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Sample records for establishing exchange bias

  1. New Trends in Magnetic Exchange Bias

    NASA Astrophysics Data System (ADS)

    Mougin, Alexandra; Mangin, Stéphane; Bobo, Jean-Francois; Loidl, Alois

    2005-05-01

    -of-plane exchange bias, depending on the field cooling direction. This is of particular interest since it allows probing of the three-dimensional spin structure of the AF layer. The interface magnetic configuration is extremely important in the perpendicular geometry, as the short-range exchange coupling competes with a long-range dipolar interaction; the induced uniaxial anisotropy must overcome the demagnetization energy to establish perpendicular anisotropy films. Those new studies are of primary importance for the magnetic media industry as perpendicular recording exhibits potential for strongly increased storage densities. 3. Parameters tuning exchange bias in polycrystalline samples and magnetic configurations: Different parameters can be used to tune the exchange bias coupling in polycrystalline samples similar to those used in devices. Particularly fascinating aspects are the questions of the appearance of exchange bias or coercivity in ferromagnet/antiferromagnet heterostructures, and its relation to magnetic configurations formed on either side of the interface. Several papers report on either growth choices or post preparation treatments that enable tuning of the exchange bias in bilayers. The additional complexity and novel features of the exchange coupled interface make the problem particularly rich. 4. Dynamics and magnetization reversal: Linear response experiments, such as ferromagnetic resonance, have been used with great success to identify interface, surface anisotropies and interlayer exchange in multilayer systems. The exchange bias structure is particularly well suited to study because interface driven changes in the spin wave frequencies in the ferromagnet can be readily related to interlayer exchange and anisotropy parameters associated with the antiferromagnet. Because the exchange bias is intimately connected with details of the magnetization process during reversal and the subsequent formation of hysteresis, considerations of time dependence and

  2. Exchange bias effect in alloys and compounds.

    PubMed

    Giri, S; Patra, M; Majumdar, S

    2011-02-23

    The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.

  3. New Trends in Magnetic Exchange Bias

    NASA Astrophysics Data System (ADS)

    Mougin, Alexandra; Mangin, Stéphane; Bobo, Jean-Francois; Loidl, Alois

    2005-05-01

    The study of layered magnetic structures is one of the hottest topics in magnetism due to the growing attraction of applications in magnetic sensors and magnetic storage media, such as random access memory. For almost half a century, new discoveries have driven researchers to re-investigate magnetism in thin film structures. Phenomena such as giant magnetoresistance, tunneling magnetoresistance, exchange bias and interlayer exchange coupling led to new ideas to construct devices, based not only on semiconductors but on a variety of magnetic materials Upon cooling fine cobalt particles in a magnetic field through the Néel temperature of their outer antiferromagnetic oxide layer, Meiklejohn and Bean discovered exchange bias in 1956. The exchange bias effect through which an antiferromagnetic AF layer can cause an adjacent ferromagnetic F layer to develop a preferred direction of magnetization, is widely used in magnetoelectronics technology to pin the magnetization of a device reference layer in a desired direction. However, the origin and effects due to exchange interaction across the interface between antiferromagneic and ferromagnetic layers are still debated after about fifty years of research, due to the extreme difficulty associated with the determination of the magnetic interfacial structure in F/AF bilayers. Indeed, in an AF/F bilayer system, the AF layer acts as “the invisible man” during conventional magnetic measurements and the presence of the exchange coupling is evidenced indirectly through the unusual behavior of the adjacent F layer. Basically, the coercive field of the F layer increases in contact with the AF and, in some cases, its hysteresis loop is shifted by an amount called exchange bias field. Thus, AF/F exchange coupling generates a new source of anisotropy in the F layer. This induced anisotropy strongly depends on basic features such as the magnetocrystalline anisotropy, crystallographic and spin structures, defects, domain patterns etc

  4. Pseudo exchange bias due to rotational anisotropy

    NASA Astrophysics Data System (ADS)

    Ehrmann, A.; Komraus, S.; Blachowicz, T.; Domino, K.; Nees, M. K.; Jakobs, P. J.; Leiste, H.; Mathes, M.; Schaarschmidt, M.

    2016-08-01

    Ferromagnetic nanostructure arrays with particle dimensions between 160 nm and 400 nm were created by electron-beam lithography. The permalloy structures consist of rectangular-shaped walls around a square open space. While measuring their magnetic properties using the Magneto-Optical Kerr Effect (MOKE), in some angular regions an exchange bias (EB) seemed to appear. This paper gives an overview of possible reasons for this "pseudo exchange bias" and shows experimentally and by means of micromagnetic simulations that this effect can be attributed to unintentionally measuring minor loops.

  5. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, A.; Michel, R.P.

    1998-07-21

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bias layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200 C, the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 {angstrom}/sec. The resulting NiO film was amorphous. 4 figs.

  6. HAMR media based on exchange bias

    NASA Astrophysics Data System (ADS)

    Elphick, K.; Vallejo-Fernandez, G.; Klemmer, T. J.; Thiele, J.-U.; O'Grady, K.

    2016-08-01

    In this work, we describe an alternative strategy for the development of heat assisted magnetic recording media. In our approach, the need for a storage material with a temperature dependent anisotropy and to provide a read out signal is separated so that each function can be optimised independently. This is achieved by the use of an exchange bias structure where a conventional CoCrPt-SiO2 recording layer is exchange biased to an underlayer of IrMn such that heating and cooling in the exchange field from the recording layer results in a shifted loop. This strategy requires the reorientation of the IrMn layer to allow coupling to the recording layer. This has been achieved by the use of an ultrathin (0.8 nm) layer of Co deposited beneath the IrMn layer. In this system, the information is in effect stored in the antiferromagnetic layer, and hence, there is no demagnetising field generated by the stored bits. A loop shift of 688 Oe has been achieved where both values of coercivity lie to one side of the origin and the information cannot be erased by a magnetic field.

  7. Experimental comparison of exchange bias measurement methodologies

    SciTech Connect

    Hovorka, Ondrej; Berger, Andreas; Friedman, Gary

    2007-05-01

    Measurements performed on all-ferromagnetic bilayer systems and supported by model calculation results are used to compare different exchange bias characterization methods. We demonstrate that the accuracy of the conventional two-point technique based on measuring the sum of the coercive fields depends on the symmetry properties of hysteresis loops. On the other hand, the recently proposed center of mass method yields results independent of the hysteresis loop type and coincides with the two-point measurement only if the loops are symmetric. Our experimental and simulation results clearly demonstrate a strong correlation between loop asymmetry and the difference between these methods.

  8. Growth of oxide exchange bias layers

    DOEpatents

    Chaiken, Alison; Michel, Richard P.

    1998-01-01

    An oxide (NiO, CoO, NiCoO) antiferromagnetic exchange bias layer produced by ion beam sputtering of an oxide target in pure argon (Ar) sputtering gas, with no oxygen gas introduced into the system. Antiferromagnetic oxide layers are used, for example, in magnetoresistive readback heads to shift the hysteresis loops of ferromagnetic films away from the zero field axis. For example, NiO exchange bia layers have been fabricated using ion beam sputtering of an NiO target using Ar ions, with the substrate temperature at 200.degree. C., the ion beam voltage at 1000V and the beam current at 20 mA, with a deposition rate of about 0.2 .ANG./sec. The resulting NiO film was amorphous.

  9. Magnetization reversal in exchange biased nanocap arrays

    NASA Astrophysics Data System (ADS)

    Guhr, I. L.; van Dijken, S.; Malinowski, G.; Fischer, P.; Springer, F.; Hellwig, O.; Albrecht, M.

    2007-05-01

    Arrays of self-assembled polystyrene spheres with various particle sizes have been used as a substrate to study the exchange bias effect along the out-of-plane direction of Pt/Co multilayers capped with IrMn layers. The evolution of the reversal process of the resulting magnetic nanocaps was investigated by magnetic force microscopy (MFM) and magnetic transmission x-ray microscopy (M-TXM). Tip-sample interaction-induced irreversible and reversible switching events have been observed during multiple scanning cycles in MFM imaging which are ascribed to the so-called training effect. During M-TXM imaging a drastic change in morphology has been found due to the x-ray exposure, leading to the formation of much larger spherical particles. Interestingly, these merged particles reveal again an exchange coupled single-domain magnetic cap with magnetic behaviour similar to magnetic films deposited directly on spheres of similar size. This paper was presented at the Materials Research Society Fall 2006 Meeting, 27 November-1 December 2006, as part of Symposium P: Nanoscale Magnets-Synthesis, Self-assembly, Properties and Applications, organized by J Fassbender, J Chapman and C A Ross.

  10. Micromagnetic modeling of overlaid exchange-biased giant magnetoresistance head

    NASA Astrophysics Data System (ADS)

    Zheng, Yuankai; You, Dan; Wu, Yihong

    2002-05-01

    Overlaid exchange-biased structures for giant magnetoresistance head have been proposed and investigated. A home-developed three-dimensional micromagnetic modeling tool has been used to simulate synthetic antiferromagnetic spin valves of this type of biased structure with dimensions of 100 nm in width and 80 nm in height. Simulation results showed that, with a properly chosen antiferromagnetic material and structure, the exchange-biasing field could be made sufficient to suppress the noise without severely reducing the sensitivity. The sensitivity of overlaid exchange-biased spin valves is 1.73 times that of the abutted hard biased ones. Microtrack profiles showed that side reading effect could be suppressed effectively with an effective exchange-biasing field over 600 Oe.

  11. Exchange bias training effect in coupled all ferromagnetic bilayer structures.

    PubMed

    Binek, Ch; Polisetty, S; He, Xi; Berger, A

    2006-02-17

    Exchange coupled bilayers of soft and hard ferromagnetic thin films show remarkable analogies to conventional antiferromagnetic/ferromagnetic exchange bias heterostructures. Not only do all these ferromagnetic bilayers exhibit a tunable exchange bias effect, they also show a distinct training behavior upon cycling the soft layer through consecutive hysteresis loops. In contrast with conventional exchange bias systems, such all ferromagnetic bilayer structures allow the observation of training induced changes in the bias-setting hardmagnetic layer by means of simple magnetometry. Our experiments show unambiguously that the exchange bias training effect is driven by deviations from equilibrium in the pinning layer. A comparison of our experimental data with predictions from a theory based upon triggered relaxation phenomena shows excellent agreement.

  12. 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.

  13. Ferromagnetic behavior and exchange bias effect in akaganeite nanorods

    SciTech Connect

    Tadic, Marin; Milosevic, Irena; Motte, Laurence; Kralj, Slavko; Saboungi, Marie-Louise

    2015-05-04

    We report ferromagnetic-like properties and exchange bias effect in akaganeite (β-FeOOH) nanorods. They exhibit a Néel temperature T{sub N} = 259 K and ferromagnetic-like hysteresis behavior both below and above T{sub N}. An exchange bias effect is observed below T{sub N} and represents an interesting behavior for akaganeite nanorods. These results are explained on the basis of a core-shell structure in which the core has bulk akaganeite magnetic properties (i.e., antiferromagnetic ordering) while the shell exhibits a disordered spin state. Thus, the nanorods show ferromagnetic properties and an exchange bias effect at the same time, increasing their potential for use in practical applications.

  14. Exchange bias in Fe/Cr double superlattices.

    SciTech Connect

    Jiang, J. S.; Felcher, G. P.; Inomata, A.; Goyette, R.; Nelson, C.; Bader, S. D.

    1999-11-30

    Utilizing the oscillatory interlayer exchange coupling in Fe/Cr superlattices, we have constructed ''double superlattice'' structures where a ferromagnetic (F) and an antiferromagnetic (AF) Fe/Cr superlattice are coupled through a Cr spacer. The minor hysteresis loops in the magnetization are shifted from zero field, i.e., the F superlattice is exchange biased by the AF one. The double superlattices are sputter-deposited with (211) epitaxy and possess uniaxial in-plane magnetic anisotropy. The magnitude of the bias field is satisfactorily described by the classic formula for collinear spin structures. The coherent structure and insensitivity to atomic-scale roughness makes it possible to determine the spin distribution by polarized neutron reflectivity, which confirms that the spin structure is collinear. The magnetic reversal behavior of the double superlattices suggests that a realistic model of exchange bias needs to address the process of nucleating local reverse domains.

  15. Dynamic enhancement of the exchange bias training effect

    NASA Astrophysics Data System (ADS)

    Sahoo, Sarbeswar; Berger, Andreas; Polisetty, Srinivas; Binek, Christian

    2007-03-01

    Exchange bias in coupled magnetic films and its accompanying training effect are fundamental interface phenomena which impact spintronic applications. Training is referred to as a gradual change of the bias field, which evolves upon cycling the soft layer through consecutive hysteresis loops. We report on its dynamic enhancement in exchange coupled bilayers of soft and hard ferromagnetic materials. Dynamic effects are induced with increasing sweep rate of the applied magnetic field from quasi-static to the fully dynamic range. A dynamically generalized theory based on triggered and partially truncated relaxation is in excellent agreement with the data. Remarkable universality of our theoretical approach is evidenced when applying the approach to the dynamic training effect of a conventional exchange bias system involving an antiferromagnetic pinning layer.

  16. Interfacial spin cluster effects in exchange bias systems

    SciTech Connect

    Carpenter, R. Vallejo-Fernandez, G.; O'Grady, K.

    2014-05-07

    In this work, the effect of exchange bias on the hysteresis loop of CoFe is observed. The evolution of the coercivities and the shift of the hysteresis loop during the annealing process has been measured for films deposited on NiCr and Cu seed layers. Through comparison of the as deposited and field annealed loops, it is clear that for an exchange biased material, the two coercivities are due to different reversal processes. This behaviour is attributed to spin clusters at the ferromagnet/antiferromagnet interface, which behave in a similar manner to a fine particle system.

  17. Competing anisotropies in exchange-biased nanostructured thin films

    NASA Astrophysics Data System (ADS)

    Goncalves, F. J. T.; Paterson, G. W.; Stamps, R. L.; O'Reilly, S.; Bowman, R.; Gubbiotti, G.; Schmool, D. S.

    2016-08-01

    The magnetic anisotropies of a patterned, exchange biased Fe50Mn50/Ni80Fe20 system are studied using ferromagnetic resonance, supplemented by Brillouin light scattering experiments and Kerr magnetometry. The exchange biased bilayer is partially etched into an antidot geometry so that the system approximates a Ni80Fe20 layer in contact with antidot structured Fe50Mn50 . Brillouin light scattering measurements of the spin wave frequency dependence on the wave vector reveal a magnonic band gap as expected for a periodic modulation of the magnetic properties. Analysis of the ferromagnetic resonance spectra reveals eightfold and fourfold contributions to the magnetic anisotropy. Additionally, the antidot patterning decreases the magnitude of the exchange bias and modifies strongly its angular dependence. Softening of all resonance modes is most pronounced for the applied magnetic field aligned within 10∘ of the antidot axis, in the direction of the bias. Given the degree to which one can tailor the ground state, the resulting asymmetry at low frequencies could make this an interesting candidate for applications such as selective/directional microwave filtering and multistate magnetic logic.

  18. Modelling exchange bias with MuMax3

    NASA Astrophysics Data System (ADS)

    De Clercq, Jonas; Vansteenkiste, Arne; Abes, Medjid; Temst, Kristiaan; Van Waeyenberge, Bartel

    2016-11-01

    The unidirectional shift of the hysteresis loop and the athermal training effect are two key features of the exchange bias phenomenon in most polycrystalline FM/AFM bilayers. We show that, by using MuMax3 which is an open source micromagnetic simulation program, we are able to reproduce experimental data (bias field and coercivity) for a polycrystalline Co/CoO bilayer. We also demonstrate that rotatable uncompensated spins can be responsible for the athermal training effect and that the reversal mechanism between the ascending and descending branch in the first hysteresis loop can be different, as has frequently been noticed in experiments.

  19. Control of quantum magnets by atomic exchange bias.

    PubMed

    Yan, Shichao; Choi, Deung-Jang; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Loth, Sebastian

    2015-01-01

    Mixing of discretized states in quantum magnets has a radical impact on their properties. Managing this effect is key for spintronics in the quantum limit. Magnetic fields can modify state mixing and, for example, mitigate destabilizing effects in single-molecule magnets. The exchange bias field has been proposed as a mechanism for localized control of individual nanomagnets. Here, we demonstrate that exchange coupling with the magnetic tip of a scanning tunnelling microscope provides continuous tuning of spin state mixing in an individual nanomagnet. By directly measuring spin relaxation time with electronic pump-probe spectroscopy, we find that the exchange interaction acts analogously to a local magnetic field that can be applied to a specific atom. It can be tuned in strength by up to several tesla and cancel external magnetic fields, thereby demonstrating the feasibility of complete control over individual quantum magnets with atomically localized exchange coupling.

  20. Magnetic stability in exchange-spring and exchange bias systems after multiple switching cycles.

    SciTech Connect

    Jiang, J. S.; Inomata, A.; You, C.-Y.; Pearson, J. E.; Bader, S. D.

    2001-06-01

    We have studied the magnetic stability in exchange bias and exchange spring systems prepared via epitaxial sputter deposition. The two interfacial exchange coupled systems, Fe/Cr(211) double superlattices consisting of a ferromagnetic and an antiferromagnetic Fe/Cr superlattice that are exchange coupled through a Cr spacer, and Sin-Co/Fe exchange-spring bilayer structures with ferromagnetically coupled hard Sin-Co layer and soft Fe layer, were epitaxially grown on suitably prepared Cr buffer layers to give rise to different microstructure and magnetic anisotropy. The magnetic stability was investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For uniaxial Fe/Cr exchange biased double superlattices and exchange spring bilayers with uniaxial Sin-Co, small but rapid initial decay in the exchange bias field HE and in the remanent magnetization is observed. However, the exchange spring bilayers with biaxial and random in-plane anisotropy in the Sin-Co layer shows gradual decay in H{sub E} and without large reduction of the magnetization. The different decay behaviors are attributed to the different microstructure and spin configuration of the pinning layers.

  1. Role of the antiferromagnetic bulk spins in exchange bias

    NASA Astrophysics Data System (ADS)

    Schuller, Ivan K.; Morales, Rafael; Batlle, Xavier; Nowak, Ulrich; Güntherodt, Gernot

    2016-10-01

    This "Critical Focused Issue" presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice.

  2. 45 CFR 155.140 - Establishment of a regional Exchange or subsidiary Exchange.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General Standards Related to the Establishment of an Exchange § 155.140 Establishment of... the PHS Act. (c) Exchange standards. Each regional or subsidiary Exchange must: (1) Otherwise meet...

  3. 45 CFR 155.140 - Establishment of a regional Exchange or subsidiary Exchange.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General Standards Related to the Establishment of an Exchange § 155.140 Establishment of... the PHS Act. (c) Exchange standards. Each regional or subsidiary Exchange must: (1) Otherwise meet...

  4. Robust isothermal electric control of exchange bias at room temperature

    NASA Astrophysics Data System (ADS)

    Binek, Christian

    2011-03-01

    Voltage-controlled spintronics is of particular importance to continue progress in information technology through reduced power consumption, enhanced processing speed, integration density, and functionality in comparison with present day CMOS electronics. Almost all existing and prototypical solid-state spintronic devices rely on tailored interface magnetism, enabling spin-selective transmission or scattering of electrons. Controlling magnetism at thin-film interfaces, preferably by purely electrical means, is a key challenge to better spintronics. Currently, most attempts to electrically control magnetism focus on potentially large magnetoelectric effects of multiferroics. We report on our interest in magnetoelectric Cr 2 O3 (chromia). Robust isothermal electric control of exchange bias is achieved at room temperature in perpendicular anisotropic Cr 2 O3 (0001)/CoPd exchange bias heterostructures. This discovery promises significant implications for potential spintronics. From the perspective of basic science, our finding serves as macroscopic evidence for roughness-insensitive and electrically controllable equilibrium boundary magnetization in magnetoelectric antiferromagnets. The latter evolves at chromia (0001) surfaces and interfaces when chromia is in one of its two degenerate antiferromagnetic single domain states selected via magnetoelectric annealing. Theoretical insight into the boundary magnetization and its role in electrically controlled exchange bias is gained from first-principles calculations and general symmetry arguments. Measurements of spin-resolved ultraviolet photoemission, magnetometry at Cr 2 O3 (0001) surfaces, and detailed investigations of the unique exchange bias properties of Cr 2 O3 (0001)/CoPd including its electric controllability provide macroscopically averaged information about the boundary magnetization of chromia. Laterally resolved X-ray PEEM and temperature dependent MFM reveal detailed microscopic information of the chromia

  5. Controllable positive exchange bias via redox-driven oxygen migration.

    PubMed

    Gilbert, Dustin A; Olamit, Justin; Dumas, Randy K; Kirby, B J; Grutter, Alexander J; Maranville, Brian B; Arenholz, Elke; Borchers, Julie A; Liu, Kai

    2016-01-01

    Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures. PMID:26996674

  6. Controllable positive exchange bias via redox-driven oxygen migration

    DOE PAGES

    Gilbert, Dustin A.; Olamit, Justin; Dumas, Randy K.; Kirby, B. J.; Grutter, Alexander J.; Maranville, Brian B.; Arenholz, Elke; Borchers, Julie A.; Liu, Kai

    2016-03-21

    We report that ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, amore » few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. Ultimately, these results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures.« less

  7. Exchange bias phenomenology and models of core/shell nanoparticles.

    PubMed

    Iglesias, Oscar; Labarta, Amílcar; Batlle, Xavier

    2008-06-01

    Some of the main experimental observations related to the occurrence of exchange bias in magnetic systems are reviewed, focusing the attention on the peculiar phenomenology associated to nanoparticles with core/shell structure as compared to thin film bilayers. The main open questions posed by the experimental observations are presented and contrasted to existing theories and models for exchange bias formulated up to date. We also present results of simulations based on a simple model of a core/shell nanoparticle in which the values of microscopic parameters such as anisotropy and exchange constants can be tuned in the core, shell and at the interfacial regions, offering new insight on the microscopic origin of the experimental phenomenology. A detailed study of the magnetic order of the interfacial spins shows compelling evidence that most of the experimentally observed effects can be qualitatively accounted within the context of this model and allows also to quantify the magnitude of the loop shifts in striking agreement with the macroscopic observed values.

  8. Controllable positive exchange bias via redox-driven oxygen migration

    NASA Astrophysics Data System (ADS)

    Gilbert, Dustin A.; Olamit, Justin; Dumas, Randy K.; Kirby, B. J.; Grutter, Alexander J.; Maranville, Brian B.; Arenholz, Elke; Borchers, Julie A.; Liu, Kai

    2016-03-01

    Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures.

  9. Controllable positive exchange bias via redox-driven oxygen migration.

    PubMed

    Gilbert, Dustin A; Olamit, Justin; Dumas, Randy K; Kirby, B J; Grutter, Alexander J; Maranville, Brian B; Arenholz, Elke; Borchers, Julie A; Liu, Kai

    2016-01-01

    Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1-x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures.

  10. Controllable positive exchange bias via redox-driven oxygen migration

    PubMed Central

    Gilbert, Dustin A.; Olamit, Justin; Dumas, Randy K.; Kirby, B. J.; Grutter, Alexander J.; Maranville, Brian B.; Arenholz, Elke; Borchers, Julie A.; Liu, Kai

    2016-01-01

    Ionic transport in metal/oxide heterostructures offers a highly effective means to tailor material properties via modification of the interfacial characteristics. However, direct observation of ionic motion under buried interfaces and demonstration of its correlation with physical properties has been challenging. Using the strong oxygen affinity of gadolinium, we design a model system of GdxFe1−x/NiCoO bilayer films, where the oxygen migration is observed and manifested in a controlled positive exchange bias over a relatively small cooling field range. The exchange bias characteristics are shown to be the result of an interfacial layer of elemental nickel and cobalt, a few nanometres in thickness, whose moments are larger than expected from uncompensated NiCoO moments. This interface layer is attributed to a redox-driven oxygen migration from NiCoO to the gadolinium, during growth or soon after. These results demonstrate an effective path to tailoring the interfacial characteristics and interlayer exchange coupling in metal/oxide heterostructures. PMID:26996674

  11. Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias.

    PubMed

    Nayak, Ajaya K; Nicklas, Michael; Chadov, Stanislav; Khuntia, Panchanana; Shekhar, Chandra; Kalache, Adel; Baenitz, Michael; Skourski, Yurii; Guduru, Veerendra K; Puri, Alessandro; Zeitler, Uli; Coey, J M D; Felser, Claudia

    2015-07-01

    Rational material design can accelerate the discovery of materials with improved functionalities. This approach can be implemented in Heusler compounds with tunable magnetic sublattices to demonstrate unprecedented magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. Our design approach is also demonstrated on a second material with a magnetic transition above room temperature, Mn-Fe-Ga, exemplifying the universality of the concept and the feasibility of room-temperature applications. These findings may lead to the development of magneto-electronic devices and rare-earth-free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.

  12. 45 CFR 155.100 - Establishment of a State Exchange.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 1 2012-10-01 2012-10-01 false Establishment of a State Exchange. 155.100 Section 155.100 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES REQUIREMENTS RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT...

  13. 45 CFR 155.100 - Establishment of a State Exchange.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 45 Public Welfare 1 2013-10-01 2013-10-01 false Establishment of a State Exchange. 155.100 Section 155.100 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES REQUIREMENTS RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT...

  14. Robust isothermal electric control of exchange bias at room temperature

    SciTech Connect

    He, X.; Vescovo, E.; Wang, Y.; Caruso, A.N.; Belashchenko, K.D.; Dowben, P.A.; Binek, C.

    2010-06-20

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr{sub 2}O{sub 3} has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr{sub 2}O{sub 3} single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Neel temperature.

  15. Robust isothermal electric control of exchange bias at room temperature.

    PubMed

    He, Xi; Wang, Yi; Wu, Ning; Caruso, Anthony N; Vescovo, Elio; Belashchenko, Kirill D; Dowben, Peter A; Binek, Christian

    2010-07-01

    Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with high-speed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr(2)O(3) has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr(2)O(3) single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature.

  16. Magnetization reversal of an individual exchange-biased permalloy nanotube

    NASA Astrophysics Data System (ADS)

    Buchter, A.; Wölbing, R.; Wyss, M.; Kieler, O. F.; Weimann, T.; Kohlmann, J.; Zorin, A. B.; Rüffer, D.; Matteini, F.; Tütüncüoglu, G.; Heimbach, F.; Kleibert, A.; Fontcuberta i Morral, A.; Grundler, D.; Kleiner, R.; Koelle, D.; Poggio, M.

    2015-12-01

    We investigate the magnetization reversal mechanism in an individual permalloy (Py) nanotube (NT) using a hybrid magnetometer consisting of a nanometer-scale SQUID (nanoSQUID) and a cantilever torque sensor. The Py NT is affixed to the tip of a Si cantilever and positioned in order to optimally couple its stray flux into a Nb nanoSQUID. We are thus able to measure both the NT's volume magnetization by dynamic cantilever magnetometry and its stray flux using the nanoSQUID. We observe a training effect and a temperature dependence in the magnetic hysteresis, suggesting an exchange bias. We find a low blocking temperature TB=18 ±2 K, indicating the presence of a thin antiferromagnetic native oxide, as confirmed by x-ray absorption spectroscopy on similar samples. Furthermore, we measure changes in the shape of the magnetic hysteresis as a function of temperature and increased training. These observations show that the presence of a thin exchange-coupled native oxide modifies the magnetization reversal process at low temperatures. Complementary information obtained via cantilever and nanoSQUID magnetometry allows us to conclude that, in the absence of exchange coupling, this reversal process is nucleated at the NT's ends and propagates along its length as predicted by theory.

  17. Exchange bias training relaxation in spin glass/ferromagnet bilayers

    NASA Astrophysics Data System (ADS)

    Chi, Xiaodan; Rui, Wenbin; Du, Jun; Zhou, Shiming; Du, An; Hu, Yong

    2016-04-01

    A canonical spin glass (SG) FeAu layer is fabricated to couple to a soft ferromagnet (FM) FeNi layer. Below the SG freezing temperature, exchange bias (EB) and training are observed. Training in SG/FM bilayers is insensitive to cooling field and may suppress the EB or change the sign of the EB field from negative to positive at specific temperatures, violating from the simple power-law or the single exponential function derived from the antiferromagnet based systems. In view of the SG nature, we employ a double decay model to distinguish the contributions from the SG bulk and the SG/FM interface to training. Dynamical properties during training under different cooling fields and at different temperatures are discussed, and the nonzero shifting coefficient in the time index as a signature of slowing-down decay for SG based systems is interpreted by means of a modified Monte Carlo Metropolis algorithm.

  18. Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems.

    SciTech Connect

    Jimenez, E.; Camarero, J.; Sort, J.; Nogues, J.; Mikuszeit, N.; Garcia-Martin, J. M.; Hoffmann, A.; Dieny, B.; Miranda, R.; Univ. Autonoma de Madrid; Univ. Autonoma de Barcelona; Inst. de Microelectronica de Madrid; SPINTEC

    2009-01-01

    Exchange bias, referred to the interaction between a ferromagnet (FM) and an antiferromagnet (AFM), is a fundamental interfacial magnetic phenomenon, which is key to current and future applications. The effect was discovered half a century ago, and it is well established that the spin structures at the FM/AFM interface play an essential role. However, currently, ad hoc phenomenological anisotropies are often postulated without microscopic justification or sufficient experimental evidence to address magnetization-reversal behavior in exchange-bias systems. We advance toward a detailed microscopic understanding of the magnetic anisotropies in exchange-bias FM/AFM systems by showing that symmetry-breaking anisotropies leave a distinct fingerprint in the asymmetry of the magnetization reversal and we demonstrate how these emerging anisotropies are correlated with the intrinsic anisotropy. Angular and vectorial resolved Kerr hysteresis loops from FM/AFM bilayers with varying degree of ferromagnetic anisotropy reveal a noncollinear anisotropy, which becomes important for ferromagnets with vanishing intrinsic anisotropy. Numerical simulations show that this anisotropy naturally arises from the inevitable spin frustration at an atomically rough FM/AFM interface. As a consequence, we show in detail how the differences observed for different materials during magnetization reversal can be understood in general terms as originating from the interplay between interfacial frustration and intrinsic anisotropies. This understanding will certainly open additional avenues to tailor future advanced magnetic materials.

  19. Exchange bias and magnetization reversal in ferromagnet/antiferromagnet antidot arrays

    NASA Astrophysics Data System (ADS)

    Luo, An; Ma, Fenghua; Hu, Yong

    2016-09-01

    Exchange bias and coercivity in ferromagnet/antiferromagnet antidot arrays magnetized perpendicularly are simulated to demonstrate the mechanism of their variations in specific nanostructures, using a modified Monte Carlo Metropolis algorithm. Three kinds of antidot array models characterized by different morphologies in the vicinity of pore are established and their magnetization behaviors are compared with that in the continuous film. An increase in the exchange bias field with a suppressed coercivity is obtained if the antiferromagnet covers the wall of pore entirely. By means of the results of the spin configurations, it is found that only the heterostructure component, e.g., the antiferromagnet can cut off the domain in the ferromagnet layer into small sizes effectively, and thus increases the pinning effect to the ferromagnet and changes the nucleation field. Moreover, the thermal stability of exchange bias in the antidot arrays is not enhanced and the coercivity is nonmonotonic with increasing temperature probably due to the magnetic field applied perpendicular to the film plane. We suggest that our numerical findings are also suitable for other nanostructures.

  20. Manipulation of competing ferromagnetic and antiferromagnetic domains in exchange-biased nanostructures

    NASA Astrophysics Data System (ADS)

    Fraile Rodríguez, Arantxa; Basaran, Ali C.; Morales, Rafael; Kovylina, Miroslavna; Llobet, Jordi; Borrisé, Xavier; Marcus, Matthew A.; Scholl, Andreas; Schuller, Ivan K.; Batlle, Xavier; Labarta, Amílcar

    2015-11-01

    Using photoemission electron microscopy combined with x-ray magnetic circular dichroism we show that a progressive spatial confinement of a ferromagnet (FM), either through thickness variation or laterally via patterning, actively controls the domains of uncompensated spins in the antiferromagnet (AF) in exchange-biased systems. Direct observations of the spin structure in both sides of the FM/AF interface in a model system, Ni /Fe F2 , show that the spin structure is determined by the balance between the competing FM and AF magnetic energies. Coexistence of exchange bias domains, with opposite directions, can be established in Ni /Fe F2 bilayers for Ni thicknesses below 10 nm. Patterning the Ni /Fe F2 heterostructures with antidots destabilizes the FM state, enhancing the formation of opposite exchange bias domains below a critical antidot separation of the order of a few Fe F2 crystal domains. The results suggest that dimensional confinement of the FM may be used to manipulate the AF spin structure in spintronic devices and ultrahigh-density information storage media. The underlying mechanism of the uncompensated AF domain formation in Ni /Fe F2 may be generic to other magnetic systems with complex noncollinear FM/AF spin structures.

  1. Tailoring exchange bias through chemical order in epitaxial FePt3 films

    NASA Astrophysics Data System (ADS)

    Saerbeck, T.; Zhu, H.; Lott, D.; Lee, H.; LeClair, P. R.; Mankey, G. J.; Stampfl, A. P. J.; Klose, F.

    2013-07-01

    Intentional introduction of chemical disorder into mono-stoichiometric epitaxial FePt3 films allows to create a ferro-/antiferromagnetic two-phase system, which shows a pronounced and controllable exchange bias effect. In contrast to conventional exchange bias systems, granular magnetic interfaces are created within the same crystallographic structure by local variation of chemical order. The amount of the exchange bias can be controlled by the relative amount and size of ferromagnetic and antiferromagnetic volume fractions and the interface between them. The tailoring of the magnetic composition alone, without affecting the chemical and structural compositions, opens the way to study granular magnetic exchange bias concepts separated from structural artifacts.

  2. Texture and magnetic properties of exchange bias systems

    SciTech Connect

    Aley, N. P.; Bowes, M.; Kroeger, R.; O'Grady, K.

    2010-05-15

    We report on the magnetic and structural properties of IrMn/CoFe exchange bias systems deposited onto a dual seed layer of NiCr(X)/Ru(5 nm), with X=2, 6, and 20 nm. Samples with the structure NiCr (Xnm)/IrMn (7 nm)/CoFe (3 nm)/Ta (10 nm) with X=2, 6, and 20 nm were prepared by dc sputtering for magnetic characterization. A second set of samples with structure NiCr (Xnm)/IrMn (10 nm) with X=2, 6, and 20 nm were deposited onto TEM grids for structural characterization by TEM. A method of manipulating of the TEM grid to allow a qualitative analysis of the in-plane texture of the samples is described and used to analyze the microstructure of these samples. The microstructure and particularly the texture are correlated with the anisotropy constant (K{sub AF}) of the antiferromagnet (AF) layer, with an optimum NiCr seed layer of 6 nm to give a maximum value of K{sub AF} of 1.2x10{sup 7} ergs/cc.

  3. Engineered magnetic domain textures in exchange bias bilayer systems

    NASA Astrophysics Data System (ADS)

    Gaul, Alexander; Hankemeier, Sebastian; Holzinger, Dennis; Müglich, Nicolas David; Staeck, Philipp; Frömter, Robert; Oepen, Hans Peter; Ehresmann, Arno

    2016-07-01

    A magnetic domain texture has been deterministically engineered in a topographically flat exchange-biased (EB) thin film system. The texture consists of long-range periodically arranged unit cells of four individual domains, characterized by individual anisotropies, individual geometry, and with non-collinear remanent magnetizations. The texture has been engineered by a sequence of light-ion bombardment induced magnetic patterning of the EB layer system. The magnetic texture's in-plane spatial magnetization distribution and the corresponding domain walls have been characterized by scanning electron microscopy with polarization analysis (SEMPA). The influence of magnetic stray fields emerging from neighboring domain walls and the influence of the different anisotropies of the adjacent domains on the Néel type domain wall core's magnetization rotation sense and widths were investigated. It is shown that the usual energy degeneracy of clockwise and counterclockwise rotating magnetization through the walls is revoked, suppressing Bloch lines along the domain wall. Estimates of the domain wall widths for different domain configurations based on material parameters determined by vibrating sample magnetometry were quantitatively compared to the SEMPA data.

  4. Exotic exchange bias at epitaxial ferroelectric-ferromagnetic interfaces

    SciTech Connect

    Paul, Amitesh Reitinger, Christoph; Kreuzpaintner, Wolfgang; Böni, Peter; Autieri, Carmine; Sanyal, Biplab; Jutimoosik, Jaru; Yimnirun, Rattikorn; Bern, Francis; Esquinazi, Pablo; Korelis, Panagiotis

    2014-07-14

    Multiferroics in spintronics have opened up opportunities for future technological developments, particularly in the field of ferroelectric (FE)-ferromagnetic (FM) oxide interfaces with functionalities. We find strong exchange bias shifts (up to 84 Oe) upon field cooling in metal-oxide (Fe/BaTiO{sub 3}) films combining FM and FE layers. The saturation magnetic moment of the FM layer is also significantly higher than in bulk (3.0 ± 0.2 μ{sub B}/atom) and the reversal mechanism occurs via a domain nucleation process. X-ray absorption spectroscopy at the Fe K-edge and Ba L3-edge indicate presence of few monolayers of antiferromagnetic FeO at the interface without the formation of any BaFeO{sub 3} layer. Polarized neutron reflectometry corroborates with our magnetization data as we perform depth profiling of the magnetic and structural densities in these bilayers. Our first principles density functional calculations support the formation of antiferromagnetic FeO layers at the interface along with an enhancement of Fe magnetic moments in the inner ferromagnetic layers.

  5. Strain-mediated multiferroic control of spontaneous exchange bias in Ni-NiO heterostructures

    NASA Astrophysics Data System (ADS)

    Domann, John P.; Sun, Wei-Yang; Schelhas, Laura T.; Carman, Greg P.

    2016-10-01

    This paper presents the measurement of strain-mediated multiferroic control of spontaneous exchange bias (SEB) in magnetostrictive nickel/nickel oxide (Ni/NiO) bilayers on ferroelectric lead magnesium niobate-lead titanate (PMN-PT). Electric field control of a positive to negative exchange bias shift was measured, with an overall shift of 40.5 Oe, corresponding to a 325% change. Observed changes in coercivity are also reported and provide insight into the role of competing anisotropies in these structures. The findings in this paper provide evidence that magnetoelastic anisotropy can be utilized to control spontaneous exchange bias (SEB). This control of SEB is accomplished by modifying a bulk anisotropy (magnetoelasticity) that adjusts the mobility of interfacial anti-ferromagnetic spins and, therefore, the magnitude of the exchange bias. The demonstrated magnetoelastic control of exchange bias provides a useful tool in the creation of future magnetoelectric devices.

  6. Controllable exchange bias in Fe/metamagnetic FeRh bilayers

    SciTech Connect

    Suzuki, Ippei; Hamasaki, Yosuke; Itoh, Mitsuru; Taniyama, Tomoyasu

    2014-10-27

    We report the studies of tuning the exchange bias at ferromagnetic Fe/metamagnetic FeRh bilayer interfaces. Fe/FeRh(111) bilayers show exchange bias in the antiferromagnetic state of FeRh while no exchange bias occurs at Fe/FeRh(001) interface. The contrasting results are attributed to the spin configurations of FeRh at the interface, i.e., the uncompensated ferromagnetic spin configuration of FeRh appears exclusively for (111) orientation. The exchange bias disappears as the bilayers are warmed above the antiferromagnetic-ferromagnetic transition temperature. The direction of the exchange bias for Fe/FeRh(111) is also found to be perpendicular to the cooling-field direction, in contrast to the commonly observed direction of exchange bias for ferromagnetic/antiferromagnetic interfaces. In view of these results, the exchange bias in Fe/FeRh bilayers with the (111) crystallographic orientation should be useful for the design of rapid writing technology for magnetic information devices.

  7. Influence of growth conditions on exchange bias of NiMn-based spin valves

    SciTech Connect

    Wienecke, Anja; Kruppe, Rahel; Rissing, Lutz

    2015-05-07

    As shown in previous investigations, a correlation between a NiMn-based spin valve's thermal stability and its inherent exchange bias exists, even if the blocking temperature of the antiferromagnet is clearly above the heating temperature and the reason for thermal degradation is mainly diffusion and not the loss of exchange bias. Samples with high exchange bias are thermally more stable than samples with low exchange bias. Those structures promoting a high exchange bias are seemingly the same suppressing thermally induced diffusion processes (A. Wienecke and L. Rissing, “Relationship between thermal stability and layer-stack/structure of NiMn-based GMR systems,” in IEEE Transaction on Magnetic Conference (EMSA 2014)). Many investigations were carried out on the influence of the sputtering parameters as well as the layer thickness on the magnetoresistive effect. The influence of these parameters on the exchange bias and the sample's thermal stability, respectively, was hardly taken into account. The investigation described here concentrates on the last named issue. The focus lies on the influence of the sputtering parameters and layer thickness of the “starting layers” in the stack and the layers forming the (synthetic) antiferromagnet. This paper includes a guideline for the evaluated sputtering conditions and layer thicknesses to realize a high exchange bias and presumably good thermal stability for NiMn-based spin valves with a synthetic antiferromagnet.

  8. Exchange bias-like effect in TbFeAl induced by atomic disorder

    NASA Astrophysics Data System (ADS)

    Nair, Harikrishnan S.; Strydom, André M.

    2016-05-01

    The exchange bias-like effect observed in the intermetallic compound TbFeAl, which displays a magnetic phase transition at T^hc ≈ 198 \\text{K} and a second one at T^lc ≈ 154 \\text{K} , is reported. Jump-like features are observed in the isothermal magnetization, M (H) , at 2 K which disappear above 8 K. The field-cooled magnetization isotherms below 10 K show loop shifts that are reminiscent of exchange bias, also supported by the training effect. A significant coercive field, Hc ≈ 1.5 \\text{T} at 2 K, is observed in TbFeAl which, after an initial increase, shows a subsequent decrease with temperature. The exchange bias field, H eb , shows a slight increase and a subsequent leveling off with temperature. It is argued that the inherent crystallographic disorder among Fe and Al and the high magnetocrystalline anisotropy related to Tb3+ lead to the exchange bias effect. TbFeAl has been recently reported to show the magnetocaloric effect and the present discovery of exchange bias makes this compound a multifunctional one. The result obtained on TbFeAl generalizes the observation of exchange bias in crystallographically disordered materials and gives impetus for the search for materials with exchange bias induced by atomic disorder.

  9. Influence of growth conditions on exchange bias of NiMn-based spin valves

    NASA Astrophysics Data System (ADS)

    Wienecke, Anja; Kruppe, Rahel; Rissing, Lutz

    2015-05-01

    As shown in previous investigations, a correlation between a NiMn-based spin valve's thermal stability and its inherent exchange bias exists, even if the blocking temperature of the antiferromagnet is clearly above the heating temperature and the reason for thermal degradation is mainly diffusion and not the loss of exchange bias. Samples with high exchange bias are thermally more stable than samples with low exchange bias. Those structures promoting a high exchange bias are seemingly the same suppressing thermally induced diffusion processes (A. Wienecke and L. Rissing, "Relationship between thermal stability and layer-stack/structure of NiMn-based GMR systems," in IEEE Transaction on Magnetic Conference (EMSA 2014)). Many investigations were carried out on the influence of the sputtering parameters as well as the layer thickness on the magnetoresistive effect. The influence of these parameters on the exchange bias and the sample's thermal stability, respectively, was hardly taken into account. The investigation described here concentrates on the last named issue. The focus lies on the influence of the sputtering parameters and layer thickness of the "starting layers" in the stack and the layers forming the (synthetic) antiferromagnet. This paper includes a guideline for the evaluated sputtering conditions and layer thicknesses to realize a high exchange bias and presumably good thermal stability for NiMn-based spin valves with a synthetic antiferromagnet.

  10. Structural and magnetic properties of (Fe/Mn) exchange-biased multilayers

    NASA Astrophysics Data System (ADS)

    El Bahoui, A.; Genevois, C.; Juraszek, J.; Bordel, C.; Ledue, D.

    2013-05-01

    Exchange-biasing of ferromagnetic (F) Fe layers by adjacent antiferromagnetic (AF) Mn layers has been investigated in (Fe/Mn)10 multilayered films. This study has been focused on the relationship between the evolution of the exchange-bias field and the evolution of the film microstructure as a function of the deposition temperature. The increase of the deposition temperature results in the formation of an Fe-Mn alloy at the interfaces and columnar features whose size increases with the deposition temperature. In parallel, the exchange-bias field decreases significantly, due to interface roughness.

  11. Exchange bias controlled by electric current: Interplay of Joule heating and the induced field

    NASA Astrophysics Data System (ADS)

    Oda, Kent; Moriyama, Takahiro; Kawaguchi, Masashi; Kamiya, Michinari; Tanaka, Kensho; Kim, Kab-Jin; Ono, Teruo

    2016-07-01

    Exchange bias is a unidirectional magnetic anisotropy developed in a bilayer of ferromagnetic and antiferromagnetic layers. Its technical importance as a “fix layer” is seen in various spintronic devices. The exchange bias can also be a probe to investigate the antiferromagnetic layer as it partly reflects the magnetic state of the antiferromagnet. In this work, we investigated the modulation of the exchange bias by a flow of electric current in Pt/Fe50Mn50/FeNi and Cu/Fe50Mn50/FeNi. We show that the exchange bias can be modulated just by applying the current due to interplay among the Joule heating, Ampere field, and current-induced effective field.

  12. Room temperature exchange bias in SmFeO3 single crystal

    NASA Astrophysics Data System (ADS)

    Wang (王晓雄), Xiaoxiong; Cheng (程相义), Xiangyi; Gao (高尚), Shang; Song (宋俊达), Junda; Ruan (阮可青), Keqing; Li (李晓光), Xiaoguang

    2016-02-01

    Exchange bias phenomenon is generally ascribed to the unidirectional magnetic shift along the field axes at interface of two magnetic materials. Room temperature exchange bias is found in SmFeO3 single crystal. The behavior after different cooling procedure is regular, and the training behavior is attributed to the athermal training and its pinning origin is attributed to the antiferromagnetic clusters. Its being single phase and occurring at room temperature make it an appropriate candidate for application.

  13. Antiferromagnetic exchange bias of a ferromagnetic semiconductor by a ferromagnetic metal

    SciTech Connect

    Olejnik, K.; Wadley, P.; Haigh, J.; Edmonds, K. W.; Campion, R. P.; Rushforth, A. W.; Gallagher, B. L.; Foxon, C. T.; Jungwirth, T.; Wunderlich, J.; Dhesi, S. S.; Cavill, S.; van der Laan, G.; Arenholz, E.

    2009-11-05

    We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish an interface layer that is strongly pinned antiferromagnetically to the Fe. The interface layer remains polarized at room temperature.

  14. Controlling disorder-mediated exchange bias in (Mn,Zn,Fe)3O4 thin films

    NASA Astrophysics Data System (ADS)

    Alaan, U. S.; Sreenivasulu, G.; Yu, K. M.; Jenkins, C.; Shafer, P.; Arenholz, E.; Srinivasan, G.; Suzuki, Y.

    2016-05-01

    We report exchange bias in (Mn,Zn,Fe)3O4 thin films that are compositionally homogeneous. We show that exchange bias in these Mn-Zn ferrite (MZFO) films can be tuned quite easily through annealing of the as-deposited films. The annealing process increases the crystallinity, as measured by X-ray diffraction (XRD). This improvement in crystallinity is accompanied by lower coercive fields, lower exchange bias fields, and higher saturation magnetizations. Exchange bias in these nominally homogeneous ferrite films is correlated with the degree of both structural and magnetic disorder. Based on the annealing experiments, we believe that these MZFO films may consist of crystalline regions that are separated from one another by disordered regions of the same nominal composition. The disordered regions serve to exchange bias the more structurally and magnetically ordered crystalline MZFO grains, leading to a shift of the magnetic hysteresis loop. Together these results indicate that the magnitude of the exchange bias can be controlled by tuning the degree of crystallinity in the system.

  15. Exchange bias in zinc ferrite-FeNiMoB based metallic glass composite thin films

    SciTech Connect

    R, Lisha; P, Geetha; B, Aravind P.; Anantharaman, M. R.; T, Hysen; Ojha, S.; Avasthi, D. K.; Ramanujan, R. V.

    2015-06-24

    The Exchange bias phenomenon and methods to manipulate the bias field in a controlled manner are thrust areas in magnetism due to its sophisticated theoretical concepts as well as advanced technological utility in the field of spintronics. The Exchange bias effect is observed as a result of ferromagnetic-antiferromagnetic (FM-AFM) exchange interaction, usually observed as a loop shift on field cooling below the Neel temperature of AFM. In the present study, we have chosen zinc ferrite which is a well known antiferromagnet, and FeNiMoB based metallic glass as the ferromagnet. The films were prepared by RF sputtering technique. The thickness and composition was obtained by RBS. The magnetic studies using SQUID VSM indicate exchange bias effect in the system. The effect of thermal annealing on exchange bias effect was studied. The observed exchange bias in the zinc ferrite-FeNiMoB system is not due to FM-AFM coupling but due to spin glass-ferromagnetic interaction.

  16. Exchange bias in zinc ferrite-FeNiMoB based metallic glass composite thin films

    NASA Astrophysics Data System (ADS)

    R, Lisha; T, Hysen; P, Geetha; B, Aravind P.; Ojha, S.; Avasthi, D. K.; Ramanujan, R. V.; Anantharaman, M. R.

    2015-06-01

    The Exchange bias phenomenon and methods to manipulate the bias field in a controlled manner are thrust areas in magnetism due to its sophisticated theoretical concepts as well as advanced technological utility in the field of spintronics. The Exchange bias effect is observed as a result of ferromagnetic-antiferromagnetic (FM-AFM) exchange interaction, usually observed as a loop shift on field cooling below the Neel temperature of AFM. In the present study, we have chosen zinc ferrite which is a well known antiferromagnet, and FeNiMoB based metallic glass as the ferromagnet. The films were prepared by RF sputtering technique. The thickness and composition was obtained by RBS. The magnetic studies using SQUID VSM indicate exchange bias effect in the system. The effect of thermal annealing on exchange bias effect was studied. The observed exchange bias in the zinc ferrite-FeNiMoB system is not due to FM-AFM coupling but due to spin glass-ferromagnetic interaction.

  17. Crystal Structure Manipulation of the Exchange Bias in an Antiferromagnetic Film

    PubMed Central

    Yuan, Wei; Su, Tang; Song, Qi; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Zhang, Zhangyuan; Ma, Xiumei; Gao, Peng; Shi, Jing; Han, Wei

    2016-01-01

    Exchange bias is one of the most extensively studied phenomena in magnetism, since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled to an antiferromagnet (AFM) and the control of the exchange bias is therefore very important for technological applications, such as magnetic random access memory and giant magnetoresistance sensors. In this letter, we report the crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3 films. By epitaxially growing twined oriented Cr2O3 thin films, of which the c axis and spins of the Cr atoms lie in the film plane, we demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy layer is tuned to in-plane from out-of-plane that has been observed in oriented Cr2O3 films. This is owing to the collinear exchange coupling between the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic exchange bias phenomenon is not possible in polycrystalline films. PMID:27329336

  18. Crystal Structure Manipulation of the Exchange Bias in an Antiferromagnetic Film

    NASA Astrophysics Data System (ADS)

    Yuan, Wei; Su, Tang; Song, Qi; Xing, Wenyu; Chen, Yangyang; Wang, Tianyu; Zhang, Zhangyuan; Ma, Xiumei; Gao, Peng; Shi, Jing; Han, Wei

    2016-06-01

    Exchange bias is one of the most extensively studied phenomena in magnetism, since it exerts a unidirectional anisotropy to a ferromagnet (FM) when coupled to an antiferromagnet (AFM) and the control of the exchange bias is therefore very important for technological applications, such as magnetic random access memory and giant magnetoresistance sensors. In this letter, we report the crystal structure manipulation of the exchange bias in epitaxial hcp Cr2O3 films. By epitaxially growing twined oriented Cr2O3 thin films, of which the c axis and spins of the Cr atoms lie in the film plane, we demonstrate that the exchange bias between Cr2O3 and an adjacent permalloy layer is tuned to in-plane from out-of-plane that has been observed in oriented Cr2O3 films. This is owing to the collinear exchange coupling between the spins of the Cr atoms and the adjacent FM layer. Such a highly anisotropic exchange bias phenomenon is not possible in polycrystalline films.

  19. Evidence of exchange bias effect originating from the interaction between antiferromagnetic core and spin glass shell

    SciTech Connect

    Zhang, X. K. Yuan, J. J.; Yu, H. J.; Zhu, X. R.; Xie, Y. M.; Tang, S. L.; Xu, L. Q.

    2014-07-14

    Spin glass behavior and exchange bias effect have been observed in antiferromagnetic SrMn{sub 3}O{sub 6−x} nanoribbons synthesized via a self-sacrificing template process. The magnetic field dependence of thermoremanent magnetization and isothermal remanent magnetization shows that the sample is good correspondence to spin glass and diluted antiferromagnetic system for the applied field H < 2 T and H > 2 T, respectively. By detailed analysis of training effect using Binek's model, we argue that the observed exchange bias effect in SrMn{sub 3}O{sub 6−x} nanoribbons arises entirely from an interface exchange coupling between the antiferromagnetic core and spin glass shell. The present study is useful for understanding the nature of shell layer and the origin of exchange bias effect in other antiferromagnetic nanosystems as well.

  20. Sign change of exchange bias in [Pt/Co]{sub 3}/IrMn multilayer

    SciTech Connect

    Yoon, Seungha; Kwon, Joonhyun; Cho, B. K.

    2014-05-07

    The properties of exchange bias in a multilayer of [Pt(1.0 nm)/Co(1.0 nm)]{sub 2}/Pt(t{sub Pt} nm)/Co(1.0 nm)/ IrMn(12.0 nm) were investigated with a variation of Pt layer thickness, t{sub Pt}. For t{sub Pt} ≤ 1.6 nm, it was typically observed that Co layers were ferromagnetically coupled while IrMn layer exhibited negative exchange bias. With increasing Pt thickness, antiferromagnetic (AF) interlayer coupling strength increased and caused AF spin configuration between the Co layers. With further increasing of Pt thickness (t{sub Pt} = 2.5 nm), the exchange bias between Co and IrMn layers was changed from negative to positive. Therefore, a large enhancement of AF interlayer coupling induced the sign change of exchange bias from negative to positive and resulted in a drastic change of switching behavior in a magnetization reversal. Both extraordinary Hall-effect and magnetoresistance were measured to verify the exchange bias direction and spin configurations upon magnetization reversal.

  1. Spin Propagation Through Antiferromagnetic Bulk Structure in Exchange Biased Magnetic Trilayers

    NASA Astrophysics Data System (ADS)

    Crumrine, Michael; Kirby, Hillary; Miller, Casey

    2013-03-01

    When an exchange bias is induced in materials with a ferromagnetic (FM) - antiferromagnetic (AF) interface, the interfacial coupling between the antiferromagnet and FM manifests itself as a shift in the magnetic hysteresis loop. It has been an unresolved issue as to the role the bulk spin of the antiferromagnet plays in exchange bias and whether or not exchange bias is entirely an interfacial effect. We fabricated several FM/AF/FM trilayer structures of Py(100Å)/FeMn(x)/Ni69Cu31(200Å) with varying antiferromagnet thicknesses and used a field cool procedure to induce an exchange bias. A Magneto-Optical Kerr Effect magnetometer was used to investigate the propagation of spin information through the antiferromagnet by examining the hysteresis loops at different angles of applied field with respect to the magnetization. It was observed that there was no induced exchange bias in the NiCu probe layer for any of the antiferromagnet thicknesses, and we conclude that the patterning of the antiferromagnetic layer transmits no spin information for thicknesses greater than 100Å.

  2. Mapping motion of antiferromagnetic interfacial uncompensated magnetic moment in exchange-biased bilayers.

    PubMed

    Zhou, X; Ma, L; Shi, Z; Fan, W J; Evans, R F L; Zheng, Jian-Guo; Chantrell, R W; Mangin, S; Zhang, H W; Zhou, S M

    2015-01-01

    In this work, disordered-IrMn3/insulating-Y3Fe5O12 exchange-biased bilayers are studied. The behavior of the net magnetic moment ΔmAFM in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic magnetoresistance. The ΔmAFM is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis loss are induced by partial rotation and irreversible switching of the ΔmAFM. In the athermal training effect, the state of the ΔmAFM cannot be recovered after one cycle of hysteresis loop. This work highlights the fundamental role of the ΔmAFM in the exchange bias and facilitates the manipulation of antiferromagnetic spintronic devices.

