterized by a perpendicular anisotropy of the Co layers and by graded interlayer coupling between them. Using magnetooptical Kerr microscopy we observed a distinct influence of magnetic domains in one Co layer on the nucleation field and positions of nucleation sites of reversed domains in the second Co layer. For sufficiently strong interlayer coupling a replication of magnetic domains from the magnetically harder layer to the magnetically softer layer is observed.

  3. Tunable Magnetic Properties of Heterogeneous Nanobrush: From Nanowire to Nanofilm

    PubMed Central

    2010-01-01

    With a bottom-up assemble technology, heterogeneous magnetic nanobrushes, consisting of Co nanowire arrays and ferromagnetic Fe70Co30 nanofilm, have been fabricated using an anodic aluminum oxide template method combining with sputtering technology. Magnetic measurement suggests that the magnetic anisotropy of nanobrush depends on the thickness of Fe70Co30 layer, and its total anisotropy originates from the competition between the shape anisotropy of nanowire arrays and nanofilm. Micromagnetic simulation result indicates that the switching field of nanobrush is 1900 Oe, while that of nanowire array is 2700 Oe. These suggest that the nanobrush film can promote the magnetization reversal processes of nanowire arrays in nanobrush. PMID:20672098

  4. Performance comparison of three-phase flux reversal permanent magnet motors in BLDC and BLAC operation mode

    NASA Astrophysics Data System (ADS)

    Štumberger, B.; Štumberger, G.; Hadžiselimović, M.; Hamler, A.; Goričan, V.; Jesenik, M.; Trlep, M.

    The paper presents a comparison of torque capability and flux-weakening performance of three-phase flux reversal permanent magnet motors with surface and inset permanent magnets. Finite element analysis is employed to determine the performance of each motor in BLDC and BLAC operation mode. It is shown that the torque capability and flux-weakening performance of surface or inset permanent magnet configuration is strongly dependent on the stator teeth number/rotor pole number combination.

  5. Hexaferrite M (Co, Ti) magnetic properties optimization

    SciTech Connect

    Autissier, D.; Rousselle, D.; Podembski, A.

    1995-09-01

    Barium hexaferrites are anisotropic iron oxides which can present high values of permeability. We have studied Ba (Co, Ti){sub x}Fe{sub 12-2x}O{sub 19} compositions. Powders are synthesized using the ceramic method: stoichiometric amounts of basic components are ground and fired at high temperature (1170{degrees}C) to obtain the desired phase. The powders are then ground for 6 hours in order to reduce the particle size. The slurry is cast in a plaster matrix. This matrix is rotated between the poles of a stationary electromagnet. Fields of approximately 500 Oe are used for the orientation procedure. Samples are then sintered for different temperatures between 1200 and 1300{degrees}C. We present results (magnetization, permeability, permittivity, orientation rate) obtained for diverse compositions (1.1magnetic properties, orientation rate, microstructure.

  6. Chitosan-coated magnetic nanoparticles prepared in one step by reverse microemulsion precipitation.

    PubMed

    López, Raúl G; Pineda, María G; Hurtado, Gilberto; León, Ramón Díaz de; Fernández, Salvador; Saade, Hened; Bueno, Darío

    2013-09-27

    Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%-7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49-53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb2+ removal from a Pb(NO3)2 aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water.

  7. Chitosan-Coated Magnetic Nanoparticles Prepared in One Step by Reverse Microemulsion Precipitation

    PubMed Central

    López, Raúl G.; Pineda, María G.; Hurtado, Gilberto; de León, Ramón Díaz; Fernández, Salvador; Saade, Hened; Bueno, Darío

    2013-01-01

    Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%–7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49–53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb2+ removal from a Pb(NO3)2 aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water. PMID:24084716

  8. Probe measurements of the three-dimensional magnetic field structure in a rotating magnetic field sustained field-reversed configuration

    SciTech Connect

    Velas, K. M.; Milroy, R. D.

    2014-01-15

    A translatable three-axis probe was constructed and installed on the translation, confinement, and sustainment upgrade (TCSU) experiment. With ninety windings, the probe can simultaneously measure B{sub r}, B{sub θ}, and B{sub z} at 30 radial positions, and can be placed at any desired axial position within the field reversed configuration (FRC) confinement chamber. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Measurements were made for odd-parity rotating magnetic field (RMF) antennas and even-parity RMF. The steady state data from applying a 10 kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Comparisons will be made to the 3D magnetic structure predicted by NIMROD simulations, with parameters adjusted to match that of the TCSU experiments. The probe provides sufficient data to utilize a Maxwell stress tensor approach to directly measure the torque applied to the FRC's electrons, which combined with a resistive torque model, yields an estimate of the average FRC resistivity.

  9. Probe measurements of the three-dimensional magnetic field structure in a rotating magnetic field sustained field-reversed configuration

    NASA Astrophysics Data System (ADS)

    Velas, K. M.; Milroy, R. D.

    2014-01-01

    A translatable three-axis probe was constructed and installed on the translation, confinement, and sustainment upgrade (TCSU) experiment. With ninety windings, the probe can simultaneously measure Br, Bθ, and Bz at 30 radial positions, and can be placed at any desired axial position within the field reversed configuration (FRC) confinement chamber. Positioning the probe at multiple axial positions and taking multiple repeatable shots allows for a full r-z map of the magnetic field. Measurements were made for odd-parity rotating magnetic field (RMF) antennas and even-parity RMF. The steady state data from applying a 10 kHz low pass filter used in conjunction with data at the RMF frequency yields a map of the full 3D rotating field structure. Comparisons will be made to the 3D magnetic structure predicted by NIMROD simulations, with parameters adjusted to match that of the TCSU experiments. The probe provides sufficient data to utilize a Maxwell stress tensor approach to directly measure the torque applied to the FRC's electrons, which combined with a resistive torque model, yields an estimate of the average FRC resistivity.

  10. Variation of Magnetic Fluctuation due to Gas Puffing in Edge Region of Reversed-Field Pinch Plasma

    NASA Astrophysics Data System (ADS)

    Yambe, Kiyoyuki; Hirano, Yoichi; Sakakita, Hajime; Koguchi, Haruhisa

    2016-09-01

    We measured the variation of magnetic and electrostatic fluctuations observed during the gas puffing in the edge region of the toroidal pinch experiment-reversed experiment (TPE-RX) reversed-field pinch plasma. In the short period in which the electron density increased slowly just after the gas puffing, the confinement of fast electrons in the core region was maintained by the decrease in the fast radial magnetic fluctuation with the deepening of the reversal of the toroidal field. During the following period in which the electron density increased rapidly, the radial gradient of electron density decreased, and the loss of fast electrons from the core region increased owing to the increase in the toroidal and radial magnetic fluctuations in the high-frequency band, although the poloidal magnetic fluctuation decreased. Therefore, the confinement of fast electrons would be maintained by keeping the radial gradient of plasma thermal pressure with a moderate neutral particle supply of small quantity in a short time.

  11. Reverse Polarity Magnetized Melt Rocks from the Cretaceous/Tertiary Chicxulub Structure, Yucatan Peninsula, Mexico

    NASA Technical Reports Server (NTRS)

    Urrutia-Fucugauchi, J.; Marin, Luis; Sharpton, Virgil L.

    1994-01-01

    We report paleomagnetic results for core samples of the breccia and andesitic rocks recovered from the Yucatan-6 Petrolcos Mexicanos exploratory well within the Chicxulub structure (about 60 km SSW from its center), northern Yucatan, Mexico. A previous study has shown that the rocks studied contain high iridium levels and shocked breccia clasts and an Ar/Ar date of 65.2 +/- 0.4 Ma. Andesitic rocks are characterized by stable single-component magnetizations with a mean inclination of -42.6 deg +/- 2.4 deg. Breccias present a complex paleomagnetic record characterized by multivectorial magnetizations with widely different initial NRM inclinations. However, after alternating field demagnetization, well defined characteristic components with upward inclinations are defined. IRM acquisition experiments, comparison of IRM and NRM coercivity spectra and the single component magnetization of the andesitic rocks indicate the occurrence of iron-rich titanomagnetites of single or pseudo-single domain states as the dominant magnetic carriers. Mean inclinations from the andesitic rocks and most of the breccia samples give a mean inclination of about -40 deg to -45 deg, indicating a reverse polarity for the characteristic magnetization that is consistent with geomagnetic chron 29R, which spans the Cretaceous/Tertiary (K/T) boundary. The inclination is also consistent with the expected value (and corresponding paleolatitude) for the site estimated from the reference polar wander curve for North America. We suggest that the characteristic magnetizations for the andesitic and breccia rocks are the result of shock heating at the time of formation of the impact structure and that the age, polarity and pateolatitude are consistent with a time at the K/T boundary.

  12. Correlation Between Microstructure and Mechanical Properties Before and After Reversion of Metastable Austenitic Stainless Steels

    NASA Astrophysics Data System (ADS)

    Fargas, Gemma; Zapata, Ana; Roa, Joan Josep; Sapezanskaia, Ina; Mateo, Antonio

    2015-12-01

    Reversion treatments are a way to improve the mechanical response of metastable austenitic stainless steels by means of grain refinement. To effectively apply those treatments, the steel must be previously deformed to induce a significant amount of martensitic transformation. In this work, the effect of reversion treatments was studied on a commercial AISI 301LN grade subjected to an industrial cold rolling process, with thickness reductions not higher than 40 pct. Microstructural changes and evolution of both monotonic and cyclic mechanical properties were investigated after cold rolling and upon reversion treatments. Results revealed that the finer austenitic microstructure obtained after reversion leads to an interesting combination of properties, with strong increments in hardness and yield strength, and also fatigue limit improvement, as compared to the initial annealed condition.

  13. Direct observation of magnetic phase coexistance and magnetization reversal in a Gd0.67Ca0.33MnO3 thin film

    SciTech Connect

    Kim J.; Nazaretski E.; Haberkorn, N.; Civale, L.; Dowden, P.; Saxena, A.; Thompson, J.D. & Movshovich, R.

    2012-01-11

    We have investigated the ferrimagnetic domain structure in a Gd{sub 0.67}Ca{sub 0.33}MnO{sub 3} thin film using magnetic force microscopy. We observe clear signs of phase separation, with magnetic islands embedded in a non-magnetic matrix. We also directly visualize the reversal of magnetization of ferrimagnetic domains as a function of temperature and attribute it to a change in the balance of magnetization of anti-aligned Mn and Gd sublattices.

  14. Combinatorial exploration of rare-earth-free permanent magnets: Magnetic and microstructural properties of Fe-Co-W thin films

    NASA Astrophysics Data System (ADS)

    Gao, T. R.; Wu, Y. Q.; Fackler, S.; Kierzewski, I.; Zhang, Y.; Mehta, A.; Kramer, M. J.; Takeuchi, I.

    2013-01-01

    We have investigated the magnetic and structural properties of Fe-Co-W films using a composition spread technique. From the magnetometry measurements, large magnetization (900 emu/cm3) and enhanced perpendicular coercive fields (2-3 kOe) of low W concentration films were observed. The synchrotron diffraction results show a structural transition from a crystalline to an amorphous state and the crystallization onset increases with increasing W concentration. The SEM and TEM characterizations show that the films with low W concentrations have vertically standing platelet-like grain structures which is ascribed to the enhanced coercive fields. Magnetometry studies indicate that as the W concentration increases, microstructural change results in evolution of magnetization reversal mechanism.

  15. Delay coordinates: a sensitive indicator of nonlinear dynamics in single charged particle motion in magnetic reversals

    NASA Astrophysics Data System (ADS)

    Chapman, Sandra C.; Watkins, Nicholas W.

    1995-08-01

    The delay coordinate technique is examined as an indicator of the regime of particle dynamics for the system of single charged particle motion in magnetic reversals. Examples of numerically integrated trajectories in both static (zero electric field) and time dependent (corresponding nonzero induction electric field) simple models for magnetic reversals are considered. In the static case, the dynamics can in principle be directly classified by constructing Poincaré surfaces of section; here we demonstrate that whilst the Poincaré surface contains the relevant information to classify the dynamics, the corresponding delay coordinate plot can provide a far more sensitive indication of the onset of nonregular behaviour. In the case of nonperiodic time dependence considered here Poincaré plots cannot in general be constructed directly. Nevertheless, delay coordinate plots can still reveal details of the phase space portrait of the system, and here are shown to indicate whether segments of stochastic motion exist in a given trajectory. It is anticipated that the delay coordinate plot technique as realized here will be a valuable tool in characterizing the behaviour in large numbers of trajectories that are evolved in time-dependent systems, thereby giving us insight into the evolution of the distribution function as a whole, either in prescribed fields or in self-consistent numerical simulations.

  16. Aging-reversing properties of thyrotropin-releasing hormone.

    PubMed

    Pierpaoli, Walter

    2013-02-01

    Thyrotropin-releasing hormone (TRH) aroused our interest when we were engaged in related experiments, so we decided to study its effects on organs, tissues, and aging-related metabolic and hormonal markers when administered in acute or chronic (oral) doses at various time points in its cyclic circadian pattern. We also wanted to determine what effects, if any, it had on aging processes in two essential systems, namely gonadal-reproductive and kidney-urinary. Our results show positive changes as a result of short-term acute and long-term chronic oral administration of TRH to old mice that included rapid correction to more juvenile levels of most typical aging-related hormonal and metabolic measurements. Remarkably, testes function was maintained by means of a 4-month oral treatment with TRH in aging mice. As we suspected upon seeing a significant increase in testes weight, TRH resulted in maintenance or even reconstitution of testes structure and function when administered in the drinking water. This was demonstrated by the active formation and proliferation of mature spermatogonia and the intensive spermatogenesis in the follicles. The same TRH treatment led to protection for the kidneys from amyloid and hyalin infiltration of tubuli and glomeruli, which typically occurs in aging mice. In fact, we observed massive deposits of amyloid and hyalin material infiltrating the shrunken glomeruli and negatively affecting filtration capacity of the untreated mice, whereas this was barely present in the TRH-treated mice. Advanced hyalin degeneration could also be observed in the tubular vessels of the untreated control mice. These experiments with TRH supplementation show clear aging-delaying and apparently even aging-reversing effects of the neuropeptide, whether it was administered parenterally or orally. TRH, like melatonin, is an anti-aging agent with a broad spectrum of activities that, because of their actions, suggest that TRH has a fundamental role in the regulation

  17. Synthesis of magnetic nickel spinel ferrite nanospheres by a reverse emulsion-assisted hydrothermal process

    SciTech Connect

    Zhang Jilin; Shi Jianxin; Gong Menglian

    2009-08-15

    Nickel ferrite nanospheres were successfully synthesized by a reverse emulsion-assisted hydrothermal method. The reverse emulsion was composed of water, cetyltrimethyl ammonium bromide, polyoxyethylene(10)nonyl phenyl ether, iso-amyl alcohol and hexane. During the hydrothermal process, beta-FeO(OH) and Ni{sub 0.75}Fe{sub 0.25}(CO{sub 3}){sub 0.125}(OH){sub 2}.0.38H{sub 2}O (INCHH) nanorods formed first and then transformed into nickel spinel ferrite nanospheres. The phase transformation mechanism is proposed based on the results of X-ray powder diffraction, transmission electron microscopy and energy-dispersive X-ray spectroscopy, etc. Nickel ferrite may form at the end of the INCHH nanorods or from the solution accompanied by the dissolution of beta-FeO(OH) and INCHH nanorods. The X-ray photoelectron spectroscopy analysis shows that a few Fe{sup 3+} ions have been reduced to Fe{sup 2+} ions during the formation of nickel ferrite. The maximum magnetization of the nickel ferrite nanospheres obtained after hydrothermal reaction for 30 h is 55.01 emu/g, which is close to that of bulk NiFe{sub 2}O{sub 4}. - Graphical abstract: Nickel ferrite nanospheres were obtained through a reverse emulsion-assisted hydrothermal process. The phase transformation as a function of reaction time was studied based on the XRD, TEM and EDS analyses.

  18. Microchemistry and magnetization reversal mechanism in melt-spun 2:17-type Sm-Co magnets

    NASA Astrophysics Data System (ADS)

    Yan, A.; Gutfleisch, O.; Gemming, T.; Müller, K.-H.

    2003-09-01

    The stability of microstructure and of microchemistry in melt-spun precipitation-hardened Sm(Co,Fe,Cu,Zr)z magnets at high temperature and its effect on the magnetic properties, especially the coercivity at room temperature, were investigated by transmission electron microscopy, nanoprobe chemical analysis, and magnetic measurements. A very large gradient of the Cu content within the 1:5-type cell boundary phase was observed in highly coercive melt-spun Sm(Co,Fe,Cu,Zr)z magnets with uniform cellular structure. After an additional isothermal aging at 850 °C for 5 min, the coercivity is reduced dramatically from 3 T to 0.16 T. This is accompanied by the disappearance of the large gradient of Cu content within the cell boundary phase. Thus, it is proposed that the high coercivity in 2:17 Sm-Co magnets originates from the large gradient of domain wall energy within the Sm(Co,Cu)5 cell boundary phase. This gradient is caused by a very rapid phase separation taking place within the cell boundary phase during slow cooling.

  19. Loess 10Be evidence for an asynchronous Brunhes-Matuyama magnetic polarity reversal

    NASA Astrophysics Data System (ADS)

    Zhou, W.; Beck, W.; Kong, X.; An, Z.; Qiang, X.; Wu, Z.; Xian, F.; Ao, H.

    2015-12-01

    In Chinese loess the Brunhes-Matuyama (B-M) geomagnetic reversal appears to occur about 25 ka prior to the established axial dipole reversal age found in many marine sediments, i.e., in Chinese loess this magnetic reversal boundary is found in glacial loess unit L8 which is thought to be correlated with Marine Isotope Stage 20 (MIS 20), in marine sediment records, however, this boundary is commonly found in interglacial period of MIS 19[1-2], leading to the debate on uncertainties of paleoclimatic correlation between the Chinese loess-paleosol sequences and marine sediments[3-5]. Based on this issue, here we propose to use the cosmogenic 10Be to address this conundrum. 10Be is a long-lived radionuclide produced in the atmosphere by cosmic ray spallation reactions and carried to the ground attached to aerosols. Its atmospheric production rate is inversely proportional to the geomagnetic field intensity [6]. This allows us to reconstruct past geomagnetic field intensity variations using 10Be concentrations recorded in different sedimentary archives. We carried out both the 10Be studies and paleogeomagnetic measurements in Luochuan and Xifeng sections in Chinese Loess Plateau. Both loess profiles show that 10Be production rate was at a maximum-an indication of the dipole field reversal-at ca. 780 ± 3 ka BP., in paleosol unit S7 corresponding to MIS 19, proving that the timing of B-M reversal recorded in Chinese loess is synchronous with that seen in marine records [1]. These results reaffirmed the conventional paleoclimatic correlation of loess-paleosol sequences with marine isotope stages and the standard loess timescale as correct. However, it is ~25 ka younger than the age (depth) of the paleogeomagnetic measurements, which show that the B-M boundary is in L8 in these two Chinese loess-paleosol sequences, demonstrating that loess magnetic overprinting has occurred. 1.Tauxe, L., et al., 1996, EARTH PLANET SC LETT, 140, 133-1462.Zhou, L.P., and Shackleton, 1999

  20. Magnetic Properties of Lunar Geologic Terranes: New Statistical Results

    NASA Technical Reports Server (NTRS)

    Halekas, J. S.; Mitchell, D. L.; Lin, R. P.; Frey, S.; Hood, L. L.; Acuna, M. H.; Binder, A.

    2002-01-01

    We use global magnetic field data and digitized geologic maps to determine the magnetic properties of lunar terranes. Average fields vary by a factor of 100 from demagnetized impact basins and craters to strongly magnetized antipodal regions. Additional information is contained in the original extended abstract.