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

    PubMed

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

    2015-10-01

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

  4. Mapping motion of antiferromagnetic interfacial uncompensated magnetic moment in exchange-biased bilayers

    PubMed Central

    Zhou, X.; Ma, L.; Shi, Z.; Fan, W. J.; Evans, R. F. L.; Zheng, Jian-Guo; Chantrell, R. W.; Mangin, S.; Zhang, H. W.; Zhou, S. M.

    2015-01-01

    In this work, disordered-IrMn3/insulating-Y3Fe5O12 exchange-biased bilayers are studied. The behavior of the net magnetic moment ΔmAFM in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic magnetoresistance. The ΔmAFM is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis loss are induced by partial rotation and irreversible switching of the ΔmAFM. In the athermal training effect, the state of the ΔmAFM cannot be recovered after one cycle of hysteresis loop. This work highlights the fundamental role of the ΔmAFM in the exchange bias and facilitates the manipulation of antiferromagnetic spintronic devices. PMID:25777540

  5. Electric-field control of exchange bias in multiferroic epitaxial heterostructures.

    PubMed

    Laukhin, V; Skumryev, V; Martí, X; Hrabovsky, D; Sánchez, F; García-Cuenca, M V; Ferrater, C; Varela, M; Lüders, U; Bobo, J F; Fontcuberta, J

    2006-12-01

    The magnetic exchange between epitaxial thin films of the multiferroic (antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft ferromagnetic (FM) layer is used to couple the magnetic response of the FM layer to the magnetic state of the antiferromagnetic one. We will show that biasing the ferroelectric YMnO3 layer by an electric field allows control of the magnetic exchange bias and subsequently the magnetotransport properties of the FM layer. This finding may contribute to paving the way towards a new generation of electric-field controlled spintronic devices.

  6. Effects of exchange bias on magnetotransport in permalloy kagome artificial spin ice

    DOE PAGES

    Le, B. L.; Rench, D. W.; Misra, R.; O’Brien, L.; Leighton, C.; Samarth, N.; Schiffer, P.

    2015-02-01

    We investigate the magnetotransport properties of connected kagome artificial spin ice networks composed of permalloy nanowires. Our data show clear evidence of magnetic switching among the wires, both in the longitudinal and transverse magnetoresistance. An unusual asymmetry with field sweep direction appears at temperatures below about 20 K that appears to be associated with exchange bias resulting from surface oxidation of permalloy, and which disappears in alumina-capped samples. These results demonstrate that exchange bias is a phenomenon that must be considered in understanding the physics of such artificial spin ice systems, and that opens up new possibilities for their control.

  7. Tiny Ni-NiO nanocrystals with exchange bias induced room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Chaghouri, Hanan Al; Tuna, F.; Santhosh, P. N.; Thomas, P. John

    2016-03-01

    Ni nanocrystals coated with a thin layer of NiO with a diameter of 5.0 nm show exchange bias induced ferromagnetism at room temperature. These particulates are freely dispersible in water and were obtained by annealing Ni nanoparticles coated with a thin amorphous layer of NiO. Particulates with diameters between 5.0 and 16.8 nm are studied. Detailed magnetic measurements reveal signs consistent with strong exchange bias including elevated blocking temperatures and tangible loop shifts. The structure of the particulates are characterized by high resolution transmission electron microscopy, energy dispersive x-ray analysis and x-ray diffraction.

  8. Improvement in both giant magnetoresistance and exchange bias through hydrogen ion irradiation at low energy

    SciTech Connect

    Shim, Jaechul; Han, Yoonsung; Lee, Jinwon; Hong, Jongill

    2008-09-01

    Irradiation of IrMn-based spin valves with 550 eV hydrogen ions increased their giant magnetoresistance and exchange bias by 20% and 60%, respectively. This significant enhancement stems from the strong (111) texture and small mosaic spread of the IrMn antiferromagnet that resulted from the microstructural reconstruction caused by the energy transfer during the bombardment by hydrogen ions, as well as by the narrow dispersion in the exchange bias. Irradiation with the hydrogen ion at low energy can improve the properties of spin valves without resulting in undue degradation in the performance or the microstructure.

  9. High temperature exchange bias effect in melt-spun Mn55Bi45alloys

    NASA Astrophysics Data System (ADS)

    Song, Yiming; Xiang, Zhen; Wang, Taolei; Niu, Junchao; Xia, Kada; Lu, Wei; Zhang, Hong; Cao, Yongze; Yoshimura, Satoru; Saito, Hitoshi

    2016-09-01

    In this paper, we report a high-temperature exchange bias (EB) effect in melt-spun Mn55Bi45 alloy ribbons. A remarkable spontaneous exchange bias (up to 1700 Oe) was achieved at temperature from 300 K to 550 K, which is far higher than what has so far been observed in other alloy systems. Such a phenomenon is attributed to the local antiferromagnetic cluster formed in the ferromagnetic matrix. The observation of high-temperature EB in the Mn55Bi45 alloy is of interest from the perspective of practical applications, and it is a good starting point for designing high-temperature spintronic devices.

  10. Exchange bias effect modified asymmetric magnetization reversal in Ni/YMnO3 multiferroic bilayers

    NASA Astrophysics Data System (ADS)

    Gong, Junlu; Zheng, Dongxing; Li, Dong; Jin, Chao; Li, Peng; Feng, Liefeng; Bai, Haili

    2016-04-01

    Exchange bias (EB) effect modified asymmetric magnetization reversal in Ni/YMnO3 multiferroic bilayers was investigated by combining anisotropic magnetoresistance (AMR) with free energy methods. The promotion and inhibition effects of EB field on magnetization rotation result in the asymmetry of magnetization reversal. The AMR curves exhibit shape transition from arc-like to sin2θH-dependence with increasing external fields due to the competition between Zeeman energy and interfacial coupling energy. The phase shift and asymmetric behaviors become weak as the EB field decreases. Our work suggests that controlling the EB effect can be an alternative way to manipulate the magnetization reversal in exchange biased systems.

  11. Magnetic field-controlled hysteresis loop bias in orthogonal exchange-spring coupling composite magnetic films

    NASA Astrophysics Data System (ADS)

    Jiang, Jun; Yu, Tian; Pan, Rui; Zhang, Qin-Tong; Liu, Pan; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Han, Xiufeng

    2016-06-01

    The exchange bias (EB) is an effective fundamental and applicational method to realize magnetic hysteresis loop shifting. However, further manipulation of EB unidirectional anisotropy is difficult after setup using either field deposition or post-annealing. In this work, we experimentally show a new approach to control the magnetic hysteresis loop bias in a [Co(0.2)/Pd(1)]5/CoFeB orthogonal exchange-spring (ES) coupling system, where the direction and strength of unidirectional anisotropy can be easily manipulated by applying an external magnetic field.

  12. Domain-size-dependent exchange bias in Co/LaFeO3

    SciTech Connect

    Scholl, A.; Nolting, F.; Seo, J.W.; Ohldag, H.; Stohr, J.; Raoux,S.; Locquet, J.-P.; Fompeyrine, J.

    2004-09-22

    X-ray microscopy using magnetic linear dichroism of a zero-field-grown, multi-domain Co/LaFeO{sub 3} ferromagnet/antiferromagnet sample shows a local exchange bias of random direction and magnitude. A statistical analysis of the local bias of individual, micron-size magnetic domains demonstrates an increasing bias field with decreasing domain size as expected for a random distribution of pinned, uncompensated spins, which are believed to mediate the interface coupling. A linear dependence with the inverse domain diameter is found.

  13. Exchange bias of the interface spin system at the Fe/MgO interface.

    PubMed

    Fan, Y; Smith, K J; Lüpke, G; Hanbicki, A T; Goswami, R; Li, C H; Zhao, H B; Jonker, B T

    2013-06-01

    The ferromagnet/oxide interface is key to developing emerging multiferroic and spintronic technologies with new functionality. Here we probe the Fe/MgO interface magnetization, and identify a new exchange bias phenomenon manifested only in the interface spin system, and not in the bulk. The interface magnetization exhibits a pronounced exchange bias, and the hysteresis loop is shifted entirely to one side of the zero field axis. However, the bulk magnetization does not, in marked contrast to typical systems where exchange bias is manifested in the net magnetization. This reveals the existence of an antiferromagnetic exchange pinning layer at the interface, identified here as FeO patches that exist even for a nominally 'clean' interface. These results demonstrate that atomic moments at the interface are non-collinear with the bulk magnetization, and therefore may affect the net anisotropy or serve as spin scattering sites. We control the exchange bias magnitude by varying the interface oxygen concentration and Fe-O bonding.

  14. Setting temperature effect in polycrystalline exchange-biased IrMn/CoFe bilayers

    SciTech Connect

    Fernandez-Outon, L. E.; Araujo Filho, M. S.; Araujo, R. E.; Ardisson, J. D.; Macedo, W. A. A.

    2013-05-07

    We study the effect of atomic interdiffusion on the exchange bias of polycrystalline IrMn/({sup 57}Fe + CoFe) multilayers due to the thermal setting process of exchange coupling during field annealing. Depth-resolved {sup 57}Fe conversion electron Moessbauer spectroscopy was used to quantify atomic interdiffusion. Vibrating sample magnetometry was used to monitor the variation of exchange bias and magnetisation. It was found that interface sharpness is only affected above {approx}350 Degree-Sign C. Three different stages for the setting of exchange bias can be inferred from our results. At the lower setting temperatures (up to 350 Degree-Sign C), the effect of field annealing involves alignment of spins and interfacial coupling due to the setting of both antiferromagnetic (AF) bulk and interface without significant interdiffusion. At a second stage (350-450 Degree-Sign C), where AF ordering dominates over diffusion effects, atomic migration and increased setting of AF spins co-exist to produce a peak in exchange bias field and coercivity. On a third stage (>450 Degree-Sign C), severe chemical intermixing reduces significantly the F/AF coupling.

  15. 45 CFR 155.1050 - Establishment of Exchange network adequacy standards.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT Exchange Functions: Certification of Qualified Health Plans § 155.1050 Establishment...

  16. 45 CFR 155.1050 - Establishment of Exchange network adequacy standards.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT Exchange Functions: Certification of Qualified Health Plans § 155.1050 Establishment...

  17. Probing the magnetic transitions in exchange-biased FePt3/Fe bilayers

    NASA Astrophysics Data System (ADS)

    Compton, R. L.; Pechan, Michael J.; Maat, S.; Fullerton, Eric E.

    2002-08-01

    Using magnetometry and ferromagnetic resonance (FMR), we have investigated the magnetic properties of exchange-biased FePt3 (110)/Fe (211) bilayer films epitaxially grown onto MgO (110). The Fe layer exhibits a large uniaxial anisotropy, the magnitude of which is quantitatively accounted for by epitaxial strains. The FePt3 layer is chemically ordered in the L12 phase which develops antiferromagnetic (AF) order below TN1=160 K. Cooling through TN1, the Fe layer becomes exchange biased and its anisotropy is reduced as a result of exchange coupling to the AF-ordered FePt3. Negative exchange bias is observed for cooling fields directed along the FePt3 in-plane [001] and out-of-plane [110] directions, whereas small positive bias is observed when cooling along the in-plane [11¯0] direction. Both the biasing and reduction in anisotropy are consistent with the FePt3 moments lying in the (11¯0) plane with the most likely spin directions being the out-of-plane [111] and [111¯] axes. A second magnetic transition is observed at TN2=100 K. This transition is reflected in the temperature dependence of the coercive field, exchange bias, and FMR resonance and linewidth. Such a transition has only been observed for slightly Fe-rich FePt3 bulk alloys as a reorientation into a second AF phase. However, our films are slightly Pt rich and neutron scattering did not indicate evidence of a transition at TN2 in similarly grown FePt3 films on MgO (110). Possible origins of the second magnetic transition in the coupled structure are discussed.

  18. Voltage controlled exchange bias in an all-thin-film Cr2O3 based heterostructure

    NASA Astrophysics Data System (ADS)

    Echtenkamp, Will; Binek, Christian

    2014-03-01

    Spintronics utilizes the electron's spin degree of freedom for an advanced generation of electronic devices with novel functionalities. Controlling magnetism by electrical means has been identified as a key challenge in the field of spintronics, and electric control of exchange bias is one of the most promising routes to address this challenge. Previously, robust isothermal electric control of exchange bias has been achieved near room temperature utilizing a bulk single crystal of Cr2O3. In this study electric control of exchange bias in an all-thin-film system is demonstrated with significant implications for device realization. In particular, voltage controlled switching of exchange bias in a Cr2O3 based magnetoelectric magnetic tunnel junction enables nonvolatile memory storage with virtually dissipationless writing at, or above, room temperature. Additionally, unique physical properties which arise due to the Cr2O3 thin film geometry are highlighted. This project is supported by NSF through MRSEC DMR 0213808, by the NRC/NRI supplement to MRSEC, and by CNFD and C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program.

  19. Diffusion mechanism of exchange bias formation in permalloy-manganese nanostructures at thermo-magnetic treatment.

    PubMed

    Blinov, I V; Krinitsina, T P; Matveev, S A; Milyaev, M A; Sedova, P N; Popov, V V; Ustinov, V V

    2012-09-01

    A mechanism of unidirectional exchange anisotropy formation at thermo-magnetic treatment of permalloy-manganese bilayers has been studied. A shift of hysteresis loops appears at annealing beginning from 230 degrees C. The maximal exchange field of 155 Oe is reached after the 250 degrees C annealing for 2 h. As demonstrated by transmission electron microscopy, the exchange bias and the coercivity growth result from an ordered anti-ferromagnetic NiFeMn phase formation due to the diffusion interaction of permalloy and manganese at annealing. PMID:23035517

  20. Determination of rotatable and frozen CoO spins and their relationship to exchange bias in CoO/Fe/Ag(001)

    SciTech Connect

    Wu, J.; Park, J.; Kim, W.; Arenholz, E.; Liberati, M.; Scholl, A.; Wu, Y.; Hwang, C.; Qiu, Z.

    2010-02-10

    The exchange bias of epitaxially grown CoO/Fe/Ag(001) was investigated using X-ray Magnetic Circular Dichroism (XMCD) and X-ray Magnetic Linear Dichroism (XMLD) techniques. A direct XMLD measurement on the CoO layer during the Fe magnetization reversal shows that the CoO compensated spins are rotatable at thinner thickness and frozen, i.e. fixed in direction to the lattice, at larger thickness. By a quantitative determination of the rotatable and frozen CoO spins as a function of the CoO film thickness, we find the remarkable result that the exchange bias is well established before frozen spins are detectable in the CoO film, contrary to the common assumption that the majority of antiferromagnetic spins need to be frozen to generate the exchange bias. We further show that the rotatable/frozen CoO spins are uniformly distributed in the CoO film.

  1. Observation of an atomic exchange bias effect in DyCo4 film.

    PubMed

    Chen, Kai; Lott, Dieter; Radu, Florin; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe

    2015-01-01

    The fundamental important and technologically widely employed exchange bias effect occurs in general in bilayers of magnetic thin films consisting of antiferromagnetic and ferromagnetic layers where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the magnetization curve of a soft ferromagnetic film. The minimization of the single magnetic grain size to increase the storage density and the subsequent demand for magnetic materials with very high magnetic anisotropy requires a system with high HEB. Here we report an extremely high HEB of 4 Tesla observed in a single amorphous DyCo4 film close to room temperature. The origin of the exchange bias can be associated with the variation of the magnetic behavior from the surface towards the bulk part of the film revealed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism techniques utilizing the bulk sensitive transmission and the surface sensitive total electron yield modes. The competition between the atomic exchange coupling in the single film and the Zeeman interaction lead to an intrinsic exchanged coupled system and the so far highest exchange bias effect HEB = 4 Tesla reported in a single film, which is accommodated by a partial domain wall formation. PMID:26675537

  2. Observation of an atomic exchange bias effect in DyCo4 film

    NASA Astrophysics Data System (ADS)

    Chen, Kai; Lott, Dieter; Radu, Florin; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe

    2015-12-01

    The fundamental important and technologically widely employed exchange bias effect occurs in general in bilayers of magnetic thin films consisting of antiferromagnetic and ferromagnetic layers where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the magnetization curve of a soft ferromagnetic film. The minimization of the single magnetic grain size to increase the storage density and the subsequent demand for magnetic materials with very high magnetic anisotropy requires a system with high HEB. Here we report an extremely high HEB of 4 Tesla observed in a single amorphous DyCo4 film close to room temperature. The origin of the exchange bias can be associated with the variation of the magnetic behavior from the surface towards the bulk part of the film revealed by X-ray absorption spectroscopy and X-ray magnetic circular dichroism techniques utilizing the bulk sensitive transmission and the surface sensitive total electron yield modes. The competition between the atomic exchange coupling in the single film and the Zeeman interaction lead to an intrinsic exchanged coupled system and the so far highest exchange bias effect HEB = 4 Tesla reported in a single film, which is accommodated by a partial domain wall formation.

  3. Exchange bias of MnPt/CoFe films prepared by ion beam deposition

    NASA Astrophysics Data System (ADS)

    Rickart, M.; Freitas, P. P.; Trindade, I. G.; Barradas, N. P.; Alves, E.; Salgueiro, M.; Muga, N.; Ventura, J.; Sousa, J. B.; Proudfoot, G.; Pearson, D.; Davis, M.

    2004-06-01

    We report on exchange bias of Mn100-xPtx/Co90Fe10 bottom-pinned bilayers prepared by ion beam deposition. The Pt content in the film was varied 6 at. % with x between 46 and 52 at. % by changing the angle of substrate relative to the target in a range of 40°. Exchange coupling for a Mn100-xPtx(20 nm)/Co90Fe10(5 nm) bilayer was found to be maximum (Jex=0.34 erg/cm2) at a composition with x=50 at. %. Structure and magnetic properties of the bilayers deposited on Ta, Ta/Ru, and Ta/Ni81Fe19 seed layers were studied by vibrating sample magnetometry, x-ray diffraction, Rutherford backscattering spectroscopy, and atomic force microscopy. Exchange bias and coercive field can be tuned as functions of the seed layer. The effect of different annealing conditions on exchange bias is discussed to improve thermal stability of the bilayers. Maximum exchange coupling is obtained at an annealing temperature TA⩾280 °C, while the blocking temperature TB keeps increasing with annealing up to TA=420 °C.

  4. Exchange bias effect in Ti doped nanocrystalline SrFeO{sub 3-δ}

    SciTech Connect

    Sendil Kumar, A. Srinath, S.

    2014-08-15

    Materials of Ti doped nanocrystalline SrFeO{sub 3-δ} were synthesized through solid state reaction. Detailed magnetization measurements were carried out in zero field cooled (ZFC) and field cooled (FC) conditions. Compounds of SrFe{sub 1-x}Ti{sub x}O{sub 3-δ} (x = 0.1 to 0.3) are found to be spin glass and parent compound is a helical antiferromagnet. Non magnetic Ti{sup 4+} reduces the strength of exchange interactions and the curvature of hysteresis is changed towards concave nature. Exchange bias is observed below the peak temperature (irreversibility in magnetization (T{sub Irr})) in ZFC-FC of SrFe{sub 1-x}Ti{sub x}O{sub 3-δ} (x = 0 to 0.3). The coercivity and exchange bias field values are found to be decreases with increase in temperature. Observed exchange bias effect is attributed to competition between antiferromagnetic superexchange and ferromagnetic double exchange interactions.

  5. Study of exchange bias and training effect in NiCr2O4

    NASA Astrophysics Data System (ADS)

    Barman, Junmoni; Bora, Tribedi; Ravi, S.

    2015-07-01

    Single phase sample of NiCr2O4 crystallized in a tetragonal structure of I41/amd space group was prepared. Ferrimagnetic transition at TC=73 K along with a large irreversibility has been observed from the magnetization measurement. The sample exhibits exchange bias phenomenon and it is explained by considering the anisotropic exchange interaction between the ferrimagnetic and the antiferromagnetic components of magnetic moment. Presence of training effect is also observed. The exchange bias field (HEB) is found to decay exponentially with increase in temperature and however, the coercive field (HCeff) follows the empirical relation HCeff = HCeff [ 1 - T/TC']2 . The maximum experimental values of HEB and HCeff are found to be 313 Oe and 4839 Oe respectively.

  6. Spin-Hall Switching of In-plane Exchange Biased Heterostructures

    NASA Astrophysics Data System (ADS)

    Mann, Maxwell; Beach, Geoffrey

    The spin Hall effect (SHE) in heavy-metal/ferromagnet bilayers generates a pure transverse spin current from in-plane charge current, allowing for efficient switching of spintronic devices with perpendicular magnetic anisotropy. Here, we demonstrate that an AFM deposited adjacent to the FM establishes a large in-plane exchange bias field, allowing operation at zero HIP. We sputtered Pt(3nm)/Co(0.9nm)/Ni80Co20O(tAF) stacks at room-temperature in an in-plane magnetic field of 3 kOe. The current-induced effective field was estimated in Hall cross devices by measuring the variation of the out-of-plane switching field as a function of JIP and HIP. The spin torque efficiency, dHSL/dJIP, is measured versus HIP for a sample with tAF =30 nm, and for a control in which NiCoO is replaced by TaOx. In the latter, dHSL/dJIP varied linearly with HIP. In the former, dHSL/dJIP varied nonlinearly with HIP and exhibited an offset indicating nonzero spin torque efficiency with zero HIP. The magnitude of HEB was 600 Oe in-plane.

  7. Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

    NASA Astrophysics Data System (ADS)

    Cortie, D. L.; Lin, K.-W.; Shueh, C.; Hsu, H.-F.; Wang, X. L.; James, M.; Fritzsche, H.; Brück, S.; Klose, F.

    2012-08-01

    We investigated a hematite α-Fe2O3/permalloy Ni80Fe20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Néel temperature of bulk α-Fe2O3 is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5-1.0 μB per Fe atom within a depth of 1-2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains.

  8. Exchange bias magnetism in films of NiFe/(Ni,Fe)O nanocrystallite dispersions

    SciTech Connect

    Hsiao, C.-H.; Chi, C.-C.; Wang, S.; Ouyang, H.; Desautels, R. D.; Lierop, J. van; Lin, K.-W.; Lin, T.-L.

    2014-05-07

    Ni{sub 3}Fe/(Ni,Fe)O thin films having a nanocrystallite dispersion morphology were prepared by a reactive ion beam-assisted deposition technique. The crystallite sizes of these dispersion-based films were observed to decrease from 8.4 ± 0.3 nm to 3.4 ± 0.3 nm as the deposition flow-rate increased from 2.78% to 7.89% O{sub 2}/Ar. Thin film composition was determined using selective area electron diffraction images and Multislice simulations. Through a detailed analysis of high resolution transmission electron microscopy images, the nanocrystallites were determined to be Ni{sub 3}Fe (a ferromagnet), NiO, and FeO (both antiferromagnets). It was determined that the interfacial molar Ni{sub 3}Fe ratio in the nanocrystallite dispersions increased slightly at first, then decreased as the oxygen content was increased; at 7.89% O{sub 2}/Ar, the interfacial molar ratio was essentially zero (only NiO and FeO remained). For nanocrystallite dispersion films grown with O{sub 2}/Ar flow-rate greater than 7.89%, no interfacial (intermixed) Ni{sub 3}Fe phase was detected, which resulted in no measurable exchange bias. Comparing the exchange bias field between the nanocrystallite dispersion films at 5 K, we observed a decrease in the magnitude of the exchange bias field as the nanocrystallite size decreased. The exchange bias coupling for all samples measured set in at essentially the same temperature (i.e., the exchange bias blocking temperature). Since the ferromagnetic/anti-ferromagnetic (FM/AFM) contact area in the nanocrystallite dispersion films increased as the nanocrystallite size decreased, the increase in the magnitude of the exchange bias could be attributed to larger regions of defects (vacancies and bond distortions) which occupied a significant portion of the FM/AFM interfaces in the nanocrystallite dispersion films.

  9. Exchange Bias Tuning for Magnetoresistive Sensors by Inclusion of Non-Magnetic Impurities.

    PubMed

    Sharma, Parikshit Pratim; Albisetti, Edoardo; Monticelli, Marco; Bertacco, Riccardo; Petti, Daniela

    2016-07-04

    The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co40Fe40B20 and 6.5 nm thick Ir22Mn78 films. By inserting Ru impurities at different concentrations in the Ir22Mn78 layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies.

  10. Half-metallic exchange bias ferromagnetic/antiferromagnetic interfaces in transition-metal chalcogenides.

    PubMed

    Nakamura, Kohji; Kato, Yoshinori; Akiyama, Toru; Ito, Tomonori; Freeman, A J

    2006-02-01

    To investigate half-metallic exchange bias interfaces, magnetic structures at ferromagnetic (FM)/antiferromagnetic (AFM) interfaces in the zinc blende transition-metal chalcogenides, and with compensated and uncompensated AFM interfaces, were determined by the full-potential linearized augmented plane-wave method. With the uncompensated AFM interface, an antiparallel alignment of the Cr and Mn moments induces an excellent half-metallicity. More striking still, in the compensated AFM interface the Cr moments in the FM layer lie perpendicular to the Mn moments in the AFM layer but the Mn moments strongly cant to induce a net moment so as to retain the half-metallicity. These findings may offer a key ingredient for exchange biased spintronic devices with 100% spin polarization, having a unidirectional anisotropy to control and manipulate spins at the nanoscale.

  11. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    SciTech Connect

    Kaur, Maninder; Jiang, Weilin; Qiang, You; Burks, Edward; Liu, Kai; Namavar, Fereydoon; Mccloy, John S.

    2014-11-03

    Iron oxide films were deposited onto Si substrates using ion-beam-assisted deposition. The films were ~300 nm thick polycrystalline magnetite with an average crystallite size of ~6 nm. Additionally, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite. However, Raman spectroscopy and x-ray diffraction both indicate that the films are single-phase magnetite. Since no direct evidence of a second phase could be found, exchange bias likely arises due to defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples have such small grains, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field. The high energy deposition process results in an oxygen-rich, argon-containing magnetite film with low temperature exchange bias due to defects at the high concentration of grain boundaries.

  12. Exchange Bias Tuning for Magnetoresistive Sensors by Inclusion of Non-Magnetic Impurities

    PubMed Central

    Sharma, Parikshit Pratim; Albisetti, Edoardo; Monticelli, Marco; Bertacco, Riccardo; Petti, Daniela

    2016-01-01

    The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co40Fe40B20 and 6.5 nm thick Ir22Mn78 films. By inserting Ru impurities at different concentrations in the Ir22Mn78 layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies. PMID:27384565

  13. Competing effects of magnetocrystalline anisotropy and exchange bias in epitaxial Fe/IrMn bilayers

    SciTech Connect

    Zhang, Wei; Bowden, Mark E.; Krishnan, Kannan M.

    2011-03-01

    We systematically investigated the possible magnetization reversal behavior in well-characterized, epitaxial, Fe/IrMn exchange-biased bilayers as a function of the antiferromagnetic (AF) layer thickness. Several kinds of multi-step loops were observed for the samples measured at various field orientations. The angular dependence of the switching fields, observed using longitudinal and transverse magneto-optic Kerr effect (MOKE), were shown to depend on the competition between the magnetocrystalline anisotropy and the exchange bias (EB). A modified ‘effective field’ model was applied to quantitatively describe the evolution of the magnetic behavior and correctly predict the occurrence of different magnetic switching processes. The dependence of the effective anisotropy fields on the AF layer thickness directly reflects the competing effects of the pinned and rotatable antiferromagnetic spins at the EB interface.

  14. Temperature evolution of nickel sulphide phases from thiourea complex and their exchange bias effect

    SciTech Connect

    Kumar, Nitesh; Raman, N.; Sundaresan, A.

    2013-12-15

    Considering the very complex phase diagram of nickel sulphide, it is quite challenging to stabilize pure phases from a single precursor. Here, we obtain nanoparticles of various phases of nickel sulphide by decomposing nickel–thiourea complex at different temperatures. The first phase in the evolution is the one with the maximum sulphur content, namely, NiS{sub 2} nanoparticles obtained at 400 °C. As the temperature is increased, nanoparticles of phases with lesser sulphur content, NiS (600 °C) and Ni{sub 3}S{sub 2} (800 °C) are formed. NiS{sub 2} nanoparticles exhibit weak ferromagnetic transition at 30 K and show a large exchange bias at 2 K. NiS nanoparticles are antiferromagnetic and show relatively smaller exchange bias effect. On the other hand, Ni{sub 3}S{sub 2} nanoparticles exhibit very weak temperature dependent magnetization. Electrical measurements show that both NiS{sub 2} and NiS are semiconductors whereas Ni{sub 3}S{sub 2} is a metal. - Graphical abstract: Pure phases of NiS{sub 2}, NiS and Ni{sub 3}S{sub 2} have been obtained by thermal decomposition of nickel–thiourea complex wherein, NiS{sub 2} nanoparticles exhibit remarkable exchange bias effect at 2 K. - Highlights: • NiS{sub 2}, NiS and Ni{sub 3}S{sub 2} nanoparticles are obtained by thermal decomposition of nickel–thiourea complex at different temperatures. • As the temperature is increased, nickel sulphide phase with lesser sulphur content is obtained. • NiS{sub 2} nanoparticles show good exchange bias property which can be explained by antiferromagnetic core and ferromagnetic shell model. • NiS{sub 2} and NiS are semiconducting while Ni{sub 3}S{sub 2} shows metallic behavior.

  15. Closed system respirometry may underestimate tissue gas exchange and bias the respiratory exchange ratio (RER).

    PubMed

    Malte, Christian Lind; Nørgaard, Simon; Wang, Tobias

    2016-02-01

    Closed respirometry is a commonly used method to measure gas exchange in animals due to its apparent simplicity. Typically, the rates of O2 uptake and CO2 excretion (VO2 and VCO2, respectively) are assumed to be in steady state, such that the measured rates of gas exchange equal those at tissue level. In other words, the respiratory gas exchange ratio (RER) is assumed to equal the respiratory quotient (RQ). However, because the gas concentrations change progressively during closure, the animal inspires air with a progressively increasing CO2 concentration and decreasing O2 concentration. These changes will eventually affect gas exchange causing the O2 and CO2 stores within the animal to change. Because of the higher solubility/capacitance of CO2 in the tissues of the body, VCO2 will be more affected than VO2, and we hypothesize therefore that RER will become progressively underestimated as closure time is prolonged. This hypothesis was addressed by a combination of experimental studies involving closed respirometry on ball pythons (Python regius) as well as mathematical models of gas exchange. We show that increased closed duration of the respirometer reduces RER by up to 13%, and these findings may explain previous reports of RER values being below 0.7. Our model reveals that the maximally possible reduction in RER is determined by the storage capacity of the body for CO2 (product of size and specific capacitance) relative to the respirometer storage capacity. Furthermore, modeling also shows that pronounced ventilatory and circulatory response to hypercapnia can alleviate the reduction in RER.

  16. Uncoupled surface spin induced exchange bias in α-MnO2 nanowires

    PubMed Central

    Li, Wenxian; Zeng, Rong; Sun, Ziqi; Tian, Dongliang; Dou, Shixue

    2014-01-01

    We have studied the microstructure, surface states, valence fluctuations, magnetic properties, and exchange bias effect in MnO2 nanowires. High purity α-MnO2 rectangular nanowires were synthesized by a facile hydrothermal method with microwave-assisted procedures. The microstructure analysis indicates that the nanowires grow in the [0 0 1] direction with the (2 1 0) plane as the surface. Mn3+ and Mn2+ ions are not found in the system by X-ray photoelectron spectroscopy. The effective magnetic moment of the manganese ions fits in with the theoretical and experimental values of Mn4+ very well. The uncoupled spins in 3d3 orbitals of the Mn4+ ions in MnO6 octahedra on the rough surface are responsible for the net magnetic moment. Spin glass behavior is observed through magnetic measurements. Furthermore, the exchange bias effect is observed for the first time in pure α-MnO2 phase due to the coupling of the surface spin glass with the antiferromagnetic α-MnO2 matrix. These α-MnO2 nanowires, with a spin-glass-like behavior and with an exchange bias effect excited by the uncoupled surface spins, should therefore inspire further study concerning the origin, theory, and applicability of surface structure induced magnetism in nanostructures. PMID:25319531

  17. Exchange bias effects in Heusler alloy Ni2MnAl/Fe bilayers

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomoki; Kubota, Takahide; Sugiyama, Tomoko; Huminiuc, Teodor; Hirohata, Atsufumi; Takanashi, Koki

    2016-06-01

    Ni2MnAl Heusler alloy thin films were epitaxially grown on MgO(1 0 0) single crystal substrates by ultra-high-vacuum magnetron sputtering technique. X-ray diffraction and transmission electron microscopy observation revealed that the structures of all the Ni2MnAl thin films were B2-ordered regardless of the deposition temperature ranging from room temperature to 600 °C. The temperature dependence of electrical resistivity showed a kink about 280 K, which was consistent with a reported value of the Néel temperature for antiferromagnetic B2-Ni2MnAl. The magnetization curves of Ni2MnAl/Fe bilayer samples showed a shift caused by the interfacial exchange interaction at 10 K. The maximum value of the exchange bias field H ex was 55 Oe corresponding to the exchange coupling energy J k of 0.03 erg cm-2.

  18. Exchange bias up to room temperature in antiferromagnetic hexagonal Mn3Ge

    NASA Astrophysics Data System (ADS)

    Qian, J. F.; Nayak, A. K.; Kreiner, G.; Schnelle, W.; Felser, C.

    2014-07-01

    Mn3.04Ge0.96 has a hexagonal crystal structure, which can be stabilized by high-temperature annealing, and shows antiferromagnetic order with a small ferromagnetic component of less than 0.1μB and a coercivity of 0.45 T. In the ordered phase, magnetization curves M(H) exhibit an exchange bias of 62 mT at T = 2 K after field cooling, which is observable up to room temperature. The exchange anisotropy is suggested to originate from the exchange interaction between the host of triangular-antiferromagnetic Mn3Ge units and embedded ferrimagnetic-like clusters. Such clusters develop when excess Mn atoms occupy empty Ge sites in the original triangular-antiferromagnetic structure of Mn3Ge.

  19. Establishing Data-Exchange Networks Through Data Management & Telecommunications.

    ERIC Educational Resources Information Center

    Evans, Evan C., III

    This paper describes several pilot systems of data management using telecommunications links, which have been tested by the Navy during an 8-year period in which emphasis has been on the development of relational database management systems, exchange protocols, and man-machine interface. An introduction discusses the background of the project,…

  20. Fingerprints of surface magnetism in Cr2O3 based exchange bias heterostructures

    NASA Astrophysics Data System (ADS)

    He, Xi; Wang, Yi; Binek, Ch.

    2009-03-01

    Magnetoelectric materials experienced a recent revival as promising components of novel spintronic devices [1, 2, 3]. Since the magnetoelectric (ME) effect is relativistically small in traditional antiferromagnetic (AF) compounds like Cr2O3 (max. αzz 4ps/m) and also cross-coupling between ferroic order parameters is typically small in the modern multiferroics, it is a challenge to electrically induce sufficient magnetization required for the envisioned device applications. In exchange bias systems the bias field depends critically on the AF interface magnetization. Hence, a strong relation between the latter and the surface magnetization of the free Cr2O3 pinning layer can be expected. Our recent research indicates that there are surface magnetic phase transitions in free Cr2O3 (111) films accompanying surface structural phase transitions. Well defined AF interface magnetization is initialized through ME annealing to T=20K. Subsequently, the interface magnetization is thermally driven through phase transitions at T=120 and 210K. Their effects on the exchange bias are studied in Cr2O3 (111)/CoPt films with the help of polar Kerr and SQUID magnetometry. [1] P. Borisov et al. Phys. Rev. Lett. 94, 117203 (2005). [2] Ch. Binek, B.Doudin, J. Phys. Condens. Matter 17, L39 (2005). [3] R. Ramesh et al. 2007 Nature Materials 6 21. Financial support by NSF through Career DMR-0547887, MRSEC DMR-0820521 and the NRI.

  1. Positive exchange bias observed in Pt-inserted Cr{sub 2}O{sub 3}/Co exchange coupled bilayers

    SciTech Connect

    Nozaki, T. Oida, M.; Ashida, T.; Shimomura, N.; Sahashi, M.; Shibata, T.

    2014-11-24

    We investigated the effect of Pt insertion on a Cr{sub 2}O{sub 3}/Co exchange coupling system. The perpendicular exchange bias μ{sub 0}H{sub ex} decreased with increasing Pt insertion layer thickness, and we observed positive μ{sub 0}H{sub ex} for samples with relatively thick Pt insertion layers. We also examined the cooling field μ{sub 0}H{sub fc} dependence of μ{sub 0}H{sub ex} for the samples. At small μ{sub 0}H{sub fc}, all samples exhibited negative μ{sub 0}H{sub ex}. With increasing μ{sub 0}H{sub fc}, a shift of μ{sub 0}H{sub ex} from negative to positive was observed. In the past, similar behaviors were observed for FeF{sub 2}/Fe systems exhibiting positive μ{sub 0}H{sub ex}. In addition, the μ{sub 0}H{sub fc} dependence of μ{sub 0}H{sub ex} was well fitted by an equation taking into account the Zeeman energy at the surface of an antiferromagnet as well as an antiferromagnetic exchange coupling. The results strongly suggest that (1) Cr{sub 2}O{sub 3} surface spin is affected by the external magnetic field and (2) the coupling at the Cr{sub 2}O{sub 3}/Pt/Co interface is antiferromagnetic.

  2. Exchange bias in Core-Shell Iron-Iron Oxide Nanoclusters

    SciTech Connect

    Kaur, Maninder; McCloy, John S.; Qiang, You

    2013-04-03

    An exchange bias study has been performed on core-shell iron-iron oxide (Fe-Fe3O4) nanoclusters (NCs) of size 11 nm and 14 nm carrying a different core to shell ratio. NCs show complicated behaviors due to competition between interfacial exchange and Zeeman energy in the presence of magnetic field during cooling. These behaviors are accompanied by the evolution of size- dependent cluster structures in the ferromagnetic-core/ferri- or antiferro-magnetic-shell. Smaller clusters have larger coercive field, exchange bias field, and vertical magnetization shift due to the greater contribution from frozen spins of shell/interfaces. These smaller clusters thus also show more dramatic changes with the training effect. Both sizes of clusters display an additional anomaly of the upper part of the hysteresis loop at 10 K under low cooling field (0.1 kOe). This anomaly decreases with number of loop cycles with same field, and disappear with large cooling field (> 0.1 kOe). It may be caused by the competition between the magnetization reversal and the magnetostatic interactions.

  3. Exchange-bias in amorphous ferromagnetic and polycrystalline antiferromagnetic bilayers: Structural study and micromagnetic modeling

    NASA Astrophysics Data System (ADS)

    Kohn, A.; Dean, J.; Kovacs, A.; Zeltser, A.; Carey, M. J.; Geiger, D.; Hrkac, G.; Schrefl, T.; Allwood, D.

    2011-04-01

    We study the role of the structure of antiferromagnetic polycrystalline metallic films in determining the magnetic properties of an exchange-coupled amorphous ferromagnetic layer. The bilayers are sputter-deposited, highly textured {111} Ir22Mn78 and Co65.5Fe14.5B20 thin films. We focus on structural characterization of Ir22Mn78 as a function of layer thickness in the range having the strongest influence over the exchange-bias field and training effect. We have used transmission electron microscopy to characterize defects in the form of interface steps and roughness, interdiffusion, twin- and grain-boundaries. Such defects can result in uncompensated magnetic spins in the antiferromagnet, which then contribute to exchange-bias. These experimental results form the basis of a general model, which uses finite element micromagnetic simulations. The model incorporates the experimental structural parameters of the bilayer by implementing a surface integral technique that allows numerical calculations to solve the transition from an amorphous to a granular structure. As a result, a detailed calculation of the underlying magnetic structure within the antiferromagnetic material is achieved. These calculations are in good agreement with micromagnetic imaging using Lorentz transmission electron microscopy and the macro-magnetic properties of these bilayers.

  4. Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

    DOE PAGES

    Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X.; et al

    2015-11-18

    E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shiftedmore » by up to |ΔHex|/Hex=8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |ΔHex|/Hc=67.5~125% in NiFe/FeMn/glass/PZN-PT and 30~38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Lastly, electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies.« less

  5. Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

    PubMed Central

    Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X.; Liu, Ming

    2015-01-01

    E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shifted by up to |∆Hex|/Hex = 8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |∆Hex|/Hc = 67.5 ~ 125% in NiFe/FeMn/glass/PZN-PT and 30 ~ 38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies. PMID:26576658

  6. Exchange bias effect in nickel zinc ferrite-mesoporous silica nanocomposites

    NASA Astrophysics Data System (ADS)

    Banerjee, Shilpi; Hajra, Partha; Mada, Mykanth Reddy; Bhaumik, Asim; Bandyopadhyay, Sri; Chakravorty, Dipankar

    2013-04-01

    Nickel zinc ferrite-mesoporous silica nanocomposite (NZF-MS) was synthesized using impregnation method. The microstructure was investigated by transmission electron microscopy. A magnetic exchange bias effect was exhibited by the nanocomposites. This was ascribed to the presence of a ferromagnetic core and antiferromagnetic shell structure. Electron microscopic studies confirmed the presence of a core-shell structure with NZF forming the core. The zero-field cooled magnetization data as a function of temperature indicated the presence of an antiferromagnetic phase which is believed to be formed by the diffusion of Fe3+ or Ni2+ ions into the silica glass.

  7. Anisotropy induced large exchange bias behavior in ball milled Ni-Co-Mn-Sb alloys

    SciTech Connect

    Nayak, Ajaya K.; Sahoo, Roshnee; Suresh, K. G.; Nigam, A. K.; Chen, X.; Ramanujan, R. V.

    2011-06-06

    We report the effect of decrease in the grain size on the structural, magnetic and exchange bias (EB) behavior in ball milled Ni{sub 50-x}Co{sub x}Mn{sub 38}Sb{sub 12} (x=0 and 5) Heusler alloys. The existence of a wide range of grain sizes in the ball milled samples results in dramatic changes in the structural and magnetic properties. For x=0, a large EB field of 3.2 kOe is observed in the ball milled sample, compared to a value of 245 Oe of the bulk sample. This increase is attributed to the enhanced exchange coupling between the soft and hard magnetic particles.

  8. Exchange Bias Effect in La1-xAgxMnO3 Nanopowders

    NASA Astrophysics Data System (ADS)

    Mihalik, M.; Antoňák, M.; Csach, K.; Fitta, M.; Mihalik, M.; Vavra, M.; Zentková, M.

    2013-01-01

    Exchange bias (EB) phenomena were first observed in the La1-xAgxMnO3 as prepared and heat treated (300 °C/2 hours) nanopowders (x = 0.10, 0.15 and 0.20) which were synthetized by self-combustion glycine-nitrate method. These nanoparticles have an average size of about 25 nm and adopt orthorhombic Pnma crystal structure. Cooling in magnetic field Hcf ≠ 0 through the Curie temperature TC shifts hysteresis loop in horizontal and vertical direction. The values of exchange bias field HE, coercive field Hc, remnant asymmetry μE and coercive magnetization μc increase with increasing value of cooling field Hcf. In addition the training effect was observed. Basic magnetic properties like the Curie temperature TC and the saturated magnetization µs increase and HE or µE decrease with heat treatment. Heat treatment at 600 °C/2 hours increases the average size of nanoparticles to about 55 nm, crystal structure changes to rhombohedral structure (space group R3c) and EB effect vanishes.

  9. Reversible electric control of exchange bias in a multiferroic field-effect device.

    PubMed

    Wu, S M; Cybart, Shane A; Yu, P; Rossell, M D; Zhang, J X; Ramesh, R; Dynes, R C

    2010-09-01

    Electric-field control of magnetization has many potential applications in magnetic memory storage, sensors and spintronics. One approach to obtain this control is through multiferroic materials. Instead of using direct coupling between ferroelectric and ferromagnetic order parameters in a single-phase multiferroic material, which only shows a weak magnetoelectric effect, a unique method using indirect coupling through an intermediate antiferromagnetic order parameter can be used. In this article, we demonstrate electrical control of exchange bias using a field-effect device employing multiferroic (ferroelectric/antiferromagnetic) BiFeO(3) as the dielectric and ferromagnetic La(0.7)Sr(0.3)MnO(3) as the conducting channel; we can reversibly switch between two distinct exchange-bias states by switching the ferroelectric polarization of BiFeO(3). This is an important step towards controlling magnetization with electric fields, which may enable a new class of electrically controllable spintronic devices and provide a new basis for producing electrically controllable spin-polarized currents.

  10. Exchange Bias and Magnetotransport in Permalloy Connected Kagome Artificial Spin Ice

    NASA Astrophysics Data System (ADS)

    Le, Brian; Rench, David; Misra, Rajiv; O'Brien, Liam; Leighton, Chris; Samarth, Nitin; Schiffer, Peter

    2015-03-01

    Artificial spin ice consists of nanoscale ferromagnets arranged in a periodic lattice, with the resultant magnetostatic interactions emulating the local magnetic behavior of spin ice. Kagome artificial spin ice consists of elongated ferromagnetic islands or nanowires arranged in a honeycomb lattice. We present magnetotransport results in connected kagome artificial spin ice composed of permalloy (Ni81Fe19) nanowires. Magnetoresistance was measured as a function of applied field strength at different temperatures. At temperatures below 20 K, the field reversal symmetry of the magnetoresistance is broken. This asymmetry appears to be associated with exchange bias due to the surface oxidation of permalloy and is suppressed in aluminum-capped samples. These results signify that exchange bias can play a substantial role in the physics of artificial spin ice that has potential as a new mode of controlling its behavior. Supported by the US Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under grant number DE-SC0010778. Work at the University of Minnesota was supported by the NSF MRSEC under award DMR-0819885 and a Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme (project no. 299376).

  11. Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys.

    PubMed

    Dong, S Y; Chen, J Y; Han, Z D; Fang, Y; Zhang, L; Zhang, C L; Qian, B; Jiang, X F

    2016-01-01

    In this work, we studied the phase transitions and exchange bias of Ni50-xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50-xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase. PMID:27170057

  12. Exchange bias caused by field-induced spin reconfiguration in Ni-Mn-Sn

    NASA Astrophysics Data System (ADS)

    ćakır, A.; Acet, M.; Farle, M.

    2016-03-01

    Exchange bias is observed in ferromagnetic/antiferromagnetic (FM/AF) layered stacks and in materials with neighboring ferromagnetic and antiferromagnetic granules. The latter is commonly observed in Ni-Mn-based martensitic Heusler alloys. In general, the exchange-bias effect is identified as horizontally shifted hysteresis loop when the system is field cooled from high temperatures. We report here loop shifts not only under field-cooled but also under zero-field-cooled conditions in magnetically granular martensitic Ni50Mn50 -xSnx Heusler alloys in the compositional range 13.0 ≥x ≥8.9 . Under zero-field-cooled conditions, the initially applied field can carry the system over energy barriers and stabilize a spin-reconfigured state so that a negatively shifted hysteresis loop can also occur here as in the field-cooled state. Spin reconfiguration occurs when the relative size of the AF and FM regions as well as the relative strength of the of AF and FM interactions are in balance.

  13. Intermartensitic Transformation and Enhanced Exchange Bias in Pd (Pt) -doped Ni-Mn-Sn alloys

    PubMed Central

    Dong, S. Y.; Chen, J. Y.; Han, Z. D.; Fang, Y.; Zhang, L.; Zhang, C. L.; Qian, B.; Jiang, X. F.

    2016-01-01

    In this work, we studied the phase transitions and exchange bias of Ni50−xMn36Sn14Tx (T = Pd, Pt; x = 0, 1, 2, 3) alloys. An intermartensitic transition (IMT), not observed in Ni50Mn36Sn14 alloy, was induced by the proper application of negative chemical pressure by Pd(Pt) doping in Ni50−xMn36Sn14Tx (T = Pd, Pt) alloys. IMT weakened and was suppressed with the increase of applied field; it also disappeared with further increase of Pd(Pt) content (x = 3 for Pd and x = 2 for Pt). Another striking result is that exchange bias effect, ascribed to the percolating ferromagnetic domains coexisting with spin glass phase, is notably enhanced by nonmagnetic Pd(Pt) addition. The increase of unidirectional anisotropy by the addition of Pd(Pt) impurities with strong spin-orbit coupling was explained by Dzyaloshinsky-Moriya interactions in spin glass phase. PMID:27170057

  14. Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers

    PubMed Central

    Rui, W. B.; Hu, Y.; Du, A.; You, B.; Xiao, M. W.; Zhang, W.; Zhou, S. M.; Du, J.

    2015-01-01

    We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1 − x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1 − x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE ∼ T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties. PMID:26348277

  15. Exchange bias properties of [Co/CoO]{sub n} multilayers

    SciTech Connect

    Oeztuerk, M.; S Latin-Small-Letter-Dotless-I n Latin-Small-Letter-Dotless-I r, E.; Demirci, E.; Erkovan, M.; Oeztuerk, O.; Akdogan, N.

    2012-11-01

    In this study, the exchange bias properties of four polycrystalline multilayer stack samples of antiferromagnetic (AF) CoO and ferromagnetic (FM) Co in the form of [CoO/Co]{sub n} with n = 1, 2, 3, and 5 are reported. The samples were grown on top of Si (001) substrates by using magnetron sputtering method. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were used to determine the structural properties of the samples. XPS measurements of cobalt oxide layer revealed the coexistence of different phases in cobalt oxide as CoO and Co{sub 3}O{sub 4}, the latter of which lowers the blocking temperature. The blocking temperature is also affected by the finite size scaling effects observed in AF layers. In-plane ferromagnetic resonance (FMR) measurements revealed uniaxial in-plane magnetic anisotropy for the samples. Low temperature vibrating sample magnetometer measurements provided exchange bias with a stepwise character. Observed steps are believed to be due to magnetization reversals of individual FM layers with varying thicknesses, each of which is pinned through two interfaces from above and below with two AFM layers, except the uppermost FM Co layer with a single AFM neighbor.

  16. Exchange bias effect in spin glass CoCr2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Zhu, Changming; Tian, Zhaoming; Wang, Liguang; Yuan, Songliu

    2015-11-01

    CoCr2O4 nanoparticles are about 5.4 nm in diameter synthesized by a hydrothermal technique. Magnetization measurements reveal that the nanoparticles exhibit a spin glass behavior below glass transition temperature. Signature of memory effect is clear in reheating curve where the step-like shape increasing with the increase of temperature is recovered after cooling process. Magnetic relaxation is performed to prove memory effect. Ageing effect is also detected in CoCr2O4 nanoparticles to verify the spin glass behavior. As temperature decreases to 5 K, which is far below the glass transition temperature, exchange bias effect can be observed clearly accompanied with a shift in field-cooled hysteresis loop. As particle size decreases to 5.4 nm, spin glass behavior appears due to the increased spin disorder effect. The spin glass phase providing a pinning force from some frozen spins to the rotatable spins gives the key to explain the exchange bias effects.

  17. Exchange bias in a mixed metal oxide based magnetocaloric compound YFe0.5Cr0.5O3

    NASA Astrophysics Data System (ADS)

    Sharma, Mohit K.; Singh, Karan; Mukherjee, K.

    2016-09-01

    We report a detailed investigation of magnetization, magnetocaloric effect and exchange bias studies on a mixed metal oxide YFe0.5Cr0.5O3 belonging to perovskite family. Our results reveal that the compound is in canted magnetic state (CMS) where ferromagnetic correlations are present in an antiferromagnetic state. Magnetic entropy change of this compound follows a power law (∆SM∼Hm) dependence of magnetic field. In this compound, inverse magnetocaloric effect (IMCE) is observed below 260 K while conventional magnetocaloric effect (CMCE) above it. The exponent 'm' is found to be independent of temperature and field only in the IMCE region. Investigation of temperature and magnetic field dependence studies of exchange bias, reveal a competition between effective Zeeman energy of the ferromagnetic regions and anisotropic exchange energy at the interface between ferromagnetic and antiferromagnetic regions. Variation of exchange bias due to temperature and field cycling is also investigated.

  18. A direct measurement of rotatable and frozen CoO spins in exchange bias system of CoO/Fe/Ag(001)

    SciTech Connect

    Wu, J.; Park, J. S.; Kim, W.; Arenholz, E.; Liberati, M.; Scholl, A.; Wu, Y. Z.; Hwang, C.; Qiu, Z. Q.

    2010-03-10

    The exchange bias of epitaxially grown CoO/Fe/Ag(001) was investigated using x-ray magnetic circular dichroism and x-ray magnetic linear dichroism (XMLD) techniques. A direct XMLD measurement on the CoO layer during the Fe magnetization reversal shows that the CoO compensated spins are rotatable at thinner thickness and frozen at larger thickness. By a quantitative determination of the rotatable and frozen CoO spins as a function of the CoO film thickness, we find the remarkable result that the exchange bias is well established before frozen spins are detectable in the CoO film. We further show that the rotatable and frozen CoO spins are uniformly distributed in the CoO film.

  19. Unwanted spatial bias in predicting establishment of an invasive insect based on simulated demographics

    NASA Astrophysics Data System (ADS)

    Gray, David R.

    2014-07-01

    A strategy to estimate the probability of successful establishment of the invasive gypsy moth (given an introduction) is growing in popularity. The strategy calls for an examination of the demographic output of a phenology model of the complete life-cycle to estimate the generational success under the climate of the location under consideration. The probability is maximal where the climate satisfies the life-cycle requirements of all life-stages of 100 % of the population every year. The probability decreases where a smaller proportion of the population has its requirements satisfied every year, or where the frequency of unsatisfactory years increases. The strategy can give an unbiased and objective estimate of the probability. However, implementation of the strategy has most often forced unnatural and overly simplistic modifications onto the demographic structure that is simulated by the phenology model, and used an inappropriate and arbitrary calendar date to estimate demographic changes from winter mortality. This produces pronounced spatial bias in the estimates of generational success, and therefore in the estimates of climate-mediated establishment probability. In an examination of the strategy, as implemented in New Zealand, one demographic simplification caused an overestimate of 21 % in a southern location; a second simplification caused an overestimate of 17 % in a northern location. One hundred percent of the generations were incorrectly considered to have failed in a northern location because of the arbitrary calendar date that was used; and 78 % of the generations were incorrectly considered successful in a southern location because of the arbitrary date.

  20. 77 FR 18309 - Patient Protection and Affordable Care Act; Establishment of Exchanges and Qualified Health Plans...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-27

    ... Request for Comment (the RFC) on August 3, 2010 (75 FR 45584) inviting the public to provide input... preamble of the Exchange establishment proposed rule, at 76 FR 41870-41871, for a detailed discussion...

  1. Exchange bias and coercivity of Ni80Fe20 layer coupled with Fe-doped Cr2O3

    NASA Astrophysics Data System (ADS)

    Ki, Sanghoon; Dho, Joonghoe

    2010-05-01

    We have investigated the exchange bias and the coercivity in the ferromagnet Ni80Fe20 (NiFe) layer coupled with a polycrystalline Cr2(1-x)Fe2xO3(CFO; x=0.1,0.25) layer, which is known as an antiferromagnet with spiral spin order. For x=0.1, the exchange bias HEX and the coercivity HC at 10 K were 152 and 230 Oe, respectively, but their magnitudes rapidly decreased from 10 to 50 K at the temperature range that showed a splitting between zero-field-cooling and field-cooling magnetization data for the CFO target. This implies that the CFO has an unknown magnetic transition around ˜50 K in addition to the spiral antiferromagnetic transition at ˜250 K. For x=0.25, on the other hand, the exchange bias rapidly decreased from ˜170 Oe at 10 K to zero at ˜90 K.

  2. Exchange bias in sputtered FM/BiFeO3 thin films (FM = Fe and Co)

    NASA Astrophysics Data System (ADS)

    Chang, H. W.; Yuan, F. T.; Shih, C. W.; Li, W. L.; Chen, P. H.; Wang, C. R.; Chang, W. C.; Jen, S. U.

    2012-04-01

    Magnetic properties of sputter-deposited ferromagnetic (FM)/BiFeO3 (BFO) films on Pt/Ti/SiO2/Si(100) substrate (FM = Co and Fe) have been investigated. Isotropic perovskite BFO single phase is obtained for 200-nm-thick BFO films deposited at 300-450 °C and BFO films at 400 °C with thickness of 50-400 nm. Large exchange bias field (HEB) of 308-400 Oe and coercivity (Hc) of 1201-3632 Oe at RT are obtained for polycrystalline Co/BFO bilayers. The roughened surface induced by high deposition temperature and increasing thickness of BFO layer enhances localized shape anisotropy of FM layer, resulting in the increase of Hc the improved crystallinity and roughened surface of BFO/Co interface might be responsible for the HEB enhancement. Additionally, comparison on the HEB in polycrystalline Co/BFO and Fe/BFO systems is also discussed.

  3. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    SciTech Connect

    Kaur, Maninder; Qiang, You; Jiang, Weilin; Burks, Edward C.; Liu, Kai; Namavar, Fereydoon; McCloy, John S.

    2014-11-07

    Iron oxide films were produced using ion-beam-assisted deposition, and Raman spectroscopy and x-ray diffraction indicate single-phase magnetite. However, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite, suggesting greater than normal disorder. Low temperature magnetometry and first-order reversal curve measurements show strong exchange bias, which likely arises from defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples contain grains ∼6 nm, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field.

  4. Unwanted spatial bias in predicting establishment of an invasive insect based on simulated demographics.

    PubMed

    Gray, David R

    2014-07-01

    A strategy to estimate the probability of successful establishment of the invasive gypsy moth (given an introduction) is growing in popularity. The strategy calls for an examination of the demographic output of a phenology model of the complete life-cycle to estimate the generational success under the climate of the location under consideration. The probability is maximal where the climate satisfies the life-cycle requirements of all life-stages of 100% of the population every year. The probability decreases where a smaller proportion of the population has its requirements satisfied every year, or where the frequency of unsatisfactory years increases. The strategy can give an unbiased and objective estimate of the probability. However, implementation of the strategy has most often forced unnatural and overly simplistic modifications onto the demographic structure that is simulated by the phenology model, and used an inappropriate and arbitrary calendar date to estimate demographic changes from winter mortality. This produces pronounced spatial bias in the estimates of generational success, and therefore in the estimates of climate-mediated establishment probability. In an examination of the strategy, as implemented in New Zealand, one demographic simplification caused an overestimate of 21% in a southern location; a second simplification caused an overestimate of 17% in a northern location. One hundred percent of the generations were incorrectly considered to have failed in a northern location because of the arbitrary calendar date that was used; and 78% of the generations were incorrectly considered successful in a southern location because of the arbitrary date. PMID:23748421

  5. Suppression of exchange bias effect in maghemite nanoparticles functionalized with H2Y

    NASA Astrophysics Data System (ADS)

    Guivar, Juan A. Ramos; Morales, M. A.; Litterst, F. Jochen

    2016-12-01

    The structural, vibrational, morphological and magnetic properties of maghemite (γ-Fe2O3) nanoparticles functionalized with polar molecules EDTA(or H4Y) and H2Y are reported. The samples were functionalized before and after total synthesis of γ-Fe2O3 nanoparticles. The molecules are anchored on the monodentate mode on the nanoparticles surface. Transmission electron microscopy (TEM) revealed the formation of maghemite nanoparticles with small diameter of 4 nm for the sample functionalized upon synthesis and 7.6 and 6.9 nm for the samples functionalized with EDTA and H2Y after the formation of nanoparticles. Exchange bias phenomena were observed in some of the samples functionalized with EDTA at temperatures below 70 K. The presence of the bias effect was discussed in terms of the formation of a thin layer of a secondary phase like lepidocrocite, and the absence of this effect was explained in terms of the chemisorption of carboxylic groups from EDTA which suppressed the canting. Studies of Mössbauer spectroscopy as a function of temperature showed slow relaxation effects and allowed discussion of the secondary phase. In the M-T curves a maximum around 116 K was associated with this secondary phase also in agreement with the Mössbauer studies. The dynamic properties were studied by AC susceptibility, the out of phase signal revealed a spin glass like regime below 36.5 K.

  6. Current-driven non-linear magnetodynamics in exchange-biased spin valves

    SciTech Connect

    Seinige, Heidi; Wang, Cheng; Tsoi, Maxim

    2015-05-07

    This work investigates the excitation of parametric resonance in exchange-biased spin valves (EBSVs). Using a mechanical point contact, high density dc and microwave currents were injected into the EBSV sample. Observing the reflected microwave power and the small rectification voltage that develops across the contact allows detecting the current-driven magnetodynamics not only in the bulk sample but originating exclusively from the small contact region. In addition to ferromagnetic resonance (FMR), parametric resonance at twice the natural FMR frequency was observed. In contrast to FMR, this non-linear resonance was excited only in the vicinity of the point contact where current densities are high. Power-dependent measurements displayed a typical threshold-like behavior of parametric resonance and a broadening of the instability region with increasing power. Parametric resonance showed a linear shift as a function of applied dc bias which is consistent with the field-like spin-transfer torque induced by current on magnetic moments in EBSV.

  7. Determination of the anisotropies and reversal process in exchange-bias bilayers using a rotational magnetization curve approach

    SciTech Connect

    Sui Wenbo; Zhu Jingyi; Li Jinyun; Chai Guozhi; Jiang Changjun; Fan Xiaolong; Xue Desheng

    2011-05-15

    Rotational magnetization curves of the exchange-bias bilayers were investigated based on the Stoner-Wohlfarth model, which can be grouped into three cases according to the magnetization reversal process. The unidirectional anisotropic field H{sub E} = 41.4 Oe, the uniaxial anisotropic field H{sub k} = 4.2 Oe and the accurate direction of the easy axis of our FeNi/FeMn exchange-bias bilayers were obtained by fitting their experimental rotational magnetization curves. During the rotational process the magnetization reversal of the bilayers is a coherent rotation with a critical magnetization reversal field H{sub 1} = 41.372 Oe.

  8. Comment on ``Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures''

    NASA Astrophysics Data System (ADS)

    Baltz, V.; Bollero, A.; Rodmacq, B.; Dieny, B.; Sort, J.

    2008-01-01

    From results at one given temperature (300K) , Malinowski [Phys. Rev. B 75, 012413 (2007)] draw the conclusion that lateral confinement of ferromagnetic-antiferromagnetic exchange-biased structures does not enhance thermally activated unpinning of the antiferromagnetic spins, which would thus contrast with a recent report [Phys. Rev. Lett. 94, 117201 (2005)], as explicitly mentioned in their manuscript. In this Comment, we discuss why such a conclusion might need revision above a “crossover temperature,” as evidenced in the literature. The value of such a crossover temperature certainly depends on the magnetic parameters of each system studied, e.g., anisotropy and exchange stiffness. From the above reasons, and contrary to the statement of Malinowski , we rather think that their results might well agree with the report to which they refer to. In our Comment we notably aim at complementing the conclusion of Malinowski by explaining why some differences between the two studies are observed at one given temperature, and why it might be expected to observe similar trends over a whole range of temperatures.

  9. Eliminating leakage current in voltage-controlled exchange-bias devices

    NASA Astrophysics Data System (ADS)

    Mahmood, Ather; Echtenkamp, Will; Street, Michael; Binek, Christian; Magnetic Heterostructures Team

    Manipulation of magnetism by electric field has drawn much attention due to the technological importance for low-power devices, and for understanding fundamental magnetoelectric phenomena. A manifestation of electrically controlled magnetism is voltage control of exchange bias (EB). Robust isothermal voltage control of EB was demonstrated near room temperature using a heterostructure of Co/Pd thin film and an exchange coupled single crystal of the antiferromagnetic Cr2O3 (Chromia). A major obstacle for EB in lithographically patterned Chromia based thin-film devices is to minimize the leakage currents at high electric fields (>10 kV/mm). By combining electrical measurements on patterned devices and conductive Atomic Force Microscopy of Chromia thin-films, we investigate the defects which form conducting paths impeding the application of sufficient voltage for demonstrating the isothermal EB switching in thin film heterostructures. Technological challenges in the device fabrication will be discussed. This project was supported by SRC through CNFD, an SRC-NRI Center, by C-SPIN, part of STARnet, and by the NSF through MRSEC Abstract DMR-0820521.

  10. Unconventional exchange bias in CoCr2O4/Cr2O3 nanocomposites

    NASA Astrophysics Data System (ADS)

    Guo, S.; Liu, X. H.; Cui, W. B.; Liu, W.; Zhao, X. G.; Li, D.; Zhang, Z. D.

    2009-03-01

    Unconventional exchange bias (EB) has been studied in CoCr2O4/Cr2O3 nanocomposites, in which the Curie temperature of the ferrimagnetic CoCr2O4 is much lower than the Néel temperature of the antiferromagnetic Cr2O3. A negative EB field of about 2.5 kOe at 5 K is achieved upon cooling in a field of 30 kOe. Meanwhile, the coercivity of the CoCr2O4 nanoparticles has been enhanced significantly by coupling with Cr2O3. The effect of the cooling field on the EB field and coercivity at 10 K has also been investigated. The domain-state model is used to interpret the unconventional EB. Cooling field may play a decisive role in the creation of the interfacial spin configuration for the unconventional EB, not only by exchange interaction between the induced magnetization of a polarized paramagnet and interfacial spins of an antiferromagnet but also by Zeeman interaction between the domain-state surplus magnetization and the external field.

  11. Origin of spontaneous exchange bias in Co/NiMn bilayer structure

    NASA Astrophysics Data System (ADS)

    Akbulut, A.; Akbulut, S.; Yildiz, F.

    2016-11-01

    Spontaneous exchange bias (EB) is reported for as deposited Si/Pt(tPt)/Ni45Mn55(tAFM/Co(tFM)/Pt(30 Å) thin film system without requiring any post annealing, deposition with field or field cooling procedures. Magnetic properties of this system were investigated with respect to thicknesses of buffer Pt layer (tPt), antiferromagnetic NiMn layer (tAFM) and ferromagnetic Co layer (tFM). Exchange coupling between NiMn and Co layers enhanced considerably by increasing tPt. In order to observe a spontaneous EB in the system, Pt buffer layer must be thicker than a certain thickness, and NiMn layer must be grown directly on the buffer layer. On the other hand, significant increments in the coercive fields (HC) were reported for thinner Pt buffer layers. The thickness ranges for Co and NiMn layers were also determined to obtain spontaneous EB. This spontaneous EB is discussed to be a result of NiMn (111) texture which is induced by Pt buffer layer. Greater EB fields (HEB) are measured for the samples in the negative field direction by the effect of annealing and field cooling (from 400 K to 300 K at 2 kOe).

  12. Biased thermohaline exchanges with the Arctic across the Iceland-Faroe Ridge in ocean climate models

    NASA Astrophysics Data System (ADS)

    Olsen, S. M.; Hansen, B.; Østerhus, S.; Quadfasel, D.; Valdimarsson, H.

    2016-04-01

    The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulate the climate of the Northern Hemisphere. The presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean, and ocean heat is directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Through these mechanisms, ocean heat and salt transports play a disproportionally strong role in the climate system, and realistic simulation is a requisite for reliable climate projections. Across the Greenland-Scotland Ridge (GSR) this occurs in three well-defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland-Faroe Ridge (IFR) have been shown to be particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last 2 decades but associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse-resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back onto the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modelled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability, while the quality of the simulated salt

  13. Electric field induced reversible 180° magnetization switching through tuning of interfacial exchange bias along magnetic easy-axis in multiferroic laminates

    SciTech Connect

    Xue, Xu; Zhou, Ziyao; Peng, Bin; Zhu, Mingmin; Zhang, Yijun; Ren, Wei; Ren, Tao; Yang, Xi; Nan, Tianxiang; Sun, Nian X.; Liu, Ming

    2015-11-18

    E-field control of interfacial exchange coupling and deterministic switching of magnetization have been demonstrated in two sets of ferromagnetic(FM)/antiferromagnetic(AFM)/ferroelectric(FE) multiferroic heterostructures, including NiFe/NiCoO/glass/PZN-PT (011) and NiFe/FeMn/glass/PZN-PT (011). We designed this experiment to achieve exchange bias tuning along the magnetic easy axis, which is critical for realizing reversible 180° magnetization deterministic switching at zero or small magnetic bias. Strong exchange coupling were established across AFM-FM interfaces, which plays an important role in voltage control of magnetization switching. Through the competition between the E-field induced uniaxial anisotropy in ferromagnetic layer and unidirectional anisotropy in antiferromagnetic layer, the exchange bias was significantly shifted by up to |ΔHex|/Hex=8% in NiFe/FeMn/glass/PZN-PT (011) and 13% in NiFe/NiCoO/glass/PZN-PT (011). In addition, the square shape of the hysteresis loop, as well as a strong shape tunability of |ΔHex|/Hc=67.5~125% in NiFe/FeMn/glass/PZN-PT and 30~38% in NiFe/NiCoO/glass/PZN-PT were achieved, which lead to a near 180° magnetization switching. Lastly, electrical tuning of interfacial exchange coupling in FM/AFM/FE systems paves a new way for realizing magnetoelectric random access memories and other memory technologies.

  14. Implications of room temperature oxidation on crystal structure and exchange bias effect in Co/CoO nanoparticles

    DOE PAGES

    Feygenson, Mikhail; Formo, Eric V.; Freeman, Katherine; Schieber, Natalie P.; Gai, Zheng; Rondinone, Adam J.

    2015-11-02

    In this study, we describe how the exchange bias effect in Co/CoO nanoparticles depends on the size focusing and temperature treatment of precursor Co nanoparticles before oxidation at ambient conditions. By appealing to magnetization, microscopy, neutron and synchrotron x-ray measurements we found that as-synthesized Co nanoparticles readily oxidize in air only after 20 days. The highest exchange bias field of 814 Oe is observed at T = 2K. When the same nanoparticles are centrifuged and annealed at 70 °C in vacuum prior to oxidation, the exchange bias field is increased to 2570 Oe. Annealing of Co nanoparticles in vacuum improvesmore » their crystallinity and prevents complete oxidation, so that Co-core/CoO-shell structure is preserved even after 120 days. The crystal structure of CoO shell in both samples is different from its bulk counterpart. Implications of such distorted CoO shells on exchange bias are discussed. Coating of Co nanoparticles with amorphous silica shell makes them resistant to oxidation, but ultimately modifies the crystal structure of both Co core and SiO2 shell.« less

  15. Implications of room temperature oxidation on crystal structure and exchange bias effect in Co/CoO nanoparticles

    SciTech Connect

    Feygenson, Mikhail; Formo, Eric V.; Freeman, Katherine; Schieber, Natalie P.; Gai, Zheng; Rondinone, Adam J.

    2015-11-02

    In this study, we describe how the exchange bias effect in Co/CoO nanoparticles depends on the size focusing and temperature treatment of precursor Co nanoparticles before oxidation at ambient conditions. By appealing to magnetization, microscopy, neutron and synchrotron x-ray measurements we found that as-synthesized Co nanoparticles readily oxidize in air only after 20 days. The highest exchange bias field of 814 Oe is observed at T = 2K. When the same nanoparticles are centrifuged and annealed at 70 °C in vacuum prior to oxidation, the exchange bias field is increased to 2570 Oe. Annealing of Co nanoparticles in vacuum improves their crystallinity and prevents complete oxidation, so that Co-core/CoO-shell structure is preserved even after 120 days. The crystal structure of CoO shell in both samples is different from its bulk counterpart. Implications of such distorted CoO shells on exchange bias are discussed. Coating of Co nanoparticles with amorphous silica shell makes them resistant to oxidation, but ultimately modifies the crystal structure of both Co core and SiO2 shell.

  16. Seeking to quantify the ferromagnetic-to-antiferromagnetic interface coupling resulting in exchange bias with various thin-film conformations

    SciTech Connect

    Hsiao, C. H.; Wang, S.; Ouyang, H.; Desautels, R. D.; Lierop, J. van; Lin, K. W.

    2014-08-07

    Ni{sub 3}Fe/(Ni, Fe)O thin films with bilayer and nanocrystallite dispersion morphologies are prepared with a dual ion beam deposition technique permitting precise control of nanocrystallite growth, composition, and admixtures. A bilayer morphology provides a Ni{sub 3}Fe-to-NiO interface, while the dispersion films have different mixtures of Ni{sub 3}Fe, NiO, and FeO nanocrystallites. Using detailed analyses of high resolution transmission electron microscopy images with Multislice simulations, the nanocrystallites' structures and phases are determined, and the intermixing between the Ni{sub 3}Fe, NiO, and FeO interfaces is quantified. From field-cooled hysteresis loops, the exchange bias loop shift from spin interactions at the interfaces are determined. With similar interfacial molar ratios of FM-to-AF, we find the exchange bias field essentially unchanged. However, when the interfacial ratio of FM to AF was FM rich, the exchange bias field increases. Since the FM/AF interface ‘contact’ areas in the nanocrystallite dispersion films are larger than that of the bilayer film, and the nanocrystallite dispersions exhibit larger FM-to-AF interfacial contributions to the magnetism, we attribute the changes in the exchange bias to be from increases in the interfacial segments that suffer defects (such as vacancies and bond distortions), that also affects the coercive fields.

  17. Tuning the ferromagnetic-antiferromagnetic interfaces of granular Co-CoO exchange bias systems by annealing

    SciTech Connect

    Menéndez, E. Modarresi, H.; Pereira, L. M. C.; Temst, K.; Vantomme, A.; Dias, T.; Geshev, J.

    2014-04-07

    The low-temperature magnetic behavior of granular Co-CoO exchange bias systems, prepared by oxygen ion implantation in Co thin films and subsequent annealing, is addressed. The thermal activation effects lead to an O migration which results in virtually pure Co areas embedded in a structurally relaxed and nearly stoichiometric CoO phase. This yields decreased training and exchange bias shifts, while the blocking temperature significantly increases, coming close to the Néel temperature of bulk CoO for samples implanted to a fluence above 1 × 10{sup 17} ions/cm{sup 2} (15% O). The dependence of the exchange bias shift on the pristine O-implanted content is analogous to that of the antiferromagnetic thickness in most ferromagnetic/antiferromagnetic systems (i.e., an increase in the exchange bias shift up to a maximum followed by a decrease until a steady state is reached), suggesting that, after annealing, the enriched Co areas might be rather similar in size for samples implanted above 1 × 10{sup 17} ions/cm{sup 2}, whereas the corresponding CoO counterparts become enlarged with pristine O content (i.e., effect of the antiferromagnet size). This study demonstrates that the magnetic properties of granular Co-CoO systems can be tailored by controllably modifying the local microstructure through annealing treatments.

  18. 75 FR 45584 - Planning and Establishment of State-Level Exchanges; Request for Comments Regarding Exchange...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-03

    ... website containing standardized comparative information on QHPs; assigning ratings to each QHP offered... certification criteria include, at a minimum: Meeting marketing requirements; ensuring a sufficient choice of... providers? b. What issues need to be considered in establishing appropriate minimum standards for...

  19. Thermal simulation of magnetization reversals for size-distributed assemblies of core-shell exchange biased nanoparticles

    NASA Astrophysics Data System (ADS)

    Richy, J.; Jay, J.-Ph.; Pogossian, S. P.; Ben Youssef, J.; Sheppard, C. J.; Prinsloo, A. R. E.; Spenato, D.; Dekadjevi, D. T.

    2016-08-01

    A temperature dependent coherent magnetization reversal model is proposed for size-distributed assemblies of ferromagnetic nanoparticles and ferromagnetic-antiferromagnetic (AF) core-shell nanoparticles. The nanoparticles are assumed to be of uniaxial anisotropy and all aligned along their easy axis. The thermal dependence is included by considering thermal fluctuations, implemented via the Néel-Arrhenius theory. Thermal and angular dependence of magnetization reversal loops, coercive field, and exchange-bias field are obtained, showing that ferromagnetic-antiferromagnetic size-distributed exchange-coupled nanoparticles exhibit temperature-dependent asymmetric magnetization reversal. Also, non-monotonic evolutions of exchange-bias and coercive fields with temperature are demonstrated. The angular dependence of coercive field with temperature exhibits a complex behavior, with the presence of an apex, whose position and amplitude are strongly temperature-dependent. The angular dependence of exchange bias with temperature exhibits complex behaviors, which depends on the AF anisotropy and exchange coupling. The resulting angular behavior demonstrates the key role of the size distribution and temperature in the magnetic response of nanoparticles.

  20. Exchange bias and coercivity for ferromagnets coupled to the domain state and spin glass state

    NASA Astrophysics Data System (ADS)

    Zhan, Xiaozhi; Mao, Zhongquan; Chen, Xi

    2016-05-01

    The exchange bias (EB) effect for systems with a ferromagnetic (FM) layer coupled to bond-diluted pinning layers has been investigated by Monte Carlo simulations. Two bond dilution concentrations are chosen to obtain two kinds of pinning layers: the antiferromagnetic domain state (DS) and the spin glass (SG) state. It is found that when coupled to the more disordered SG state, the ferromagnet shows enhanced EB with higher coercivity due to larger amounts of both frozen and reversible spins at the pinning interface. Spin configurations of the FM/DS interface layer reveal that reversible spins are mostly found in domain boundaries and small domains, while most spins in large domains maintain antiferromagnetic coupling and contribute to the EB effect. The coercivity is linear to the amount of interface reversible spins, but with different slopes in the temperature ranges above or below the blocking temperature t B. This bimodal temperature-dependent coercivity indicates a sudden change in macroscopic interface coupling at the temperature t B.

  1. Exchange bias due to defects and domains in the volume of the antiferromagnet

    NASA Astrophysics Data System (ADS)

    Guntherodt, Gernot

    2001-03-01

    The exchange bias (EB) coupling at ferro-/antiferromagnetic interfaces of epitaxially grown Co/CoO layers can intentionally be increased by a factor up to 4 upon introducing nonmagnetic defects in the volume of the antiferromagnet away from the interface. This leads to the stabilization of volume domains in the antiferromagnet(AF). Hence, EB is primarily not due to roughness at the interface, but rather due to a domain state (DS) in the volume of the AF. Monte Carlo simulations of a simple model of a ferromagnetic layer on a diluted Ising-type AF layer exhibit EB and qualitatively explain its dependence on dilution, temperature and cooling field as well as training effects and relaxation behavior. The experimental dependence of the EB field on the thickness t of the antiferromagnetic CoO layer is also consistent with the DS model. For nondiluted CoO layers the EB field decreases above t=5 nm, whereas for diluted CoO the EB field increases and saturates for t>20 nm. Work supported by DFG (Germany) through SFB 341 and SFB 491.

  2. Interplay between magnetocrystalline anisotropy and exchange bias in epitaxial CoO/Co films

    NASA Astrophysics Data System (ADS)

    Liu, Hao-Liang; Brems, Steven; Zeng, Yu-Jia; Temst, Kristiaan; Vantomme, André; Van Haesendonck, Chris

    2016-05-01

    The interplay between magnetocrystalline anisotropy and exchange bias is investigated in CoO/Co bilayer films, which are grown epitaxially on MgO (0 0 1), by magnetization reversal measurements based on the anisotropic magnetoresistance (AMR) effect. While an asymmetric magnetization reversal survives after training for cooling field (CF) along the hard axis, the magnetization reversal becomes symmetric and is dominated in both branches of the hysteresis loop by domain wall motion before and after training for CF along the easy axis. When performing an in-plane hysteresis loop perpendicular to the CF, the hysteresis loop along the easy axis becomes asymmetric: magnetization rotation dominates in the ascending branch, while there is a larger contribution of domain wall motion in the descending branch. Furthermore, the azimuthal angular dependence of the AMR shows two minima after performing a perpendicular hysteresis loop, instead of only one minimum after training. Relying on the extended Fulcomer and Charap model, these effects can be related to an increased deviation of the average uncompensated antiferromagnetic magnetization from the CF direction. This model provides a consistent interpretation of training and asymmetry of the magnetization reversal for epitaxial films with pronounced magnetocrystalline anisotropy as well as for the previously investigated polycrystalline films.

  3. 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.

  4. Multilevel Thermally Assisted Magnetoresistive Random-Access Memory Based on Exchange-Biased Vortex Configurations

    NASA Astrophysics Data System (ADS)

    de Araujo, C. I. L.; Alves, S. G.; Buda-Prejbeanu, L. D.; Dieny, B.

    2016-08-01

    A concept of multilevel thermally assisted magnetoresistive random-access memory is proposed and investigated by micromagnetic simulations. The storage cells are magnetic tunnel junctions in which the storage layer is exchange biased and in a vortex configuration. The reference layer is an unpinned soft magnetic layer. The stored information is encoded via the position of the vortex core in the storage layer. This position can be varied along two degrees of freedom: the radius and the in-plane angle. The information is read out from the amplitude and phase of the tunnel magnetoresistance signal obtained by applying a rotating field on the cell without heating the cell. Various configurations are compared in which the soft reference layer consists of either a simple ferromagnetic layer or a synthetic antiferromagnetic sandwich (SAF). Among those, the most practical one comprises a SAF reference layer in which the magnetostatic interaction between the SAF and storage layer is minimized. This type of cell should allow one to store at least 40 different states per cell representing more than five bits per cell.

  5. Large exchange bias in polycrystalline ribbons of Ni56Mn21Al22Si1

    NASA Astrophysics Data System (ADS)

    Singh, Rohit; Ingale, Babita; Varga, Lajos K.; Khovaylo, Vladimir V.; Taskaev, S.; Chatterjee, Ratnamala

    2015-11-01

    Large exchange bias (EB) effect is demonstrated in a Ni56Mn21Al22Si1 polycrystalline ribbon that shows spin-glass behaviour below 68 K and superparamagnetic (SPM) behaviour above this temperature. The average magnetic moment μ of the SPM clusters is estimated to be considerably smaller than that reported for other Heusler alloy systems that demonstrate spin glass behaviour and EB effect. The M-H loops measured in field-cooled (FC) conditions show significant asymmetry that is observed to be strongly field and temperature dependant. The maximum EB field (HEB ~2.6 kOe at 20 kOe and 2 K) is much larger than that reported for any metallic alloy system with conventional EB effect. The dependence of HEB on temperature shows an exponential decrease. An approach towards enhancement of the EB effect in this conventional EB system can be realized via manipulation of SPM or superferromagnetic (SFM) cluster size with variation of cooling magnetic field.

  6. 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

    2016-01-01

    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. PMID:26940861

  7. Manipulation of Superparamagnetic Beads on Patterned Exchange-Bias Layer Systems for Biosensing Applications

    PubMed Central

    Ehresmann, Arno; Koch, Iris; Holzinger, Dennis

    2015-01-01

    A technology platform based on a remotely controlled and stepwise transport of an array arrangement of superparamagnetic beads (SPB) for efficient molecular uptake, delivery and accumulation in the context of highly specific and sensitive analyte molecule detection for the application in lab-on-a-chip devices is presented. The near-surface transport of SPBs is realized via the dynamic transformation of the SPBs’ magnetic potential energy landscape above a magnetically stripe patterned Exchange-Bias (EB) thin film layer systems due to the application of sub-mT external magnetic field pulses. In this concept, the SPB velocity is dramatically influenced by the magnitude and gradient of the magnetic field landscape (MFL) above the magnetically stripe patterned EB substrate, the SPB to substrate distance, the magnetic properties of both the SPBs and the EB layer system, respectively, as well as by the properties of the external magnetic field pulses and the surrounding fluid. The focus of this review is laid on the specific MFL design in EB layer systems via light-ion bombardment induced magnetic patterning (IBMP). A numerical approach is introduced for the theoretical description of the MFL in comparison to experimental characterization via scanning Hall probe microscopy. The SPB transport mechanism will be outlined in terms of the dynamic interplay between the EB substrate’s MFL and the pulse scheme of the external magnetic field. PMID:26580625

  8. Substantial reduction of critical current for magnetization switching in an exchange-biased spin valve.

    PubMed

    Jiang, Y; Nozaki, T; Abe, S; Ochiai, T; Hirohata, A; Tezuka, N; Inomata, K

    2004-06-01

    Great interest in current-induced magnetic excitation and switching in a magnetic nanopillar has been caused by the theoretical predictions of these phenomena. The concept of using a spin-polarized current to switch the magnetization orientation of a magnetic layer provides a possible way to realize future 'current-driven' devices: in such devices, direct switching of the magnetic memory bits would be produced by a local current application, instead of by a magnetic field generated by attached wires. Until now, all the reported work on current-induced magnetization switching has been concentrated on a simple ferromagnet/Cu/ferromagnet trilayer. Here we report the observation of current-induced magnetization switching in exchange-biased spin valves (ESPVs) at room temperature. The ESPVs clearly show current-induced magnetization switching behaviour under a sweeping direct current with a very high density. We show that insertion of a ruthenium layer between an ESPV nanopillar and the top electrode effectively decreases the critical current density from about 10(8) to 10(7) A cm(-2). In a well-designed 'antisymmetric' ESPV structure, this critical current density can be further reduced to 2 x 10(6) A cm(-2). We believe that the substantial reduction of critical current could make it possible for current-induced magnetization switching to be directly applied in spintronic devices, such as magnetic random-access memory.

  9. Towards Rare-Earth-Free Permanent Magnets: Exchange Bias In Binary Manganese-based Alloys

    NASA Astrophysics Data System (ADS)

    Marion, Joshua Leland

    Quantum-mechanical exchange interactions between phases in ferromagnetic/antiferromagnetic (FM/AF) magnetic nanocomposite systems can result in useful effects such as exchange bias (Hex) and remanence enhancement. These effects are more pronounced in nanostructured systems than in their coarse-grained counterparts due to improved interphase contact and can be developed to create good permanent magnetic behavior, but are currently poorly understood in bulk three-dimensional systems. To achieve this goal, factors such as the magnetic and structural phase identity, chemistry, size, shape, and character are investigated. To this end, synthesis, characterization and analysis of the magnetic and structural properties of nanocomposites are carried out on MnX (X = Cu, Al) alloys comprised of nanostructured FM and AF phases. It is recommended for future work that Fe be added to augment the FM response of the nanostructured MnX alloys. Cu30Mn70 and Al45Mn55 ribbons are fabricated using the nonequilibrium technique of rapid solidification via melt-spinning to access and retain metastable nanostructured states, then subject to post-synthesis processing techniques — thermal annealing and cryogenic milling — to investigate the effects of structural modifications on the magnetic response. X-ray diffraction (XRD) analyses of the crystal structure show the as-quenched ribbons consist of two majority crystallographic phases with slightly different lattice dimensions. Superconducting quantum interference device (SQUID) magnetometry reveals prominent hysteresis shifts of ˜10-13 kOe at T = 10 K, attributed to the Hex effect. These data suggest that nanoscopic disproportionation of local Mn content causes a structural and corresponding magnetic phase separation into FM Mn-poor and AF Mn-rich regions; exchange interactions between these regions produce the large low-temperature Hex values observed. Interestingly, magnetic and calorimetric analyses of Al45Mn 55 melt-spun ribbons also

  10. Effect of Ni precursor solution concentration on the magnetic properties and exchange bias of Ni-NiO nanoparticulate systems

    NASA Astrophysics Data System (ADS)

    Roy, Aparna; De Toro, J. A.; Amaral, V. S.; Marques, D. P.; Ferreira, J. M. F.

    2014-09-01

    We report on a comparative study of the exchange bias effect and magnetic properties of Ni-NiO nanoparticulate systems synthesized by the chemical reduction of NiCl2 solution of two different molar concentrations—1 M (high) and 0.05 M (low)—followed by annealing of the dried precipitate in the temperature range 400-600 °C in air. Interestingly, the samples derived from the low molarity solution have higher Ni content and larger crystallite size than those prepared from their high molarity counterparts. These molarity dependent features subsequently modulate the magnitude of the exchange bias field in the samples, which is found to be absent or small in the 0.05 M series, but of moderate value in the 1 M samples. The different physical attributes of the particles derived from different concentrations of Ni-precursor solution are explained by invoking different nucleation kinetics and supersaturation degrees surrounding the viable growing nucleus. Furthermore, an observed increase of exchange bias with increasing annealing temperature, in contrast to the reported agglomeration of particles on annealing and subsequent reduction in bias magnitude, has been explained in correlation to the Ni-NiO interface density.

  11. Low temperature exchange bias in [DyFe(2)/YFe(2)] superlattices: effect of the thermo-magnetic preparation.

    PubMed

    Dumesnil, K; Dufour, C; Fernandez, S; Oudich, M; Avisou, A; Rogalev, A; Wilhelm, F

    2009-06-10

    The effect of the thermo-magnetic preparation on exchange bias is investigated in an exchange-coupled [3 nm DyFe(2)/12 nmYFe(2)](22) superlattice. X-ray magnetic circular dichroism (XMCD) experiments at low temperature reveal that exchange bias originates from the quenched DyFe(2) magnetization, biasing the unpinned YFe(2) reversal. This quenched configuration can be tailored by changing the cooling field or the magnetic preparation at 300 K before zero-field cooling. Changing the amplitude of the cooling field induces interface domain walls and tends to modify the orientation of the pinning moments at the interfaces. This results in the observation of single loops and in the continuous variation of the bias field as a function of the cooling field. A specific magnetic preparation (field cycling) at 300 K induces different remanent states with lateral domains in the pinning layer, which remain unchanged at low temperature after zero-field cooling and behave independently. This gives rise to combined loops, whose shape reflects the domain populations. PMID:21825599

  12. Multi-omics data driven analysis establishes reference codon biases for synthetic gene design in microbial and mammalian cells.

    PubMed

    Ang, Kok Siong; Kyriakopoulos, Sarantos; Li, Wei; Lee, Dong-Yup

    2016-06-01

    In this study, we analyzed multi-omics data and subsets thereof to establish reference codon usage biases for codon optimization in synthetic gene design. Specifically, publicly available genomic, transcriptomic, proteomic and translatomic data for microbial and mammalian expression hosts, Escherichia coli, Saccharomyces cerevisiae, Pichia pastoris and Chinese hamster ovary (CHO) cells, were compiled to derive their individual codon and codon pair frequencies. Then, host dependent and -omics specific codon biases were generated and compared by principal component analysis and hierarchical clustering. Interestingly, our results indicated the similar codon bias patterns of the highly expressed transcripts, highly abundant proteins, and efficiently translated mRNA in microbial cells, despite the general lack of correlation between mRNA and protein expression levels. However, for CHO cells, the codon bias patterns among various -omics subsets are not distinguishable, forming one cluster. Thus, we further investigated the effect of different input codon biases on codon optimized sequences using the codon context (CC) and individual codon usage (ICU) design parameters, via in silico case study on the expression of human IFNγ sequence in CHO cells. The results supported that CC is more robust design parameter than ICU for improved heterologous gene design. PMID:26850284

  13. 78 FR 15553 - Patient Protection and Affordable Care Act; Establishment of Exchanges and Qualified Health Plans...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-03-11

    ... located in the main lobby of the building. A stamp- in clock is available for persons wishing to retain a... for Employers, 77 FR 18310 (Mar. 27, 2012) (to be codified at 45 CFR parts 155, 156, & 157). In the... Care Act; Establishment of Exchanges and Qualified Health Plans; Proposed Rule, 76 FR 41866 (July...

  14. Martensitic transition, magnetic, magnetocaloric and exchange bias properties of Fe-substituted Mn-Ni-Sn Heusler alloys

    NASA Astrophysics Data System (ADS)

    Sharma, Jyoti; Suresh, K. G.

    2016-12-01

    In this report, effect of Fe substitution on martensitic transition, magnetic, magnetocaloric and exchange bias (EB) properties of Mn50Ni40-xFexSn10 (x=0, 0.5, 1, 1.5, 2 and 3) Heusler alloys series has been investigated systematically. Fe substitution has been found to affect the ferromagnetic/antiferromagnetic interactions significantly in both the martensite and austenite phases. Martensitic transition temperature decreases with increasing Fe content, which is attributed to the decrease in number of average valence electrons per atom (e/a ratio) of these alloys. Large magnetic entropy change (ΔSM) and refrigerant capacity (RC) have been observed in these alloys, as a maximum ΔSM of ~12.6 J/kg. K is observed for composition x=0.5. Present alloys have also been found to show large exchange bias properties, as maximum exchange bias fields (HEB) of 890 Oe and 810 Oe are observed for x=0 and 0.5, respectively at 5 K. Composition and temperature dependencies of EB are associated with the change in exchange anisotropy at interfaces of competing magnetic phases. Study of minor loop and training effect also corroborates with the presence of EB in these alloys.

  15. Switching of perpendicular exchange bias in Pt/Co/Pt/α-Cr{sub 2}O{sub 3}/Pt layered structure using magneto-electric effect

    SciTech Connect

    Toyoki, Kentaro; Shiratsuchi, Yu Kobane, Atsushi; Harimoto, Shotaro; Onoue, Satoshi; Nomura, Hikaru; Nakatani, Ryoichi

    2015-05-07

    Switching of the perpendicular exchange bias polarity using a magneto-electric (ME) effect of α-Cr{sub 2}O{sub 3} was investigated. From the change in the exchange bias field with the electric field during the ME field cooling, i.e., the simultaneous application of both magnetic and electric fields during the cooling, we determined the threshold electric field to switch the perpendicular exchange bias polarity. It was found that the threshold electric field was inversely proportional to the magnetic field indicating that the EH product was constant. The high EH product was required to switch the exchange bias for the film possessing the high exchange anisotropy energy density, which suggests that the energy gain by the ME effect has to overcome the interfacial exchange coupling energy to reverse the interfacial antiferromagnetic spin.

  16. Measuring Population Health Using Electronic Health Records: Exploring Biases and Representativeness in a Community Health Information Exchange.

    PubMed

    Dixon, Brian E; Gibson, P Joseph; Frederickson Comer, Karen; Rosenman, Marc

    2015-01-01

    Assessment is a core function of public health. Comprehensive clinical data may enhance community health assessment by providing up-to-date, representative data for use in public health programs and policies, especially when combined with community-level data relevant to social determinants. In this study we examine routinely collected and geospatially-enhanced EHR data to assess population health at various levels of geographic granularity available from a regional health information exchange. We present preliminary findings and discuss important biases in EHR data. Future work is needed to develop methods for correcting for those biases to support routine epidemiology work of public health.

  17. Negative magnetization and exchange bias effect in Ni1.4Mn2Ga0.6

    NASA Astrophysics Data System (ADS)

    Albagami, Abdullah; Khan, Mahmud

    Ni-Mn-X based Heusler alloys have attracted significant interest in recent years due to their multifunctional properties. Exchange bias (EB) is one such property that results from competing magnetic interactions in these alloys. The EB effect is typically observed in materials where ferromagnetic (FM) and antiferromagnetic (AFM) interactions co-exist. Since the discovery of EB effect in CoO (AFM) coated Co (FM) nanoparticles by Meikle John and Bean in 1956, a significant amount of research efforts have been made on this subject. Here, we have performed an experimental study on the magnetic and exchange bias properties of polycrystalline Ni1.4Mn2Ga0.6 alloy by X-ray diffraction, dc magnetization, and ac susceptibility measurements. The material exhibits a ferromagnetic Curie temperature of ~300 K. The magnetization versus field data obtained at 5 K under zero field condition exhibits a double shifted hysteresis loop that disappears at higher temperatures. When the sample is cooled from room temperature to 5 K in applied magnetic fields, exchange bias is observed, whose magnitude is strongly dependent on the cooling field. A maximum exchange bias field of 730 Oe is observed under field cooling condition at 5 K. A negative magnetization is observed in the magnetization versus temperature data obtained at magnetic fields smaller than 75 Oe. The experimental results are explained in terms of the competing ferromagnetic and antiferromagnetic exchange interaction that exist in the materials due to the Mn atoms occupying multiple crystalline sites resulting in a spin glass-type frustrated ground state.

  18. Self-establishing communities enable cooperative metabolite exchange in a eukaryote.

    PubMed

    Campbell, Kate; Vowinckel, Jakob; Mülleder, Michael; Malmsheimer, Silke; Lawrence, Nicola; Calvani, Enrica; Miller-Fleming, Leonor; Alam, Mohammad T; Christen, Stefan; Keller, Markus A; Ralser, Markus

    2015-10-26

    Metabolite exchange among co-growing cells is frequent by nature, however, is not necessarily occurring at growth-relevant quantities indicative of non-cell-autonomous metabolic function. Complementary auxotrophs of Saccharomyces cerevisiae amino acid and nucleotide metabolism regularly fail to compensate for each other's deficiencies upon co-culturing, a situation which implied the absence of growth-relevant metabolite exchange interactions. Contrastingly, we find that yeast colonies maintain a rich exometabolome and that cells prefer the uptake of extracellular metabolites over self-synthesis, indicators of ongoing metabolite exchange. We conceived a system that circumvents co-culturing and begins with a self-supporting cell that grows autonomously into a heterogeneous community, only able to survive by exchanging histidine, leucine, uracil, and methionine. Compensating for the progressive loss of prototrophy, self-establishing communities successfully obtained an auxotrophic composition in a nutrition-dependent manner, maintaining a wild-type like exometabolome, growth parameters, and cell viability. Yeast, as a eukaryotic model, thus possesses extensive capacity for growth-relevant metabolite exchange and readily cooperates in metabolism within progressively establishing communities.

  19. Self-establishing communities enable cooperative metabolite exchange in a eukaryote

    PubMed Central

    Campbell, Kate; Vowinckel, Jakob; Mülleder, Michael; Malmsheimer, Silke; Lawrence, Nicola; Calvani, Enrica; Miller-Fleming, Leonor; Alam, Mohammad T; Christen, Stefan; Keller, Markus A; Ralser, Markus

    2015-01-01

    Metabolite exchange among co-growing cells is frequent by nature, however, is not necessarily occurring at growth-relevant quantities indicative of non-cell-autonomous metabolic function. Complementary auxotrophs of Saccharomyces cerevisiae amino acid and nucleotide metabolism regularly fail to compensate for each other's deficiencies upon co-culturing, a situation which implied the absence of growth-relevant metabolite exchange interactions. Contrastingly, we find that yeast colonies maintain a rich exometabolome and that cells prefer the uptake of extracellular metabolites over self-synthesis, indicators of ongoing metabolite exchange. We conceived a system that circumvents co-culturing and begins with a self-supporting cell that grows autonomously into a heterogeneous community, only able to survive by exchanging histidine, leucine, uracil, and methionine. Compensating for the progressive loss of prototrophy, self-establishing communities successfully obtained an auxotrophic composition in a nutrition-dependent manner, maintaining a wild-type like exometabolome, growth parameters, and cell viability. Yeast, as a eukaryotic model, thus possesses extensive capacity for growth-relevant metabolite exchange and readily cooperates in metabolism within progressively establishing communities. DOI: http://dx.doi.org/10.7554/eLife.09943.001 PMID:26499891

  20. Biasing Potential Replica Exchange Multi-Site λ-Dynamics for Efficient Free Energy Calculations

    PubMed Central

    Armacost, Kira A.; Goh, Garrett B.; Brooks, Charles L.

    2016-01-01

    Traditional free energy calculation methods are well known for their drawbacks in scalability and speed in converging results particularly for calculations with large perturbations. In the present work, we report on the development of biasing potential replica exchange multi-site λ-dynamics (BP-REX MSλD), which is a free energy method that is capable of performing simultaneous alchemical free energy transformations, including perturbations between flexible moieties. BP-REX MSλD and the original MSλD are applied to a series of symmetrical 2,5-benzoquinone derivatives covering a diverse chemical space and range of conformational flexibility. Improved λ-space sampling is observed for the BP-REX MSλD simulations, yielding a 2–5-fold increase in the number of transitions between substituents compared to traditional MSλD. We also demonstrate the efficacy of varying the value of c, the parameter that controls the ruggedness of the landscape mediating the sampling of λ-states, based on the flexibility of the fragment. Finally, we developed a protocol for maximizing the transition frequency between fragments. This protocol reduces the “kinetic barrier” for alchemically transforming fragments by grouping and ordering based on volume. These findings are applied to a challenging test set involving a series of geldanamycin-based inhibitors of heat shock protein 90 (Hsp90). Even though the perturbations span volume changes by as large as 60 Å3, the values for the free energy change achieve an average unsigned error (AUE) of 1.5 kcal/mol relative to experimental Kd measurements with a reasonable correlation (R = 0.56). Our results suggest that the BP-REX MSλD algorithm is a highly efficient and scalable free energy method, which when utilized will enable routine calculations on the order of hundreds of compounds using only a few simulations. PMID:26579773

  1. Numerical study of the influence of interfacial roughness on the exchange bias properties of ferromagnetic/antiferromagnetic bilayers

    NASA Astrophysics Data System (ADS)

    Moritz, J.; Bacher, P.; Dieny, B.

    2016-09-01

    Exchange bias and coercivity are both studied numerically in antiferromagnetic/ferromagnetic (AFM/FM) bilayers in the presence of a rough interface. The roughness is modeled by an AFM atomic mesa of variable width, in a periodic bidimensional system. Unlike the flat interface case, roughness can favor the presence of magnetic interfacial frustration or the formation of sharp magnetic domain walls pinned within the first AFM planes, inside the AFM mesa, in a Peierls potential well. We demonstrate by using athermal steepest-descent calculations that irreversible processes can occur during the hysteresis loops, when the AFM mesa width is less than half of the system period. In this case, the depinning of the domain wall from the Peierls potential well during the descending branch is not followed by its rewinding in a certain range of the AFM anisotropy. This leads to a large increase of both exchange bias and coercivity at low temperature and to an athermal training effect. When the thermal activation is taken into account by using Monte Carlo simulations, we show that a random walk of the domain wall occurs within the AFM layer. These processes induce changes in the AFM spin configuration when the system is cycled several times and produce a thermally activated training effect. Our simulations, interpreted in the context of periodic Peierls potential, provide an explanation for two important features of the exchange bias phenomenon, i.e., the thermal variation of its characteristic fields and the different contributions giving rise to the training effect (AFM bulk vs interface). More generally, the presence of interfacial atomic roughness reduces both exchange bias and coercivity with respect to the perfect interface case.

  2. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    DOE PAGES

    Feygenson, Mikhail; Bauer, John C; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S; Kevin, Beyer; et al

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron scattering, synchrotron x-ray diffraction and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatchmore » between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed across the interface to accommodate an excess of oxygen released during the reduction of magnetite.« less

  3. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    SciTech Connect

    Feygenson, Mikhail; Bauer, John C.; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S.; Beyer, Kevin A.; Dai, Sheng

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron-scattering, synchrotron x-ray diffraction, and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wustite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into the FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed, presumably across the interface to accommodate an excess of oxygen released during the reduction of magnetite

  4. Exchange bias properties of 140 nm-sized dipolarly interacting circular dots with ultrafine IrMn and NiFe layers

    NASA Astrophysics Data System (ADS)

    Spizzo, F.; Tamisari, M.; Chinni, F.; Bonfiglioli, E.; Gerardino, A.; Barucca, G.; Bisero, D.; Fin, S.; Del Bianco, L.

    2016-02-01

    We studied the exchange bias effect in an array of IrMn(3 nm)/NiFe(3 nm) circular dots (size ~140 nm and center-to-center distance ~200 nm, as revealed by microscopy analyses), prepared on a large area (3×3 mm2) by electron beam lithography and lift-off, using dc sputtering deposition. Hysteresis loops were measured by SQUID magnetometer at increasing values of temperature T (in the 5-300 K range) after cooling from 300 K down to 5 K in zero field (ZFC mode) and in a saturating magnetic field (FC mode). The exchange bias effect disappears above T~200 K and, at each temperature, the exchange field HEX measured in ZFC is substantially lower than the FC one. Micromagnetic calculations indicate that, at room temperature, each dot is in high-remanence ground state, but magnetic dipolar interactions establish a low-remanence configuration of the array as a whole. Hence, at low temperature, following the ZFC procedure, the exchange anisotropy in the dot array is averaged out, tending to zero. However, even the FC values of HEX and of the coercivity HC are definitely smaller compared to those measured in a reference continuous film with the same stack configuration (at T=5 K, HEX~90 Oe and HC~180 Oe in the dots and HEX~1270 Oe and HC~860 Oe in the film). Our explanation is based on the proven glassy magnetic nature of the ultrathin IrMn layer, implying the existence of magnetic correlations among the spins, culminating in a collective freezing below T~100 K. We propose, also by the light of micromagnetic simulations, that the small dot size imposes a spatial constraint on the magnetic correlation length among the IrMn spins so that, even at the lowest temperature, their thermal stability, especially at the dot border, is compromised.

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

    PubMed Central

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

    2014-01-01

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

  6. Off-easy-plane antiferromagnetic spin canting in coupled FePt/NiO bilayer structure with perpendicular exchange bias

    NASA Astrophysics Data System (ADS)

    Gao, Tenghua; Itokawa, Nobuhide; Wang, Jian; Yu, Youxing; Harumoto, Takashi; Nakamura, Yoshio; Shi, Ji

    2016-08-01

    We report on the investigation of perpendicular exchange bias in FePt (001 ) /NiO (1 ¯1 ¯1 ) orthogonal exchange couple with FePt partially L 10 ordered. From initial magnetization curve measurement and magnetic domain imaging, we find that, for the as-grown bilayer structure, the FePt layer experiences a small-angle magnetization rotation when it is magnetized near to saturation in film normal direction. After field cooling, the bilayer structure shows a significant enhancement of perpendicular magnetic anisotropy, indicating the field mediated coupling between the spins across the FePt/NiO interface. According to Koon's theoretical calculation on the basis of lowest energy ferromagnetic/antiferromagnetic coupling configuration for compensated spins at antiferromagnetic side, we consider slightly slanted Ni spins at the interface off the (1 ¯1 ¯1 ) easy plane can stabilize the spin coupling between FePt and NiO and result in the observed exchange bias in this paper. This consideration was further confirmed by stripe domain width calculation.

  7. Interfacial ferromagnetism and exchange bias in CaRuO3/CaMnO3 superlattices.

    PubMed

    He, C; Grutter, A J; Gu, M; Browning, N D; Takamura, Y; Kirby, B J; Borchers, J A; Kim, J W; Fitzsimmons, M R; Zhai, X; Mehta, V V; Wong, F J; Suzuki, Y

    2012-11-01

    We have found ferromagnetism in epitaxially grown superlattices of CaRuO(3)/CaMnO(3) that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the CaMnO(3) layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the CaMnO(3) thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of CaMnO(3) at each interface. The interfacial moment alternates between the 1 μ(B)/interface Mn ion for even CaMnO(3) layers and the 0.5 μ(B)/interface Mn ion for odd CaMnO(3) layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic CaMnO(3) layers.

  8. Exchange bias effect and glassy-like behavior of EuCrO3 and CeCrO3 nano-powders

    NASA Astrophysics Data System (ADS)

    Taheri, M.; Kremer, R. K.; Trudel, S.; Razavi, F. S.

    2015-09-01

    The magnetic properties of nano-sized EuCrO3 and CeCrO3 powders, synthesized by a solution combustion method, were investigated using DC/AC magnetization measurements. An exchange bias effect, magnetization irreversibility and AC susceptibility dispersion in these samples provided evidence for the presence of the spin disorder magnetic phase. The exchange bias phenomenon, which is assigned to the exchange coupling between the glassy-like shell and canted antiferromagnetic core, showed the opposite sign in EuCrO3 and CeCrO3 at low temperatures, suggesting different exchange interactions at the interfaces in these compounds. We also observed a sign reversal of exchange bias in CeCrO3 at different temperatures.

  9. Exchange bias effect and glassy-like behavior of EuCrO{sub 3} and CeCrO{sub 3} nano-powders

    SciTech Connect

    Taheri, M. Razavi, F. S.; Kremer, R. K.; Trudel, S.

    2015-09-28

    The magnetic properties of nano-sized EuCrO{sub 3} and CeCrO{sub 3} powders, synthesized by a solution combustion method, were investigated using DC/AC magnetization measurements. An exchange bias effect, magnetization irreversibility and AC susceptibility dispersion in these samples provided evidence for the presence of the spin disorder magnetic phase. The exchange bias phenomenon, which is assigned to the exchange coupling between the glassy-like shell and canted antiferromagnetic core, showed the opposite sign in EuCrO{sub 3} and CeCrO{sub 3} at low temperatures, suggesting different exchange interactions at the interfaces in these compounds. We also observed a sign reversal of exchange bias in CeCrO{sub 3} at different temperatures.

  10. The role of the (111) texture on the exchange bias and interlayer coupling effects observed in sputtered NiFe/IrMn/Co trilayers

    SciTech Connect

    Castro, I. L.; Nascimento, V. P.; Passamani, E. C.; Takeuchi, A. Y.; Larica, C.; Tafur, M.; Pelegrini, F.

    2013-05-28

    Magnetic properties of sputtered NiFe/IrMn/Co trilayers grown on different seed layers (Cu or Ta) deposited on Si (100) substrates were investigated by magnetometry and ferromagnetic resonance measurements. Exchange bias effect and magnetic spring behavior have been studied by changing the IrMn thickness. As shown by X-ray diffraction, Ta and Cu seed layers provoke different degrees of (111) fcc-texture that directly affect the exchange bias and indirectly modify the exchange spring coupling behavior. Increasing the IrMn thickness, it was observed that the coupling angle between the Co and NiFe ferromagnetic layers increases for the Cu seed system, but it reduces for the Ta case. The results were explained considering (i) different anisotropies of the Co and IrMn layers induced by the different degree of the (111) texture and (ii) the distinct exchange bias set at the NiFe/IrMn and IrMn/Co interfaces in both systems. The NiFe and Co interlayer coupling angle is strongly correlated with both exchange bias and exchange magnetic spring phenomena. It was also shown that the highest exchange bias field occurs when an unstressed L1{sub 2} IrMn structure is stabilized.

  11. Ferromagnetic resonance study of the misalignment between anisotropy axes in exchange-biased NiFe/FeMn/Co trilayers

    NASA Astrophysics Data System (ADS)

    Barreto, P. G.; Sousa, M. A.; Pelegrini, F.; Alayo, W.; Litterst, F. J.; Baggio-Saitovitch, E.

    2014-05-01

    Exchange-biased NiFe/FeMn/Co trilayers were grown by dc magnetron sputtering and analyzed by in-plane ferromagnetic resonance using Q-band microwaves. The experiments revealed that distinct Co and NiFe resonance modes were excited by the microwave field. A misalignment between the anisotropy axes of the magnetic layers was deduced from the angular variations of the resonance fields, which also showed the effects of uniaxial and unidirectional anisotropies. A phenomenological model was used to fit the experimental results taking also into account a rotatable anisotropy field associated to the domain structure of the FeMn layer and the magnetic history of the films.

  12. Large exchange bias effect in LaCr0.9Ru0.1O3

    NASA Astrophysics Data System (ADS)

    Sarkar, Babusona; Dalal, Biswajit; De, S. K.

    2016-11-01

    The incorporation of tetravalent Ru (10%) into antiferromagnetic spin structure of LaCrO3 leads to mixed valence states of Cr (Cr2+ and Cr3+). Highly delocalized 4d orbital of Ru induces prominent ferromagnetic (FM) component in antiferromagnetic (AFM) matrix of parent compound. The complex magnetic interaction across the interface of FM and AFM regions gives rise to large exchange bias field (HEB) of about 10 kOe. The inverse and normal magnetocaloric effect for magnetic field up to 50 kOe coexists in a single material due to multiple magnetic phase transitions with temperature.

  13. Tunable exchange bias-like effect in patterned hard-soft two-dimensional lateral composites with perpendicular magnetic anisotropy

    SciTech Connect

    Hierro-Rodriguez, A. Alvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M.; Teixeira, J. M.; Vélez, M.

    2014-09-08

    Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo{sub 5} thin films with perpendicular magnetic anisotropy. Their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. Thus, the spatial modulation of thicknesses leads to an exchange coupled system with hard/soft magnetic regions in which rotatable anisotropy of the thicker elements provides an extra tool to design the global magnetic behavior of the patterned lateral composite. Kerr microscopy studies (domain imaging and magneto-optical Kerr effect magnetometry) reveal that the resulting hysteresis loops exhibit a tunable exchange bias-like shift that can be switched on/off by the applied magnetic field.

  14. Magnetism and associated exchange bias in Ni2-xCoxMn1.4Ga0.6

    NASA Astrophysics Data System (ADS)

    Chapai, Ramakanta; Khan, Mahmud

    2016-04-01

    A series of Ni2-xCoxMn1.4Ga0.6 Heusler alloys have been systematically investigated by x-ray diffraction, dc magnetization, and ac susceptibility measurements. For all Co concentration, the alloys exhibit the L10 martensitic structure at room temperature. Interestingly, Co doping simultaneously causes a reduction in the ferromagnetic exchange interaction and enhancement of magnetic anisotropy in Ni2-xCoxMn1.4Ga0.6. Exchange bias effects under both zero field cooled and field cooled condition have been observed in all alloys for x<0.3. The ac susceptibility data show frequency dependence that changes with increasing Co concentration, indicating a change of ground state from spin glass to super spin glass. The experimental results are explained considering the atomic radii of Ni and Co and the fundamental magnetic interactions in Heusler alloys.