  1. 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

  2. Magnetization reversal in mixed ferrite-chromite perovskites with non magnetic cation on the A-site

    NASA Astrophysics Data System (ADS)

    Billoni, Orlando V.; Pomiro, Fernando; Cannas, Sergio A.; Martin, Christine; Maignan, Antoine; Carbonio, Raul E.

    2016-11-01

    In this work, we have performed Monte Carlo simulations in a classical model for RFe1-x Cr x O3 with R  =  Y and Lu, comparing the numerical simulations with experiments and mean field calculations. In the analyzed compounds, the antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak ferromagnetism due to a canting of the antiferromagnetically ordered spins. This model is able to reproduce the magnetization reversal (MR) observed experimentally in a field cooling process for intermediate x values and the dependence with x of the critical temperatures. We also analyzed the conditions for the existence of MR in terms of the strength of DM interactions between Fe3+ and Cr3+ ions with the x values variations.

  3. Magnetization reversal in mixed ferrite-chromite perovskites with non magnetic cation on the A-site.

    PubMed

    Billoni, Orlando V; Pomiro, Fernando; Cannas, Sergio A; Martin, Christine; Maignan, Antoine; Carbonio, Raul E

    2016-11-30

    In this work, we have performed Monte Carlo simulations in a classical model for RFe1-x Cr x O3 with R  =  Y and Lu, comparing the numerical simulations with experiments and mean field calculations. In the analyzed compounds, the antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak ferromagnetism due to a canting of the antiferromagnetically ordered spins. This model is able to reproduce the magnetization reversal (MR) observed experimentally in a field cooling process for intermediate x values and the dependence with x of the critical temperatures. We also analyzed the conditions for the existence of MR in terms of the strength of DM interactions between Fe(3+) and Cr(3+) ions with the x values variations.

  4. Magnetic properties of biomineral particles produced by bacteria Klebsiella oxytoca

    NASA Astrophysics Data System (ADS)

    Raĭkher, Yu. L.; Stepanov, V. I.; Stolyar, S. V.; Ladygina, V. P.; Balaev, D. A.; Ishchenko, L. A.; Balasoiu, M.

    2010-02-01

    Ferrihydrite nanoparticles (2-5 nm in size) produced by bacteria Klebsiella oxytoca in the course of biomineralization of iron salt solutions from a natural medium exhibit unique magnetic properties: they are characterized by both the antiferromagnetic order inherent in a bulk ferrihydrite and the spontaneous magnetic moment due to the decompensation of spins in sublattices of a nanoparticle. The magnetic susceptibility enhanced by the superantiferromagnetism effect and the magnetic moment independent of the magnetic field provide the possibility of magnetically controlling these natural objects. This has opened up the possibilities for their use in nanomedicine and bioengineering. The results obtained from measurements of the magnetic properties of the ferrihydrite produced by Klebsiella oxytoca in its two main crystalline modifications are reported, and the data obtained are analyzed theoretically. This has made it possible to determine numerical values of the magnetic parameters of real biomineral nanoparticles.

  5. Modeling of magnetic properties of polymer bonded Nd-Fe-B magnets with surface modifications

    NASA Astrophysics Data System (ADS)

    Xiao, Jun; Otaigbe, Joshua U.; Jiles, David C.

    2000-07-01

    The effects of surface modification on the magnetic properties of polymer-bonded Nd-Fe-B magnets have been studied. Two sets of Nd-Fe-B powders, coated and uncoated, were blended and compression molded with polyphenylene sulfide in isotropic form. Their magnetic properties were measured using a Helmholtz coil and a SQUID. The results showed that the effect of the coating significantly improved the irreversible loss in flux and energy product of the polymer-bonded magnets. The results have been interpreted using an isotropic model of hysteresis that takes into account energy losses. The modeling showed that the presence of soft magnetic materials in the Nd-Fe-B powders caused by oxidation reduces the interaction among magnetic particles, however, the coating treatment alters the magnetic properties by increasing the remanence of polymer-bonded magnets via increasing the interparticle coupling coefficient.

  6. Magnetic properties of superconducting Bi/Ni bilayers

    NASA Astrophysics Data System (ADS)

    Zhou, Hexin; Gong, Xinxin; Jin, Xiaofeng

    2017-01-01

    The magnetic properties of an unexpected superconducting bilayer consisting of non-superconducting Bi and ferromagnetic Ni have been investigated. A large magnetization signal is observed when the sample is cooled below the superconducting transition temperature in zero magnetic field, which has the same direction with the magnetization of the adjacent Ni layer. Interestingly, this Bi/Ni bilayer shows opposite responses to external magnetic field in zero field cooling (ZFC) process and field cooling (FC) process. It behaves diamagnetically in ZFC while paramagnetically in FC. Besides, magnetic hysteresis loops below the superconducting transition temperature show flux pinning and flux jumping effects.

  7. Modeling and measurements of magnetic stochasticity and transport in the MST reversed field pinch

    NASA Astrophysics Data System (ADS)

    Hudson, Ben

    2002-11-01

    Results from experimental measurements and modeling of stochastic transport are beginning to agree. The modeling was done with a field line tracing code, which uses spatial profiles from a 3-D nonlinear MHD code, DEBS, and incorporates experimentally measured edge fluctuations. The modeling finds good agreement with Rechester - Rosenbluth diffusion just inside the reversal surface, where the islands highly overlap, and diverges from Rechester - Rosenbluth elsewhere. Electron heat transport is measured experimentally and agrees with the model to within a factor of three. Measurements of the drop in electron thermal transport in plasmas where fluctuations are suppressed by current profile manipulation are in agreement with the model. Recent measurements of the confinement of run-away electrons observed in the core suggest reformation of magnetic flux surfaces from a previously stochastic field. The modeling clearly shows this transition in profiles of radial magnetic field line diffusion. In addition we have started modeling of fast ion motion and new results on the effect of magnetic field stochasticity on the ion confinement will be reported. Work supported by U.S. D.O.E.

  8. Magnetization reversal mechanism in patterned (square to wave-like) Py antidot lattices

    NASA Astrophysics Data System (ADS)

    Tahir, N.; Zelent, M.; Gieniusz, R.; Krawczyk, M.; Maziewski, A.; Wojciechowski, T.; Ding, J.; Adeyeye, A. O.

    2017-01-01

    The effects of shape and geometry of antidot (square, bi-component, and wave-like) lattices (ADLs) on the magnetization reversal processes and magnetic anisotropy has been systematically investigated by magneto-optical Kerr effect based microscopy. Our experimental results were reproduced by micromagnetic simulations, which highlight the qualitative agreement with the experimental results. We have demonstrated that a small antidot in the center of a unit cell in the square ADL is sufficient to induce additional easy axes with large coercive fields. In wave-like patterns, narrow channels connecting smaller and larger antidots (bi-component ADL) further drastically change the anisotropy map, creating the high coercive fields along a wide angular range (90°) of directions parallel to the channels. In simulated results, we have observed formation of periodic domain structures in all ADLs, however, in the case of a wave-like pattern it is most regular and moreover two different periodic patterns are stabilized at different applied magnetic field values. The formation of 360° domain walls were also observed in wave-like ADL where these domains are formed along the lines connecting adjacent larger and smaller antidots, perpendicular to the channels. These findings point out the possibility of exploiting ADLs with complex unit cells in magnonic or spintronic applications.

  9. Evolution of magnetic properties and exchange interactions in Ru doped YbCrO3

    NASA Astrophysics Data System (ADS)

    Dalal, Biswajit; Sarkar, Babusona; Ashok, Vishal Dev; De, S. K.

    2016-10-01

    Magnetic properties of YbCr1-x Ru x O3 as a function of temperature and magnetic field have been investigated to explore the intriguing magnetic phenomena in rare-earth orthochromites. A quantitative analysis of x-ray photoelectron spectroscopy confirms the mixed valence state (Yb3+ and Yb2+) of Yb ions for the highest doped sample. Field-cooled magnetization reveals a broad peak around 75 K and then becomes zero at about 20-24 K, due to the antiparallel coupling between Cr3+ and Yb3+ moments. An increase of the Ru4+ ion concentration leads to a slight increase of compensation temperature T comp from 20 to 24 K, but the Néel temperature remains constant. A larger value of the magnetic moment of Yb ions gives rise to negative magnetization at low temperature. An external magnetic field significantly modifies the temperature dependent magnetization. Simulation of temperature dependent magnetization data, below T N, based on the three (two) magnetic sub-lattice model predicts stronger intra-sublattice exchange interaction than that of inter-sublattice. Thermal hysteresis and Arrot plots suggest first order magnetic phase transition. Random substitution of Ru4+ ion reduces the magnetic relaxation time. Weak ferromagnetic component in canted antiferromagnetic system and negative internal magnetic field cause zero-field-cooled exchange bias effect. Large magnetocrystalline anisotropy associated with Ru creates high coercivity in the Ru doped sample. A maximum value of magnetocaloric effect is found around the antiferromagnetic ordering of Yb3+ ions. Antiferromagnetic transition at about 120 K and temperature induced magnetization reversal lead to normal and inverse magnetocaloric effects in the same material.

  10. Influencing the properties of dysprosium single-molecule magnets with phosphorus donor ligands.

    PubMed

    Pugh, Thomas; Tuna, Floriana; Ungur, Liviu; Collison, David; McInnes, Eric J L; Chibotaru, Liviu F; Layfield, Richard A

    2015-07-01

    Single-molecule magnets are a type of coordination compound that can retain magnetic information at low temperatures. Single-molecule magnets based on lanthanides have accounted for many important advances, including systems with very large energy barriers to reversal of the magnetization, and a di-terbium complex that displays magnetic hysteresis up to 14 K and shows strong coercivity. Ligand design is crucial for the development of new single-molecule magnets: organometallic chemistry presents possibilities for using unconventional ligands, particularly those with soft donor groups. Here we report dysprosium single-molecule magnets with neutral and anionic phosphorus donor ligands, and show that their properties change dramatically when varying the ligand from phosphine to phosphide to phosphinidene. A phosphide-ligated, trimetallic dysprosium single-molecule magnet relaxes via the second-excited Kramers' doublet, and, when doped into a diamagnetic matrix at the single-ion level, produces a large energy barrier of 256 cm(-1) and magnetic hysteresis up to 4.4 K.

  11. Influencing the properties of dysprosium single-molecule magnets with phosphorus donor ligands

    PubMed Central

    Pugh, Thomas; Tuna, Floriana; Ungur, Liviu; Collison, David; McInnes, Eric J.L.; Chibotaru, Liviu F.; Layfield, Richard A.

    2015-01-01

    Single-molecule magnets are a type of coordination compound that can retain magnetic information at low temperatures. Single-molecule magnets based on lanthanides have accounted for many important advances, including systems with very large energy barriers to reversal of the magnetization, and a di-terbium complex that displays magnetic hysteresis up to 14 K and shows strong coercivity. Ligand design is crucial for the development of new single-molecule magnets: organometallic chemistry presents possibilities for using unconventional ligands, particularly those with soft donor groups. Here we report dysprosium single-molecule magnets with neutral and anionic phosphorus donor ligands, and show that their properties change dramatically when varying the ligand from phosphine to phosphide to phosphinidene. A phosphide-ligated, trimetallic dysprosium single-molecule magnet relaxes via the second-excited Kramers' doublet, and, when doped into a diamagnetic matrix at the single-ion level, produces a large energy barrier of 256 cm−1 and magnetic hysteresis up to 4.4 K. PMID:26130418

  12. Magnetization reversal and giant coercivity in Co(Cr0.7Mn0.3)2O4

    NASA Astrophysics Data System (ADS)

    Padam, R.; Kumar, R.; Grover, A. K.; Pal, D.

    2014-04-01

    We demonstrate the evaluation of temperature and magnetic field dependent magnetization of single phase sample of cubic spinel Co(Cr0.7Mn0.3(2O4. It has been noticed that 30% Mn substitution for Cr in CoCr2O4 leads to the huge reversal of temperature dependent magnetization below compensation temperature, Tcomp ˜ 82.9 K. In addition to this, sample is found to exhibit giant coercivity, reaching about 1.54 T at 3K, similar to hard magnetic materials. These intriguing phenomena are ascribed to the presence of magneto-crystalline anisotropy in the sample.

  13. Resonant vortex-core reversal in magnetic nano-spheres as robust mechanism of efficient energy absorption and emission

    NASA Astrophysics Data System (ADS)

    Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Jae-Hyeok; Kim, Min-Kwan

    2016-08-01

    We report on novel vortex-core reversal dynamics in nano-spheres of single-vortex spin configuration as revealed by micromagnetic simulations combined with analytical derivations. When the frequency of an AC magnetic field is tuned to the frequency of the vortex-core precession around the direction of a given static field, oscillatory vortex-core reversals occur, and additionally, the frequency is found to change with both the strength of the applied AC field and the particle size. Such resonant vortex-core reversals in nano-spheres may provide a new and efficient means of energy absorption by, and emission from, magnetic nanoparticles, which system can be effectively implemented in bio-applications such as magnetic hyperthermia.

  14. Resonant vortex-core reversal in magnetic nano-spheres as robust mechanism of efficient energy absorption and emission

    PubMed Central

    Kim, Sang-Koog; Yoo, Myoung-Woo; Lee, Jehyun; Lee, Jae-Hyeok; Kim, Min-Kwan

    2016-01-01

    We report on novel vortex-core reversal dynamics in nano-spheres of single-vortex spin configuration as revealed by micromagnetic simulations combined with analytical derivations. When the frequency of an AC magnetic field is tuned to the frequency of the vortex-core precession around the direction of a given static field, oscillatory vortex-core reversals occur, and additionally, the frequency is found to change with both the strength of the applied AC field and the particle size. Such resonant vortex-core reversals in nano-spheres may provide a new and efficient means of energy absorption by, and emission from, magnetic nanoparticles, which system can be effectively implemented in bio-applications such as magnetic hyperthermia. PMID:27531408

  15. Magnetic Properties of Strontium Hexaferrite Nanostructures Measured with Magnetic Force Microscopy

    PubMed Central

    Li, Qiang; Song, Jie; Saura-Múzquiz, Matilde; Besenbacher, Flemming; Christensen, Mogens; Dong, Mingdong

    2016-01-01

    Magnetic property is one of the important properties of nanomaterials. Direct investigation of the magnetic property on the nanoscale is however challenging. Herein we present a quantitative measurement of the magnetic properties including the magnitude and the orientation of the magnetic moment of strontium hexaferrite (SrFe12O19) nanostructures using magnetic force microscopy (MFM) with nanoscale spatial resolution. The measured magnetic moments of the as-synthesized individual SrFe12O19 nanoplatelets are on the order of ~10−16 emu. The MFM measurements further confirm that the magnetic moment of SrFe12O19 nanoplatelets increases with increasing thickness of the nanoplatelet. In addition, the magnetization directions of nanoplatelets can be identified by the contrast of MFM frequency shift. Moreover, MFM frequency imaging clearly reveals the tiny magnetic structures of a compacted SrFe12O19 pellet. This work demonstrates the mesoscopic investigation of the intrinsic magnetic properties of materials has a potential in development of new magnetic nanomaterials in electrical and medical applications. PMID:27174466

  16. Magnetic Properties of Strontium Hexaferrite Nanostructures Measured with Magnetic Force Microscopy.

    PubMed

    Li, Qiang; Song, Jie; Saura-Múzquiz, Matilde; Besenbacher, Flemming; Christensen, Mogens; Dong, Mingdong

    2016-05-13

    Magnetic property is one of the important properties of nanomaterials. Direct investigation of the magnetic property on the nanoscale is however challenging. Herein we present a quantitative measurement of the magnetic properties including the magnitude and the orientation of the magnetic moment of strontium hexaferrite (SrFe12O19) nanostructures using magnetic force microscopy (MFM) with nanoscale spatial resolution. The measured magnetic moments of the as-synthesized individual SrFe12O19 nanoplatelets are on the order of ~10(-16) emu. The MFM measurements further confirm that the magnetic moment of SrFe12O19 nanoplatelets increases with increasing thickness of the nanoplatelet. In addition, the magnetization directions of nanoplatelets can be identified by the contrast of MFM frequency shift. Moreover, MFM frequency imaging clearly reveals the tiny magnetic structures of a compacted SrFe12O19 pellet. This work demonstrates the mesoscopic investigation of the intrinsic magnetic properties of materials has a potential in development of new magnetic nanomaterials in electrical and medical applications.

  17. Magnetic Properties of Strontium Hexaferrite Nanostructures Measured with Magnetic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Song, Jie; Saura-Múzquiz, Matilde; Besenbacher, Flemming; Christensen, Mogens; Dong, Mingdong

    2016-05-01

    Magnetic property is one of the important properties of nanomaterials. Direct investigation of the magnetic property on the nanoscale is however challenging. Herein we present a quantitative measurement of the magnetic properties including the magnitude and the orientation of the magnetic moment of strontium hexaferrite (SrFe12O19) nanostructures using magnetic force microscopy (MFM) with nanoscale spatial resolution. The measured magnetic moments of the as-synthesized individual SrFe12O19 nanoplatelets are on the order of ~10-16 emu. The MFM measurements further confirm that the magnetic moment of SrFe12O19 nanoplatelets increases with increasing thickness of the nanoplatelet. In addition, the magnetization directions of nanoplatelets can be identified by the contrast of MFM frequency shift. Moreover, MFM frequency imaging clearly reveals the tiny magnetic structures of a compacted SrFe12O19 pellet. This work demonstrates the mesoscopic investigation of the intrinsic magnetic properties of materials has a potential in development of new magnetic nanomaterials in electrical and medical applications.

  18. Magnetism in nanoparticles: tuning properties with coatings.

    PubMed

    Crespo, Patricia; de la Presa, Patricia; Marín, Pilar; Multigner, Marta; Alonso, José María; Rivero, Guillermo; Yndurain, Félix; González-Calbet, José María; Hernando, Antonio

    2013-12-04

    This paper reviews the effect of organic and inorganic coatings on magnetic nanoparticles. The ferromagnetic-like behaviour observed in nanoparticles constituted by materials which are non-magnetic in bulk is analysed for two cases: (a) Pd and Pt nanoparticles, formed by substances close to the onset of ferromagnetism, and (b) Au and ZnO nanoparticles, which were found to be surprisingly magnetic at the nanoscale when coated by organic surfactants. An overview of theories accounting for this unexpected magnetism, induced by the nanosize influence, is presented. In addition, the effect of coating magnetic nanoparticles with biocompatible metals, oxides or organic molecules is also reviewed, focusing on their applications.

  19. Magnetization reversal of a Nd-Cu-infiltrated Nd-Fe-B nanocrystalline magnet observed with small-angle neutron scattering

    SciTech Connect

    Saito, Kotaro Ono, Kanta; Ueno, Tetsuro; Yano, Masao; Shoji, Tetsuya; Sakuma, Noritsugu; Manabe, Akira; Kato, Akira; Harada, Masashi; Keiderling, Uwe

    2015-05-07

    The magnetization reversal process of Nd-Fe-B nanocrystalline magnets infiltrated with Nd-Cu alloy was examined using small-angle neutron scattering (SANS). The magnetic-field dependence of SANS intensity revealed a qualitative difference between Nd-Cu-infiltrated samples and as-deformed samples. Insufficient magnetic isolation along the direction perpendicular to the nominal c-axis is expected from comparable SANS intensities for different ranges of q values along this direction. For small q values near the coercivity field, Nd-Cu-infiltrated samples show a noticeable reduction in SANS intensity along the nominal c-axis, which is parallel to the external magnetic field. This indicates less spatial fluctuation of magnetic moments in Nd-Cu-infiltrated samples, owing to magnetically isolated Nd{sub 2}Fe{sub 14}B grains.

  20. Extremely low-frequency magnetic fields can impair spermatogenesis recovery after reversible testicular damage induced by heat.