  15. Exchange bias effect in Bi{sub 2}Fe{sub 3}AlO{sub 9} ceramics

    SciTech Connect

    Huang, S.; Shi, L. R.; Sun, H. G.; Zhu, C. M.; Tian, Z. M.; Yuan, S. L.

    2014-11-10

    The exchange bias (EB) effect is observed in Bi{sub 2}Fe{sub 3}AlO{sub 9} polycrystalline ceramics. The EB field (H{sub EB}), vertical magnetization shift, and coercive field show a strong dependence on the cooling fields. When a larger applied field is used to measure the hysteresis loop, the EB effect is suppressed. The induced spin-glass-like phase via Al{sup 3+} doping is responsible for the EB effect below the spin-glass temperature (T{sub SG}) of ∼25 K. Moreover, the H{sub EB} varies nonmonotonically with temperature above T{sub SG}, which is interpreted using a random field model with the exchange coupling between ferromagnetic clusters and an antiferromagnetic phase.

  16. Temperature dependence of exchange bias and training effect in Co/CoO film with induced uniaxial anisotropy

    NASA Astrophysics Data System (ADS)

    Wu, R.; Fu, J. B.; Zhou, D.; Ding, S. L.; Wei, J. Z.; Zhang, Y.; Du, H. L.; Wang, C. S.; Yang, Y. C.; Yang, J. B.

    2015-06-01

    The exchange bias effect and training effect of the Co/CoO film with induced uniaxial anisotropy were investigated as functions of temperature. It was found that both effects exhibited drastic differences along the easy and the hard axes. Along the easy axis, the magnetization reversal was dominated by domain wall motion throughout the whole temperature range. However, along the hard axis, the magnetization reversal was dominated by domain wall motion and domain rotation at temperatures below and above 150 K, respectively. The crossover of the two reversal modes characterized with significant asymmetry in the hysteresis loop was observed along the hard axis at 150 K due to the interplay between the exchange and uniaxial anisotropies. Significant difference of training effect in the two directions was observed and ascribed to the differences of the duration and intensity of the interaction between ferromagnetic and antiferromagnetic spins in the two magnetization reversal modes.

  17. Anisotropic behavior of exchange bias effect in tensile-deformed Pt{sub 3}Fe single crystal

    SciTech Connect

    Kobayashi, Satoru Morita, Ryo

    2015-05-07

    Plastic strain in Pt{sub 3}Fe causes changes in the atomic arrangement around the (111) glide plane and induces ferromagnetism even at room temperature. We have performed detailed magnetization measurements on a Pt{sub 3}Fe single crystal with plastic strains of 11.6% under magnetic fields in various directions with respect to the [100] strain axis in order to elucidate the reversal mechanism of induced ferromagnetic domains. We observed that by decreasing the angle between the magnetization direction and strain axis, hysteresis loops are strongly sheared, which is associated with a large increase in coercivity. We also observed that an exchange bias effect appears for all field orientations, but the exchange field maximizes for an intermediate field direction. On the other hand, both phenomena are insensitive to magnetic fields perpendicular to the [100] strain axis. These observations were explained by a single-domain model with uniaxial anisotropy along the [100] strain axis.

  18. The effects of size and orientation on magnetic properties and exchange bias in Co3O4 mesoporous nanowires

    NASA Astrophysics Data System (ADS)

    Zeng, R.; Wang, J. Q.; Chen, Z. X.; Li, W. X.; Dou, S. X.

    2011-04-01

    Co3O4 mesoporous nanowires with average single crystalline grain sizes of about 8 nm, 12nm, 25 nm, and 45 nm were synthesized by sintering of microwave-assisted hydrothermal processed belt-Co(OH)2 precursors at 300-500 °C for 2 h. Microstructure analysis was conducted by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FESEM), transmission electron microscopy (TEM), and high resolution TEM (HRTEM) to confirm the composition, structure, and orientation in the nanowires. Systematic magnetic measurements have also been conducted on the nanowires. It was found that the size and orientation have significant effects on the magnetic and exchange bias properties. The interesting finding was made that room temperature ferromagnetism appeared at 350 °C in the high orientation samples. Systematic comparison and analysis of the relationships among the grain size, microstructure, orientation (texture), surface electric structure (O vacancies), and defects with magnetic properties (ferromagnetism, coercive field, exchange bias, etc.) are presented in this work.

  19. Giant zero field cooled spontaneous exchange bias effect in phase separated La{sub 1.5}Sr{sub 0.5}CoMnO{sub 6}

    SciTech Connect

    Krishna Murthy, J.; Venimadhav, A.

    2013-12-16

    We report a giant zero field cooled exchange bias (ZEB) effect (∼0.65 T) in La{sub 1.5}Sr{sub 0.5}CoMnO{sub 6} sample. Magnetic study has revealed a reentrant spin glass ∼90 K, phase separation to spin glass and ferromagnetic phases below 50 K and canted antiferromagnetic transition ∼10 K. A small conventional exchange bias (CEB) is established with the advent of spontaneous phase separation down to 10 K. Giant ZEB and enhanced CEB effects are found only below 10 K and are attributed to the large unidirectional anisotropy at the interface of isothermally field induced ferromagnetic phase and canted antiferromagnetic background.

  20. Influence of 8-Oxoguanosine on the Fine Structure of DNA Studied with Biasing-Potential Replica Exchange Simulations

    SciTech Connect

    Kara, Mahmut; Zacharias, Martin W.

    2013-03-05

    Chemical modification or radiation can cause DNA damage, which plays a crucial role for mutagenesis of DNA, carcinogenesis, and aging. DNA damage can also alter the fine structure of DNA that may serve as a recognition signal for DNA repair enzymes. A new, advanced sampling replica-exchange method has been developed to specifically enhance the sampling of conformational substates in duplex DNA during molecular dynamics (MD) simulations. The approach employs specific biasing potentials acting on pairs of pseudodihedral angles of the nucleic acid backbone that are added in the replica simulations to promote transitions of the most common substates of the DNA backbone. The sampled states can exchange with a reference simulation under the control of the original force field. The application to 7,8-dihydro-8oxo-guanosine, one of the most common oxidative damage in DNA indicated better convergence of sampled states during 10 ns simulations compared to 20 times longer standard MD simulations. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions, including explicit solvent and ions. The biasing potential-replica exchange MD simulations indicated significant differences in the population of nucleic acid backbone substates in the case of 7,8-dihydro-8oxo-guanosine compared to a regular guanosine in the same sequence context. This concerns both the ratio of the B-DNA substates BI and BII associated with the backbone dihedral angles ε and z but also coupled changes in the backbone dihedral angles a and g. Such differences may play a crucial role in the initial recognition of damaged DNA by repair enzymes.

  1. Influence of 8-Oxoguanosine on the Fine Structure of DNA Studied with Biasing-Potential Replica Exchange Simulations

    PubMed Central

    Kara, Mahmut; Zacharias, Martin

    2013-01-01

    Chemical modification or radiation can cause DNA damage, which plays a crucial role for mutagenesis of DNA, carcinogenesis, and aging. DNA damage can also alter the fine structure of DNA that may serve as a recognition signal for DNA repair enzymes. A new, advanced sampling replica-exchange method has been developed to specifically enhance the sampling of conformational substates in duplex DNA during molecular dynamics (MD) simulations. The approach employs specific biasing potentials acting on pairs of pseudodihedral angles of the nucleic acid backbone that are added in the replica simulations to promote transitions of the most common substates of the DNA backbone. The sampled states can exchange with a reference simulation under the control of the original force field. The application to 7,8-dihydro-8oxo-guanosine, one of the most common oxidative damage in DNA indicated better convergence of sampled states during 10 ns simulations compared to 20 times longer standard MD simulations. It is well suited to study systematically the fine structure and dynamics of large nucleic acids under realistic conditions, including explicit solvent and ions. The biasing potential-replica exchange MD simulations indicated significant differences in the population of nucleic acid backbone substates in the case of 7,8-dihydro-8oxo-guanosine compared to a regular guanosine in the same sequence context. This concerns both the ratio of the B-DNA substates BI and BII associated with the backbone dihedral angles ε and ζ but also coupled changes in the backbone dihedral angles α and γ. Such differences may play a crucial role in the initial recognition of damaged DNA by repair enzymes. PMID:23473492

  2. Epitaxial growth of intermetallic MnPt films on oxides and large exchange bias

    DOE PAGES

    Liu, Zhiqi; Biegalski, Michael D.; Hsu, Shang-Lin; Shang, Shunli; Marker, Cassie; Liu, Jian; Li, Li; Fan, Lisha S.; Meyer, Tricia L.; Wong, Anthony T.; et al

    2015-11-05

    High-quality epitaxial growth of intermetallic MnPt films on oxides is achieved, with potential for multiferroic heterostructure applications. Antisite-stabilized spin-flipping induces ferromagnetism in MnPt films, although it is robustly antiferromagnetic in bulk. Thus, highly ordered antiferromagnetic MnPt films exhibit superiorly large exchange coupling with a ferromagnetic layer.

  3. Mercury vapor air-surface exchange measured by collocated micrometeorological and enclosure methods - Part II: Bias and uncertainty analysis

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Sommar, J.; Lin, C.-J.; Feng, X.

    2015-05-01

    Dynamic flux chambers (DFCs) and micrometeorological (MM) methods are extensively deployed for gauging air-surface Hg0 gas exchange. However, a systematic evaluation of the precision of the contemporary Hg0 flux quantification methods is not available. In this study, the uncertainty in Hg0 flux measured by the relaxed eddy accumulation (REA) method, the aerodynamic gradient method (AGM), the modified Bowen ratio (MBR) method, as well as DFC of traditional (TDFC) and novel (NDFC) designs, are assessed using a robust data set from two field intercomparison campaigns. The absolute precision in Hg0 concentration difference (ΔC) measurements is estimated at 0.064 ng m-3 for the gradient-based MBR and AGM systems. For the REA system, the parameter is Hg0 concentration (C) dependent at 0.069 + 0.022C. During the campaigns, 57 and 62 % of the individual vertical gradient measurements are found to be significantly different from 0, while for the REA technique, the percentage of significant observations is lower. For the chambers, non-significant fluxes are confined to a few night-time periods with varying ambient Hg0 concentrations. Relative bias for DFC-derived fluxes is estimated to be ~ ±10, and ~ 85% of the flux bias is within ±2 ng m-2 h-1 in absolute terms. The DFC flux bias follows a diurnal cycle, which is largely affected by the forced temperature and irradiation bias in the chambers. Due to contrasting prevailing micrometeorological conditions, the relative uncertainty (median) in turbulent exchange parameters differs by nearly a factor of 2 between the campaigns, while that in ΔC measurement is fairly consistent. The estimated flux uncertainties for the triad of MM techniques are 16-27, 12-23 and 19-31% (interquartile range) for the AGM, MBR and REA methods, respectively. This study indicates that flux-gradient-based techniques (MBR and AGM) are preferable to REA in quantifying Hg0 flux over ecosystems with low vegetation height. A limitation of all Hg0 flux

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  6. Magnetoelectric switching of perpendicular exchange bias in Pt/Co/α-Cr{sub 2}O{sub 3}/Pt stacked films

    SciTech Connect

    Toyoki, Kentaro; Shiratsuchi, Yu Kobane, Atsushi; Nakatani, Ryoichi; Mitsumata, Chiharu; Kotani, Yoshinori; Nakamura, Tetsuya

    2015-04-20

    We report the realization of magnetoelectric switching of the perpendicular exchange bias in Pt/Co/α-Cr{sub 2}O{sub 3}/Pt stacked films. The perpendicular exchange bias was switched isothermally by the simultaneous application of magnetic and electric fields. The threshold electric field required to switch the perpendicular exchange bias was found to be inversely proportional to the magnetic field, which confirmed the magnetoelectric mechanism of the process. The observed temperature dependence of the threshold electric field suggested that the energy barrier of the antiferromagnetic spin reversal was significantly lower than that assuming the coherent rotation. Pulse voltage measurements indicated that the antiferromagnetic domain propagation dominates the switching process. These results suggest an analogy of the electric-field-induced magnetization with a simple ferromagnet.

  7. Metastable magnetic state and exchange bias training effect in Mn-rich YMnO3 thin films

    NASA Astrophysics Data System (ADS)

    Kumar, Manish; Choudhary, R. J.; Phase, D. M.

    2015-04-01

    The magnetic nature of stoichiometric and Mn rich hexagonal YMnO3 films grown at different oxygen partial pressures is investigated. The stoichiometric YMnO3 thin film showed antiferromagnetic ordering below 72 K while the film having excess Mn content revealed metastable magnetic behaviour at a temperature of less than 42 K. The metastable magnetic behaviour in this sample is attributed to the competing anti-ferromagnetic and ferromagnetic phase fractions (caused by Mn2+ ions that originated due to excess Mn content). Also, in the metastable regime the exchange bias effect is observed, which is further supported by the training effect. Both the samples reveal room temperature ferroelectric behaviour.

  8. Exchange bias and magnetization reversal in Ni(Cr1-xFex)2O4 (x=0-0.20)

    NASA Astrophysics Data System (ADS)

    Barman, Junmoni; Babu, P. D.; Ravi, S.

    2016-11-01

    Exchange bias and magnetization reversal in single phase samples of Ni(Cr1-xFex)2O4 (x=0-0.20) were studied through magnetic measurements. Substitution of Fe for Cr changes the crystal structure at room temperature from tetragonal (space group: I41/amd) to cubic (space group: Fd 3 bar m) form. Temperature variation of magnetization measurements show that these samples undergo ferrimagnetic transitions and the transition temperature (TC) increases from 73 K for x=0.0 to 314 K for x=0.20. An interesting magnetization reversal phenomenon was observed for x=0.06 sample with a magnetic compensation temperature of 49 K. M-H loop measurements at different temperature show the signature of presence of strong antiferromagnetic interactions especially at low temperature (T<50 K). Tunable exchange bias behavior with a maximum exchange bias field of 5670 Oe is observed for x=0.06 sample and it is explained by considering the exchange anisotropy between the ferrimagnetic and the antiferromagnetic components. The exchange bias field and the vertical shift in magnetization decrease exponentially with increase in temperature.

  9. Exchange bias effect in multiferroic CoCr2O4/Cr2O3 nanogranular system synthesized through a phase segregation route

    NASA Astrophysics Data System (ADS)

    Tian, Zhaoming; Chen, Jingting; Yuan, Songliu; Tang, Jianbang; Huo, Shaoxin; Duan, Hanning

    2011-09-01

    A nanogranular system of multiferroic CoCr2O4 nanoparticles embedded in an antiferromagnetic Cr2O3 matrix has been synthesized through a high-temperature phase segregation route from a Co-doped Cr2O3 matrix. Magnetic studies show that exchange bias fields (HEB) accompanying vertical magnetization shifts (MShift) are observed at low temperatures after field cooled from 350 K. The corresponding exchange bias field can be as large as 1420 Oe, and the vertical magnetization shift reaches 0.116 emu/g at 10 K. The exchange bias field decreases with temperature increasing and disappears at T ≈ 70 K, while the coercive field (HC) initially increases with the temperature up to 40 K, and thereafter, it decreases to zero at 100 K. This exchange bias behavior is discussed in terms of the existence of exchange coupling between the ferrimagnetic CoCr2O4 core and spin glass-like phase at the interfaces.

  10. Mercury vapor air-surface exchange measured by collocated micrometeorological and enclosure methods - Part II: Bias and uncertainty analysis

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Sommar, J.; Lin, C.-J.; Feng, X.

    2015-02-01

    Dynamic flux chambers (DFCs) and micrometeorological (MM) methods are extensively deployed for gauging air-surface Hg0 gas exchange. However, a systematic evaluation of the precision of the contemporary Hg0 flux quantification methods is not available. In this study, the uncertainty in Hg0 flux measured by relaxed eddy accumulation (REA) method, aerodynamic gradient method (AGM), modified Bowen-ratio (MBR) method, as well as DFC of traditional (TDFC) and novel (NDFC) designs is assessed using a robust data-set from two field intercomparison campaigns. The absolute precision in Hg0 concentration difference (Δ C) measurements is estimated at 0.064 ng m-3 for the gradient-based MBR and AGM system. For the REA system, the parameter is Hg0 concentration (C) dependent at 0.069+0.022C. 57 and 62% of the individual vertical gradient measurements were found to be significantly different from zero during the campaigns, while for the REA-technique the percentage of significant observations was lower. For the chambers, non-significant fluxes are confined to a few nighttime periods with varying ambient Hg0 concentration. Relative bias for DFC-derived fluxes is estimated to be ~ ±10%, and ~ 85% of the flux bias are within ±2 ng m-2 h-1 in absolute term. The DFC flux bias follows a diurnal cycle, which is largely dictated by temperature controls on the enclosed volume. Due to contrasting prevailing micrometeorological conditions, the relative uncertainty (median) in turbulent exchange parameters differs by nearly a factor of two between the campaigns, while that in Δ C measurements is fairly stable. The estimated flux uncertainties for the triad of MM-techniques are 16-27, 12-23 and 19-31% (interquartile range) for the AGM, MBR and REA method, respectively. This study indicates that flux-gradient based techniques (MBR and AGM) are preferable to REA in quantifying Hg0 flux over ecosystems with low vegetation height. A limitation of all Hg0 flux measurement systems investigated

  11. Self Exchange Bias and Bi-stable Magneto-Resistance States in Amorphous TbFeCo and TbSmFeCo Thin Films

    NASA Astrophysics Data System (ADS)

    Ma, Chung; Li, Xiaopu; Lu, Jiwei; Poon, Joseph; Comes, Ryan; Devaraj, Arun; Spurgeon, Steven

    Amorphous ferrimagetic TbFeCo and TbSmFeCo thin films are found to exhibit strong perpendicular magnetic anisotropy. Self exchange bias effect and bi-stable magneto-resistance states are observed near compensation temperature by magnetic hysteresis loop, anomalous Hall effect and transverse magneto-resistance measurements. Atom probe tomography, scanning transmission electron microscopy, and energy dispersive spectroscopy mapping have revealed two nanoscale amorphous phases with different Tb concentration distributed within the amorphous films. The observed exchange anisotropy originates from the exchange interaction between the two nanoscale amorphous phases. Exchange bias effect is used for increasing stability in spin valves and magnetic tunneling junctions. This study opens up a new platform for using amorphous ferrimagnetic thin films that require no epitaxial growth in nanodevices.. The work was supported by the Defense Threat Reduction Agency Grant and the U.S. Department of Energy.

  12. The influence of oxidation process on exchange bias in egg-shaped FeO/Fe3O4 core/shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Leszczyński, Błażej; Hadjipanayis, George C.; El-Gendy, Ahmed A.; Załęski, Karol; Śniadecki, Zbigniew; Musiał, Andrzej; Jarek, Marcin; Jurga, Stefan; Skumiel, Andrzej

    2016-10-01

    Egg-shaped nanoparticles with a core-shell morphology were synthesized by thermal decomposition of an iron oleate complex. XRD and M(T) magnetic measurements confirmed the presence of FeO (wustite) and Fe3O4 (magnetite) phases in the nanoparticles. Oxidation of FeO to Fe3O4 was found to be the mechanism for the shell formation. As-made nanoparticles exhibited high values of exchange bias at 2 K. Oxidation led to decrease of exchange field from 2880 Oe (in as-made sample) to 330 Oe (in oxidized sample). At temperatures higher than the Néel temperature of FeO (200 K) there was no exchange bias. An interesting observation was made showing the exchange field to be higher than the coercive field at temperatures close to magnetite's Verwey transition.

  13. Temperature dependent exchange bias training effect in single-crystalline BiFeO{sub 3}/Co bilayers

    SciTech Connect

    He, M. C.; You, B.; Tu, H. Q.; Rui, W. B.; Gao, Y.; Zhang, Y. Q.; Sheng, Y.; Xu, Q. Y. E-mail: jdu@nju.edu.cn; Xu, Y. B.; Du, J. E-mail: jdu@nju.edu.cn

    2015-05-07

    Single-crystalline BiFeO{sub 3} (BFO)/Co bilayers were prepared by combined pulsed laser deposition and magnetron sputtering on (001) SrTiO{sub 3} substrates. Exchange bias (EB) and accompanying training effect have been studied as a function of temperature (T) between 5 K and 300 K. A non-monotonic exchange field variation with sharp increase below 100 K has been observed. In the meanwhile, strong training effect was recorded when T < 100 K and it weakens monotonically with increasing T up to 300 K. These temperature dependent EB and training effect may be caused by the uncompensated spins in both the interfacial spin-glass (SG) phase at low temperature and the antiferromagnetic BFO layer at higher temperature. The low temperature EB training results can be well fitted by a modified Binek's model considering asymmetric changes of the pinning SG spins at the descending and the ascending branches.

  14. Tunable exchange bias in dilute magnetic alloys – chiral spin glasses

    PubMed Central

    Hudl, Matthias; Mathieu, Roland; Nordblad, Per

    2016-01-01

    A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, ΔM. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of ΔM at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction. PMID:26817418

  15. Extensive and biased intergenomic nonreciprocal DNA exchanges shaped a nascent polyploid genome, Gossypium (cotton).

    PubMed

    Guo, Hui; Wang, Xiyin; Gundlach, Heidrun; Mayer, Klaus F X; Peterson, Daniel G; Scheffler, Brian E; Chee, Peng W; Paterson, Andrew H

    2014-08-01

    Genome duplication is thought to be central to the evolution of morphological complexity, and some polyploids enjoy a variety of capabilities that transgress those of their diploid progenitors. Comparison of genomic sequences from several tetraploid (AtDt) Gossypium species and genotypes with putative diploid A- and D-genome progenitor species revealed that unidirectional DNA exchanges between homeologous chromosomes were the predominant mechanism responsible for allelic differences between the Gossypium tetraploids and their diploid progenitors. Homeologous gene conversion events (HeGCEs) gradually subsided, declining to rates similar to random mutation during radiation of the polyploid into multiple clades and species. Despite occurring in a common nucleus, preservation of HeGCE is asymmetric in the two tetraploid subgenomes. At-to-Dt conversion is far more abundant than the reciprocal, is enriched in heterochromatin, is highly correlated with GC content and transposon distribution, and may silence abundant A-genome-derived retrotransposons. Dt-to-At conversion is abundant in euchromatin and genes, frequently reversing losses of gene function. The long-standing observation that the nonspinnable-fibered D-genome contributes to the superior yield and quality of tetraploid cotton fibers may be explained by accelerated Dt to At conversion during cotton domestication and improvement, increasing dosage of alleles from the spinnable-fibered A-genome. HeGCE may provide an alternative to (rare) reciprocal DNA exchanges between chromosomes in heterochromatin, where genes have approximately five times greater abundance of Dt-to-At conversion than does adjacent intergenic DNA. Spanning exon-to-gene-sized regions, HeGCE is a natural noninvasive means of gene transfer with the precision of transformation, potentially important in genetic improvement of many crop plants.

  16. Unexpected magnetism, Griffiths phase, and exchange bias in the mixed lanthanide Pr0.6Er0.4Al2

    SciTech Connect

    Pathak, Arjun K.; Paudyal, D.; Jayasekara, W. T.; Calder, S.; Kreyssig, A.; Goldman, Alan I.; Gschneidner, Karl A.

    2014-06-01

    We report an unusual coexistence of ferromagnetism and ferrimagnetism, and metamagnetism in Pr0.6Er0.4Al2. In addition, this compound retains a clear Griffiths phase behavior even at 1 kOe magnetic field and shows a large exchange bias after field cooling from the paramagnetic state. The crystal-field excitations and opposite exchange interactions between nearest-neighbor and next-nearest-neighbor rare earth sites explain these behaviors.

  17. Strong perpendicular exchange bias in epitaxial La(0.7)Sr(0.3)MnO3:BiFeO3 nanocomposite films through vertical interfacial coupling.

    PubMed

    Zhang, Wenrui; Chen, Aiping; Jian, Jie; Zhu, Yuanyuan; Chen, Li; Lu, Ping; Jia, Quanxi; MacManus-Driscoll, Judith L; Zhang, Xinghang; Wang, Haiyan

    2015-09-01

    An exchange bias effect with perpendicular anisotropy is of great interest owing to potential applications such as read heads in magnetic storage devices with high thermal stability and reduced dimensions. Here we report a novel approach for achieving perpendicular exchange bias by orienting the ferromagnetic/antiferromagnetic coupling in the vertical geometry through a unique vertically aligned nanocomposite (VAN) design. Our results demonstrate robust perpendicular exchange bias phenomena in micrometer-thick films employing a prototype material system of antiferromagnetic BiFeO3 and ferromagnetic La0.7Sr0.3MnO3. The unique response of exchange bias to a perpendicular magnetic field reveals the existence of exchange coupling along their vertical heterointerfaces, which exhibits a strong dependence on their strain states. This VAN approach enables a large selection of material systems for achieving perpendicular exchange bias, which could lead to advanced spintronic devices.

  18. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    SciTech Connect

    Letellier, F.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-28

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

  19. Direct imaging of thermally-activated grain-boundary diffusion in Cu/Co/IrMn/Pt exchange-bias structures using atom-probe tomography

    NASA Astrophysics Data System (ADS)

    Letellier, F.; Lechevallier, L.; Lardé, R.; Le Breton, J.-M.; Akmaldinov, K.; Auffret, S.; Dieny, B.; Baltz, V.

    2014-11-01

    Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400 °C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500 °C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500 °C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer.

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

    PubMed

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

    2015-10-01

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

  1. Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition

    SciTech Connect

    D'Addato, Sergio; Spadaro, Maria Chiara; Luches, Paola; Valeri, Sergio; Grillo, Vincenzo; Rotunno, Enzo; Roldan Gutierrez, Manuel A.; Pennycook, Stephen J.; Ferretti, Anna Maria; Capetti, Elena; Ponti, A.

    2015-01-01

    Films of magnetic Ni@NiO core–shell nanoparticles (NPs, core diameter d ≅ 12 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core-shell interface, and magnetic properties. Different values of NiO shell thickness ts could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopy (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field Hbias is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core–shell NPs with desired magnetic properties.

  2. Conformational sampling of oligosaccharides using Hamiltonian replica exchange with two-dimensional dihedral biasing potentials and the weighted histogram analysis method (WHAM).

    PubMed

    Yang, Mingjun; MacKerel, Alexander D

    2015-02-10

    Oligosaccharides and polysaccharides exert numerous functional roles in biology through their structural diversity and conformational properties. To investigate their conformational properties using computational methods, Hamiltonian replica exchange (H-REX) combined with two-dimensional grid-based correction maps as biasing potentials (bpCMAP) significantly improves the sampling efficiency about glycosidic linkages. In the current study, we extend the application of H-REX with bpCMAP to complex saccharides and establish systematic procedures for bpCMAP construction, determination of replica distribution, and data analysis. Our main findings are that (1) the bpCMAP for each type of glycosidic linkage can be constructed from the corresponding disaccharide using gas-phase umbrella sampling simulations, (2) the replica distribution can be conveniently determined following the exact definition of the average acceptance ratio based on the assigned distribution of biasing potentials, and (3) the extracted free energy surface (or potential of mean force (PMF)) can be improved using the weighted histogram analysis method (WHAM) allowing for the inclusion of data from the excited state replicas in the calculated probability distribution. The method is applied to a branched N-glycan found on the HIV gp120 protein, and a linear N-glycan. Considering the general importance of N-glycans and the wide appreciation of the sampling problem, the present method represents an efficient procedure for the conformational sampling of complex oligo- and polysaccharides under explicit solvent conditions. More generally, the use of WHAM is anticipated to be of general utility for the calculation of PMFs from H-REX simulations in a wide range of macromolecular systems. PMID:25705140

  3. Enhanced exchange bias effect in size modulated Sm{sub 0.5}Ca{sub 0.5}MnO{sub 3} phase separated manganite

    SciTech Connect

    Giri, S. K.; Nath, T. K.; Yusuf, S. M.; Mukadam, M. D.

    2014-03-07

    The effect of grain size modulation on exchange bias effect in CE-type antiferromagnetic Sm{sub 0.5}Ca{sub 0.5}MnO{sub 3} phase separated manganite is reported here. With the reduction of particle size, ferromagnetic clusters are found to form in the charge ordered antiferromagnetic matrix and gradually become larger. The horizontal and vertical shifts of the magnetic hysteresis loops in the field cooled magnetization process clearly indicate the size dependent exchange bias effect and it can be tuned with the reduction of particle sizes. The values of exchange bias parameter, i.e., exchange bias field (H{sub E}), coercivity (H{sub C}), remanence asymmetry (M{sub E}), and magnetic coercivity (M{sub C}) are found to depend strongly on the particle size. The variations of H{sub E} follow non-monotonic dependencies with reduction in particle size and show maximum (1205 Oe) at particle size of 150 nm at T = 5 K, which can be ascribed due to the changes in uncompensated surface spins. The values of H{sub E} and M{sub E} are found to decrease exponentially with increasing temperature below the spin- or cluster-glass like freezing temperature. The spin relaxation model has been employed for analysis of large magnetic training effect. The linear relationship between H{sub E} and M{sub E} further confirms the role of uncompensated surface spins. In view of spintronics application of manganites, the present observation of large exchange bias shift in this half-doped manganite may have great technological importance.

  4. Strong room temperature exchange bias in self-assembled BiFeO3-Fe3O4 nanocomposite heteroepitaxial films

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Mi; Weal, Emily; Bi, Zhenxing; Wang, Haiyan; Kursumovic, Ahmed; Fix, Thomas; Blamire, Mark G.; MacManus-Driscoll, Judith L.

    2013-01-01

    Self-assembled, nanocomposite heteroepitaxial films of BiFeO3 + Fe3O4 (x BiFeO3 + (1 - x) Fe3O4), where x = 0.5 or 0.9, were grown on (011) SrTiO3. Depending on the value of x and on the film thickness, either exchange bias or exchange enhancement of coercivity was demonstrated. In epitaxially and highly strained (7%) films of 250 nm thickness, and for x = 0.9, exchange bias (HEB) values of 40 Oe and HEB/HC ratios of 0.5 were achieved. Most crucially, these effects were measured at room temperature, showing the high potential of chemically compatible BiFeO3 + Fe3O4 for achieving room temperature magnetoelectricity.

  5. Exchange scattering as the driving force for ultrafast all-optical and bias-controlled reversal in ferrimagnetic metallic structures

    NASA Astrophysics Data System (ADS)

    Kalashnikova, A. M.; Kozub, V. I.

    2016-02-01

    Experimentally observed ultrafast all-optical magnetization reversal in ferrimagnetic metals and heterostructures based on antiferromagnetically coupled ferromagnetic d - and f -metallic layers relies on intricate energy and angular momentum flow between electrons, phonons, and spins. Here we treat the problem of angular momentum transfer in the course of ultrafast laser-induced dynamics in a ferrimagnetic metallic system using microscopical approach based on the system of rate equations. We show that the magnetization reversal is supported by a coupling of d and f subsystems to delocalized s or p electrons. The latter can transfer spin between the two subsystems in an incoherent way owing to the (s ;p )-(d ;f ) exchange scattering. Since the effect of the external excitation in this process is reduced to the transient heating of the mobile electron subsystem, we also discuss the possibility to trigger the magnetization reversal by applying a voltage bias pulse to antiferromagnetically coupled metallic ferromagnetic layers embedded in point contact or tunneling structures. We argue that such devices allow controlling reversal with high accuracy. We also suggest using the anomalous Hall effect to register the reversal, thus playing a role of reading probes.

  6. Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition

    DOE PAGES

    D'Addato, Sergio; Spadaro, Maria Chiara; Luches, Paola; Valeri, Sergio; Grillo, Vincenzo; Rotunno, Enzo; Roldan Gutierrez, Manuel A.; Pennycook, Stephen J.; Ferretti, Anna Maria; Capetti, Elena; et al

    2015-01-01

    Films of magnetic Ni@NiO core–shell nanoparticles (NPs, core diameter d ≅ 12 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core-shell interface, and magnetic properties. Different values of NiO shell thickness ts could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopymore » (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field Hbias is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core–shell NPs with desired magnetic properties.« less

  7. Néel walls between tailored parallel-stripe domains in IrMn/CoFe exchange bias layers

    SciTech Connect

    Ueltzhöffer, Timo Schmidt, Christoph; Ehresmann, Arno; Krug, Ingo; Nickel, Florian; Gottlob, Daniel

    2015-03-28

    Tailored parallel-stripe magnetic domains with antiparallel magnetizations in adjacent domains along the long stripe axis have been fabricated in an IrMn/CoFe Exchange Bias thin film system by 10 keV He{sup +}-ion bombardment induced magnetic patterning. Domain walls between these domains are of Néel type and asymmetric as they separate domains of different anisotropies. X-ray magnetic circular dichroism asymmetry images were obtained by x-ray photoelectron emission microscopy at the Co/Fe L{sub 3} edges at the synchrotron radiation source BESSY II. They revealed Néel-wall tail widths of 1 μm in agreement with the results of a model that was modified in order to describe such walls. Similarly obtained domain core widths show a discrepancy to values estimated from the model, but could be explained by experimental broadening. The rotation senses in adjacent walls were determined, yielding unwinding domain walls with non-interacting walls in this layer system.

  8. Exchange bias and crystal structure of epitaxial (111) FePt/BiFeO{sub 3} sputtered thin films

    SciTech Connect

    Chiu, Shang-Jui; Hsiao, Shih-Nan Lee, Hsin-Yi; Huang, Li-Chun; Yu, Ge-Ping; Chang, Huang-Wei

    2014-05-07

    Crystallographic structure and magnetic properties of the epitaxial FePt (10 nm)/BiFeO{sub 3} (BFO) (10 nm) bilayer films grown on (111) SrTiO{sub 3} (STO) substrates with different deposition temperatures of FePt layers (T{sub d}) have been investigated using magnetron sputtering. Out-of-plane radial scan along (111) direction and off-normal (002) azimuthal scan, determined by synchrotron radiation x-ray diffractometry, evidence that the FePt layers were well epitaxially grown on the (111) epitaxial BFO layers for the samples with T{sub d} = 300 and 700 °C. On the contrary, for the bilayer films with T{sub d} = 500 °C, the FePt and BFO layers exhibit low epitaxial quality. Large in-plane exchange bias field (H{sub eb}) values of 45–412 Oe are obtained for the L1{sub 0}-FePt/BFO bilayer films measured with applied field of 12 kOe at room temperature. The change of effective interfacial area, observed by scanning electron microscopy, between FePt island-like particles and BFO continuous layers, and epitaxiality of the bilayer were correlated with the evolution of H{sub eb}.

  9. Magnetization reversal in Ni/FeF2 heterostructures with the coexistence of positive and negative exchange bias

    NASA Astrophysics Data System (ADS)

    Kovylina, Miroslavna; Morales, Rafael; Labarta, Amílcar; Batlle, Xavier

    2012-12-01

    Magnetization reversal mechanisms are studied in Ni/FeF2 heterostructures with the coexistence of positive and negative exchanged bias (PEB/NEB), showing single and double hysteresis loops (DHL) in magnetoresistance measurements. Micromagnetic simulations show that PEB and NEB domains of a minimum critical size must be introduced in order to reproduce the occurrence of DHLs. The simulations reveal that different magnetic configurations and, hence, different magnetization reversal processes take place in a ferromagnet (FM) on top of minority PEB domains that are either greater or smaller than the critical size. In particular, for the case of DHLs, core reversal of a depthwise domain wall is observed over minority PEB domains when the magnetic field is decreased from positive saturation. As the field is further decreased, a complex domain-wall evolution takes place in the FM, including the dependences of the domain-wall width and domain size on the magnetic field and distance from the antiferromagnet (AF). These effects should be taken into account when the domain size is estimated from data measured by depth-dependent techniques since they average the distribution of domain sizes in the FM for different distances from the AF.

  10. Doping dependent magnetism and exchange bias in CaMn{sub 1−x}W{sub x}O{sub 3} manganites

    SciTech Connect

    Markovich, V. Gorodetsky, G.; Fita, I.; Wisniewski, A.; Puzniak, R.; Naumov, S. V.; Mostovshchikova, E. V.; Telegin, S. V.; Jung, G.

    2014-09-07

    Magnetic properties of CaMn{sub 1−x}W{sub x}O{sub 3} (0 ≤ x ≤ 0.1) have been investigated, and the research was focused on the exchange bias (EB) phenomenon in CaMn{sub 0.93}W{sub 0.07}O{sub 3}. Magnetic ground state was found to be dependent on tungsten doping level and the following states were distinguished: (i) G-type antiferromagnetic (AFM) state with a weak ferromagnetic (FM) component at x = 0 and 0.04; (ii) mostly orbitally ordered C-type AFM at x = 0.07 and 0.1. For the studied manganites, spontaneous magnetization increases sharply with increasing doping level reaching M{sub 0} ≈ 9.5 emu/g at T = 10 K for x = 0.04, and then decreases rapidly reaching zero for x = 0.1. Exchange bias effect, manifested by vertical and horizontal shifts in the hysteresis loop for field cooled sample, has been observed in CaMn{sub 0.93}W{sub 0.07}O{sub 3}. Exchange bias field, coercivity, remanence asymmetry, and magnetic coercivity depend strongly on temperature, cooling field, and maximal measuring field. Horizontal and vertical shifts of magnetization loop sharply decrease with increasing temperature and vanish above 70 K, whereas coercivity and magnetic coercivity disappear only above 100 K (temperature of transition to the G-type AFM state). The exchange bias field H{sub EB} increases with increasing cooling field H{sub cool} and goes through a broad maximum at 40 kOe, while the remanence asymmetry increases monotonously in the entire investigated cooling field range, up to 50 kOe. For the compound with x = 0.07, the size of the FM regions ≈2 nm was estimated from the dependence of exchange bias field H{sub EB} upon H{sub cool}. It is suggested that the exchange bias originates from interface exchange coupling between small FM clusters and the G-type AFM phase inside the primary C-type orbitally ordered AFM phase.

  11. Azimuthal angular dependence of exchange bias in FeMn/Py bilayers with Ta/Cu hybrid underlayers: Effect of deposition sequence and sense of rotation

    NASA Astrophysics Data System (ADS)

    Kim, Ki-Yeon; Choi, Hyeok-Cheol; You, Chun-Yeol

    2014-03-01

    We have investigated the azimuthal angular dependent exchange bias of bottom-pinned Py(5nm)/FeMn(5nm) and top-pinned FeMn(5nm)/Py(5nm) bilayers prepared at the same deposition condition except deposition order by vector MOKE experiment. It was found that exchange biased (EB) direction is not collinear with an applied magnetic field during deposition. Second, the critical angle at which the phase of a transverse loop reverses is once (160° @CCW, 170 ~ 175° @CW) for Py/FeMn bilayer and twice (155 ~ 160°, 340 ~ 345° @CCW, 10 ~ 15°, 195-200° @CW) for FeMn/Py bilayer. Therefore, phase of transverse loop remains the same as the initial transverse loop or reverse after 360° rotation, depending on deposition sequence. Third, hysteresis is observed in the transverse magnetization component only if hysteresis loops are measured consecutively between cw and ccw directions over the angular range including the critical angle. This is considered to originate from thermally activated irreversible rearrangement of uncompensated AF spins via interface exchange coupling. Fourth, exchange bias field and coercivity of top-pinned FeMn/Py bilayers with Ta/Cu underlayers are enhanced compared with those of bottom-pinned Py/FeMn bilayers. This is in consistent with our previous results.

  12. Large spontaneous exchange bias and giant magnetoresistance in Ni50Mn37-xFexIn13(x=2-4) Heusler alloys

    NASA Astrophysics Data System (ADS)

    Jing, Chao; Liu, Yang; Zheng, Dong; Wang, Xiaolong; Sun, Junkun; Zhang, Yuanlei; Liu, Changqin; Deng, Dongmei; Feng, Zhenjie; Xu, Kun; Li, Zhe

    2016-09-01

    In the present work, we have obtained a large zero-field cooled exchange-bias (spontaneous exchange bias, SEB) in Ni50Mn35Fe2In13 Heusler alloy. The experimental results indicate that the sample with x=2 exhibits super-spin glass (SSG), super-paramagnetic (SPM), super-ferromagnetic (SFM) and antiferromagnetic (AFM) behaviors in the martensite state at low temperature. Contributing to the complex magnetic interactions, a large SEB effect with the value of 1567 Oe was obtained at 5 K. At the same time, a non-monotonic behavior of spontaneous exchange bias field (spontaneous HEB) was observed with the variation of temperature, which is resulted from the competition between the volume fraction of SFM clusters and the exchange coupling of the SFM-AFM interface. In addition, during martensitic transformation (MT), extraordinary electrical transport properties of Ni50Mn37-xFexIn13 (x=2-4) alloys have been observed under various external magnetic field. The maximal value of the giant magnetoresistance (GMR) reaches about 57% at 135 K under the external magnetic field change of 50 kOe. The effect of field induced reverse martensitic transformation (FIRMT) on the GMR has been also discussed.

  13. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys.

    PubMed

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance.

  14. Enhanced exchange bias and improved ferromagnetic properties in Permalloy–BiFe0.95Co0.05O3 core–shell nanostructures

    PubMed Central

    Javed, K.; Li, W. J.; Ali, S. S.; Shi, D. W.; Khan, U.; Riaz, S.; Han, X. F.

    2015-01-01

    Hybrid core–shell nanostructures consisting of permalloy (Ni80Fe20) and multiferroic(BiFeO3, BFO/BiFe0.95Co0.05O3, BFC) materials were synthesized by a two-step method, based on wet chemical impregnation and subsequent electrodeposition within porous alumina membranes. Structural and magnetic characterizations have been done to investigate doping effect on magnetic properties and exchange bias. The magnetometry analysis revealed significant enhancements of the exchange bias and coercivity in NiFe-BFC core-shell nanostructures as compared with NiFe-BFO core-shell nanostructures. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes between adjacent layers of core-shell structure. It indicates that it is possible to improve properties of multiferroic composites by site-engineering method. Our approach opens a pathway to obtain optimized nanostructured multiferroic composites exhibiting tunable magnetic properties. PMID:26658956

  15. Optimization of exchange bias in Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} Heusler alloy layers

    SciTech Connect

    Hirohata, Atsufumi; Izumida, Keisuke; Ishizawa, Satoshi; Nakayama, Tadachika; Sagar, James

    2014-05-07

    We have fabricated and investigated IrMn{sub 3}/Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} stacks to meet the criteria for future spintronic device applications which requires low-temperature crystallisation (<250 °C) and a large exchange bias H{sub ex} (>500 Oe). Such a system would form the pinned layer in spin-valve or tunnel junction applications. We have demonstrated that annealing at 300 °C which can achieve crystalline ordering in the Co{sub 2}FeAl{sub 0.5}Si{sub 0.5} layer giving ∼80% of the predicted saturation magnetisation. We have also induced an exchange bias of ∼240 Oe at the interface. These values are close to the above criteria and confirm the potential of using antiferromagnet/Heusler-alloy stacks in current Si-based processes.

  16. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys.

    PubMed

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  17. Tuning exchange bias by Co doping in Mn₅₀Ni{sub 41–x}Sn₉Co{sub x} melt-spun ribbons

    SciTech Connect

    Zhao, D. W.; Li, G. K.; Wang, S. Q.; Ma, L. Zhen, C. M.; Hou, D. L.; Wang, W. H.; Liu, E. K.; Chen, J. L.; Wu, G. H.

    2014-09-14

    In Mn₅₀Ni{sub 41–x}Sn₉Co{sub x} ribbons, the exchange bias field is very sensitive to the Co content. Based on both theoretical and experimental studies, it has been found that with increasing Co content, the pinned phase (ferromagnetic phase) remains almost unchanged while the pinning phase is changed from a canonical spin glass to a cluster spin glass and finally to a ferromagnetic phase. Changing the Co content in Mn₅₀Ni{sub 41–x}Sn₉Co{sub x} alloys has been proven to be an effective way of tuning the magnetic anisotropy and the phase structure of the pinning phase. With different Co contents, a continuous tuning of the exchange bias field from 345 Oe to 3154 Oe is realized.

  18. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    PubMed Central

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-01-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance. PMID:27478090

  19. Magnetic stability under magnetic cycling of MgO-based magnetic tunneling junctions with an exchange-biased synthetic antiferromagnetic pinned layer

    NASA Astrophysics Data System (ADS)

    Hao, Qiang; Reid, Cameron; Xiao, Gang; Chan, Hon Ming

    2016-02-01

    We investigate the magnetic stability and endurance of MgO-based magnetic tunnel junctions (MTJs) with an exchange-biased synthetic antiferromagnetic (SAF) pinned layer. When a uniaxially cycling switching field is applied along the easy axis of the free magnetic layer, the magnetoresistance varies only by 1.7% logarithmically with the number of cycles, while no such change appears in the case of a rotating field. This observation is consistent with the effect of the formation and motion of domain walls in the free layer, which create significant stray fields within the pinned hard layer. Unlike in previous studies, the decay we observed only occurs during the first few starting cycles (<20), at which point there is no further variance in all performance parameters up to 107 cycles. Exchange-biased SAF structure is ideally suited for solid-state magnetic sensors and magnetic memory devices.

  20. Large exchange bias enhancement in (Pt(or Pd)/Co)/IrMn/Co trilayers with ultrathin IrMn thanks to interfacial Cu dusting

    SciTech Connect

    Vinai, G.; Moritz, J.; Bandiera, S.; Prejbeanu, I. L.; Dieny, B.

    2014-04-21

    The magnitude of exchange bias (H{sub ex}) at room temperature can be significantly enhanced in IrMn/Co and (Pt(or Pd)/Co)/IrMn/Co structures thanks to the insertion of an ultrathin Cu dusting layer at the IrMn/Co interface. The combination of trilayer structure and interfacial Cu dusting leads to a three-fold increase in H{sub ex} as compared to the conventional IrMn/Co bilayer structure, with an increased blocking temperature (T{sub B}) and a concave curvature of the temperature dependence H{sub ex}(T), ideal for improved Thermally Assisted-Magnetic Random Access Memory storage layer. This exchange bias enhancement is ascribed to a reduction of the spin frustration at the IrMn/Co interface thanks to interfacial Cu addition.

  1. Enhanced exchange bias and improved ferromagnetic properties in Permalloy-BiFe0.95Co0.05O3 core-shell nanostructures

    NASA Astrophysics Data System (ADS)

    Javed, K.; Li, W. J.; Ali, S. S.; Shi, D. W.; Khan, U.; Riaz, S.; Han, X. F.

    2015-12-01

    Hybrid core-shell nanostructures consisting of permalloy (Ni80Fe20) and multiferroic(BiFeO3, BFO/BiFe0.95Co0.05O3, BFC) materials were synthesized by a two-step method, based on wet chemical impregnation and subsequent electrodeposition within porous alumina membranes. Structural and magnetic characterizations have been done to investigate doping effect on magnetic properties and exchange bias. The magnetometry analysis revealed significant enhancements of the exchange bias and coercivity in NiFe-BFC core-shell nanostructures as compared with NiFe-BFO core-shell nanostructures. The enhancements can be attributed to the effective reduction of ferromagnet domain sizes between adjacent layers of core-shell structure. It indicates that it is possible to improve properties of multiferroic composites by site-engineering method. Our approach opens a pathway to obtain optimized nanostructured multiferroic composites exhibiting tunable magnetic properties.

  2. Giant spontaneous exchange bias triggered by crossover of superspin glass in Sb-doped Ni50Mn38Ga12 Heusler alloys

    NASA Astrophysics Data System (ADS)

    Tian, Fanghua; Cao, Kaiyan; Zhang, Yin; Zeng, Yuyang; Zhang, Rui; Chang, Tieyan; Zhou, Chao; Xu, Minwei; Song, Xiaoping; Yang, Sen

    2016-08-01

    A spontaneous exchange bias (SEB) discovered by Wang et al. [Phys. Rev. Lett. 106 (2011) 077203.] after zero-field cooling (ZFC) has attracted recent attention due to its interesting physics. In this letter, we report a giant SEB tuned by Sb-doping in Ni50Mn38Ga12-xSbx Heusler alloys. Such an SEB was switched on below the blocking temperature of approximately 50 K. The maximum exchange bias HE can arrive at 2930 Oe in a Ni50Mn38Ga10Sb2 sample after ZFC to 2 K. Further studies showed that this SEB was attributable to interaction of superspin glass (SSG) and antiferromagnetic matix, which was triggered by the crossover of SSG from canonical spin glass to a cluster spin glass. Our results not only explain the underlying physics of SEB, but also provide a way to tune and control the SEB performance.

  3. 78 FR 33233 - Patient Protection and Affordable Care Act; Establishment of Exchanges and Qualified Health Plans...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-04

    ... Health Plans; Exchange Standards for Employers, 77 FR 18310 (March 27, 2012) (to be codified at 45 CFR... Payment Parameters for 2014, 78 FR 15410 (March 11, 2013) (to be codified at 45 CFR parts 153, 155, 156... Health Plans; Small Business Health Options Program, 77 FR 15553 (March 11, 2013) (to be codified at...

  4. 76 FR 41865 - Patient Protection and Affordable Care Act; Establishment of Exchanges and Qualified Health Plans

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-15

    ... Systems CHIP Children's Health Insurance Program CMS Centers for Medicare & Medicaid Services DOL U.S... relating to Exchanges, published in the Federal Register on August 3, 2010 (75 FR 45584). Second, ] Initial... March 14, 2011 (76 FR 13553). Fourth, two proposed regulations, including this one, are published...

  5. Study of angular dependence of exchange bias and misalignment in uniaxial and unidirectional anisotropy in NiFe(111)/FeMn(111)/CoFeB(amorphous) stack

    NASA Astrophysics Data System (ADS)

    Singh, Braj Bhusan; Chaudhary, Sujeet

    2015-07-01

    We report the investigation of the in-plane azimuthal angular dependence of the magnetization reversal in the ion beam sputtered exchanged biased NiFe(111)/FeMn(111)/CoFeB(amorphous) stack. Compared to the as-deposited case, the magnetic annealing resulted in 3 fold enhancement in exchange bias but decrease in coercivity. The observed cosine dependence of exchange biased CoFeB layer on the in-plane azimuthal angle of applied field is corroborated with Meiklejohn and Bean model. The training effect associated with the exchange bias showed unconventional increase in coercivity after first cycle of hysteresis loop, while the exchange bias decreases sharply, and for subsequent cycles the exchange bias follows the empirical relation based on the energy dissipation in the AF layer. The ferromagnetic resonance (FMR) measurements also exhibited the in-plane azimuthal angle dependence of the magnetic resonance field indicating that the uniaxial and unidirectional anisotropies are not collinear, although they lie in the same plane. However, no misalignment between the unidirectional anisotropy and the exchange bias direction is observed. The misalignment angle between the uniaxial and unidirectional anisotropy, as measured by FMR, is found to be 10° and 14° for CoFeB and NiFe, respectively. This misalignment is attributed to the interface roughness as revealed by x-ray reflectance measurements.

  6. Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization.

    PubMed

    Chen, Chih-Jung; Chiang, Ray-Kuang; Kamali, Saeed; Wang, Sue-Lein

    2015-09-14

    Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ∼4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (H(E)), an enhanced coercivity field (H(C)), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of H(E) was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (T(N)) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy.

  7. Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization.

    PubMed

    Chen, Chih-Jung; Chiang, Ray-Kuang; Kamali, Saeed; Wang, Sue-Lein

    2015-09-14

    Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ∼4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (H(E)), an enhanced coercivity field (H(C)), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of H(E) was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (T(N)) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy. PMID:26243163

  8. Exchange bias effect in Au-Fe3O4 dumbbell nanoparticles induced by the charge transfer from gold

    SciTech Connect

    Feygenson, Mikhail; Bauer, John C; Gai, Zheng; Marques, Carlos; Aronson, Meigan C.; Teng, Xiaowei; Su, Dong; Stanic, Vesna; Urban, Volker S; Kevin, Beyer; Dai, Sheng

    2015-08-10

    We have studied the origin of the exchange bias effect in the Au-Fe3O4 dumbbell nanoparticles in two samples with different sizes of the Au seed nanoparticles (4.1 and 2.7 nm) and same size of Fe3O4 nanoparticles (9.8 nm). The magnetization, small-angle neutron scattering, synchrotron x-ray diffraction and scanning transmission electron microscope measurements determined the antiferromagnetic FeO wüstite phase within Fe3O4 nanoparticles, originating at the interface with the Au nanoparticles. The interface between antiferromagnetic FeO and ferrimagnetic Fe3O4 is giving rise to the exchange bias effect. The strength of the exchange bias fields depends on the interfacial area and lattice mismatch between both phases. We propose that the charge transfer from the Au nanoparticles is responsible for a partial reduction of the Fe3O4 into FeO phase at the interface with Au nanoparticles. The Au-O bonds are formed across the interface to accommodate an excess of oxygen released during the reduction of magnetite.

  9. Establishing Porosity Gradients within Metal-Organic Frameworks Using Partial Postsynthetic Ligand Exchange.

    PubMed

    Liu, Chong; Zeng, Chenjie; Luo, Tian-Yi; Merg, Andrea D; Jin, Rongchao; Rosi, Nathaniel L

    2016-09-21

    Crystalline 3-D materials bearing interlinked domains of differential porosity and functionality offer the potential for organizing and shuttling molecular and nanoscale matter to specific locations within 3-D space. Here, we present methods for creating prototype MOF materials that have such structural features. Specifically, the process of pore expansion via ligand exchange was studied for an isoreticular series of mesoporous MOFs based on bMOF-100. It was found that pore expansion occurs incrementally in small steps and that it proceeds gradually in an "outside→in" fashion within individual crystals. The ligand exchange reaction can be terminated prior to complete crystal conversion to yield intermediate product MOFs, denoted bMOF-100/102 and bMOF-102/106, which bear descending porosity gradients from the crystal periphery to the crystal core. As a proof of concept, size-sensitive incorporation of a gold-thiolate nanocluster, Au133(SR)52, selectively in the bMOF-102/106 crystal periphery region was accomplished via cation exchange. These new methods open up the possibility of controlling molecular organization and transport within porous MOF materials. PMID:27593173

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

    PubMed

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

    2015-10-01

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

  11. Positive to negative zero-field cooled exchange bias in La0.5Sr0.5Mn0.8Co0.2O3 ceramics

    PubMed Central

    Shang, Cui; Guo, Shaopu; Wang, Ruilong; Sun, Zhigang; Xiao, Haibo; Xu, Lingfang; Yang, Changping; Xia, Zhengcai

    2016-01-01

    Exchange bias effect obtained after zero-field cooling from unmagnetized state usually exhibits a shift of hysteresis loop negative to the direction of the initial magnetic field, known as negative zero-field cooled exchange bias. Here, positive zero-field cooled exchange bias is reported in La0.5Sr0.5Mn0.8Co0.2O3 ceramics. In addition, a transition from positive to negative exchange bias has been observed with increasing initial magnetization field and measurement temperature. Based on a simple spin bidomain model with variable interface, two type of interfacial spin configuration formed during the initial magnetization process are proposed to interpret the observed phenomenon. PMID:27168382

  12. Positive to negative zero-field cooled exchange bias in La0.5Sr0.5Mn0.8Co0.2O3 ceramics.

    PubMed

    Shang, Cui; Guo, Shaopu; Wang, Ruilong; Sun, Zhigang; Xiao, Haibo; Xu, Lingfang; Yang, Changping; Xia, Zhengcai

    2016-01-01

    Exchange bias effect obtained after zero-field cooling from unmagnetized state usually exhibits a shift of hysteresis loop negative to the direction of the initial magnetic field, known as negative zero-field cooled exchange bias. Here, positive zero-field cooled exchange bias is reported in La0.5Sr0.5Mn0.8Co0.2O3 ceramics. In addition, a transition from positive to negative exchange bias has been observed with increasing initial magnetization field and measurement temperature. Based on a simple spin bidomain model with variable interface, two type of interfacial spin configuration formed during the initial magnetization process are proposed to interpret the observed phenomenon. PMID:27168382

  13. 77 FR 31513 - Patient Protection and Affordable Care Act; Establishment of Exchanges and Qualified Health Plans...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-29

    ... HUMAN SERVICES 45 CFR Parts 155, 156, and 157 RIN 0938-AQ67 Patient Protection and Affordable Care Act... Federal Register on March 27, 2012, entitled ``Patient Protection and Affordable Care Act; Establishment... rule regarding the codification of section 1413(c) of the Affordable Care Act. To align the...