    PubMed

    Tenorio, Bruno Mendes; Ferreira Filho, Moisés Bonifacio Alves; Jimenez, George Chaves; de Morais, Rosana Nogueira; Peixoto, Christina Alves; Nogueira, Romildo de Albuquerque; da Silva Junior, Valdemiro Amaro

    2014-06-01

    Male infertility is often related to reproductive age couples experiencing fertility-related issues. Men may have fertility problems associated with reversible testicular damage. Considering that men have been increasingly exposed to extremely low-frequency magnetic fields generated by the production, distribution and use of electricity, this study analyzed whether 60 Hz and 1 mT magnetic field exposure may impair spermatogenesis recovery after reversible testicular damage induced by heat shock using rats as an experimental model. Adult male rats were subjected to a single testicular heat shock (HS, 43 °C for 12 min) and then exposed to the magnetic field for 15, 30 and 60 d after HS. Magnetic field exposure during the spermatogenesis recovery induced changes in testis components volume, cell ultrastructure and histomorphometrical parameters. Control animals had a reestablished and active spermatogenesis at 60 d after heat shock, while animals exposed to magnetic field still showed extensive testicular degeneration. Magnetic field exposure did not change the plasma testosterone. In conclusion, extremely low-frequency magnetic field may be harmful to fertility recovery in males affected by reversible testicular damage.

  1. 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.

  2. Electronic and magnetic properties of nanoribbons

    NASA Astrophysics Data System (ADS)

    Fernando, Gayanath; Zhang, Zhiwei; Kocharian, Armen

    We have performed tight-binding calculations with open boundary conditions on a set of twisted nanoribbons (4x100), monitoring the band structure as a function of the twist angle θ. When this angle is zero, the ribbon is rectangular and when it is 60 degrees, the ribbon is cut from a honeycomb lattice. Depending on the parameters of the tight-binding model and the filling factor, semi-metallic or insulating behavior is observed. We have also studied the electronic structure of such ribbons due to the adsorption of small atoms such as nitrogen, a magnetic field and the Rashba spin-orbit interaction. The role of the adsorbed atoms and the Rashba term with regard to the conducting properties and the symmetry breaking of the ribbons will be discussed in some detail. In addition, the effects of electronic correlations on selected small ribbons will be examined. The authors acknowledge the computing facilities provided by the Center for Functional Nanomaterials, Brookhaven National Laboratory supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

  3. Magnetic properties of nanocomposites formed by magnetic nanoparticles embedded in a non-magnetic matrix: a simulation approach.

    PubMed

    Serna, J Ceballos; Restrepo-Parra, E; Rojas, J C Riaño

    2012-06-01

    In this work, simulations of magnetic properties of nanocomposites formed by magnetic nanoparticles embedded in a non magnetic matrix are presented. These simulations were carried by means of the Monte Carlo Method and Heisenberg model. Properties as magnetization and Hysteresis loops were obtained varying different parameters as the nanoparticle size, distance between nanoparticles and temperature. The model employed includes interaction between ions belonging to each nanoparticle and also the interaction between nanoparticles. Results show that the magnetization and the coercive force decrease as a function of the nanoparticles distance.

  4. Non-resonant fishbone-like modes in tokamak plasmas with reversed magnetic shear

    NASA Astrophysics Data System (ADS)

    Wang, Xian-Qu; Wang, Xiao-Gang

    2016-03-01

    Energetic ion excited non-resonant fishbone-like modes (FLMs) of m / n  >  1 is investigated for reversed magnetic shear configurations. It is found that the mode can be destabilized by trapped fast ions with a similar excitation mechanism as m / n  =  1 fishbones but with a local interchange-like mode structure, which is in agreement with previous experiments (Toi et al 1999 Nucl. Fusion 39 1929). The dispersion relation of the mode is derived for m / n  >  1. The radial mode structure is then studied by numerically solving the eigenvalue equation. Effects of on/off-axis heating, the width of the particle distribution, the beam energy and the energy distribution on the mode are discussed in detail. Nonlinear analysis of the mode is also carried out by a modified predator-prey model.

  5. Measurement and modelling of magnetic properties of soft magnetic composite material under 2D vector magnetisations

    NASA Astrophysics Data System (ADS)

    Guo, Y. G.; Zhu, J. G.; Zhong, J. J.

    2006-07-01

    This paper reports the measurement and modelling of magnetic properties of SOMALOY TM 500, a soft magnetic composite (SMC) material, under different 2D vector magnetisations, such as alternating along one direction, circularly and elliptically rotating in a 2D plane. By using a 2D magnetic property tester, the B- H curves and core losses of the SMC material have been measured with different flux density patterns on a single sheet square sample. The measurements can provide useful information for modelling of the magnetic properties, such as core losses. The core loss models have been successfully applied in the design of rotating electrical machines with SMC core.

  6. Magnetic properties of stainless steels at room and cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Oxley, Paul; Goodell, Jennifer; Molt, Robert

    2009-07-01

    The magnetic properties of ten types of ferritic and martensitic stainless steels have been measured at room temperature and at 77 K. The steel samples studied were in the annealed state as received from the manufacturer. Our room temperature measurements indicate significantly harder magnetic properties than those quoted in the ASM International Handbook, which studied fully annealed stainless steel samples. Despite having harder magnetic properties than fully annealed steels some of the as-received steels still display soft magnetic properties adequate for magnetic applications. The carbon content of the steels was found to affect the permeability and coercive force, with lower-carbon steels displaying significantly higher permeability and lower coercive force. The decrease in coercive force with reduced carbon content is attributed to fewer carbide inclusions which inhibit domain wall motion. Cooling to 77 K resulted in harder magnetic properties. Averaged over the ten steels tested the maximum permeability decreased by 8%, the coercive force increased by 14%, and the residual and saturation flux densities increased by 4% and 3%, respectively. The change in coercive force when cooled is comparable to the theoretical prediction for iron, based on a model of domain wall motion inhibited by inclusions. The modest changes of the magnetic properties indicate that the stainless steels can still be used in magnetic applications at very low temperatures.

  7. The electric properties of low-magnetic-loss magnetic composites containing Zn-Ni-Fe particles

    NASA Astrophysics Data System (ADS)

    Hidaka, Nobuhiro; Ishitsuka, Masayuki; Shirakata, Yasushi; Teramoto, Akinobu; Ohmi, Tadahiro

    2009-10-01

    Recently, magnetic composites consisting of magnetic particles dispersed in a polymer matrix have been widely discussed for miniaturizing high-frequency electronic components such as antennae. Previously, we investigated the influence of the manufacturing process on the homogeneous dispersion of magnetic particles in the polymer and on the magnetic properties of the magnetic composites. In order to miniaturize electronic components, it is crucial to be able to independently control the permeability and permittivity in magnetic composites. This paper investigates the anisotropy and frequency dependence of the dielectric properties of magnetic composites fabricated from 20 vol% Zn5Ni75Fe20 flaked particles. The permittivity of magnetic composites fabricated from Zn5Ni75Fe20 flaked particles is anisotropic: at 1 GHz, the relative permittivities parallel and perpendicular to the plane of the specimens are 27.2 and 16.9, respectively. The permittivity varied little between frequencies of 50 MHz and 10 GHz.

  8. Nano/ultrafine grained austenitic stainless steel through the formation and reversion of deformation-induced martensite: Mechanisms, microstructures, mechanical properties, and TRIP effect

    SciTech Connect

    Shirdel, M.; Mirzadeh, H.; Parsa, M.H.

    2015-05-15

    A comprehensive study was carried out on the strain-induced martensitic transformation, its reversion to austenite, the resultant grain refinement, and the enhancement of strength and strain-hardening ability through the transformation-induced plasticity (TRIP) effect in a commercial austenitic 304L stainless steel with emphasis on the mechanisms and the microstructural evolution. A straightforward magnetic measurement device, which is based on the measurement of the saturation magnetization, for evaluating the amount of strain-induced martensite after cold rolling and reversion annealing in metastable austenitic stainless steels was used, which its results were in good consistency with those of the X-ray diffraction (XRD) method. A new parameter called the effective reduction in thickness was introduced, which corresponds to the reasonable upper bound on the obtainable martensite fraction based on the saturation in the martensitic transformation. By means of thermodynamics calculations, the reversion mechanisms were estimated and subsequently validated by experimental results. The signs of thermal martensitic transformation at cooling stage after reversion at 850 °C were found, which was attributed to the rise in the martensite start temperature due to the carbide precipitation. After the reversion treatment, the average grain sizes were around 500 nm and the nanometric grains of the size of ~ 65 nm were also detected. The intense grain refinement led to the enhanced mechanical properties and observation of the change in the work-hardening capacity and TRIP effect behavior. A practical map as a guidance for grain refining and characterizing the stability against grain growth was proposed, which shows the limitation of the reversion mechanism for refinement of grain size. - Graphical abstract: Display Omitted - Highlights: • Nano/ultrafine grained austenitic stainless steel through martensite treatment • A parameter descriptive of a reasonable upper bound on

  9. Magnetization Reversal by Out-of-plane Voltage in BiFeO3-based Multiferroic Heterostructures

    PubMed Central

    Wang, J. J.; Hu, J.M.; Peng, Ren-Ci; Gao, Y.; Shen, Y.; Chen, L. Q.; Nan, C. W.

    2015-01-01

    Voltage controlled 180° magnetization reversal has been achieved in BiFeO3-based multiferroic heterostructures, which is promising for the future development of low-power spintronic devices. However, all existing reports involve the use of an in-plane voltage that is unfavorable for practical device applications. Here, we investigate, using phase-field simulations, the out-of-plane (i.e., perpendicular to heterostructures) voltage controlled magnetism in heterostructures consisting of CoFe nanodots and (110) BiFeO3 thin film or island. It is predicted that the in-plane component of the canted magnetic moment at the CoFe/BiFeO3 interface can be reversed repeatedly by applying a perpendicular voltage across the bottom (110) BiFeO3 thin film, which further leads to an in-plane magnetization reversal in the overlaying CoFe nanodot. The non-volatility of such perpendicular voltage controlled magnetization reversal can be achieved by etching the continuous BiFeO3 film into isolated nanoislands with the same in-plane sizes as the CoFe nanodot. The findings would provide general guidelines for future experimental and engineering efforts on developing the electric-field controlled spintronic devices with BiFeO3-based multiferroic heterostructures. PMID:25995062

  10. The Aharanov-Bohm effect, magnetic monopoles and reversal in spin-ice lattices.

    PubMed

    Pollard, Shawn D; Zhu, Yimei

    2013-06-01

    The proof of the Aharonov-Bohm (AB) effect has been one of the most important experiments of the last century and used as essential evidence for the theory of gauge fields. In this article, we look at its fundamental relation to the Dirac monopole and string. Despite the Dirac string being invisible to the AB effect, it can be used to study emergent quasiparticles in condensed matter settings that behave similar to the fundamental monopoles and strings between them. We utilize phase-imaging method based on the AB effect to study the ordering in a one-model system - that of frustrated spin ice - to understand the ordering processes that occur during a magnetic field reversal cycle. The reversal is linked to the propagation of monopole defects linked by flux channels, reminiscent of Dirac strings. Monopole interactions govern the defect densities within the lattice. Furthermore, we exploit these interactions to propose a new ordering method in which high degrees of ground-state ordering can be achieved in a frustrated system.

  11. Correlation of magnetic properties with deformation in electrical steels

    NASA Astrophysics Data System (ADS)

    Papadopoulou, S.

    2016-03-01

    This paper investigates the utilization of magnetic Barkhausen Noise (MBN) and hysteresis loops methods for the non-destructive characterization of deformed electrical steel samples. For this reason electrical steel samples were subjected to uniaxial tensile tests on elastic and plastic region of deformations. Both the MBN and hysteresis loops were measured. The results shown a strong degradation of the magnetic properties on plastically strains. This was attributed to the irreversible movement of the magnetic domain walls, due to the presence of high dislocation density. The resulting magnetic properties were further evaluated by examining the microstructure of the deformed samples by using scanning electron microscopy.

  12. Structure and magnetic properties of Zn-Ti-substituted Ba-ferrite particles for magnetic recording

    NASA Astrophysics Data System (ADS)

    Wang, C. S.; Wei, F. L.; Lu, M.; Han, D. H.; Yang, Z.

    1998-03-01

    The formation process of Zn-Ti-doped Ba-ferrite particles was investigated by the X-ray diffraction technique, transmission electron microscope and magnetic measurements. The effects of heating temperature Th and the Zn-Ti substitution x on the microstructure and magnetic properties of BaFe 12-2 xZn xTi x O 19 particles with x=0.10-0.80 were studied. The temperature dependence of magnetic properties of these particles was measured.

  13. Magnetic and magnetothermal properties and the magnetic phase diagram of high purity single crystalline terbium along the easy magnetization direction

    SciTech Connect

    Zverev, V. I.; Tishin, A. M.; Chernyshov, A. S.; Mudryk, Ya; Gschneidner Jr., Karl A.; Pecharsky, Vitalij K.

    2014-01-21

    The magnetic and magnetothermal properties of a high purity terbium single crystal have been re-investigated from 1.5 to 350 K in magnetic fields ranging from 0 to 75 kOe using magnetization, ac magnetic susceptibility and heat capacity measurements. The magnetic phase diagram has been refined by establishing a region of the fan-like phase broader than reported in the past, by locating a tricritical point at 226 K, and by a more accurate definition of the critical fields and temperatures associated with the magnetic phases observed in Tb.

  14. Influence of membrane properties on physically reversible and irreversible fouling in membrane bioreactors.

    PubMed

    Tsuyuhara, T; Hanamoto, Y; Miyoshi, T; Kimura, K; Watanabe, Y

    2010-01-01

    This study aimed to examine the impact of membrane properties on membrane fouling in membrane bioreactor (MBR). Membrane fouling was divided into two categories: physically reversible and irreversible fouling. Membrane properties related to each type of membrane fouling were investigated separately. Five microfiltration (MF) and one ultrafiltration (UF) membranes with different properties (pore size, contact angle, roughness, zeta potential, and pure water permeability) were examined with a laboratory-scale MBR, fed with synthetic wastewater. Two separate experiments were conducted: the first to examine physically reversible fouling, and the second to examine physically irreversible fouling. The correlation between the degree of each type of fouling and membrane properties was studied. High correlation was observed between the degree of physically reversible fouling and roughness (R(2)=0.96). In contrast, with regard to physically irreversible fouling, strong correlation between roughness and degree of membrane fouling can only be found in the case of MF membranes. Except for the membrane with the highest roughness, the degree of physically irreversible fouling can be well correlated with pure water permeability (lower pure water permeability results in higher degree of physically irreversible fouling) including UF membrane. On the basis of the results obtained in this study, it can be concluded that roughness is an important factor in determination of physically reversible fouling regardless of the types of membrane (i.e. MF or UF membranes) and evolutions of physically irreversible fouling can be mitigated when an MBR is operated with membranes with smooth surface and high pure water permeability.

  15. Simultaneous enhancement of magnetic and mechanical properties in Ni-Mn-Sn alloy by Fe doping

    PubMed Central

    Tan, Changlong; Tai, Zhipeng; Zhang, Kun; Tian, Xiaohua; Cai, Wei

    2017-01-01

    Both magnetic-field-induced reverse martensitic transformation (MFIRMT) and mechanical properties are crucial for application of Ni-Mn-Sn magnetic shape memory alloys. Here, we demonstrate that substitution of Fe for Ni can simultaneously enhance the MFIRMT and mechanical properties of Ni-Mn-Sn, which are advantageous for its applications. The austenite in Ni44Fe6Mn39Sn11 shows the typical ferromagnetic magnetization with the highest saturation magnetization of 69 emu/g at 223 K. The result shows that an appropriate amount of Fe substitution can really enhance the ferromagnetism of Ni50Mn39Sn11 alloy in austenite, which directly leads to the enhancement of MFIRMT. Meanwhile, the mechanical property significantly improves with Fe doping. When there is 4 at.% Fe added, the compressive and maximum strain reach the maximum value (approximately 725.4 MPa and 9.3%). Furthermore, using first-principles calculations, we clarify the origin of Fe doping on martensitic transformation and magnetic properties. PMID:28230152

  16. Magnetic properties in an alternating-spin ferromagnetic Ising chain

    NASA Astrophysics Data System (ADS)

    Eloy, D.; Ramos, F. B.

    2011-08-01

    Using the transfer matrix technique, we investigated the magnetic properties of a ferromagnetic Ising chain with alternating-spins ( S, S') and single-ion anisotropy. We have calculated some physical quantities of interest such as the z component of the total magnetization per particle ( m) and magnetic susceptibility. In the regime of low temperatures, we observed the existence of magnetization plateaus. We constructed the phase diagrams of the magnetization in terms of the magnetic field and of the single-ion anisotropy for the case {1}/{2}≤(S,S')≤{9}/{2}. We were able to find a general rule for the magnetic transitions. We observed that the saturation value of the magnetization is msat=(S+S')/2.

  17. Magnetic properties of synthetic eumelanin--preliminary results.

    PubMed

    Cano, M E; Castañeda-Priego, R; Gil-Villegas, A; Sosa, M A; Schio, P; de Oliveira, A J A; Chen, F; Baffa, O; Graeff, C F O

    2008-01-01

    We report an experimental and theoretical study of magnetic properties of synthetic eumelanin. The magnetization curves are determined by using both a vibrating sample magnetometer and a superconducting quantum interferometer device in an extended range of magnetic fields ranging from -10 kOe to 10 kOe at different temperatures. We find that the eumelanin magnetization can be qualitatively explained in terms of a simple model of dipolar spheres with an intrinsic magnetic moment. The latter one is experimentally measured by using X-band electron paramagnetic resonance. Our findings indicate that synthetic melanins are superparamagnetic.

  18. Magnetic Properties of Nanoparticle Matrix Composites

    DTIC Science & Technology

    2015-06-02

    been optimized for each composition of Fe-Pt and their spin isomers have been studied to find the magnetic moments of the lowest energy structures ...numbers in brackets below the structures refer to the energy (eV) relative to the lowest energy isomer and the magnetic moment (µB). Red (blue) balls...Approved for public release; distribution is unlimited. Distribution is unlimited structures . The magnetic moments increase systematically by 4µB when a

  19. Enhancement in magnetic properties of magnesium substituted bismuth ferrite nanoparticles

    SciTech Connect

    Xu, Jianlong; Xie, Dan E-mail: RenTL@mail.tsinghua.edu.cn; Teng, Changjiu; Zhang, Xiaowen; Zhang, Cheng; Sun, Yilin; Ren, Tian-Ling E-mail: RenTL@mail.tsinghua.edu.cn; Zeng, Min; Gao, Xingsen; Zhao, Yonggang

    2015-06-14

    We report a potential way to effectively improve the magnetic properties of BiFeO{sub 3} (BFO) nanoparticles through Mg{sup 2+} ion substitution at the Fe-sites of BFO lattice. The high purity and structural changes induced by Mg doping are confirmed by X-ray powder diffractometer and Raman spectra. Enhanced magnetic properties are observed in Mg substituted samples, which simultaneously exhibit ferromagnetic and superparamagnetic properties at room temperature. A physical model is proposed to support the observed ferromagnetism of Mg doped samples, and the superparamagnetic properties are revealed by the temperature dependent magnetization measurements. The improved magnetic properties and soft nature obtained by Mg doping in BFO nanoparticles demonstrate the possibility of BFO nanoparticles to practical applications.

  20. Enhancement in magnetic properties of magnesium substituted bismuth ferrite nanoparticles

    NASA Astrophysics Data System (ADS)

    Xu, Jianlong; Xie, Dan; Teng, Changjiu; Zhang, Xiaowen; Zhang, Cheng; Sun, Yilin; Ren, Tian-Ling; Zeng, Min; Gao, Xingsen; Zhao, Yonggang

    2015-06-01

    We report a potential way to effectively improve the magnetic properties of BiFeO3 (BFO) nanoparticles through Mg2+ ion substitution at the Fe-sites of BFO lattice. The high purity and structural changes induced by Mg doping are confirmed by X-ray powder diffractometer and Raman spectra. Enhanced magnetic properties are observed in Mg substituted samples, which simultaneously exhibit ferromagnetic and superparamagnetic properties at room temperature. A physical model is proposed to support the observed ferromagnetism of Mg doped samples, and the superparamagnetic properties are revealed by the temperature dependent magnetization measurements. The improved magnetic properties and soft nature obtained by Mg doping in BFO nanoparticles demonstrate the possibility of BFO nanoparticles to practical applications.