  14. Inversion of exchange bias and complex magnetization reversal in full-nitride epitaxial γ‧-Fe4N/CoN bilayers

    NASA Astrophysics Data System (ADS)

    Li, Z. R.; Mi, W. B.; Wang, X. C.; Bai, H. L.

    2015-04-01

    Exchange bias has been observed in the full-nitride epitaxial γ‧-Fe4N/CoN bilayers. With the increase of temperature, the sign of exchange bias (EB) is inverse, which is independent on the cooling field and training effect. This novel behavior appears in the bilayers with different CoN and γ‧-Fe4N thicknesses. The inversion of EB sign not only occurs at low temperatures, but also takes place even at 200 K for the 10 and 12 nm thick CoN layer. With the decreased γ‧-Fe4N layer thickness, the inversion temperature of EB sign shows a roughly increased tendency. For the bilayer with a 4 nm-thick γ‧-Fe4N, the interfacial magnetization reversal presents a complex trend, which is considered as the combined actions of the disordered ferromagnetic spins and various competed magnetic structures. This new manifestation of EB has been discussed in terms of the complicated interfacial spin structures and frustration effects due to the competition between the ferromagnetic and antiferromagnetic exchange interactions at the interface.

  15. Microscopic model for exchange bias from grain-boundary disorder in a ferromagnet/antiferromagnet thin film with a nanocrystalline microstructure

    SciTech Connect

    Cortie, D. L.; Biternas, A. G.; Chantrell, R. W.; Wang, X. L.; Klose, F.

    2014-07-21

    Monte Carlo spin simulations were coupled to a Voronoi microstructure-generator to predict the magnitude and behavior of exchange bias in a ferromagnet/antiferromagnet (AF) thin film bilayer with a nanocrystalline microstructure. Our model accounts for the effects of irregular grain-shapes, finite-sized particles, and the possible presence of local random-fields originating from the antiferromagnet's grain-boundary regions. As the grain-boundary represents a crystal-structure distortion, we model the local effect on the exchange constants in the Gaussian approximation which can cause regions resembling a spin glass confined to an unusual 2D topology. Although an ensemble of completely disconnected AF grains isolated by non-magnetic barriers provides a small exchange bias, the introduction of a spin-glass network at the boundaries causes a four-fold enhancement in the magnitude of the loop-shift. This implies the importance of local grain-boundary behavior in defect-engineered antiferromagnets.

  16. EXCHANGE

    SciTech Connect

    Boltz, J.C.

    1992-09-01

    EXCHANGE is published monthly by the Idaho National Engineering Laboratory (INEL), a multidisciplinary facility operated for the US Department of Energy (DOE). The purpose of EXCHANGE is to inform computer users about about recent changes and innovations in both the mainframe and personal computer environments and how these changes can affect work being performed at DOE facilities.

  17. Synthesis and controllable oxidation of monodisperse cobalt-doped wüstite nanoparticles and their core-shell stability and exchange-bias stabilization

    NASA Astrophysics Data System (ADS)

    Chen, Chih-Jung; Chiang, Ray-Kuang; Kamali, Saeed; Wang, Sue-Lein

    2015-08-01

    Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ~4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (HE), an enhanced coercivity field (HC), and a pronounced vertical shift, thus indicating the presence of a strong exchange bias coupling effect. More importantly, the onset temperature of HE was found to be higher than 200 K, which suggests that cobalt doping increases the Néel temperature (TN) of the CWT core. In general, the results show that the homogeneous dispersion of Co in iron precursors improves the stability of the final CWT nanoparticles. Moreover, the CoFe2O4 shells formed following oxidation increase the oxidation resistance of the CWT cores and enhance their anisotropy energy.Cobalt-doped wüstite (CWT), Co0.33Fe0.67O, nanoparticles were prepared via the thermal decomposition of CoFe2-oleate complexes in organic solvents. A controllable oxidation process was then performed to obtain Co0.33Fe0.67O/CoFe2O4 core-shell structures with different core-to-shell volume ratios and exchange bias properties. The oxidized core-shell samples with a ~4 nm CoFe2O4 shell showed good resistance to oxygen transmission. Thus, it is inferred that the cobalt ferrite shell provides a better oxidation barrier performance than magnetite in the un-doped case. The hysteresis loops of the oxidized 19 nm samples exhibited a high exchange bias field (HE), an enhanced coercivity field (HC), and a pronounced vertical shift, thus

  18. Establishing a Markerless Genetic Exchange System for Methanosarcina mazei Strain Gö1 for Constructing Chromosomal Mutants of Small RNA Genes

    PubMed Central

    Ehlers, Claudia; Jäger, Dominik; Schmitz, Ruth A.

    2011-01-01

    A markerless genetic exchange system was successfully established in Methanosarcina mazei strain Gö1 using the hpt gene coding for hypoxanthine phosphoribosyltransferase. First, a chromosomal deletion mutant of the hpt gene was generated conferring resistance to the purine analog 8-aza-2,6-diaminopurine (8-ADP). The nonreplicating allelic exchange vector (pRS345) carrying the pac-resistance cassette for direct selection of chromosomal integration, and the hpt gene for counterselection was introduced into this strain. By a pop-in and ultimately pop-out event of the plasmid from the chromosome, allelic exchange is enabled. Using this system, we successfully generated a M. mazei deletion mutant of the gene encoding the regulatory non-coding RNA sRNA154. Characterizing M. mazeiΔsRNA154 under nitrogen limiting conditions demonstrated differential expression of at least three cytoplasmic proteins and reduced growth strongly arguing for a prominent role of sRNA154 in regulation of nitrogen fixation by posttranscriptional regulation. PMID:21941461

  19. Patient Protection and Affordable Care Act; establishment of the multi-state plan program for the Affordable Insurance Exchanges.

    PubMed

    2013-03-11

    The U.S. Office of Personnel Management (OPM) is issuing a final regulation establishing the Multi-State Plan Program (MSPP) pursuant to the Patient Protection and Affordable Care Act, as amended by the Health Care and Education Reconciliation Act of 2010, referred to collectively as the Affordable Care Act. Through contracts with OPM, health insurance issuers will offer at least two multi-State plans (MSPs) on each of the Affordable Insurance Exchanges (Exchanges). One of the issuers must be non-profit. Under the law, an MSPP issuer may phase in the States in which it offers coverage over 4 years, but it must offer MSPs on Exchanges in all States and the District of Columbia by the fourth year in which the MSPP issuer participates in the MSPP. This rule aims to balance adhering to the statutory goals of MSPP while aligning its standards to those applying to qualified health plans to promote a level playing field across health plans.

  20. Thermally driven asymmetric responses of grains versus spin-glass related distributions of blocking temperature in exchange biased Co/IrMn bilayers

    SciTech Connect

    Baltz, V.

    2013-02-11

    Controlling ferromagnetic/antiferromagnetic blocking temperatures in exchange biased based devices appears crucial for applications. The blocking temperature is ascribed to the ability of both antiferromagnetic grains and interfacial spin-glass-like phases to withstand ferromagnetic magnetization reversal. To better understand the respective contributions of grains versus spin-glass, blocking temperature distributions were measured after various thermal treatments for cobalt/iridium-manganese bilayers. The high-temperature contribution linked to antiferromagnetic grains shifts towards lower temperatures above a threshold thermal annealing. In contrast, the occurrence and evolution of training effects for the low-temperature contribution only agree with its inferred interfacial spin-glass-like origin.

  1. Lamellar magnetism and exchange bias in billion-year-old titanohematite with nanoscale ilmenite exsolution lamellae: I. Mineral and magnetic characterization

    NASA Astrophysics Data System (ADS)

    McEnroe, Suzanne A.; Robinson, Peter; Miyajima, Nobuyoshi; Fabian, Karl; Dyar, Darby; Sklute, Elizabeth

    2016-07-01

    Recent high-resolution aeromagnetic surveys in South Norway have revealed numerous remanent anomalies over Mesoproterozoic metamorphic rocks. Studies on the nature of the minerals that are the remanent carriers has led to discoveries of titanohematite samples with unusual magnetic properties caused by nanoscale exsolution lamellae with their related lamellar magnetism. Here we focus on a rock unit dominated by quartz-plagioclase-biotite granulite containing titanohematite grains with a strong lattice-preferred orientation parallel to regional foliation. When samples with their natural remanent magnetization (NRM), acquired nearly 1 billion years ago, are cooled to 10 K and hysteresis loops measured, these loops show bi-modal exchange bias caused by the magnetism induced within the ilmenite by antiferromagnetic coupling with the adjacent lamellar NRM. By contrast when the samples are cooled in a strong magnetic field (1.5 Tesla), this results in unimodal lamellar magnetism, and, below the TN of ilmenite it adopts a consistent negative orientation, giving rise to unimodal negative exchange bias of >500 mT. The results presented here cover the chemical and magnetic properties, Mossbauer results and transmission electron microscopy of the titanohematite and ilmenite lamellae. Initial magnetic experiments indicated the shifts found in the exchange-bias experiments were directly related to the orientation of the sample to the applied field and the initial state of the NRM. In most samples with these unusual magnetic properties, ilmenite lamellae could not be seen in an optical or a scanning electron microscope. However magnetic experiments gave proof of the presence of ilmenite, later confirmed by Mössbauer spectroscopy. Several attempts were made to identify ilmenite in TEM studies, finally successful in showing ilmenite lamellae parallel to (001) of hematite with thicknesses ˜1.2 to 1.7 nm and aspect ratios 7-13. Here we compare new TEM images and the magnetic

  2. Observation of giant exchange bias in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy

    SciTech Connect

    Sharma, Jyoti; Suresh, K. G.

    2015-02-16

    We report a giant exchange bias (EB) field of 3520 Oe in bulk Mn{sub 50}Ni{sub 42}Sn{sub 8} Heusler alloy. The low temperature magnetic state of the martensite phase has been studied by DC magnetization and AC susceptibility measurements. Frequency dependence of spin freezing temperature (T{sub f}) on critical slowing down relation and observation of memory effect in zero field cooling mode confirms the super spin glass (SSG) phase at low temperatures. Large EB is attributed to the strong exchange coupling between the SSG clusters formed by small regions of ferromagnetic order embedded in an antiferromagnetic (AFM) matrix. The temperature and cooling field dependence of EB have been studied and related to the change in unidirectional anisotropy at SSG/AFM interface. The training effect also corroborates with the presence of frozen (SSG) moments at the interface and their role in EB.

  3. Effect of ball milling and thermal treatment on exchange bias and magnetocaloric properties of Ni48Mn39.5Sn10.5Al2 ribbons

    NASA Astrophysics Data System (ADS)

    Czaja, P.; Przewoźnik, J.; Fitta, M.; Bałanda, M.; Chrobak, A.; Kania, B.; Zackiewicz, P.; Wójcik, A.; Szlezynger, M.; Maziarz, W.

    2016-03-01

    The combined effect of ball milling and subsequent heat treatment on microstructure, magnetic, magnetocaloric and exchange bias properties of Ni48Mn39.5Sn10.5Al2 ribbons is reported. The annealing treatment results in the increase of the critical martensitic transformation temperature. The magnetic entropy change ΔSM of the order of 7.9 and -2.3 J kg K-1 for the annealed 50-32 μm powder fraction is determined. This is less than in the as melt spun ribbon but appears at a considerably higher temperature. At the same time EB is decreased due to annealing treatment. This decrease is attributed to the strengthened ferromagnetic exchange coupling due heat induced stress and structural relaxation.

  4. Exchange bias in Fe/Fe{sub 3}O{sub 4} core-shell magnetic nanoparticles mediated by frozen interfacial spins.

    SciTech Connect

    Ong, Q. K.; Wei, A.; Lin, X.-M.; Center for Nanoscale Materials; Purdue Univ.

    2009-10-01

    The magnetization curves of monodisperse Fe/Fe{sub 3}O{sub 4} core-shell and Fe{sub 3}O{sub 4} hollow-shell nanoparticles reveal an unusual exchange-bias effect. Hysteresis measurements of core-shell particles at 5 K after field cooling exhibit a large loop shift associated with unidirectional anisotropy whereas Fe{sub 3}O{sub 4} hollow-shell nanoparticles support much smaller shifts. Both core-shell and hollow-shell particles exhibit sharp demagnetization jumps at low fields associated with a sudden switching of shell moments. Temperature-dependent magnetization of core-shell particles at high fields shows a deviation between field-cooled and zero-field-cooled curves below 30 K, suggesting the presence of frozen spins at the interface. These frozen interfacial spins play an important role in mediating the exchange coupling between the ferromagnetic core and ferrimagnetic shell.

  5. Amorphous FeCoSiB for exchange bias coupled and decoupled magnetoelectric multilayer systems: Real-structure and magnetic properties

    SciTech Connect

    Hrkac, V.; Strobel, J.; Kienle, L.; Lage, E.; Köppel, G.; McCord, J.; Quandt, E.; Meyners, D.

    2014-10-07

    The effect of field annealing for exchanged biased multilayer films is studied with respect to the resultant structural and magnetic film properties. The presented multilayer stacks comprise repeating sequences of Ta/Cu/(1 1 1) textured antiferromagnetic Mn₇₀Ir₃₀ /amorphous ferromagnetic Fe₇₀.₂Co₇.₈Si₂B₁₀. Within the ferromagnetic layers crystalline filaments are observed. An additional Ta layer between the antiferromagnet and ferromagnet is used in order to investigate and separate the influence of the common Mn₇₀Ir₃₀/Fe₇₀.₂Co₇.₈Si₁₂B₁₀ interface on the occurring filaments and structural changes. In situ and ex situ transmission electron microscopy is used for a comprehensive structure characterization of multilayer stacks for selected temperature stages. Up to 250 °C, the multilayers are structurally unaltered and preserve the as-deposited condition. A deliberate increase to 350 °C exhibits different crystallization processes for the films, depending on the presence of crystal nuclei within the amorphous ferromagnetic layer. The influence of volume-to-surface ratio of the multilayer stacks to the crystallization process is emphasized by the comparison of in situ and ex situ investigations as the respective specimen thickness is changed. Complementary magnetic studies reveal a defined exchange bias obtained at the first annealing step and a decrease of total anisotropy field with partial crystallization after the subsequent annealing at 350 °C.

  6. Brillouin Light Scattering study of the rotatable magnetic anisotropy in exchange biased bilayers of Ni81 Fe19 Ir20 Mn80

    NASA Astrophysics Data System (ADS)

    Rodríguez, Roberto; Oliveira, Alexandre; Estrada, Francisco; Santos, Obed; Azevedo, Antonio; Rezende, Sergio

    It is known that when a ferromagnet (FM) is in atomic contact with an antiferromagnet (AF) the exchange coupling between the FM and AF spins at the interface induces a unidirectional anisotropy in the ferromagnetic film. This effect is known as exchange bias (EB). Despite the large amount of research on this topic there are still several aspects of the EB mechanism that are not well understood. One of this aspects is the origin of the rotatable anisotropy in polycrystalline AFs. By means of Brillouin Light Scattering (BLS) measurements, we investigated the dependence of the rotatable anisotropy field HRA and exchange field HE with the magnitude of the external magnetic field (Ho) in FM/AM bilayers of Ni81Fe19(10nm)/Ir20Mn80(tAF) . We developed an algorithm to numerically fit the in-plane angular dependence of the magnon frequency, at a fixed value of Ho measured by BLS. From the fit parameters we were able to investigate HRA and HE dependency on Ho. The results reveal that HRA value depends on Ho, so we argue that AF grain distribution at the interface is partially modified by the applied field strength. Contrary to this, the relation between HE and Ho is not straightforward, remaining constant at high values of Ho.

  7. Patient Protection and Affordable Care Act; establishment of exchanges and qualified health plans; exchange standards for employers. Final rule, Interim final rule.

    PubMed

    2012-03-27

    This final rule will implement the new Affordable Insurance Exchanges ("Exchanges"), consistent with title I of the Patient Protection and Affordable Care Act of 2010 as amended by the Health Care and Education Reconciliation Act of 2010, referred to collectively as the Affordable Care Act. The Exchanges will provide competitive marketplaces for individuals and small employers to directly compare available private health insurance options on the basis of price, quality, and other factors. The Exchanges, which will become operational by January 1, 2014, will help enhance competition in the health insurance market, improve choice of affordable health insurance, and give small businesses the same purchasing clout as large businesses.

  8. Patient Protection and Affordable Care Act; establishment of exchanges and qualified health plans; exchange standards for employers. Final rule, Interim final rule.

    PubMed

    2012-03-27

    This final rule will implement the new Affordable Insurance Exchanges ("Exchanges"), consistent with title I of the Patient Protection and Affordable Care Act of 2010 as amended by the Health Care and Education Reconciliation Act of 2010, referred to collectively as the Affordable Care Act. The Exchanges will provide competitive marketplaces for individuals and small employers to directly compare available private health insurance options on the basis of price, quality, and other factors. The Exchanges, which will become operational by January 1, 2014, will help enhance competition in the health insurance market, improve choice of affordable health insurance, and give small businesses the same purchasing clout as large businesses. PMID:22479737

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  10. Exchange bias of CoO1-δ/(NiFe,Fe) system with blocking temperature beyond Néel temperature of bulk CoO

    NASA Astrophysics Data System (ADS)

    Ding, S. L.; Wu, R.; Fu, J. B.; Wen, X.; Du, H. L.; Liu, S. Q.; Han, J. Z.; Yang, Y. C.; Wang, C. S.; Zhou, D.; Yang, J. B.

    2015-10-01

    The exchange bias effects in pulsed laser deposited CoO1-δ/(NiFe,Fe) bilayers were investigated. An anomalously high blocking temperature (TB) of 325 K was obtained for the as-deposited CoO1-δ/ferromagnet bilayers, which is 33 K higher than the Néel temperature of the bulk CoO (TN = 292 K). The amount of oxygen vacancies δ in the CoO1-δ film can be controlled by a post-annealing treatment in the O2 atmosphere. The TB of the CoO1-δ/ferromagnet bilayers increases with an increasing δ from δ = 0 to δ = 0.16. Our results indicate that the high TB of CoO1-δ/ferromagnet bilayers originates from the enhancement of the magnetic interaction in the CoO1-δ layer owing to O2- vacancies.

  11. Exchange bias and magnetic properties induced by intrinsic structural distortion in CaMn{sub 3}O{sub 6} nanoribbons

    SciTech Connect

    Yu, J. Y. Huang, K.; Wu, H. Y.; Feng, Y.; Tang, Z.; Zhang, L.; Wang, L.

    2014-01-13

    Single-crystalline CaMn{sub 3}O{sub 6} nanoribbons have been synthesized by a molten-salt method. To explore the origin of the magnetism of nanosized antiferromagnetic (AFM) manganites, a comparative study has been conducted for CaMn{sub 3}O{sub 6} (CMO-1) and post-growth vacuum annealed (CMO-2) nanoribbons. A lattice expansion resulting from oxygen release during vacuum annealing is observed. Correspondingly, AFM ordering in CMO-2 is further suppressed, and ferromagnetism and spin-glass (SG)-like behavior are significantly enhanced, which are presumed attributable to the intrinsic structural distortions induced by oxygen vacancies. In this case, side and surface effects are not decisive factors. In addition, this study provided observations of the exchange bias effect in manganite nanoribbons with an AFM-SG-like-ferromagnetic (FM) structure, as compared with the typical AFM-core-FM-shell.

  12. Dependence of BiFeO3 thickness on exchange bias in BiFeO3/ Co2FeAl multiferroic structures

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Zhang, D. L.; Wang, Y. H.; Miao, J.; Xu, X. G.; Jiang, Y.

    2011-01-01

    We have grown BiFeO3 (BFO) thin films with different thickness on Si/SiO2/Ti/Pt(111) substrates by pulsed laser deposition. Half-metallic Co2FeAl (CFA) films with a thickness of 5 nm were then grown on the BFO films by magnetron sputtering. Through the magnetic hysteresis loops of the BFO/CFA heterostructure, we observe a direct correlation between the thickness of the BFO film and exchange bias (EB) field. The EB field exhibits fluctuation behavior with a cyclical BFO thickness of 60 nm, which is close to the spiral modulation wavelength (62 nm) of BFO. It indicates the influence of spiral modulation on the EB in the BFO/CFA multiferroic structure.

  13. Phase separation and exchange biasing in the ferromagnetic IV-VI semiconductor Ge{sub 1-x}Mn{sub x}Te

    SciTech Connect

    Lechner, R. T.; Springholz, G.; Hassan, M.; Groiss, H.; Kirchschlager, R.; Stangl, J.; Hrauda, N.; Bauer, G.

    2010-07-12

    Ferromagnetic Ge{sub 1-x}Mn{sub x}Te grown by molecular beam epitaxy with Mn content of x{sub Mn}approx =0.5 is shown to exhibit a strong tendency for phase separation. At higher growth temperatures apart from the cubic Ge{sub 0.5}Mn{sub 0.5}Te, a hexagonal MnTe and a rhombohedral distorted Ge{sub 0.83}Mn{sub 0.17}Te phase is formed. This coexistence of antiferromagnetic MnTe and ferromagnetic Ge{sub 0.5}Mn{sub 0.5}Te results in magnetic exchange-bias effects.

  14. Temperature and thickness dependence of tunneling anisotropic magnetoresistance in exchange-biased Py/IrMn/MgO/Ta stacks

    NASA Astrophysics Data System (ADS)

    Reichlová, H.; Novák, V.; Kurosaki, Y.; Yamada, M.; Yamamoto, H.; Nishide, A.; Hayakawa, J.; Takahashi, H.; Maryško, M.; Wunderlich, J.; Marti, X.; Jungwirth, T.

    2016-07-01

    We investigate the thickness and temperature dependence of a series of Ni{}0.8Fe{}0.2/Ir{}0.2Mn{}0.8 bilayer samples with varying thickness ratio of the ferromagnet/antiferromagnet ({{t}}{{FM}}/{{t}}{{AFM}}) in order to explore the exchange coupling strengths in tunneling anisotropic magnetoresistance (TAMR) devices. Specific values of {{t}}{{FM}}/{{t}}{{AFM}} lead to four distinct scenarios with specific electric responses to moderate magnetic fields. The characteristic dependence of the measured TAMR signal on applied voltage allows us to confirm its persistence up to room temperature despite an overlapped contribution by a thermal magnetic noise.

  15. Coexistance of magnetoelectric effect and exchange bias in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film

    NASA Astrophysics Data System (ADS)

    Barman, Rahul; Kaur, Davinder

    2016-05-01

    In the present study structural, magnetic and ferroelectric properties of Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film, grown on LaNiO3 coated Si (100) substrate has been systematically investigated. Ni50.3Mn36.9Sb12.8 film exhibits L21 structure with preferred (220) orientation. The bottom LaNiO3 layer was implemented to favor the growth of pervoskite BiFeO3 film with (l00) orientation. The shift in hysteresis loop up to 34 Oe from the origin was observed at 300 K which is mainly due to the coupling of FM-AFM spins at the interface. Besides the exchange bias effect, large coupling between ferromagnetic and ferroelectric order parameters was also found with maximum coupling sensitivity of 7.58 V/cm-Oe at 300K in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure thin film. The observed magneto-electric effect in this heterostructure is due to the transfer of strain from ferromagnetic shape memory alloy Ni50.3Mn36.9Sb12.8 layer to multiferroic BiFeO3 layer in the presence of magnetic field. Hence, coexistence of magneto-electric coupling and exchange bias in Ni50.3Mn36.9Sb12.8/BiFeO3 heterostructure make them a promising candidate for various multifunctional MEMS devices.

  16. Effect of L1{sub 2} ordering in antiferromagnetic Ir-Mn epitaxial layer on exchange bias of FePd films

    SciTech Connect

    Chang, Y. C.; Duh, J. G. E-mail: lin.yg@nsrrc.org.tw; Hsiao, S. N. E-mail: lin.yg@nsrrc.org.tw; Liu, S. H.; Su, S. H.; Chiu, K. F.; Hsieh, W. C.; Chen, S. K.; Lin, Y. G. E-mail: lin.yg@nsrrc.org.tw; Lee, H. Y.; Sung, C. K.

    2015-05-07

    Two series of samples of single-layer IrMn and IrMn/FePd bilayer films, deposited on a single-crystal MgO substrate at different IrMn deposition temperatures (T{sub s} = 300–700 °C), were investigated using magnetron sputtering. L1{sub 2} ordering was revealed for the 30 nm-thick IrMn epitaxial (001) films with T{sub s} ≥ 400 °C, determined by synchrotron radiation x-ray diffractometry (XRD). XRD results also provide evidence of the epitaxial growth of the IrMn films on MgO substrate. Increasing T{sub s} from 400 to 700 °C monotonically increases the ordering parameter of L1{sub 2} phases from 0.17 to 0.81. An in-plane exchange bias field (H{sub eb}) of 22 Oe is obtained in a 10 nm-thick FePd film that is deposited on the disordered IrMn films. As the L1{sub 2} ordering of the IrMn layers increases, the H{sub eb} gradually decreases to 0 Oe, meaning that the exchange bias behavior vanishes. The increased surface roughness, revealed by atomic force microscopy, of the epitaxial IrMn layers with increasing T{sub s} cannot be the main cause of the decrease in H{sub eb} due to the compensated surface spins regardless of the disordered and ordered (001) IrMn layers. The change of antiferromagnetic structure from the A1 to the L1{sub 2} phase was correlated with the evolution of H{sub eb}.

  17. Correlation of exchange bias with magneto-structural effects across the compensation temperature of Co(Cr1-xFex)2O4 (x = 0.05 and 0.075)

    NASA Astrophysics Data System (ADS)

    Kumar, Ram; Padam, R.; Rayaprol, S.; Siruguri, Vasudeva; Pal, D.

    2016-03-01

    A small amount of Fe (5% and 7.5%) substitution in the Cr-site of the multiferroic compound CoCr2O4 leads to a magnetization reversal. In these compounds, we report a sign change in the exchange bias across the compensation temperature, accompanied by a non-monotonic change in the local moments across the compensation temperature. Such non-monotonic change in the magnetic moments is triggered by a similar change in the lattice structure. We relate here the sign change of exchange bias with that of the crystalline energy of the lattice and the Zeeman energy term arising from the anti-site disorder.

  18. Shape anisotropy and exchange bias in magnetic flattened nanospindles with metallic/oxide core/shell structures.

    PubMed

    Mendoza-Reséndez, Raquel; Luna, Carlos

    2012-09-01

    A preliminary study of the magnetic phenomenology of Fe and Fe90Co10 nanospindles with axial ratio equal to 5 is presented. These nanospindles are constituted by single-domains single-crystals coated by oxide surface layer and assembled in chains into the nanospindle. The thermal dependence of the coercive field and the saturation magnetization in the temperature range from 4 K up to room temperature indicates that the coercive field is roughly proportional to the saturation magnetization (which follows the T3/2 Bloch law) at temperatures above the blocking temperature of the oxide. This suggests that the predominant source of magnetic anisotropy in this temperature range is the shape anisotropy. However, at temperatures below the oxide blocking temperature, the magnetic coupling between the spins of the oxide and the nanocrystals is produced at the interface. This exchange coupling enhances the effective anisotropy of the nanospindles and the coercive field increases more abruptly than the saturation of magnetization as temperature decreases.

  19. Griffiths phase, spin-phonon coupling, and exchange bias effect in double perovskite Pr{sub 2}CoMnO{sub 6}

    SciTech Connect

    Liu, Wenjie; Shi, Lei Zhou, Shiming; Zhao, Jiyin; Li, Yang; Guo, Yuqiao

    2014-11-21

    The ceramic Pr{sub 2}CoMnO{sub 6} of double perovskite structure is prepared by a solid-state reaction and the magnetic properties, phonon behaviors are studied in detail. Two ferromagnetic transitions at T{sub C1} ∼ 172 K and T{sub C2} ∼ 140 K are observed in the temperature-dependent magnetization curves, respectively. Furthermore, a detail analysis on the magnetic susceptibility reveals that a short-range ferromagnetic clustered state exists above T{sub C1}, which can be well described as the Griffiths phase with a well-defined Griffiths temperature T{sub G} ∼ 210 K. The presence of the B-site antisite defects is considered to contribute to the observed Griffiths singularity. Temperature-dependent Raman scattering experiment reveals an obvious softening of the phonon mode involving stretching vibrations of the (Co/Mn)O{sub 6} octahedra in FM temperature regions, indicating a close correlation between magnetism and lattice in Pr{sub 2}CoMnO{sub 6}. On the other hand, it is found that the phonon softening extends up to T{sub G}, which further confirms the preformation of the short-range ferromagnetic clusters up to T{sub G}. Moreover, the field-cooling magnetic hysteresis loop reveals that exchange bias phenomena is present, which is supposed to origin from the exchange coupling between Co/Mn ordered ferromagnetic phases with antiferromagnetic antiphase boundaries caused by the partially Co/Mn antisite disorders. These findings give a systematic understanding on the magnetic interaction in Pr{sub 2}CoMnO{sub 6} which is closely related to the lattice and atomic distribution, and add special interest for application of this material.

  20. Exchange bias and surface effects in bimagnetic CoO -core /Co0.5Ni0.5Fe2O4 -shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Lavorato, Gabriel; Winkler, Elin; Ghirri, Alberto; Lima, Enio; Peddis, Davide; Troiani, Horacio E.; Fiorani, Dino; Agostinelli, Elisabetta; Rinaldi, Daniele; Zysler, Roberto D.

    2016-08-01

    Bimagnetic nanoparticles have been proposed for the design of new materials with controlled properties, which requires a comprehensive investigation of their magnetic behavior due to multiple effects arising from their complex structure. In this work we fabricated bimagnetic core/shell nanoparticles formed by an ˜3 -nm antiferromagnetic (AFM) CoO core encapsulated within an ˜1.5 -nm ferrimagnetic (FiM) Co0.5Ni0.5Fe2O4 shell, aiming at studying the enhancement of the magnetic anisotropy and the surface effects of a ferrimagnetic oxide shell. The magnetic properties of as-synthesized and annealed samples were analyzed by ac and dc magnetization measurements. The results indicate that the magnetic response of the as-synthesized particles is governed by the superparamagnetic behavior of the interacting nanoaggregates of spins that constitute the disordered ferrimagnetic shell, whose total moments block at =49 K and collectively freeze in a superspin-glass-type state at =3 K. On the other hand, annealed nanoparticles are superparamagnetic at room temperature and behave as an exchange-coupled system below the blocking temperature =70 K, with enhanced coercivity HC(10 K) ˜14.6 kOe and exchange bias field HE B(10 K) ˜2.3 kOe, compared with the as-synthesized system where HC(10 K) ˜5.5 kOe and HE B(10 K) ˜0.8 kOe. Our results, interpreted using different models for thermally activated and surface relaxation processes, can help clarify the complex magnetic behavior of many core/shell and hollow nanoparticle systems.

  1. Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

    NASA Astrophysics Data System (ADS)

    Machavarapu, Ramudu; Jakob, Gerhard

    2015-03-01

    We report the effect of substrate temperature (TS) and Ar gas pressure (PD) on the martensitic transformations, magnetic and exchange bias (EB) properties in Heusler type Ni-Co-Mn-Sn epitaxial thin films. Martensitic transformation temperatures and EB fields at 5 K were found to increase with increasing TS. The observed maximum EB value of 320 Oe after field cooling in the film deposited at 650 ∘C is high among the values reported for Ni-Mn-Sn thin films which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AF) phases in the martensitic state. In the case of PD variation, with increase in PD, martensitic transformation temperatures were increased and a sharp transformation was observed in the film deposited at 0.06 mbar. Magnetization values at 5 K were higher for increasing PD. These observations are attributed to the compositional shift. EB effect is also present in these films. Microstructural features observed using atomic force microscopy (AFM) shows a fine twinning and reduced precipitation with increase in PD, which is also confirmed from the scanning electron microscopy (SEM) images. EB effects in both series were confirmed from the training effect. Target ageing effect has been observed in the films deposited before and after ninety days of time interval. This has been confirmed both on substrate temperature and Ar gas pressure variations.

  2. Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn0.85Fe0.15NiGe alloy

    NASA Astrophysics Data System (ADS)

    Dutta, P.; Pramanick, S.; Das, D.; Chatterjee, S.

    2016-09-01

    The magnetic and magneto-functional behavior of a Fe-doped MnNiGe alloy with nominal composition Mn0.85Fe0.15NiGe have been investigated in ambient as well as in high pressure conditions. The alloy undergoes a first order martensitic phase transition (MPT) around 200 K and also shows a large conventional magnetocaloric effect (MCE) ( Δ S∼ -21 J kg‑1 K‑1 for magnetic field (H) changing from 0–50 kOe) around the transition in ambient conditions. The application of external hydrostatic pressure (P) results in a shift in MPT towards the lower temperature and a clear decrease in the saturation moment of the alloy at 5 K. The peak value of MCE is also found to decrease with increasing external P (∼18 J kg‑1 K‑1 decrease in Δ S has been observed for P  =  12.5 kbar). The most interesting observation is the occurrence of the exchange bias effect (EBE) on application of external P. The competing ferromagnetic and antiferromagnetic interaction in the presence of external P plays the pivotal role towards the observation of P induced EBE.

  3. Hydrostatic pressure tuned magneto-structural transition and occurrence of pressure induced exchange bias effect in Mn0.85Fe0.15NiGe alloy

    NASA Astrophysics Data System (ADS)

    Dutta, P.; Pramanick, S.; Das, D.; Chatterjee, S.

    2016-09-01

    The magnetic and magneto-functional behavior of a Fe-doped MnNiGe alloy with nominal composition Mn0.85Fe0.15NiGe have been investigated in ambient as well as in high pressure conditions. The alloy undergoes a first order martensitic phase transition (MPT) around 200 K and also shows a large conventional magnetocaloric effect (MCE) ( Δ S˜ -21 J kg-1 K-1 for magnetic field (H) changing from 0-50 kOe) around the transition in ambient conditions. The application of external hydrostatic pressure (P) results in a shift in MPT towards the lower temperature and a clear decrease in the saturation moment of the alloy at 5 K. The peak value of MCE is also found to decrease with increasing external P (˜18 J kg-1 K-1 decrease in Δ S has been observed for P  =  12.5 kbar). The most interesting observation is the occurrence of the exchange bias effect (EBE) on application of external P. The competing ferromagnetic and antiferromagnetic interaction in the presence of external P plays the pivotal role towards the observation of P induced EBE.

  4. Magnetoresistance and exchange bias in high Mn content melt-spun Mn46Ni42Sn11Sb1 alloy ribbon

    NASA Astrophysics Data System (ADS)

    Qingxue, Huang; Fenghua, Chen; Mingang, Zhang; Xiaohong, Xu

    2016-05-01

    Highly textured Heusler alloy Mn46Ni42Sn11Sb1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic transformation (MT), and magnetoresistance (MR) properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 kOe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias (EB) effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon. Project supported by the National Basic Research Program of China (Grant No. 2012CB722801), the Postdoctoral Science Foundation of China (Grant No. 2015M571285), the National Natural Science Foundation of China (Grant No. 51401140), the Postdoctoral Research Station Foundation of Taiyuan University of Science and Technology, China (Grant Nos. 20142014, 20152041, and 20151082), the Natural Science Foundation of Shanxi Province, China (Grants Nos. 2015021019, 2015091011, and 2015081011), and the Key Team of Scientific and Technological Innovation of Shanxi Province, China (Grant No. 2013131009).

  5. Mixing antiferromagnets to tune NiFe-[IrMn/FeMn] interfacial spin-glasses, grains thermal stability, and related exchange bias properties

    NASA Astrophysics Data System (ADS)

    Akmaldinov, K.; Ducruet, C.; Portemont, C.; Joumard, I.; Prejbeanu, I. L.; Dieny, B.; Baltz, V.

    2014-05-01

    Spintronics devices and in particular thermally assisted magnetic random access memories require a wide range of ferromagnetic/antiferromagnetic (F/AF) exchange bias (EB) properties and subsequently of AF materials to fulfil diverse functionality requirements for the reference and storage. For the reference layer, large EB energies and high blocking temperature (TB) are required. In contrast, for the storage layer, mostly moderate TB are needed. One of the present issues is to find a storage layer with properties intermediate between those of IrMn and FeMn and in particular: (i) with a TB larger than FeMn for better stability at rest-T but lower than IrMn to reduce power consumption at write-T and (ii) with improved magnetic interfacial quality, i.e., with reduced interfacial glassy character for lower properties dispersions. To address this issue, the EB properties of F/AF based stacks were studied for various mixed [IrMn/FeMn] AFs. In addition to EB loop shifts, the F/AF magnetic interfacial qualities and the AF grains thermal stability are probed via measurements of the low- and high-temperature contributions to the TB distributions, respectively. A tuning of the above three parameters is observed when evolving from IrMn to FeMn via [IrMn/FeMn] repetitions.

  6. Tuning exchange bias in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles: Impacts of interface and surface spins

    SciTech Connect

    Khurshid, Hafsa E-mail: phanm@usf.edu Phan, Manh-Huong E-mail: phanm@usf.edu Mukherjee, Pritish; Srikanth, Hariharan E-mail: phanm@usf.edu

    2014-02-17

    A comparative study has been performed of the exchange bias (EB) effect in Fe/γ-Fe{sub 2}O{sub 3} core-shell nanoparticles with the same thickness of the γ-Fe{sub 2}O{sub 3} shell (∼2 nm) and the diameter of the Fe core varying from 4 nm to 11 nm. Transmission electron microscopy (TEM) and high-resolution TEM confirmed the high quality of the core-shell nanostructures. A systematic analysis of magnetization versus magnetic field measurements under zero-field-cooled and field-cooled regimes using the Meiklejohn-Bean model and deconvoluting superparamagnetic and paramagnetic contribution to the total magnetic moment Langevin function shows that there exists a critical particle size (∼10 nm), above which the spins at the interface between Fe and γ-Fe{sub 2}O{sub 3} contribute primarily to the EB, but below which the surface spin effect is dominant. Our finding yields deeper insight into the collective contributions of interface and surface spins to the EB in core-shell nanoparticle systems, knowledge of which is the key to manipulating EB in magnetic nanostructures for spintronics applications.

  7. Mixing antiferromagnets to tune NiFe-[IrMn/FeMn] interfacial spin-glasses, grains thermal stability, and related exchange bias properties

    SciTech Connect

    Akmaldinov, K.; Ducruet, C.; Portemont, C.; Joumard, I.; Prejbeanu, I. L.; Dieny, B.; Baltz, V.

    2014-05-07

    Spintronics devices and in particular thermally assisted magnetic random access memories require a wide range of ferromagnetic/antiferromagnetic (F/AF) exchange bias (EB) properties and subsequently of AF materials to fulfil diverse functionality requirements for the reference and storage. For the reference layer, large EB energies and high blocking temperature (T{sub B}) are required. In contrast, for the storage layer, mostly moderate T{sub B} are needed. One of the present issues is to find a storage layer with properties intermediate between those of IrMn and FeMn and in particular: (i) with a T{sub B} larger than FeMn for better stability at rest-T but lower than IrMn to reduce power consumption at write-T and (ii) with improved magnetic interfacial quality, i.e., with reduced interfacial glassy character for lower properties dispersions. To address this issue, the EB properties of F/AF based stacks were studied for various mixed [IrMn/FeMn] AFs. In addition to EB loop shifts, the F/AF magnetic interfacial qualities and the AF grains thermal stability are probed via measurements of the low- and high-temperature contributions to the T{sub B} distributions, respectively. A tuning of the above three parameters is observed when evolving from IrMn to FeMn via [IrMn/FeMn] repetitions.

  8. A CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction coupled to an in-plane exchange-biased magnetic layer

    SciTech Connect

    Zhu, M. Chong, H.; Vu, Q. B.; Vo, T.; Brooks, R.; Stamper, H.; Bennett, S.; Piccirillo, J.

    2015-05-25

    We report a stack structure which utilizes an in-plane exchange-biased magnetic layer to influence the coercivity of the bottom CoFeB layer in a CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction. By employing a thickness wedge deposition technique, we were able to study various aspects of this stack using vibrating sample magnetometer including: (1) the coupling between two CoFeB layers as a function of MgO thickness; and (2) the coupling between the bottom CoFeB and the in-plane magnetic layer as a function of Ta spacer thickness. Furthermore, modification of the bottom CoFeB coercivity allows one to measure tunneling magnetoresistance and resistance-area product (RA) of CoFeB/MgO/CoFeB in this pseudo-spin-valve format using current-in-plane-tunneling technique, without resorting to (Co/Pt){sub n} or (Co/Pd){sub n} multilayer pinning.

  9. Investigations on Ni-Co-Mn-Sn thin films: Effect of substrate temperature and Ar gas pressure on the martensitic transformations and exchange bias properties

    SciTech Connect

    Machavarapu, Ramudu Jakob, Gerhard

    2015-03-15

    We report the effect of substrate temperature (T{sub S}) and Ar gas pressure (P{sub D}) on the martensitic transformations, magnetic and exchange bias (EB) properties in Heusler type Ni-Co-Mn-Sn epitaxial thin films. Martensitic transformation temperatures and EB fields at 5 K were found to increase with increasing T{sub S}. The observed maximum EB value of 320 Oe after field cooling in the film deposited at 650 {sup ∘}C is high among the values reported for Ni-Mn-Sn thin films which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AF) phases in the martensitic state. In the case of P{sub D} variation, with increase in P{sub D}, martensitic transformation temperatures were increased and a sharp transformation was observed in the film deposited at 0.06 mbar. Magnetization values at 5 K were higher for increasing P{sub D}. These observations are attributed to the compositional shift. EB effect is also present in these films. Microstructural features observed using atomic force microscopy (AFM) shows a fine twinning and reduced precipitation with increase in P{sub D}, which is also confirmed from the scanning electron microscopy (SEM) images. EB effects in both series were confirmed from the training effect. Target ageing effect has been observed in the films deposited before and after ninety days of time interval. This has been confirmed both on substrate temperature and Ar gas pressure variations.

  10. A CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction coupled to an in-plane exchange-biased magnetic layer

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Chong, H.; Vu, Q. B.; Vo, T.; Brooks, R.; Stamper, H.; Bennett, S.; Piccirillo, J.

    2015-05-01

    We report a stack structure which utilizes an in-plane exchange-biased magnetic layer to influence the coercivity of the bottom CoFeB layer in a CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction. By employing a thickness wedge deposition technique, we were able to study various aspects of this stack using vibrating sample magnetometer including: (1) the coupling between two CoFeB layers as a function of MgO thickness; and (2) the coupling between the bottom CoFeB and the in-plane magnetic layer as a function of Ta spacer thickness. Furthermore, modification of the bottom CoFeB coercivity allows one to measure tunneling magnetoresistance and resistance-area product (RA) of CoFeB/MgO/CoFeB in this pseudo-spin-valve format using current-in-plane-tunneling technique, without resorting to (Co/Pt)n or (Co/Pd)n multilayer pinning.

  11. Origin of spin-glass and exchange bias in La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} nanoparticles

    SciTech Connect

    Silva, R. B. da; Araújo, J. H. de; Soares, J. M.; Machado, F. L. A.

    2014-03-21

    The structure and the magnetic properties of nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} with average particles size d in the range of 67-367 nm prepared by a sol-gel method were investigated in detail. The samples were characterized by X-ray diffraction, scanning electron microscopy, specific heat, Mössbauer spectroscopy, ac susceptibility, and magnetization measurements. Exchange bias with vertical magnetization shift was found in all samples. Charge ordering and antiferromagnetism were observed close to 200 K for large particles (d ≥ 304 nm) samples, while for particles with intermediated and smaller values (d ≤ 156 nm) a cluster-glass like behaviour and a short range charge ordering were seen near 115 K and 200 K, respectively. The spin-glass like and exchange bias behaviour in nanopowdered samples of La{sub 1∕3}Sr{sub 2∕3}FeO{sub 3−γ} are associated to compact Fe{sup 3+} antiferromagnetic (AF) clusters caused by an oxygen deficiency, which was found to be higher in the samples with the smallest average particles sizes. The effect of exchange bias and vertical magnetization shifts are explained by a simple model involving the interaction of one AF phase with a canted AF phase.

  12. Enhancement of exchange bias and training effect in ion-beam sputtered Fe{sub 46}Mn{sub 54}/Ni{sub 81}Fe{sub 19} bilayers

    SciTech Connect

    Fulara, Himanshu; Chaudhary, Sujeet Kashyap, Subhash C.; Granville, Simon

    2014-01-28

    We present a remarkable enhancement by 300% of the exchange-bias field at room temperature, without affecting the coercivity value, via optimum magnetic annealing (250 °C/3 kOe) in ion-beam sputtered FeMn(30 nm)/NiFe(10 nm) bilayers. This specific behavior has been attributed to a higher degree of γ-FeMn(111) orientation that offers more interfacial FeMn moments to get pinned with the moments of the adjacent NiFe layer. Unlike the absence of training effect at room temperature, a pronounced training effect and an accompanying magnetization reversal asymmetry are evidenced upon field cooling below 50 K due to the presence of biaxial exchange induced anisotropy across the interdiffused FeMn/NiFe interface. The present findings not only have technological significance but also are of relevance to the understanding of interfacial spin disorder and frustration in these exchange-biased systems.

  13. Photo-carrier control of exchange bias in BiFeO{sub 3}/La{sub 2/3}Sr{sub 1/3}MnO{sub 3} thin films

    SciTech Connect

    Sung, K. D.; Lee, T. K.; Park, Y. A.; Hur, N.; Jung, J. H.

    2014-06-23

    We report the facile control of exchange bias in BiFeO{sub 3}/La{sub 2/3}Sr{sub 1/3}MnO{sub 3} (BFO/LSMO) thin films on an SrTiO{sub 3} (STO) substrate using light irradiation. Illumination with weak red light (λ: 630 nm, intensity: ∼1 mW/cm{sup 2}) reduced the exchange bias field (H{sub E}) of BFO/LSMO from +30 Oe in the dark to −2 Oe with red light. In accompanying the decrease of H{sub E}, the resistance of BFO/LSMO significantly increased. These results were attributed to the reduction in the hole-doping ratio of LSMO and the weakened exchange coupling between Fe and Mn spins at the interface, resulting from photo-injected electrons from the STO substrate. Successive turning on/off of red light gives rise to cyclical change of corresponding H{sub E}, which should be useful for applications like photo-controlled tunneling magnetoresistance devices.

  14. A new perspective on self-reversed thermo-remanent magnetization and room-temperature magnetic exchange bias in quenched and annealed ferri-ilmenite solid solutions

    NASA Astrophysics Data System (ADS)

    Robinson, P.; Harrison, R. J.; Fabian, K.; McEnroe, S. A.; Miyajima, N.

    2012-04-01

    kinds of regions, one dominated by A-ordering containing smaller regions of B-ordering and the other dominated by B-ordering with smaller regions of A-ordering. The key feature for self-reversal is that small and shrinking domains became progressively Fe-enriched compared to their larger neighbors, and the elusive "x-phase" is explained as a less strongly ordered Fe-enriched phase near APBs during coarsening. We pursued these studies further with TEM of the APB's and demonstrating chemical phase separation in a synthetic composition FeTiO3 = 0.61. Subsequent annealing of this sample showed self-reversed TRM and room-temperature magnetic exchange bias. Analysis of charge balance across APB's showed the significant role of contact layers and disordered layers. Monte Carlo simulations demonstrated the necessity for Fe-enrichment in the diminishing phase. A theoretical approach to the ferri-ilmenite phase diagram showed potential for metastable chemical phase separation over a wide composition range, related to the order parameter Q, at temperatures well above phase separation over a limited composition range related to a chemical solvus. A key feature of the new perspective is the recognition of simple antiferromagnetic coupling across the APBs. Evidence suggests negative magnetic (antiferromagnetic) coupling required for magnetic self-reversal can only be maintained when the antiphase domains are smaller than ~ 50 nm.

  15. Antisite disorder driven spontaneous exchange bias effect in La(2-x)Sr(x) CoMnO₆ (0  ⩽  x  ⩽  1).

    PubMed

    Krishna Murthy, J; Chandrasekhar, K D; Wu, H C; Yang, H D; Lin, J Y; Venimadhav, A

    2016-03-01

    Doping at the rare-earth site by divalent alkaline-earth ions in perovskite lattice has witnessed a variety of magnetic and electronic orders with spatially correlated charge, spin and orbital degrees of freedom. Here, we report an antisite disorder driven spontaneous exchange bias effect as a result of hole carrier (Sr(2+)) doping in La(2-x)Sr(x)CoMnO6 (0  <  x  <  1) double perovskites. X-ray diffraction and Raman spectroscopy have evidenced an increase in disorder with the increase of Sr content up to x  =  0.5 and thereby a decrease from x  =  0.5 to 1. X-ray absorption spectroscopy has revealed that only Co is present in the mixed valence of Co(2+) and Co(3+) states with Sr doping to compensate the charge neutrality. Magnetotransport is strongly correlated with the increase of antisite disorder. The antisite disorder at the B-site interrupts the long-range ferromagnetic order by introducing various magnetic interactions and instigates reentrant glassy dynamics, phase separation and canted type antiferromagnetic behavior with the decrease of temperature. This leads to a novel magnetic microstructure with unidirectional anisotropy that causes a spontaneous exchange bias effect that can be tuned with the amount of antisite disorder. PMID:26823459

  16. Exchange-bias effect at La0.75Sr0.25MnO3/LaNiO3 interfaces

    SciTech Connect

    Rojas Sánchez, J. C.; Nelson-Cheeseman, B.; Granada, M.; Arenholz, E.; Steren, L. B.

    2012-03-26

    In this paper, we show that ferromagnetic/paramagnetic La0.75Sr0.25MnO3/LaNiO3 multilayers present an unexpected magnetic exchange-bias effect (EBE), observed in field-cooled magnetization loops. The exchange-bias field and the enhancement of the coercivity vanish around 50 K. We demonstrate that the oxidation state of the Ni and Mn cations changes from Mn3+-Ni3+ to Mn4+-Ni2+ in the layers close to the interface probed by x-ray absorption spectroscopy measurements. The variation of the valence states is accompanied by a change in the magnetic behavior of the cations at the La0.75Sr0.25MnO3/LaNiO3 interface, possibly giving rise to the formation of magnetic or magnetically frustrated regions that may pin the ferromagnetic a0.75Sr0.25MnO3 layers and explain the EBE.

  17. Large coercivity and exchange bias in [Fe{sub 1-{delta}}(FeO){sub {delta}}]{sub x}(TiO{sub 2}){sub 1-x} granular films

    SciTech Connect

    Cheng, Y. H.; Wang, C. H.; Luo, X. G.; Liu, Hui; Wang, W. H.; Zhang, X. H.; Li, L. Y.; Zheng, R. K.

    2013-05-13

    [Fe{sub 1-{delta}}(FeO){sub {delta}}]{sub x}(TiO{sub 2}){sub 1-x} (0{<=}{delta}{<=}0.91, 0.34{<=}x{<=}0.54) granular films were fabricated by magnetron sputtering. Large coercivity (H{sub C} = 10.5 kOe) and exchange-bias-field (H{sub E} = 6.5 kOe) at 5 K were found in the film with {delta}=0.84 and x = 0.48. AC susceptibility measurements exhibit a frequency (f) dependent peak T{sub f} in the in-phase susceptibility curve. The fitting of the relation of T{sub f} vs f with both the Vogel-Fulcher law and critical slowing down theory indicate that the evident enhancement of the H{sub C} and H{sub E} can be qualitatively ascribed to the existence of cluster-spin glass state. The results may help to deeply understand the origin of exchange bias and related effects.

  18. Strain-mediated electric-field control of exchange bias in a Co90Fe10/BiFeO3/SrRuO3/PMN-PT heterostructure.

    PubMed

    Wu, S Z; Miao, J; Xu, X G; Yan, W; Reeve, R; Zhang, X H; Jiang, Y

    2015-01-01

    The electric-field (E-field) controlled exchange bias (EB) in a Co90Fe10/BiFeO3 (BFO)/SrRuO3/PMN-PT heterostructure has been investigated under different tensile strain states. The in-plane tensile strain of the BFO film is changed from +0.52% to +0.43% as a result of external E-field applied to the PMN-PT substrate. An obvious change of EB by the control of non-volatile strain has been observed. A magnetization reversal driven by E-field has been observed in the absence of magnetic field. Our results indicate that a reversible non-volatile E-field control of a ferromagnetic layer through strain modulated multiferroic BFO could be achieved at room temperature. PMID:25752272

  19. Strain-mediated electric-field control of exchange bias in a Co90Fe10/BiFeO3/SrRuO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Wu, S. Z.; Miao, J.; Xu, X. G.; Yan, W.; Reeve, R.; Zhang, X. H.; Jiang, Y.

    2015-03-01

    The electric-field (E-field) controlled exchange bias (EB) in a Co90Fe10/BiFeO3 (BFO)/SrRuO3/PMN-PT heterostructure has been investigated under different tensile strain states. The in-plane tensile strain of the BFO film is changed from +0.52% to +0.43% as a result of external E-field applied to the PMN-PT substrate. An obvious change of EB by the control of non-volatile strain has been observed. A magnetization reversal driven by E-field has been observed in the absence of magnetic field. Our results indicate that a reversible non-volatile E-field control of a ferromagnetic layer through strain modulated multiferroic BFO could be achieved at room temperature.

  20. Strain-mediated electric-field control of exchange bias in a Co90Fe10/BiFeO3/SrRuO3/PMN-PT heterostructure

    PubMed Central

    Wu, S. Z.; Miao, J.; Xu, X. G.; Yan, W.; Reeve, R.; Zhang, X. H.; Jiang, Y.

    2015-01-01

    The electric-field (E-field) controlled exchange bias (EB) in a Co90Fe10/BiFeO3 (BFO)/SrRuO3/PMN-PT heterostructure has been investigated under different tensile strain states. The in-plane tensile strain of the BFO film is changed from +0.52% to +0.43% as a result of external E-field applied to the PMN-PT substrate. An obvious change of EB by the control of non-volatile strain has been observed. A magnetization reversal driven by E-field has been observed in the absence of magnetic field. Our results indicate that a reversible non-volatile E-field control of a ferromagnetic layer through strain modulated multiferroic BFO could be achieved at room temperature. PMID:25752272

  1. Estimation of bias with the single-zone assumption in measurement of residential air exchange using the perfluorocarbon tracer gas method

    PubMed Central

    Van Ryswyk, K; Wallace, L; Fugler, D; MacNeill, M; Héroux, M È; Gibson, M D; Guernsey, J R; Kindzierski, W; Wheeler, A J

    2015-01-01

    Residential air exchange rates (AERs) are vital in understanding the temporal and spatial drivers of indoor air quality (IAQ). Several methods to quantify AERs have been used in IAQ research, often with the assumption that the home is a single, well-mixed air zone. Since 2005, Health Canada has conducted IAQ studies across Canada in which AERs were measured using the perfluorocarbon tracer (PFT) gas method. Emitters and detectors of a single PFT gas were placed on the main floor to estimate a single-zone AER (AER1z). In three of these studies, a second set of emitters and detectors were deployed in the basement or second floor in approximately 10% of homes for a two-zone AER estimate (AER2z). In total, 287 daily pairs of AER2z and AER1z estimates were made from 35 homes across three cities. In 87% of the cases, AER2z was higher than AER1z. Overall, the AER1z estimates underestimated AER2z by approximately 16% (IQR: 5–32%). This underestimate occurred in all cities and seasons and varied in magnitude seasonally, between homes, and daily, indicating that when measuring residential air exchange using a single PFT gas, the assumption of a single well-mixed air zone very likely results in an under prediction of the AER. PMID:25399878

  2. Altering the exchange bias in Co90Fe10/(Co,Fe)O bilayers by changing the antiferromagnet's magnetism via interfacial ion-beam bombardment and different single crystalline MgO substrates

    NASA Astrophysics Data System (ADS)

    Shueh, C.; Liu, C.-H.; Skoropata, E.; Wu, T.-H.; van Lierop, J.; Lin, K.-W.

    2013-05-01

    In this study, we investigated the exchange bias (coupling) effects in CoFe/(Co,Fe)O bilayers by using different single crystal substrates of MgO(100) and MgO(110) and Ar ion-beam bombardment on the surface of the bottom antiferromagnet (Co,Fe)O layer before capping with ferromagnet CoFe. In the CoFe/(Co,Fe)O/MgO(110) bilayer, above the irreversibility temperature (Tirr. ˜ 170 K), there was a rapid decrease in M(T) with increasing temperature, unlike the CoFe/(Co,Fe)O/MgO(100) film that showed an increased Tirr. ˜ 300 K and no observable decrease in M(T) above Tirr. The different M vs T zero-field-cooled/field-cooled behavior of the CoFe/(Co,Fe)O bilayers on MgO(100) and MgO(110) indicated that the FM CoFe spin orientations were affected by the different substrates used via exchange coupling to the AF (Co,Fe)O layer altered by MgO.

  3. Exchange bias effect in epitaxial La{sub 0.67}Ca{sub 0.33}MnO{sub 3}/SrMnO{sub 3} thin film structure

    SciTech Connect

    Yu, T.; Ning, X. K.; Liu, W. Feng, J. N.; Zhao, X. G.; Zhang, Z. D.

    2014-08-28

    Bilayers consisting of La{sub 0.67}Ca{sub 0.33}MnO{sub 3} (LCMO) and SrMnO{sub 3} (SMO) have been prepared by pulsed-laser deposition on SrTiO{sub 3} (001) substrates. Unconventional magnetic coupling was found after cooling in a small field. The LCMO/SMO bilayers exhibit an exchange bias field of 209 Oe, which vanishes as the temperature rises above 90 K. A small magnetization has been found above the Curie temperature of the pure LCMO thin films. Spin-cluster-like antiferromagnetic (AFM)/ferromagnetic (FM) clusters have been deduced to exist at the interface due to the competing types of magnetic order at the interface. The magnetic relaxation is found to follow a double-exponential equation and a slow relaxation process is observed due to the strong exchange coupling between AFM/FM clusters and the LCMO layer. We speculate that the short-range high-temperature FM order of the Mn{sup 3+} and Mn{sup 4+} moments above the Curie temperature at the interface gives rise to the magnetic regions that pin the FM LCMO layer as the temperature decreases.

  4. Magnetization jumps and exchange bias induced by a partially disordered antiferromagnetic state in (FeTiO{sub 3}){sub 0.9}-(Fe{sub 2}O{sub 3}){sub 0.1}

    SciTech Connect

    Song, P.; Li, G. K.; Ma, L. Zhen, C. M.; Hou, D. L.; Wang, W. H.; Liu, E. K.; Chen, J. L.; Wu, G. H.

    2014-06-07

    Magnetization jumps (MJs) and the exchange bias (EB) effect are simultaneously observed in the mixed-spin oxide (FeTiO{sub 3}){sub 0.9}-(Fe{sub 2}O{sub 3}){sub 0.1} at 2.0 K. Dc and ac susceptibility measurements confirm a reentrant spin glass phase with a partially disordered antiferromagnetic (PDA) state below the irreversibility temperature (T{sub ir} = 60 K). Antiferromagnetic (AFM) Fe{sup 3+} clusters are nested in AFM Fe{sup 2+} lattices forming a triangular lattice, in which 2/3 of the magnetic moments order antiferromagnetically with each other leaving the remaining 1/3 “confused.” This geometric frustration in the triangular lattice leads to a PDA state that is the ground state of the AFM triangular configuration. The PDA state, in the presence of a critical trigger field, evolves into a ferromagnetic (FM) state, and induces the AFM spins of the Fe{sup 2+} ions to enter a FM state, resulting in the MJs. Meanwhile, the FM spins of Fe{sup 2+} can serve as the pinned phase, and the AFM spins of Fe{sup 3+} can serve as the pinning phase, resulting in the EB effect. Thus, we point out that the PDA state is very likely to be at the origin of the MJs and the EB effect.

  5. Cooling field tuned magnetic phase transition and exchange bias-like effect in Y{sub 0.9}Pr{sub 0.1}CrO{sub 3}

    SciTech Connect

    Deng, Dongmei E-mail: dyu@ansto.gov.au Feng, Zhenjie; Jing, Chao; Ren, Wei; Cao, Shixun; Zhang, Jincang E-mail: dyu@ansto.gov.au; Zheng, Jiashun; Yu, Dehong E-mail: dyu@ansto.gov.au Sun, Dehui; Avdeev, Maxim; Wang, Baomin; Lu, Bo

    2015-09-07

    Cooling magnetic field dependence of magnetic phase transition has been observed in Y{sub 0.9}Pr{sub 0.1}CrO{sub 3}. G{sub z}F{sub x} order (spin structure of PrCrO{sub 3}) is dominant after zero field cooling (ZFC), whereas G{sub x}F{sub z} order (spin structure of YCrO{sub 3}) is dominant after cooling under a field higher than 100 Oe. Positive/negative exchange bias-like effect, with large vertical shift and small horizontal shift, has been observed after FC/ZFC process. The vertical shift can be attributed to the frozen ordered Pr{sup 3+} and Cr{sup 3+} spins in magnetic domains, because of the strong coupling between Pr{sup 3+} and Cr{sup 3+} sublattices; while the horizontal shift is a result of the pinning of spins at the interfaces. The frozen structure is generated by the field used for the measurement of the initial magnetization curve of M(H) for the ZFC cooled sample, while it is generated by the cooling field for the sample cooled under a cooling field higher than 100 Oe.

  6. Classifying sex biased congenital anomalies

    SciTech Connect

    Lubinsky, M.S.

    1997-03-31

    The reasons for sex biases in congenital anomalies that arise before structural or hormonal dimorphisms are established has long been unclear. A review of such disorders shows that patterning and tissue anomalies are female biased, and structural findings are more common in males. This suggests different gender dependent susceptibilities to developmental disturbances, with female vulnerabilities focused on early blastogenesis/determination, while males are more likely to involve later organogenesis/morphogenesis. A dual origin for some anomalies explains paradoxical reductions of sex biases with greater severity (i.e., multiple rather than single malformations), presumably as more severe events increase the involvement of an otherwise minor process with opposite biases to those of the primary mechanism. The cause for these sex differences is unknown, but early dimorphisms, such as differences in growth or presence of H-Y antigen, may be responsible. This model provides a useful rationale for understanding and classifying sex-biased congenital anomalies. 42 refs., 7 tabs.

  7. Indiana Health Information Exchange

    Cancer.gov

    The Indiana Health Information Exchange is comprised of various Indiana health care institutions, established to help improve patient safety and is recognized as a best practice for health information exchange.

  8. Biased Allostery.

    PubMed

    Edelstein, Stuart J; Changeux, Jean-Pierre

    2016-09-01

    G-protein-coupled receptors (GPCRs) constitute a large group of integral membrane proteins that transduce extracellular signals from a wide range of agonists into targeted intracellular responses. Although the responses can vary depending on the category of G-proteins activated by a particular receptor, responses were also found to be triggered by interactions of the receptor with β-arrestins. It was subsequently discovered that for the same receptor molecule (e.g., the β-adrenergic receptor), some agonists have a propensity to specifically favor responses by G-proteins, others by β-arrestins, as has now been extensively studied. This feature of the GPCR system is known as biased agonism and is subject to various interpretations, including agonist-induced conformational change versus selective stabilization of preexisting active conformations. Here, we explore a complete allosteric framework for biased agonism based on alternative preexisting conformations that bind more strongly, but nonexclusively, either G-proteins or β-arrestins. The framework incorporates reciprocal effects among all interacting molecules. As a result, G-proteins and β-arrestins are in steric competition for binding to the cytoplasmic surface of either the G-protein-favoring or β-arrestin-favoring GPCR conformation. Moreover, through linkage relations, the strength of the interactions of G-proteins or β-arrestins with the corresponding active conformation potentiates the apparent affinity for the agonist, effectively equating these two proteins to allosteric modulators. The balance between response alternatives can also be influenced by the physiological concentrations of either G-proteins or β-arrestins, as well as by phosphorylation or interactions with positive or negative allosteric modulators. The nature of the interactions in the simulations presented suggests novel experimental tests to distinguish more fully among alternative mechanisms. PMID:27602718

  9. Solar array/spacecraft biasing

    NASA Technical Reports Server (NTRS)

    Fitzgerald, D. J.

    1981-01-01

    Biasing techniques and their application to the control of spacecraft potential is discussed. Normally when a spacecraft is operated with ion thrusters, the spacecraft will be 10-20 volts negative of the surrounding plasma. This will affect scientific measurements and will allow ions from the charge-exchange plasma to bombard the spacecraft surfaces with a few tens of volts of energy. This condition may not be tolerable. A proper bias system is described that can bring the spacecraft to or near the potential of the surrounding plasma.

  10. Establishing the next generation at work: leader generativity as a moderator of the relationships between leader age, leader-member exchange, and leadership success.

    PubMed

    Zacher, Hannes; Rosing, Kathrin; Henning, Thomas; Frese, Michael

    2011-03-01

    In this study, the authors investigated leader generativity as a moderator of the relationships between leader age, leader-member exchange, and three criteria of leadership success (follower perceptions of leader effectiveness, follower satisfaction with leader, and follower extra effort). Data came from 128 university professors paired with one research assistant each. Results showed positive relationships between leader age and leader generativity, and negative relationships between leader age and follower perceptions of leader effectiveness and follower extra effort. Consistent with expectations based on leadership categorization theory, leader generativity moderated the relationships between leader age and all three criteria of leadership success, such that leaders high in generativity were better able to maintain high levels of leadership success at higher ages than leaders low in generativity. Finally, results of mediated moderation analyses showed that leader-member exchange quality mediated these moderating effects. The findings suggest that, in combination, leader age and the age-related construct of generativity importantly influence leadership processes and outcomes.

  11. A Southern Washington Chronosequence Study: The Impact of Interannual Climate Variability on Ecosystem Exchange of Carbon, Water, and Energy in a Newly Established and Old-Growth Coniferous Forest

    NASA Astrophysics Data System (ADS)

    Wharton, S.; Schroeder, M.; Falk, M.; Paw U, K.

    2005-12-01

    The T.T. Munger Research Natural Area of southern Washington provides a unique opportunity to study carbon exchange between coniferous forests and the atmosphere in a region that experiences a significant amount of forest harvesting disturbance and interannual climate variability. Here we present initial biometeorological measurements of carbon and water exchange at a 10 year old Douglas-fir stand with the goal of gaining information on how regional climate change will affect the carbon and hydrological budgets of a newly established forest. The young forest is 1.25 km from the Wind River Canopy Crane Research Facility, an AMERIFLUX site that has been continuously measuring carbon, water, and energy fluxes at an old-growth forest since 1998. Though still in its infancy, data from this chronosequence study will be used to quantify how sensitive net ecosystem exchange (NEE) of carbon is to interannual climate variability at different aged stands of the Washington western Cascades. Because the young stand is in close proximity to the old-growth forest, the climates at both forests will be identical, though the microclimates will not. The response in NEE at the young stand during the seasonal drought may be very different from that at the old-growth forest due to dissimilar canopy understory composition, which will lead to site differences in soil moisture and soil temperature. How this affects respiration rates and photosynthetic rates at both stands is one of the questions that will be addressed by this study. As the chronosequence study progresses, we hope to show any sensitivities that a newly established forest has to climate variability and in conjuncture with data from the old-growth stand, give the global carbon community important information on the forest carbon sequestration potential of the Pacific Northwest.

  12. Temperature trend biases

    NASA Astrophysics Data System (ADS)

    Venema, Victor; Lindau, Ralf

    2016-04-01

    In an accompanying talk we show that well-homogenized national dataset warm more than temperatures from global collections averaged over the region of common coverage. In this poster we want to present auxiliary work about possible biases in the raw observations and on how well relative statistical homogenization can remove trend biases. There are several possible causes of cooling biases, which have not been studied much. Siting could be an important factor. Urban stations tend to move away from the centre to better locations. Many stations started inside of urban areas and are nowadays more outside. Even for villages the temperature difference between the centre and edge can be 0.5°C. When a city station moves to an airport, which often happened around WWII, this takes the station (largely) out of the urban heat island. During the 20th century the Stevenson screen was established as the dominant thermometer screen. This screen protected the thermometer much better against radiation than earlier designs. Deficits of earlier measurement methods have artificially warmed the temperatures in the 19th century. Newer studies suggest we may have underestimated the size of this bias. Currently we are in a transition to Automatic Weather Stations. The net global effect of this transition is not clear at this moment. Irrigation on average decreases the 2m-temperature by about 1 degree centigrade. At the same time, irrigation has increased significantly during the last century. People preferentially live in irrigated areas and weather stations serve agriculture. Thus it is possible that there is a higher likelihood that weather stations are erected in irrigated areas than elsewhere. In this case irrigation could lead to a spurious cooling trend. In the Parallel Observations Science Team of the International Surface Temperature Initiative (ISTI-POST) we are studying influence of the introduction of Stevenson screens and Automatic Weather Stations using parallel measurements

  13. Developing biases

    PubMed Central

    van de Vijver, Ruben; Baer-Henney, Dinah

    2014-01-01

    German nouns may alternate from singular to plural in two different ways. Some singular forms that end in a voiceless obstruent have a plural in which this obstruent is voiced. Another alternation concerns the vowel. Some singular forms with a back vowel have a plural form in which this back vowel is front. For each noun it has to be established individually whether it alternates or not. The voicing alternation is phonetically grounded, but the vowel alternation is not. Knowledge about such alternations involves two things. First, it involves knowledge of which words alternate and which words do not and second, it involves the ability to extend the alternations to novel words. We studied the knowledge of which words alternate and the proportion to which they alternate in two corpus studies. We studied the knowledge of speakers concerning which words alternate and what generalizations can be based upon these words by means of a production study. The production study involved words and nonces. We asked twenty 5 year-olds, twenty 7 year-olds, and ten adults to produce the plural for a given singular word and a plural for a given singular nonce. In the corpus study we found that both alternations occur with the same frequency. In the production of alternations in words we found that participants in all age groups make few mistakes. With respect to the production of alternations in nonce words, we found that the proportion of voicing alternations decreases with age, while the proportion of vowel alternations increases. We explain this change in the ability to generalize the alternations to nonces on the basis of the confidence speakers can have in a generalization. Young children have a small lexicon and they can form relatively unreliable generalizations on lexical distributions. They are, however, proficient users of language and have great phonetic experience. They can more confidently form generalizations on the basis of this experience. Adults have a large lexicon

  14. Divertor bias experiments

    NASA Astrophysics Data System (ADS)

    Staebler, G. M.

    1994-06-01

    Electrical biasing of the divertor target plates has recently been implemented on several tokamaks. The results of these experiments to date will be reviewed in this paper. The bias electrode configuration is unique in each experiment. The effects of biasing on the scrape-off layer (SOL) plasma also differ. By comparing results between machines, and using theoretical models, an understanding of the basic physics of biasing begins to emerge. Divertor biasing has been demonstrated to have a strong influence on the particle and energy transport within the SOL. The ability to externally control the SOL plasma with biasing has promising applications to future tokamak reactors.

  15. Demonstrating the Correspondence Bias

    ERIC Educational Resources Information Center

    Howell, Jennifer L.; Shepperd, James A.

    2011-01-01

    Among the best-known and most robust biases in person perception is the correspondence bias--the tendency for people to make dispositional, rather than situational, attributions for an actor's behavior. The correspondence bias appears in virtually every social psychology textbook and in many introductory psychology textbooks, yet the authors'…

  16. Bias in Grading

    ERIC Educational Resources Information Center

    Malouff, John

    2008-01-01

    Bias in grading can be conscious or unconscious. The author describes different types of bias, such as those based on student attractiveness or performance in prior courses, and a variety of methods of reducing bias, including keeping students anonymous during grading and using detailed criteria for subjective grading.

  17. Contextual Modulation of Biases in Face Recognition

    PubMed Central

    Felisberti, Fatima Maria; Pavey, Louisa

    2010-01-01

    Background The ability to recognize the faces of potential cooperators and cheaters is fundamental to social exchanges, given that cooperation for mutual benefit is expected. Studies addressing biases in face recognition have so far proved inconclusive, with reports of biases towards faces of cheaters, biases towards faces of cooperators, or no biases at all. This study attempts to uncover possible causes underlying such discrepancies. Methodology and Findings Four experiments were designed to investigate biases in face recognition during social exchanges when behavioral descriptors (prosocial, antisocial or neutral) embedded in different scenarios were tagged to faces during memorization. Face recognition, measured as accuracy and response latency, was tested with modified yes-no, forced-choice and recall tasks (N = 174). An enhanced recognition of faces tagged with prosocial descriptors was observed when the encoding scenario involved financial transactions and the rules of the social contract were not explicit (experiments 1 and 2). Such bias was eliminated or attenuated by making participants explicitly aware of “cooperative”, “cheating” and “neutral/indifferent” behaviors via a pre-test questionnaire and then adding such tags to behavioral descriptors (experiment 3). Further, in a social judgment scenario with descriptors of salient moral behaviors, recognition of antisocial and prosocial faces was similar, but significantly better than neutral faces (experiment 4). Conclusion The results highlight the relevance of descriptors and scenarios of social exchange in face recognition, when the frequency of prosocial and antisocial individuals in a group is similar. Recognition biases towards prosocial faces emerged when descriptors did not state the rules of a social contract or the moral status of a behavior, and they point to the existence of broad and flexible cognitive abilities finely tuned to minor changes in social context. PMID:20886086

  18. Queries for Bias Testing

    NASA Technical Reports Server (NTRS)

    Gordon, Diana F.

    1992-01-01

    Selecting a good bias prior to concept learning can be difficult. Therefore, dynamic bias adjustment is becoming increasingly popular. Current dynamic bias adjustment systems, however, are limited in their ability to identify erroneous assumptions about the relationship between the bias and the target concept. Without proper diagnosis, it is difficult to identify and then remedy faulty assumptions. We have developed an approach that makes these assumptions explicit, actively tests them with queries to an oracle, and adjusts the bias based on the test results.

  19. Chromatography process development in the quality by design paradigm I: Establishing a high-throughput process development platform as a tool for estimating "characterization space" for an ion exchange chromatography step.

    PubMed

    Bhambure, R; Rathore, A S

    2013-01-01

    This article describes the development of a high-throughput process development (HTPD) platform for developing chromatography steps. An assessment of the platform as a tool for establishing the "characterization space" for an ion exchange chromatography step has been performed by using design of experiments. Case studies involving use of a biotech therapeutic, granulocyte colony-stimulating factor have been used to demonstrate the performance of the platform. We discuss the various challenges that arise when working at such small volumes along with the solutions that we propose to alleviate these challenges to make the HTPD data suitable for empirical modeling. Further, we have also validated the scalability of this platform by comparing the results from the HTPD platform (2 and 6 μL resin volumes) against those obtained at the traditional laboratory scale (resin volume, 0.5 mL). We find that after integration of the proposed correction factors, the HTPD platform is capable of performing the process optimization studies at 170-fold higher productivity. The platform is capable of providing semi-quantitative assessment of the effects of the various input parameters under consideration. We think that platform such as the one presented is an excellent tool for examining the "characterization space" and reducing the extensive experimentation at the traditional lab scale that is otherwise required for establishing the "design space." Thus, this platform will specifically aid in successful implementation of quality by design in biotech process development. This is especially significant in view of the constraints with respect to time and resources that the biopharma industry faces today.

  20. Attentional bias in math anxiety.

    PubMed

    Rubinsten, Orly; Eidlin, Hili; Wohl, Hadas; Akibli, Orly

    2015-01-01

    Cognitive theory from the field of general anxiety suggests that the tendency to display attentional bias toward negative information results in anxiety. Accordingly, the current study aims to investigate whether attentional bias is involved in math anxiety (MA) as well (i.e., a persistent negative reaction to math). Twenty seven participants (14 with high levels of MA and 13 with low levels of MA) were presented with a novel computerized numerical version of the well established dot probe task. One of six types of prime stimuli, either math related or typically neutral, was presented on one side of a computer screen. The prime was preceded by a probe (either one or two asterisks) that appeared in either the prime or the opposite location. Participants had to discriminate probe identity (one or two asterisks). Math anxious individuals reacted faster when the probe was at the location of the numerical related stimuli. This suggests the existence of attentional bias in MA. That is, for math anxious individuals, the cognitive system selectively favored the processing of emotionally negative information (i.e., math related words). These findings suggest that attentional bias is linked to unduly intense MA symptoms.

  1. Attentional bias in math anxiety.

    PubMed

    Rubinsten, Orly; Eidlin, Hili; Wohl, Hadas; Akibli, Orly

    2015-01-01

    Cognitive theory from the field of general anxiety suggests that the tendency to display attentional bias toward negative information results in anxiety. Accordingly, the current study aims to investigate whether attentional bias is involved in math anxiety (MA) as well (i.e., a persistent negative reaction to math). Twenty seven participants (14 with high levels of MA and 13 with low levels of MA) were presented with a novel computerized numerical version of the well established dot probe task. One of six types of prime stimuli, either math related or typically neutral, was presented on one side of a computer screen. The prime was preceded by a probe (either one or two asterisks) that appeared in either the prime or the opposite location. Participants had to discriminate probe identity (one or two asterisks). Math anxious individuals reacted faster when the probe was at the location of the numerical related stimuli. This suggests the existence of attentional bias in MA. That is, for math anxious individuals, the cognitive system selectively favored the processing of emotionally negative information (i.e., math related words). These findings suggest that attentional bias is linked to unduly intense MA symptoms. PMID:26528208

  2. Attentional bias in math anxiety

    PubMed Central

    Rubinsten, Orly; Eidlin, Hili; Wohl, Hadas; Akibli, Orly

    2015-01-01

    Cognitive theory from the field of general anxiety suggests that the tendency to display attentional bias toward negative information results in anxiety. Accordingly, the current study aims to investigate whether attentional bias is involved in math anxiety (MA) as well (i.e., a persistent negative reaction to math). Twenty seven participants (14 with high levels of MA and 13 with low levels of MA) were presented with a novel computerized numerical version of the well established dot probe task. One of six types of prime stimuli, either math related or typically neutral, was presented on one side of a computer screen. The prime was preceded by a probe (either one or two asterisks) that appeared in either the prime or the opposite location. Participants had to discriminate probe identity (one or two asterisks). Math anxious individuals reacted faster when the probe was at the location of the numerical related stimuli. This suggests the existence of attentional bias in MA. That is, for math anxious individuals, the cognitive system selectively favored the processing of emotionally negative information (i.e., math related words). These findings suggest that attentional bias is linked to unduly intense MA symptoms. PMID:26528208

  3. The meaning of the bias uncertainty measure.

    PubMed

    Bartley, David L

    2008-08-01

    Characterization of measurement uncertainty in terms of root sums of squares of both unknown systematic as well as random error components is given meaning in the sense of prediction intervals. Both types of errors are commonly encountered with industrial hygiene air monitoring of hazardous substances. Two extreme types of measurement methods are presented for illustrating how confidence levels may be ascribed to prediction intervals defined by such uncertainty values. In the case of method calibration at each measurement, systematic error or bias may enter from a biased calibrant. At another extreme, a single initial method evaluation may leave residual bias owing to random error in the evaluation itself or to the use of a biased reference method. Analysis is simplified through new simple approximations to probabilistic limits (quantiles) on the magnitude of a non-central Student t-distributed random variable. Connection is established between traditional confidence limits, accuracy measures in the case of bias minimization and an uncertainty measure.

  4. Are all biases missing data problems?

    PubMed Central

    Howe, Chanelle J.; Cain, Lauren E.; Hogan, Joseph W.

    2015-01-01

    Estimating causal effects is a frequent goal of epidemiologic studies. Traditionally, there have been three established systematic threats to consistent estimation of causal effects. These three threats are bias due to confounders, selection, and measurement error. Confounding, selection, and measurement bias have typically been characterized as distinct types of biases. However, each of these biases can also be characterized as missing data problems that can be addressed with missing data solutions. Here we describe how the aforementioned systematic threats arise from missing data as well as review methods and their related assumptions for reducing each bias type. We also link the assumptions made by the reviewed methods to the missing completely at random (MCAR) and missing at random (MAR) assumptions made in the missing data framework that allow for valid inferences to be made based on the observed, incomplete data. PMID:26576336

  5. Interpretation biases in paranoia.

    PubMed

    Savulich, George; Freeman, Daniel; Shergill, Sukhi; Yiend, Jenny

    2015-01-01

    Information in the environment is frequently ambiguous in meaning. Emotional ambiguity, such as the stare of a stranger, or the scream of a child, encompasses possible good or bad emotional consequences. Those with elevated vulnerability to affective disorders tend to interpret such material more negatively than those without, a phenomenon known as "negative interpretation bias." In this study we examined the relationship between vulnerability to psychosis, measured by trait paranoia, and interpretation bias. One set of material permitted broadly positive/negative (valenced) interpretations, while another allowed more or less paranoid interpretations, allowing us to also investigate the content specificity of interpretation biases associated with paranoia. Regression analyses (n=70) revealed that trait paranoia, trait anxiety, and cognitive inflexibility predicted paranoid interpretation bias, whereas trait anxiety and cognitive inflexibility predicted negative interpretation bias. In a group comparison those with high levels of trait paranoia were negatively biased in their interpretations of ambiguous information relative to those with low trait paranoia, and this effect was most pronounced for material directly related to paranoid concerns. Together these data suggest that a negative interpretation bias occurs in those with elevated vulnerability to paranoia, and that this bias may be strongest for material matching paranoid beliefs. We conclude that content-specific biases may be important in the cause and maintenance of paranoid symptoms.

  6. Political bias is tenacious.

    PubMed

    Ditto, Peter H; Wojcik, Sean P; Chen, Eric Evan; Grady, Rebecca Hofstein; Ringel, Megan M

    2015-01-01

    Duarte et al. are right to worry about political bias in social psychology but they underestimate the ease of correcting it. Both liberals and conservatives show partisan bias that often worsens with cognitive sophistication. More non-liberals in social psychology is unlikely to speed our convergence upon the truth, although it may broaden the questions we ask and the data we collect.

  7. Investigating Test Bias.

    ERIC Educational Resources Information Center

    Hoepfner, Ralph; Strickland, Guy P.

    This study investigates the question of test bias to develop an index of the appropriateness of a test to a particular socioeconomic or racial-ethnic group. Bias is defined as an item by race interaction in an analysis-of-variance design. The sample of 172 third graders at two integrated schools in a large California school district, included 26…

  8. Sampler bias -- Phase 1

    SciTech Connect

    Blanchard, R.J.

    1995-03-07

    This documents Phase 1 determinations on sampler induced bias for four sampler types used in tank characterization. Each sampler, grab sampler or bottle-on-a-string, auger sampler, sludge sampler and universal sampler, is briefly discussed and their physical limits noted. Phase 2 of this document will define additional testing and analysis to further define Sampler Bias.

  9. Long-range magnetic interactions and proximity effects in an amorphous exchange-spring magnet.

    PubMed

    Magnus, F; Brooks-Bartlett, M E; Moubah, R; Procter, R A; Andersson, G; Hase, T P A; Banks, S T; Hjörvarsson, B

    2016-01-01

    Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality. PMID:27291298

  10. Long-range magnetic interactions and proximity effects in an amorphous exchange-spring magnet

    PubMed Central

    Magnus, F.; Brooks-Bartlett, M. E.; Moubah, R.; Procter, R. A.; Andersson, G.; Hase, T. P. A.; Banks, S. T.; Hjörvarsson, B.

    2016-01-01

    Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effects and long-range magnetic interactions are needed to capture the extent of the induced magnetization. The results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality. PMID:27291298

  11. Biased predecision processing.

    PubMed

    Brownstein, Aaron L

    2003-07-01

    Decision makers conduct biased predecision processing when they restructure their mental representation of the decision environment to favor one alternative before making their choice. The question of whether biased predecision processing occurs has been controversial since L. Festinger (1957) maintained that it does not occur. The author reviews relevant research in sections on theories of cognitive dissonance, decision conflict, choice certainty, action control, action phases, dominance structuring, differentiation and consolidation, constructive processing, motivated reasoning, and groupthink. Some studies did not find evidence of biased predecision processing, but many did. In the Discussion section, the moderators are summarized and used to assess the theories. PMID:12848220

  12. Gender bias in the force concept inventory?

    NASA Astrophysics Data System (ADS)

    Dietz, R. D.; Pearson, R. H.; Semak, M. R.; Willis, C. W.

    2012-02-01

    Could the well-established fact that males tend to score higher than females on the Force Concept Inventory (FCI) be due to gender bias in the questions? The eventual answer to the question hinges on the definition of bias. We assert that a question is biased only if a factor other than ability (in this case gender) affects the likelihood that a student will answer the question correctly. The statistical technique of differential item functioning allows us to control for ability in our analysis of student performance on each of the thirty FCI questions. This method uses the total score on the FCI as the measure of ability. We conclude that the evidence for gender bias in the FCI questions is marginal at best.

  13. Introduction to Unconscious Bias

    NASA Astrophysics Data System (ADS)

    Schmelz, Joan T.

    2010-05-01

    We all have biases, and we are (for the most part) unaware of them. In general, men and women BOTH unconsciously devalue the contributions of women. This can have a detrimental effect on grant proposals, job applications, and performance reviews. Sociology is way ahead of astronomy in these studies. When evaluating identical application packages, male and female University psychology professors preferred 2:1 to hire "Brian” over "Karen” as an assistant professor. When evaluating a more experienced record (at the point of promotion to tenure), reservations were expressed four times more often when the name was female. This unconscious bias has a repeated negative effect on Karen's career. This talk will introduce the concept of unconscious bias and also give recommendations on how to address it using an example for a faculty search committee. The process of eliminating unconscious bias begins with awareness, then moves to policy and practice, and ends with accountability.

  14. Estimating Bias Error Distributions

    NASA Technical Reports Server (NTRS)

    Liu, Tian-Shu; Finley, Tom D.

    2001-01-01

    This paper formulates the general methodology for estimating the bias error distribution of a device in a measuring domain from less accurate measurements when a minimal number of standard values (typically two values) are available. A new perspective is that the bias error distribution can be found as a solution of an intrinsic functional equation in a domain. Based on this theory, the scaling- and translation-based methods for determining the bias error distribution arc developed. These methods are virtually applicable to any device as long as the bias error distribution of the device can be sufficiently described by a power series (a polynomial) or a Fourier series in a domain. These methods have been validated through computational simulations and laboratory calibration experiments for a number of different devices.

  15. Political bias is tenacious.

    PubMed

    Ditto, Peter H; Wojcik, Sean P; Chen, Eric Evan; Grady, Rebecca Hofstein; Ringel, Megan M

    2015-01-01

    Duarte et al. are right to worry about political bias in social psychology but they underestimate the ease of correcting it. Both liberals and conservatives show partisan bias that often worsens with cognitive sophistication. More non-liberals in social psychology is unlikely to speed our convergence upon the truth, although it may broaden the questions we ask and the data we collect. PMID:26786070

  16. Establishing operations

    PubMed Central

    Michael, Jack

    1993-01-01

    The first two books on behavior analysis (Skinner, 1938; Keller & Schoenfeld, 1950) had chapter-length coverage of motivation. The next generation of texts also had chapters on the topic, but by the late 1960s it was no longer being given much treatment in the behavior-analytic literature. The present failure to deal with the topic leaves a gap in our understanding of operant functional relations. A partial solution is to reintroduce the concept of the establishing operation, defined as an environmental event, operation, or stimulus condition that affects an organism by momentarily altering (a) the reinforcing effectiveness of other events and (b) the frequency of occurrence of that part of the organism's repertoire relevant to those events as consequences. Discriminative and motivative variables can be distinguished as follows: The former are related to the differential availability of an effective form of reinforcement given a particular type of behavior; the latter are related to the differential reinforcing effectiveness of environmental events. An important distinction can also be made between unconditioned establishing operations (UEOs), such as food deprivation and painful stimulation, and conditioned establishing operations (CEOs) that depend on the learning history of the organism. One type of CEO is a stimulus that has simply been paired with a UEO and as a result may take on some of the motivative properties of that UEO. The warning stimulus in avoidance procedures is another important type of CEO referred to as reflexive because it establishes its own termination as a form of reinforcement and evokes the behavior that has accomplished such termination. Another CEO is closely related to the concept of conditional conditioned reinforcement and is referred to as a transitive CEO, because it establishes some other stimulus as a form of effective reinforcement and evokes the behavior that has produced that other stimulus. The multiple control of human

  17. Assessment of bias for MRI diffusion tensor imaging using SIMEX.

    PubMed

    Lauzon, Carolyn B; Asman, Andrew J; Crainiceanu, Ciprian; Caffo, Brian C; Landman, Bennett A

    2011-01-01

    Diffusion Tensor Imaging (DTI) is a Magnetic Resonance Imaging method for measuring water diffusion in vivo. One powerful DTI contrast is fractional anisotropy (FA). FA reflects the strength of water's diffusion directional preference and is a primary metric for neuronal fiber tracking. As with other DTI contrasts, FA measurements are obscured by the well established presence of bias. DTI bias has been challenging to assess because it is a multivariable problem including SNR, six tensor parameters, and the DTI collection and processing method used. SIMEX is a modem statistical technique that estimates bias by tracking measurement error as a function of added noise. Here, we use SIMEX to assess bias in FA measurements and show the method provides; i) accurate FA bias estimates, ii) representation of FA bias that is data set specific and accessible to non-statisticians, and iii) a first time possibility for incorporation of bias into DTI data analysis. PMID:21995019

  18. Validation of an interpretation bias assessment for body dissatisfaction.

    PubMed

    Martinelli, Mary K; Holzinger, Jayne B; Chasson, Gregory S

    2014-09-01

    Currently, research on interpretation bias and body dissatisfaction is limited. The few experimental paradigms that have been used to explore this phenomenon utilized a method that may not accurately capture the nature of interpretation bias as explained by cognitive theory. The present study investigated the reliability and validity of a novel computerized assessment of interpretation bias (WSAP) for body dissatisfaction, which may more accurately reflect the cognitive processing involved in such bias by implementing the Word Sentence Association Paradigm (WSAP), a previously established method of measuring interpretation bias in other clinical populations. Undergraduate females (n=214) completed the WSAP and other measures. Results indicate initial support for the WSAP as a valid, reliable measure of interpretation bias for body dissatisfaction. Although preliminary, this study contributes to the minimal research in this area and serves as the first psychometric investigation of the WSAP to measure such interpretation bias for body dissatisfaction.

  19. A Review of Established Guidelines and Standards for International Education Travel and Exchange Programs for Students. Report of the Department of Education to the Governor and the General Assembly of Virgina. House Document No. 25.

    ERIC Educational Resources Information Center

    Virginia State General Assembly, Richmond. House.

    This study of existing guidelines and standards for international travel by students in local school divisions is the result of a Virginia Department of Education team effort over four months. The interdisciplinary team reviewed guidelines and standards for international travel and student exchange programs from major organizations and developed…

  20. Halo velocity bias

    NASA Astrophysics Data System (ADS)

    Biagetti, Matteo; Desjacques, Vincent; Kehagias, Alex; Riotto, Antonio

    2014-11-01

    It has been recently shown that any halo velocity bias present in the initial conditions does not decay to unity, in agreement with predictions from peak theory. However, this is at odds with the standard formalism based on the coupled-fluids approximation for the coevolution of dark matter and halos. Starting from conservation laws in phase space, we discuss why the fluid momentum conservation equation for the biased tracers needs to be modified in accordance with the change advocated in Baldauf et al. Our findings indicate that a correct description of the halo properties should properly take into account peak constraints when starting from the Vlasov-Boltzmann equation.

  1. Terahertz Bloch oscillator with a modulated bias.

    PubMed

    Hyart, Timo; Alexeeva, Natalia V; Mattas, Jussi; Alekseev, Kirill N

    2009-04-10

    Electrons performing Bloch oscillations in an energy band of a dc-biased superlattice in the presence of weak dissipation can potentially generate THz fields at room temperature. The realization of such a Bloch oscillator is a long-standing problem due to the instability of a homogeneous electric field in conditions of negative differential conductivity. We establish the theoretical feasibility of stable THz gain in a long superlattice device in which the bias is quasistatically modulated by microwave fields. The modulation waveforms must have at least two harmonics in their spectra.

  2. Own Variety Bias

    PubMed Central

    García, Andrea Ariza

    2015-01-01

    In a language identification task, native Belgian French and native Swiss French speakers identified French from France as their own variety. However, Canadian French was not subject to this bias. Canadian and French listeners didn’t claim a different variety as their own.

  3. Biased to Learn Language

    ERIC Educational Resources Information Center

    Sebastian-Galles, Nuria

    2007-01-01

    Some recent publications that explore the foundations of early language development are reviewed in this article. The review adopts the pivotal idea that infants' advancements are helped by the existence of different types of biases. The infant's discovery of the phonological properties of the language of the environment, as well as their learning…

  4. Optically biased laser gyro

    SciTech Connect

    Anderson, D.Z.; Chow, W.W.; Scully, M.O.; Sanders, V.E.

    1980-10-01

    We describe a four-mode ring laser that exhibits none of the mode-locking characteristics that plague laser gyros. This laser is characterized by a bias that changes sign with a change in the direction of rotation and prevents the counterpropagating modes from locking. A theoretical analysis explaining the experimental results is outlined.

  5. Own Variety Bias.

    PubMed

    Sloos, Marjoleine; García, Andrea Ariza

    2015-10-01

    In a language identification task, native Belgian French and native Swiss French speakers identified French from France as their own variety. However, Canadian French was not subject to this bias. Canadian and French listeners didn't claim a different variety as their own. PMID:27648211

  6. Enhanced magnetic behavior, exchange bias effect, and dielectric property of BiFeO{sub 3} incorporated in (BiFeO{sub 3}){sub 0.50} (Co{sub 0.4}Zn{sub 0.4}Cu{sub 0.2} Fe{sub 2}O{sub 4}){sub 0.5} nanocomposite

    SciTech Connect

    Mukhopadhyay, K.; Mahapatra, A. S.; Sutradhar, S.; Chakrabarti, P. K.

    2014-03-15

    Nanoparticles of BiFeO{sub 3} (BFO) are incorporated in the nanocomposite of (BiFeO{sub 3}){sub 0.50} (Co{sub 0.4}Zn{sub 0.4}Cu{sub 0.2} Fe{sub 2}O{sub 4}){sub 0.5}, (BFO-CZCF) and these are prepared by chemical route. The formation of pure crystallographic phase of each component (BFO and CZCF) in the nanocomposite of BFO-CZCF has been confirmed by Rietveld analysis of the X-ray diffractograms using FULLPROF program. Morphology, average particle size and its distribution, crystallographic phase etc. are obtained from the high-resolution transmission electron microscopy of BFO-CZCF. Magnetic measurements of BFO-CZCF have been carried out to explore the modulation of magnetic behavior of BFO in BFO-CZCF. Interestingly, magnetization of BFO-CZCF has been drastically enhanced compared to that of the pristine BFO. An exchange bias effect is also observed in the M vs. H loops of BFO-CZCF recorded in field cooled and zero field cooled conditions, which suggest that nanoparticles of BFO (AFM) are encapsulated by nanoparticles of CZCF (FM) in BFO-CZCF. Thermal variation of dielectric constant of BFO-CZCF is recorded in the range of 300 to 1073 K and a ferroelectric to paraelectric transition is observed at ∼728 K. Enhanced magnetic property of BFO would quite interesting for this important multiferroic.

  7. Human liver alcohol dehydrogenase: amino acid substitution in the beta 2 beta 2 Oriental isozyme explains functional properties, establishes an active site structure, and parallels mutational exchanges in the yeast enzyme.

    PubMed Central

    Jörnvall, H; Hempel, J; Vallee, B L; Bosron, W F; Li, T K

    1984-01-01

    The homodimeric Oriental beta 2 beta 2 isozyme of human liver alcohol dehydrogenase, corresponding to an allelic variant at the ADH2 gene locus, was studied in order to define the amino acid exchange in relation to the beta 1 beta 1 isozyme, the predominant allelic form among Caucasians. Sequence analysis reveals that the amino acid substitution occurs at position 7 of the largest CNBr fragment, corresponding to position 47 of the whole protein chain. Here, the beta 2 form has a histidine residue, while, in common with other characterized mammalian liver alcohol dehydrogenases, the beta 1 form has an arginine residue. This exchange does not affect the adjacent cysteine-46 residue, which is a protein ligand to the active-site zinc atom, thus clarifying previously inconsistent results. The histidine/arginine-47 mutational replacement corresponds to a position that binds the pyrophosphate group of the coenzyme NAD(H); this explains the functional differences between the beta 1 beta 1 and beta 2 beta 2 isozymes, including both a lower pH optimum and higher turnover number of beta 2 beta 2, which is likely to be the mutant form. The exchange demonstrates the existence of parallel but separate mutations in the evolution of alcohol dehydrogenases because these mammalian enzymes differ at exactly the same position by the same type of substitution as is found between a mutant and the wild-type constitutive forms of the corresponding yeast enzyme. PMID:6374651

  8. Optimism Bias in Fans and Sports Reporters.

    PubMed

    Love, Bradley C; Kopeć, Łukasz; Guest, Olivia

    2015-01-01

    People are optimistic about their prospects relative to others. However, existing studies can be difficult to interpret because outcomes are not zero-sum. For example, one person avoiding cancer does not necessitate that another person develops cancer. Ideally, optimism bias would be evaluated within a closed formal system to establish with certainty the extent of the bias and the associated environmental factors, such that optimism bias is demonstrated when a population is internally inconsistent. Accordingly, we asked NFL fans to predict how many games teams they liked and disliked would win in the 2015 season. Fans, like ESPN reporters assigned to cover a team, were overly optimistic about their team's prospects. The opposite pattern was found for teams that fans disliked. Optimism may flourish because year-to-year team results are marked by auto-correlation and regression to the group mean (i.e., good teams stay good, but bad teams improve).

  9. Optimism Bias in Fans and Sports Reporters

    PubMed Central

    Love, Bradley C.

    2015-01-01

    People are optimistic about their prospects relative to others. However, existing studies can be difficult to interpret because outcomes are not zero-sum. For example, one person avoiding cancer does not necessitate that another person develops cancer. Ideally, optimism bias would be evaluated within a closed formal system to establish with certainty the extent of the bias and the associated environmental factors, such that optimism bias is demonstrated when a population is internally inconsistent. Accordingly, we asked NFL fans to predict how many games teams they liked and disliked would win in the 2015 season. Fans, like ESPN reporters assigned to cover a team, were overly optimistic about their team’s prospects. The opposite pattern was found for teams that fans disliked. Optimism may flourish because year-to-year team results are marked by auto-correlation and regression to the group mean (i.e., good teams stay good, but bad teams improve). PMID:26352146

  10. Educators Exchange: A Program Evaluation.

    ERIC Educational Resources Information Center

    Armstrong, William B.

    The Educators Exchange Program (EEP) was established under a training and educational exchange agreement reached by California's San Diego Community College District (SDCCD) and the republic of Mexico. In the program, the District provided a 4-week technological training program to faculty at Centros de Capacitacion Tecnologica Industrial…

  11. Unbiased isotope equilibrium factors from partial isotope exchange experiments in 3-exchange site systems

    NASA Astrophysics Data System (ADS)

    Agrinier, Pierre; Javoy, Marc

    2016-09-01

    Two methods are available in order to evaluate the equilibrium isotope fractionation factors between exchange sites or phases from partial isotope exchange experiments. The first one developed by Northrop and Clayton (1966) is designed for isotope exchanges between two exchange sites (hereafter, the N&C method), the second one from Zheng et al. (1994) is a refinement of the first one to account for a third isotope exchanging site (hereafter, the Z method). In this paper, we use a simple model of isotope kinetic exchange for a 3-exchange site system (such as hydroxysilicates where oxygen occurs as OH and non-OH groups like in muscovite, chlorite, serpentine, or water or calcite) to explore the behavior of the N&C and Z methods. We show that these two methods lead to significant biases that cannot be detected with the usual graphical tests proposed by the authors. Our model shows that biases originate because isotopes are fractionated between all these exchanging sites. Actually, we point out that the variable mobility (or exchangeability) of isotopes in and between the exchange sites only controls the amplitude of the bias, but is not essential to the production of this bias as previously suggested. Setting a priori two of the three exchange sites at isotopic equilibrium remove the bias and thus is required for future partial exchange experiments to produce accurate and unbiased extrapolated equilibrium fractionation factors. Our modeling applied to published partial oxygen isotope exchange experiments for 3-exchange site systems (the muscovite-calcite (Chacko et al., 1996), the chlorite-water (Cole and Ripley, 1998) and the serpentine-water (Saccocia et al., 2009)) shows that the extrapolated equilibrium fractionation factors (reported as 1000 ln(α)) using either the N&C or the Z methods lead to bias that may reach several δ per mil in a few cases. These problematic cases, may be because experiments were conducted at low temperature and did not reach high

  12. Assessing Bias in Search Engines.

    ERIC Educational Resources Information Center

    Mowshowitz, Abbe; Kawaguchi, Akira

    2002-01-01

    Addresses the measurement of bias in search engines on the Web, defining bias as the balance and representation of items in a collection retrieved from a database for a set of queries. Assesses bias by measuring the deviation from the ideal of the distribution produced by a particular search engine. (Author/LRW)

  13. Negativity bias and basic values.

    PubMed

    Schwartz, Shalom H

    2014-06-01

    Basic values explain more variance in political attitudes and preferences than other personality and sociodemographic variables. The values most relevant to the political domain are those likely to reflect the degree of negativity bias. Value conflicts that represent negativity bias clarify differences between what worries conservatives and liberals and suggest that relations between ideology and negativity bias are linear. PMID:24970450

  14. HEAT EXCHANGER

    DOEpatents

    Fox, T.H. III; Richey, T. Jr.; Winders, G.R.

    1962-10-23

    A heat exchanger is designed for use in the transfer of heat between a radioactive fiuid and a non-radioactive fiuid. The exchanger employs a removable section containing the non-hazardous fluid extending into the section designed to contain the radioactive fluid. The removable section is provided with a construction to cancel out thermal stresses. The stationary section is pressurized to prevent leakage of the radioactive fiuid and to maintain a safe, desirable level for this fiuid. (AEC)

  15. Assessment of the possibility of establishing material cycling in an experimental model of the bio-technical life support system with plant and human wastes included in mass exchange

    NASA Astrophysics Data System (ADS)

    Tikhomirov, A. A.; Ushakova, S. A.; Velichko, V. V.; Tikhomirova, N. A.; Kudenko, Yu. A.; Gribovskaya, I. V.; Gros, J.-B.; Lasseur, Ch.

    2011-05-01

    A pilot model of a bio-technical life support system (BTLSS) including human and plant wastes has been developed at the Institute of Biophysics SB RAS (Krasnoyarsk, Russia). This paper describes the structure of the photosynthesizing unit of the system, which includes wheat, chufa and vegetables. The study substantiates the simultaneous use of neutral and biological substrates for cultivating plants. A novel physicochemical method for the involvement of human wastes in the cycling has been employed, which enables the use of recycled products as nutrients for plants. Inedible plant biomass was subjected to biological combustion in the soil-like substrate (SLS) and was thus involved in the system mass exchange; NaCl contained in native urine was returned to the human through the consumption of Salicornia europaea, an edible salt-concentrating plant. Mass transfer processes in the studied BLSS have been examined for different chemical components.

  16. Synchronous Spin-Exchange Optical Pumping.

    PubMed

    Korver, A; Thrasher, D; Bulatowicz, M; Walker, T G

    2015-12-18

    We demonstrate a new approach to precision NMR with hyperpolarized gases designed to mitigate NMR shifts due to the alkali spin-exchange field. The NMR bias field is implemented as a sequence of alkali (Rb) 2π pulses, allowing the Rb polarization to be optically pumped transverse to the bias field. When the Rb polarization is modulated at the noble-gas (Xe) NMR resonance, spin-exchange collisions buildup a precessing transverse Xe polarization. We study and mitigate novel NMR broadening effects due to the oscillating spin-exchange field. Spin-exchange frequency shifts are suppressed 2500×, and Rb magnetometer gain measurements project photon shot-noise limited NMR frequency uncertainties below 10  nHz/sqrt[Hz]. PMID:26722919

  17. Attentional bias modification encourages healthy eating.

    PubMed

    Kakoschke, Naomi; Kemps, Eva; Tiggemann, Marika

    2014-01-01

    The continual exposure to unhealthy food cues in the environment encourages poor dietary habits, in particular consuming too much fat and sugar, and not enough fruit and vegetables. According to Berridge's (2009) model of food reward, unhealthy eating is a behavioural response to biased attentional processing. The present study used an established attentional bias modification paradigm to discourage the consumption of unhealthy food and instead promote healthy eating. Participants were 146 undergraduate women who were randomly assigned to two groups: one was trained to direct their attention toward pictures of healthy food ('attend healthy' group) and the other toward unhealthy food ('attend unhealthy' group). It was found that participants trained to attend to healthy food cues demonstrated an increased attentional bias for such cues and ate relatively more of the healthy than unhealthy snacks compared to the 'attend unhealthy' group. Theoretically, the results support the postulated link between biased attentional processing and consumption (Berridge, 2009). At a practical level, they offer potential scope for interventions that focus on eating well.

  18. Heat exchanger

    SciTech Connect

    Drury, C.R.

    1988-02-02

    A heat exchanger having primary and secondary conduits in heat-exchanging relationship is described comprising: at least one serpentine tube having parallel sections connected by reverse bends, the serpentine tube constituting one of the conduits; a group of open-ended tubes disposed adjacent to the parallel sections, the open-ended tubes constituting the other of the conduits, and forming a continuous mass of contacting tubes extending between and surrounding the serpentine tube sections; and means securing the mass of tubes together to form a predetermined cross-section of the entirety of the mass of open-ended tubes and tube sections.

  19. The intentionality bias and schizotypy.

    PubMed

    Moore, J W; Pope, A

    2014-01-01

    The "intentionality bias" refers to our automatic tendency to judge other people's actions to be intentional. In this experiment we extended research on this effect in two key ways. First, we developed a novel nonlinguistic task for assessing the intentionality bias. This task used video stimuli of ambiguous movements. Second, we investigated the relationship between the strength of this bias and schizotypy (schizophrenia-like symptoms in healthy individuals). Our results showed that the intentionality bias was replicated for the video stimuli and also that this bias is stronger in those individuals scoring higher on the schizotypy rating scales. Overall these findings lend further support for the existence of the intentionality bias. We also discuss the possible relevance of these findings for our understanding of certain symptoms of schizophrenic illness.

  20. Manitoba Exchange.

    ERIC Educational Resources Information Center

    Coss, Maurice

    Planning ideas and follow-up activities are described for a reciprocal exchange program between groups of 5th and 6th grade students in Manitoba who are "twinned" with another school in the province. Emphasis is on providing learning experiences which help students become familiar with the economic activity in the area, with the local government…

  1. Heat exchanger

    DOEpatents

    Wolowodiuk, Walter

    1976-01-06

    A heat exchanger of the straight tube type in which different rates of thermal expansion between the straight tubes and the supply pipes furnishing fluid to those tubes do not result in tube failures. The supply pipes each contain a section which is of helical configuration.

  2. Heat exchanger

    DOEpatents

    Daman, Ernest L.; McCallister, Robert A.

    1979-01-01

    A heat exchanger is provided having first and second fluid chambers for passing primary and secondary fluids. The chambers are spaced apart and have heat pipes extending from inside one chamber to inside the other chamber. A third chamber is provided for passing a purge fluid, and the heat pipe portion between the first and second chambers lies within the third chamber.

  3. Permanent magnet flux-biased magnetic actuator with flux feedback

    NASA Technical Reports Server (NTRS)

    Groom, Nelson J. (Inventor)

    1991-01-01

    The invention is a permanent magnet flux-biased magnetic actuator with flux feedback for adjustably suspending an element on a single axis. The magnetic actuator includes a pair of opposing electromagnets and provides bi-directional forces along the single axis to the suspended element. Permanent magnets in flux feedback loops from the opposing electromagnets establish a reference permanent magnet flux-bias to linearize the force characteristics of the electromagnets to extend the linear range of the actuator without the need for continuous bias currents in the electromagnets.

  4. Biased ligands: pathway validation for novel GPCR therapeutics.

    PubMed

    Rominger, David H; Cowan, Conrad L; Gowen-MacDonald, William; Violin, Jonathan D

    2014-06-01

    G protein-coupled receptors (GPCRs), in recent years, have been shown to signal via multiple distinct pathways. Furthermore, biased ligands for some receptors can differentially stimulate or inhibit these pathways versus unbiased endogenous ligands or drugs. Biased ligands can be used to gain a deeper understanding of the molecular targets and cellular responses associated with a GPCR, and may be developed into therapeutics with improved efficacy, safety and/or tolerability. Here we review examples and approaches to pathway validation that establish the relevance and therapeutic potential of distinct pathways that can be selectively activated or blocked by biased ligands.

  5. Biased ligands: pathway validation for novel GPCR therapeutics.

    PubMed

    Rominger, David H; Cowan, Conrad L; Gowen-MacDonald, William; Violin, Jonathan D

    2014-06-01

    G protein-coupled receptors (GPCRs), in recent years, have been shown to signal via multiple distinct pathways. Furthermore, biased ligands for some receptors can differentially stimulate or inhibit these pathways versus unbiased endogenous ligands or drugs. Biased ligands can be used to gain a deeper understanding of the molecular targets and cellular responses associated with a GPCR, and may be developed into therapeutics with improved efficacy, safety and/or tolerability. Here we review examples and approaches to pathway validation that establish the relevance and therapeutic potential of distinct pathways that can be selectively activated or blocked by biased ligands. PMID:24834870

  6. Audibility and visual biasing in speech perception

    NASA Astrophysics Data System (ADS)

    Clement, Bart Richard

    Although speech perception has been considered a predominantly auditory phenomenon, large benefits from vision in degraded acoustic conditions suggest integration of audition and vision. More direct evidence of this comes from studies of audiovisual disparity that demonstrate vision can bias and even dominate perception (McGurk & MacDonald, 1976). It has been observed that hearing-impaired listeners demonstrate more visual biasing than normally hearing listeners (Walden et al., 1990). It is argued here that stimulus audibility must be equated across groups before true differences can be established. In the present investigation, effects of visual biasing on perception were examined as audibility was degraded for 12 young normally hearing listeners. Biasing was determined by quantifying the degree to which listener identification functions for a single synthetic auditory /ba-da-ga/ continuum changed across two conditions: (1)an auditory-only listening condition; and (2)an auditory-visual condition in which every item of the continuum was synchronized with visual articulations of the consonant-vowel (CV) tokens /ba/ and /ga/, as spoken by each of two talkers. Audibility was altered by presenting the conditions in quiet and in noise at each of three signal-to- noise (S/N) ratios. For the visual-/ba/ context, large effects of audibility were found. As audibility decreased, visual biasing increased. A large talker effect also was found, with one talker eliciting more biasing than the other. An independent lipreading measure demonstrated that this talker was more visually intelligible than the other. For the visual-/ga/ context, audibility and talker effects were less robust, possibly obscured by strong listener effects, which were characterized by marked differences in perceptual processing patterns among participants. Some demonstrated substantial biasing whereas others demonstrated little, indicating a strong reliance on audition even in severely degraded acoustic

  7. Question format shifts bias away from the emphasised response in tests of recognition memory.

    PubMed

    Mill, Ravi D; O'Connor, Akira R

    2014-11-01

    The question asked to interrogate memory has potential to influence response bias at retrieval, yet has not been systematically investigated. According to framing effects in the field of eyewitness testimony, retrieval cueing effects in cognitive psychology and the acquiescence bias in questionnaire responding, the question should establish a confirmatory bias. Conversely, according to findings from the rewarded decision-making literature involving mixed incentives, the question should establish a disconfirmatory bias. Across three experiments (ns=90 [online], 29 [laboratory] and 29 [laboratory]) we demonstrate a disconfirmatory bias - "old?" decreased old responding. This bias is underpinned by a goal-driven mechanism wherein participants seek to maximise emphasised response accuracy at the expense of frequency. Moreover, we demonstrate that disconfirmatory biases can be generated without explicit reference to the goal state. We conclude that subtle aspects of the test environment influence retrieval to a greater extent than has been previously considered. PMID:25279434

  8. Question format shifts bias away from the emphasised response in tests of recognition memory.

    PubMed

    Mill, Ravi D; O'Connor, Akira R

    2014-11-01

    The question asked to interrogate memory has potential to influence response bias at retrieval, yet has not been systematically investigated. According to framing effects in the field of eyewitness testimony, retrieval cueing effects in cognitive psychology and the acquiescence bias in questionnaire responding, the question should establish a confirmatory bias. Conversely, according to findings from the rewarded decision-making literature involving mixed incentives, the question should establish a disconfirmatory bias. Across three experiments (ns=90 [online], 29 [laboratory] and 29 [laboratory]) we demonstrate a disconfirmatory bias - "old?" decreased old responding. This bias is underpinned by a goal-driven mechanism wherein participants seek to maximise emphasised response accuracy at the expense of frequency. Moreover, we demonstrate that disconfirmatory biases can be generated without explicit reference to the goal state. We conclude that subtle aspects of the test environment influence retrieval to a greater extent than has been previously considered.