  1. Influence of a large amount of Co substitution on the magnetic properties of NdFeCoGaB magnets (abstract)

    NASA Astrophysics Data System (ADS)

    Tsutai, A.; Sakai, I.; Sahashi, M.; Inomata, K.

    1990-05-01

    We have found that a NdFeCoGaB sintered magnet containing 30 at. % Co still shows high coercive force in spite of such a large amount of Co substitution. The Curie temperature of the magnet is higher than that of the ternary NdFeB magnet by 280 °C. As a result, the following magnetic properties have been attained for Nd14.5Fe46Co30Ga1B8.5: Tc=590 °C, Br =11.7 kG, Hci =14.3 kOe, and (BH)max=32 MG Oe. Furthermore, in this magnet there exists an additional phase, Nd1(FeCoGa)4B1 with Ce1Co4B1 structure, which, as far as authors know, has not been reported to exist in the NdFeB-based magnets. In this study we investigated the magnetic properties and microstructure of Nd14.5Fe76-xCoxGa1B8.5 (x=16-50) sintered magnets. The high coercive force can be obtained in the Co-content region from 16 to 30 at. %. In particular, the magnet with 30 at. % Co shows coercive force as high as 14.3 kOe. However, further substitution of Co drastically deteriorates the magnetic properties. The coercive force of the magnet with 50 at. % Co is less than 1 kOe. From the metallographical point of view, the above-mentioned Nd1(FeCoGa)4B1 phase is not observed in the magnets containing less than 30 at. % Co. This phase abruptly appears in the magnet with 30 at. % Co and its amount increases with increasing Co content. The strongest x-ray-diffraction peak observed in the magnet with 50 at. % Co comes from the Nd1(FeCoGa)4B1 phase. The demagnetization-curve measurements suggest that reverse magnetic domains are nucleated in the Nd1(FeCoGa)4B1 phase at a low reverse magnetic field. It is noteworthy that the magnet with 30 at. % Co maintains the high coercive force in spite of the existence of such a soft magnetic phase. Details will be discussed in the coming session.

  2. Formation mechanisms of magnetic bubbles in an M -type hexaferrite: Role of chirality reversal at domain walls

    NASA Astrophysics Data System (ADS)

    Nakajima, H.; Kotani, A.; Harada, K.; Ishii, Y.; Mori, S.

    2016-12-01

    We examined the formation mechanisms of magnetic bubbles in an M -type hexaferrite via Lorentz microscopy. When magnetic fields were perpendicularly applied to a thin sample of BaF e12-x-0.05S cxM g0.05O19(x = 1.6 ) , Bloch lines, which were identified as reversals of domain-wall chirality, appeared, and magnetic bubbles were formed when the magnetic stripes were pinched off at these Bloch lines. The number of Bloch lines increased with the amount of Sc in BaF e12 -x -0.05S cxM g0.05O19 , probably because of the reduction in magnetic anisotropy. A Lorentz microscopic observation revealed that Bloch lines with high magnetostatic energy may play an important role in the formation of magnetic bubbles.

  3. Distance dependence of magnetic field effect inside confined environment of reverse micelles

    NASA Astrophysics Data System (ADS)

    Sarangi, Manas Kumar; Basu, Samita

    2013-06-01

    In this article, we emphasize on the distance dependence of the magnetic field effect (MFE) on the donoracceptor (D-A) pair inside the confined environment of AOT/H2O/n-heptane reverse micellar (RMs) system. For this study N, N-dimethyl aniline (DMA) is used as an electron donor while the protonated form of Acr is treated as an electron acceptor. We report of the occurrence of an associated excited state proton transfer with the photoinduced electron transfer between Acr and DMA forming corresponding radical pair (RP) and radical ion pairs (RIP). The fate of these reaction products has been tested in the presence of an external magnetic field (˜0.08T) by varying the size of the RMs. The MFE between Acr and DMA has been compared to the results with the earlier reported interactions between Acr and TEA (Chemical Physics Letters, 2011, 506, 205-210). We accentuate the importance of the localization of the D and A inside the RMs, and the intervening distance between the pair to be the critical component for observing substantial MFE.

  4. Simulations of microwave electron heating on field-reversed configuration driven by rotating magnetic field

    NASA Astrophysics Data System (ADS)

    Yang, Xiaokang; Petrov, Yuri; Koehn, Alf; Cohen, Sam; Ceccherini, Francesco; Galeotti, Laura; Dettrick, Sean; Binderbauer, Michl

    2016-10-01

    The rotating magnetic field-driven field-reversed configuration (FRC), such as Rotamak or PFRC experiment, was recently proposed as a test bench at Tri Alpha Energy to experimentally pioneer the study of microwave electron heating. In order to provide guidelines to the choice of microwave frequency and antenna position, as well as the desired target plasma profile, extensive simulations have been conducted with use of the GENRAY-C ray-tracing code for a wide range of frequencies from smaller than fundamental electron cyclotron resonant (ECR) frequency up to more than 30 harmonics of ECR. Based on the operational parameters of Rotamak plasma, simulations indicate that microwaves at a frequency around 10 GHz can heat electrons inside the separatrix layer. The physics of heating mechanism is similar for both the Rotamak and the C-2U FRC plasma, meaning that the magnitude of magnetic field goes down along the direction of ray propagation, therefore the rays, after the O-X-B mode conversion, encounter a basin of high harmonic EC resonances and mostly damp the power in the vicinity of the upper-hybrid resonance layer Detailed simulation results and plans for a future test bench will be presented.

  5. Magnetic Field Response and Chiral Symmetry of Time Reversal Invariant Topological Superconductors

    NASA Astrophysics Data System (ADS)

    Dumitrescu, Eugen; Sau, Jay D.; Tewari, Sumtanta

    2014-03-01

    We study the magnetic ?eld response of the Majorana Kramers pairs of a one-dimensional time-reversal invariant (TRI) superconductors (class DIII) with or without a coexisting chirality symmetry. For unbroken TR and chirality invariance the parameter regimes for nontrivial values of the (Z2) DIII-invariant and the (Z) BDI chiral invariant coincide. However, broken TR may or may not be accompanied by broken chirality, and if chiral symmetry is unbroken the pair of Majorana fermions (MFs) at a given end survives the loss of TR symmetry in an entire plane perpendicular to the spin-orbit coupling field. Conversely, we show that broken chirality may or may not be accompanied by broken TR, and if TR is unbroken, the pair of MFs survives the loss of broken chirality. In addition to explaining the anomalous magnetic field response of all the DIII class TS systems proposed in the literature, we provide a realistic route to engineer a ``true'' TR-invariant TS, whose pair of MFs at each end is split by an applied Zeeman field in arbitrary direction. We also prove that, quite generally, the splitting of the MFs by TR-breaking fields in TRI superconductors is highly anisotropic in spin space, even in the absence of the topological chiral symmetry.

  6. Switching field distribution and magnetization reversal process of FePt dot patterns

    NASA Astrophysics Data System (ADS)

    Ishio, S.; Takahashi, S.; Hasegawa, T.; Arakawa, A.; Sasaki, H.; Yan, Z.; Liu, X.; Kondo, Y.; Yamane, H.; Ariake, J.; Suzuki, M.; Kawamura, N.; Mizumaki, M.

    2014-06-01

    The fabrication of FePt nanodots with a high structural quality and the control of their switching fields are key issues in realizing high density bit pattern recording. We have prepared FePt dot patterns for dots with 15-300 nm diameters by electron beam lithography and re-annealing, and studied the relation between magnetization reversal process and structure of FePt nanodots. The switching field (Hsw) of dot patterns re-annealed at 710 °C for 240 min showed a bimodal distribution, where a higher peak was found at 5-6 T, and a lower peak was found at 2 T. It was revealed by cross-sectional TEM analysis that the structure of dots in the pattern can be classified into two groups. One group has a high degree of order with well-defined [0 0 1] crystalline growth, and the other group includes structurally-disturbed dots like [1 1 1] growth and twin crystals. This structural inhomogeneity causes the magnetic switching field distribution observed.

  7. Radial current density effects on rotating magnetic field current drive in field-reversed configurations

    SciTech Connect

    Clemente, R. A.; Gilli, M.; Farengo, R.

    2008-10-15

    Steady state solutions, suitable for field-reversed configurations (FRCs) sustained by rotating magnetic fields (RMFs) are obtained by properly including three-dimensional effects, in the limit of large FRC elongation, and the radial component of Ohm's law. The steady electrostatic potential, necessary to satisfy Ohm's law, is considered to be a surface function. The problem is analyzed at the midplane of the configuration and it is reduced to the solution of two coupled nonlinear differential equations for the real and imaginary parts of the phasor associated to the longitudinal component of the vector potential. Additional constraints are obtained by requesting that the steady radial current density and poloidal magnetic flux vanish at the plasma boundary which is set at the time-averaged separatrix. The results are presented in terms of the degree of synchronism of the electrons with the RMF and compared with those obtained when radial current effects are neglected. Three important differences are observed when compared with the case without radial current density. First, at low penetration of the RMF into the plasma there is a significant increase in the driven azimuthal current. Second, the RMF amplitude necessary to access the high synchronism regime, starting from low synchronism, is larger and the difference appears to increase as the separatrix to classical skin depth ratio increases. Third, the minimum RMF amplitude necessary to sustain almost full synchronism is reduced.

  8. Novel method of doxorubicin-SPION reversible association for magnetic drug targeting.

    PubMed

    Munnier, E; Cohen-Jonathan, S; Linassier, C; Douziech-Eyrolles, L; Marchais, H; Soucé, M; Hervé, K; Dubois, P; Chourpa, I

    2008-11-03

    A new method of reversible association of doxorubicin (DOX) to superparamagnetic iron oxide nanoparticles (SPION) is developed for magnetically targeted chemotherapy. The efficacy of this approach is evaluated in terms of drug loading, delivery kinetics and cytotoxicity in vitro. Aqueous suspensions of SPION (ferrofluids) were prepared by coprecipitation of ferric and ferrous chlorides in alkaline medium followed by surface oxidation by ferric nitrate and surface treatment with citrate ions. The ferrofluids were loaded with DOX using a pre-formed DOX-Fe(2+) complex. The resulting drug loading was as high as 14% (w/w). This value exceeds the maximal loading known from literature up today. The release of DOX from the nanoparticles is strongly pH-dependent: at pH 7.4 the amount of drug released attains a plateau of approximately 85% after 1h, whereas at pH 4.0 the release is almost immediate. At both pH, the released drug is iron-free. The in vitro cytotoxicity of the DOX-loaded SPION on the MCF-7 breast cancer cell line is similar to that of DOX in solution or even higher, at low-drug concentrations. The present study demonstrates the potential of the novel method of pH-sensitive DOX-SPION association to design novel magnetic nanovectors for chemotherapy.

  9. Magnetic properties of the LL5 ordinary chondrite Chelyabinsk (fall of February 15, 2013)

    NASA Astrophysics Data System (ADS)

    Bezaeva, Natalia S.; Badyukov, Dmitry D.; Nazarov, Mikhail A.; Rochette, Pierre; Feinberg, Joshua M.; Markov, Gennadiy P.; Borschneck, Daniel; Demory, FrançOis; Gattacceca, JéRôMe; Borisovskiy, Sergey E.; Skripnik, Anna Ya

    2014-06-01

    Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite's magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low-field magnetic susceptibility (χ0), the anisotropy of χ0, hysteresis loops, first-order reversal curves, Mössbauer spectroscopy, and X-ray microtomography. The REM and REM' paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth's magnetic field acquired during entry into our planet's atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show logχ0 = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where χ0 is in 10-9 m3 kg-1). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal-rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite's room-temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization.

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

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  11. Collisionless reversed magnetic shear trapped electron instability and contribution of sidebands to anomalous transport

    NASA Astrophysics Data System (ADS)

    Rogister, André L.; Singh, Raghvendra

    2005-11-01

    By keeping account of the trapped electron ∇B and curvature drifts, it is found that the spatial decay of the collisionless electron drift wave is governed either by the trapped electron response or by the resonant interaction of ions with the sidebands of the primary oscillation. In the former case, pairs of spatially bounded unstable and damped solutions are obtained for negative magnetic shear (ŝ<0) if, as usual, LTe=1/∂rlnTe<0; there are no bounded solutions if ŝLTe<0. In the latter case, there is either a set of bounded damped solutions if ηi>0 or a set of bounded unstable solutions if ηi<0. The unstable modes have a radiating character and the growth rates are γ ˜(2n+1)√1+2q2 ∣ŝ∣∣LNωe*/qR∣ (n is the Hermite polynomial solution index, q the safety factor, ŝ the magnetic shear parameter, R the major radius, ωe* the electron diamagnetic frequency, LN=1/∂rlnNe, and ηi=LN/LTi).The sidebands are responsible for unusually large ratios Qe/TeΓe, where Qe and Γe are the anomalous electron energy flux and the particle flux. These results may explain the box-type Te profile observed in lower hybrid current drive reversed magnetic shear plasmas on the Japan Atomic Energy Research Institute Tokamak 60 Upgrade (JT-60U) [H. Ninomiya and the JT-60U Team, Phys. Fluids B 4, 2070 (1992)]. It is finally demonstrated that the ballooning hypothesis generally leads to conflicting requirements: it is thus hardly relevant for the electron drift branch! The "radiating" boundary condition that has formerly been imposed on the slab solution is finally discussed.

  12. Magnetic unmixing of first-order reversal curve diagrams using principal component analysis

    NASA Astrophysics Data System (ADS)

    Lascu, Ioan; Harrison, Richard J.; Li, Yuting; Muraszko, Joy R.; Channell, James E. T.; Piotrowski, Alexander M.; Hodell, David A.

    2015-09-01

    We describe a quantitative magnetic unmixing method based on principal component analysis (PCA) of first-order reversal curve (FORC) diagrams. For PCA, we resample FORC distributions on grids that capture diagnostic signatures of single-domain (SD), pseudosingle-domain (PSD), and multidomain (MD) magnetite, as well as of minerals such as hematite. Individual FORC diagrams are 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 imposed by data scatter. We investigate temporal variations of two EMs in bulk North Atlantic sediment cores collected from the Rockall Trough and the Iberian Continental Margin. Sediments from each site contain a mixture of magnetosomes and granulometrically distinct detrital magnetite. We also quantify the spatial variation of three EM components (a coarse silt-sized MD component, a fine silt-sized PSD component, and a mixed clay-sized component containing both SD magnetite and hematite) in surficial sediments along the flow path of the North Atlantic Deep Water (NADW). These samples were separated into granulometric fractions, which helped constrain EM definition. PCA-based unmixing reveals systematic variations in EM relative abundance as a function of distance along NADW flow. Finally, we apply PCA to the combined data set 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 multicomponent magnetic mixtures, a fundamental task of rock magnetic studies.

  13. Viking magnetic properties experiment - Extended mission results

    NASA Technical Reports Server (NTRS)

    Hargraves, R. B.; Collinson, D. W.; Arvidson, R. E.; Cates, P. M.

    1979-01-01

    The backhoe magnets on Viking Lander (VL) 2 were successfully cleaned, followed by a test involving successive insertions of the cleaned backhoe into the surface. Rapid saturation of the magnets confirmed evidence from primary mission results that the magnetic mineral in the Martian surface is widely distributed, most probably in the form of composite particles of magnetic and nonmagnetic minerals. An image of the VL 2 backhoe taken via the X4 magnifying mirror demonstrates the fine-grained nature of the attracted magnetic material. The presence of maghemite and its occurrence as a pigment in, or a thin coating on, all mineral particles or as discrete, finely divided and widely distributed crystallites, are consistent with data from the inorganic analysis experiments and with laboratory simulations of results of the biology experiments on Mars.

  14. EM Properties of Magnetic Minerals at RADAR Frequencies

    NASA Technical Reports Server (NTRS)

    Stillman, D. E.; Olhoeft, G. R.

    2005-01-01

    Previous missions to Mars have revealed that Mars surface is magnetic at DC frequency. Does this highly magnetic surface layer attenuate RADAR energy as it does in certain locations on Earth? It has been suggested that the active magnetic mineral on Mars is titanomaghemite and/or titanomagnetite. When titanium is incorporated into a maghemite or magnetite crystal, the Curie temperature can be significantly reduced. Mars has a wide range of daily temperature fluctuations (303K - 143K), which could allow for daily passes through the Curie temperature. Hence, the global dust layer on Mars could experience widely varying magnetic properties as a function of temperature, more specifically being ferromagnetic at night and paramagnetic during the day. Measurements of EM properties of magnetic minerals were made versus frequency and temperature (300K- 180K). Magnetic minerals and Martian analog samples were gathered from a number of different locations on Earth.

  15. Magnetic properties of a nanoribbon: An effective-field theory

    NASA Astrophysics Data System (ADS)

    Wang, Jiu-Ming; Jiang, Wei; Zhou, Chen-Long; Shi, Zuo; Wu, Chuang

    2017-02-01

    An effective-field theory is proposed to study magnetic properties of a nanoribbon. The model consists of a core spin-3/2 and shell spin-2 with a ferrimagnetic exchange coupling, which is described by transverse Ising model with the anisotropy. Based on the differential operator technique, the magnetization and the susceptibility formulas of the nanoribbon are given. Numerical results of the magnetization, the susceptibility, the hysteresis loop of the system are discussed for specific values of the parameters. Magnetization plateaus exhibits on the magnetization curves at low temperature. The exchange coupling, the anisotropy and the transverse field have important roles in the magnetic properties for the nanoribbon. Results may provide some guidance to design in the nanoribbons.

  16. The magnetic properties of powdered and compacted microcrystalline permalloy

    NASA Astrophysics Data System (ADS)

    Kollár, P.; Olekšáková, D.; Füzer, J.; Kováč, J.; Roth, S.; Polański, K.

    2007-03-01

    The aim of this work is to investigate the magnetic properties of powdered and compacted microcrystalline Ni-Fe (81 wt% of Ni) permalloy. It was found by investigating the influence of mechanical milling on the magnetic properties of powder samples prepared by milling of the ribbon that the alloy remains a solid solution with stable structure during the whole milling process. With decreasing particle size the rotation of magnetization vector gradually becomes dominant magnetization process and thus coercivity increases. After compaction of the powder by uniaxial hot pressing the magnetic contact between powder particles is recreated and for resulting bulk the displacement of the domain walls becomes dominant magnetization process with coercivity of 11 A/m (comparable with the coercivity of conventional permalloy).

  17. Magnetic properties of cobalt ferrite synthesized by hydrothermal method

    NASA Astrophysics Data System (ADS)

    Allaedini, Ghazaleh; Tasirin, Siti Masrinda; Aminayi, Payam

    2015-05-01

    In this study, the magnetic properties of nanocrystalline cobalt ferrite synthesized via the hydrothermal method have been investigated. The structural properties of the produced powders were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The observed XRD pattern confirmed the spinel/cubic structure of the prepared cobalt ferrite. The SEM pictures show that the simple hydrothermal method produces uniform sphere-shaped nanopowders. Moreover, infrared spectroscopy was used to confirm the formation of cobalt ferrite particles. Magnetic hysteresis was measured using a vibrating sample magnetometer in a maximum field of 10 kOe. The magnetization of the prepared nanoparticles was investigated, and the saturation magnetization ( M s), remanence ( M r), and coercivity ( H c) were derived from the hysteresis loops. The results revealed that the cobalt ferrite nanoparticles synthesized via the simple hydrothermal method exhibit superior magnetic properties.