  9. Sequential biases in accumulating evidence

    PubMed Central

    Huggins, Richard; Dogo, Samson Henry

    2015-01-01

    Whilst it is common in clinical trials to use the results of tests at one phase to decide whether to continue to the next phase and to subsequently design the next phase, we show that this can lead to biased results in evidence synthesis. Two new kinds of bias associated with accumulating evidence, termed ‘sequential decision bias’ and ‘sequential design bias’, are identified. Both kinds of bias are the result of making decisions on the usefulness of a new study, or its design, based on the previous studies. Sequential decision bias is determined by the correlation between the value of the current estimated effect and the probability of conducting an additional study. Sequential design bias arises from using the estimated value instead of the clinically relevant value of an effect in sample size calculations. We considered both the fixed‐effect and the random‐effects models of meta‐analysis and demonstrated analytically and by simulations that in both settings the problems due to sequential biases are apparent. According to our simulations, the sequential biases increase with increased heterogeneity. Minimisation of sequential biases arises as a new and important research area necessary for successful evidence‐based approaches to the development of science. © 2015 The Authors. Research Synthesis Methods Published by John Wiley & Sons Ltd. PMID:26626562

  10. Magnetic stability of novel exchange coupled systems

    SciTech Connect

    Inomata, A.; Jiang, J. S.; You, C.-Y.; Pearson, J. E.; Bader, S. D.

    1999-11-08

    The magnetic stability of two different interracial exchange coupled systems are investigated using the magneto-optic Kerr effect during repeated reversal of the soft layer magnetization by field cycling up to 10{sup 7} times. For Fe/Cr double-superlattice exchange biased systems, small but rapid initial decay of exchange bias field H{sub E} and the remanent magnetization is observed. Also the Sin-Co/Fe bilayers grown epitaxially with uniaxial in-plane anisotropy show similar decay. However, the H{sub E} of biaxial and random in-plane bilayers, shows gradual decay without large reduction of the magnetization. These different decay behaviors explained by their different microstructure and interracial spin configurations.

  11. Cognitive bias in forensic anthropology: visual assessment of skeletal remains is susceptible to confirmation bias.

    PubMed

    Nakhaeizadeh, Sherry; Dror, Itiel E; Morgan, Ruth M

    2014-05-01

    An experimental study was designed to examine cognitive biases within forensic anthropological non-metric methods in assessing sex, ancestry and age at death. To investigate examiner interpretation, forty-one non-novice participants were semi randomly divided into three groups. Prior to conducting the assessment of the skeletal remains, two of the groups were given different extraneous contextual information regarding the sex, ancestry and age at death of the individual. The third group acted as a control group with no extraneous contextual information. The experiment was designed to investigate if the interpretation and conclusions of the skeletal remains would differ amongst participants within the three groups, and to assess whether the examiners would confirm or disagree with the given extraneous context when establishing a biological profile. The results revealed a significant biasing effect within the three groups, demonstrating a strong confirmation bias in the assessment of sex, ancestry and age at death. In assessment of sex, 31% of the participants in the control group concluded that the skeleton remains were male. In contrast, in the group that received contextual information that the remains were male, 72% concluded that the remains were male, and in the participant group where the context was that the remains were of a female, 0% of the participants concluded that the remains were male. Comparable results showing bias were found in assessing ancestry and age at death. These data demonstrate that cognitive bias can impact forensic anthropological non-metric methods on skeletal remains and affects the interpretation and conclusions of the forensic scientists. This empirical study is a step in establishing an evidence base approach for dealing with cognitive issues in forensic anthropological assessments, so as to enhance this valuable forensic science discipline.

  12. Steady-State Density Functional Theory for Finite Bias Conductances.

    PubMed

    Stefanucci, G; Kurth, S

    2015-12-01

    In the framework of density functional theory, a formalism to describe electronic transport in the steady state is proposed which uses the density on the junction and the steady current as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential, and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds. At small currents these steps emerge as the equilibrium xc discontinuity bifurcates. The formalism is applied to a model benzene junction, finding perfect agreement with the orthodox theory of Coulomb blockade. PMID:26571349

  13. Steady-State Density Functional Theory for Finite Bias Conductances.

    PubMed

    Stefanucci, G; Kurth, S

    2015-12-01

    In the framework of density functional theory, a formalism to describe electronic transport in the steady state is proposed which uses the density on the junction and the steady current as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential, and an xc contribution to the bias. For weakly coupled junctions the xc potentials exhibit steps in the density-current plane which are shown to be crucial to describe the Coulomb blockade diamonds. At small currents these steps emerge as the equilibrium xc discontinuity bifurcates. The formalism is applied to a model benzene junction, finding perfect agreement with the orthodox theory of Coulomb blockade.

  14. Cognitive Bias in Systems Verification

    NASA Technical Reports Server (NTRS)

    Larson, Steve

    2012-01-01

    Working definition of cognitive bias: Patterns by which information is sought and interpreted that can lead to systematic errors in decisions. Cognitive bias is used in diverse fields: Economics, Politics, Intelligence, Marketing, to name a few. Attempts to ground cognitive science in physical characteristics of the cognitive apparatus exceed our knowledge. Studies based on correlations; strict cause and effect is difficult to pinpoint. Effects cited in the paper and discussed here have been replicated many times over, and appear sound. Many biases have been described, but it is still unclear whether they are all distinct. There may only be a handful of fundamental biases, which manifest in various ways. Bias can effect system verification in many ways . Overconfidence -> Questionable decisions to deploy. Availability -> Inability to conceive critical tests. Representativeness -> Overinterpretation of results. Positive Test Strategies -> Confirmation bias. Debiasing at individual level very difficult. The potential effect of bias on the verification process can be managed, but not eliminated. Worth considering at key points in the process.

  15. Observational biases for transiting planets

    NASA Astrophysics Data System (ADS)

    Kipping, David M.; Sandford, Emily

    2016-09-01

    Observational biases distort our view of nature, such that the patterns we see within a surveyed population of interest are often unrepresentative of the truth we seek. Transiting planets currently represent the most informative data set on the ensemble properties of exoplanets within 1 AU of their star. However, the transit method is inherently biased due to both geometric and detection-driven effects. In this work, we derive the overall observational biases affecting the most basic transit parameters from first principles. By assuming a trapezoidal transit and using conditional probability, we infer the expected distribution of these terms both as a joint distribution and in a marginalized form. These general analytic results provide a baseline against which to compare trends predicted by mission-tailored injection/recovery simulations and offer a simple way to correct for observational bias. Our results explain why the observed population of transiting planets displays a non-uniform impact parameter distribution, with a bias towards near-equatorial geometries. We also find that the geometric bias towards observed planets transiting near periastron is attenuated by the longer durations which occur near apoastron. Finally, we predict that the observational bias with respect to ratio-of-radii is super-quadratic, scaling as (RP/R⋆)5/2, driven by an enhanced geometric transit probability and modestly longer durations.

  16. Composite ion exchange materials

    SciTech Connect

    Amarasinghe, S.; Zook, L.; Leddy, J.

    1994-12-31

    Composite ion exchange materials can be formed by sorbing ion exchange polymers on inert, high surface area substrates. In general, the flux of ions and molecules through these composites, as measured electrochemically, increases as the ratio of the surface area of the substrate increases relative to the volume of the ion exchanger. This suggests that fields and gradients established at the interface between the ion exchanger and substrate are important in determining the transport characteristics of the composites. Here, the authors will focus on composites formed with a cation exchange polymer, Nafion, and two different types of microbeads: polystyrene microspheres and polystyrene coated magnetic microbeads. For the polystyrene microbeads, scanning electron micrographs suggest the beads cluster in a self-similar manner, independent of the bead diameter. Flux of Ru(NH3)63+ through the composites was studied as a function of bead fraction, bead radii, and fixed surface area with mixed bead sizes. Flux was well modeled by surface diffusion along a fractal interface. Magnetic composites were formed with columns of magnetic microbeads normal to the electrode surface. Flux of Ru(NH3)63+ through these composites increased exponentially with bead fraction. For electrolyses, the difference in the molar magnetic susceptibility of the products and reactants, Dcm, tends to be non-zero. For seven redox reactions, the ratio of the flux through the magnetic composites to the flux through a Nafion film increases monotonically with {vert_bar}Dcm{vert_bar}, with enhancements as large as thirty-fold. For reversible species, the electrolysis potential through the magnetic composites is 35 mV positive of that for the Nafion films.

  17. Effective bias and potentials in steady-state quantum transport: A NEGF reverse-engineering study

    NASA Astrophysics Data System (ADS)

    Karlsson, Daniel; Verdozzi, Claudio

    2016-03-01

    Using non-equilibrium Green's functions combined with many-body perturbation theory, we have calculated steady-state densities and currents through short interacting chains subject to a finite electric bias. By using a steady-state reverse-engineering procedure, the effective potential and bias which reproduce such densities and currents in a non-interacting system have been determined. The role of the effective bias is characterised with the aid of the so-called exchange-correlation bias, recently introduced in a steady-state density-functional- theory formulation for partitioned systems. We find that the effective bias (or, equivalently, the exchange-correlation bias) depends strongly on the interaction strength and the length of the central (chain) region. Moreover, it is rather sensitive to the level of many-body approximation used. Our study shows the importance of the effective/exchange-correlation bias out of equilibrium, thereby offering hints on how to improve the description of density- functional-theory based approaches to quantum transport.

  18. Chemical exchange program analysis.

    SciTech Connect

    Waffelaert, Pascale

    2007-09-01

    As part of its EMS, Sandia performs an annual environmental aspects/impacts analysis. The purpose of this analysis is to identify the environmental aspects associated with Sandia's activities, products, and services and the potential environmental impacts associated with those aspects. Division and environmental programs established objectives and targets based on the environmental aspects associated with their operations. In 2007 the most significant aspect identified was Hazardous Materials (Use and Storage). The objective for Hazardous Materials (Use and Storage) was to improve chemical handling, storage, and on-site movement of hazardous materials. One of the targets supporting this objective was to develop an effective chemical exchange program, making a business case for it in FY07, and fully implementing a comprehensive chemical exchange program in FY08. A Chemical Exchange Program (CEP) team was formed to implement this target. The team consists of representatives from the Chemical Information System (CIS), Pollution Prevention (P2), the HWMF, Procurement and the Environmental Management System (EMS). The CEP Team performed benchmarking and conducted a life-cycle analysis of the current management of chemicals at SNL/NM and compared it to Chemical Exchange alternatives. Those alternatives are as follows: (1) Revive the 'Virtual' Chemical Exchange Program; (2) Re-implement a 'Physical' Chemical Exchange Program using a Chemical Information System; and (3) Transition to a Chemical Management Services System. The analysis and benchmarking study shows that the present management of chemicals at SNL/NM is significantly disjointed and a life-cycle or 'Cradle-to-Grave' approach to chemical management is needed. This approach must consider the purchasing and maintenance costs as well as the cost of ultimate disposal of the chemicals and materials. A chemical exchange is needed as a mechanism to re-apply chemicals on site. This will not only reduce the quantity of

  19. Brown coals as natural electron-ion-exchangers

    SciTech Connect

    Kossov, I.I.; Aleksandrov, I.V.; Kamneva, A.I.

    1984-01-01

    The existence of electron-ion-exchange properties in brown coals has been established. The influence of the redox properties of the organic and mineral fractions of the coals on their capacity for electron exchange has been shown.

  20. The intentionality bias in schizophrenia.

    PubMed

    Peyroux, Elodie; Strickland, Brent; Tapiero, Isabelle; Franck, Nicolas

    2014-11-30

    The tendency to over-interpret events of daily life as resulting from voluntary or intentional actions is one of the key aspects of schizophrenia with persecutory delusions. Here, we ask whether this characteristic may emerge from the abnormal activity of a basic cognitive process found in healthy adults and children: the intentionality bias, which refers to the implicit and automatic inclination to interpret human actions as intentional (Rosset, 2008, Cognition 108, 771-780). In our experiment, patients with schizophrenia and healthy controls were shown sentences describing human actions in various linguistic contexts, and were asked to indicate whether the action was intentional or not. The results indicated that people with schizophrenia exhibited a striking bias to over attribute intentionality regardless of linguistic context, contrary to healthy controls who did not exhibit such a general intentionality bias. Moreover, this study provides some insight into the cognitive mechanisms underlying this bias: an inability to inhibit the automatic attribution of intentionality.

  1. Magnetic bearings with zero bias

    NASA Technical Reports Server (NTRS)

    Brown, Gerald V.; Grodsinsky, Carlos M.

    1991-01-01

    A magnetic bearing operating without a bias field has supported a shaft rotating at speeds up to 12,000 rpm with the usual four power supplies and with only two. A magnetic bearing is commonly operated with a bias current equal to half of the maximum current allowable in its coils. This linearizes the relation between net force and control current and improves the force slewing rate and hence the band width. The steady bias current dissipates power, even when no force is required from the bearing. The power wasted is equal to two-thirds of the power at maximum force output. Examined here is the zero bias idea. The advantages and disadvantages are noted.

  2. Bias and design in software specifications

    NASA Technical Reports Server (NTRS)

    Straub, Pablo A.; Zelkowitz, Marvin V.

    1990-01-01

    Implementation bias in a specification is an arbitrary constraint in the solution space. Presented here is a model of bias in software specifications. Bias is defined in terms of the specification process and a classification of the attributes of the software product. Our definition of bias provides insight into both the origin and the consequences of bias. It also shows that bias is relative and essentially unavoidable. Finally, we describe current work on defining a measure of bias, formalizing our model, and relating bias to software defects.

  3. Knowledge Exchange with Sistema Scotland

    ERIC Educational Resources Information Center

    Allan, Julie; Moran, Nikki; Duffy, Celia; Loening, Gica

    2010-01-01

    This paper reports on a knowledge exchange project, funded by the Scottish Funding Council and undertaken by a group of researchers from three higher education institutions in Scotland and the project partner, Sistema Scotland. This newly established charity is attempting to implement a major programme of social change, developed in Venezuela,…

  4. Carbon exchange by establishing biofuel crops in Central Illinois

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Perennial grass biofuels may contribute to long-term carbon sequestration in soils, thereby providing a broad range of environmental benefits at multiple scales. To quantify those benefits, the carbon balance was investigated over three perennial grass biofuel crops miscanthus (Miscanthus giganteus)...

  5. Segmented heat exchanger

    DOEpatents

    Baldwin, Darryl Dean; Willi, Martin Leo; Fiveland, Scott Byron; Timmons, Kristine Ann

    2010-12-14

    A segmented heat exchanger system for transferring heat energy from an exhaust fluid to a working fluid. The heat exchanger system may include a first heat exchanger for receiving incoming working fluid and the exhaust fluid. The working fluid and exhaust fluid may travel through at least a portion of the first heat exchanger in a parallel flow configuration. In addition, the heat exchanger system may include a second heat exchanger for receiving working fluid from the first heat exchanger and exhaust fluid from a third heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the second heat exchanger in a counter flow configuration. Furthermore, the heat exchanger system may include a third heat exchanger for receiving working fluid from the second heat exchanger and exhaust fluid from the first heat exchanger. The working fluid and exhaust fluid may travel through at least a portion of the third heat exchanger in a parallel flow configuration.

  6. Cognitive Biases Questionnaire for Psychosis

    PubMed Central

    Peters, Emmanuelle R.

    2014-01-01

    Objective: The Cognitive Biases Questionnaire for psychosis (CBQp) was developed to capture 5 cognitive distortions (jumping to conclusions, intentionalising, catastrophising, emotional reasoning, and dichotomous thinking), which are considered important for the pathogenesis of psychosis. Vignettes were adapted from the Cognitive Style Test (CST),1 relating to “Anomalous Perceptions” and “Threatening Events” themes. Method: Scale structure, reliability, and validity were investigated in a psychosis group, and CBQp scores were compared with those of depressed and healthy control samples. Results: The CBQp showed good internal consistency and test-retest reliability. The 5 biases were not independent, with a 2-related factor scale providing the best fit. This structure suggests that the CBQp assesses a general thinking bias rather than distinct cognitive errors, while Anomalous Perception and Threatening Events theme scores can be used separately. Total CBQp scores showed good convergent validity with the CST, but individual biases were not related to existing tasks purporting to assess similar reasoning biases. Psychotic and depressed populations scored higher than healthy controls, and symptomatic psychosis patients scored higher than their nonsymptomatic counterparts, with modest relationships between CBQp scores and symptom severity once emotional disorders were partialled out. Anomalous Perception theme and Intentionalising bias scores showed some specificity to psychosis. Conclusions: Overall, the CBQp has good psychometric properties, although it is likely that it measures a different construct to existing tasks, tentatively suggested to represent a bias of interpretation rather than reasoning, judgment or decision-making processes. It is a potentially useful tool in both research and clinical arenas. PMID:23413104

  7. Northeast Regional Exchange, Annual Report, January 1982.

    ERIC Educational Resources Information Center

    1982

    The activities of Northeast Regional Exchange, Inc. (NEREX) during its first year of operation are delineated in this report. The newest member of the national network of Research and Development Exchanges (RDx), this service agency was established to promote educational improvement in the seven northeastern states: Connecticut, Maine,…

  8. Facing the partner influences exchanges in force

    PubMed Central

    Takagi, Atsushi; Bagnato, Carlo; Burdet, Etienne

    2016-01-01

    Many studies in psychology have documented how the behaviour of verbally communicating pairs is affected by social factors such as the partner’s gaze. However, few studies have examined whether physically interacting pairs are influenced by social factors. Here, we asked two partners to exchange forces with one another, where the goal was to accurately replicate the force back onto the other. We first measured an individual’s accuracy in reproducing a force from a robot. We then tested pairs who knowingly exchanged forces whilst separated by a curtain. These separated pairs exchanged forces as two independent individuals would, hence the force reproduction accuracy of partners is not affected by knowingly reproducing a force onto a nonvisible partner. On the other hand, pairs who exchanged forces whilst facing one another consistently under-reproduced the partner’s force in comparison to separated partners. Thus, the force reproduction accuracy of subjects is strongly biased by facing a partner. PMID:27739492

  9. Diamond nucleation under bias conditions

    SciTech Connect

    Stoeckel, R.; Stammler, M.; Janischowsky, K.; Ley, L.; Albrecht, M.; Strunk, H.P.

    1998-01-01

    The so-called bias pretreatment allows the growth of heteroepitaxial diamond films by plasma chemical vapor deposition on silicon (100) surfaces. We present plan-view and cross-sectional transmission electron micrographs of the substrate surface at different phases of the bias pretreatment. These observations are augmented by measurements of the etch rates of Si, SiC, and different carbon modifications under plasma conditions and the size distribution of oriented diamond crystals grown after bias pretreatment. Based on these results a new model for diamond nucleation under bias conditions is proposed. First, a closed layer of nearly epitaxially oriented cubic SiC with a thickness of about 10 nm is formed. Subplantation of carbon into this SiC layer causes a supersaturation with carbon and results in the subcutaneous formation of epitaxially oriented nucleation centers in the SiC layer. Etching of the SiC during the bias pretreatment as well as during diamond growth brings these nucleation centers to the sample surface and causes the growth of diamonds epitaxially oriented on the Si/SiC substrate. {copyright} {ital 1998 American Institute of Physics.}

  10. Biased signaling at chemokine receptors.

    PubMed

    Corbisier, Jenny; Galès, Céline; Huszagh, Alexandre; Parmentier, Marc; Springael, Jean-Yves

    2015-04-10

    The ability of G protein-coupled receptors (GPCRs) to activate selective signaling pathways according to the conformation stabilized by bound ligands (signaling bias) is a challenging concept in the GPCR field. Signaling bias has been documented for several GPCRs, including chemokine receptors. However, most of these studies examined the global signaling bias between G protein- and arrestin-dependent pathways, leaving unaddressed the potential bias between particular G protein subtypes. Here, we investigated the coupling selectivity of chemokine receptors CCR2, CCR5, and CCR7 in response to various ligands with G protein subtypes by using bioluminescence resonance energy transfer biosensors monitoring directly the activation of G proteins. We also compared data obtained with the G protein biosensors with those obtained with other functional readouts, such as β-arrestin-2 recruitment, cAMP accumulation, and calcium mobilization assays. We showed that the binding of chemokines to CCR2, CCR5, and CCR7 activated the three Gαi subtypes (Gαi1, Gαi2, and Gαi3) and the two Gαo isoforms (Gαoa and Gαob) with potencies that generally correlate to their binding affinities. In addition, we showed that the binding of chemokines to CCR5 and CCR2 also activated Gα12, but not Gα13. For each receptor, we showed that the relative potency of various agonist chemokines was not identical in all assays, supporting the notion that signaling bias exists at chemokine receptors.

  11. Long-range magnetic interactions and proximity effects in an amorphous exchange-spring magnet

    DOE PAGES

    Magnus, F.; Brooks-Bartlett, M. E.; Moubah, R.; Procter, R. A.; Andersson, G.; Hase, T. P. A.; Banks, S. T.; Hjorvarsson, B.

    2016-06-13

    Low-dimensional magnetic heterostructures are a key element of spintronics, where magnetic interactions between different materials often define the functionality of devices. Although some interlayer exchange coupling mechanisms are by now well established, the possibility of direct exchange coupling via proximity-induced magnetization through non-magnetic layers is typically ignored due to the presumed short range of such proximity effects. Here we show that magnetic order can be induced throughout a 40-nm-thick amorphous paramagnetic layer through proximity to ferromagnets, mediating both exchange-spring magnet behaviour and exchange bias. Furthermore, Monte Carlo simulations show that nearest-neighbour magnetic interactions fall short in describing the observed effectsmore » and long-range magnetic interactions are needed to capture the extent of the induced magnetization. Lastly, the results highlight the importance of considering the range of interactions in low-dimensional heterostructures and how magnetic proximity effects can be used to obtain new functionality.« less

  12. Educator Exchange Resource Guide.

    ERIC Educational Resources Information Center

    Garza, Cris; Rodriguez, Victor

    This resource guide was developed for teachers and administrators interested in participating in intercultural and international exchange programs or starting an exchange program. An analysis of an exchange program's critical elements discusses exchange activities; orientation sessions; duration of exchange; criteria for participation; travel,…

  13. Heuristic-biased stochastic sampling

    SciTech Connect

    Bresina, J.L.

    1996-12-31

    This paper presents a search technique for scheduling problems, called Heuristic-Biased Stochastic Sampling (HBSS). The underlying assumption behind the HBSS approach is that strictly adhering to a search heuristic often does not yield the best solution and, therefore, exploration off the heuristic path can prove fruitful. Within the HBSS approach, the balance between heuristic adherence and exploration can be controlled according to the confidence one has in the heuristic. By varying this balance, encoded as a bias function, the HBSS approach encompasses a family of search algorithms of which greedy search and completely random search are extreme members. We present empirical results from an application of HBSS to the realworld problem of observation scheduling. These results show that with the proper bias function, it can be easy to outperform greedy search.

  14. Anchoring bias in online voting

    NASA Astrophysics Data System (ADS)

    Yang, Zimo; Zhang, Zi-Ke; Zhou, Tao

    2012-12-01

    Voting online with explicit ratings could largely reflect people's preferences and objects' qualities, but ratings are always irrational, because they may be affected by many unpredictable factors like mood, weather and other people's votes. By analyzing two real systems, this paper reveals a systematic bias embedding in the individual decision-making processes, namely people tend to give a low rating after a low rating, as well as a high rating following a high rating. This so-called anchoring bias is validated via extensive comparisons with null models, and numerically speaking, the extent of bias decays with voting interval in a logarithmic form. Our findings could be applied in the design of recommender systems and considered as important complementary materials to previous knowledge about anchoring effects on financial trades, performance judgments, auctions, and so on.

  15. Measurement of Receptor Signaling Bias.

    PubMed

    Kenakin, Terry

    2016-01-01

    G protein-coupled receptors (GPCRs) are often pleiotropically linked to numerous cellular signaling mechanisms in cells, and it is now known that many agonists differentially activate some signaling pathways at the expense of others. The mechanism for this effect is the stabilization of different active receptor states by different agonists, and it leads to varying qualities of efficacy for different agonists. Agonist bias is a powerful mechanism to amplify beneficial signals and diminish harmful signals, and thus improve the overall profile of agonist ligands. This unit describes a method to quantify agonist bias with a scale that enables medicinal chemists to amplify or reduce these effects in new molecules. The method is based on the Black/Leff operational model and yields a statistical estimate of the confidence for bias measurements. © 2016 by John Wiley & Sons, Inc. PMID:27636109

  16. Unpacking the Evidence of Gender Bias

    ERIC Educational Resources Information Center

    Fulmer, Connie L.

    2010-01-01

    The purpose of this study was to investigate gender bias in pre-service principals using the Gender-Leader Implicit Association Test. Analyses of student-learning narratives revealed how students made sense of gender bias (biased or not-biased) and how each reacted to evidence (surprised or not-surprised). Two implications were: (1) the need for…

  17. Measurement Bias Detection through Factor Analysis

    ERIC Educational Resources Information Center

    Barendse, M. T.; Oort, F. J.; Werner, C. S.; Ligtvoet, R.; Schermelleh-Engel, K.

    2012-01-01

    Measurement bias is defined as a violation of measurement invariance, which can be investigated through multigroup factor analysis (MGFA), by testing across-group differences in intercepts (uniform bias) and factor loadings (nonuniform bias). Restricted factor analysis (RFA) can also be used to detect measurement bias. To also enable nonuniform…

  18. A Reconsideration of Bias in the News.

    ERIC Educational Resources Information Center

    Stevenson, Robert L.; Greene, Mark T.

    This paper discusses three conceptual problems--point of view, unit of bias, and behavioral response--with using content analysis to study news bias. The paper shows that the point of view of the content analyst is not appropriate if one wants to see how news consumers define and react to bias, that the unit of bias should be the specific instance…

  19. Collection Development and the Psychology of Bias

    ERIC Educational Resources Information Center

    Quinn, Brian

    2012-01-01

    The library literature addressing the role of bias in collection development emphasizes a philosophical approach. It is based on the notion that bias can be controlled by the conscious act of believing in certain values and adhering to a code of ethics. It largely ignores the psychological research on bias, which suggests that bias is a more…

  20. The Truth and Bias Model of Judgment

    ERIC Educational Resources Information Center

    West, Tessa V.; Kenny, David A.

    2011-01-01

    We present a new model for the general study of how the truth and biases affect human judgment. In the truth and bias model, judgments about the world are pulled by 2 primary forces, the truth force and the bias force, and these 2 forces are interrelated. The truth and bias model differentiates force and value, where the force is the strength of…

  1. Without Bias: A Guidebook for Nondiscriminatory Communication.

    ERIC Educational Resources Information Center

    Pickens, Judy E., Ed.; And Others

    This guidebook discusses ways to eliminate various types of discrimination from business communications. Separately authored chapters discuss eliminating racial and ethnic bias; eliminating sexual bias; achieving communication sensitive about handicaps of disabled persons; eliminating bias from visual media; eliminating bias from meetings,…

  2. The Threshold of Embedded M Collider Bias and Confounding Bias

    ERIC Educational Resources Information Center

    Kelcey, Benjamin; Carlisle, Joanne

    2011-01-01

    Of particular import to this study, is collider bias originating from stratification on retreatment variables forming an embedded M or bowtie structural design. That is, rather than assume an M structural design which suggests that "X" is a collider but not a confounder, the authors adopt what they consider to be a more reasonable position and…

  3. Research Review: Attention Bias Modification (ABM)--A Novel Treatment for Anxiety Disorders

    ERIC Educational Resources Information Center

    Bar-Haim, Yair

    2010-01-01

    Attention bias modification (ABM) is a newly emerging therapy for anxiety disorders that is rooted in current cognitive models of anxiety and in established experimental data on threat-related attentional biases in anxiety. This review describes the evidence indicating that ABM has the potential to become an enhancing tool for current…

  4. 45 CFR 155.106 - Election to operate an Exchange after 2014.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General Standards Related to the Establishment of an Exchange § 155.106 Election to operate...

  5. 45 CFR 155.106 - Election to operate an Exchange after 2014.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General Standards Related to the Establishment of an Exchange § 155.106 Election to operate...

  6. 77 FR 72581 - Patient Protection and Affordable Care Act; Establishment of the Multi-State Plan Program for the...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-05

    ... Care Act; Establishment of the Multi- State Plan Program for the Affordable Insurance Exchanges... Care Act; Establishment of the Multi-State Plan Program for the Affordable Insurance Exchanges AGENCY... Affordable Insurance Exchanges (Exchanges). Under the law, an MSPP issuer may phase in the States in which...

  7. Bias in Dynamic Monte Carlo Alpha Calculations

    SciTech Connect

    Sweezy, Jeremy Ed; Nolen, Steven Douglas; Adams, Terry R.; Trahan, Travis John

    2015-02-06

    A 1/N bias in the estimate of the neutron time-constant (commonly denoted as α) has been seen in dynamic neutronic calculations performed with MCATK. In this paper we show that the bias is most likely caused by taking the logarithm of a stochastic quantity. We also investigate the known bias due to the particle population control method used in MCATK. We conclude that this bias due to the particle population control method is negligible compared to other sources of bias.

  8. Biased Signaling of Protease-Activated Receptors

    PubMed Central

    Zhao, Peishen; Metcalf, Matthew; Bunnett, Nigel W.

    2014-01-01

    In addition to their role in protein degradation and digestion, proteases can also function as hormone-like signaling molecules that regulate vital patho-physiological processes, including inflammation, hemostasis, pain, and repair mechanisms. Certain proteases can signal to cells by cleaving protease-activated receptors (PARs), a family of four G protein-coupled receptors. PARs are expressed by almost all cell types, control important physiological and disease-relevant processes, and are an emerging therapeutic target for major diseases. Most information about PAR activation and function derives from studies of a few proteases, for example thrombin in the case of PAR1, PAR3, and PAR4, and trypsin in the case of PAR2 and PAR4. These proteases cleave PARs at established sites with the extracellular N-terminal domains, and expose tethered ligands that stabilize conformations of the cleaved receptors that activate the canonical pathways of G protein- and/or β-arrestin-dependent signaling. However, a growing number of proteases have been identified that cleave PARs at divergent sites to activate distinct patterns of receptor signaling and trafficking. The capacity of these proteases to trigger distinct signaling pathways is referred to as biased signaling, and can lead to unique patho-physiological outcomes. Given that a different repertoire of proteases are activated in various patho-physiological conditions that may activate PARs by different mechanisms, signaling bias may account for the divergent actions of proteases and PARs. Moreover, therapies that target disease-relevant biased signaling pathways may be more effective and selective approaches for the treatment of protease- and PAR-driven diseases. Thus, rather than mediating the actions of a few proteases, PARs may integrate the biological actions of a wide spectrum of proteases in different patho-physiological conditions. PMID:24860547

  9. Maintenance of motility bias during cyanobacterial phototaxis.

    PubMed

    Chau, Rosanna Man Wah; Ursell, Tristan; Wang, Shuo; Huang, Kerwyn Casey; Bhaya, Devaki

    2015-04-01

    Signal transduction in bacteria is complex, ranging across scales from molecular signal detectors and effectors to cellular and community responses to stimuli. The unicellular, photosynthetic cyanobacterium Synechocystis sp. PCC6803 transduces a light stimulus into directional movement known as phototaxis. This response occurs via a biased random walk toward or away from a directional light source, which is sensed by intracellular photoreceptors and mediated by Type IV pili. It is unknown how quickly cells can respond to changes in the presence or directionality of light, or how photoreceptors affect single-cell motility behavior. In this study, we use time-lapse microscopy coupled with quantitative single-cell tracking to investigate the timescale of the cellular response to various light conditions and to characterize the contribution of the photoreceptor TaxD1 (PixJ1) to phototaxis. We first demonstrate that a community of cells exhibits both spatial and population heterogeneity in its phototactic response. We then show that individual cells respond within minutes to changes in light conditions, and that movement directionality is conferred only by the current light directionality, rather than by a long-term memory of previous conditions. Our measurements indicate that motility bias likely results from the polarization of pilus activity, yielding variable levels of movement in different directions. Experiments with a photoreceptor (taxD1) mutant suggest a supplementary role of TaxD1 in enhancing movement directionality, in addition to its previously identified role in promoting positive phototaxis. Motivated by the behavior of the taxD1 mutant, we demonstrate using a reaction-diffusion model that diffusion anisotropy is sufficient to produce the observed changes in the pattern of collective motility. Taken together, our results establish that single-cell tracking can be used to determine the factors that affect motility bias, which can then be coupled with

  10. Designing health insurance exchanges: key decisions.

    PubMed

    Starc, Amanda; Kolstad, Jonathan T

    2012-02-01

    A cornerstone of health care reform is the establishment of state-level insurance exchanges where individuals and small businesses can purchase health insurance in an online marketplace. States are required to develop an exchange by 2014, or participate in a federal one. The exchanges will help people without employer-sponsored insurance find and choose a health plan to meet their needs. This Issue Brief reviews the experience of Massachusetts in developing a health insurance exchange and offers policymakers guidance on key features and likely consumer responses. PMID:22451998

  11. Corrosive resistant heat exchanger

    DOEpatents

    Richlen, Scott L.

    1989-01-01

    A corrosive and errosive resistant heat exchanger which recovers heat from a contaminated heat stream. The heat exchanger utilizes a boundary layer of innocuous gas, which is continuously replenished, to protect the heat exchanger surface from the hot contaminated gas. The innocuous gas is conveyed through ducts or perforations in the heat exchanger wall. Heat from the heat stream is transferred by radiation to the heat exchanger wall. Heat is removed from the outer heat exchanger wall by a heat recovery medium.

  12. Attributional Bias and Course Evaluations.

    ERIC Educational Resources Information Center

    Gigliotti, Richard J.; Buchtel, Foster S.

    1990-01-01

    How self-serving bias affects evaluations of college courses was tested for 691 students by comparing a model predicting that evaluations reflect actual grades with a model predicting that evaluations reflect confirmation or disconfirmation of expectations. Results support course evaluation validity by indicating a minimal effect of self-serving…

  13. Combating Anti-Muslim Bias

    ERIC Educational Resources Information Center

    Shah, Nirvi

    2011-01-01

    America's 2.5 million Muslims make up less than 1% of the U.S. population, according to the Pew Research Center. Many Muslim students face discrimination and some cases have warranted investigation by the U.S. Department of Education's Office of Civil Rights. Muslim groups have reported widespread bias as well. For many Muslim…

  14. Stereotype Formation: Biased by Association

    ERIC Educational Resources Information Center

    Le Pelley, Mike E.; Reimers, Stian J.; Calvini, Guglielmo; Spears, Russell; Beesley, Tom; Murphy, Robin A.

    2010-01-01

    We propose that biases in attitude and stereotype formation might arise as a result of learned differences in the extent to which social groups have previously been predictive of behavioral or physical properties. Experiments 1 and 2 demonstrate that differences in the experienced predictiveness of groups with respect to evaluatively neutral…

  15. Key Words in Instruction. Bias

    ERIC Educational Resources Information Center

    Callison, Daniel

    2005-01-01

    Two challenging criteria for judging information involve bias and authority. In both cases, judgments may not be clearly possible. In both cases, there may be degrees or levels of acceptability. For students to gain experience and to demonstrate skills in making judgments, they need opportunities to consider a wide spectrum of resources under a…

  16. Bayesian ROC curve estimation under verification bias.

    PubMed

    Gu, Jiezhun; Ghosal, Subhashis; Kleiner, David E

    2014-12-20

    Receiver operating characteristic (ROC) curve has been widely used in medical science for its ability to measure the accuracy of diagnostic tests under the gold standard. However, in a complicated medical practice, a gold standard test can be invasive, expensive, and its result may not always be available for all the subjects under study. Thus, a gold standard test is implemented only when it is necessary and possible. This leads to the so-called 'verification bias', meaning that subjects with verified disease status (also called label) are not selected in a completely random fashion. In this paper, we propose a new Bayesian approach for estimating an ROC curve based on continuous data following the popular semiparametric binormal model in the presence of verification bias. By using a rank-based likelihood, and following Gibbs sampling techniques, we compute the posterior distribution of the binormal parameters intercept and slope, as well as the area under the curve by imputing the missing labels within Markov Chain Monte-Carlo iterations. Consistency of the resulting posterior under mild conditions is also established. We compare the new method with other comparable methods and conclude that our estimator performs well in terms of accuracy. PMID:25269427

  17. Biased Brownian dynamics for rate constant calculation.

    PubMed

    Zou, G; Skeel, R D; Subramaniam, S

    2000-08-01

    An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, and it associates a probability weight with each trajectory. A simulation loses weight when movement is along the biasing force and gains weight when movement is against the biasing force. The sampling of trajectories is then biased, but the sampling is unbiased when the trajectory outcomes are multiplied by their weights. With a suitable choice of the biasing force, more reacted trajectories are sampled. As a consequence, the variance of the estimate is reduced. In our test case, biased Brownian dynamics gives a sevenfold improvement in central processing unit (CPU) time with the choice of a simple centripetal biasing force.

  18. Biased Brownian dynamics for rate constant calculation.

    PubMed

    Zou, G; Skeel, R D; Subramaniam, S

    2000-08-01

    An enhanced sampling method-biased Brownian dynamics-is developed for the calculation of diffusion-limited biomolecular association reaction rates with high energy or entropy barriers. Biased Brownian dynamics introduces a biasing force in addition to the electrostatic force between the reactants, and it associates a probability weight with each trajectory. A simulation loses weight when movement is along the biasing force and gains weight when movement is against the biasing force. The sampling of trajectories is then biased, but the sampling is unbiased when the trajectory outcomes are multiplied by their weights. With a suitable choice of the biasing force, more reacted trajectories are sampled. As a consequence, the variance of the estimate is reduced. In our test case, biased Brownian dynamics gives a sevenfold improvement in central processing unit (CPU) time with the choice of a simple centripetal biasing force. PMID:10919998

  19. 45 CFR 155.200 - Functions of an Exchange.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General...)(H) and 1411 of the Affordable Care Act. (c) Oversight and financial integrity. The Exchange must... section 1313 of the Affordable Care Act. (d) Quality activities. The Exchange must evaluate...

  20. 45 CFR 155.200 - Functions of an Exchange.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT General... of the Affordable Care Act. (c) Oversight and financial integrity. The Exchange must perform required... Affordable Care Act. (d) Quality activities. The Exchange must evaluate quality improvement strategies...

  1. Setting Up an Exchange Operation in the Small Special Library.

    ERIC Educational Resources Information Center

    Carter, Harriet H.

    1978-01-01

    Describes the planning process and the procedures established to get the Fels Research Institute Library started in exchange activities through the ALA Duplicates Exchange Union and the MLA Exchange. Methods for evaluating the success of these programs after one year are explained. (Author/MBR)

  2. Atlantic Telehealth Knowledge Exchange.

    PubMed

    Dwyer, Patricia; Hagerman, Valerie; Ingram, Chris-Anne; MacFarlane, Ron; McCourt, Sherry

    2004-01-01

    Atlantic Canada has some of the earliest, most comprehensive, well-established networks, and innovative applications for telehealth in the country. The region offers a range of models for telehealth, in terms of management structure, coordination, funding, equipment, utilization, and telehealth applications. Collectively, this diversity, experience, and wealth of knowledge can significantly contribute to the development of a knowledge base for excellence in telehealth services. There is no formal process in place for the sharing of information amongst the provinces. Information sharing primarily occurs informally through professional contacts and participation in telehealth organizations. A core group of organizations partnered to develop a process for knowledge exchange to occur. This type of collaborative approach is favored in Atlantic Canada, given the region's economy and available resources. The Atlantic Telehealth Knowledge Exchange (ATKE) project centred on the development of a collaborative structure, information sharing and dissemination, development of a knowledge repository and sustainability. The project is viewed as a first step in assisting telehealth stakeholders with sharing knowledge about telehealth in Atlantic Canada. Significant progress has been made throughout the project in increasing the profile of telehealth in Atlantic Canada. The research process has captured and synthesized baseline information on telehealth, and fostered collaboration amongst telehealth providers who might otherwise have never come together. It has also brought critical awareness to the discussion tables of governments and key committees regarding the value of telehealth in sustaining our health system, and has motivated decision makers to take action to integrate telehealth into e-health discussions.

  3. Cognitive debiasing 1: origins of bias and theory of debiasing.

    PubMed

    Croskerry, Pat; Singhal, Geeta; Mamede, Sílvia

    2013-10-01

    Numerous studies have shown that diagnostic failure depends upon a variety of factors. Psychological factors are fundamental in influencing the cognitive performance of the decision maker. In this first of two papers, we discuss the basics of reasoning and the Dual Process Theory (DPT) of decision making. The general properties of the DPT model, as it applies to diagnostic reasoning, are reviewed. A variety of cognitive and affective biases are known to compromise the decision-making process. They mostly appear to originate in the fast intuitive processes of Type 1 that dominate (or drive) decision making. Type 1 processes work well most of the time but they may open the door for biases. Removing or at least mitigating these biases would appear to be an important goal. We will also review the origins of biases. The consensus is that there are two major sources: innate, hard-wired biases that developed in our evolutionary past, and acquired biases established in the course of development and within our working environments. Both are associated with abbreviated decision making in the form of heuristics. Other work suggests that ambient and contextual factors may create high risk situations that dispose decision makers to particular biases. Fatigue, sleep deprivation and cognitive overload appear to be important determinants. The theoretical basis of several approaches towards debiasing is then discussed. All share a common feature that involves a deliberate decoupling from Type 1 intuitive processing and moving to Type 2 analytical processing so that eventually unexamined intuitive judgments can be submitted to verification. This decoupling step appears to be the critical feature of cognitive and affective debiasing.

  4. Woven heat exchanger

    DOEpatents

    Piscitella, Roger R.

    1987-01-01

    In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

  5. Woven heat exchanger

    DOEpatents

    Piscitella, Roger R.

    1987-05-05

    In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

  6. Measurement bias in activation-recovery intervals from unipolar electrograms

    PubMed Central

    Hanson, Ben; Taggart, Peter

    2014-01-01

    The activation-recovery interval (ARI) calculated from unipolar electrograms is regularly used as a convenient surrogate measure of local cardiac action potential durations (APD). This method enables important research bridging between computational studies and in vitro and in vivo human studies. The Wyatt method is well established as a theoretically sound method for calculating ARIs; however, some studies have observed that it is prone to a bias error in measurement when applied to positive T waves. This article demonstrates that recent theoretical and computational studies supporting the use of the Wyatt method are likely to have underestimated the extent of this bias in many practical experimental recording scenarios. This work addresses these situations and explains the measurement bias by adapting existing theoretical expressions of the electrogram to represent practical experimental recording configurations. A new analytic expression for the electrogram's local component is derived, which identifies the source of measurement bias for positive T waves. A computer implementation of the new analytic model confirms our hypothesis that the bias is systematically dependent on the electrode configuration. These results provide an aid to electrogram interpretation in general, and this work's outcomes are used to make recommendations on how to minimize measurement error. PMID:25398981

  7. Variable-bias coin tossing

    NASA Astrophysics Data System (ADS)

    Colbeck, Roger; Kent, Adrian

    2006-03-01

    Alice is a charismatic quantum cryptographer who believes her parties are unmissable; Bob is a (relatively) glamorous string theorist who believes he is an indispensable guest. To prevent possibly traumatic collisions of self-perception and reality, their social code requires that decisions about invitation or acceptance be made via a cryptographically secure variable-bias coin toss (VBCT). This generates a shared random bit by the toss of a coin whose bias is secretly chosen, within a stipulated range, by one of the parties; the other party learns only the random bit. Thus one party can secretly influence the outcome, while both can save face by blaming any negative decisions on bad luck. We describe here some cryptographic VBCT protocols whose security is guaranteed by quantum theory and the impossibility of superluminal signaling, setting our results in the context of a general discussion of secure two-party computation. We also briefly discuss other cryptographic applications of VBCT.

  8. Belief bias and relational reasoning.

    PubMed

    Roberts, Maxwell J; Sykes, Elizabeth D A

    2003-01-01

    When people evaluate categorical syllogisms, they tend to reject unbelievable conclusions and accept believable ones irrespective of their validity. Typically, this effect is particularly marked for invalid conclusions that are possible, but do not necessarily follow, given the premises. However, smaller believability effects can also be detected for other types of conclusion. Three experiments are reported here, in which an attempt was made to determine whether belief bias effects can manifest themselves on the relational inference task. Subjects evaluated the validity of conclusions such as William the Conqueror was king after the Pyramids were built (temporal task) or Manchester is north of Bournemouth (spatial task) with respect to their premises. All of the major findings for equivalent categorical syllogism tasks were replicated. However, the overall size of the main effect of believability appears to be related to task presentation, a phenomenon not previously identified for categorical syllogisms and which current theories of belief bias have difficulty explaining.

  9. Casuistry and social category bias.

    PubMed

    Norton, Michael I; Vandello, Joseph A; Darley, John M

    2004-12-01

    This research explored cases where people are drawn to make judgments between individuals based on questionable criteria, in particular those individuals' social group memberships. We suggest that individuals engage in casuistry to mask biased decision making, by recruiting more acceptable criteria to justify such decisions. We present 6 studies that demonstrate how casuistry licenses people to judge on the basis of social category information but appear unbiased--to both others and themselves--while doing so. In 2 domains (employment and college admissions decisions), with 2 social categories (gender and race), and with 2 motivations (favoring an in-group or out-group), the present studies explored how participants justify decisions biased by social category information by arbitrarily inflating the relative value of their preferred candidates' qualifications over those of competitors.

  10. Girl child and gender bias.

    PubMed

    Chowdhry, D P

    1995-01-01

    This article identifies gender bias against female children and youth in India. Gender bias is based on centuries-old religious beliefs and sayings from ancient times. Discrimination is reflected in denial or ignorance of female children's educational, health, nutrition, and recreational needs. Female infanticide and selective abortion of female fetuses are other forms of discrimination. The task of eliminating or reducing gender bias will involve legal, developmental, political, and administrative measures. Public awareness needs to be created. There is a need to reorient the education and health systems and to advocate for gender equality. The government of India set the following goals for the 1990s: to protect the survival of the girl child and practice safe motherhood; to develop the girl child in general; and to protect vulnerable girl children in different circumstances and in special groups. The Health Authorities should monitor the laws carefully to assure marriage after the minimum age, ban sex determination of the fetus, and monitor the health and nutrition of pre-school girls and nursing and pregnant mothers. Mothers need to be encouraged to breast feed, and to breast feed equally between genders. Every village and slum area needs a mini health center. Maternal mortality must decline. Primary health centers and hospitals need more women's wards. Education must be universally accessible. Enrollments should be increased by educating rural tribal and slum parents, reducing distances between home and school, making curriculum more relevant to girls, creating more female teachers, and providing facilities and incentives for meeting the needs of girl students. Supplementary income could be provided to families for sending girls to school. Recreational activities must be free of gender bias. Dowry, sati, and devdasi systems should be banned.

  11. Self regulating body bias generator

    NASA Technical Reports Server (NTRS)

    Hass, Kenneth (Inventor)

    2004-01-01

    The back bias voltage on a functional circuit is controlled through a closed loop process. A delay element receives a clock pulse and produces a delay output. The delay element is advantageously constructed of the same materials as the functional circuit so that the aging and degradation of the delay element parallels the degradation of the functional circuit. As the delay element degrades, the transistor switching time increases, increasing the time delay of the delay output. An AND gate compares a clock pulse to an output pulse of the delay element, the AND output forming a control pulse. A duty cycle of the control pulse is determined by the delay time between the clock pulse and the delay element output. The control pulse is received at the input of a charge pump. The charge pump produces a back bias voltage which is then applied to the delay element and to the functional circuit. If the time delay produced by the delay element exceeds the optimal delay, the duty cycle of the control pulse is shortened, and the back bias voltage is lowered, thereby increasing the switching speed of the transistors in the delay element and reducing the time delay. If the throughput of the delay element is too fast, the duty cycle of the control pulse is lengthened, raising the back bias voltage produced by the charge pump. This, in turn, lowers the switching speed of the transistors in both the delay element and the functional circuit. The slower switching speed in the delay element increases time delay. In this manner, the switching speed of the delay element, and of the functional circuit, is maintained at a constant level over the life of the circuit.

  12. SEASAT altimeter timing bias estimation

    NASA Astrophysics Data System (ADS)

    Marsh, J. G.; Williamson, R. G.

    1982-04-01

    The calibration of the altimeter observation time tags to the millisecond level of accuracy is fundamental to the processing of the data. Initial analyses of the SEASAT altimeter data indicated the presence of a time calibration bias which produced altimeter measurement errors in excess of a meter. A technique has been developed for the solution of the time tag bias based upon the analysis of sea surface height discrepancies at ground track intersections. This technique has permitted very good separation of the dominant once per revolution ephemeris error, which amounts to about 1.5 m rms, from the timing error signature. Furthermore, the technique does not depend upon the availability of precise geoid data. The application of this technique to a global set of SEASAT altimeter data covering the time period of July 28-August 9, 1978, has resulted in a value of -81.0±2 ms for the time tag bias. This value agrees to within 2.9 ms of the value derived at the University of Texas from a similar analysis of the altimeter data. Furthermore, these values corroborate the revised value of -79.4 ms derived at NASA/Wallops Flight Center and the Johns Hopkins University/Applied Physics Lab from a reexamination of the internal instrument time delays. The modeling of oceanic tides and the orbit computations are the major error sources in these analyses.

  13. Generalization of the FRAM's Bias

    SciTech Connect

    Duc T. Vo

    2005-10-01

    The Fixed-Energy Response-Function Analysis with Multiple Efficiency (FRAM) code was developed at Los Alamos National Laboratory to measure the gamma-ray spectrometry of the isotopic composition of plutonium, uranium, and other actinides. Its reported uncertainties of the results come from the propagation of the statistics in the peak areas only. No systematic error components are included in the reported uncertainties. We have done several studies and found that the FRAM's statistical precision can be reasonably represented by its reported uncertainties. The FRAM's biases or systematic uncertainties can come from a variety of sources and can be difficult to determine. We carefully examined the FRAM analytical results of the archival plutonium data and of the data specifically acquired for this isotopic uncertainty analysis project and found the relationship between the bias and other parameters. We worked out the equations representing the biases of the measured isotopes from each measurement using the internal parameters in the spectrum such as peak resolution and shape, region of analysis, and burnup (for plutonium) or enrichment (for uranium).

  14. Response bias in plaintiffs' histories.

    PubMed

    Lees-Haley, P R; Williams, C W; Zasler, N D; Marguilies, S; English, L T; Stevens, K B

    1997-11-01

    This study investigated response bias in self-reported history of factors relevant to the assessment of traumatic brain injury, toxic brain injury and related emotional distress. Response bias refers to systematic error in self-report data. A total of 446 subjects (comprising 131 litigating and 315 non-litigating adults from five locations in the United States) completed a symptom questionnaire. Data were obtained from university faculty and students, from patients in clinics specializing in physiatry neurology, and family medicine, and from plaintiffs undergoing forensic neuropsychological evaluations. Comparisons were made for litigant and non litigant ratings of their past and current cognitive and emotional functioning, including life in general, ability to concentrate, memory, depression, anxiety, alcohol, drugs, ability to work or attend school, irritability, headaches, confusion, self-esteem, and fatigue. Although there is no basis for hypothesizing plaintiffs to be healthier than the general population, plaintiffs rated their pre-injury functioning superior to non-plaintiffs. These findings suggest that response biases need to be taken into account by forensic examiners when relying on litigants' self-reports of pre-injury status.

  15. Woven heat exchanger

    DOEpatents

    Piscitella, R.R.

    1984-07-16

    This invention relates to a heat exchanger for waste heat recovery from high temperature industrial exhaust streams. In a woven ceramic heat exchanger using the basic tube-in-shell design, each heat exchanger consisting of tube sheets and tube, is woven separately. Individual heat exchangers are assembled in cross-flow configuration. Each heat exchanger is woven from high temperature ceramic fiber, the warp is continuous from tube to tube sheet providing a smooth transition and unitized construction.

  16. The Probability Distribution for a Biased Spinner

    ERIC Educational Resources Information Center

    Foster, Colin

    2012-01-01

    This article advocates biased spinners as an engaging context for statistics students. Calculating the probability of a biased spinner landing on a particular side makes valuable connections between probability and other areas of mathematics. (Contains 2 figures and 1 table.)

  17. Micromagnetic simulation of ferrimagnetic TbFeCo films with exchange coupled nanophases

    NASA Astrophysics Data System (ADS)

    Ma, Chung T.; Li, Xiaopu; Poon, S. Joseph

    2016-11-01

    Amorphous ferrimagnetic TbFeCo thin films are found to exhibit exchange bias effect near the compensation temperature by magnetic hysteresis loop measurement. The observed exchange anisotropy is believed to originate from the exchange interaction between the two nanoscale amorphous phases distributed within the films. Here, we present a computational model of phase-separated TbFeCo using micromagnetic simulation. Two types of cells with different Tb concentration are distributed within the simulated space to obtain a heterogeneous structure consisting of two nanoscale amorphous phases. Each cell contains separated Tb and FeCo components, forming two antiferromagnetically coupled sublattices. Using this model, we are able to show the existence of exchange bias effect, and the shift in hysteresis loops is in agreement with experiment. The micromagnetic model developed herein for a heterogeneous magnetic material may also account for some recent measurements of exchange bias effect in crystalline films.

  18. The Nonverbal Transmission of Intergroup Bias: A Model of Bias Contagion with Implications for Social Policy

    PubMed Central

    Weisbuch, Max; Pauker, Kristin

    2013-01-01

    Social and policy interventions over the last half-century have achieved laudable reductions in blatant discrimination. Yet members of devalued social groups continue to face subtle discrimination. In this article, we argue that decades of anti-discrimination interventions have failed to eliminate intergroup bias because such bias is contagious. We present a model of bias contagion in which intergroup bias is subtly communicated through nonverbal behavior. Exposure to such nonverbal bias “infects” observers with intergroup bias. The model we present details two means by which nonverbal bias can be expressed—either as a veridical index of intergroup bias or as a symptom of worry about appearing biased. Exposure to this nonverbal bias can increase perceivers’ own intergroup biases through processes of implicit learning, informational influence, and normative influence. We identify critical moderators that may interfere with these processes and consequently propose several social and educational interventions based on these moderators. PMID:23997812

  19. Examining Event-Related Potential (ERP) Correlates of Decision Bias in Recognition Memory Judgments

    PubMed Central

    Hill, Holger; Windmann, Sabine

    2014-01-01

    Memory judgments can be based on accurate memory information or on decision bias (the tendency to report that an event is part of episodic memory when one is in fact unsure). Event related potentials (ERP) correlates are important research tools for elucidating the dynamics underlying memory judgments but so far have been established only for investigations of accurate old/new discrimination. To identify the ERP correlates of bias, and observe how these interact with ERP correlates of memory, we conducted three experiments that manipulated decision bias within participants via instructions during recognition memory tests while their ERPs were recorded. In Experiment 1, the bias manipulation was performed between blocks of trials (automatized bias) and compared to trial-by-trial shifts of bias in accord with an external cue (flexibly controlled bias). In Experiment 2, the bias manipulation was performed at two different levels of accurate old/new discrimination as the memory strength of old (studied) items was varied. In Experiment 3, the bias manipulation was added to another, bottom-up driven manipulation of bias induced via familiarity. In the first two Experiments, and in the low familiarity condition of Experiment 3, we found evidence of an early frontocentral ERP component at 320 ms poststimulus (the FN320) that was sensitive to the manipulation of bias via instruction, with more negative amplitudes indexing more liberal bias. By contrast, later during the trial (500–700 ms poststimulus), bias effects interacted with old/new effects across all three experiments. Results suggest that the decision criterion is typically activated early during recognition memory trials, and is integrated with retrieved memory signals and task-specific processing demands later during the trial. More generally, the findings demonstrate how ERPs can help to specify the dynamics of recognition memory processes under top-down and bottom-up controlled retrieval conditions. PMID

  20. Gender Bias: Recent Research and Interventions.

    ERIC Educational Resources Information Center

    New Jersey Research Bulletin, 1996

    1996-01-01

    This annotated bibliography lists 14 publications about recent research on gender bias and interventions to reduce gender bias in schools. The bibliography is divided into two sections: current research and intervention. The first includes descriptions of studies examining the following topics: gender bias in U.S. schools and its effects;…

  1. Outcome-Reporting Bias in Education Research

    ERIC Educational Resources Information Center

    Pigott, Therese D.; Valentine, Jeffrey C.; Polanin, Joshua R.; Williams, Ryan T.; Canada, Dericka D.