  18. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; Yu, Guojun

    2012-05-01

    Ferronematic materials composed of 4-cyano-4'-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δ n) and figure of merit of optical properties ( Q = Δ n/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of Q R exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field.

  19. Investigation on microstructure and magnetic properties of Sm2Co17 magnets aged at high temperature

    NASA Astrophysics Data System (ADS)

    Feng, Haibo; Chen, Hongsheng; Guo, Zhaohui; Pan, Wei; Zhu, Minggang; Li, Wei

    2011-04-01

    The Sm2Co17 magnet is the most promising candidate for high temperature applications. The microstructure evolutions and losses in the magnetic properties of the magnet in high temperature aging status have been investigated. The Sm(CobalFe0.22Cu0.068Zr0.025)7.75 magnets were prepared using the conventional powder sintering method. The magnet samples were isothermally aged at 500°C, 600 °C, and 700 °C for 72 h, respectively. The magnetic properties and the demagnetization curve were kept invariable for the magnet samples aged at 500 °C. The coercivity Hcj of the magnet samples decreased with increasing aging temperature. The Hcj decreased from 29.2 kOe for the original status samples to 10.8 kOe for the samples aged at 700 °C. The cell structure in the magnet is not destroyed after aging at 700 °C for 72 h. The deterioration of the magnetic properties and the demagnetization-curve squareness was caused by an increasing lattice mismatch between the 2:17R cell phase and the cell-boundary 1:5H phase, and by an increasing cell diameter for the magnet sample aged at a high temperature.

  20. Element-specific magnetization reversal in Fe/Ce multilayers:. a study by X-ray magnetic circular dichroism and the magneto-optic Kerr effect

    NASA Astrophysics Data System (ADS)

    Münzenberg, M.; Arend, M.; Felsch, W.; Pizzini, S.; Fontaine, A.; Neisius, T.; Pascarelli, S.

    2000-10-01

    Fe/Ce multilayers are magnetically soft with coercive fields of a few Oersteds. In this artificial system, the itinerant 5d electrons of Ce are magnetically polarized by hybridization with the spin-split 3d states of Fe. To obtain an insight into the magnetization reversal process, the element selectivity of X-ray magnetic circular dichroism was used to measure the magnetization of the Ce-5d electrons as a function of an applied magnetic field. Comparison with the magnetization curves studied by the magneto-optic Kerr effect, which averages over the whole system, revealed that the coercivity in the hysteresis of the ordered Ce-5d moments is reduced by 50%. We propose that this is an effect of the magnetically disturbed interface or of the complex non-collinear magnetic structure of the Ce layers detected by recent experiments of X-ray resonant magnetic scattering. The results are compared to the X-ray dichroic and Kerr hysteresis loops of the multilayers Fe/La/Ce/La and Fe/CeH 2- δ. These systems are magnetically harder and their coercivities are identical.

  1. Effect of the stimulus frequency and pulse number of repetitive transcranial magnetic stimulation on the inter-reversal time of perceptual reversal on the right superior parietal lobule

    NASA Astrophysics Data System (ADS)

    Nojima, Kazuhisa; Ge, Sheng; Katayama, Yoshinori; Ueno, Shoogo; Iramina, Keiji

    2010-05-01

    The aim of this study is to investigate the effect of the stimulus frequency and pulses number of repetitive transcranial magnetic stimulation (rTMS) on the inter-reversal time (IRT) of perceptual reversal on the right superior parietal lobule (SPL). The spinning wheel illusion was used as the ambiguous figures stimulation in this study. To investigate the rTMS effect over the right SPL during perceptual reversal, 0.25 Hz 60 pulse, 1 Hz 60 pulse, 0.5 Hz 120 pulse, 1 Hz 120 pulse, and 1 Hz 240 pulse biphasic rTMS at 90% of resting motor threshold was applied over the right SPL and the right posterior temporal lobe (PTL), respectively. As a control, a no TMS was also conducted. It was found that rTMS on 0.25 Hz 60 pulse and 1 Hz 60 pulse applied over the right SPL caused shorter IRT. In contrast, it was found that rTMS on 1 Hz 240-pulse applied over the right SPL caused longer IRT. On the other hand, there is no significant difference between IRTs when the rTMS on 0.5 Hz 120 pulse and 1 Hz 120 pulse were applied over the right SPL. Therefore, the applying of rTMS over the right SPL suggests that the IRT of perceptual reversal is effected by the rTMS conditions such as the stimulus frequency and the number of pulses.

  2. Magnetization reversal of Co/Au multilayer stripes with keV-He+ ion bombardment induced coercivity gradient

    NASA Astrophysics Data System (ADS)

    Urbaniak, M.; Stobiecki, F.; Gaul, A.; Ehresmann, A.

    2015-08-01

    Magnetization reversal of perpendicular anisotropy [Co/Au]\\text{N} multilayers patterned into micrometer wide stripes with a coercivity gradient along the stripes was investigated with polar magnetooptical Kerr effect microscopy. 1 mm-long stripes were bombarded with He+ ions of 10 keV energy to induce the gradient. It was shown that short pulses of a magnetic field applied perpendicularly to the sample plane move domain walls between up- and down-magnetized areas in a direction of regions with higher coercivities.

  3. Electronic and magnetic properties of Am and Cm

    SciTech Connect

    Edelstein, N.

    1985-02-01

    A review of the present status of the analyses of the optical spectra of Am and Cm in various oxidation states is given. From these analyses, the magnetic properties of the ground states of these ions can be determined. These predicted values are compared with the various magnetic measurements available.

  4. Elastic properties of DNA linked flexible magnetic filaments

    NASA Astrophysics Data System (ADS)

    Ērglis, K.; Zhulenkovs, D.; Sharipo, A.; Cēbers, A.

    2008-05-01

    Elastic properties of magnetic filaments linked by DNA in solutions of univalent and bivalent salts with different pH values are investigated through their deformation in an external field. A strong dependence of the bending modulus in bivalent salt solution on the pH is shown. Experimental results are interpreted on the basis of the magnetic elastica.

  5. Synthesis and Magnetic Properties of CoPt Nanoparticles

    NASA Astrophysics Data System (ADS)

    Trung, Truong Thanh; Nhung, Do Thi; Nam, Nguyen Hoang; Luong, Nguyen Hoang

    2016-07-01

    Magnetic nanoparticles CoPt were prepared by the chemical reduction of cobalt (II) chloride and chloroplatinic acid, then the samples were ultrasonicated for 2 h. After annealing at various temperatures from 400°C to 700°C for 1 h, the samples showed hard magnetic properties with coercivity up to 1.15 kOe at room temperature.

  6. Synthesis and magnetic properties of nickel nanoparticles

    NASA Astrophysics Data System (ADS)

    Singh, Jaiveer; Patel, Tarachand; Kaurav, Netram; Okram, Gunadhor S.

    2016-05-01

    Monodisperse nickel nanoparticles (Ni-NPs) were synthesized via a thermal decomposition process. The NPs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). They were spherical with mean diameter of 4 nm. Zero field cooled (ZFC) and field cooled (FC) magnetization versus temperature data displayed interesting magnetic interactions. ZFC showed a peak at 4.49 K, indicating the super paramagnetic behavior. Magnetic anisotropic constant was estimated to be 4.62×105 erg/cm3 and coercive field was 168 Oe at 3 K.

  7. Magnetic porous composite material: Synthesis and properties

    NASA Astrophysics Data System (ADS)

    Peretyat'ko, P. I.; Kulikov, L. A.; Melikhov, I. V.; Perfil'ev, Yu. D.; Pal', A. F.; Timofeev, M. A.; Gudoshnikov, S. A.; Usov, N. A.

    2015-10-01

    A new method of obtaining magnetic porous composite materials is described, which is based on the self-propagating high-temperature synthesis (SHS) in the form of solid-phase combustion. The SHS process involves transformation of the nonmagnetic α-Fe2O3 particles (contained in the initial mixture) into magnetic Fe3O4 particles. The synthesized material comprises a porous carbonaceous matrix with immobilized Fe3O4 particles. The obtained composite has been characterized by electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The sorption capacity of the porous material has been studied.

  8. Crystal structure, magnetic properties and advances in hexaferrites: A brief review

    NASA Astrophysics Data System (ADS)

    Jotania, Rajshree

    2014-10-01

    Hexaferrites are hard magnetic materials and specifically ferri-magnetic oxides with hexagonal magnetoplumbite type crystallographic structure. Hexagonal ferrites are used as permanent magnets, high-density perpendicular and magneto-optical recording media, and microwave devices like resonance isolators, filters, circulators, phase shifters because of their high magnetic permeability, high electrical resistivity and moderable permittivity. In addition to these; hexagonal ferrites have excellent chemical stability, mechanical hardness and low eddy current loss at high frequencies. The preparation of hexaferrites is a complicated process. Various experimental techniques like standard ceramic techniques, solvent free synthesis route, co precipitation, salt-melt, ion exchange, sol-gel, citrate synthesis, hydrothermal synthesis, spray drying, water-in-oil microemulsion, reverse micelle etc are used to prepare hexaferrite materials. Structural, dielectric and magnetic properties, crystallite size of hexaferrites depend upon nature of substituted ions, method of preparation, sintering temperature and time. The recent interest is nanotechnology, the development of hexaferrite fibres and composites with carbon nano tubes (CNT). Magnetic properties of some doped and un-doped hexaferrites are discussed here. Recent advances in hexaferrites also highlighted in present paper.

  9. Nanoscaled Magnetic Electrodeposited Structures on the Basis of Ion Group Metals: Preparation, Structure, Magnetic and Magnetoresistive Properties

    DTIC Science & Technology

    2000-01-01

    anisotropy components. The contribution of the surface anisotropy constant to the perpendicular magnetic anisotropy becomes predominant when the magnetic layer...increase (Fig.4). Additional evidence of the development of perpendicular magnetic anisotropy can be seen from the magnetization reversal curves...films with perpendicular magnetic anisotropy , Phys.Stat.Sol.(a), 25, 359-363. 8. Fedosyuk V.M., Kasyutich 0.1., Sheleg M.U. (1989),J.Electrochem.Soc

  10. Size and property bimodality in magnetic nanoparticle dispersions: single domain particles vs. strongly coupled nanoclusters.

    PubMed

    Wetterskog, E; Castro, A; Zeng, L; Petronis, S; Heinke, D; Olsson, E; Nilsson, L; Gehrke, N; Svedlindh, P

    2017-03-23

    The widespread use of magnetic nanoparticles in the biotechnical sector puts new demands on fast and quantitative characterization techniques for nanoparticle dispersions. In this work, we report the use of asymmetric flow field-flow fractionation (AF4) and ferromagnetic resonance (FMR) to study the properties of a commercial magnetic nanoparticle dispersion. We demonstrate the effectiveness of both techniques when subjected to a dispersion with a bimodal size/magnetic property distribution: i.e., a small superparamagnetic fraction, and a larger blocked fraction of strongly coupled colloidal nanoclusters. We show that the oriented attachment of primary nanocrystals into colloidal nanoclusters drastically alters their static, dynamic, and magnetic resonance properties. Finally, we show how the FMR spectra are influenced by dynamical effects; agglomeration of the superparamagnetic fraction leads to reversible line-broadening; rotational alignment of the suspended nanoclusters results in shape-dependent resonance shifts. The AF4 and FMR measurements described herein are fast and simple, and therefore suitable for quality control procedures in commercial production of magnetic nanoparticles.

  11. Recovery of soft magnetic properties of FeNiSm films by Ta interlayer

    NASA Astrophysics Data System (ADS)

    Xi, L.; Sun, Q. J.; Li, X. Y.; Zhou, J. J.; Du, J. H.; Ma, J. H.; Wang, Z.; Shi, X. N.; Zuo, Y. L.; Xue, D. S.

    2011-08-01

    The magnetic properties of FeNiSm thin films with different thicknesses, different Ta interlayer thicknesses and different numbers of Ta interlayers were investigated. The single layer FeNiSm shows in-plane uniaxial anisotropy at a thickness below critical value, but shows weak perpendicular anisotropy with a stripe domain structure at thickness above the critical value. Experiments indicate that one or more Ta interlayers inserted into thick FeNiSm films with weak perpendicular anisotropy were effective not only in canceling the perpendicular anisotropy, but also in recovering the in-plane uniaxial anisotropy. Blocking of the columnar growth of FeNi grains by the Ta interlayer is considered to be responsible for this spin reorientation phenomenon. Moreover, the magnetization reversal mechanism in FeNiSm films with uniaxial anisotropy can be ascribed to coherent rotation when the applied field is close to the hard axis and to domain-wall unpinning when the applied field is close to the easy axis. The dynamic magnetic properties of FeNiSm films with uniaxial anisotropy were investigated in the frequency range 0.1-5 GHz. The degradation of the soft magnetic properties of magnetic thin films due to the growth of columnar grains can be avoided by insertion of a Ta interlayer.

  12. Hydrophilic magnetic nanoclusters with thermo-responsive properties and their drug controlled release

    NASA Astrophysics Data System (ADS)

    Meerod, Siraprapa; Rutnakornpituk, Boonjira; Wichai, Uthai; Rutnakornpituk, Metha

    2015-10-01

    Synthesis and drug controlled release properties of thermo-responsive magnetic nanoclusters grafted with poly(N-isopropylacrylamide) (poly(NIPAAm)) and poly(NIPAAm-co-poly(ethylene glycol) methyl ether methacrylate) (PEGMA) copolymers were described. These magnetic nanoclusters were synthesized via an in situ radical polymerization in the presence of acrylamide-grafted magnetic nanoparticles (MNPs). Poly(NIPAAm) provided thermo-responsive properties, while PEGMA played a role in good water dispersibility to the nanoclusters. The ratios of PEGMA to NIPAAm in the (co)polymerization in the presence of the MNPs were fine-tuned such that the nanoclusters with good water dispersibility, good magnetic sensitivity and thermo responsiveness were obtained. The size of the nanoclusters was in the range of 50-100 nm in diameter with about 100-200 particles/cluster. The nanoclusters were well dispersible in water at room temperature and can be suddenly agglomerated when temperature was increased beyond the lower critical solution temperature (LCST) (32 °C). The release behavior of an indomethacin model drug from the nanoclusters was also investigated. These novel magnetic nanoclusters with good dispersibility in water and reversible thermo-responsive properties might be good candidates for the targeting drug controlled release applications.

  13. Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2

    NASA Astrophysics Data System (ADS)

    Baker, P. J.; Lancaster, T.; Blundell, S. J.; Brooks, M. L.; Hayes, W.; Prabhakaran, D.; Pratt, F. L.

    2005-09-01

    We report muon-spin rotation, heat capacity, magnetization, and ac magnetic susceptibility measurements of the magnetic properties of the layered spin- 1/2 antiferromagnet NaNiO2 . These show the onset of long-range magnetic order below TN=19.5K . Rapid muon depolarization, persisting from TN to about 5 K above TN , is consistent with the presence of short-range magnetic order. The temperature and frequency dependence of the ac susceptibility suggests that magnetic clusters persist above 25 K and that their volume fraction decreases with increasing temperature. A frequency dependent peak in the ac magnetic susceptibility at Tsf=3K is observed, consistent with a slowing of spin fluctuations at this temperature. A partial magnetic phase diagram is deduced.

  14. Studying the reversal mode of the magnetization vector versus applied field angle using generalized magneto-optical ellipsometry

    SciTech Connect

    Pufall, M. R.; Berger, A.

    1999-10-26

    The authors used the technique of vector Generalized Magneto-optical Ellipsometry to study the behavior of the magnetization vector of a 50 Co thin film as a function of external field magnitude and direction. With this method, which determines the both the direction and magnitude of the magnetization, averaged over the 1 mm incident laser beam, they were able to determine the relative contributions of magnetization rotation and domain formation to the reversal of M. The Co sample had a uniaxial in-plane anisotropy. The authors found that when the angle between the applied field and the easy axis was greater than {approximately} 40 degrees, the reversal occurred primarily by rotation of the magnetization, accompanied by a small reduction of the magnitude of M. In this angular region, the critical field-the field at which there is a large jump in the angle of M -- as a function of applied field angle followed a coherent rotation model. However, at applied field angles less than 40 degrees to the easy axis, they found a larger reduction in {vert_bar}M{vert_bar} occurring before and during the jump in the magnetization angle. The jump also occurred at fields much lower than those predicted by the coherent rotation model, indicating a reversal mode initiated by domain formation.

  15. Reversible Tuning of Individual Carbon Nanotube Mechanical Properties via Defect Engineering.

    PubMed

    Zhang, Bin; Zhao, Longze; Cheng, Yong; Golberg, Dmitri; Wang, Ming-Sheng

    2016-08-10

    The structural defects that inevitably exist in real-world carbon nanotubes (CNTs) are generally considered undesirable because they break the structural perfection and may result in drastically degraded CNT properties. On the other hand, the deliberate defect introduction can provide a possibility to tailor the tube mechanical properties. Herein, we present a fully controllable technique to handle defects by using in situ transmission electron microscopy (TEM). Young's modulus, quality factor of the resonation and tensile strength of CNTs can be controllably, reversibly, and repeatedly tuned. Parallel high-resolution visualizing of structural defects suggests that the property tuning cycles are primarily attributed to the reversible conversion of defects at the atomic scale: the defects are created in the form of vacancies and interstitials under electron irradiation, and they vanish through the recombination via current-induced annealing. For applications, such as reversible frequency-tuned CNT resonators, this defect-engineering technique is demonstrated to be uniquely precise; the frequency may be tuned with 0.1%/min accuracy, improved by 1 order of magnitude compared with the existing approaches. We believe that these results will be highly valuable in a variety of property-tunable CNT-based composites and devices.

  16. Perpendicular magnetization reversal in Pt/[Co/Ni]3/Al multilayers via the spin Hall effect of Pt

    NASA Astrophysics Data System (ADS)

    Rojas-Sánchez, J.-C.; Laczkowski, P.; Sampaio, J.; Collin, S.; Bouzehouane, K.; Reyren, N.; Jaffrès, H.; Mougin, A.; George, J.-M.

    2016-02-01

    We experimentally investigate the current-induced magnetization reversal in Pt/[Co/Ni]3/Al multilayers combining the anomalous Hall effect and magneto-optical Kerr effect techniques in crossbar geometry. The magnetization reversal occurs through nucleation and propagation of a domain of opposite polarity for a current density of the order of 3 × 1011 A/m2. In these experiments, we demonstrate a full control of each stage: (i) the Ørsted field controls the domain nucleation and (ii) domain-wall propagation occurs by spin torque from the Pt spin Hall effect. This scenario requires an in-plane magnetic field to tune the domain wall center orientation along the current for efficient domain wall propagation. Indeed, as nucleated, domain walls are chiral and Néel-like due to the interfacial Dzyaloshinskii-Moriya interaction.

  17. Spontaneous increase of magnetic flux and chiral-current reversal in bosonic ladders: Swimming against the tide

    NASA Astrophysics Data System (ADS)

    Vekua, Teimuraz; Greschner, Sebastian; Piraud, Marie; Heidrich-Meisner, Fabain; McCulloch, Ian; Schollwoeck, Uli

    The interplay between the spontaneous symmetry breaking and the wave-like nature of quantum particles in lattice produces an extraordinary behavior of the chiral current of interacting bosonic particles in the presence of a uniform magnetic flux defined on a two-leg ladder. While non-interacting as well as strongly interacting particles, stirred by the magnetic field circulate along the system's boundary in the counterclockwise direction, for certain interactions between particles and at sufficiently low temperature, the circulation direction of chiral current can be spontaneously reversed in vortex lattice states. Chiral-current reversal is counter-intuitive many-body effect produced by synthetic magnetism and it can be observed up to temperatures T=0.5J, where J is a hopping rate along ladder. Besides this effect we present first numerical evidence of vortex lattice states in interacting bosonic ladders with flux and a state with spontaneously imbalanced density between the ladder legs.