    2013-01-01

    Outcome-reporting bias occurs when primary studies do not include information about all outcomes measured in a study. When studies omit findings on important measures, efforts to synthesize the research using systematic review techniques will be biased and interpretations of individual studies will be incomplete. Outcome-reporting bias has been…

  2. Attentional Bias for Exercise-Related Images

    ERIC Educational Resources Information Center

    Berry, Tanya R.; Spence, John C.; Stolp, Sean M.

    2011-01-01

    This research examined attentional bias toward exercise-related images using a visual probe task. It was hypothesized that more-active participants would display attentional bias toward the exercise-related images. The results showed that men displayed attentional bias for the exercise images. There was a significant interaction of activity level…

  3. Using Newspapers to Study Media Bias.

    ERIC Educational Resources Information Center

    Kirman, Joseph M.

    1992-01-01

    Suggests that students can learn to recognize media bias by studying media reports of current events or historical topics. Describes a study unit using media coverage of the second anniversary of the Palestinian uprising against Israel. Discusses lesson objectives, planning, defining bias teaching procedures, and criteria for determining bias. (DK)

  4. Culturally Biased Assumptions in Counseling Psychology

    ERIC Educational Resources Information Center

    Pedersen, Paul B.

    2003-01-01

    Eight clusters of culturally biased assumptions are identified for further discussion from Leong and Ponterotto's (2003) article. The presence of cultural bias demonstrates that cultural bias is so robust and pervasive that is permeates the profession of counseling psychology, even including those articles that effectively attack cultural bias…

  5. Sex-biased transcriptome evolution in Drosophila.

    PubMed

    Assis, Raquel; Zhou, Qi; Bachtrog, Doris

    2012-01-01

    Sex-biased genes are thought to drive phenotypic differences between males and females. The recent availability of high-throughput gene expression data for many related species has led to a burst of investigations into the genomic and evolutionary properties of sex-biased genes. In Drosophila, a number of studies have found that X chromosomes are deficient in male-biased genes (demasculinized) and enriched for female-biased genes (feminized) and that male-biased genes evolve faster than female-biased genes. However, studies have yielded vastly different conclusions regarding the numbers of sex-biased genes and forces shaping their evolution. Here, we use RNA-seq data from multiple tissues of Drosophila melanogaster and D. pseudoobscura, a species with a recently evolved X chromosome, to explore the evolution of sex-biased genes in Drosophila. First, we compare several independent metrics for classifying sex-biased genes and find that the overlap of genes identified by different metrics is small, particularly for female-biased genes. Second, we investigate genome-wide expression patterns and uncover evidence of demasculinization and feminization of both ancestral and new X chromosomes, demonstrating that gene content on sex chromosomes evolves rapidly. Third, we examine the evolutionary rates of sex-biased genes and show that male-biased genes evolve much faster than female-biased genes, which evolve at similar rates to unbiased genes. Analysis of gene expression among tissues reveals that this trend may be partially due to pleiotropic effects of female-biased genes, which limits their evolutionary potential. Thus, our findings illustrate the importance of accurately identifying sex-biased genes and provide insight into their evolutionary dynamics in Drosophila.

  6. Charge amplifier with bias compensation

    DOEpatents

    Johnson, Gary W.

    2002-01-01

    An ion beam uniformity monitor for very low beam currents using a high-sensitivity charge amplifier with bias compensation. The ion beam monitor is used to assess the uniformity of a raster-scanned ion beam, such as used in an ion implanter, and utilizes four Faraday cups placed in the geometric corners of the target area. Current from each cup is integrated with respect to time, thus measuring accumulated dose, or charge, in Coulombs. By comparing the dose at each corner, a qualitative assessment of ion beam uniformity is made possible. With knowledge of the relative area of the Faraday cups, the ion flux and areal dose can also be obtained.

  7. Chemical and magnetic properties of rapidly cooled metastable ferri-ilmenite solid solutions: implications for magnetic self-reversal and exchange bias—I. Fe-Ti order transition in quenched synthetic ilmenite 61

    NASA Astrophysics Data System (ADS)

    Fabian, Karl; Miyajima, Nobuyoshi; Robinson, Peter; McEnroe, Suzanne A.; Ballaran, Tiziana Boffa; Burton, Benjamin P.

    2011-09-01

    Quenched ferri-ilmenite solid solutions X FeTiO3+ (1 -X) Fe2O3 with X≈ 0.60 contain chemical and magnetic structures important for understanding the unusual magnetic properties in this series, including self-reversal in igneous rocks and exchange bias. Here we study a composition X= 0.61, annealed at 1055 °C, above the Fe-Ti ordering temperature, then quenched. Presence of two interface-coupled phases is established by pot-bellied character of the room-temperature magnetic hysteresis loop, and large negative magnetic exchange bias below 30 K. Transmission electron microscopy (TEM) dark-field imaging with the 003 reflection shows dominant Fe-Ti disordered antiferromagnetic and lesser ordered ferrimagnetic phases, the latter in lenses ≤8 nm thick. Parts of the ordered phase are in antiphase relationship, shown by high-resolution TEM imaging of Fe-rich and Ti-rich layers. TEM-EDX analyses indicate chemical phase separation during quench, with dominant compositions X= 0.56-0.63, extremes 0.50 and 0.70. Thermomagnetic experiments indicate compositions X= 0.56-0.61 are antiferromagnetic, X= 0.61-0.64 are ferrimagnetic. A sample held ˜5 min at 1063 K, increased in order, demonstrated by twofold increase in induced moment at 1 T. This then acquired self-reversed thermoremanent magnetization between 490 and 440 K. Progressive annealings of another sample at 773 K, 973 K, 1023 K and 1063 K, followed by cooling in a 1 T field, produced positive room-temperature magnetic exchange bias, only for 1023 K and 1063 K runs. These properties suggest growth of ordered regions from disordered regions, and expansion of some ordered domains against others across antiphase boundaries, thus creating self-organized structures essential for magnetic self-reversal and magnetic exchange bias.

  8. Challenges in bias correcting climate change simulations

    NASA Astrophysics Data System (ADS)

    Maraun, Douglas; Shepherd, Ted; Zappa, Giuseppe; Gutierrez, Jose; Widmann, Martin; Hagemann, Stefan; Richter, Ingo; Soares, Pedro; Mearns, Linda

    2016-04-01

    Biases in climate model simulations - if these are directly used as input for impact models - will introduce further biases in subsequent impact simulations. In response to this issue, so-called bias correction methods have been developed to post-process climate model output. These methods are now widely used and a crucial component in the generation of high resolution climate change projections. Bias correction is conceptually similar to model output statistics, which has been successfully used for several decades in numerical weather prediction. Yet in climate science, some authors outrightly dismiss any form of bias correction. Starting from this seeming contradiction, we highlight differences between the two contexts and infer consequences and limitations for the applicability of bias correction to climate change projections. We first show that cross validation approaches successfully used to evaluate weather forecasts are fundamentally insufficient to evaluate climate change bias correction. We further demonstrate that different types of model mismatches with observations require different solutions, and some may not sensibly be mitigated. In particular we consider the influence of large-scale circulation biases, biases in the persistence of weather regimes, and regional biases caused by an insufficient representation of the flow-topography interaction. We conclude with a list of recommendations and suggestions for future research to reduce, to post-process, and to cope with climate model biases.

  9. A “Scientific Diversity” Intervention to Reduce Gender Bias in a Sample of Life Scientists

    PubMed Central

    Moss-Racusin, Corinne A.; van der Toorn, Jojanneke; Dovidio, John F.; Brescoll, Victoria L.; Graham, Mark J.; Handelsman, Jo

    2016-01-01

    Mounting experimental evidence suggests that subtle gender biases favoring men contribute to the underrepresentation of women in science, technology, engineering, and mathematics (STEM), including many subfields of the life sciences. However, there are relatively few evaluations of diversity interventions designed to reduce gender biases within the STEM community. Because gender biases distort the meritocratic evaluation and advancement of students, interventions targeting instructors’ biases are particularly needed. We evaluated one such intervention, a workshop called “Scientific Diversity” that was consistent with an established framework guiding the development of diversity interventions designed to reduce biases and was administered to a sample of life science instructors (N = 126) at several sessions of the National Academies Summer Institute for Undergraduate Education held nationwide. Evidence emerged indicating the efficacy of the “Scientific Diversity” workshop, such that participants were more aware of gender bias, expressed less gender bias, and were more willing to engage in actions to reduce gender bias 2 weeks after participating in the intervention compared with 2 weeks before the intervention. Implications for diversity interventions aimed at reducing gender bias and broadening the participation of women in the life sciences are discussed. PMID:27496360

  10. A "Scientific Diversity" Intervention to Reduce Gender Bias in a Sample of Life Scientists.

    PubMed

    Moss-Racusin, Corinne A; van der Toorn, Jojanneke; Dovidio, John F; Brescoll, Victoria L; Graham, Mark J; Handelsman, Jo

    2016-01-01

    Mounting experimental evidence suggests that subtle gender biases favoring men contribute to the underrepresentation of women in science, technology, engineering, and mathematics (STEM), including many subfields of the life sciences. However, there are relatively few evaluations of diversity interventions designed to reduce gender biases within the STEM community. Because gender biases distort the meritocratic evaluation and advancement of students, interventions targeting instructors' biases are particularly needed. We evaluated one such intervention, a workshop called "Scientific Diversity" that was consistent with an established framework guiding the development of diversity interventions designed to reduce biases and was administered to a sample of life science instructors (N = 126) at several sessions of the National Academies Summer Institute for Undergraduate Education held nationwide. Evidence emerged indicating the efficacy of the "Scientific Diversity" workshop, such that participants were more aware of gender bias, expressed less gender bias, and were more willing to engage in actions to reduce gender bias 2 weeks after participating in the intervention compared with 2 weeks before the intervention. Implications for diversity interventions aimed at reducing gender bias and broadening the participation of women in the life sciences are discussed. PMID:27496360

  11. The Protestant Establishment Revisited

    ERIC Educational Resources Information Center

    Baltzell, E. Digby

    1976-01-01

    The author's book, "The Protestant Establishment: Aristocracy and Caste in America", is highly critical of the WASP (White-Anglo-Saxon-Protestant) establishment and proposed the development and need for some sort of upper-class ruling-group. Here is a re-evaluation of his book, now thirteen years old, by the author. (Author/RK)

  12. Numeracy and framing bias in epilepsy.

    PubMed

    Choi, Hyunmi; Wong, John B; Mendiratta, Anil; Heiman, Gary A; Hamberger, Marla J

    2011-01-01

    Patients with epilepsy are frequently confronted with complex treatment decisions. Communicating treatment risks is often difficult because patients may have difficulty with basic statistical concepts (i.e., low numeracy) or might misconceive the statistical information based on the way information is presented, a phenomenon known as "framing bias." We assessed numeracy and framing bias in 95 adults with chronic epilepsy and explored cognitive correlates of framing bias. Compared with normal controls, patients with epilepsy had significantly poorer performance on the Numeracy scale (P=0.02), despite a higher level of education than normal controls (P<0.001). Compared with patients with higher numeracy, patients with lower numeracy were significantly more likely to exhibit framing bias. Abstract problem solving performance correlated with the degree of framing bias (r=0.631, P<0.0001), suggesting a relationship between aspects of executive functioning and framing bias. Poor numeracy and susceptibility framing bias place patients with epilepsy at risk for uninformed decisions.

  13. Charge exchange system

    DOEpatents

    Anderson, Oscar A.

    1978-01-01

    An improved charge exchange system for substantially reducing pumping requirements of excess gas in a controlled thermonuclear reactor high energy neutral beam injector. The charge exchange system utilizes a jet-type blanket which acts simultaneously as the charge exchange medium and as a shield for reflecting excess gas.

  14. Electrical and thermal control of magnetic exchange interactions.

    PubMed

    Fransson, Jonas; Ren, Jie; Zhu, Jian-Xin

    2014-12-19

    We investigate the far-from-equilibrium nature of magnetic anisotropy and exchange interactions between molecular magnets embedded in a tunnel junction. By mapping to an effective spin model, these magnetic interactions can be divided into three types: isotropic Heisenberg, anisotropic Ising, and anisotropic Dzyaloshinski-Moriya contributions, which are attributed to the background nonequilibrium electronic structures. We further demonstrate that both the magnetic self- and exchange interactions can be controlled either electrically by gating and tuning the voltage bias, or thermally by adjusting the temperature bias. We show that the Heisenberg and Ising interactions scale linearly, while the Dzyaloshinski-Moriya interaction scales quadratically, with the molecule-lead coupling strength. The interactions scale linearly with the effective spin polarizations of the leads and the molecular coherence. Our results pave a way for smart control of magnetic exchange interactions at atomic and molecular levels.

  15. Social reward shapes attentional biases.

    PubMed

    Anderson, Brian A

    2016-01-01

    Paying attention to stimuli that predict a reward outcome is important for an organism to survive and thrive. When visual stimuli are associated with tangible, extrinsic rewards such as money or food, these stimuli acquire high attentional priority and come to automatically capture attention. In humans and other primates, however, many behaviors are not motivated directly by such extrinsic rewards, but rather by the social feedback that results from performing those behaviors. In the present study, I examine whether positive social feedback can similarly influence attentional bias. The results show that stimuli previously associated with a high probability of positive social feedback elicit value-driven attentional capture, much like stimuli associated with extrinsic rewards. Unlike with extrinsic rewards, however, such stimuli also influence task-specific motivation. My findings offer a potential mechanism by which social reward shapes the information that we prioritize when perceiving the world around us. PMID:25941868

  16. Increased hindsight bias in schizophrenia.

    PubMed

    Woodward, Todd S; Moritz, Steffen; Arnold, Michelle M; Cuttler, Carrie; Whitman, Jennifer C; Lindsay, D Stephen

    2006-07-01

    An underlying theme common to prominent theoretical accounts of cognition in schizophrenia is that information processing is disproportionately influenced by recently/currently encountered information relative to the influence of previously learned information. In this study, the authors tested this account by using the hindsight bias or knew-it-all-along (KIA) paradigm, which demonstrates that newly acquired knowledge influences recall of past events. In line with the account that patients with schizophrenia display a disproportionately strong influence of recently encountered information relative to the influence of previously learned information, patients displayed a KIA effect that was significantly greater than in controls. This result is discussed in the context of the cognitive underpinnings of the KIA effect and delusion formation. PMID:16846264

  17. Lipid exchange between membranes.

    PubMed Central

    Jähnig, F

    1984-01-01

    The exchange of lipid molecules between vesicle bilayers in water and a monolayer forming at the water surface was investigated theoretically within the framework of thermodynamics. The total number of exchanged molecules was found to depend on the bilayer curvature as expressed by the vesicle radius and on the boundary condition for exchange, i.e., whether during exchange the radius or the packing density of the vesicles remains constant. The boundary condition is determined by the rate of flip-flop within the bilayer relative to the rate of exchange between bi- and monolayer. If flip-flop is fast, exchange is independent of the vesicle radius; if flip-flop is slow, exchange increases with the vesicle radius. Available experimental results agree with the detailed form of this dependence. When the theory was extended to exchange between two bilayers of different curvature, the direction of exchange was also determined by the curvatures and the boundary conditions for exchange. Due to the dependence of the boundary conditions on flip-flop and, consequently, on membrane fluidity, exchange between membranes may partially be regulated by membrane fluidity. PMID:6518251

  18. Approximate strip exchanging.

    PubMed

    Roy, Swapnoneel; Thakur, Ashok Kumar

    2008-01-01

    Genome rearrangements have been modelled by a variety of primitives such as reversals, transpositions, block moves and block interchanges. We consider such a genome rearrangement primitive Strip Exchanges. Given a permutation, the challenge is to sort it by using minimum number of strip exchanges. A strip exchanging move interchanges the positions of two chosen strips so that they merge with other strips. The strip exchange problem is to sort a permutation using minimum number of strip exchanges. We present here the first non-trivial 2-approximation algorithm to this problem. We also observe that sorting by strip-exchanges is fixed-parameter-tractable. Lastly we discuss the application of strip exchanges in a different area Optical Character Recognition (OCR) with an example.

  19. Symmetry as Bias: Rediscovering Special Relativity

    NASA Technical Reports Server (NTRS)

    Lowry, Michael R.

    1992-01-01

    This paper describes a rational reconstruction of Einstein's discovery of special relativity, validated through an implementation: the Erlanger program. Einstein's discovery of special relativity revolutionized both the content of physics and the research strategy used by theoretical physicists. This research strategy entails a mutual bootstrapping process between a hypothesis space for biases, defined through different postulated symmetries of the universe, and a hypothesis space for physical theories. The invariance principle mutually constrains these two spaces. The invariance principle enables detecting when an evolving physical theory becomes inconsistent with its bias, and also when the biases for theories describing different phenomena are inconsistent. Structural properties of the invariance principle facilitate generating a new bias when an inconsistency is detected. After a new bias is generated. this principle facilitates reformulating the old, inconsistent theory by treating the latter as a limiting approximation. The structural properties of the invariance principle can be suitably generalized to other types of biases to enable primal-dual learning.

  20. Publication Bias in Methodological Computational Research

    PubMed Central

    Boulesteix, Anne-Laure; Stierle, Veronika; Hapfelmeier, Alexander

    2015-01-01

    The problem of publication bias has long been discussed in research fields such as medicine. There is a consensus that publication bias is a reality and that solutions should be found to reduce it. In methodological computational research, including cancer informatics, publication bias may also be at work. The publication of negative research findings is certainly also a relevant issue, but has attracted very little attention to date. The present paper aims at providing a new formal framework to describe the notion of publication bias in the context of methodological computational research, facilitate and stimulate discussions on this topic, and increase awareness in the scientific community. We report an exemplary pilot study that aims at gaining experiences with the collection and analysis of information on unpublished research efforts with respect to publication bias, and we outline the encountered problems. Based on these experiences, we try to formalize the notion of publication bias. PMID:26508827

  1. Professional Culture and Climate: Addressing Unconscious Bias

    NASA Astrophysics Data System (ADS)

    Knezek, Patricia

    2016-10-01

    Unconscious bias reflects expectations or stereotypes that influence our judgments of others (regardless of our own group). Everyone has unconscious biases. The end result of unconscious bias can be an accumulation of advantage or disadvantage that impacts the long term career success of individuals, depending on which biases they are subject to. In order to foster a professional culture and climate, being aware of these unconscious biases and mitigating against them is a first step. This is particularly important when judgements are needed, such as in cases for recruitment, choice of speakers for conferences, and even reviewing papers submitted for publication. This presentation will cover how unconscious bias manifests itself, what evidence exists to demonstrate it exists, and ways it can be addressed.

  2. Quantum Criticality in the Biased Dicke Model

    PubMed Central

    Zhu, Hanjie; Zhang, Guofeng; Fan, Heng

    2016-01-01

    The biased Dicke model describes a system of biased two-level atoms coupled to a bosonic field, and is expected to produce new phenomena that are not present in the original Dicke model. In this paper, we study the critical properties of the biased Dicke model in the classical oscillator limits. For the finite-biased case in this limit, We present analytical results demonstrating that the excitation energy does not vanish for arbitrary coupling. This indicates that the second order phase transition is avoided in the biased Dicke model, which contrasts to the original Dicke model. We also analyze the squeezing and the entanglement in the ground state, and find that a finite bias will strongly modify their behaviors in the vicinity of the critical coupling point. PMID:26786239

  3. Cognitive Biases and Nonverbal Cue Availability in Detecting Deception

    ERIC Educational Resources Information Center

    Burgoon, Judee K.; Blair, J. Pete; Strom, Renee E.

    2008-01-01

    In potentially deceptive situations, people rely on mental shortcuts to help process information. These heuristic judgments are often biased and result in inaccurate assessments of sender veracity. Four such biases--truth bias, visual bias, demeanor bias, and expectancy violation bias--were examined in a judgment experiment that varied nonverbal…

  4. When Do Children Exhibit a "Yes" Bias?

    ERIC Educational Resources Information Center

    Okanda, Mako; Itakura, Shoji

    2010-01-01

    This study investigated whether one hundred and thirty-five 3- to 6-year-old children exhibit a yes bias to various yes-no questions and whether their knowledge status affects the production of a yes bias. Three-year-olds exhibited a yes bias to all yes-no questions such as "preference-object" and "knowledge-object" questions pertaining to…

  5. Who are you expecting? Biases in face perception reveal prior expectations for sex and age.

    PubMed

    Watson, Tamara Lea; Otsuka, Yumiko; Clifford, Colin Walter Giles

    2016-01-01

    A person's appearance contains a wealth of information, including indicators of their sex and age. Because first impressions can set the tone of subsequent relationships, it is crucial we form an accurate initial impression. Yet prior expectation can bias our decisions: Studies have reported biases to respond "male" when asked to report a person's sex from an image of their face and to place their age closer to their own. Perceptual expectation effects and cognitive response biases may both contribute to these inaccuracies. The current research used a Bayesian modeling approach to establish the perceptual biases involved when estimating the sex and age of an individual from their face. We demonstrate a perceptual bias for male and older faces evident under conditions of uncertainty. This suggests the well-established male bias is perceptual in origin and may be impervious to cognitive control. In comparison, the own age anchor effect is not operationalized at the perceptual level: The perceptual expectation is for a face of advanced age. Thus, distinct biases in the estimation of age operate at the perceptual and cognitive levels. PMID:26842858

  6. Field emission from bias-grown diamond thin films in a microwave plasma

    DOEpatents

    Gruen, Dieter M.; Krauss, Alan R.; Ding, Ming Q.; Auciello, Orlando

    2002-01-01

    A method of producing diamond or diamond like films in which a negative bias is established on a substrate with an electrically conductive surface in a microwave plasma chemical vapor deposition system. The atmosphere that is subjected to microwave energy includes a source of carbon, nitrogen and hydrogen. The negative bias is maintained on the substrate through both the nucleation and growth phase of the film until the film is continuous. Biases between -100V and -200 are preferred. Carbon sources may be one or more of CH.sub.4, C.sub.2 H.sub.2 other hydrocarbons and fullerenes.

  7. The truth and bias model of judgment.

    PubMed

    West, Tessa V; Kenny, David A

    2011-04-01

    We present a new model for the general study of how the truth and biases affect human judgment. In the truth and bias model, judgments about the world are pulled by 2 primary forces, the truth force and the bias force, and these 2 forces are interrelated. The truth and bias model differentiates force and value, where the force is the strength of the attraction and the value is the location toward which the judgment is attracted. The model also makes a formal theoretical distinction between bias and moderator variables. Two major classes of biases are discussed: biases that are measured with variables (e.g., assumed similarity) and directional bias, which refers to the extent to which judgments are pulled toward 1 end of the judgment continuum. Moderator variables are conceptualized as variables that affect the accuracy and bias forces but that do not affect judgments directly. We illustrate the model with 4 examples. We discuss the theoretical, empirical, methodological, measurement, and design implications of the model. PMID:21480740

  8. The truth and bias model of judgment.

    PubMed

    West, Tessa V; Kenny, David A

    2011-04-01

    We present a new model for the general study of how the truth and biases affect human judgment. In the truth and bias model, judgments about the world are pulled by 2 primary forces, the truth force and the bias force, and these 2 forces are interrelated. The truth and bias model differentiates force and value, where the force is the strength of the attraction and the value is the location toward which the judgment is attracted. The model also makes a formal theoretical distinction between bias and moderator variables. Two major classes of biases are discussed: biases that are measured with variables (e.g., assumed similarity) and directional bias, which refers to the extent to which judgments are pulled toward 1 end of the judgment continuum. Moderator variables are conceptualized as variables that affect the accuracy and bias forces but that do not affect judgments directly. We illustrate the model with 4 examples. We discuss the theoretical, empirical, methodological, measurement, and design implications of the model.

  9. Chronic and acute biases in perceptual stabilization

    PubMed Central

    Al-Dossari, Munira; Blake, Randolph; Brascamp, Jan W.; Freeman, Alan W.

    2015-01-01

    When perceptually ambiguous stimuli are presented intermittently, the percept on one presentation tends to be the same as that on the previous presentation. The role of short-term, acute biases in the production of this perceptual stability is relatively well understood. In addition, however, long-lasting, chronic bias may also contribute to stability. In this paper we develop indices for both biases and for stability, and show that stability can be expressed as a sum of contributions from the two types of bias. We then apply this analytical procedure to binocular rivalry, showing that adjustment of the monocular contrasts can alter the relative contributions of the two biases. Stability is mainly determined by chronic bias when the contrasts are equal, but acute bias dominates stability when right-eye contrast is set lower than left-eye contrast. Finally, we show that the right-eye bias persists in continuous binocular rivalry. Our findings reveal a previously unappreciated contribution of chronic bias to stable perception. PMID:26641947

  10. Deterministic photon bias in speckle imaging

    NASA Technical Reports Server (NTRS)

    Beletic, James W.

    1989-01-01

    A method for determining photo bias terms in speckle imaging is presented, and photon bias is shown to be a deterministic quantity that can be calculated without the use of the expectation operator. The quantities obtained are found to be identical to previous results. The present results have extended photon bias calculations to the important case of the bispectrum where photon events are assigned different weights, in which regime the bias is a frequency dependent complex quantity that must be calculated for each frame.

  11. delta-biased Josephson tunnel junctions

    SciTech Connect

    Monaco, R.; Mygind, J.; Koshelets, V. P.; Dmitriev, P.

    2010-02-01

    The behavior of a long Josephson tunnel junction drastically depends on the distribution of the dc bias current. We investigate the case in which the bias current is fed in the central point of a one-dimensional junction. Such junction configuration has been recently used to detect the persistent currents circulating in a superconducting loop. Analytical and numerical results indicate that the presence of fractional vortices leads to remarkable differences from the conventional case of uniformly distributed dc bias current. The theoretical findings are supported by detailed measurements on a number of delta-biased samples having different electrical and geometrical parameters.

  12. Development of bias in analytical predictions based on behavior of platforms during hurricanes

    SciTech Connect

    Aggarwal, R.K.; Dolan, D.K.; Cornell, C.A.

    1996-12-31

    A Joint Industry Project (JIP) was initiated by 13 oil companies and the US Minerals Management Service (MMS), wherein a methodology was developed to use information from observed platform conditions resulting from Andrew and the hurricane hindcast data with capacity, reliability, and Bayesian updating analyses to determine a measure of differences (biases) in the analytical predictions and field observations. The procedures used for structural integrity analysis were also improved as a result of this study. Phase 1 of this project completed in October 1993 defined a global bias factor. A study of foundation behavior was completed following Phase 1 and determined bias factors specific to foundation failure modes. This paper presents the approach followed in the most recent phase of this project in which bias factors specific to jacket and two foundation failure modes (lateral and axial) were developed. This study utilized an updated storm hindcast, improved analysis models, and a more detailed calibration procedure. The three bias factors were developed and were found to differ significantly. The bias factors developed through this study have provided means to further improve procedures used in the assessment of existing platforms. The proper use of these new analytical methodologies and bias factors will produce more appropriate and cost-effective mitigation measures for safe platform operations. The methodology for establishing bias factors developed and proven in these projects is applicable to other offshore regions and production systems with specific environmental, geotechnical, material and structure features.

  13. The Mediating Effect of Self-Evaluation Bias of Competence on the Relationship between Parental Emotional Support and Children's Academic Functioning

    ERIC Educational Resources Information Center

    Côté, Sébastien; Bouffard, Thérèse; Vezeau, Carole

    2014-01-01

    Background: It is well established that children's self-evaluation bias of competence is related to the quality of parent-child emotional relationship. Such biases are linked to children's academic functioning and achievement. Links have also been established between the quality of parent-child emotional relationship and children's…

  14. Method for removing atomic-model bias in macromolecular crystallography

    DOEpatents

    Terwilliger, Thomas C.

    2006-08-01

    Structure factor bias in an electron density map for an unknown crystallographic structure is minimized by using information in a first electron density map to elicit expected structure factor information. Observed structure factor amplitudes are combined with a starting set of crystallographic phases to form a first set of structure factors. A first electron density map is then derived and features of the first electron density map are identified to obtain expected distributions of electron density. Crystallographic phase probability distributions are established for possible crystallographic phases of reflection k, and the process is repeated as k is indexed through all of the plurality of reflections. An updated electron density map is derived from the crystallographic phase probability distributions for each one of the reflections. The entire process is then iterated to obtain a final set of crystallographic phases with minimum bias from known electron density maps.

  15. Alcohol breath test: gas exchange issues.

    PubMed

    Hlastala, Michael P; Anderson, Joseph C

    2016-08-01

    The alcohol breath test is reviewed with a focus on gas exchange factors affecting its accuracy. The basis of the alcohol breath test is the assumption that alveolar air reaches the mouth during exhalation with no change in alcohol concentration. Recent investigations have shown that alcohol concentration is altered during its transit to the mouth. The exhaled alcohol concentration is modified by interaction with the mucosa of the pulmonary airways. Exhaled alcohol concentration is not an accurate indicator of alveolar alcohol concentration. Measuring alcohol concentration in the breath is very different process than measuring a blood level from air equilibrated with a blood sample. Airway exchange of alcohol leads to a bias against certain individuals depending on the anatomic and physiologic characteristics. Methodological modifications are proposed to improve the accuracy of the alcohol breath test to become fair to all. PMID:27197859

  16. Establishing American Colleges Abroad.

    ERIC Educational Resources Information Center

    Greene, William E.

    1990-01-01

    Describes the growing involvement of U.S. two-year colleges in establishing programs abroad to enable foreign students to complete one or two years of college-level work in their home country before transferring to U.S. universities. Highlights the activities of several community colleges in the Pacific Rim. Identifies conditions basic to future…

  17. Nonsurvivable momentum exchange system

    NASA Technical Reports Server (NTRS)

    Roder, Russell (Inventor); Ahronovich, Eliezer (Inventor); Davis, III, Milton C. (Inventor)

    2007-01-01

    A demiseable momentum exchange system includes a base and a flywheel rotatably supported on the base. The flywheel includes a web portion defining a plurality of web openings and a rim portion. The momentum exchange system further includes a motor for driving the flywheel and a cover for engaging the base to substantially enclose the flywheel. The system may also include components having a melting temperature below 1500 degrees Celsius. The momentum exchange system is configured to demise on reentry.

  18. Zero-bias spin separation

    NASA Astrophysics Data System (ADS)

    Ganichev, Sergey D.; Bel'Kov, Vasily V.; Tarasenko, Sergey A.; Danilov, Sergey N.; Giglberger, Stephan; Hoffmann, Christoph; Ivchenko, Eougenious L.; Weiss, Dieter; Wegscheider, Werner; Gerl, Christian; Schuh, Dieter; Stahl, Joachim; de Boeck, Jo; Borghs, Gustaaf; Prettl, Wilhelm

    2006-09-01

    The generation, manipulation and detection of spin-polarized electrons in low-dimensional semiconductors are at the heart of spintronics. Pure spin currents, that is, fluxes of magnetization without charge current, are quite attractive in this respect. A paradigmatic example is the spin Hall effect, where an electrical current drives a transverse spin current and causes a non-equilibrium spin accumulation observed near the sample boundary. Here we provide evidence for an another effect causing spin currents which is fundamentally different from the spin Hall effect. In contrast to the spin Hall effect, it does not require an electric current to flow: without bias the spin separation is achieved by spin-dependent scattering of electrons in media with suitable symmetry. We show, by free-carrier absorption of terahertz (THz) radiation, that spin currents flow in a wide range of temperatures. Moreover, the experimental results provide evidence that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy-relaxation processes.

  19. Haploinsufficiency predictions without study bias

    PubMed Central

    Steinberg, Julia; Honti, Frantisek; Meader, Stephen; Webber, Caleb

    2015-01-01

    Any given human individual carries multiple genetic variants that disrupt protein-coding genes, through structural variation, as well as nucleotide variants and indels. Predicting the phenotypic consequences of a gene disruption remains a significant challenge. Current approaches employ information from a range of biological networks to predict which human genes are haploinsufficient (meaning two copies are required for normal function) or essential (meaning at least one copy is required for viability). Using recently available study gene sets, we show that these approaches are strongly biased towards providing accurate predictions for well-studied genes. By contrast, we derive a haploinsufficiency score from a combination of unbiased large-scale high-throughput datasets, including gene co-expression and genetic variation in over 6000 human exomes. Our approach provides a haploinsufficiency prediction for over twice as many genes currently unassociated with papers listed in Pubmed as three commonly-used approaches, and outperforms these approaches for predicting haploinsufficiency for less-studied genes. We also show that fine-tuning the predictor on a set of well-studied ‘gold standard’ haploinsufficient genes does not improve the prediction for less-studied genes. This new score can readily be used to prioritize gene disruptions resulting from any genetic variant, including copy number variants, indels and single-nucleotide variants. PMID:26001969

  20. 17 CFR 10.114 - Acceleration of establishment of restitution procedure.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 17 Commodity and Securities Exchanges 1 2010-04-01 2010-04-01 false Acceleration of establishment of restitution procedure. 10.114 Section 10.114 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION RULES OF PRACTICE Restitution Orders § 10.114 Acceleration of establishment...

  1. 17 CFR 10.114 - Acceleration of establishment of restitution procedure.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 17 Commodity and Securities Exchanges 1 2014-04-01 2014-04-01 false Acceleration of establishment of restitution procedure. 10.114 Section 10.114 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION RULES OF PRACTICE Restitution Orders § 10.114 Acceleration of establishment...

  2. 17 CFR 10.114 - Acceleration of establishment of restitution procedure.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 17 Commodity and Securities Exchanges 1 2012-04-01 2012-04-01 false Acceleration of establishment of restitution procedure. 10.114 Section 10.114 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION RULES OF PRACTICE Restitution Orders § 10.114 Acceleration of establishment...

  3. 17 CFR 10.114 - Acceleration of establishment of restitution procedure.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 17 Commodity and Securities Exchanges 1 2013-04-01 2013-04-01 false Acceleration of establishment of restitution procedure. 10.114 Section 10.114 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION RULES OF PRACTICE Restitution Orders § 10.114 Acceleration of establishment...

  4. 17 CFR 10.114 - Acceleration of establishment of restitution procedure.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 17 Commodity and Securities Exchanges 1 2011-04-01 2011-04-01 false Acceleration of establishment of restitution procedure. 10.114 Section 10.114 Commodity and Securities Exchanges COMMODITY FUTURES TRADING COMMISSION RULES OF PRACTICE Restitution Orders § 10.114 Acceleration of establishment...

  5. Text Exchange System

    NASA Technical Reports Server (NTRS)

    Snyder, W. V.; Hanson, R. J.

    1986-01-01

    Text Exchange System (TES) exchanges and maintains organized textual information including source code, documentation, data, and listings. System consists of two computer programs and definition of format for information storage. Comprehensive program used to create, read, and maintain TES files. TES developed to meet three goals: First, easy and efficient exchange of programs and other textual data between similar and dissimilar computer systems via magnetic tape. Second, provide transportable management system for textual information. Third, provide common user interface, over wide variety of computing systems, for all activities associated with text exchange.

  6. Understanding Implicit Bias: What Educators Should Know

    ERIC Educational Resources Information Center

    Staats, Cheryl

    2016-01-01

    The desire to ensure the best for children is precisely why educators should become aware of the concept of implicit bias: the attitudes or stereotypes that affect our understanding, actions, and decisions in an unconscious manner. Operating outside of our conscious awareness, implicit biases are pervasive, and they can challenge even the most…

  7. The Antifeminist Bias in Traditional Criticism.

    ERIC Educational Resources Information Center

    Rogers, Katharine M.

    Ten recent articles and books are cited in this paper as examples of a continuing antifeminist bias in literary criticism. Several forms of this bias are discussed, including an imperviousness to the feminist awareness, a refusal to recognize it, and open irritation by some critics that women are now finding a voice in literary criticism. A…

  8. Biases in Children's and Adults' Moral Judgments

    ERIC Educational Resources Information Center

    Powell, Nina L.; Derbyshire, Stuart W. G.; Guttentag, Robert E.

    2012-01-01

    Two experiments examined biases in children's (5/6- and 7/8-year-olds) and adults' moral judgments. Participants at all ages judged that it was worse to produce harm when harm occurred (a) through action rather than inaction (omission bias), (b) when physical contact with the victim was involved (physical contact principle), and (c) when the harm…

  9. Gender Bias in Lebanese Language Classes

    ERIC Educational Resources Information Center

    Mougharbel, Ghada M.; Bahous, Rima

    2010-01-01

    Gender bias, though often implicit and unnoticed, exists in many forms and in different situations. The purpose of this study is to investigate whether gender bias exists in Lebanese language classrooms. Semi-structured interviews, questionnaires, and nonparticipant observational techniques were used for data collection. Results reveal…

  10. A Reconsideration of Bias in the News.

    ERIC Educational Resources Information Center

    Stevenson, Robert L.; Greene, Mark T.

    1980-01-01

    Discusses conceptual problems with the traditional approach to the study of news bias; reports on a study conducted with 73 college students, which yielded data supporting the thesis that what news consumers see as biased news is often material that is discrepant with what they already believe. (GT)

  11. Hindsight Bias and Developing Theories of Mind

    ERIC Educational Resources Information Center

    Bernstein, Daniel M.; Atance, Cristina; Meltzoff, Andrew N.; Loftus, Geoffrey R.

    2007-01-01

    Although "hindsight bias" (the "I knew it all along" phenomenon) has been documented in adults, its development has not been investigated. This is despite the fact that hindsight bias errors closely resemble the errors children make on theory of mind (ToM) tasks. Two main goals of the present work were to (a) create a battery of hindsight tasks…

  12. Distinctive characteristics of sexual orientation bias crimes.

    PubMed

    Stacey, Michele

    2011-10-01

    Despite increased attention in the area of hate crime research in the past 20 years, sexual orientation bias crimes have rarely been singled out for study. When these types of crimes are looked at, the studies are typically descriptive in nature. This article seeks to increase our knowledge of sexual orientation bias by answering the question: What are the differences between sexual orientation motivated bias crimes and racial bias crimes? This question is examined using data from the National Incident Based Reporting System (NIBRS) and multiple regression techniques. This analysis draws on the strengths of NIBRS to look at the incident characteristics of hate crimes and distinguishing characteristics of sexual orientation crimes. Specifically this analysis looks at the types and seriousness of offenses motivated by sexual orientation bias as opposed to race bias as well as victim and offender characteristics. The findings suggest that there are differences between these two types of bias crimes, suggesting a need for further separation of the bias types in policy and research.

  13. Response Bias in Needs Assessment Studies.

    ERIC Educational Resources Information Center

    Calsyn, Robert J.; Klinkenberg, W. Dean

    1995-01-01

    Agencies conducting needs assessments in which respondents are asked about their awareness of the agency must be alert to a bias that inflates awareness (agency awareness acquiescence). A study with 157 college students demonstrated such awareness bias, which was related to the impression management component of social desirability. (SLD)

  14. Understanding Unconscious Bias and Unintentional Racism

    ERIC Educational Resources Information Center

    Moule, Jean

    2009-01-01

    Unconscious biases affect one's relationships, whether they are fleeting relationships in airports or longer term relationships between teachers and students, teachers and parents, teachers and other educators. In this article, the author argues that understanding one's possible biases is essential for developing community in schools.…

  15. Framing Bias among Expert and Novice Physicians.

    ERIC Educational Resources Information Center

    Christensen, Caryn; And Others

    1991-01-01

    A study explored the responses of medical students, resident physicians, and experienced physicians to 12 vignettes describing hypothetical patients to determine the relationship between clinical experience and susceptibility to bias in treatment decisions resulting from presentation of possible outcomes. Framing bias was most evident in the…

  16. Distinctive Characteristics of Sexual Orientation Bias Crimes

    ERIC Educational Resources Information Center

    Stacey, Michele

    2011-01-01

    Despite increased attention in the area of hate crime research in the past 20 years, sexual orientation bias crimes have rarely been singled out for study. When these types of crimes are looked at, the studies are typically descriptive in nature. This article seeks to increase our knowledge of sexual orientation bias by answering the question:…

  17. The Battle over Studies of Faculty Bias

    ERIC Educational Resources Information Center

    Gravois, John

    2007-01-01

    The American Federation of Teachers (AFT) recently commissioned a study to review the research that finds liberal bias run amok in academe. Believing that the AFT is not a dispassionate observer of this debate, this article provides "The Chronicle of Higher Education's" survey of the genre. The studies reviewed include: (1) "Political Bias in the…

  18. Racially Biased Policing: Determinants of Citizen Perceptions

    ERIC Educational Resources Information Center

    Weitzer, Ronald; Tuch, Steven A.

    2005-01-01

    The current controversy surrounding racial profiling in America has focused renewed attention on the larger issue of racial bias by the police. Yet little is known about the extent of police racial bias and even less about public perceptions of the problem. This article analyzes recent national survey data on citizens' views of and reported…

  19. Exploratory Studies of Bias in Achievement Tests.

    ERIC Educational Resources Information Center

    Green, Donald Ross; Draper, John F.

    This paper considers the question of bias in group administered academic achievement tests, bias which is inherent in the instruments themselves. A body of data on the test of performance of three disadvantaged minority groups--northern, urban black; southern, rural black; and, southwestern, Mexican-Americans--as tryout samples in contrast to…

  20. Sex Bias in Job Evaluation Procedures.

    ERIC Educational Resources Information Center

    Arvey, Richard D.

    1986-01-01

    Outlines issues pertaining to possible sex bias in job evaluation procedures and reviews relevant research. Gives attention to possible sex bias in job analysis procedures, choice and weighting of factors, and reliability and validity issues. Discusses future research needs, particularly reliability and validity aspects of job evaluation…

  1. How Many Hindsight Biases Are There?

    ERIC Educational Resources Information Center

    Blank, Hartmut; Nestler, Steffen; von Collani, Gernot; Fischer, Volkhard

    2008-01-01

    The answer is three: questioning a conceptual default assumption in hindsight bias research, we argue that the hindsight bias is not a unitary phenomenon but consists of three separable and partially independent subphenomena or components, namely, memory distortions, impressions of foreseeability and impressions of necessity. Following a detailed…

  2. Adaptive Variable Bias Magnetic Bearing Control

    NASA Technical Reports Server (NTRS)

    Johnson, Dexter; Brown, Gerald V.; Inman, Daniel J.

    1998-01-01

    Most magnetic bearing control schemes use a bias current with a superimposed control current to linearize the relationship between the control current and the force it delivers. With the existence of the bias current, even in no load conditions, there is always some power consumption. In aerospace applications, power consumption becomes an important concern. In response to this concern, an alternative magnetic bearing control method, called Adaptive Variable Bias Control (AVBC), has been developed and its performance examined. The AVBC operates primarily as a proportional-derivative controller with a relatively slow, bias current dependent, time-varying gain. The AVBC is shown to reduce electrical power loss, be nominally stable, and provide control performance similar to conventional bias control. Analytical, computer simulation, and experimental results are presented in this paper.

  3. Exploring the various interpretations of "test bias".

    PubMed

    Warne, Russell T; Yoon, Myeongsun; Price, Chris J

    2014-10-01

    Test bias is a hotly debated topic in society, especially as it relates to diverse groups of examinees who often score low on standardized tests. However, the phrase "test bias" has a multitude of interpretations that many people are not aware of. In this article, we explain five different meanings of "test bias" and summarize the empirical and theoretical evidence related to each interpretation. The five meanings are as follows: (a) mean group differences, (b) differential predictive validity, (c) differential item functioning, (d) differing factor structures of tests, and (e) unequal consequences of test use for various groups. We explain in this article why meanings (a) and (e) are not actual forms of test bias and that there are serious concerns about (b). In our conclusion, we discuss the benefits of standardized testing for diverse examinees and urge readers to be careful and precise in their use of the phrase "test bias."

  4. Is a Persistent Global Bias Necessary for the Establishment of Planar Cell Polarity?

    PubMed Central

    Fischer, Sabine; Houston, Paul; Monk, Nicholas A. M.; Owen, Markus R.

    2013-01-01

    Planar cell polarity (PCP)–the coordinated polarisation of a whole field of cells within the plane of a tissue–relies on the interaction of three modules: a global module that couples individual cellular polarity to the tissue axis, a local module that aligns the axis of polarisation of neighbouring cells, and a readout module that directs the correct outgrowth of PCP-regulated structures such as hairs and bristles. While much is known about the molecular components that are required for PCP, the functional details of–and interactions between–the modules remain unclear. In this work, we perform a mathematical and computational analysis of two previously proposed computational models of the local module (Amonlirdviman et al., Science, 307, 2005; Le Garrec et al., Dev. Dyn., 235, 2006). Both models can reproduce wild-type and mutant phenotypes of PCP observed in the Drosophila wing under the assumption that a tissue-wide polarity cue from the global module persists throughout the development of PCP. We demonstrate that both models can also generate tissue-level PCP when provided with only a transient initial polarity cue. However, in these models such transient cues are not sufficient to ensure robustness of the resulting cellular polarisation. PMID:23593163

  5. Parent Leadership Exchange: The First Five Years

    ERIC Educational Resources Information Center

    Institute for Responsive Education, 2005

    2005-01-01

    The overall goal of the Parent Leadership Exchange (PLE) is to improve student outcomes by increasing the capacity of family and community members to help children achieve high academic standards. To achieve this goal, PLE established a continuing resource to increase the leadership skills of parent leaders, paid or volunteer, working in…

  6. Extension Learning Exchange: Lessons from Nicaragua

    ERIC Educational Resources Information Center

    Treadwell, Paul; Lachapelle, Paul; Howe, Rod

    2013-01-01

    There is a clear need to support global professional development, international education, and collaborative learning opportunities in Extension. The program described here established an international learning exchange in Nicaragua to lead to global professional development and future international collaboration. The primary lessons and outcomes…

  7. Kinetic models of immediate exchange

    NASA Astrophysics Data System (ADS)

    Heinsalu, Els; Patriarca, Marco

    2014-08-01

    We propose a novel kinetic exchange model differing from previous ones in two main aspects. First, the basic dynamics is modified in order to represent economies where immediate wealth exchanges are carried out, instead of reshufflings or uni-directional movements of wealth. Such dynamics produces wealth distributions that describe more faithfully real data at small values of wealth. Secondly, a general probabilistic trading criterion is introduced, so that two economic units can decide independently whether to trade or not depending on their profit. It is found that the type of the equilibrium wealth distribution is the same for a large class of trading criteria formulated in a symmetrical way with respect to the two interacting units. This establishes unexpected links between and provides a microscopic foundations of various kinetic exchange models in which the existence of a saving propensity is postulated. We also study the generalized heterogeneous version of the model in which units use different trading criteria and show that suitable sets of diversified parameter values with a moderate level of heterogeneity can reproduce realistic wealth distributions with a Pareto power law.

  8. Solvent-dependent cation exchange in metal-organic frameworks.

    PubMed

    Brozek, Carl K; Bellarosa, Luca; Soejima, Tomohiro; Clark, Talia V; López, Núria; Dincă, Mircea

    2014-06-01

    We investigated which factors govern the critical steps of cation exchange in metal-organic frameworks by studying the effect of various solvents on the insertion of Ni(2+) into MOF-5 and Co(2+) into MFU-4l. After plotting the extent of cation insertion versus different solvent parameters, trends emerge that offer insight into the exchange processes for both systems. This approach establishes a method for understanding critical aspects of cation exchange in different MOFs and other materials.

  9. Establishment of Intestinal Bacteriology

    PubMed Central

    MITSUOKA, Tomotari

    2014-01-01

    Research on intestinal bacteria began around the end of the 19th century. During the last 5 decades of the 20th century, research on the intestinal microbiota made rapid progress. At first, in my work, I first developed a method of comprehensive analysis of the intestinal microbiota, and then I established classification and identification methods for intestinal anaerobes. Using these methods I discovered a number of ecological rules governing the intestinal microbiota and the role of the intestinl microbiota in health and disease. Moreover, using germfree animals, it was proven that the intestinal microbiota has a role in carcinogenesis and aging in the host. Thus, a new interdisciplinary field, “intestinal bacteriology” was established. PMID:25032084

  10. Medical journal peer review: process and bias.

    PubMed

    Manchikanti, Laxmaiah; Kaye, Alan D; Boswell, Mark V; Hirsch, Joshua A

    2015-01-01

    Scientific peer review is pivotal in health care research in that it facilitates the evaluation of findings for competence, significance, and originality by qualified experts. While the origins of peer review can be traced to the societies of the eighteenth century, it became an institutionalized part of the scholarly process in the latter half of the twentieth century. This was a response to the growth of research and greater subject specialization. With the current increase in the number of specialty journals, the peer review process continues to evolve to meet the needs of patients, clinicians, and policy makers. The peer review process itself faces challenges. Unblinded peer review might suffer from positive or negative bias towards certain authors, specialties, and institutions. Peer review can also suffer when editors and/or reviewers might be unable to understand the contents of the submitted manuscript. This can result in an inability to detect major flaws, or revelations of major flaws after acceptance of publication by the editors. Other concerns include potentially long delays in publication and challenges uncovering plagiarism, duplication, corruption and scientific misconduct. Conversely, a multitude of these challenges have led to claims of scientific misconduct and an erosion of faith. These challenges have invited criticism of the peer review process itself. However, despite its imperfections, the peer review process enjoys widespread support in the scientific community. Peer review bias is one of the major focuses of today's scientific assessment of the literature. Various types of peer review bias include content-based bias, confirmation bias, bias due to conservatism, bias against interdisciplinary research, publication bias, and the bias of conflicts of interest. Consequently, peer review would benefit from various changes and improvements with appropriate training of reviewers to provide quality reviews to maintain the quality and integrity of

  11. Eye Movements while Reading Biased Homographs: Effects of Prior Encounter and Biasing Context on Reducing the Subordinate Bias Effect

    PubMed Central

    Leinenger, Mallorie; Rayner, Keith

    2013-01-01

    Readers experience processing difficulties when reading biased homographs preceded by subordinate-biasing contexts. Attempts to overcome this processing deficit have often failed to reduce the subordinate bias effect (SBE). In the present studies, we examined the processing of biased homographs preceded by single-sentence, subordinate-biasing contexts, and varied whether this preceding context contained a prior instance of the homograph or a control word/phrase. Having previously encountered the homograph earlier in the sentence reduced the SBE for the subsequent encounter, while simply instantiating the subordinate meaning produced processing difficulty. We compared these reductions in reading times to differences in processing time between dominant-biased repeated and non-repeated conditions in order to verify that the reductions observed in the subordinate cases did not simply reflect a general repetition benefit. Our results indicate that a strong, subordinate-biasing context can interact during lexical access to overcome the activation from meaning frequency and reduce the SBE during reading. PMID:24073328

  12. 77 FR 47474 - Self-Regulatory Organizations; Chicago Board Options Exchange, Incorporated; Notice of Filing and...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-08

    ... Immediate Effectiveness of a Proposed Rule Change To Establish a Rule Regarding Records of Written... Rule Change The Exchange proposes to establish a rule regarding records of written complaints that is.... Purpose The Exchange proposes to establish Rule 53.7--CBSX Record of Written Complaints to...

  13. The role of the input on the development of the LC bias: a crosslinguistic comparison.

    PubMed

    Gonzalez-Gomez, Nayeli; Hayashi, Akiko; Tsuji, Sho; Mazuka, Reiko; Nazzi, Thierry

    2014-09-01

    Previous studies have described the existence of a phonotactic bias called the Labial-Coronal (LC) bias, corresponding to a tendency to produce more words beginning with a labial consonant followed by a coronal consonant (i.e. "bat") than the opposite CL pattern (i.e. "tap"). This bias has initially been interpreted in terms of articulatory constraints of the human speech production system. However, more recently, it has been suggested that this presumably language-general LC bias in production might be accompanied by LC and CL biases in perception, acquired in infancy on the basis of the properties of the linguistic input. The present study investigates the origins of these perceptual biases, testing infants learning Japanese, a language that has been claimed to possess more CL than LC sequences, and comparing them with infants learning French, a language showing a clear LC bias in its lexicon. First, a corpus analysis of Japanese IDS and ADS revealed the existence of an overall LC bias, except for plosive sequences in ADS, which show a CL bias across counts. Second, speech preference experiments showed a perceptual preference for CL over LC plosive sequences (all recorded by a Japanese speaker) in 13- but not in 7- and 10-month-old Japanese-learning infants (Experiment 1), while revealing the emergence of an LC preference between 7 and 10 months in French-learning infants, using the exact same stimuli. These crosslinguistic behavioral differences, obtained with the same stimuli, thus reflect differences in processing in two populations of infants, which can be linked to differences in the properties of the lexicons of their respective native languages. These findings establish that the emergence of a CL/LC bias is related to exposure to a linguistic input.

  14. Clinicians’ Implicit Ethnic/Racial Bias and Perceptions of Care Among Black and Latino Patients

    PubMed Central

    Blair, Irene V.; Steiner, John F.; Fairclough, Diane L.; Hanratty, Rebecca; Price, David W.; Hirsh, Holen K.; Wright, Leslie A.; Bronsert, Michael; Karimkhani, Elhum; Magid, David J.; Havranek, Edward P.

    2013-01-01

    PURPOSE We investigated whether clinicians’ explicit and implicit ethnic/racial bias is related to black and Latino patients’ perceptions of their care in established clinical relationships. METHODS We administered a telephone survey to 2,908 patients, stratified by ethnicity/race, and randomly selected from the patient panels of 134 clinicians who had previously completed tests of explicit and implicit ethnic/racial bias. Patients completed the Primary Care Assessment Survey, which addressed their clinicians’ interpersonal treatment, communication, trust, and contextual knowledge. We created a composite measure of patient-centered care from the 4 subscales. RESULTS Levels of explicit bias were low among clinicians and unrelated to patients’ perceptions. Levels of implicit bias varied among clinicians, and those with greater implicit bias were rated lower in patient-centered care by their black patients as compared with a reference group of white patients (P = .04). Latino patients gave the clinicians lower ratings than did other groups (P <.0001), and this did not depend on the clinicians’ implicit bias (P = .98). CONCLUSIONS This is among the first studies to investigate clinicians’ implicit bias and communication processes in ongoing clinical relationships. Our findings suggest that clinicians’ implicit bias may jeopardize their clinical relationships with black patients, which could have negative effects on other care processes. As such, this finding supports the Institute of Medicine’s suggestion that clinician bias may contribute to health disparities. Latinos’ overall greater concerns about their clinicians appear to be based on aspects of care other than clinician bias. PMID:23319505

  15. 75 FR 65975 - Exchange Visitor Program-Secondary School Students

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-10-27

    ... adoption of 22 CFR Part 62--Exchange Visitor Program, establishing a student exchange program (14 FR 4592... the general public on current best practices in the industry (see 74 FR 45385, September 2, 2009). The... language addressing each matter were consolidated into a Notice of Proposed Rulemaking (NPRM) (see 75...

  16. Social Representation of Intercultural Exchange in an International University

    ERIC Educational Resources Information Center

    Kudo, Kazuhiro

    2016-01-01

    This paper provides an interpretive investigation into the social representation of intercultural exchange at one of the newly established international universities in Japan. The author conducted quasi-structured interviews with 5 staff members and 22 students to gain insight into their perceptions of intercultural exchange and interactions. The…

  17. 45 CFR 155.105 - Approval of a State Exchange.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 45 Public Welfare 1 2013-10-01 2013-10-01 false Approval of a State Exchange. 155.105 Section 155.105 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES REQUIREMENTS RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT...

  18. 45 CFR 155.230 - General standards for Exchange notices.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 1 2012-10-01 2012-10-01 false General standards for Exchange notices. 155.230 Section 155.230 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES REQUIREMENTS RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE...

  19. 45 CFR 155.230 - General standards for Exchange notices.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT..., electronically, provided that the requirements for electronic notices in 42 CFR 435.918 are met, except that the individual market Exchange is not required to implement the process specified in 42 CFR 435.918(b)(1)...

  20. 45 CFR 155.105 - Approval of a State Exchange.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 1 2012-10-01 2012-10-01 false Approval of a State Exchange. 155.105 Section 155.105 Public Welfare DEPARTMENT OF HEALTH AND HUMAN SERVICES REQUIREMENTS RELATING TO HEALTH CARE ACCESS EXCHANGE ESTABLISHMENT STANDARDS AND OTHER RELATED STANDARDS UNDER THE AFFORDABLE CARE ACT...