  18. Magnetic properties of alluvial soils polluted with heavy metals

    NASA Astrophysics Data System (ADS)

    Dlouha, S.; Petrovsky, E.; Boruvka, L.; Kapicka, A.; Grison, H.

    2012-04-01

    Magnetic properties of soils, reflecting mineralogy, concentration and grain-size distribution of Fe-oxides, proved to be useful tool in assessing the soil properties in terms of various environmental conditions. Measurement of soil magnetic properties presents a convenient method to investigate the natural environmental changes in soils as well as the anthropogenic pollution of soils with several risk elements. The effect of fluvial pollution with Cd, Cu, Pb and Zn on magnetic soil properties was studied on highly contaminated alluvial soils from the mining/smelting district (Příbram; CZ) using a combination of magnetic and geochemical methods. The basic soil characteristics, the content of heavy metals, oxalate, and dithionite extractable iron were determined in selected soil samples. Soil profiles were sampled using HUMAX soil corer and the magnetic susceptibility was measured in situ, further detailed magnetic analyses of selected distinct layers were carried out. Two types of variations of magnetic properties in soil profiles were observed corresponding to indentified soil types (Fluvisols, and Gleyic Fluvisols). Significantly higher values of topsoil magnetic susceptibility compared to underlying soil are accompanied with high concentration of heavy metals. Sequential extraction analysis proved the binding of Pb, Zn and Cd in Fe and Mn oxides. Concentration and size-dependent parameters (anhysteretic and isothermal magnetization) were measured on bulk samples in terms of assessing the origin of magnetic components. The results enabled to distinguish clearly topsoil layers enhanced with heavy metals from subsoil samples. The dominance of particles with pseudo-single domain behavior in topsoil and paramagnetic/antiferromagnetic contribution in subsoil were observed. These measurements were verified with room temperature hysteresis measurement carried out on bulk samples and magnetic extracts. Thermomagnetic analysis of magnetic susceptibility measured on

  19. Transport Properties of Equilibrium Argon Plasma in a Magnetic Field

    SciTech Connect

    Bruno, D.; Laricchiuta, A.; Chikhaoui, A.; Kustova, E. V.; Giordano, D.

    2005-05-16

    Electron electrical conductivity coefficients of equilibrium Argon plasma in a magnetic field are calculated up to the 12th Chapman-Enskog approximation at pressure of 1 atm and 0.1 atm for temperatures 500K-20000K; the magnetic Hall parameter spans from 0.01 to 100. The collision integrals used in the calculations are discussed. The convergence properties of the different approximations are assessed. The degree of anisotropy introduced by the presence of the magnetic field is evaluated. Differences with the isotropic case can be very substantial. The biggest effects are visible at high ionization degrees, i.e. high temperatures, and at strong magnetic fields.

  20. Thermal to electricity conversion using thermal magnetic properties

    DOEpatents

    West, Phillip B [Idaho Falls, ID; Svoboda, John [Idaho Falls, ID

    2010-04-27

    A system for the generation of Electricity from Thermal Energy using the thermal magnetic properties of a Ferromagnetic, Electrically Conductive Material (FECM) in one or more Magnetic Fields. A FECM is exposed to one or more Magnetic Fields. Thermal Energy is applied to a portion of the FECM heating the FECM above its Curie Point. The FECM, now partially paramagnetic, moves under the force of the one or more Magnetic Fields. The movement of the FECM induces an electrical current through the FECM, generating Electricity.

  1. Structural and Magnetic Properties of Thin Film of Iron Nitride

    NASA Astrophysics Data System (ADS)

    Kayani, Zohra Nazir; Riaz, Saira; Naseem, Shahzad

    2014-12-01

    The nano-crystalline iron nitride films with a mixture of γ-Fe4N, ɛFe3N and αFe2N phases were synthesized on copper substrate by sol-gel technology. The structure, morphology and magnetic properties of the samples were characterized using X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometer. The films are ferromagnetic at room temperature. Magnetic properties such as coercive forces and saturation magnetization were found to be 398 Oestered and 32.92 emu/cm3, respectively.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  3. Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

    NASA Astrophysics Data System (ADS)

    Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

    1993-03-01

    Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

  4. Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

    NASA Technical Reports Server (NTRS)

    Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

    1993-01-01

    Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

  5. Passive Superconducting Flux Conservers for Rotating-Magnetic-Field-Driven Field-Reversed Configurations

    SciTech Connect

    Oz, E.; Myers, C. E.; Edwards, M. R.; Berlinger, B.; Brooks, A.; Cohen, S. A.

    2011-01-05

    The Princeton Field-Reversed Configuration (PFRC) experiment employs an odd-parity rotating magnetic field (RMFo) current drive and plasma heating system to form and sustain high-Β plasmas. For radial confinement, an array of coaxial, internal, passive, flux-conserving (FC) rings applies magnetic pressure to the plasma while still allowing radio-frequency RMFo from external coils to reach the plasma. The 3 ms pulse duration of the present experiment is limited by the skin time (τfc) of its room-temperature copper FC rings. To explore plasma phenomena with longer characteristic times, the pulse duration of the next-generation PFRC-2 device will exceed 100 ms, necessitating FC rings with (τfc > 300 ms. In this paper we review the physics of internal, discrete, passive FCs and describe the evolution of the PFRC's FC array. We then detail new experiments that have produced higher performance FC rings that contain embedded high-temperature superconducting (HTS) tapes. Several HTS tape winding configurations have been studied and a wide range of extended skin times, from 0.4 s to over 103 s, has been achieved. The new FC rings must carry up to 3 kA of current to balance the expected PFRC-2 plasma pressure, so the dependence of the HTS-FC critical current on the winding configuration and temperature was also studied. From these experiments, the key HTS-FC design considerations have been identified and HTS-FC rings with the desired performance characteristics have been produced.

  6. Defective graphene and nanoribbons: electronic, magnetic and structural properties

    NASA Astrophysics Data System (ADS)

    Guerra, Thiago; Azevedo, Sérgio; Machado, Marcelo

    2016-03-01

    We make use of first-principles calculations, based on the density functional theory (DFT), to investigate the alterations at the structural, energetic, electronic and magnetic properties of graphene and zigzag graphene nanoribbons (ZGNRs) due to the inclusion of different types of line and punctual defects. For the graphene it is found that the inclusion of defects breaks the translational symmetry of the crystal with drastic changes at its electronic structure, going from semimetallic to semiconductor and metallic. Regarding the magnetic properties, no magnetization is observed for the defective graphene. We also show that the inclusion of defects at ZGNRs is a good way to create and control pronounced peaks at the Fermi level. Furthermore, defective ZGNRs structures show magnetic moment by supercell up to 2.0 μ B . For the non defective ZGNRs is observed a switch of the magnetic coupling between opposite ribbon edges from the antiferromagnetic to the ferrimagnetic and ferromagnetic configurations.

  7. Characterizing the Properties of Coronal Magnetic Null Points

    NASA Astrophysics Data System (ADS)

    Barnes, Graham; DeRosa, Marc; Wagner, Eric

    2015-08-01

    The topology of the coronal magnetic field plays a role in a wide range of phenomena, from Coronal Mass Ejections (CMEs) through heating of the corona. One fundamental topological feature is the null point, where the magnetic field vanishes. These points are natural sites of magnetic reconnection, and hence the release of energy stored in the magnetic field. We present preliminary results of a study using data from the Helioseismic and Magnetic Imager aboard NASA's Solar Dynamics Observatory to characterize the properties and evolution of null points in a Potential Field Source Surface model of the coronal field. The main properties considered are the lifetime of the null points, their distribution with height, and how they form and subsequently vanish.This work is supported by NASA/LWS Grant NNX14AD45G, and by NSF/SHINE grant 1357018.

  8. Magnetic properties of ErN films

    NASA Astrophysics Data System (ADS)

    Meyer, C.; Ruck, B. J.; Preston, A. R. H.; Granville, S.; Williams, G. V. M.; Trodahl, H. J.

    2010-07-01

    We report a magnetization study of stoichiometric ErN nanocrystalline films grown on Si and protected by a GaN passivating layer. According to the temperature dependence of the resistivity the films are heavily doped semiconductors. Above 100 K the magnetization data fit well to a Curie-Weiss behavior with a moment expected within the free-ion ErJ={15}/{2} multiplet. Below 50 K the Curie-Weiss plot steepens to an effective moment corresponding to that in the crystal-field determined quartet ground state, and develops a clear paramagnetic Curie-Weiss temperature of about 4.5 K. Zero-field- and field-cooled magnetization curves and the AC susceptibility firmly establish a ferromagnetic ground state within that multiplet below a Curie temperature of 6.3±0.7 K. Due to the (1 1 1) texture of the film the comparison between the magnetization behavior, when the field is applied parallel and perpendicular to the film plane, gives new information about the magnetic structure. An arrangement of the moments according to the model derived from neutron diffraction for bulk HoN is strongly suggested.

  9. Metastable epitaxial magnets: A study of growth and magnetic properties

    NASA Astrophysics Data System (ADS)

    Wu, Stella Zhong

    1997-11-01

    Recent advancement in the information storage industry is demanding more fundamental understanding of magnetic systems, especially the magnetic thin films, surfaces, and interfaces. In this work, we were focusing on ultrathin ferromagnetic thin films of Ni on Cu(100), Cu(110) and Cu(111) single crystal substrates, and FeNi and CoNi binary alloy films on Cu(100) with varying atomic concentration. The growth of these films by molecular beam epitaxy was monitored using a number of experimental techniques. A pseudomorphic layer-by-layer growth was achieved which resulted in an fcc metastable crystalline structure with a ferromagnetic phase. The magnetic anisotropy behavior of these thin films was monitored using surface magneto-optic Kerr effect magnetometer at both polar and longitudinal geometries, and various spin reorientation transitions were found. The measurements of Curie temperature as a variation of film thickness as well as atomic concentration resulted in the proposal of a finite-size scaling law. By using this scaling law, the bulk Curie temperature for these metastable fcc binary alloys can be extrapolated, showing that Fe atoms exist in a low-spin ferromagnetic phase. In the Ni films, a dimensionality crossover from bulk to a 2-dimensional system at a few monolayer thickness was established. By alloying, we have been able to tune the electron occupation number in the 3d band. Combined with the 3d electronic band structure information we have gained by using ultraviolet photoemission spectroscopy study of these systems at normal emission, a conclusion of continuous band filling in CoNi alloy system was drawn. However, FeNi films show a different behavior at a certain composition. The recent collaboration with synchrotron radiation facility has enabled us to quantitatively characterize the spin moment and orbital moment from each element. An x-ray magnetic circular dichroism (XMCD) study was performed on CoNi alloy system, and resulted in the conclusion of

  10. Controlling electronic and magnetic properties of ultra narrow multilayered nanowires

    NASA Astrophysics Data System (ADS)

    Panigrahi, Puspamitra

    Interest in the study of magnetic/non-magnetic multilayered structures took a giant leap since Grunberg and his group established that the interlayer exchange coupling (IEC) is a function of the non-magnetic spacer width. This interest was further fuelled by the discovery of the phenomenal Giant Magnetoresistance (GMR) effect. In fact, in 2007 Albert Fert and Peter Grunberg were awarded the Nobel Prize in Physics for their contribution to the discovery of GMR. GMR is the key property that is being used in the read-head of the present day computer hard drive as it requires a high sensitivity in the detection of magnetic field. The recent increase in demand for device miniaturization encouraged researchers to look for GMR in nanoscale multilayered structures. In this context, one dimensional (1-D) multilayered nanowire structure has shown tremendous promise as a viable candidate for ultra sensitive read head sensors. In fact, the phenomenal giant magnetoresistance (GMR) effect, which is the novel feature of the currently used multilayered thin film, has already been observed in multilayered nanowire systems at ambient temperature. Geometrical confinement of the supper lattice along the 2-dimensions (2-D) to construct the 1-D multilayered nanowire prohibits the minimization of magnetic interaction-offering a rich variety of magnetic properties in nanowire that can be exploited for novel functionality. In addition, introduction of non-magnetic spacer between the magnetic layers presents additional advantage in controlling magnetic properties via tuning the interlayer magnetic interaction. Despite of a large volume of theoretical works devoted towards the understanding of GMR and IEC in super lattice structures, limited theoretical calculations are reported in 1-D multilayered systems. Thus to gauge their potential application in new generation magneto-electronic devices, in this thesis, I have discussed the usage of first principles density functional theory (DFT) in

  11. Reverse pharmacognosy: identifying biological properties for plants by means of their molecule constituents: application to meranzin.

    PubMed

    Do, Quoc-Tuan; Lamy, Cécile; Renimel, Isabelle; Sauvan, Nancy; André, Patrice; Himbert, Franck; Morin-Allory, Luc; Bernard, Philippe

    2007-10-01

    Reverse pharmacognosy aims at finding biological targets for natural compounds by virtual or real screening and identifying natural resources that contain the active molecules. We report herein a study focused on the identification of biological properties of meranzin, a major component isolated from Limnocitrus littoralis (Miq.) Swingle. Selnergy, an IN SILICO biological profiling software, was used to identify putative binding targets of meranzin. Among the 400 screened proteins, 3 targets were selected: COX1, COX2 and PPARgamma. Binding tests were realised for these 3 protein candidates, as well as two negative controls. The predictions made by Selnergy were consistent with the experimental results, meaning that these 3 targets can be modulated by an extract containing this compound in a suitable concentration. These results demonstrate that reverse pharmacognosy and its inverse docking component is a powerful tool to identify biological properties for natural molecules and hence for plants containing these compounds.

  12. Reverse draining of a magnetic soap film — Analysis and simulation of a thin film equation with non-uniform forcing

    NASA Astrophysics Data System (ADS)

    Moulton, D. E.; Lega, J.

    2009-11-01

    We analyze and classify equilibrium solutions of the one-dimensional thin film equation with no-flux boundary conditions and in the presence of a spatially dependent external forcing. We prove theorems that shed light on the nature of these equilibrium solutions, guarantee their validity, and describe how they depend on the properties of the external forcing. We then apply these results to the reverse draining of a one-dimensional magnetic soap film subject to an external non-uniform magnetic field. Numerical simulations illustrate the convergence of the solutions towards equilibrium configurations. We then present bifurcation diagrams for steady state solutions. We find that multiple stable equilibrium solutions exist for fixed parameters, and uncover a rich bifurcation structure to these solutions, demonstrating the complexity hidden in a relatively simple looking evolution equation. Finally, we provide a simulation describing how numerical solutions traverse the bifurcation diagram, as the amplitude of the forcing is slowly increased and then decreased.

  13. Reversal magnetization dependence with the Cr and Fe oxidation states in YFe1-xCrxO3 (0≤x≤1) perovskites

    NASA Astrophysics Data System (ADS)

    Fabian, F. A.; Pedra, P. P.; Moura, K. O.; Duque, J. G. S.; Meneses, C. T.

    2016-06-01

    In this work, we have carried out a detailed study of the magnetic and structural properties of YFe1-xCrxO3 (0≤x≤1) samples with orthorhombic structure obtained by co-precipitation method. Analysis of X-ray diffraction data using Rietveld refinement show that all samples present an orthorhombic crystal system with space group Pnma. Besides, we have observed a reduction of unit cell volume with increasing of the Cr concentration. SEM images show the formation of grains of micrometer order. X-ray Absorption near edge spectroscopy (XANES) measurements show a shift of absorption edge which can be indicate there is (i) different oxidation states to Fe and Cr ions and/or (ii) a changing in the point symmetry of Fe and Cr ions to the compounds. The magnetization measurements indicate a continuous decreasing of the magnetic transition temperature as function of chromium doping. The reversal magnetization effect was observed to concentrations around x=0.5. Besides, the deviation of the Curie-Weiss law and a weak ferromagnetic behavior observed at room temperature in the M vs H curves can be attributed to the strong magnetic interactions between the transition metals with different oxidation states.

  14. Nuclear magnetic resonance properties of lunar samples.

    NASA Technical Reports Server (NTRS)

    Kline, D.; Weeks, R. A.

    1972-01-01

    Nuclear magnetic resonance spectra of Na-23, Al-27, and P-31 in fines samples 10084,60 and 14163,168 and in crystalline rock samples 12021,55 and 14321,166, have been recorded over a range of frequencies up to 20 MHz. A shift in the field at which maximum absorption occurs for all of the spectra relative to the field at which maximum absorption occurs for terrestrial analogues is attributed to a sample-dependent magnetic field at the Na, Al, and P sites opposing the laboratory field. The magnitude of these fields internal to the samples is sample dependent and varies from 5 to 10 G. These fields do not correlate with the iron content of the samples. However, the presence of single-domain particles of iron distributed throughout the plagioclase fraction that contains the principal fraction of Na and Al is inferred from electron magnetic resonance spectra shapes.

  15. Reversible Tailoring of Mechanical Properties of Carbon Nanotube Forests by Immersing in Solvents

    DTIC Science & Technology

    2014-12-07

    Author’s personal copy Reversible tailoring of mechanical properties of carbon nanotube forests by immersing in solvents Parisa Pour Shahid Saeed...December 2013 Available online 7 December 2013 A B S T R A C T The mechanical behavior of carbon nanotube (CNT) forests soaked in three solvents – tol- uene...solvents, produces the lowest vdW forces between individual CNTs. Furthermore, wet–dry cycling of CNT forests shows the revers- ibility and

  16. Magnetic properties of 42CrMo4 steel

    NASA Astrophysics Data System (ADS)

    Bulin, T.; Svabenska, E.; Hapla, M.; Roupcova, P.; Ondrusek, C.; Schneeweiss, O.

    2017-02-01

    Low alloyed high-grade chrome-molybdenum ferritic steel was investigated from the point of views of magnetic properties in dependence on heat and mechanical treatment. This steel can be used as components of magnetic circuits or some parts in electrical equipment. The basic information on structure and phase composition was obtained by optical and scanning electron microscopy, X-ray Powder Diffraction and Mössbauer Spectroscopy. The temperature stability of the material was proved by measurements of temperature dependences of magnetic moment. The magnetic parameters were obtained by measuring of magnetic hysteresis loops in dependence on saturation field and their frequencies. The results are discussed from the point of view of possible applications as a magnetic material in the very extremely environment, where high mechanical stresses and elevated temperatures can occur.

  17. Extended magnetohydrodynamic simulations of field reversed configuration formation and sustainment with rotating magnetic field current drive

    NASA Astrophysics Data System (ADS)

    Milroy, R. D.; Kim, C. C.; Sovinec, C. R.

    2010-06-01

    Three-dimensional simulations of field reversed configuration (FRC) formation and sustainment with rotating magnetic field (RMF) current drive have been performed with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. The Hall term is a zeroth order effect with strong coupling between Fourier components, and recent enhancements to the NIMROD preconditioner allow much larger time steps than was previously possible. Boundary conditions to capture the effects of a finite length RMF antenna have been added, and simulations of FRC formation from a uniform background plasma have been performed with parameters relevant to the translation, confinement, and sustainment-upgrade experiment at the University of Washington [H. Y. Guo, A. L. Hoffman, and R. D. Milroy, Phys. Plasmas 14, 112502 (2007)]. The effects of both even-parity and odd-parity antennas have been investigated, and there is no evidence of a disruptive instability for either antenna type. It has been found that RMF effects extend considerably beyond the ends of the antenna, and that a large n =0 Bθ can develop in the open-field line region, producing a back torque opposing the RMF.

  18. Time-Reversal Symmetry Violation in Molecules Induced by Nuclear Magnetic Quadrupole Moments

    NASA Astrophysics Data System (ADS)

    Flambaum, V. V.; DeMille, D.; Kozlov, M. G.

    2014-09-01

    Recent measurements in paramagnetic molecules improved the limit on the electron electric dipole moment (EDM) by an order of magnitude. Time-reversal (T) and parity (P) symmetry violation in molecules may also come from their nuclei. We point out that nuclear T, P-odd effects are amplified in paramagnetic molecules containing deformed nuclei, where the primary effects arise from the T, P-odd nuclear magnetic quadrupole moment (MQM). We perform calculations of T, P-odd effects in the molecules TaN, ThO, ThF+, HfF+, YbF, HgF, and BaF induced by MQMs. We compare our results with those for the diamagnetic TlF molecule, where the T, P-odd effects are produced by the nuclear Schiff moment. We argue that measurements in molecules with MQMs may provide improved limits on the strength of T, P-odd nuclear forces, on the proton, neutron, and quark EDMs, on quark chromo-EDMs, and on the QCD θ term and CP-violating quark interactions.

  19. Variation of magnetic properties with mischmetal content in the resource saving magnets of MM-Fe-B ribbons

    NASA Astrophysics Data System (ADS)

    Li, Zhu-bai; Wang, Li-chen; Geng, Xiao-peng; Hu, Feng-xia; Sun, Ji-rong; Shen, Bao-gen

    2017-03-01

    Magnetic materials of MM-Fe-B (MM=mischmetal) ribbons were prepared using melt spinning method by varying the content of MM. The ribbons contain minor phases besides the main phase of Re2Fe14B. X-ray techniques show that the diffraction peak intensities of the minor phase Fe3B vary with the content of constituent elements, indicating that the amount of minor phase could be tunable. The squareness of hysteresis loop is the best in MM13Fe80.5B6.5 ribbons, which should mainly ascribe to the less amount of minor phase. Henkel plots verify the more uniform magnetization reversals in MM13Fe80.5B6.5 ribbons, and the energy product achieves to the maximum of 12.74 MGOe with the coercivity of 6.50 kOe. With the increase of MM content the coercivity increases monotonically, and reaches to 9.13 kOe in MM15Fe77.5B7.5 ribbons, which should be related with the nature of the defects in the main phase. These investigations show that optimizing the content of constituent elements and phase constitution could improve magnetic properties in the resource-saving magnets of MM-Fe-B ribbons.

  20. Effect of maghemization on the magnetic properties of pseudo-single-domain magnetite particles

    NASA Astrophysics Data System (ADS)

    Almeida, T.; Muxworthy, A. R.; Kasama, T.; Williams, W.; Damsgaard, C.; Frandsen, C.; Pennycook, T. J.; Dunin-Borkowski, R.

    2015-12-01

    magnetic hysteresis measurements, including first-order reversal curve analysis. The coercivity of the grains is shown to increase with reaction temperature up to 180 ºC, but subsequently decreases after heating above 200 ºC; this magnetic behavior is attributed to the growth of a γ-Fe2O3 shell with magnetic properties distinct from the Fe3O4 core.

  1. Magnetic properties of a classical XY spin dimer in a "planar" magnetic field

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion; Prenga, Dode

    2016-10-01

    Single-molecule magnetism originates from the strong intra-molecular magnetic coupling of a small number of interacting spins. Such spins generally interact very weakly with the neighboring spins in the other molecules of the compound, therefore, inter-molecular spin couplings are negligible. In certain cases the number of magnetically coupled spins is as small as a dimer, a system that can be considered the smallest nanomagnet capable of storing non-trivial magnetic information on the molecular level. Additional interesting patterns arise if the spin motion is confined to a two-dimensional space. In such a scenario, clusters consisting of spins with large-spin values are particularly attractive since their magnetic interactions can be described well in terms of classical Heisenberg XY spins. In this work we calculate exactly the magnetic properties of a nanomagnetic dimer of classical XY spins in a "planar" external magnetic field. The problem is solved by employing a mathematical approach whose idea is the introduction of auxiliary spin variables into the starting expression of the partition function. Results for the total internal energy, total magnetic moment, spin-spin correlation function and zero-field magnetic susceptibility can serve as a basis to understand the magnetic properties of large-spin dimer building blocks.

  2. Magnetic and Electrical Properties of Ferromagnetic Semiconductors,

    DTIC Science & Technology

    magnetism and of the mechanism of the electronic conductivity of ferromagnetic semiconductors in connection with their chemical composition and crystalline ... structure . The basic groups of oxide compounds of 4f- and 3d-transition metals with maximum spin values were selected for the studies in this work. The

  3. Magnetic Properties of Radiation Damage in Pu

    SciTech Connect

    McCall, S; Fluss, M J; Chung, B W; McElfresh, M; Chapline, G; Jackson, D

    2004-10-27

    First, we review earlier studies reporting possible magnetic characteristics for radiation defects in Pu. We then report, for {alpha}-Pu, two studies of the excess magnetic susceptibility (EMS) due to radiation damage, as a function of time and temperature. We have observed several annealing stages associated with the EMS of the accumulated self-damage and we report that annealing begins at {approx}31K, while below that temperature the displacement damage from self-irradiation of the Pu alpha particle emission and the U recoil are immobile. A detailed investigation was made of this EMS well below the first annealing stage as a function of temperature (2K < T < 15K) and time in a magnetic field of 2T. A linear increase in magnetic susceptibility is seen as a function of time for all isotherms. The excess susceptibility per alpha decay, determined from a linear fit of the slope of the time dependent EMS, is reasonably described with a Curie-Weiss law exhibiting a small negative Weiss temperature. We conclude by describing some future experiments in light of the present results.

  4. Statistical thermodynamics of magnetic fluids. Monte Carlo calculation of the magnetic properties

    SciTech Connect

    Berkovskii, B.M.; Kalikmanov, V.I.; Filinov, V.S.

    1988-07-01

    An approach is proposed, and a modification of the Monte Carlo method is presented, for the calculation of the equilibrium thermodynamic properties of a magnetic fluid. The magnetization and mean energy are calculated. It is shown that the behavior of these properties differs from Langevin behavior, as a result of taking particle interactions into account. The results obtained are in good agreement with experimental data.

  5. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  6. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy

    PubMed Central

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-01-01

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques. PMID:27138030

  7. Giant and reversible room-temperature elastocaloric effect in a single-crystalline Ni-Fe-Ga magnetic shape memory alloy.

    PubMed

    Li, Yang; Zhao, Dewei; Liu, Jian

    2016-05-03

    Good mechanical properties and large adiabatic temperature change render Heusler-type Ni2FeGa-based magnetic shape memory alloys as a promising candidate material for solid-state mechanical cooling application at ambient conditions. Superelastic behavior and associated elastocaloric effect strongly reply on deformation conditions (e.g. applied strain rate and strain level) of stress-induced martensitic transformations. With the aim of developing high-performance elastic cooling materials, in this work, we have carried out a systematic study on a Ni54Fe19Ga27 [420]-oriented single crystal by exploring the interaction between dynamic deformation parameters and thermal response. A giant and reversible adiabatic temperature change of ±7.5 K triggered by a low stress of 30 MPa was achieved. Such a high specific cooling performance thus offers the great advantage for the small scale solid-state mechanical cooling applications. Besides, a significant temporary residual strain effect has been observed at high strain rate, which is unfavorable for reversible elastocaloric effect but can be overcome by reducing stress hysteresis, and/or by elevating initial environmental temperature. The established criterion for the desirable reversible elastocaloric properties goes beyond the present system, and can be applicable for other shape memory alloys used for elastic cooling techniques.

  8. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Orbital magnetization in semiconductors

    NASA Astrophysics Data System (ADS)

    Fang, Cheng; Wang, Zhi-Gang; Li, Shu-Shen; Zhang, Ping

    2009-12-01

    This paper theoretically investigates the orbital magnetization of electron-doped (n-type) semiconductor heterostructures and of hole-doped (p-type) bulk semiconductors, which are respectively described by a two-dimensional electron/hole Hamiltonian with both the included Rashba spin-orbit coupling and Zeeman splitting terms. It is the Zeeman splitting, rather than the Rashba spin-orbit coupling, that destroys the time-reversal symmetry of the semiconductor systems and results in nontrivial orbital magnetization. The results show that the magnitude of the orbital magnetization per hole and the Hall conductance in the p-type bulk semiconductors are about 10-2-10-1 effective Bohr magneton and 10-1-1 e2/h, respectively. However, the orbital magnetization per electron and the Hall conductance in the n-type semiconductor heterostructures are too small to be easily observed in experiment.

  9. Final Report on Development of Optimized Field-Reversed Configuration Plasma Formation Techniques for Magnetized Target Fusion

    SciTech Connect

    Lynn, Alan

    2013-11-01

    The University of New Mexico (UNM) proposed a collaboration with Los Alamos National Laboratory (LANL) to develop and test methods for improved formation of field-reversed configuration (FRC) plasmas relevant to magnetized target fusion (MTF) energy research. MTF is an innovative approach for a relatively fast and cheap path to the production of fusion energy that utilizes magnetic confinement to assist in the compression of a hot plasma to thermonuclear conditions by an external driver. LANL is currently pursing demonstration of the MTF concept via compression of an FRC plasma by a metal liner z-pinch in conjunction with the Air Force Research Laboratory in Albuquerque, NM. A key physics issue for the FRC's ultimate success as an MTF target lies in the initial pre-ionization (PI) stage. The PI plasma sets the initial conditions from which the FRC is created. In particular, the PI formation process determines the amount of magnetic flux that can be trapped to form the FRC. A ringing theta pinch ionization (RTPI) technique, such as currently used by the FRX-L device at LANL, has the advantages of high ionization fraction, simplicity (since no additional coils are required), and does not require internal electrodes which can introduce impurities into the plasma. However RTPI has been shown to only trap 50% of the initial bias flux at best and imposes additional engineering constraints on the capacitor banks. The amount of trapped flux plays an important role in the FRC's final equilibrium, transport, and stability properties, and provides increased ohmic heating of the FRC through induced currents as the magnetic field decays. Increasing the trapped flux also provides the route to greatest potential gains in FRC lifetime, which is essential to provide enough time to translate and compress the FRC effectively. In conjunction with LANL we initially planned to develop and test a microwave break- down system to improve the initial PI plasma formation. The UNM team would

  10. Synthesis and magnetic properties of Ta/NdFeB-based composite microwires

    SciTech Connect

    Szary, P. Périgo, E. A.; Michels, A.; Luciu, I.; Duday, D.; Wirtz, T.; Choquet, P.

    2015-05-07

    Magnetic NdFeB-based microwire composites have been prepared by the direct current magnetron sputtering technique in a specifically designed sputtering chamber for thin-film deposition in wire geometry. As substrate wire material, we have employed steel and Ta. Annealing of the substrate wires during the deposition process was performed by ohmic heating through the application of a direct current. Samples were characterized by means of vibrating sample magnetometry (VSM) and scanning electron microscopy. Best properties have been encountered when using Ta wires as core (substrate) material. The VSM data show a dramatic impact of the current applied during the deposition process on the magnetic properties. For higher current values, i.e., higher annealing temperatures, the wires exhibit a reversal process that is typical for a two-phase system. Moreover, an increase of the coercive field (and remanent magnetization) is observed, which is ascribed to a modification of the magnetic phase present in the sample due to the annealing. We find an indication for the formation of a magnetic easy-axis direction which is azimuthally oriented around the wire axis.

  11. Tuned Magnetic Properties of L10-MnGa/Co(001) Films by Epitaxial Strain

    PubMed Central

    Kim, Dongyoo; Vitos, Levente

    2016-01-01

    We demonstrate that the interface structure has a significant influence on the magnetic state of MnGa/Co films consisting of L10-MnGa on face-centered-cubic Co(001) surface. We reveal an antiferromagnetic to ferromagnetic magnetization reversal as a function of the lateral lattice constant. The magnetization reversal mainly originates from localized states and weak hybridization at interface due to charge redistribution between muffin-tin spheres and interstitial region. The magnetic anisotropy energy of Mn/Co interface system is enhanced with increasing in-plane lattice constant, which is ascribed to the interface interactions and the above magnetization reversal. PMID:26781348

  12. Magnetic properties of solid oxygen under pressure (Review Article)

    NASA Astrophysics Data System (ADS)

    Freiman, Yu. A.

    2015-11-01

    Solid oxygen is a unique crystal combining properties of a simple molecular solid and a magnet. Unlike ordinary magnets, the exchange interaction in solid oxygen acts on a background of weak Van der Waals forces, providing a significant part of the total lattice energy. Therefore, the magnetic and lattice properties of solid oxygen are very closely related. This manifests itself in a very rich phase diagram and numerous anomalies of thermal, magnetic and optical properties. Low-temperature low-pressure α-O2 is a two-sublattice collinear Neel antiferromagnet. At a pressure of ˜6 GPa, α-O2 is transformed into δ-O2, in which three different magnetic structures are realized upon increasing temperature. At ˜8 GPa δ-O2 is transformed into ɛ-O2. In this transition, O2 molecules combine into four-molecule clusters (O2)4. This transformation is accompanied by a magnetic collapse. This review describes the evolution of the magnetic structure with increasing pressure, and analyzes the causes behind this behavior.

  13. Topological properties of the time-reversal-symmetric Kitaev chain and applications to organic superconductors

    NASA Astrophysics Data System (ADS)

    Dumitrescu, E.; Tewari, Sumanta

    2013-12-01

    We show that the pair of Majorana modes at each end of a 1D spin triplet superconductor with Δ↑↑=-Δ↓↓=pΔ0 (two time reversed copies of the Kitaev p-wave chain) are topologically robust to perturbations such as mixing by the Sz=0 component of the order parameter (Δ↑↓=Δ↓↑), transverse hopping, nonagnetic disorder, and also, importantly, to time-reversal (TR) breaking perturbations such as applied Zeeman fields/magnetic impurities and the mixing by the Sy=0 component of the order parameter (Δ↑↑=Δ↓↓). We show that the robustness to TR-breaking results from a hidden chiral symmetry, which places the system in the BDI class in the presence of the generic TR-breaking perturbations (the TR-invariant system is both DIII and BDI). Our work has important implications for the quasi-1D organic superconductors (TMTSF)2X (X =PF6,CIO4) (Bechgaard salts) and Li0.9Mo6O17, which have been proposed as triplet superconductors with equal spin pairing (Δ↑↑,Δ↓↓≠0,Δ↑↓=0) in the presence of magnetic fields.

  14. Magnetic properties and magnetic hardening mechansim of Pt-Co-B alloys

    NASA Technical Reports Server (NTRS)

    Qiu, Ning; Flanagan, F.; Wittig, James E.

    1994-01-01

    The intrinsic coercivity is found to be maximized in the Pt42Co45B13 ternary alloy which is undercooled and rapidly solidified (quenched using a 70 m/s wheel speed after undercooling), and then annealed (800 C for 2400 min). The same alloy, processed at slower cooling rates and annealed in the same way, has a much larger scale microstructure and a much lower resulting magnetic coercivity. The microstructure which would optimize the coercitvity of this coercivity of this ternary alloy is a completely ordered L1(sub zero) Pt-Co matrix with a submicron magnetic single-domion Co-boride precipitate. The L1(sub zero) phase is highly anistropic magnetically while the Co-boride precipate is somewhat less so. Annealing treatments designed to produced single-domain Co-boride precipitates enhance the coercivity. This suggests that the refined microstructures is responsible for the high coercivities found in the rapidly solidified and annealed alloy. The magnetic domain wall thickness for a Co-boride precipitate is determined from both experimental observation and theoretical calculation in order to evaluate its influence on the coercivity of the alloy. The effects of the pinning of domain walls and the barrier to the nucleation of reverse domains on the coercivity are discussed. Both microstrucutral analysis and theoretical calculation indicate that the high coercivities in the Pt42Co45B13 alloy are due to the difficult nucleation of reverse magnetic domains.

  15. Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains

    NASA Astrophysics Data System (ADS)

    Chang, Liao; Winklhofer, Michael; Roberts, Andrew P.; Heslop, David; Florindo, Fabio; Dekkers, Mark J.; Krijgsman, Wout; Kodama, Kazuto; Yamamoto, Yuhji

    2013-12-01

    marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic "hard" component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial.

  16. Changes in magnetic properties of neutron irradiated RPV steel

    SciTech Connect

    Park, D.G.; Hong, J.H.; Ok, C.I.; Kim, J.W.; Kim, H.C.

    1998-07-01

    Conventional magnetic parameters and Barkhausen noise have been measured in pressure vessel steel samples both as-received and irradiated with doses of up to 10{sup 18} n/cm{sup 2}. The conventional magnetic parameters, i.e., coercive force, remanence and maximum induction did not change significantly with irradiation, whereas the Barkhausen noise amplitude and energy during a magnetization cycle decreased markedly with irradiation dose. A three stage variation of Barkhausen noise with neutron dose was observed in the present work, namely an initial decrease, a near plateau and rapid decrease. The three stage variation with neutron dose is in qualitative agreement with computer simulations of the radiation damage process performed by Beeler. The hardness also varied in three stages in a reverse manner with transition at the same doses.

  17. Influence of Reversibly Associating Side Group Bond Strength on Viscoelastic Properties of Polymer Melts

    NASA Astrophysics Data System (ADS)

    Lewis, Christopher; Stewart, Kathleen; Anthamatten, Mitchell

    2013-03-01

    Reversible hydrogen-bonding between side-groups of linear polymers can sharply influence a material's dynamic mechanical behavior, giving rise to valuable shape memory and self-healing properties. Here, we investigate how bond-strength affects the bulk rheological behavior of functional poly(n-butyl acrylate) (PBA) melts. A series of random copolymers containing three different reversibly bonding groups (aminopyridine, carboxylic acid, and ureidopyrimidinone) were synthesized to systematically vary the side-group hydrogen bond strength (~26, 40, 70 kJ/mol). The materials' volumetric hydrogen-bond energy densities can be tuned by adjusting the side-group composition. By comparing the viscoelastic behavior of materials containing an equivalent bond energy density, with different bonding groups, the efficacy and cooperativity of reversible binding can be directly examined. Melt rheology results are interpreted using a state-of-ease model that assumes continuous mechanical equilibrium between applied stress and resistive stresses of entropic origin arising from a network of reversible bonds. The authors acknowledge support from funding provided by the National Science Foundation under Grant DMR-0906627

  18. Sign reversal of magnetization and tunable exchange bias field in NdCr1-xFexO3 (x=0.05-0.2)

    NASA Astrophysics Data System (ADS)

    Bora, Tribedi; Ravi, S.

    2015-07-01

    Magnetization reversal and tunable exchange bias behavior are observed in NdCr1-xFexO3 compounds for x=0.05-0.20. The magnetic compensation temperature (Tcomp) is found to increase with increase in Fe concentration and its maximum value is 198 K for x=0.15 sample. The observed magnetization reversal is explained by considering the competition between the weak ferromagnetic component of Cr3+ ions and the paramagnetic moments of Nd3+ and Fe3+ ions under the influence of negative internal magnetic field. The exchange anisotropy between the above two components of magnetic moments give rise to tunable positive and negative exchange bias fields. The sign reversal of exchange bias field also coincides with Tcomp. Bipolar switching of magnetization is demonstrated at Tmagnetic field.

  19. Relationships of the group velocity of the time-reversed Lamb wave with bone properties in cortical bone in vitro.

    PubMed

    Lee, Kang Il; Yoon, Suk Wang

    2017-02-27

    The present study aims to investigate the feasibility of using the time-reversed Lamb wave as a new method for noninvasive characterization of long cortical bones. The group velocity of the time-reversed Lamb wave launched by using the modified time reversal method was measured in 15 bovine tibiae, and their correlations with the bone properties of the tibia were examined. The group velocity of the time-reversed Lamb wave showed significant positive correlations with the bone properties (r=0.55-0.81). The best univariate predictor of the group velocity of the time-reversed Lamb wave was the cortical thickness, yielding an adjusted squared correlation coefficient (r(2)) of 0.64. These results imply that the group velocity of the time-reversed Lamb wave, in addition to the velocities of the first arriving signal and the slow guided wave, could potentially be used as a discriminator for osteoporosis.

  20. The symmetry properties of planetary magnetic fields

    NASA Technical Reports Server (NTRS)

    Raedler, Karl-Heinz; Ness, Norman F.

    1990-01-01

    This paper provides a comparative study of the geometrical structures of the magnetic fields of earth, Jupiter, Saturn, and Uranus, starting from the traditional multipolar representations of these fields. For earth, Jupiter, and Saturn, the centered dipole, quadrupole, and octupole contributions are included, while at Uranus only the dipole and quadrupole contributions are considered. It is found that there are a number of common features of the magnetic fields of earth and Jupiter. Compared to earth and Jupiter, the Saturnian field exhibits not only a high degree of symmetry about the rotation axis but also a high degree of antisymmetry about the equatorial plane. The Uranian field shows strong deviations from both such symmetries. Nevertheless, there remain features common to all four planets.

  1. Basic magnetic properties of bituminous coal

    USGS Publications Warehouse

    Alexander, C.C.; Thorpe, A.N.; Senftle, F.E.

    1979-01-01

    Magnetic susceptibility and other static magnetic parameters have been measured on a number of bituminous coals from various locations in the United States. The paramagnetic Curie constant correlates negatively with carbon concentration on a moisture-free basis. The major contribution to the total paramagnetism comes from the mineral matter rather than from free radicals or broken bonds. Analysis of the data indicates that the specific paramagnetism is generally lower in the mineral matter found in high-ash compared to low-ash coal. A substantial number of the coal specimens tested also had a ferromagnetic susceptibility which appeared to be associated with magnetite. Magnetite and ??-iron spherules, possibly of meteoritic or volcanic origin, were found in several specimens. ?? 1979.

  2. Recent advances in magnetic nanoparticles with bulk-like properties

    NASA Astrophysics Data System (ADS)

    Batlle, Xavier

    2013-03-01

    Magnetic nanoparticles (NP) are an excellent example of nanostructured materials and exhibit fascinating properties with applications in high-density recording and biomedicine. Controlling the effects of the nanostructure and surface chemistry and magnetism at the monolayer level have become relevant issues. As the size is reduced below 100 nm, deviations from bulk behavior have been attributed to finite-size effects and changes in the magnetic ordering at the surface, thus giving rise to a significant decrease in the magnetization and increase in the magnetic anisotropy. The existence of a surface spin glass-like state due to magnetic frustration has been widely suggested in ferrimagnetic NP. However, in this talk, we will show that high crystal quality magnetite Fe3-xO4 NP of about a few nanometers in diameter and coated with different organic surfactants display bulk-like structural, magnetic and electronic properties. Magnetic measurements, transmission electron microscopy, X-ray absorption and magnetic circular dichroism and Monte Carlo simulations, evidenced that none of the usual particle-like behavior is observed in high quality NP of a few nm. Consequently, the magnetic and electronic disorder phenomena typically observed in those single-phase ferrimagnetic NP should not be considered as an intrinsic effect. We also performed a real-space characterization at the sub-nanometer scale, combining scanning transmission electron microscopy, electron energy loss spectroscopy and electron magnetic chiral dichroism. For the first time, we found that the surface magnetization is as high as about 70% of that of the core. The comparison to density functional theory suggested the relevance of the strong surface bond between the Fe ions and the organic surfactant. All the foregoing demonstrates the key role of both the crystal quality and surface bond on the physical properties of ferrimagnetic NP and paves the way to the fabrication of the next generation of NP with

  3. Microstructure and magnetic properties of FINEMET nanowires

    NASA Astrophysics Data System (ADS)

    Chiriac, H.; Corodeanu, S.; Óvári, T.-A.; Lupu, N.

    2013-05-01

    FINEMET (Fe73.5Cu1Nb3Si13.5B9) glass-coated nanowires and submicron wires with metallic nucleus diameters (Φm) between 100 and 500 nm and the glass coating thickness (tg) of 5 μm are reported for the first time. The microstructure of annealed ultrathin glass-coated wires evolves into a nanocrystalline one (DO3 nanograins of 10-20 nm embedded into the residual amorphous matrix) after annealing at 550 °C and 600 °C for 60 min. Despite the similar size of the nanograins, the volume occupied by them relative to the total volume increases from 50%-53% after annealing at 550 °C to 63%-65% after annealing at 600 °C, due to the increase in their number. This is reflected in a more accurate manner in the domain wall velocity measurements than in variation of the magnetic characteristics such as M(H), relative magnetic permeability or switching field. The magnetically softest nanocrystalline phase is formed at larger values of annealing temperature (Ta) for thinner wires, since larger temperature is needed to grow a sufficient number of DO3 grains at distances below the exchange length among them.

  4. Reversible Structural Swell-Shrink and Recoverable Optical Properties in Hybrid Inorganic-Organic Perovskite.

    PubMed

    Zhang, Yupeng; Wang, Yusheng; Xu, Zai-Quan; Liu, Jingying; Song, Jingchao; Xue, Yunzhou; Wang, Ziyu; Zheng, Jialu; Jiang, Liangcong; Zheng, Changxi; Huang, Fuzhi; Sun, Baoquan; Cheng, Yi-Bing; Bao, Qiaoliang

    2016-07-26

    Ion migration in hybrid organic-inorganic perovskites has been suggested to be an important factor for many unusual behaviors in perovskite-based optoelectronics, such as current-voltage hysteresis, low-frequency giant dielectric response, and the switchable photovoltaic effect. However, the role played by ion migration in the photoelectric conversion process of perovskites is still unclear. In this work, we provide microscale insights into the influence of ion migration on the microstructure, stability, and light-matter interaction in perovskite micro/nanowires by using spatially resolved optical characterization techniques. We observed that ion migration, especially the migration of MA(+) ions, will induce a reversible structural swell-shrink in perovskites and recoverably affect the reflective index, quantum efficiency, light-harvesting, and photoelectric properties. The maximum ion migration quantity in perovskites was as high as approximately 30%, resulting in lattice swell or shrink of approximately 4.4%. Meanwhile, the evidence shows that ion migration in perovskites could gradually accelerate the aging of perovskites because of lattice distortion in the reversible structural swell-shrink process. Knowledge regarding reversible structural swell-shrink and recoverable optical properties may shed light on the development of optoelectronic and converse piezoelectric devices based on perovskites.

  5. Spontaneous Increase of Magnetic Flux and Chiral-Current Reversal in Bosonic Ladders: Swimming against the Tide

    NASA Astrophysics Data System (ADS)

    Greschner, S.; Piraud, M.; Heidrich-Meisner, F.; McCulloch, I. P.; Schollwöck, U.; Vekua, T.

    2015-11-01

    The interplay between spontaneous symmetry breaking in many-body systems, the wavelike nature of quantum particles and lattice effects produces an extraordinary behavior of the chiral current of bosonic particles in the presence of a uniform magnetic flux defined on a two-leg ladder. While noninteracting as well as strongly interacting particles, stirred by the magnetic field, circulate along the system's boundary in the counterclockwise direction in the ground state, interactions stabilize vortex lattices. These states break translational symmetry, which can lead to a reversal of the circulation direction. Our predictions could readily be accessed in quantum gas experiments with existing setups or in arrays of Josephson junctions.

  6. The Reversed Role of Magnets in St. Louis: Implications for Black Student Outcomes

    ERIC Educational Resources Information Center

    Grooms, Ain A.; Williams, Sheneka M.

    2015-01-01

    Magnet schools were originally created to attract a diverse student population. Using data from the 23 magnet schools in St. Louis, this longitudinal study is twofold: first, to review the performance outcomes of the magnet schools across a 5-year period, between 2005-2006 and 2009-2010, and second, to examine whether the magnet schools are…

  7. Magnetic Properties of ni Nanowires Grown in Mesoporous Silicon Templates

    NASA Astrophysics Data System (ADS)

    Dolgiy, A. L.; Redko, S. V.; Yanushkevich, K. I.

    2013-05-01

    Magnetic properties of Ni nanowires electrochemically deposited into pores of mesoporous silicon template under the stationary galvanostatic regime were investigated by measuring the temperature dependence (77-700 K) of the specific magnetization σ. The measured σ values were lower with respect to that of bulk Ni. The Curie temperature, TC, derived from σ(T) for low deposition times of Ni was less (575 K) than that for bulk Ni (630 K). This is caused by dimensional effects of Ni nanoparticles.

  8. GEMAS: Unmixing magnetic properties of European agricultural soil

    NASA Astrophysics Data System (ADS)

    Fabian, Karl; Reimann, Clemens; Kuzina, Dilyara; Kosareva, Lina; Fattakhova, Leysan; Nurgaliev, Danis

    2016-04-01

    High resolution magnetic measurements provide new methods for world-wide characterization and monitoring of agricultural soil which is essential for quantifying geologic and human impact on the critical zone environment and consequences of climatic change, for planning economic and ecological land use, and for forensic applications. Hysteresis measurements of all Ap samples from the GEMAS survey yield a comprehensive overview of mineral magnetic properties in European agricultural soil on a continental scale. Low (460 Hz), and high frequency (4600 Hz) magnetic susceptibility k were measured using a Bartington MS2B sensor. Hysteresis properties were determined by a J-coercivity spectrometer, built at the paleomagnetic laboratory of Kazan University, providing for each sample a modified hysteresis loop, backfield curve, acquisition curve of isothermal remanent magnetization, and a viscous IRM decay spectrum. Each measurement set is obtained in a single run from zero field up to 1.5 T and back to -1.5 T. The resulting data are used to create the first continental-scale maps of magnetic soil parameters. Because the GEMAS geochemical atlas contains a comprehensive set of geochemical data for the same soil samples, the new data can be used to map magnetic parameters in relation to chemical and geological parameters. The data set also provides a unique opportunity to analyze the magnetic mineral fraction of the soil samples by unmixing their IRM acquisition curves. The endmember coefficients are interpreted by linear inversion for other magnetic, physical and chemical properties which results in an unprecedented and detailed view of the mineral magnetic composition of European agricultural soils.

  9. Dust properties and magnetic field geometry towards LDN 1570

    NASA Astrophysics Data System (ADS)

    Eswaraiah, C.; Maheswar, G.; Pandey, A. K.

    2015-03-01

    We have performed both optical linear polarimetric and photometric observations of an isolated dark globule LDN 1570 aim to study the dust polarizing and extinction properties and to map the magnetic field geometry so as to understand not only the importance of magnetic fields in formation and evolution of clouds but also the correlation of the inferred magnetic field structure with the cloud structure and its dynamics. Dust size indicators (R V and λ max ) reveal for the presence of slightly bigger dust grains towards the cloud region. The inferred magnetic field geometry, which closely follows the cloud structure revealed by Herschel images, suggest that the cloud could have been formed due to converging material flows along the magnetic field lines.

  10. Studying the magnetic properties of CoSi single crystals

    SciTech Connect

    Narozhnyi, V. N. Krasnorussky, V. N.

    2013-05-15

    The magnetic properties of CoSi single crystals have been measured in a range of temperatures T = 5.5-450 K and magnetic field strengths H {<=} 11 kOe. A comparison of the results for crystals grown in various laboratories allowed the temperature dependence of magnetic susceptibility {chi}(T) = M(T)/H to be determined for a hypothetical 'ideal' (free of magnetic impurities and defects) CoSi crystal. The susceptibility of this ideal crystal in the entire temperature range exhibits a diamagnetic character. The {chi}(T) value significantly increases in absolute value with decreasing temperature and exhibits saturation at the lowest temperatures studied. For real CoSi crystals of four types, paramagnetic contributions to the susceptibility have been evaluated and nonlinear (with respect to the field) contributions to the magnetization have been separated and taken into account in the calculations of {chi}(T).

  11. Structural and magnetic properties of granular CoPd multilayers

    NASA Astrophysics Data System (ADS)

    Vivas, L. G.; Figueroa, A. I.; Bartolomé, F.; Rubín, J.; García, L. M.; Deranlot, C.; Petroff, F.; Ruiz, L.; González-Calbet, J. M.; Brookes, N. B.; Wilhelm, F.; Rogalev, A.; Bartolomé, J.

    2016-02-01

    Multilayers of bimetallic CoPd alloyed and assembled nanoparticles, prepared by room temperature sequential sputtering deposition on amorphous alumina, were studied by means of high-resolution transmission electron microscopy, x-ray diffraction, SQUID-based magnetometry and x-ray magnetic circular dichroism. Alloying between Co and Pd in these nanoparticles gives rise to a high perpendicular magnetic anisotropy. Their magnetic properties are temperature dependent: at low temperature, the multilayers are ferromagnetic with a high coercive field; at intermediate temperature the behavior is of a soft-ferromagnet, and at higher temperature, the perpendicular magnetic anisotropy in the nanoparticles disappears. The magnetic orbital moment to spin moment ratio is enhanced compared with Co bare nanoparticles and Co fcc bulk.

  12. Microstructure and Magnetic Properties of Bulk Nanocrystalline MnAl

    SciTech Connect

    Chaturvedi, A; Yaqub, R; Baker, I

    2014-01-22

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

  13. Reversible Control of Nanoparticle Functionalization and Physicochemical Properties by Dynamic Covalent Exchange.

    PubMed

    Della Sala, Flavio; Kay, Euan R

    2015-03-27

    Existing methods for the covalent functionalization of nanoparticles rely on kinetically controlled reactions, and largely lack the sophistication of the preeminent oligonucleotide-based noncovalent strategies. Here we report the application of dynamic covalent chemistry for the reversible modification of nanoparticle (NP) surface functionality, combining the benefits of non-biomolecular covalent chemistry with the favorable features of equilibrium processes. A homogeneous monolayer of nanoparticle-bound hydrazones can undergo quantitative dynamic covalent exchange. The pseudomolecular nature of the NP system allows for the in situ characterization of surface-bound species, and real-time tracking of the exchange reactions. Furthermore, dynamic covalent exchange offers a simple approach for reversibly switching-and subtly tuning-NP properties such as solvophilicity.

  14. Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique

    NASA Astrophysics Data System (ADS)

    Thakur, Sangeeta; Katyal, S. C.; Singh, M.

    2007-12-01

    Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473K at higher frequency range of 9-19MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108Ωcm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773K).

  15. Magnetic and Mechanical Properties of Hard Magnetic Alloys 30Kh21K3M and 30Kh20K2M2V

    NASA Astrophysics Data System (ADS)

    Stel'mashok, S. I.; Milyaev, I. M.; Yusupov, V. S.; Milyaev, A. I.

    2017-01-01

    The magnetic and mechanical properties of two hard magnetic alloys (30Kh21K3M and 30Kh20K2M2V) of the Fe - Cr - Co system in anisotropic and isotropic conditions produced by traditional induction melting and by the method of powder metallurgy with subsequent pressure treatment of the metal are studied. The obtained regression equations for B r , H cB and ( BH )max describe the quantities adequately in the used range of variation of factors. The response surfaces and their sections in the phase space of the heat treatment factors are plotted. The results of the analysis of the proportion of residual induction in anisotropic and isotropic states are used to infer that the model of the mechanism of magnetization reversal of hard magnetic alloys of the class considered needs amending.

  16. Size dependent structural and magnetic properties of FeO-Fe3O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Lak, Aidin; Kraken, Mathias; Ludwig, Frank; Kornowski, Andreas; Eberbeck, Dietmar; Sievers, Sibylle; Litterst, F. J.; Weller, Horst; Schilling, Meinhard

    2013-11-01

    The magnetic properties of monodisperse FeO-Fe3O4 nanoparticles with different mean sizes and volume fractions of FeO synthesized via decomposition of iron oleate were correlated to their crystallographic and phase compositional features by exploiting high resolution transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy and field and zero field cooled magnetization measurements. A model describing the phase transformation from a pure Fe3O4 phase to a mixture of Fe3O4, FeO and interfacial FeO-Fe3O4 phases as the particle size increases was established. The reduced magnetic moment in FeO-Fe3O4 nanoparticles was attributed to the presence of differently oriented Fe3O4 crystalline domains in the outer layers and paramagnetic FeO phase. The exchange bias energy, dominating magnetization reversal mechanism and superparamagnetic blocking temperature in FeO-Fe3O4 nanoparticles depend strongly on the relative volume fractions of FeO and the interfacial phase.The magnetic properties of monodisperse FeO-Fe3O4 nanoparticles with different mean sizes and volume fractions of FeO synthesized via decomposition of iron oleate were correlated to their crystallographic and phase compositional features by exploiting high resolution transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy and field and zero field cooled magnetization measurements. A model describing the phase transformation from a pure Fe3O4 phase to a mixture of Fe3O4, FeO and interfacial FeO-Fe3O4 phases as the particle size increases was established. The reduced magnetic moment in FeO-Fe3O4 nanoparticles was attributed to the presence of differently oriented Fe3O4 crystalline domains in the outer layers and paramagnetic FeO phase. The exchange bias energy, dominating magnetization reversal mechanism and superparamagnetic blocking temperature in FeO-Fe3O4 nanoparticles depend strongly on the relative volume fractions of FeO and the interfacial phase. Electronic supplementary

  17. Enhanced magnetic properties of cobalt-doped graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Kaur, Navjot; Pal, Kaushik

    2017-04-01

    We have studied structural and magnetic properties of reduced graphene nanoribbons (GNRs) and cobalt (Co)-doped GNRs. The effect of Co was also investigated on the magnetic properties of pristine GNRs, which play vital role in contribution of calculated magnetic moment. Herein, we have synthesized the pristine GNRs and Co-doped GNRs via a simple chemical refluxing process. The analysis of synthesised materials were carried out using different techniques such as Field emission scanning electron microscopy (FESEM) with EDAX analysis and X-ray diffraction pattern were confirmed the doping of Co into the GNRs. Moreover, from morphological analysis (FESEM), impurity or dopant (Co) shows as adsorbed at the surface of GNRs. Raman analysis has proved that the incorporation of Co into graphitic structure creates more defective sites. The results obtained from VSM analysis is clearly revealed that enhanced saturation magnetization (Ms) from 13.08 × 10-2 emu/g to 37.35 × 10-2 emu/g, due to the presence of unbalanced electron spins in Co which may be responsible for higher saturation magnetization in case of Co-doped GNRs as comparison of pristine GNRs. The obtained interesting magnetic properties of Co-doped GNRs create much attention towards various applications including spintronics devices and some related fields.

  18. Single crystal Processing and magnetic properties of gadolinium nickel

    SciTech Connect

    Shreve, Andrew John

    2012-01-01

    GdNi is a rare earth intermetallic material that exhibits very interesting magnetic properties. Spontaneous magnetostriction occurs in GdNi at T{sub C}, on the order of 8000ppm strain along the c-axis and only until very recently the mechanism causing this giant magnetostriction was not understood. In order to learn more about the electronic and magnetic structure of GdNi, single crystals are required for anisotropic magnetic property measurements. Single crystal processing is quite challenging for GdNi though since the rare-earth transition-metal composition yields a very reactive intermetallic compound. Many crystal growth methods are pursued in this study including crucible free methods, precipitation growths, and specially developed Bridgman crucibles. A plasma-sprayed Gd2O3 W-backed Bridgman crucible was found to be the best means of GdNi single crystal processing. With a source of high-quality single crystals, many magnetization measurements were collected to reveal the magnetic structure of GdNi. Heat capacity and the magnetocaloric effect are also measured on a single crystal sample. The result is a thorough report on high quality single crystal processing and the magnetic properties of GdNi.

  19. Magnetic nanoparticles: surface effects and properties related to biomedicine applications.

    PubMed

    Issa, Bashar; Obaidat, Ihab M; Albiss, Borhan A; Haik, Yousef

    2013-10-25

    Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10-100 μm), viruses, genes, down to proteins (3-50 nm). The optimization of the nanoparticles' size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.

  20. Magnetic Nanoparticles: Surface Effects and Properties Related to Biomedicine Applications

    PubMed Central

    Issa, Bashar; Obaidat, Ihab M.; Albiss, Borhan A.; Haik, Yousef

    2013-01-01

    Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10–100 μm), viruses, genes, down to proteins (3–50 nm). The optimization of the nanoparticles’ size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents. PMID:24232575